A Study of Heavy Flavor Physics in the Lepton Sector

在名古屋大学建立了对τ轻子对的产生和衰变以及B夸克的稀有衰变进行高统计模拟并从实验数据中抽取样本的装置。名古屋大学负责管理贝儿合作项目中τ轻子事件的略读数据。这些样品通过“hepnet-J”网络向贝儿的合作者开放。一个是在相当低的统计量（10^量级）下预期有相当大的结果的过程<6-7>，例如τ对产生中的CP/T破坏，τ的电偶极矩（EDM），τ衰变中的Cp破坏，τ衰变中轻子味破坏的搜索。其他一些是我们需要积累高统计量的过程，如τ衰变末态强子质量谱的精确测量，与轻子相关的b夸克的FCNC稀有衰变，τ对产生的CP/T不对称性表明τ的EDM。利用τ的衰变模eμ，eπ，μπ，eρ，μ ρ，πρ，ππ，ρρ，得到了新的τ EDM上限，比现有的上限小一个数量级.τ→ππ^0ν的衰变角分布在测量范围内满足CP对称性。研究了τ→μγ过程中轻子味破坏的情况。对于FCNC衰变B → sll，我们寻找了B → K（*）e^+e^-和B → K（*）μ^+μ^-的互斥过程，首次得到了B → Kl^+l^-的相当大的衰变分支分数，这是迄今只得到上限的衰变分支分数。通过对奇异强子态的积累，我们还得到了包含B → sll过程的相当大的分支分数，这些结果在LP 01、ICHEP 00、ICHEP 02和Heavy Flavor Workshop等国际会议上发表。

Facility of making high statistics simulation of production and decays of τ lepton pairs and rare decays of b quark, and skimming these samples from experimental data, are established in Nagoya University. Nagoya University takes responsibility of managing skimmed data of τ lepton events in the Belle collaboration. Those samples are opened to Belle collaborators through network "hepnet-J".Physics analyses were carried out in two stages. One were processes from which sizeable results were expected with rather low statistics (order of 10^<6-7>) such as CP/T violation in τ pair production, electric dipole moment (EDM) of τ, Cp violation in τ decays, a search for lepton flavor violation in τ decays. Others were processes we needed to accumulate high statistics, such as precision measurement of hadron mass spectrum in τ decay final states, and FCNC rare decay of b-quark associated with leptons.CP/T asymmetry in τ pair production indicates EDM of τ. We obtained new upper limit of τ EDM, one order of magnitude smaller than the existing ones, using τ decay modes to eμ, eπ, μπ, eρ, μρ, πρ, ππ, ρρ. Decay angular distribution of τ→ππ^0ν satisfied CP symmetry within a measurement limit. Lepton flavor violation was examined in the search for τ→μγ process. We have got smaller upper limit than the present best value, and analysis is in progress aiming to renew the limit by order of magnitude.As for the FCNC decay b → sll, we searched exclusive process of B → K(*)e^+e^- and B → K(*)μ^+μ^-, and first obtained sizeable decay branching fraction of B → Kl^+l^-, for which only upper limit had been obtained. Accumulating strange hadronic states we also obtained sizeable branching fraction of inclusive b → sll process.Those results were presented in journals and several international conferences like LP01, ICHEP00, ICHEP02, and heavy flavor workshop.