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

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Discussion Overview

The discussion revolves around the methods used to measure the mass of the tau particle for the first time, particularly focusing on the experimental techniques employed in the context of electron-positron collisions and the challenges associated with measuring decay products and missing energy.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the initial measurement of the tau mass, noting the complications arising from missing energy due to neutrinos in the decay process.
  • Another participant suggests consulting the original paper by M. Perl et al. for detailed methodology.
  • A participant mentions that the tau mass was inferred from the center-of-mass energy at which specific events were observed, questioning the accuracy of this method.
  • There is a discussion about the constraints set on the tau mass and the methods used to reduce error margins over time, with uncertainty expressed regarding the role of neutrino energy in these measurements.
  • One participant asserts that neutrino energy is irrelevant for both the discovery and modern mass measurements, emphasizing that energy measurements stem from the production process rather than decay products.
  • A link to a paper is provided that purportedly details a precise measurement method for the tau mass.
  • Another participant mentions the use of tau decay data to measure the tau mass, referencing specific collaborations and suggesting that the endpoint of certain spectra could yield accurate mass measurements.

Areas of Agreement / Disagreement

Participants express differing views on the relevance of neutrino energy in the measurement process, and there is no consensus on the methods used to achieve the current precision of the tau mass measurement. The discussion remains unresolved regarding the specifics of the measurement techniques and their implications.

Contextual Notes

There are limitations regarding the assumptions made about the measurement methods, particularly concerning the role of missing energy and the statistical accumulation of data over time. The discussion also highlights the dependence on specific experimental setups and collaborations.

kelly0303
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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!
 
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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
 
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So the masses were inferred by at which center-of-mass and above (~4GeV) they started seeing the emu events, right?
 
Vanadium 50 said:
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.
 
kelly0303 said:
The error in pdg

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

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