L3 $\tau$ Physics Analysis
G.M. Chen · CERN Document Server (European Organization for Nuclear Research) · 1991
Three works a.round the L3τphysics were done by the author:The first is e/ 7t separation.Based on the analysis of L3 calorimeter beam test d事ta，" key" cut was introduced , and was found to be very powerful to sepa~ rate e ／ πin the energy rang♀ above 10 GeV, while .:1cut ts good for that below 10 GeV.Thus, in the Energy ra.ng巳 from 4 to 20 Gev, e ／ πseparation is better than 94% .The second is a program for Energy Flow analysis.While e 4 e -collide, the energy 川11 not ;iisa.ppear.a.long wi主h the newly produced particles, the energy flows away from the colliding point.and is absorbed and re 民d OUl by the d~tector.The program is aimed to sepa.rate particles, and to optmize the enrgy calculation of che particles.Mainly, the program is for τphysics, but it.aiso serves as a basic software for Bhabha, Di -muon and hadron physics.In the program, ou.toma.ticangie opening and closing ma.chnism is introduced to match.sub-detector tracks.The para.meters used in the m~chnism was optmized by Monte Carlo hadron events.Beam test results ar啻 used t。 identify pa.rticies.Th 巳 ef ficiency of identification is improved with the help of monte 巳ar 哥 vents and the computer scanning of the rea.1 events.The enrgy of a particle is calculated based on the beam test energy caliberation, then optmizeq by fitting the total energy of the real events to the beam energy.Thus, the efficiency of particle ID is better than 95% and the energy resolution for rea.1 Bha.bha events is 1.9% and tha.t for real hadron events is 10.9% .The program was accepted by the L3 Colla.bora.tio民 and wa圃 rel 事 ued to the L3 users.The last a.nd the major one is L3τphysics analysis itself. 『 ， ， a••AUsing the data recorded by the L3 detector at LEP during the 1990 runnin 莓 period, corresponding to an integrated !uminosity 5. 5 pb 飞 as well as a large amount of Monte Carlo data, a.n e/ µ/h identifying scheme is introduced.Based on the final state particle identification, 2669 events were selected asτevents.Through carefully studing of these events, the τtopological branch ratio was found to be as follows: 1 prong: 86.25% 士 1. 25 %(stat.)士 1.58(sys.) 3 prong: 13.66% 士 0.51% 士 0.77 5 prong: 0.09% 士 0.05% 土 0.04% and e宽 elusive brac.hratio: e μ b.a.dron 17.7% 士 0.6% 士 0.6% 17.0% 士 0.5% 士 0.5% 65.3% 士 1.1 %土 1.0% From the measurements of the cross section of z0 叫 τ 气 τ 丁 we found: ru= 83.20 土 2.98 This result is in favour of lepton universality, comparing with r阳 measured by the L3 experiment.r '' U ing the measured cross sections and asymmetries, the effective vector and axial vector coupling constants of the z 0 to charged leptons are obtained: 运v = -0.063士 0.023 g .. = -0.498士 0.004 The primary results of the asymmetry of polarization are also given: τ → ev -ii A.= -0.128 土 0.184 τ 『 µv v τ『 1t v λ ＝ -0.227 士 0.168 ..\= -0.245 士 0.