Stupid question. How the devil does a particle of mass 125 GeV decay to two particles of mass around 80 GeV each? What are the actual observed end products?
That’s not a stupid question at all. Basically, the W and Z bosons are just virtual particles here, that decay very quickly, so that Heisenberg’s uncertainty principle (∆E * ∆t ≥ ℏ/2) is satisfied. The observed end products are four leptons (i.e. electrons, muons or taus plus the associated neutrinos), which add up to a mass much less then 125 GeV – the rest is in their kinetic energy.
Okay. So they’re actually talking about the 4l channel, which on theoretical grounds must involve an intermediate heavy (and virtual) boson. I opine that when the boson is virtual, ie there’s no mass peak in the two-lepton spectra, you ought not to say that you’ve observed the ‘2W’ channel, even if that’s the Feynman diagram you draw to explain the observation.
One exception though: In the Quantum Diaries post Dreaded_Anomaly mentioned, I’m fine with them talking about H → W W and H → Z Z decays, because they’re only talking about spin conservation at that one point – no need to mention the end products there. (But that wasn’t what you were talking about, I guess.)
Stupid question. How the devil does a particle of mass 125 GeV decay to two particles of mass around 80 GeV each? What are the actual observed end products?
That’s not a stupid question at all. Basically, the W and Z bosons are just virtual particles here, that decay very quickly, so that Heisenberg’s uncertainty principle (∆E * ∆t ≥ ℏ/2) is satisfied. The observed end products are four leptons (i.e. electrons, muons or taus plus the associated neutrinos), which add up to a mass much less then 125 GeV – the rest is in their kinetic energy.
Okay. So they’re actually talking about the 4l channel, which on theoretical grounds must involve an intermediate heavy (and virtual) boson. I opine that when the boson is virtual, ie there’s no mass peak in the two-lepton spectra, you ought not to say that you’ve observed the ‘2W’ channel, even if that’s the Feynman diagram you draw to explain the observation.
I mostly agree with you.
One exception though: In the Quantum Diaries post Dreaded_Anomaly mentioned, I’m fine with them talking about H → W W and H → Z Z decays, because they’re only talking about spin conservation at that one point – no need to mention the end products there. (But that wasn’t what you were talking about, I guess.)