Measurement of the anomalous magnetic and electric dipole moments of the tau lepton

Abstract

0370-2693r98r$ -see front matter q 1998 Elsevier Science B.V. All rights reserved.Ž . PII: S 0 3 7 0 -2 6 9 3 9 8 0 0 7 3 6 -9 ( ) M. Acciarri et al.r Physics Letters B 434 1998 169- AbstractWe analyse e q e y ™ ttg events using 100 pb y1 of data collected by the L3 experiment during the 1991-1995 LEP runs at the Z pole. From the energy of the photons and their isolation from the tau decay products, we determine the anomalous magnetic and electric dipole moments of the tau to be, respectively: a s 0.004 " 0.027 " 0.023; t d s 0.0 " 1.5 " 1.3 = 10 y16 e P cm. Ž .t This is a direct measurement of these t form factors at q 2 s 0. q 1998 Elsevier Science B.V. All rights reserved.

Model-independent sensitivity estimates for the electromagnetic dipole moments of the τ -lepton at the CLIC

“…11-14 and Tables III-V. These are compared with experimental results of earlier studies for a linear collider as published by the BELLE, DELPHI, L3, and OPAL Collaborations [42][43][44][45][46]. Our results for the twophoton process γγ → τ þ τ − at the CLIC could improve the sensitivity on anomalous electromagnetic dipole moments of τ-lepton with respect to the existing experimental bounds (see Table I) by 2 orders of magnitude.…”

“…Relative systematic cross-section errors of the process e þ e − → e þ e − τ þ τ − are given in Table II. The process e þ e − → e þ e − τ þ τ − was also studied with the L3 detector for center-of-mass energies 161 GeV ≤ ffiffi ffi s p ≤ 209 GeV at LEP [43]. The anomalous magnetic and electric dipole moments of the τ-lepton via the process pp → ppτ þ τ − with 2% of the total systematic uncertainties at the LHC were investigated phenomenologically in Ref.…”

“…With these parameters as input, we established model-independent sensitivity estimates on the electromagnetic dipole moments of the τ-lepton at 95% C.L. We obtain strong sensitivity in comparison to the bounds given by the DELPHI, L3, OPAL, BELLE, and ARGUS Collaborations [42][43][44][45][46] (see Table I). …”

Electroweak couplings of the τ lepton

“…While 's at LEP are quite clean, the analysis of this data is highly nontrivial, requiring per mil accuracy on signal and background. A comparison of observed data [8] to a detailed theoretical calculation [9] of the expected spectrum including all interference and mass terms gives the likelihood distribution shown in figure 2b. If the mass is neglected [7], the large interference between the Standard Model and ¾ contributions is not included.…”

Search for the Electric Dipole Moment of the τ Lepton

“…Up to now, searches for the electric dipole form factor d τ have been performed at LEP [5,6] in the reaction e + e − → τ + τ − γ and by ARGUS [7] in the e + e − → τ + τ − reaction and the following upper limits at 95% confidence level were obtained: −3.1 < d τ < 3.1 (10 −16 ecm) from L3 [5], −3.8 < d τ < 3.6 (10 −16 ecm) from OPAL [6] and |Re(d τ )| < 4.6 × 10 −16 ecm, |Im(d τ )| < 1.8 × 10 −16 ecm from ARGUS [7].…”