Tag Archives: particle

CERN found a new particle — a tetraquark

Four quarks’ the charm, it seems, as CERN reported the discovery of a new physical particle created from four charm quarks — the ‘tetraquark’

Illustration of a tetraquark composed of two charm quarks and two charm antiquarks.
Image credits CERN.

Although the discovery marks a major breakthrough in a decades-long research effort, the paper describing it has not yet been peer-reviewed, so take it with a grain of salt. It is, however, signed by over 800 researchers, part of the LHCb collaboration at CERN and was “presented at a recent seminar”.

Being newly-discovered, we don’t really know much about the tetraquark itself. However, it should help us better understand how quarks bind themselves together to form particles such as protons or neutrons.

Old particles, new tricks

Quarks are elemental particles — as far as we can tell, they are what everything is made of. We’ve observed them coming together into groups of two and three to form hadrons. We’ve also theorized that four- and five-quark hadrons exist.

“Particles made up of four quarks are already exotic, and the one we have just discovered is the first to be made up of four heavy quarks of the same type, specifically two charm quarks and two charm antiquarks,” says the Giovanni Passaleva, spokesperson of the LHCb collaboration.

“Up until now, LHCb and other experiments had only observed tetraquarks with two heavy quarks at most and none with more than two quarks of the same type.”

Such unusual particles are an ideal “laboratory” in which to study the strong interaction, one of the four known fundamental forces of nature. The strong interaction is what binds elemental particles together to form atoms and matter. A better understanding of the strong interaction could let us better estimate what particles should and shouldn’t be able to form under normal conditions.

The new tetraquark is ideal from this point of view as its a relatively simple particle against which we can test our current models. It is as of yet still unclear whether it’s a “true tetraquark” or not — that is, whether it’s a four-quark particle or two two-quark particles interacting in a molecule-like state.

The team found this tetraquark by looking for “bumps” — an excess of collision events over a known background value — in records from the first and second runs of the Large Hadron Collider, taken from 2009 to 2013 and 2015 to 2018 respectively. The bump has a statistical significance of more than five standard deviations, which, the authors explain, is the usual threshold for claiming the discovery of a new particle. The bump also corresponds to the predicted mass of four-charm-quark-particles.

The paper “Observation of structure in the J/ψ-pair mass spectrum” has been published in the pre-print level ArXiv.

Decade-old debate put to rest with new measurement of proton diameter

We now have an accurate measurement of how large protons are.

Image via Pixabay.

Back in 2010, a team of physicists set their field (figuratively) on fire. They measured the radius of a proton and found it to be 4% smaller than expected. Physicists are very passionate about this kind of stuff and it sparked a huge debate. Now, researchers from York University have put the debate to rest by taking a precise measurement of the size of the proton.

How big is something very small?

“The level of precision required to determine the proton size made this the most difficult measurement our laboratory has ever attempted,” said Distinguished Research Professor Eric Hessels, Department of Physics & Astronomy, who led the study.

The exact size of the proton is an important unsolved problem in fundamental physics today, one which the present study addresses. The team reports that protons measure 0.833 femtometers in diameter (a femtometer is one-trillionth of a millimeter). This measurement is roughly 5% percent smaller than the previously-accepted radius value.

“After eight years of working on this experiment, we are pleased to record such a high-precision measurement that helps to solve the elusive proton-radius puzzle,” said Hessels.

The exact measurement of the proton’s radius would have significant consequences for the understanding of the laws of physics, such as the theory of quantum electrodynamics, which describes how light and matter interact. Hessels says that the study didn’t exist in a vacuum — three previous studies were pivotal in attempting to resolve the discrepancy between electron-based and muon-based determinations of the proton size.

The 2010 study was the first to use muonic hydrogen to determine the proton size (whereas previous experiments used regular hydrogen). Hydrogen atoms are made up of one proton and one electron In the 2010 experiment, the team replaced the electron with a muon, a related (but heavier) particle.

While a 2017 study using simple hydrogen agreed with the 2010 muon-based result, a 2018 experiment, also using hydrogen, supported the pre-2010 value. Hessels and his team spent the last eight years trying to get to the bottom of the issue and understand why researchers were getting different results when measuring with muons rather than electrons.

The team carried out a high-precision measurement using a technique they developed for this purpose, the frequency-offset separated oscillatory fields technique (FOSOF). In essence, they used a fast beam of hydrogen atoms created by shooting protons through hydrogen molecules. Their result agrees with the value found in the 2010 study.

