Light new particles generate asymmetries in e+e- to tau+tau- that allow model-dependent constraints on tau dipole moments, including non-zero effects without electron polarization via imaginary parts.
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$\tau$ dipole moments via radiative leptonic $\tau$ decays
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abstract
We propose a new method to probe the magnetic and electric dipole moments of the $\tau$ lepton using precise measurements of the differential rates of radiative leptonic $\tau$ decays at high-luminosity $B$ factories. Possible deviations of these moments from the Standard Model values are analyzed in an effective Lagrangian approach, thus providing model-independent results. Analytic expressions for the relevant non-standard contributions to the differential decay rates are presented. Earlier proposals to probe the $\tau$ dipole moments are examined. A detailed feasibility study of our method is performed in the conditions of the Belle and Belle II experiments at the KEKB and Super-KEKB colliders, respectively. This study shows that our approach, applied to the planned full set of Belle II data for radiative leptonic $\tau$ decays, has the potential to improve the present experimental bound on the $\tau$ anomalous magnetic moment. On the contrary, its foreseen sensitivity is not expected to lower the current experimental limit on the $\tau$ electric dipole moment.
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First differential cross-sections for γγ→ττ in Pb+Pb collisions yield 95% CL intervals -0.057 < a_τ < 0.035 and |d_τ| < 2.7×10^{-16} e cm.
This work provides a comprehensive analysis of light new physics contributions to tau lepton dipole moments, detailing interpretations of asymmetry measurements for spin-0 and spin-1 bosons, their decoupling to the EFT limit, and a case study of a tauphilic vector boson at Belle II.
Z-boson exchange contributes ~3e-6 to the relevant asymmetries while four-fermion operators can reach ~1e-5 times Wilson coefficients, with loop insertions offering an additional path to a_tau without beam polarization.
Future lepton colliders can improve existing constraints on the tau lepton's dipole moments by several orders of magnitude through complementary channels.
Obtains 95% CL exclusion and 3σ/5σ sensitivity limits on a_τ and d_τ from PbPb collisions at FCC-hh with comparisons to other future colliders.
citing papers explorer
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Light new physics and the $\tau$ lepton dipole moments: prospects at Belle II
Light new particles generate asymmetries in e+e- to tau+tau- that allow model-dependent constraints on tau dipole moments, including non-zero effects without electron polarization via imaginary parts.
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Differential measurements of $\gamma\gamma\to\tau\tau$ and constraints on $\tau$-lepton electromagnetic moments in Pb+Pb collisions at $\sqrt{s_{_\text{NN}}} = 5.02$ TeV with ATLAS
First differential cross-sections for γγ→ττ in Pb+Pb collisions yield 95% CL intervals -0.057 < a_τ < 0.035 and |d_τ| < 2.7×10^{-16} e cm.
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Light new physics and the $\tau$ lepton dipole moments
This work provides a comprehensive analysis of light new physics contributions to tau lepton dipole moments, detailing interpretations of asymmetry measurements for spin-0 and spin-1 bosons, their decoupling to the EFT limit, and a case study of a tauphilic vector boson at Belle II.
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Four-fermion operators, $Z$-boson exchange, and $\tau$ lepton dipole moments
Z-boson exchange contributes ~3e-6 to the relevant asymmetries while four-fermion operators can reach ~1e-5 times Wilson coefficients, with loop insertions offering an additional path to a_tau without beam polarization.
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Probing $\tau$ lepton dipole moments at future Lepton Colliders
Future lepton colliders can improve existing constraints on the tau lepton's dipole moments by several orders of magnitude through complementary channels.
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Probing electromagnetic moments of the tau lepton in PbPb collisions at the FCC-hh
Obtains 95% CL exclusion and 3σ/5σ sensitivity limits on a_τ and d_τ from PbPb collisions at FCC-hh with comparisons to other future colliders.