The Physics of Beauty, or How Beauty Hadrons Are Revealing Particle Mysteries
Particle physics is complicated, to undersell it. It draws from many disciplines and requires great technology and space to gather any results at all. It should therefore be clear that enduring mysteries are out there, and we wish to test further and hopefully solve them. One aspect that is showing great promise is beauty – of a hadron type. What else could this possibly be about? Certainly not mine. Anyway, lets look at how beauty can reveal hidden secrets of the Universe.
The Standard Model of Physics is one of the most successful theories of physics. Period. IT has been tested thousands of different ways and holds up to scrutiny. But issues are still present. Amongst them is the matter/antimatter imbalance, how gravity plays a role, how are all the forces tied together, the discrepancy between the expected and measured values of the Higgs Boson, and more. This all means that one of our best scientific theories is just an approximation, with missing pieces still to be found (Wilkinson 59-60).
Beauty Hadron Mechanics
A beauty hadron is a meson that is made of a beauty (bottom) quark and an anti-down quark (quarks are further subatomic components and have many different iterations). The beauty hadron (which has a ton of energy, about 5 giga-electron-volts, roughly a helium nucleus. This gives them the ability to travel a “great distance” of 1 centimeter before they break down into lighter particles. Because of this energy level, different decay processes are theoretically possible. The two big ones for new physical theories are both are presented below but to translate the jargon into something more recognizable we have two possibilities. One involves the beauty hadron decaying into a D meson (a charm quark with an antidown quark)) and a W boson (acting as a virtual particle) which itself decays into an anti-tau neutrino and a tau neutrino which carries a negative charge. The other decay scenario involves our beauty hadron decaying into a K meson (a strange quark and an antidown quark) with a Z boson that becomes a muon and an anti-muon. Because of the consequences of the conservation of energy and rest energy (e=mc^2), the mass of the products is less than that of the beauty hadron, for kinetic energy is dissipated to the system around the decay, but that isn’t the cool part. It’s those W and Z bosons, for they are 16 times as massive as the beauty hadron yet are not a violation of the rules previously mentioned. That is because for these decay processes they act like virtual particles, but others are possible under a quantum mechanic property known as lepton universality which essentially states that lepton/boson interactions are the same no matter the type. From it we know that the probability of a W boson decaying into a tau lepton and an anti-neutrino should be the same as it decaying into a muon and an electron (Wilkinson 60-2, Koppenburg).
Crucial to the study of beauty hadrons is the Large Hadron Collider beauty (LHCb) experiment running at CERN. Unlike its counterparts there, LHCb doesn’t generate particles in its study but looks at the hadrons produced by the main LHC and their decay products. The 27 kilometer LHC empties into LHCb, which is 4 kilometers from CERN headquarters and measures 10 by 20 meters. Any incoming particles are recorded by the experiment as they encounter a large magnet, a calorimeter, and a path tracer. Another key detector is the ring-imaging Cherenkov (RICH) counter, which looks for a certain light pattern caused by Cherenkov radiation that can inform scientists of what kind of decay they witnessed (Wilkinson 58, 60).
Results and Possibilities
That lepton universality mentioned earlier has been shown through LHCb to have some issues, for the data shows the tau version is a more prevalent decay path than the muon one. A possible explanation would be a new type of Higgs particle that would be more massive and therefore generate more of a tau route than a muon one when it decays, but data doesn’t point to their existence as likely. Another possible explanation would be a leptoquark, a hypothetical interaction between a lepton and a quark which would distort sensor readings. Also possible would be a different Z boson that is an “exotic, heavier cousin” of the one we are used to which would become a quark/lepton mix. To test for these possibilities, we would need to look at the ratio of the decay route with a Z boson to decay routes that give an electron pair as opposed to a muon pair, denoted as RK*. We would also need to look at a similar ratio involving the K meson route, denoted as RK. If the Standard Model is indeed true, then these ratios should be roughly the same. According to data from the LHCb crew, RK* is 0.69 with a standard deviation of 2.5 and RK is 0.75 with a standard deviation of 2.6. That isn’t to the 5 sigma standard that classifies the findings as significant, but it’s certainly a smoking gun to some possible new physics out there. Maybe there is an inherent reference to one decay route over another (Wilkinson 62-3, Koppenburg).
Koppenburg, Patrick and Zdenek Dolezal, Maria Smizanska. “Rare decays of b hadrons.” arXiv:1606.00999v5.
Wilkinson, Guy. “Measuring Beauty.” Scientific American Nov. 2017. Print. 58-63.
Questions & Answers
© 2019 Leonard Kelley