The paper “A measurement of the atomic hydrogen Lamb shift and the proton charge radius” has been published in the journal Science.

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.

Liniac 4.

CERN celebrates completion of Liniac 4, its most powerful linear accelerator

In about three years from now, the LHC will receive its most powerful linear accelerator yet.

Liniac 4.

Image credits CERN.

The Large Hadron Collider (LHC) is set to get an upgrade. During a ceremony today, CERN inaugurated its newest linear accelerator, Linac 4. By 2021, it will feed CERN’s accelerator complex with higher-energy particle beams than currently possible, allowing the collider to reach higher luminosity levels.

“We are delighted to celebrate this remarkable accomplishment. Linac 4 is a modern injector and the first key element of our ambitious upgrade programme, leading up to the High-Luminosity LHC. This high-luminosity phase will considerably increase the potential of the LHC experiments for discovering new physics and measuring the properties of the Higgs particle in more detail,” said CERN Director General Fabiola Gianotti.

While there’s a lot of enthusiasm around Liniac 4, CERN researchers will have to be patient until they can start toying with the new gear. The accelerator will have to pass an extensive period of testing before it’s connected to the accelerator complex at CERN, which will take place during the upcoming technical shut down scheduled for 2019-2020.

During the shutdown, Liniac 4 will replace Liniac 2, which has been in service since 1978, becoming the first part of CERN’s accelerator chain and supplying proton beams for all the facility’s needs. Liniac 4 measures in at about 90 meters long (295 feet), and will be installed 12 meters underground. The device took almost 10 years to build.

What does it do, though?

The linear accelerator is the first essential component of an accelerator chain. It’s the bit where the particles are produced and given initial acceleration, and it’s here that the researchers can tweak the density and intensity of the beams.

The plan is to have this new accelerator send negative hydrogen ions (a regular hydrogen atom with one extra electron) to the Proton Synchrotron Booster (PSB), which will further accelerate these ions and strip them of the electrons in the process. Liniac 4 is designed to bring the beam up to 160 MeV energy, over three times more than its predecessor could churn out. By using hydrogen ions in the process together with this increase in energy output, the researchers will be able to double the intensity of the final beam delivered to the LHC, which should help increase its luminosity (the number of particles colliding withing a standard length of time) almost five-fold by 2025.

Armed with the Liniac 4, the LHC should be able to churn out about 10 times as much data in 2025-2035 than before. The so-called High-Luminosity LHC will help scientists glean more accurate measurements of the fundamental particles than ever before and allow them the possibility of observing rare processes that occur beyond the machine’s present sensitivity level.

New measurement of a proton leaves us with more questions than answers

Six years ago, physicists announced the results of a new measurement of the proton — and the particle turned out to be too short. Since then, a lot of effort has been put into checking their results — and again, the latest measurements have revealed smaller than expected results. Physicists are now left scratching their collective heads trying to pin down the elusive measurements of this particle.

Image via Pixabay

Protons are positively charged particles that, together with neutrons, form the nuclei of atoms. They’re really, really tiny — for years, the proton’s radius was set at about 0.877 femtometers. One femtometer being equal to 10−15 meters, slightly over a quadrillionth of a meter in diameter. This number, however, was changed in 2010, when Randolf Pohl from the Max Planck Institute of Quantum Optics in Germany used a novel measuring technique and got a better measurement for a proton’s size.

His team started from a simple hydrogen atom — which has one proton and one electron — and substituted its electron for a heavier particle called a muon. They then fired a laser at the altered atom, measuring the resulting change in its energy levels to calculate the size of the nucleus — which in the case of hydrogen is a single proton. They reported that their measurement of the particle came out 4% smaller than what other methods showed.

Measurements performed in 2013 confirmed the findings, setting the world of particle physics ablaze trying to find the answer to the “proton radius puzzle.”

Pohl also applied this technique to deuterium, a hydrogen isotope with one proton and one neutron — also known as a deutron in this case — in the nucleus. Accurately calculating the size of the deutron took plenty of time. Today, the team published the long-awaited result and, you’ll never guess it, it came up short again, this time by 0.8%.

Evangeline J. Downie at the George Washington University in Washington DC says that these numbers show the proton radius puzzle is here to stay.

“It tells us that there’s still a puzzle,” says Downie. “It’s still very open, and the only thing that’s going to allow us to solve it is new data.”

