Tag Archives: particle physics

What is dark matter? A deep dive

If you’ve been following our space articles, you may have come across something called “dark matter”. It’s the most abundant type of matter in the universe — our best models have established that dark matter comprises 84.4% of the matter contained in the known universe — but we still don’t really understand just what it is. Dark matter is something that we know is out there, but we have little idea what it’s made of.

Credit: News-G.

Wait, so how do we know it’s even real?

“Regular” matter (technically called baryonic matter) is made of electrons, protons, and neutrons. Cosmologists define the three particles as baryons –technically speaking, electrons are something else, but that’s beside the point here. Baryons make up gas, gas makes up stars, stars go boom and make planets and other things — including you. Yes, you are made of star stuff — baryonic star stuff, to be precise.

All this is done thanks to the electromagnetic (EM) force that forms chemical bonds, glueing regular atoms together But Dark Matter (DM) plays a different game.

Dark matter doesn’t interact with things the way baryonic matter does. It doesn’t scatter or absorb light, but it still has a gravitational pull. So if there are beings made of dark matter living right here, right now, you probably wouldn’t even know it because the perception of touch is felt when your sensory nerves send the message to your brain, and these nerves work thanks to the EM force.

We can’t touch dark matter, and no optical instruments can detect, so how do we ‘see’ it? Indirectly, for starters. Look for gravity, if there isn’t enough visible mass to explain to explain the gravitational pull felt by a region of the universe, then there something there. Invisible does not mean non-existant. If it weren’t for its gravity effect, there would be little indication of dark matter existing.

The main observational evidence for dark matter is the orbital speeds of stars in the arms of spiral galaxies. If Kepler and Newton were correct, stars’ velocity would decrease with the orbital radius in a specific way. But this was not observed by Vera Rubin and Kent Ford, who tracked this relationship. Instead, Rubin and Ford got a velocity vs radius relation that looked like the stars had a nearly constant behavior from a certain point of the galactic orbit.

This could only be explained if there would be a lot more matter somewhere that we’re not seeing. Something was pulling at these stars gravitationally, and that something is dark matter.

Rotation curve of a typical spiral galaxy: predicted (A) and observed (B). Dark matter can explain the ‘flat’ appearance of the velocity curve out to a large radius. Credits: Phil Hibbs.

Another important evidence of dark matter comes from galaxy superclusters like 1E 0657-558. Astronomers observed that within this cluster, there are two groups of galaxies placed in a peculiar position to one another. 

If you look at the Hubble Space Telescope image below (1st and 2nd), you’ll notice that there are many galaxies on the left and another group on the opposite side. When astronomers observed in X-ray, they concluded that these two clusters collided and left a gas trace of the shock. The faster cluster was like a bullet (it’s even named the Bullet Cluster) passing through the slower one at around 3000–4000 km/s nearly 100-200 million years ago (3rd pic).

Visible light image from the Hubble Space Telescope, NASA, ESA and the Magellan Telescope, University of Arizona
Visible light image from the Hubble Space Telescope, NASA, ESA and the Magellan Telescope, University of Arizona
X-ray light image from the Chandra X-ray Observatory: NASA, CXC

But one of the most convincing evidence of dark matter came with gravitational lensing.

Scientists used gravitational lensing to estimate the mass of the objects involved in the collision. They found that the galaxies which hadn’t collided agreed with the weak lensing detections. This indicates those galaxies are ahead of ‘the X-ray evidence’ (below, 1st image). Since dark matter doesn’t interact with nearly anything, in this phenomenon, we see a bunch of mass (blue) moving faster than the gas (purple), barely affecting the baryonic matter (2nd image).

Dark matter map: NASA, STScI; ESO; University Arizona
Composite image (visible, dark matter map, X-ray): NASA, ESA, ESO, University Arizona

So what is Dark Matter?

Just because we don’t know what dark matter is doesn’t mean we have no idea. In fact, researchers have a few theories and are considering several plausible candidates.

There are three ways to classify dark matter. Cold dark matter describes the formation of the large-scale structure of the universe and is the fundamental component of the matter in the universe. It’s called cold because it moves ‘slowly’ compared to the speed of light.

Weakly interacting massive particles (WIMPs) are the candidates for cold dark matter particles. They supposedly interact via weak nuclear force. The particles which belong to this group are thought to be the lightest particles of the supersymmetric theories. Neutral examples of these particles could have been produced in the early universe, and later participated in the formation of galaxy clusters.

Hot dark matter is the opposite, it moves close to the speed of light. The warm candidate particles are thought to be less interactive than neutrinos.

Another candidate particle for dark matter is the sterile neutrino — a hypothetical particle that interacts only via gravity and not via any of the other fundamental forces. These would be responsible for forming warm dark matter. They also seem to be heavier than the standard neutrino, and have a longer lifetime before they break down.

Neutrinos were thought to be the best candidates for dark matter. Neutrinos are weird particles — they barely interact with things, and even then only gravitationally (which is a weak interaction). Besides, they do not possess electrical charge, which is why they do not interact electromagnetically. However, the neutrino temperature is high and they decouple (stop interacting with other forms of matter) only at relativistic velocities. If dark matter was made of neutrinos, the universe would have looked radically different.

Massive Compact Halo Objects (MACHOs) represent a different type of candidate. They’re no WIMPs at least. They aren’t particles either, but rather brown dwarfs, planets like Jupiter, black holes in galactic haloes. The best possible MACHOs are primordial black holes( PBHs). Different from the ordinary black holes we see in the center of galaxies, PBHs are thought to have been created nearly 10 seconds after the Big Bang. No evidence for such objects has yet been discovered, but it’s still an open possibility.

Detecting dark matter

Many ideas for the detection of each plausible candidate have been developed.

Through cosmology, the main evidence comes from the Cosmic Microwave Background (CMB).  Yes, the same radiation Dr. Darcy Lewis detected (for real) in the TV miniseries WandaVision. It is the remnant electromagnetic radiation from when the universe was a 380,000-year-old baby.

The best CMB observations we have currently are from the Planck satellite 2018 survey. Different amounts of matter have distinct signals in the CMB observations, forming the temperature power spectrum.

Four Possible Models of the Universe. The yellow square marks the present in all four cases, and for all four, the Hubble constant is equal to the same value at the present time. Time is measured in the vertical direction. The first two universes on the left are ones in which the rate of expansion slows over time. The one on the left will eventually slow, come to a stop and reverse, ending up in a “big crunch,” while the one next to it will continue to expand forever, but ever-more slowly as time passes. The “coasting” universe is one that expands at a constant rate given by the Hubble constant throughout all of the cosmic time. The accelerating universe on the right will continue to expand faster and faster forever. Credits: Physics LibreTexts.

If the theory is correct, the shape of the power spectrum is different for different amounts of matter. There’s such a thing known as the critical density of the universe, which describes the density of the universe if it was coasting, expanding but not accelerating, and if it stopped its expansion. When you divide the density of the observable matter by the critical density, you get its density parameter (Ω).

