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%.

We have measured the beam-normal single-spin asymmetry An in the elastic scattering of 1-3 GeV transversely polarized electrons from 1 H and for the first time from 4 He, 12 C, and 208 Pb. For 1 H, 4 He and 12 C, the measurements are in agreement with calculations that relate An to the imaginary part of the two-photon exchange amplitude including inelastic intermediate states. Surprisingly, the 208 Pb result is significantly smaller than the corresponding prediction using the same formalism. These results suggest that a systematic set of new An measurements might emerge as a new and sensitive probe of the structure of heavy nuclei.

[ [ ) . frJ r;y;)Prepared for the U.S. Department of Energy under Contract Number DE-AC03-76SF00098..... DISCLAIMERThis document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. ABSTRACTAlthough scintillation has been discovered in many inorganic crystals during the past 40 years, there is continued interest in finding compounds with improved scintillation properties. However, the testing of candidate compounds has thus far been limited to those available as crystals of suitable quality and size. We describe a method using synchrotron x-radiation for measuring the fluorescence properties of powders, which makes accessible a much larger number of compounds. We present results for 85 compounds tested by this method. Scintillation from several compounds was discovered, notably CeF3 and PbC03.

We have measured the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from 4He at an average scattering angle = 5.7 degrees and a four-momentum transfer Q2 = 0.091 GeV2 . From these data, for the first time, the strange electric form factor of the nucleon G(E)s can be isolated. The measured asymmetry of A(PV) = (6.72 +/- 0.84(stat) +/- 0.21(syst) x 10(-6) yields a value of G(E)s = -0.038 +/- 0.042(stat) +/- 0.010(syst), consistent with zero.