Tag Archives: meson

New LHC results could be a back-breaker for the Standard Model of Physics

We can’t call it a major discovery. Not yet. However, there are some indications that researchers working at the Large Hadron Collider (LHC) have discovered something beyond our current understanding of Physics – something that’s outside the Standard Model.

“To put it in terms of the cinema, where we once only had a few leaked scenes from an much-anticipated blockbuster, the LHC has finally treated fans to the first real trailer,” says Prof. Mariusz Witek (IFJ PAN), one of the members of the team that made the discovery.

Image via CERN.

The LHC is the world’s largest and most powerful particle collider, the largest, most complex experimental facility ever built and the single largest machine in the world. With it, physicists hope to uncover some of the most daunting secrets of the Universe and to better understand the sub-atomic particle world, which governs interaction between all types of matter.

The Standard Model is a theory that attempts to classify all the subatomic particles in the world, as well as the interactions between them. So far, everything that the LHC found confirmed the Standard Model, including the famous Higgs Boson – one of the pivotal points of particle physics. But this was bound to happen at some point. The Standard Model is incomplete, and there are significant gaps in our understanding of physics. Most notably, the model doesn’t account for gravity at all, which leaves a shed load of unanswered questions.

“Up to now all measurements match the predictions of the standard model,” said lead researcher Mariusz Witek, from the Institute of Nuclear Physics of the Polish Academy of Sciences. “However, we know that the standard model cannot explain all the features of the Universe. It doesn’t predict the masses of particles or tell us why fermions are organised in three families. How did the dominance of matter over antimatter in the universe come about? What is dark matter? Those questions remain unanswered.”

The discrepancy deals with  particle called the B meson, a meson composed of a bottom antiquark and either an up, down, strange or charm quark — yes, those are real names and yes, particle physics is strange. The Standard Model predicts very specific decay frequencies and angles, but the theory doesn’t match the observations, so something else is at work.

At this point, it absolutely has to be said that this is not a confirmed discovery. We need more data to be sure that what’s found is for real. However, if it does turn out to be real, it means we may be dealing with a completely new particle. We’re going to have to wait for confirmation, and that may take a while.

“Just like it is with a good movie: everybody wonders what’s going to happen in the end, and nobody wants to wait for it,” says Witek.

Scientists believe they’ve found a particle made entirely of strong nuclear force – a glueball

After decades of searching, researchers believe they have finally discovered a glueball – a proposed particle that consists solely of gluon particles, without valence quarks, that is instrumental to the Standard Model of Physics, but hasn’t been observed until now.

A crash course in particle physics

Nucleons consist (left) of quarks (matter particles) and gluons (force particles). A glueball (right) is made up purely of gluons. Image via Physorg.

There are four forces governing the basic interactions of particles – these are called the fundamental forces: gravity, electromagnetic, weak nuclear and strong nuclear. All the interactions in the universe can be described by some combination of these forces. Now, in 1970, physicists tried to write down how these forces interact with each other at the subatomic level, and predicted all the particles that they believe make up the universe. The current formulation was finalized in the mid-1970s upon experimental confirmation and since then, further experiments have confirmed the validity of the Standard Model.

According to the model, protons and neutrons are made of minuscule elementary particles called quarks. These quarks are held together by even smaller particles, gluons. Gluons are massless particles somewhat similar to photons – just like photons are responsible for exerting the electromagnetic force, gluons are responsible for exerting the strong nuclear force. In a way, they are strong nuclear force.

“In particle physics, every force is mediated by a special kind of force particle, and the force particle of the strong nuclear force is the gluon,” explains one of the researchers, Anton Rebhan from the Vienna University of Technology.

Finding glueballs

But there is one major difference: while photons aren’t affected by the force they exert, gluons are. In other words, gluons can’t be held together by strong nuclear force, but they can do exert strong magnetic force on other particles; that’s just how the strange world of particle physics sometimes works.

However, while glueballs are massless on their own, their interactions with other glueballs does give them a mass, which means that scientists can theoretically detect them, albeit indirectly, through their disintegration process, but that’s extremely difficult because in particle accelerators, glueballs tend to mix with other particles (namely meson states).

However, Rebhan and his team published a report in Physical Review Letters which gives a lot of hope for detecting these particles.

“Our calculations show that it is indeed possible for glueballs to decay predominantly into strange quarks,” he says.

They will now analyze more data from the Large Hadron Collider at CERN (TOTEM and LHCb) in Switzerland and an accelerator experiment in Beijing (BESIII) to help confirm their find.

“These results will be crucial for our theory,” says Rebhan. “For these multi-particle processes, our theory predicts decay rates which are quite different from the predictions of other, simpler models. If the measurements agree with our calculations, this will be a remarkable success for our approach.”

 

LHC signals hint at flaws in the Standard Model of Physics

An intriguing signal reported at the LHC might signal some “cracks” in the Standard Model – the theory which describes how different forces interact with each other.

A view inside the LHCb experiment’s muon detector at the Large Hadron Collider. Image credits: CERN.

The LHC has already accumulated a trove of valuable data, and researchers are still working on analyzing it. Now, a study on data gathered during 2011–12 at the collider at CERN suggests that in some particular decays, some short-lived particles (B-mesons) create some particles (taus) more than others (muons); but according to the Standard Model, the decay should be happening at the same rate, so something is clearly not as expected. Let’s explain that a bit.

Quarks are elementary particles – they’re the smallest thing we know of, the very basis of subatomic particles. Hadrons are composite particles made of quarks. Mesons are a specific type of hadrons made from one quark and one anti-quark – and B-mesons are a type of mesons. They are very short-lived, so studying their decay is particularly difficult. The discrepancy that was observed is so small we can’t rule out a statistical fluctuation (a satisfying statistical threshold has not yet been reported).