The temperature power spectrum is modeled according to the different amounts of ingredients in the universe, more matter or less matter changes its shape. Planck’s observations have shown that the matter density parameter is Ω h² ~0.14, so if the shape of the graph corresponds to that value we have evidence of the amount of dark matter in the universe.

Temperature power spectrum for different matter densities. Credits: Wayne Hu.

There are also ways to detect dark matter directly, not through cosmology but through particle physics. The Large Hadron Collider (LHC) is the most powerful particle accelerator, can collide protons at extremely high (relativistic) speeds, generating a bunch of scattered particles that are then measured by the detectors.

Physicists hope to find dark matter by comparing the energy before and after the collision. Since the dark matter particles are elusive, the missing energy could explain their presence. However, no experiment has observed dark matter so far — though researchers are still looking.

Another underground experiment uses high purity sodium iodide crystals as detectors. The detectors at DAMA/LIBRA (Large sodium Iodide Bulk for RAre processes), for example, try to observe an annual variation of regular matter colliding with WIMPs due to the planet’s motion around the Sun which means we’re changing our velocity relative to the galactic dark matter halo. The problem is that DAMA’s 20 years’ worth of data didn’t have enough statistical significance. However, in an identical experiment meant to directly detect dark matter, called ANAIS (Annual modulation with NaI Scintillators), in 3 years scientists gathered more reliable data indicating this method is not conducive to finding dark matter anytime soon. 

To get a better picture of the challenge in having a conclusive result, take a look at the image below. All those lines and colorful contours represent the results of different experiments, none of them seem to agree. That’s the problem with dark matter, we still don’t have the evidence to match any theory we came up with — and we can’t really rule out any possibilities either.

WIMP discovery limit (thick dashed orange) compared with current limits
and regions of interest. Credits: J. Billard and E. Figueroa-Feliciano.

The questions of what dark matter is and how it works still have no satisfying answer. There are many detection experiments being planned and conducted in order to explain and verify different hypotheses, but nothing conclusive thus far. Let’s hope we don’t have to wait another 20 years to figure out if one experiment is right or wrong. Unfortunately, groundbreaking discoveries can take a lot of time, especially in astrophysics. While we wait, dark matter will continue to entertain our imagination.

The article was primarily based on the 2020 Review of Particle Physics from Particle Data Group’s Dark Matter category.

Inside the Super-Kamiokande neutrino detector, Japan. (Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo)

Neutrino! A Hauntingly Significant Particle

For one week every year, physicists from all over the globe come together to discuss the physics surrounding one particle — the neutrino. It may seem tempting to conclude that dedicating an entire week-long conference to a single particle is hyperbole at best. Especially true when considering that this particle is so weakly interacting, that as you have been reading this opening paragraph, hundreds of billions of them have streamed through every square inch of your body. It’s no wonder some scientists have neutrinos on the brain, with so many constantly passing through it. 

The first detection of a neutrino in a bubble chamber in 1970 (Argonne National Laboratory) 

These neutrinos emerge from a variety of sources; the majority of those that reach us here on Earth originate from the Sun, created by the nuclear processes that power our star, others are created in the upper atmosphere when it is struck by cosmic rays. Even more exotic neutrinos originate from violent cosmic events like gamma-ray bursts and supernovae outside our solar system. 

The study of neutrinos is so vital to modern physics that it could explain lingering conundrums such as the nature of dark matter and even deliver the key to a quantum theory of gravity. But, the discovery of the neutrino has humble origins, merging from the need to preserve some of physics’ earliest and most important governing principles. 

Saving the laws of conservation

The discovery of a new element or phenomena in physics is usually born from the observation of a missing piece of the Universe’s overall jigsaw, the need to explain some facet of nature that defies expectation. With neutrinos, initial speculation began in the 1930s when one of the fathers of quantum physics Wolfgang Pauli noticed that in beta-decay, both energy and angular momentum were not being conserved. Neutron decayed into protons and electrons — but these daughter products had less energy and angular momentum than their parent. 

This violated the conservation laws for both properties, but Pauli postulated that if there were some non-interacting particle carrying away energy and angular momentum, that would prevent such a violation. Beta-decay actually resulted in a proton, an electron and a neutrino — more specifically an antineutrino. 

Beta-decay as it understood today results in three daughter particles with the anti-neutrino carrying away the missing energy that troubled Pauli.  

It would be another two decades, give or take, before American physicists Clyde Cowan and Frederick Reines, from Washington New York Universities respectively, would conduct an eponymous experiment to detect neutrinos being emitted from a nuclear reactor. The hunt for more neutrinos was on, and it would require ever more complex and sensitive methods and equipment, pushing the limits of experimental physics. 

A ghost in the particle zoo: What is a neutrino?

Neutrinos are fundamental particles that, as mentioned above, are almost massless and completely chargeless. In fact, the mass of neutrinos is so tiny that for many years, scientists believed it was zero. They are certainly far smaller than the other elementary particles. 

This lack of substantial mass and charge means that of the Universe’s four fundamental forces; neutrinos barely ‘feel’ gravity and aren’t influenced by electromagnetic forces at all. Likewise, the strong nuclear force — mainly at play between protons and neutrons in atomic nuclei— has no baring on neutrinos. Only the weak force — which mitigates how atoms decay and how fundamental particles change ‘flavour’ — has any real effect on the neutrino. 

In many respects, neutrinos are very similar to electrons in terms of the influences they feel. And just like electrons, neutrinos are classed as ‘leptons’ — particles with a ‘spin’ of 1/2 that do not interact with the strong force. 

The particle zoo according to the standard model of particle physics. Each lepton is ‘haunted’ by its own ‘ghost particle’ neutrino (Wikipedia Commons/MissMJ/PBS NOVA/Fermilab/Particle Data Group)

Leptons can roughly be divided into two distinct families — charged and uncharged — and within these categories, further subcategories exist. So for example; the most famous of the charged leptons, the electron, comes accompanied by the muon and the tau, 200 times and 3,500 times the mass of the electron respectively. Of course, each of these comes with a corresponding anti-particle — the positron, the anti-muon and the anti-tau. 

But this symmetry runs deeper; each of these particles also comes with a corresponding neutrino — the electron neutrino, the muon neutrino and the tau neutrino. On the rare occasion that one of these particles does interact with matter, it produces its corresponding charged lepton. 

Thus, as neutrinos whizz through space at near the speed of light, they barely interact with any matter they encounter. Effectively they are ghosts haunting the particle zoo. This leads us to an interesting question; how to capture a ghost? 

Who you gonna call? Cowan and Reines (who were you expecting?)

Neutrinos ‘ghostly’ nature means that it’s very difficult, to catch them directly. This means that early neutrino detection was indirect, observing the rare effects they have on other matter, or even the effect that matter has on yet more matter. 

