A few days ago, I received a text message from a friend of mine that works as a particle physicist. All it said was “Up, Strange, and Bottom”. I won’t divulge any additional information, so as to protect their identity, but I immediately knew what they were referring to. My source wasn’t involved with the project, but I knew that he was close to those that were. The particle physics community isn’t very large, but is highly competitive, so secrecy around important new discoveries is usually pretty intense.
This morning, it was revealed that a particle physics group at Fermilab had finally found the Xi-sub-b particle and that the results were going to be published in Physical Review Letters, which is the NEJM of the physics world.
This is actually a really big deal – not as big of a deal as the discovery of the Higgs boson would be, but still significant. It was predicted by the Standard Model, but like several particles, had yet to be directly observed. The fact that it actually exists probably has the folks at the LHC salivating like a Pavlovian mutt, since it continues to imply that the Standard Model is correct and that the Higgs is actually out there to be found.
Since I doubt anyone will actually read the article, I’ll give a little synopsis. First of all, the particle in question is a baryon and like all baryons is made up of three quarks. Quarks are elementary particles which make up familiar things like protons and neutrons, but can also be combined to produce other particles, such as this Xi-sub-b particle recently discovered at Fermilab.
There are six types of quarks, referred to as flavors: up, down, strange, charm, top, and bottom. As an example, a proton is comprised of two up quarks and one down quark. An up quark has a charge of +2e/3 while a down quark has a charge of -1e/3. So, two up quarks and a down quark yield a particle with a net charge of +e, which as we all know is the charge of a proton. However, if we were to change an up quark into a down quark, we would end up with a charge of +2e/3 and -2e/3, or a net charge of zero. Since charge has to be conserved, the proton emits a positron and becomes a neutron (I simplify quite a bit – the real story is somewhat more complicated and an additional particle called an electron neutrino is also emitted). This process is what +β-decay is and a similar process called -β-decay goes in the opposite direction, where a down quark is replaced by an up quark and an electron is emitted instead.
The particle discovered at Fermilab is made of an up, strange, and bottom quark, so you can run through the arithmetic and look up some of the details on these particles to find out that the particle is neutrally charged. The lifetime of the particle and its rest mass aren’t available yet, but I will probably post a link once the paper is published. Truly, an exciting time.