Several other similar experiments, both at Pohl’s and other labs around the world, are already underway. One such experiment will re-use the muon technique to measure the nucleus size of heavier atoms, such as helium.

Pohl believes the issue may not be with the proton itself, but rather with an incorrect measurement of the Rydberg constant which describes the wavelengths of light emitted by an excited atom. This constant’s value has been established very precisely in other experiments however, so something has to have gone really wrong for it to be inaccurate.

One other explanation proposes new particles that cause unexpected interactions between the proton and the muon, without changing its relationship with the electron. That could mean that the key to the puzzle lies beyond the standard model of particle physics.

“If at some point in the future, somebody will discover something beyond the standard model, it would be like this,” says Pohl.

Foamy gold is mostly empty, floats on coffee

Imagine a nugget of real, 20 carat gold floating merrily on the milk foam of your cup of warm cappuccino — scientists from ETH Zurich have found a way to do it. It’s not super-cappuccino, or diamond-strong foam — scientists led by Raffaele Mezzenga, Professor of Food and Soft Materials at ETH have produced a novel foam of gold, a three-dimensional material that is actually mostly…empty.

This 20 carats gold foam is lighter than milk foam.
Image via ethz

“The so-called aerogel is a thousand times lighter than conventional gold alloys. It is lighter than water and almost as light as air,” says Mezzenga.

To the naked eye it looks just like a sturdy, shiny block of conventional gold, but that’s where the resemblance ends — this foamy gold (that’s what I’m calling it) is soft and malleable by hand. It’s 98 percent air held together loosely by gold (four-fifths of the solid material) and milk protein fibrils (one-fifth), qualifying it as 20 carat gold.

The material is created by first heating milk proteins until they coalesce into nanometre-fine fibres named amyloid fibrils. The fibrils are placed in a solution of gold salt, where they interlace into a basic structure that the gold crystallizes on in small particles. The end result is a gel-like gold fibre network.

“One of the big challenges was how to dry this fine network without destroying it,” explains Gustav Nyström, postdoc in Mezzenga’s group and first author of the study.

Air drying wasn’t viable as it could damage the gold structure, so the scientists opted for a gentler but more laborious process that relies on carbon dioxide, assisted by the Professor of Process Engineering Marco Mazzotti.

This method of production, where the metal particles crystallize during the manufacture of the protein scaffold rather than after its completion, is novel. And one of its biggest advantages is that it makes it easy to create a homogeneous gold aerogel that mimics gold alloys perfectly.

It also allows scientists numerous possibilities to influence the properties of the material.

“The optical properties of gold depend strongly on the size and shape of the gold particles,” says Nyström. “Therefore we can even change the colour of the material. When we change the reaction conditions in order that the gold doesn’t crystallise into microparticles but rather smaller nanoparticles, it results in a dark-red gold.”

A foam of amyloid protein filaments without gold (top), with gold microparticles (middle) and gold nanoparticles (below).
Image via ethz

The new material could be used in many of the applications where gold is currently being used, says Mezzenga. The substance’s properties, including its lighter weight, smaller material requirement and porous structure, have their advantages. Applications in watches and jewellery are only one possibility.

Another use demonstrated by the scientists is chemical catalysis: since the highly porous material has a huge surface, chemical reactions that depend on the presence of gold can be run in a very efficient manner. The material could also be used in applications where light is absorbed or reflected. Finally, the scientists have also shown how it becomes possible to manufacture pressure sensors with it.

“At normal atmospheric pressure the individual gold particles in the material do not touch, and the gold aerogel does not conduct electricity,” explains Mezzenga. “But when the pressure is increased, the material gets compressed and the particles begin to touch, making the material conductive.”

The world’s first image of light as both a particle and a wave

We see light every day, and yet, we don’t truly understand it; it’s either a particle or a wave, or both at the same time… and we don’t really know why. Now, for the first time, researchers have captured an image of light behaving as a particle and a wave at the same time.

Wave-Particle Duality

The wave signature is on the top of the image, while the photons are at the bottom. Image: Fabrizio Carbone/EPFL

Christian Huygens, who was a contemporary of Isaac Newton, suggested that light travels in waves. Isaac Newton, however, thought that light was composed of particles that were too small to detect individually. Strangely enough.. they were both right. In 1801 a physicist in England, Thomas Young, performed experiments which revealed that light is a wave. In the 1890s, Maxwell’s equations described light behavior in such an elegant way that many scientists thought not much was left to say about it.