The initial key to detecting a neutrino goes back to beta-decay, the process that first alerted Pauli to their existence. If that interaction could run in reverse, inverse beta-decay, then an electron neutrino should occasionally interact with a proton to produce a neutron and a positron. The latter being crucial in detecting this interaction, as it is their annihilation upon meeting an electron and the creation of distinctive gamma rays, that tips the researchers off to the presence of a neutrino.

Obviously, the rarity of interactions between neutrinos and matter means two things are needed by researchers hoping to spot the signature of such a process; a lot of neutrinos and a lot of matter for these neutrinos to interact with. After Cowan and Reines abandoned the idea of experimenting with the neutrino flux from atomic bomb tests, the duo decided to use a nuclear reactor at Los Alamos, home of the Manhatten Project, as a source of the particles.

For their ‘matter target,’ the team used two extremely large tanks of water, sandwiched between tanks filled with a liquid scintillator — a substance that gives off flashes of light when struck by gamma rays. These flashes can then be detected by devices that convert photons into electrical signals–photomultiplier tubes.

Reines and Cowan’s improved neutrino detector in 1956 the year they made the first successful measurement of a neutrino. (Reines and Cowan, 1956)

Thus, in 1956, after refining their detector Cowan and Reines made the first indirect measurement of neutrinos, not spotting outgoing particles produced in beta decay, but instead inferring incoming neutrinos triggering inverse beta decay. On June 14 of that year, they sent a telegram to Wolfgang Pauli revealing discovery of the neutrino. He replied: “Thanks for the message. Everything comes to him who knows how to wait.”

The methods of neutrino detection would develop from here, often involving huge vats of liquids as ‘target’ matter. Sometimes surprising substances at that. 

Help! Some of our neutrinos are missing!

When you think of complex and sensitive science experiments and the apparatus that they involve, dry cleaning fluid probably doesn’t immediately spring to mind. But, thanks to astrophysicists Raymond Davis and John Norris Bahcall, the story of neutrino detection can be told without touching on this mundane cleaning liquid.

The intention of the duo was to collect neutrinos emitted by a much larger nuclear furnace than that used by Cowan and Reines, Davis and Bahcall would study solar neutrinos emitted by our star. The ‘Homestake experiment’ was conducted almost 5,000 feet underground in the Homestake mine in South Dakota with 100,000 gallons of perchloroethylene — a substance most commonly used for dry cleaning — between 1970 and 1994. Neutrino detectors since have followed this trend, buried underground to protect them from false signals arising from bombardment with cosmic rays. 

Davis and Bahcall’s Homestake mine detector tank containing 100,000 gallons of trichloroethylene buried 5,000 feet beneath the ground (Brookhaven National Laboratory) 

During the early years of operations, the astrophysicists discovered a problem with neutrinos coming from the Sun. There weren’t enough of them.

Bachall had calculated the rate at which the team’s detector should capture neutrinos, but during the course the experiment, the neutrinos counted totalled only a third of this number. At first, the assumption was that the duo had made some error in their calculations, but repeated checking failed to uncover any mistakes. 

What the Homestake experiment had actually uncovered was the so-called ‘solar neutrino problem.’ A problem that would take nearly four decades to resolve. Interestingly, a solution to the seeming deficit in neutrino flux from the Sun had already been proposed by soviet nuclear physicist Bruno Pontecorvo in 1957 —which he reworked and revised in 1968. 

Pontecorvo had suggested that if electron neutrinos leaving the Sun had mass, then they could change ‘flavour’ during the journey to Earth and our waiting detectors. So a sample of ‘pure’ electron neutrinos would arrive as a ‘mixed batch’ of electron neutrinos, muon neutrinos and tau neutrinos. The detectors at Homesake were only capable of detecting electron neutrinos, hence why 2/3 of the emitted solar neutrinos were ‘missing.’

Physicists were initially reluctant to take Pontecorvo’s theory under serious consideration, mainly perhaps, as it required a major revision to the standard model of particle physics.

Image obtained with the ESO Schmidt Telescope of the Tarantula Nebula in the Large Magellanic Cloud. Supernova 1987A is clearly visible as the very bright star in the middle right. At the time of this image, the supernova was visible with the unaided eye. (ESO)

Despite this heel-dragging, in February of 1987 photons from a type II supernova, 168,000 light-years from Earth, were detected. The observation of SN1987A, as it became known, confirmed that neutrinos did indeed possess some mass. If they didn’t they would travel at the speed of light and thus, neutrinos from the SN1987A would have struck the Earth at the same time as the photons from that event. 

Unfortunately, this alone couldn’t solve the solar neutrino issue. As detection of neutrinos was so difficult, it was impossible to draw firm conclusions from this one event. The issue would be soon resolved however, thanks mainly to observations made by the Super-Kamiokande detector in Japan and data collected by the Sudbury Neutrino Observatory (SNO), Canada, in 1998 and 1999 respectively.

Out in the cold: Neutrino detection today

The award of the 2002 Nobel Prize in physics to Ray Davies for his detection of solar neutrinos really signalled that the age of neutrino physics had arrived. Further to this, the 2015 prize would be awarded to Takaaki Kajita in Japan and Arthur B. McDonald in Canada, for their work in discovering neutrino flavour oscillation and solving the solar neutrino problem at Super-Kamiokande and the Sudbury Neutrino Observatories respectively. 

The interior of the Super-Kamiokande detector in Japan is lined with 13,000 sensors to pinpoint signs of neutrinos. (Kamioka Observatory, ICRR (Institute for Cosmic Ray Research), The University of Tokyo)

Like the Homestake detector, both of these detectors consist of giant tanks of liquid buried deep within the Earth. Super-Kamiokande sits 3,000 feet under Mount Ikeno, 50,000 tonnes of ultrapure water and 13,000 photomultiplier tubes detecting Cherenkov radiation, created when neutrinos cause electrons to move faster through the water than even light can. 

This may seem counterintuitive, nothing moves faster than light, right? That’s a vacuum. Through materials, electrons can move faster than photons in that same material, if still not as fast as light in a vacuum. The same logic explains why neutrons can escape from the core of the Sun faster than light. Photons are forced to interact with the dense material in a star’s core, whilst neutrinos can pass through without impediment. 

Outside view of the Sudbury Neutrino Observatory detector (Courtesy of SNO)

The SNO detector isn’t quite on as large a scale as Super-Kamiokande, containing 1,000 tonnes of hard water, around 10,000 photomultiplier tubes, but its depth at nearly 7000 feet beneath makes it truly imposing. 

But, when it comes to neutrino detectors, it’s hard to imagine one as truly isolated as the aptly IceCube Neutrino Observatory — or just IceCube. The CERN operated observatory located in Anartacia consists of thousands of spherical optical sensors named Digital Optical Modules (DOMs) buried at depths ranging from around 5000- 8000 feet across a cubic kilometre. 

