Physicists May Have Discovered 'New Force of Nature' in LHC Experiment

The Large Hadron Collider, (LHC), sparked excitement worldwide in March when particle physicists presented tantalizing evidence for new Physics and possibly a new force.
Our new result from CERN's massive particle collider appears to support the idea.

The standard model is our current best theory about particles and forces. It describes all we know about the physical stuff in the world with unerring accuracy.

We know that the standard model is the most popular scientific theory yet it cannot be denied that it is incomplete.

It only describes three of the four fundamental forces: the electromagnetic force, strong and weak forces, and gravity. It cannot explain why dark matter, which astronomy says dominates the Universe and how it survived the Big Bang.

LHCb experiment. (CERN).

Many physicists believe there are more cosmic ingredients out there. Studying a variety fundamental particles called beauty quarks, which is an especially promising way to find clues about what else may be out there, is therefore a popular way to discover them.

The beauty quarks (sometimes called bottom quarks) are fundamental particles that make up larger particles. Six types of quarks are available: up, down and strange. They are also called charm, beauty/bottom, truth/top, and beauty/bottom. For example, the protons in the atomic nucleus are made up of quarks that are either up or down.

Beauty quarks, which are unstable, live for an average of 1.5 trillionths seconds before they become other particles. The existence of fundamental particles or forces can have a strong influence on the way that beauty quarks degrade.

Through the weak force, a beauty quark becomes a collection of lighter particles such as electrons when it decays. Subtly altering the frequency at which beauty quarks decompose into different types is one way a new force in nature could make itself known.

March's paper was based upon data from LHCb, one of four large particle detectors that records the results of ultra-high-energy collisions caused by the LHC. (The LHCb "b" stands for "beauty."

It discovered that beauty quarks were decomposing into electrons, and their heavier cousins, called muons, at different rates. This was really surprising, as the standard model states that the muon is essentially a carbon copy electron, except it's 200 times more heavy.

This means that all forces should pull on electrons, muons with equal strength. If a beauty quark is converted into electrons or muons by the weak force it should do so as often as possible.

My colleagues discovered that muon decay only occurred about 85 percent of the time as electron decay. If the result is correct, it is possible to explain this effect by a new force in nature that pulls electrons and muons differently.

Particle physicists were thrilled by the result. For decades we have been looking for evidence of something other than the standard model, but despite ten years spent at the LHC, no conclusive results have been achieved.

It would be hugely significant to discover a new force in nature, which could lead to answers to some of the most difficult questions in modern science.

Neue results

Although the results were intriguing, they weren't conclusive. Every measurement comes with some uncertainty or "error". This case, there was a 1 in 1000 chance that the result was due to random statistical wobbles or "three Sigma" in particle physics parlance.

Although one in 1,000 might not seem like much, we do a lot of measurements in particle Physics. So, you might expect some outliers to be found by chance.

We need five sigma to be certain that the effect is true. This would mean less than one in a million chances of it being due to statistical error.

We need to decrease the error size, which can be achieved by collecting more data. This can be achieved by simply running the experiment longer and recording more decays.

The LHCb experiment is being upgraded in order to record collisions at an even higher rate. This will enable us to take more precise measurements. We can still get useful information from the data we have already collected by searching for similar decays that are more difficult to detect.

This is what I and my colleagues have done. We don't actually study beauty quark decays because they are bound together with other quarks. This allows us to create larger particles.

The March study examined beauty quarks that were paired with "up" quarks. The results of our study looked at two types of decay: one that involved beauty quarks paired up with "down" quearks, and another where they were also paired up with up quarks.

It doesn't matter if the pairing is different. However, the decay going on deep below is the same, so we would expect to see the exact same effect, if indeed there is a new force.

This is exactly what we have seen. The muon decays occurred around 70% less often than the electron decays. However, there was a greater error. This means that the result is "two sigmas" away from the standard model (around two in a hundred chance to be a statistical anomaly).

The result doesn't provide enough evidence to support a new force by itself. However, it is consistent with the previous results and further supports the notion that we may be at the edge of major breakthroughs.

We should be cautious. We still have a long way to go before we can say with certainty that we are actually seeing the influence of a fifth force in nature.

My colleagues and I are working together to extract as much information from the existing data as possible, while we prepare for the first run in the upgraded LHCb experiment.

Other experiments at LHC and the Belle 2 in Japan are gaining similar results. It is exciting to imagine that the next few years or months could bring new insight into the fundamental elements of the Universe.

Harry Cliff, University of Cambridge particle physicist

This article was republished by The Conversation under Creative Commons. You can read the original article.