Then, on Dec. 14, 1900, Max Planck came along and introduced a stunningly simple, yet strangely unsettling, concept: that light must carry energy in discrete, specific quantities. Before you know it, the particle nature came back with a vengeance; to make things even more interesting, Louis De Broglie demonstrated that every physical object actually has wave properties – in a way, everything is both a wave and matter at the same time. This is called the wave-particle duality.

As Einstein wrote:

“It seems as though we must use sometimes the one theory and sometimes the other, while at times we may use either. We are faced with a new kind of difficulty. We have two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do”.

This seems to be most intriguing in the case of light – it seems that light behaves selectively depending on the environmental constraints. Sometimes it’s a wave, sometimes it’s a particle… and sometimes it’s both. Scientists have only ever been able to capture an image of light as either a particle or a wave, and never both at the same time… until now.

The first Wave-Particle image

The key to this success lies in the unusual experimental design. The team from the École Polytechnique Fédérale de Lausanne in Switzerland have managed to use electrons to image light by firing a pulse of laser light at a single strand of nanowire suspended on a piece of graphene film. This caused the nanowire to vibrate, and in turn, to send light particles (photons) along two possible directions. When light particles that are travelling on opposite directions meet and overlap on the wire, they form a wave. Known as a ‘standing wave’, this state creates light that radiates around the nanowire.

That’s a pretty creative setup in its own right, but it’s not gonna give you a wave-particle image, so they needed to take it one step further. They sent a stream of electrons into the area nearby the nanowire, forcing an interaction between the electrons and the light that had been confined on the nanowire. This caused the electrons to either speed up or slow down; using an ultrafast electron,  they could visualise the standing wave, “which acts as a fingerprint of the wave-nature of light,” the press release explains. So they were able to capture as  a wave (its fingerprint actually; at the top of the image) and as photons (in the bottom of the image).

“This experiment demonstrates that, for the first time ever, we can film quantum mechanics – and its paradoxical nature – directly,” one of the team, physicist  Fabrizio Carbone, said in a press release. “Being able to image and control quantum phenomena at the nanometer scale like this opens up a new route towards quantum computing.”

The team in Switzerland also put together the adorable video above, explaining their experiment.

Journal Reference: L Piazza, T.T.A. Lummen, E Quiñonez, Y Murooka, B.W. Reed, B Barwick & F Carbone. Simultaneous observation of the quantization and the interference pattern of a plasmonic near-field. Nature Communications 6, Article number: 6407 doi:10.1038/ncomms7407



Large Hadron Collider hints at infant Universe

Despite several setbacks and technical difficulties, the Large Hadrdon Collider is already starting to live up to it’s nickname, the Big Bang machine. Researchers have pinpointed what may very well be the dense, hot state state of matter that is believed to have filled the Universe during its first nanoseconds.

Generally speaking, quarks are bound together in groups of two or three, stuck together by gluons. However, right after the Big Bang, it was so hot that the quarks broke free, and the matter became a free flow of quarks and gluons.

In the snapshots taken from LHC’s detector, a flow similar to this has been observed.

Full report here.

LHC – we have a collision !

“It’s a great day to be a particle physicist,” said CERN director general Rolf Heuer. “A lot of people have waited a long time for this moment.”


The LHC had been going on a promising streak for quite a while now; however, the encountered problems (mostly engineering, but also physics) were huge. Imagine firing arrows on the face of the ocean and making them collide – that was the task for the engineers and physicists at CERN.

They did achieve collisions before, but this is the first one to reach a significant energy, 7 Tev (teraelectronvolts, which is pretty much 1.6 x 10^-7 Joules; doesn’t sound like much, unless you’re a particle). The previous record was at about 2.36 TeV.

Achieving a collision of this level marks the official start of the LHC programme and the next 18 to 24 months are expected to produce trillions of high-energy collisions. So what does this mean ? If they don’t find the Higgs boson, does that mean we’ll have to rewrite physics ? Probably not. It will just show us which of the current competing theories is right. But what happens if they are all wrong ? Well… for the time being, let’s just hope that won’t happen and wait for the current updates from Cern.

You can watch a live webcast from the LHC , twitter updates or track their status in graphical form. Either way, this collision marks the beginning of a new era in modern physics.

Oh, PS : the world is still here.

