Tau (particle)

τ
CompositionElementary particle
StatisticsFermionic
GenerationThird
InteractionsGravity, Electromagnetic, Weak
Symbol
τ
AntiparticleAntitau (
τ+
)
DiscoveredMartin Lewis Perl et al. (1975)[1][2]
Mass1776.86±0.12 MeV/c2[3]
Mean lifetime(2.903±0.005)×10−13 s[3]
Electric charge−1 e[3]
Color chargeNone
Spin1/2[3]
Weak isospinLH: −1/2, RH: 0
Weak hyperchargeLH: -1, RH: −2

The tau (τ), also called the tau lepton, tau particle, or tauon, is an elementary particle similar to the electron, with negative electric charge and a 2. Together with the electron, the muon, and the three neutrinos, it is a lepton. Like all elementary particles with half-integer spin, the tau has a corresponding antiparticle of opposite charge but equal mass and spin, which in the tau's case is the antitau (also called the positive tau). Tau particles are denoted by
τ
and the antitau by
τ+
.

Tau leptons have a lifetime of 2.9×10−13 s and a mass of 1776.86 MeV/c2 (compared to 105.66 MeV/c2 for muons and 0.511 MeV/c2 for electrons). Since their interactions are very similar to those of the electron, a tau can be thought of as a much heavier version of the electron. Because of their greater mass, tau particles do not emit as much bremsstrahlung radiation as electrons; consequently they are potentially highly penetrating, much more so than electrons.

Because of their short lifetime, the range of the tau is mainly set by their decay length, which is too small for bremsstrahlung to be noticeable. Their penetrating power appears only at ultra-high velocity and energy (above petaelectronvolt energies), when time dilation extends their path-length.[4]

As with the case of the other charged leptons, the tau has an associated tau neutrino, denoted by
ν
τ
.

History

The tau was anticipated in a 1971 paper by Yung-su Tsai.[5] Providing the theory for this discovery, the tau was detected in a series of experiments between 1974 and 1977 by Martin Lewis Perl with his and Tsai's colleagues at the Stanford Linear Accelerator Center (SLAC) and Lawrence Berkeley National Laboratory (LBL) group.[2] Their equipment consisted of SLAC's then-new
e+

e
colliding ring, called SPEAR, and the LBL magnetic detector. They could detect and distinguish between leptons, hadrons and photons. They did not detect the tau directly, but rather discovered anomalous events:

We have discovered 64 events of the form


e+
+
e

e±
+
μ
+ at least two undetected particles

for which we have no conventional explanation.

The need for at least two undetected particles was shown by the inability to conserve energy and momentum with only one. However, no other muons, electrons, photons, or hadrons were detected. It was proposed that this event was the production and subsequent decay of a new particle pair:


e+
+
e

τ+
+
τ

e±
+
μ
+ 4
ν

This was difficult to verify, because the energy to produce the
τ+

τ
pair is similar to the threshold for D meson production. The mass and spin of the tau was subsequently established by work done at DESY-Hamburg with the Double Arm Spectrometer (DASP), and at SLAC-Stanford with the SPEAR Direct Electron Counter (DELCO),

The symbol τ was derived from the Greek τρίτον (triton, meaning "third" in English), since it was the third charged lepton discovered.[6]

Martin Lewis Perl shared the 1995 Nobel Prize in Physics with Frederick Reines. The latter was awarded his share of the prize for experimental discovery of the neutrino.

Other Languages
Afrikaans: Tau (deeltjie)
العربية: تاوون
беларуская: Тау-лептон
български: Таон
bosanski: Tau-čestica
brezhoneg: Tauon
català: Leptó tau
čeština: Tauon
dansk: Tauon
Deutsch: Τ-Lepton
Ελληνικά: Ταυ λεπτόνιο
Esperanto: Taŭono
فارسی: تاو (ذره)
français: Tau (particule)
Gaeilge: Tóón
한국어: 타우 입자
հայերեն: Տաու (մասնիկ)
हिन्दी: टाऊ (कण)
hrvatski: Tau lepton
Bahasa Indonesia: Tau (partikel)
italiano: Tauone
Latina: Tauon
latviešu: Tau daļiņa
lietuvių: Taonas
magyar: Tau-lepton
македонски: Тау-честичка
Nederlands: Tau (lepton)
日本語: タウ粒子
norsk nynorsk: Tau-lepton
ਪੰਜਾਬੀ: ਟਾਓ (ਕਣ)
پنجابی: ٹاؤ لپٹن
Plattdüütsch: Tau-Lepton
polski: Taon
português: Tau (partícula)
русский: Тау-лептон
Simple English: Tau lepton
slovenčina: Tauón
slovenščina: Lepton tau
српски / srpski: Tau lepton
srpskohrvatski / српскохрватски: Tauon
svenska: Tau-lepton
українська: Тау-лептон
Tiếng Việt: Tau (hạt)
中文: Τ子