The isolated IceCube lab at the Amundsen-Scott South Pole Station in Antarctica monitors the world’s largest neutrino telescope, which consists of more than 5000 optical sensors held in a cubic kilometre of the polar ice cap (NSF/S Lidström)

Each DOM is attached to a string within 59 other units and possesses its own photomultiplier tube and data gathering computer sending information to a central ‘counting-house.’

In 2013, three years after it began operations, IceCube detected 28 neutrinos from outside our solar system, and the facility is able to detect neutrinos across a wider range of energies than its undeniably impressive contemporaries. 

A diagram of the IceCube units (Nasa-verve — IceCube Science Team — Francis Halzen, Department of Physics, University of Wisconsin)

Over the coming years, researchers at facilities such as Super-Kamiokande and SNO will push neutrino science into investigations that could answer some of physics’ most fundamental mysteries — including attempts to uncover the nature of dark matter. Meanwhile, the detection of sterile neutrinos at IceCube could even help verify string theory as a valid unification theory bringing together general relativity and quantum physics and creating a model of quantum gravity.

The truth is, insignificant though its interactions are, the role of the neutrino in the physics that govern the Universe is anything but.

Quark-Gluon Plasma that filled the early Universe investigated by ALICE

The secrets of the Quark-Gluon Plasma that filled the early universe are being unlocked by the ALICE collaboration at CERN with the first measurement of the flow of bottomonium particles.

Quark-Gluon Plasma that filled the early Universe investigated by ALICE (Author's Collection)

Quark-Gluon Plasma that filled the early Universe investigated by ALICE (Author’s Collection)


In a paper presented at the European Physical Society’s conference on high-energy physics, the ‘A Large Ion Collider Experiment’ (ALICE) collaboration has documented the first-ever measurement of the flow of a heavy meson particle — bottomonium.

The measurement of particles like bottomonium — a type of ‘upsilon’ particle — helps the researchers understand the Quark-Gluon Plasma (QGP) that filled the hot, dense early universe. 

By observing pairs of ‘heavy electrons’ — known as muons — produced by the decay of bottomonium, the team discovered bottomonium particles have small values of elliptic flow — a measure of how uniform energy and momentum is distributed across the particles when viewed from the beamline. 

This is quite unexpected as all other hadrons investigated thus far have exhibited significant elliptic flow. 

David Evans, a professor of high energy physics at the University of Birmingham, leads the UK participation in ALICE.

He says: “ Elliptical flow measurements in ALICE show that the Quark-Gluon Plasma flows like an almost perfect liquid, with the light quarks (up, down, strange, and charm) flowing with the system.”

“The fact that no significant elliptical flow is seen for the bottomonium suggests b-quarks are only produced in the initial collision of the lead ions, before the QGP is formed.”

The ALICE team’s results seem to support existing theories that bottonium and other upsilon particles split into their constituents during the early stages of their interactions with plasma.

This gives the researchers a better insight at the conditions in the early moments of the universe when it was filled with a plasma composed of free quarks and gluons. 

Evans continues: “This makes b-quarks (and particles made up of b-quarks) an ideal probe for studying the QGP as they experience the entire evolution of the system.”

Bottomonium particles — probing the Quark-Gluon Plasma at the dawn of the universe

Taking a trip through the ‘particle zoo’ to discover what these bottomonium particles actually are, helps us understand their role in the ALICE experiment. 

The six known types of quarks on the left and how they come together to form protons and neutrons on the right
The six known types of quarks on the left and how they come together to form protons and neutrons on the right

Bottonium is a heavy meson — particles which consist of a quark and its own antiparticle. In the case of bottomonium, a bottom (or beauty quark) — b quark — and its antiparticle counterpart.

These subatomic particles are extremely unstable, existing for short periods of time and only at high energies before decaying into other particles. When bottomonium decays it leaves behind a pair of ‘heavy electrons’ called muons. 

Bottomonium particles — which are formed in the LHC by the violent collision of heavy lead-lead ions — provide an excellent probe of the Quark-Gluon Plasma which filled the universe just a few millionths of a second after the big bang. 

Being produced so early in the collision event means bottomonium particles ‘experience’ the entire evolution of the plasma — from the moment it is produced to the moment it cools down and enters a state in which hadrons can form.

This extremely early stage in the universe’s evolution would have been the only time in history that quarks and gluons existed freely in plasma and not bound together in a state called ‘confinement’ in protons, neutrons and other hadrons.

These particles were only able to exist in this free state because of the incredible heat in the universe at this point. In our era, quarks and gluons are never observed as free particles.

Thus, it takes a tremendous amount of energy, to recreate these huge temperatures. At the moment, the Large Hadron Collider (LHC) is the only piece of apparatus on Earth capable of doing this, with collisions in the LHC able to generate temperatures a 100 thousand times hotter than the Sun. 

At these temperatures, protons and neutrons ‘melt’, freeing quarks and gluons from confinement, thus creating a Quark-Gluon Plasma and allowing them to form short-lived, unstable particles like bottonium. 

ALICE: Collision queen

The ALICE collaboration — consisting of over a 1000 scientists operating a 10-thousand-tonne, 16m tall detector buried 56m under the Alps — achieves this high-energy feat by slamming together beams of lead ions rather than the proton-proton collisions used in other LHC experiments. 

The decay of upsilon particles — another type of meson — into muon pairs as the result of a lead-lead collision. The red lines track the two muons the orange lines track the other particles produced (CERN)
The decay of upsilon particles — another type of meson — into muon pairs as the result of a lead-lead collision. The red lines track the two muons the orange lines track the other particles produced (CERN)

The benefit of colliding lead ions is that, as ALICE is looking to create Quark-Gluon Plasma, the more quarks available to it, the better the chance of observing something significant. 

A single proton and neutron each contain three quarks but as lead ions contain at least 56 protons and at least 204 neutrons this leaves the team with far more quarks to play with. 

ALICE then measures this plasma as it expands and cools, but it is still unable to measure the particles created directly— instead deducing the presence and properties of QGP from the signatures on pairs of muons it produced by decay. 

One of these signatures is the elliptic flow — the collective movement of the produced particles determined by several factors like particle type, mass, the angle at which the particles meet and the momentum they possess as they collide —  which is what the team measured. The flow is created by the expansion of hot plasma after the collision of the lead ions.

Upgrading ALICE: More collisions. More Quarks. More Results

Perhaps the most promising thing about ALICE’s mission to probe the early universe and its conditions is the fact that the forthcoming high-luminosity upgrade only promises to yield more data for researchers to investigate.

The ALICE Experiment is about to be revitalised (CERN)

The upgrade — which CERN hopes will be operational by 2021— aims to increase the luminosity of the LHC by a factor of 10. Luminosity, as described in reference to particle accelerators, is proportional to the number of collisions that occur. Thus increasing the luminosity also means increasing the number of collisions.