The most absurd explanation you’ll hear today

Well, the talk is on homeopathy, but this is really not about homeopathy. It’s about the “physics” explanation, and how it manages to be so absurd that it basically urinates on pretty much modern science in just 5 minutes (which is quite an achievement, truth be told). With no disrespect, how she got the “Dr.” title is beyond me, and I hope this is a joke. Actually, I hope she’s on some hard drugs; heavy stuff, really. Then, I could understand. So without further ado, here’s the easiest way to get dumber I’ve come across:

LHC produces first results

Since the Large Hadron Collider went back in business, all sort of rumors have been circling the scientific circles (and not only). However, until these rumors are proven wrong or right, the first official paper on proton collisions from the Large Hadron Collider has been published in this week’s edition of Springer’s European Physical Journal C. .


Designed to reach the highest energy ever explored in particle accelerators, it features a circular tunnel with the circumference of 27 km. Since it’s been recommissioned, a total of 284 collisions have been recorded, all of which have been analyzed and interpreted. The researchers have been able to determine what is called ‘pseudorapidity density’ (the average number of charged particles that are emitted perpendicular to the beam direction. The goal of this was to compare the results with those obtained in the case of proton-antiproton collisions that took place in the same conditions.

The paper was published by ALICE (a Large Ion Collider Experiment that brings together authors from 113 institutions). As well as the actual results, the paper also explains how their detecting and analyzing system works. The results are not only consistent with earlier measurements, but they also fit the theoretical model produced by researchers.

Dr. Jürgen Schukraft from CERN and ALICE spokesperson said: “This important benchmark test illustrates the excellent functioning and rapid progress of the LHC accelerator, and of both the hardware and software of the ALICE experiment, in this early start-up phase. LHC and its experiments have finally entered the phase of physics exploitation.”

CERN is back in business with the first collisions


The researchers and engineers operating the Large Hadron Collider have smashed together for the first time protons, in what is considered a huge step forward by pretty much everybody working at the huge physics experiment.

The particles were accelerated on Monday, through the LHC’s 27 km and then ‘drove’ into each other, in an attempt to recreate the conditions that took place a few moments after the Big Bang. This attempt is crucial for our understanding of physics, and here’s why.

Researchers are trying to find signs of what has been called the Higgs boson. This subatomic particle lies at the foundation of our understanding of particle physics, but despite the fact that it’s so important, we have yet to actually discover it. It’s expected that the LHC will provide the sought after particle and confirm our current theories. However, if not, we may be forced to rethink pretty much all of our particle physics.

The people operating this amazing particle accelerator seem quite ecstatic, as you can see below.


“It’s a great achievement to have come this far in so short a time,” said Cern’s director-general Rolf Heuer. But we need to keep a sense of perspective – there’s still much to do before we can start the LHC physics programme.”

Fabiola Gianotti, spokesperson for the Atlas scientific team, commented: “This is great news, the start of a fantastic era of physics and hopefully discoveries after 20 years’ work by the international community.”

We’ll keep you posted with what’s going on at the LHC, and we’re pretty psyched to see how things are going. There’s definitely more to come.

The man who got his head into a particle accelerator


We’ve all heard stories about soviet scientists, and Hollywood played quite an important role in that. Really few of those stories are actually true, but here’s one that will probably baffle you; it did this to Russian physicists and doctors. First of all, it has to be said that by the time the USSR divided, they had created more than 50 science towns, that lost their funding after it collapsed, quitting research.

A thing that they were really interested about was particle accelerators, because the sum of the parts is very different than the total. Actually, a soviet scientists used a very interesting analogy.
it’s like two Soviet Fiats colliding to produce a bus and a Mercedes Benz 600. The story of Anatoli Bugorski is definitely a very interesting one. When he looked into a particle accelerator to check a piece of the equipment (yeah, they’re not really into safety at work) a particle entered his head. In 1978 the proton beam entered his head measuring about 200,000 rads, collided with the inside of his head, and exited measuring about 300,000 rads.

He was blinded by the light of more than a thousand suns, but felt no pain. His face was really swollen and the doctors he was taken too were expecting to see him die in a few days. He didn’t. After that, they expected to see paralysis and other really bad symptoms. These didn’t appeared. As a matter of fact he continues to live a normal life and actually works in scientific fields.

Despite the fact that he would want to help other western scientists, he doesn’t want to leave the science city of Protvino; these towns are half dead, half hopeful, and half brilliant. The unglamorous miracle of their survival is not really that amazing, especially when a particle moving at the speed of sound or faster goes throught your head.