But physicists are excited because a similar thing has been reported at two other experiments: the ‘BaBar’ experiment at the SLAC National Accelerator Laboratory in Menlo Park, California, which reported it in 2012, and the ‘Belle’ experiment at Japan’s High Energy Accelerator Research Organization (KEK) in Tsukuba, which reported its latest results at a conference in May. LHCb’s result is “bang on” the previous two. as Mitesh Patel, a physicist at Imperial College London who works on the experiment, explained.

“A 2-sigma difference in a single measurement isn’t interesting by itself,” says Tara Shears, a particle physicist at the University of Liverpool, UK, and a member of the LHCb collaboration. “But a series of 2-sigma differences, found in different types of decay and independently by different people in a different experiment, become very intriguing indeed.”

The “2-sigma” difference is an indicator of accuracy used in control charts. When comparing 2-sigma vs 3-sigma control charts, 3-sigma control charts help ensure process stability whereas 2 sigma control charts are used to detect small shifts in the project or process. For such discoveries, 5-sigma is usually required, while this discovery only has 2.1-sigma. But as Patel said, a series of 2-sigma is worth much more than just one, isolated event.

Since the 1970s, experiments have time and again proved the accuracy of the standard model – with surprising consistency. However, the Standard Model is incomplete at best, and quite possibly inexact as well. Its failure to account for gravity and dark matter seems to suggest that it’s merely an approximation of some other, underlying, and even more intriguing truth.

The finding will be published in Physical Review Letters this month (it’s already published on the arXiv pre-print server).

LHC rare findings deal major blow to supersymmetry

Researchers at the Large Hadron Collider have detected one of the rarest decay particle found in nature, dealing a big blow to the supersymmetry theory in the process.

SUperSYmmetry

“Supersymmetry may not be dead but these latest results have certainly put it into hospital.”, explained Prof Chris Parkes, who is the spokesperson for the UK participation in the LHCb experiment.

Supersymmetry, or SuSy, in short, has gained popularity as a way to explain some inconsistencies in the widespread accepted subatomic model – The Standard Model. The results were reported at the Hadron Collider Physics conference in Kyoto, and were released in a yet unpublished paper.

SuSy claims that all particles of one spin have other particles that differ by half a unit of spin and are known as superpartner. If this were true, it could explain dark matter and other phenomena we still don’t understand yet.

LHC strikes back

The theory was becoming more and more popular throughout the scientific circles, but LHCb had a different story; it measured the decay between a particle known as a Bs meson into two particles known as muons. This is the first time this decay was observed, and the team calculated that for every 1.000.000.000 decays, this specific type of decay happens only 3 times; if supersymmetry were followed to the letter, the decay would happen far more often. This particular experiment was one of the golden tests for the theory, and it failed – badly.

Prof Val Gibson, leader of the Cambridge University LHCb team was quite snappy about the whole thing: “[it is] putting our supersymmetry theory colleagues in a spin“.

Cementing the Standard Model

The result were, in fact, exactly in the line of what you would expect from the Standard Model.

“If new physics exists, then it is hiding very well behind the Standard Model,” commented Cambridge physicist Dr Marc-Olivier Bettler, a member of the analysis team.

The results are not entirely ruling out the existence of superparticles, but they’re really running out of places to hide. Therefore, it was quite surprising to see the response of Prof John Ellis of King’s College London, one of the theory’s biggest supporters:

“In fact,” he said, “(it) was actually expected in (some) supersymmetric models. I certainly won’t lose any sleep over the result.”

Is it just denial, or does he know something we don’t?

New exotic particle behaviour found at CERN

The Large Hadron Collider at CERN has started doing some serious business. This time, an extremely rare particle containing equal parts of matter and antimatter popped up during experiments at the world’s largest and hottest particle accelerator.

CREDIT: CERN/Maximilien Brice, Rachel Barbier

 

The particle, named a B meson is made out of one quark (the building blocks of protons and neutrons) and one antiquark (the building blocks of antiprotons and antineutrons). What are antiprotons and antineutrons ? Well, they are just like their positive brothers… only they are negative. They have the exact same properties, only opposite in signs. For example, an antiproton has the exact same charge a proton has, but it is negative instead of positive.

All normal particles are thought to have antimatter analogues, and when matter and antimatter meets, they destroy each other. Scientists believe that at first, matter and antimatter were created equally, but if this is the case, then where is all the antimatter ? The most plausible solution would be that a huge quantity of matter and antimatter annihilated each other, and the remaining matter is what we see in our universe today.

The particle in case, the B meson, is thought to have been common right after the Big Bang, but it is believed that at the moment, it doesn’t occure naturally in nature. They aren’t stable, and after created, quickly start decaying; this process, a B meson decay has long been theoretized, but never seen before.

“Our experiment is set up to measure the decays of B mesons,” sayd Sheldon Stone, physicist at Syracuse University. “We discovered some new and interesting decay modes of B mesons, which hadn’t ever been seen before.”

Studying this type of behaviour can provide the answer to the ultimate question of antimatter – why do we see all this matter around us today, and no antimatter. Meanwhile, the search for the elusive Higgs boson is continued.

“When the universe was created in the Big Bang about 14 billion years ago, the number of particles and antiparticles was the same,” Stone said. “One of the major questions that we really don’t know the answer to is why are there particles around now and not antiparticles. By studying the differences we can learn maybe what the physics is behind that difference.”