We reevaluate the two form factors relevant for the ηπ second-class τ decay mode, making systematic use of analyticity, unitarity, combined with updated inputs to the NLO chiral constraints. We focus in particular on the shape of the ρ resonance peak which is a background-free signature of a second-class current. Its dispersive construction requires the scattering amplitude which we derive from a family of Khuri-Treiman equations solutions constrained with accurate recent results on the Dalitz plot.
In the framework of a Simplest Little Higgs Model (SLHM), we calculate the total cross section for the reaction and thereafter we get a limit on the characteristic energy scale of the model f, , which in turn induces bounds on the anomalous Magnetic Moment (MM) and the Electric Dipole Moment (EDM) of the tau-neutrino. We consider initial-state radiation, and neglect W and photon exchange diagrams. The results are based on the data reported by the L3 Collaboration at LEP, and compare favorably with the limits obtained in other models, complementing previous studies on the dipole moments.
I give an overview of what we know at present about the Hadronic Ligh-by-Light Scattering Contribution to the anomalous magnetic moment of the muon in the Standard Model.
Impact of τ leptons on the frontiers of particle physics are overviewed. These include studies of the Higgs, SUSY and other new particles in different exotic models decaying to τ leptons, searches for lepton flavor violation and charge-parity violation in τ decays, tests of lepton universality, and || determination from τ decays.
OPERA is a neutrino oscillation experiment aiming to prove the tau neutrino appearance for the first time. A tau decay is identified by the detection of its characteristic decay topologies in nuclear emulsion films. OPERA reported the detection of a first tau neutrino event in 2010. We recently detected a second tau neutrino event in the 2011 run sample. The primary vertex has two charged particles of which one exhibits a three-prong vertex in the plastic base of a film after a flight length of 1.54 mm. It satisfies all the selection criteria to be a tau neutrino interaction. Especially the azimuthal angle in the transverse plane between the tau candidate track and the primary track is almost 180 degrees. The number of tau to 3π signal events expected in the analyzed sample is 0.18, the number of background events is 0.05. Considering all modes, the signal expectation is 1.91 events and the background 0.18 events.
The leptonic decay provides opportunities for testing the Standard Model and for searching for new physics. In this report, recent measurements obtained at the B factories are introduced. The results are consistent with the Standard Model expectations, and lead to a stringent constraint on new physics models including charged Higgs bosons.
Measurements of the and cross-sections at the LHC with data taken at are reported for the ATLAS, CMS, and LHCb experiments. All results are found to agree with the Standard Model.
We analyse Belle data on the decay using a dispersive representation of the vector form factor which is consistent with chiral symmetry and preserves analyticity and unitarity exactly. We fit the unknown theoretical parameters from the data, determining the values of the related low-energy observables and . The implementation of isospin breaking effects is also discussed [D. G. Dumm, P. Roig, arXiv:1301.6973].
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：