As an example of the usefulness of this upgrade, whereas the LHC produced 3 million Higgs boson particles in 2017, the High-Luminosity LHC is expected to produce 15 million per year.

In addition to the High-Luminosity upgrade — on which work began in 2018 — ALICE will also several other upgrades and improvements. As a result of these improvements, the ALICE team expect an overall gain of 100 times the current results.

Evans says: “With this huge increase in statistics and a new inner detector in ALICE, we will be able to measure particles made of b-quarks with much higher precision.”

As such, the experiment stands a very good chance of significantly improving our knowledge of the quark-gluon plasma and the conditions in the early universe, with these new bottomonium results pointing the way.

Evans concludes: “[The upgrades] allow us to probe the properties of the QGP in much more detail and hence learn more about the evolution of the early universe.”

Physics discover the most exciting form of matter: Excitonium

Researchers from the University of Illinois made a discovery that left the scientific world positively excited. They discovered a new form of matter postulated over 50 years ago, consisting of a boson, a composite material that can allow it to act as a superfluid, superconductor, and an insulating electronic crystal. If that sounds bizarre… well, it kind of is.

Artist’s depiction of the collective excitons of an excitonic solid. These excitations can be thought of as propagating domain walls (yellow) in an otherwise ordered solid exciton background (blue). Image courtesy of Peter Abbamonte, U. of I. Department of Physics and Frederick Seitz Materials Research Laboratory.

The more you dive into the world of particle physics, the stranger things get. The laws of physics themselves start to change if you go down to a small enough scale, with quantum mechanics taking over the more familiar laws of macroscopic physics. A form of matter called a Bose-Einstein condensate (BEC) somewhat bridges the gap between the two. BECs are basically a state of matter in which extremely cold atoms clump up together and behave as a single entity, called a boson. Photons, for instance, are a type of boson, as are some more complex quasiparticles such as plasmons, and phonons.

Excitonium is a type of a condensate made up of excitons — a type of quasiparticles formed in a quantum mechanical pairing from an escaped electron and the hole it left behind. It all starts with a semiconductor, a material with electrical properties somewhere in the middle, between those of a conductor and an insulator. Basically, when an electron on the edge of a semiconductor’s valence band gets excited, it moves on to the conduction side, which is empty. Since all electrons have a negative charge, this leaves behind a “hole” in the valence band, which acts as a positively charged entity. The negative electron and the positive hole are drawn to each other, forming a type of boson called an exciton. The fact that the hole acts as a particle itself can be attributed to the surrounding crowd of electrons. But that understanding makes the pairing no less strange and wonderful, researchers say.

Excitonium was first proposed half a century ago and was hotly debated by particle physicists. But now, researchers have finally managed to prove its existence and create it. When a largely theoretical particle is proven to also physically exist, the result can only be, well, exciting.

“Ever since the term ‘excitonium’ was coined in the 1960s by Harvard theoretical physicist Bert Halperin, physicists have sought to demonstrate its existence,” says Peter Abbamonte, lead researcher on the new study. “Theorists have debated whether it would be an insulator, a perfect conductor, or a superfluid – with some convincing arguments on all sides. Since the 1970s, many experimentalists have published evidence of the existence of excitonium, but their findings weren’t definitive proof and could equally have been explained by a conventional structural phase transition.”

U of I Professor of Physics Peter Abbamonte (center) works with graduate students Anshul Kogar (right) and Mindy Rak (left) in his laboratory at the Frederick Seitz Materials Research Laboratory. Photo by L. Brian Stauffer, University of Illinois at Urbana-Champaign.

The finding could have important ramifications. Excitonium exhibits macroscopic properties of a superconductor, or superfluid, or insulating electronic crystal. These properties make the finding significant not only from a scientific point of view but also from a practical one. It’s not clear yet what the applications of excitonium could be, but it exhibits some enviable properties. Still, for now, it sheds some much-needed light on the often counterintuitive world of quantum mechanics. The study is also a testament to how much research technology has progressed — until only a few years ago, we just didn’t have the necessary tools to create such materials.

“This result is of cosmic significance,” Abbamonte concluded.

The research was published in the journal Science.

Scientists find “Angel Particle” — a particle that’s its own antiparticle

Confirming a theory from the 1920s, Stanford physicists have found evidence of a particle that is its own antiparticle.

An anti-story

In 1928, British physicist Paul Dirac sent ripples through the world of science when he made a stunning prediction: every fundamental particle in the universe has an antiparticle — a particle with the same mass, but opposite charge. When matter and antimatter meet, they annihilate themselves, going out with a BANG. While his prediction was met with some skepticism, it didn’t take long for scientists to discover the first antimatter particle: the position. After the positron — the electron’s anti-particle — was confirmed, Dirac’s theory really took off.

But in 1937, things got even more bizarre. Another brilliant physicist, Ettore Majorana, said that some particles known as fermions can be their own antiparticles. A fermion can be an elementary particle, such as the electron, or it can be a composite particle, such as the proton. But how could such a particle be its own anti-particle? At a first glance, that doesn’t even seem to make sense, but many physicists supported Majorana’s theory.

So fermions were split into two categories: Dirac fermions and Majorana fermions. But the first was certainly a broader category than the second. In order for a particle to be its own anti-particle, it needed to not have a charge; otherwise, it just wouldn’t make sense. All of the Standard Model fermions except the neutrino have charges — so that means they’re Dirac fermions and have antiparticles. The only one whose nature was not settled was the neutrino. Well, it took a much longer time, but scientists believe they’ve finally found a Majorana fermion.

Cloud chamber photograph of the first positron ever observed. Credits: Carl D. Anderson.

A smoking gun

Now, a team of Stanford scientists carried out a series of experiments on exotic matter. Following a plan proposed by Shoucheng Zhang, professor of physics at Stanford, his colleagues and collaborators are confident they’ve found evidence of this phenomenon.

“Our team predicted exactly where to find the Majorana fermion and what to look for as its ‘smoking gun’ experimental signature,” said Zhang, a theoretical physicist and one of the senior authors of the research paper. “This discovery concludes one of the most intensive searches in fundamental physics, which spanned exactly 80 years.”

It’s not the first time this has been suggested. In 2016, researchers from the Fermi National Accelerator Laboratory suggested that the neutrino might be its own antiparticle. But this is the first time a clear indication of such particles has been found.

“It does seem to be a really clean observation of something new,” commented Frank Wilczek, a theoretical physicist and Nobel laureate at the Massachusetts Institute of Technology who was not involved in the study.

“It’s not fundamentally surprising, because physicists have thought for a long time that Majorana fermions could arise out of the types of materials used in this experiment. But they put together several elements that had never been put together before, and engineering things so this new kind of quantum particle can be observed in a clean, robust way is a real milestone.”

