Tau mass -- How was it measured for the first time?

[kelly0303]

Hello! How was the tau massed measured for the first time? I read that tau was discovered by $e^+e^-$ collisions and they looked for an excess of of end products containing an electron, a muon and some missing energy (coming from the decay the 2 resulting tau's). But the missing energy would come from 4 neutrinos, so you would have a lot of uncertainty in predicting the mass of tay just by measuring the energy of the produced electron and muon. How did they do it? Thanks!

 

[Vanadium 50]

If you want to know how something was originally done, you should read the original paper. M. Perl et al. Phys.Rev.Lett. 35 (1975) 1489-1492

 

[ChrisVer]

So the masses were inferred by at which center-of-mass and above (~4GeV) they started seeing the emu events, right?

 

[kelly0303]

If you want to know how something was originally done, you should read the original paper. M. Perl et al. Phys.Rev.Lett. 35 (1975) 1489-1492

So I see that they set a constraint on the mass between 1.6 and 2 GeV. In order to reduce the error to the value we have today, did they just accumulate more statistics, or did they use some other method? The error in pdg is about 0.1 MeV, and I am not sure how can you set that limit using the method they used in this paper, as the uncertainty in the missing energy of the neutrinos is much higher.

 

[Vanadium 50]

The error in pdg

The PDG has references to how each and every one of the input values were obtained.

 

[mfb]

The neutrino energy is irrelevant, both for the discovery paper and for the most precise modern mass measurements. The decay products are just detected to see that taus were produced. The energy measurement comes from the production process which doesn't involve neutrinos.

 

[ChrisVer]

Here you can find yourself a way they precisely measure the tau mass:
https://arxiv.org/pdf/1405.1076.pdf

 

[vanhees71]

May favorites are the $\tau$-decay data to an even and an odd number of pions (+neutrino), because from these we get the $VV$ and $AA$ current-current correlation functions (ALEPH and OPAL collaborations). I don't know how accurate this is concerning the $\tau$ mass, but the endpoint of these spectra should be a good measurement of the $\tau$ mass. too.