Precision Measurement of the Weak Mixing Angle in Møller Scattering

Abstract

We report on a precision measurement of the parity-violating asymmetry in fixed target electronelectron (Møller) scattering: AP V = (−131 ± 14 (stat.) ± 10 (syst.)) × 10 −9 , leading to the determination of the weak mixing angle sin 2 θ eff W = 0.2397 ± 0.0010 (stat.) ± 0.0008 (syst.), evaluated at Q 2 = 0.026 GeV 2 . Combining this result with the measurements of sin 2 θ eff W at the Z 0 pole, the running of the weak mixing angle is observed with over 6σ significance. The measurement sets constraints on new physics effects at the TeV scale.PACS numbers: 11.30. Er, 12.15.Lk, 12.15.Mm, 13.66.Lm, 13.88.+e, 14.60.Cd Precision measurements of weak neutral current processes at low energies rigorously test the Standard Model of electroweak interactions. Such measurements are sensitive to new physics effects at TeV energies, and are complementary to searches at high energy colliders.One class of low-energy electroweak measurements involves scattering of longitudinally polarized electrons from unpolarized targets, allowing for the determination of a parity-violating asymmetry Z is due to higher order amplitudes involving virtual weak vector bosons and fermions in quantum loops, referred to as electroweak radiative corrections [4,5].To date, the most precise low-energy determinations of the weak mixing angle come from studies of parity violation in atomic transitions [6] and measurements of the neutral current to charge current cross section ratios in neutrino-nucleon deep inelastic scattering [7]. In this Letter, we present a measurement of the weak mixing angle in electron-electron (Møller) scattering, a purely leptonic reaction with little theoretical uncertainty. We have previously reported the first observation of A P V in Møller scattering [8]. Here, we report on a significantly improved measurement of A P V resulting in a precision determination of sin 2 θ eff W at low momentum transfer. At a beam energy of ≃ 50 GeV available at End Station A at SLAC and a center-of-mass scattering angle of 90• , A P V in Møller scattering is predicted to be ≃ 320 parts per billion (ppb) at tree level [9]. Electroweak radiative corrections [4,5] and the experimental acceptance reduce the measured asymmetry by more than 50%.

Non-unitarity of the leptonic mixing matrix: present bounds and future sensitivities

“…(3.10). The SLAC-E158 experiment has measured the parity-violating coefficient g ee V A in fixed target polarized Møller scattering [35]. The left-right cross-section asymmetry A ee LR reduces to an interference term of the electroweak with the QED amplitude.…”

Theoretical overview of atomic parity violation

“…Generally, atomic PNC is one of a few probes of electroweak coupling below the Z-pole. Competing and at the same time complementary experiments include determination of the weak charge of electron at SLAC [11] and ν-nucleus deep inelastic scattering by the NuTeV collaboration [12]. With an upgrade at Jefferson Lab, an even more accurate constraint on electroweak coupling is expected to come from a P-violating e − p scattering experiment (Qweak collaboration) [13].…”

The Formalism Based on the Model of the Vector Field Inhomogeneity in the Generalized Clifford Algebra

“…Вероятно, с формулой (14) связана «бегучесть» угла Вайнберга, предсказанная в Стандартной модели [4] и подтвержденная в эксперименте [5]. Также «бегучесть констант», возможно, и «конфайнмент» связаны с вкладом энергии в 4-х ток.…”