The Stanford experiments focused on quasiparticles — not truly particles, but particle-like excitations that arise out of the collective behavior of electrons in superconducting materials, which conduct electricity with 100 percent efficiency. As you’d imagine, the experiments were complex and laborious, but we can understand them by taking it step by step.

Creating quasiparticles

They stacked such a superconductor material on top of a topological insulator, a material which behaves as an insulator in its interior but allows the passing of current on its sides. With this material sandwich, they created a superconducting topological insulator — a material which is amazing at conducting current but only on its sides.

It was also tweaked to be magnetic, so that electrons would flow in one way on one side, and in the opposite way on the other side. When Zhang swept a magnet over it, he made the electrons slow down, stop, or even change direction. This wasn’t a linear, smooth process. As it so often happens in quantum mechanics, the process happened in abrupt steps — quanta. At some point in the process, the desired quasiparticles emerged, in pairs.

Zhang and his collaborators then observed these pairs split up, deflected out of the path of flow. They measured the flow of the individual quasiparticles that kept forging ahead. They behaved just like electrons, their movement being determined by the magnetic field. Their movement was also done in steps, but these steps were twice smaller than the electron steps. This was the smoking gun they were looking for. These were the Majorana fermions.

They named them the “angel particle,” a reference to the Angels & Demons book where a secret group plans to destroy the Vatican using a matter-antimatter bomb.

Here’s a lengthy presentation of the process, if you really want to get a feel for what it entailed.

But this isn’t quite like the real thing, says Professor Giorgio Gratta, who also works at Stanford and studies such interactions. He believes that particles and quasiparticles are different beasts and we can learn different things from them. Gratta believes that the quest for understanding if the neutrino is its own antiparticle continues.

“The quasiparticles they observed are essentially excitations in a material that behave like Majorana particles,” Gratta said. “But they are not elementary particles and they are made in a very artificial way in a very specially prepared material. It’s very unlikely that they occur out in the universe, although who are we to say?”

“On the other hand, neutrinos are everywhere, and if they are found to be Majorana particles we would show that nature not only has made this kind of particles possible but, in fact, has literally filled the universe with them.”

In March 1938, Italian physicist Ettore Majorana disappeared under mysterious circumstances while going by ship from Palermo to Naples. We don’t really know what happened to him. Some said he wanted to escape Fascist Italy and lived in Venezuela. Others say he was killed. But if he could see this, no doubt, his smile would stretch from ear to ear.

Journal Reference: Vlad S. Pribiag — A twist on the Majorana fermion. DOI: 10.1126/science.aao0793

What the proposed new particle accelerator's size could look like compared to the LHC. Credit: CERN.

Physicists dream up LHC 2.0: a new particle accelerator three times bigger than the current LHC

The new particle accelerator will allow physicists to smash particle beams together with a power equivalent to 10 million lightning strikes. Image credit: CERN

The new particle accelerator will allow physicists to smash particle beams together with a power equivalent to 10 million lightning strikes. Image credit: CERN

The Large Hadron Collider at the European particle physics laboratory CERN, near Geneva in Switzerland, is the most complex experimental facility ever built. Its 27-kilometre ring of superconducting magnets makes it the world’s largest and most powerful particle accelerator in the world. Since it first started up in 2008, the LHC has already made monumental contributions to physics. Without the LHC, it would’ve been impossible to confirm the existence of the now famous Higgs boson, the so-called ‘God particle’ thought to be responsible for lending things mass.

Surely, the future has many other scientific discoveries in store for the $4 billion scientific facility. But meanwhile, some of the world’s foremost physicists are already drafting plans for a new, improved LHC 2.0.

This week in Berlin, 500 scientists met to hammer out the new LHC or the Future Circular Collider (FCC), as they’ve named it. EuroCirCol, a four-year European-funded study, is responsible for tracing out the new particle accelerator. Some of the proposed upgrades so far include:

  • An 80-100 kilometre-long circuit (50-62 miles) instead of the LHC’s 27 kilometres (17 miles). That’s three times bigger.
  • It will be located so close to its predecessor on the France-Switzerland border that the two rings will literally overlap.
  • Double-strength magnets will help smash protons and other particles with a strength of up to 100 Tera electron Volts, which is equivalent to 10 million lightning strikes all firing at the same point and seven times more powerful than the LHC.
  • The number of Z bosons produced by FCC-ee (up to 1013),  is expected to be almost six orders of magnitude larger than the number of Z bosons collected at LEP (2×107), and up to four orders of magnitude larger than that envisioned with a linear collider (a few 109).

What the proposed new particle accelerator's size could look like compared to the LHC. Credit: CERN.

What the proposed new particle accelerator’s size could look like compared to the LHC. Credit: CERN.

The FCC will also likely require immense computing power and storage hardware. The LHC collides beams at 20 MHz and every collision is measured and is temporarily stored on hardware to be analyzed. Each recorded event is around 10 MB in size resulting in roughly 5 Zettabytes per year of data being processed. For comparison, the total permanently recorded data on Earth is 0.5 Zettabytes and the total amount of information analyzed by the entire planet is 10 Zettabytes per year.

“5% of the Universe is directly observable. The Standard Model of Particle Physics describes it precisely. What about the remaining 95%?,” a statement on the FCC website reads.

“Yet many questions about our Universe remain unanswered. Is there more matter in the Universe than what is visible? What is dark matter made of? What happened to antimatter after the Big Bang? Are there extra dimensions in the Universe and, if so, can we explore them? To get answers and find out more about our Universe, scientists have to carry out experiments in more powerful particle accelerators. The higher energy frontier will expand our horizons and may shed light to the missing pieces of the puzzle of Nature.”

The physicists reckon the upgrade that will smash particles at dazzling energies will help them find hidden particles that are possibly even heavier than the Hiss boson which LHC confirmed in 2012. On a more practical level, the FCC could lead to more radiation-resistant materials that can be used in nuclear reactors.

It took the LHC about 30 years to switch on since the first sketches on the drawing board in the 1980s to the last nut and bolt. The FCC team hopes to have a thorough plan worked out by next year but no one hopes to see it operational any sooner than 20 years from now.

Meanwhile, the LHC will be busy churning out particles and, in the process, advance our understanding of fundamental physics. Just earlier this year, it found five new subatomic particles. And the LHC is slated for an upgrade of its own when sometimes in the mid-2020s it will see new hardware meant to boost particle collision rate and accuracy. After the new upgrade is ready, it will change its name too into the High Luminosity Large Hadron Collider (HL-LHC).


China plans to build world’s first super collider


Photo from inside CERN’s particle accelerator. Photo: Martial Trezzini/epa/Corbis

A group of Chinese physicists, working with international collaborators, have announced their plans of building a  52-kilometre underground particle accelerator that would smash together electrons and positrons to unravel the fundamental building blocks of life. The project would offer means of probing these sort of fundamental questions that are unavailable to the Large Hadron Collider at CERN, an oval-shaped 26km underground tunnel where the famous Higgs boson was confirmed. Physicists say that the proposed US$3-billion machine is within technological grasp and could be ready by 2028. More importantly, however, the upcoming particle accelerator will become the first stepping stone for a much grander and ambitious project – a super collider.

