https://www.youtube.com/watch?v=VQjXHoZitU0

There may be a chink in the standard model.

sibeen said:

https://www.youtube.com/watch?v=VQjXHoZitU0

There may be a chink in the standard model.

Now that’s very interesting. I had never heard of “lepton universality”.

Now to think more carefully about the consequences of quarks decaying into leptons. Baryon number is conserved. Lepton number is conserved. Except in the case of proton decay (unproved) in which a baryon such as a proton can decay to a lepton such as a positron.

Mesons don’t count as baryons because quarks are paired with antiquarks. So some mesons (not all) can decay to leptons.

Racking my brain, I don’t think quarks can decay into leptons in the standard model. If that’s impossible then “lepton universality” doesn’t exist.

B meson decay is quoted. Now a B meson is just a heavier version of a Kaon. Kaons are very much easier to produce and study than B mesons. So why use B mesons? Or to put it another way, if a B meson is able to decay into an electron-positron pair then a Kaon must also be able to decay in that way.

LHCb – that’s right, that’s the B meson factory.

Probability of 1 in 100, not enough to call it. But still. Quark decaying to lepton is the real kicker for me in here. Unless I’m missing the obvious, let’s explore the obvious, weak decay.

The standard example of weak decay is beta decay, a neutron decays to a proton emitting an electron. That’s a change in quark type. Let’s apply it to Kaon decay, start with a down and anti-strange. If the anti-strange decays to an anti-down and a muon then it is possible (but not essential) for the down and anti-down to annihilate into a gamma ray that becomes a particle-antiparticle pair of leptons. Aha, so meson decaying to leptons does make sense, I was missing the obvious.

The proportions by which the resulting leptons are electron-positron vs muon-antimuon depend on the energy released. So they shouldn’t be exactly the same, because the heavier muons are harder to produce than lighter electrons. The higher the decay energy, the more the proportions produced should approach unity. So for a lower energy decay of a kaon, the standard model would predict a ratio of electrons to muons produced of more than 1. So that’s why they’re not looking at kaon decay. For the higher energy decay of a B meson, the difference in mass between the muon and electron becomes insignificant relative to the high energy of B meson decay, and the ratio of electron production to muon production should approach 1.

That’s lepton universality.

I apologise, it was obvious ;-)

So let’s turn to the experiments at LHCb in the video. Early results said that muons were produced 25% less often, with more data that shrank to 15% less often.

Yeah, OK, very interesting, not enough to call it. There have been literally hundreds of results in particle physics with that level of significance that have vanished as more data becomes available. The video doesn’t say if it’s a two-sided statistical test or a one-sided test for statistical significance, the difference is a factor of two.