The Large Hadron Collider (LHC) is currently on the long road to re-start, but for physicists poring over the huge wealth of data stored from countless trillions of particle collisions already carried out by the world’s most powerful particle accelerator, the work never paused.
And this week, at the LHC Physics meeting in New York City, researchers who are currently analyzing data from one of the LHC’s seven detectors announced an intriguing finding. As reported by Symmetry Magazine, the finding — which isn’t quite a discovery (yet) — focuses on the production of electrons, muons and taus in the post-collision soup of particles that are produced inside the LHCb detector.
Messing with the Standard Model
In a nutshell, these three types of subatomic particle — all known as “leptons” — should be produced in equal numbers as decay products after the two counter-rotating ‘beams’ of protons inside the LHC’s superconducting electromagnets collide with one another. The Standard Model predicts this and, so far, experiments have yet to prove otherwise.
“The Standard Model doesn’t distinguish between muons and electrons in these decays,” said particle physicist Tom Blake, a Royal Society University Research Fellow. “As far as our equations are concerned, they are the same particle, so we should see them produced in near equal amounts.”
The Standard Model is the all-encompassing theory of quantum mechanics and has been formulated over decades of theory and experimentation. It is a reliable “universal recipe book” of sorts that can predict what types of particle will be generated inside the LHC’s detectors. But there are some holes in the Standard Model — most notably the fact that gravity doesn’t ‘fit’; we don’t know what dark matter is; and why the Universe is mostly matter (and not antimatter).
In an effort to possibly detect physics beyond the Standard Model (i.e. ‘new’ physics that could explain some of the Standard Model’s shortcomings), physicists are looking closely at the data spewing from the LHC in the hope of seeing patterns that cannot be explained using our current understanding of physics theory.
Although it is just a hint, LHCb physicists are baffled as to why the production of electrons, muons and taus should be defying Standard Model predictions. According to decay measurements, electrons were produced 25 percent more often than muons. If the Standard Model were a cake recipe, it would be like throwing all the ingredients for a chocolate cake into a bowl, baking it and then getting a vanilla cake out of the oven. Obviously there’s something not quite right with the cake recipe.
In 2013, Discovery News reported on a related LHCb finding that there is a discrepancy in the decays of B-mesons. B-mesons, which are hadrons composed of a quark and anti-quark, decay in a very specific way and physicists noticed a non-random pattern in the angular distribution of decay products that was not predicted by the Standard Model. Once again, the recipe appears to be slightly askew.
Could there be some commonality between these two findings? Last year, LHCb physicists suggested that supersymmetry may have a part to play in the B-meson results and the same could be said for the lepton decay products in this latest work.
“If we continue to see this discrepancy, it could be evidence of a new particle—like a heavier cousin of the Z boson-interfering with the muon production,” said co-investigator Michel De Cian, postdoc at the University of Heidelberg.
Supersymmetry (a.k.a. SUSY) is a theory beyond the Standard Model that predicts the existence of more massive “superpartner” particles for all normal particles — in this case a Z boson “superpartner” could be the source of the interference, throttling muon production.
As yet, there is little evidence for SUSY, but as physicists look forward to the LHC recommencing collisions in 2015, everyone will be looking out of more discrepancies, potentially piecing together more evidence for physics beyond the Standard Model.
Source: Symmetry Magazine