The super collider that never was

European and US teams have both shown interest in building their own super collider, but the huge amount of research needed before such a machine could be built means that the earliest date either can aim for is 2035. In fact, the US planned a building something like this in 1993 – the  Superconducting Super Collider (SSC)  or Desertron, as it was nicknamed, in Texas. Its planned ring circumference was 87.1 kilometres (54.1 mi) with an energy of 20 TeV per proton or 40 TeV collision energy. This would have made it eight times more powerful than the Large Hadron Collider at CERN, but Congress eventually canceled the project after it contested its utility and $2 billion had already been spent.

Now, China is inclined to make this giant leap which will put the country at the very forefront of particle physics, according to the announcement made by the country’s Institute of High Energy Physics. The country wants to  work towards a more immediate goal than a super collider by 2035, however, and in the meantime it plans on building an electron-positron collider, which should allow the Higgs boson to be studied with greater precision than at the much smaller Large Hadron Collider (LHC) at CERN.


By examining in detail the interactions of the Higgs boson with other particles, the proposed Chinese collider should, for example, be able to detect whether the Higgs is a simple particle or something more exotic. This kind of data will help researchers tell whether the God particle – the fundamental particle thought to be responsible for granting mass to matter – fits within predictions made by the standard model of particle physics, or whether, for example, multiple types of Higgs boson exist.

For China, this is a huge leap forward and some are questioning whether the country wants to bite more than it can chew. China’s largest particle accelerator is only 240 meters long and only ten years ago China’s own physicists would have thought something like this out of reach. The country’s firm economic growth has changed all this and puts it in a position where it can commit to projects other countries can’t even dream of, including the US.

Used to isolation, China plans on building and operating the huge particle accelerator aided by international support, but officials said they don’t plan on waiting – if there isn’t any intention from the international community to help, they’re more than fine with working alone on this. Guido Tonelli, a particle physicist and former head of one of the two major experiments at CERN, says however that China will have to collaborate with the rest of the world if its project is to be a success because of its weakest point – manpower. While making remarkable advances, China’s particle physics community is yet to small to host and operate something as grand as a super collider. At CERN, for instance, physicists from all over the world are working there, including Europe, the US, Japan and, of course, China.

Realistically, only one super collider can be built in the world in the coming decades. As such, the world NEEDS to collaborate to make sure this project finds ist best home and leaders. Physics is not about politics.

Scientists search for unparticle in the Earth’s mantle – find nothing, still happy

Particles and unparticles


Ok, we know a lot about particles – from electrons and neutrons to the more elusive quarks and leptons, and to the holy Graal of the Standard Model – the Higgs boson; but what’s an unparticle? Well, the Standard Model is just a theory, and there are other theories out there. Unparticle physics postulates that matter that cannot be explained in terms of particles using only the Standard Model of particle physics, because its components are scale invariant. But we have to dive even deeper into the world of physics if we are to understand what this theory claims.

There are four forces that we know of in the Universe: gravitation, electromagnetics, weak nuclear and strong nuclear; every physicist would gladly sell his soul to the devil for a theory that could unify these four forces into a single theory – this would broaden our understanding of the universe so much, it would open a golden age for research of all kind; but at the moment, we’re not even close to that paradigm shift.

But unparticle physicists claim things are even more complicated, and there also exists a fifth force of nature, which is a long-range spin-spin interaction and could loosely be viewed as a version of magnetism that does not weaken as quickly with distance.

Earth as a particle accelerator


When you stick a magnet to the fridge, it sticks there because the electrons in the magnet and those in the fridge’s steel exterior are all spinning around in the same direction. But longer-range spin-spin interactions are much more of a question mark.

Theory says this fifth force should tweak the amount of energy needed to flip the spin of an electron or neutron, due to interaction with another particle far away. At least, this is what Larry Hunter of Amherst College in Massachusetts and his colleagues claim. They created an experiment which uses the Earth itself as a source of electrons, narrowing down the search for a new force-bearing particle, placing tighter limits on how big the force it carries can be. As a bonus, if their research turns out to be correct, this could also hold important geophysical information on the processes that take place in the mantle.

Believers in this fifth force are split into three camps, depending on where the force can come from: the first possible particle is the unparticle, which behaves like photons (light particles) in some ways, and like particles of matter in others. The second is one called the Z’ (Z-prime), a lighter cousin of the Z boson that carries the weak nuclear force, while the third camp believes there is no new particle at all, but the theory of relativity has some component that is affecting spin.

The unparticle and the mantle

earth mantle

The researchers set out to create what is called an electron map – the spin directions and densities of electrons inside the Earth. To make the map they used the known strength and direction of the Earth’s magnetic field everywhere within the planet’s mantle and crust, again narrowing down

Extreme conditions in the planet’s mantle can affect the spins of electrons in various minerals, and these in turn affect the Earth’s magnetic field. So when researchers analyzed the geomagnetic data, they were able to infer the electron spins and how these spins would interact with particles in the lab via the fifth force (with a certain degree of uncertainty).

Comparing the results of three previous laboratory spin experiments to look for signs that electrons in Earth’s mantle had influenced what was measured showed them nothing – which actually places a useful constraint on their theory – it tells us that the force must be very weak.

“We often spend a decade struggling to get a factor of 10 improvement in a measurement,” says Hunter. “This was like an incredible gift, as we didn’t even have to do a new experiment.”

So basically, even though they elegantly avoid this point, this research could also be the demise of their theory; instead, they choose to interpret it as a constraint that will tell them how not to look for it in the future.

“It’s one of those low probability but high pay-off activities,” he says. “Boy, if you see something, it really is exciting.”

Via NewScientist

New, great open-access deal for particle physics

Fantastic news for physics lovers: pretty much all particle physics articles will now be open-source, thanks to a deal between a consortium and 12 journals.

In the most remarkable attempt to make hard, peer-reviewed science available to readers, the Sponsoring Consortium for Open Access Publishing in Particle Physics (SCOAP3) is close to securing all particle-physics articles — about 7,000 publications last year — free on journal’s websites.

Particle physics is already a paragon of open source, with most studies being published on he preprint server arXiv, but most peer-reviewed studies were still published in subscription journals – a quite contested method, due to the practices of publishing companies, most notably, Elsevier. Basically, in order to receive access to the articles and journals they are most interested in, entities such as universities and institutes are forced to strike deals in which they buy more than they are interested in; but that will, hopefully change in the nearby future.


The new deal stipulates that research groups do not need to arrange open publication of their work, and over 90 percent work in the field will be published open source, as of 2014. Salvatore Mele, who leads the project from CERN, Europe’s high-energy physics laboratory near Geneva, Switzerland, and home of the LHC announced the details, and seemed quite pleased with this development.

