LHC Hints Of New Physics For Particle Physics
Researchers have produced a confirmation of an anomaly in particle physics that no theory has predicted. Is this finally solid evidence of the new physics we’ve been searching for?
The Standard Model of physics has been extraordinarily successful for decades. Its description of particles, forces and their interactions describe our universe with exquisite detail. It has distilled hundreds of particles and their complex interactions down to just 12 fundamental particles (6 quarks and 6 leptons) and an assortment of their force carriers (photons, gluons, gravitons etc). When the Large Hadron Collider (LHC) found the Higgs in 2012, the last major particle predicted by this model had finally been checked off that big list.
Yet the standard model does not explain all we see. It does not say anything for example about gravity or the biggest mysteries of all, Dark Energy and Dark Matter. And these are just the known mysteries. Finding new physics that go beyond the standard model has therefore become increasingly compelling.
Now we finally have something that just might point the way to this new physics and open doors to us with unimaginable vistas and potential on the other side.
Researchers have been going over the data collected by the LHCb detectors at the Large Hadron Collider. I’m not even talking about the higher energy experiments that started this year. They are still going over the mountain of information collected during its first run from 2010 to 2013. Hidden in this data they found something that I’m sure they got drunk over once they determined its significance.
The LHC essentially smashes protons together with incredible force to see what particles and forces emerge from the debris. This isn’t just debris from the protons however. It’s not like smashing two tractors together and finding pieces of a carburetor and engine parts. It’s more like smashing them together and finding enough parts for 3 tractors with some of those parts clearly for a backhoe. This is of course all thanks to the most famous equation ever, E=mc2 2. Energy is equivalent to mass after all and all of the considerable energy of motion put into the colliding protons comes out as mass.
The collisions aren’t straightforward either. It’s not simple protons colliding, really, and not just the constituent quarks either. The strong-force-carrying gluons also collide. The gluons are also constantly morphing into innumerable quark-antiquark virtual particles and these take part in the collisions as well.
The result is a lot of big and small collisions all producing lots of particles. Some of these particles are called Mesons (B+ mesons). These are composed of a quark and an anti-quark and they go through life fast and furious since they only live for a fraction of a microsecond. At the end of their tiny allotment of time, some of the mesons decay into a further shower of particles and some of these are the focus of this latest research…Leptons.
Leptons are cool.
They are fundamental particles that come in 2 classes, charged and uncharged. The most famous and important charged lepton is our good friend the electron. He’s kind of important considering he’s directly tied to all chemical properties plus all the electronic-device gods we worship on a daily basis. Luckily electrons are stable and last for a long time, otherwise…..well, it’s best not to think about it. The other two charged leptons are quite different. The muon is 105 times as massive as the electron and is unstable, lasting only for a couple millionths of a second. The Tau is the 3rd charged lepton and it’s similarly unstable but it’s mass is a whopping 1,777 times that of an electron. He’s a chubby subatomic particle.
According to the standard model, all these leptons should be treated the same way by the other forces such as how many are produced during the decay of mesons (once you account for their differing masses of course). This property of leptons is called Lepton Universality and it is an important part of the standard model. I’ll give you the first part of a quote by co-author and team lead Hassan Jawahery, Distinguished University Professor of Physics:
“Lepton Universality is truly enshrined in the Standard Model…”
The LHCb researchers found that this universality assumed by the standard model could be incorrect. The production of leptons by the decay of the mesons were not symmetrical as theory predicts. More of one was produced over another. The power of this discovery is also magnified by the fact that they are not the first to see this effect. Similar results were found in the U.S. in 2012 by the BaBar experiment at the Stanford Linear Accelerator Centre. But it gets even better. Those results were found by smashing together electrons, not protons. Replicating an experiment is great for upping the confidence in a result. Replicating it using a different methodology is even better.
So what does this mean? (I bet you know already)
I’ll give Hassan’s full quote now:
“Lepton universality is truly enshrined in the Standard Model. If this universality is broken, we can say that we’ve found evidence for non-standard physics.”
So yes, this could be the first solid hint of new physics we’ve been looking for. It could mean that the Standard Model is wrong because it is unaware of some unknown particle or force or field that is interfering with the meson decay process. If we find out what this is, who knows what weird and wonderful directions it could take particle physics.
Keep in mind that though this is very encouraging news, even taking the replication into account, we can’t just assume the conclusion is true and move on. The observed differences that have been measured only had a significance of 2.6 standard deviations which means that there is a one in a hundred chance that what has been seen is due to a statistical fluctuation. That’s not close enough to the gold standard usually required. To increase confidence further, they will need to take more measurements from the data-set from run 1 of the LHC. This of course will be augmented with all the new data that will come pouring in from the LHC’s second run which is ramping up now.
So cross your fingers that some cool and weird shit might be revealing itself in particle physics soon.
Image Credit: EurekAlert/CERN/LHCb Collaboration