It is “the most systematic attempt to convert all the journals in a given field to open access”, says Peter Suber, a philosopher at Earlham College in Richmond, Indiana, and a proponent of open access.

The consortium managed to do this by inviting the journals to bid for three-year open-access publishing contracts, and ranked them by an undisclosed algorithm that weighed their fees against their impact factors and the licences and delivery formats they offer. The journals won big, gaining an average of €1,200 (US$1,550) per paper, but the biggest winners here are the public and physics. The consortium will pay this from an annual budget of approximately 12 million dollars, funded not by authors or research grants, but by pledges from more than a thousand libraries, funding agencies and research consortia across the world.

Source: Nature

A computer graphic shows a typical Higgs boson candidate event, including two high-energy photons. (C) CERN

Rumors of imminent Higgs boson announcement run amok on science blogs. Discovery might be announced next week

The Higgs boson or the God particle, as it’s also been commonly referred to, is a hypothetical particle that endows other elementary particles with mass. Confirming its existence is of crucial importance to physicists at the moment, otherwise scientists would be forced to rethink another method of imputing mass to particles.  Last year, scientists at CERN registered a hint; a tiny hint of the Higgs boson, when Atlas and CMS, two experimental teams at the Geneva particle accelerator facility, interdependently registered unusual bumps in their data. In December, rumors had it that the elementary particle would soon be unveiled, only to warrant an official statement from Geneva that results are still far from conclusive.

The most elaborate ‘manhunt’ in history

A computer graphic shows a typical Higgs boson candidate event, including two high-energy photons. (C) CERN

A computer graphic shows a typical Higgs boson candidate event, including two high-energy photons. (C) CERN

Recently, a new wave of enthusiasm has sparked science blogs to speculate that we’re in for an imminent announcement from CERN that will once and far all decide if indeed this hypothetical particle exists or not. “The bottom line though is now clear: there’s something there which looks like a Higgs is supposed to look,” wrote Peter Woit, a mathematician and  Columbia professor. “If this years peaks are not exactly in the same place as last years then the combined significance could be considerably less,” reads a skeptical entry at the Vixra blog. Tomasso Dorigo, an experimental particle physicist, settled to offer his own take on the probability of such a find. These are just a few of the myriad of impressions currently circulating around the God particle.

These was sparked after a team of physicists gathered in a room at CERN on Friday to begin crunching new data from the Large Hadron Collider this year. They’ll be at it for a whole week. The new results should settle whether last year’s anomaly was indeed a simple fluke, or the scientists are on the right path; if so this would mark only the beginning of an even larger road ahead for the CERN researchers. Nevertheless, in all likelihood, these results will be made public at the International Conference on High Energy Physics, or Ichep, in Melbourne, Australia, starting July 4.

“Please do not believe the blogs,” Fabiola Gianotti, the spokeswoman for the team known as Atlas.

Personally, I’ve well went past getting too excited over simple rumors – only cold and officially released facts should matter at this time; it will keep you sane too.

How to find the Higgs boson

Dr. Higgs first theorized that if particles were to be hit hard enough, by the right amount of energy, its own quantum particle would be produced. With this goal in mind, the Large Hadron Collider accelerates protons to energies of four trillion electron volts around a 17-mile underground racetrack at CERN, before colliding them together.  The Atlas group hypothesized the Higgs boson’s mass at 124 billion electron volts, while the CMS group came up with 126 billion electron volts – a proton weighs in at one billion electron volts and an electron at half a million electron volts.

How can the scientists be certain that they’ve found Higgs boson? Well, it all lies in probability. To be certain, scientists need to find a 5 sigma signal in at least one channel of one experiment.  Wired‘s Adam Mann explains, “In the rigorous world of high-energy physics, researchers wait to see a 5-sigma signal, which has only a 0.000028 percent probability of happening by chance, before claiming a ‘discovery,'” or or one chance in 3.5 million that it is a fluke background fluctuation. Adding, “The latest Higgs rumors suggest nearly-there 4-sigma signals are turning up at both of the two separate LHC experiments that are hunting for the particle.”

This week, the BaBar experiment, which has ran for a decade at US Department of Energy’s SLAC National Accelerator Laboratory, found hints of flaws in the Standard Model of Physics, after data revealed  certain particle decay happening at a pace far exceeding predictions. The excess decays has to be still confirmed, but they claim that data already rules out the Two Higgs Doublet Model.

Next month’s International Conference on High Energy Physics might host the announcement of the century for particle physics or the Higgs boson final resting place. We’re patiently waiting.

Interview with Professor Higgs, who explains what it will mean to him if scientists at CERN confirm the existence of the Higgs boson.

via New York Times

Antimatter trapped for 15 minutes at CERN

The team operating the Antihydrogen Laser Physics Apparatus (ALPHA) at the CERN laboratory in Geneva, Switzerland reported storing antimatter for approximately 1000 seconds, which might not seem like much of a big deal, but it is about 10.000 times longer than the previous record !

A cloud of antihydrogen

This study will hopefully reveal more about the elusive antimatter, and whether this is in fact the true mirror image of matter. With this thought in mind, the ALPHA team set out to find a way to capture antimatter for as long as possible; they devised an antimagnetic trap to help them capture a cloud of antihydrogen. The thing about antimatter is that it creates a bang whenever it comes in contact with matter, thus making it almost impossible to store for a long time.

In previous experiments, researchers would open the trap and observe the collisions between antimatter and the trace gases; the collisions either annihilated the antimatter or gave it enough energy to escape the trap. But this time, the people at CERN did things a little differently.

They waited much longer before opening the trap, and they cooled the antiprotons, which lowered the energy of antimatter, allowed more to be captured, thus raising the chance that some of it will be captured for a longer period of time.

Capturing antimatter for a longer time will allow further experiments to be conducted on it, such as checking if the energy levels of the antihydrogen and hydrogen are the same.

Elusive Antimatter

When introduced, antimatter was a revolutionary concept, and rejected by many physicists at the moment. In recent years, it has been shown that with the right process, it can be captured for a limited amount of time, which was generally restricted to a fraction of a second. CERN particle physicists shattered that ‘record’, capturing it for a much longer period, almost enough to perform some experiments on it.

In particle physics, antimatter is an extension of antiparticles to matter. If you have, say a hydrogen atom, which is made out of 1 proton (positively charged) and 1 electron (negatively charged), an antihydrogen atom will be made out of 1 antiproton and one positron.

It is theoretized that when the Universe was formed, matter and antimatter were created in equal amounts, but the question remains: where is all the antimatter ? We are all made out of matter (you, me, trees, planets, etc), but it is almost impossible to even get a glimpse of antimatter. This is why researchers hope to capture it for longer periods of time, thus allowing the possibility of experiments which would shed some light on some of the most important questions in physics at the moment.