Author/Authors :
HAPPEX Collaboration، نويسنده , , K.A. Aniol، نويسنده , , D.S. Armstrong، نويسنده , , T. Averett، نويسنده , , M. Baylac، نويسنده , , E. Burtin، نويسنده , , J. Calarco، نويسنده , , G.D. Cates، نويسنده , , C. Cavata، نويسنده , , Z. Chai، نويسنده , , C.C. Chang، نويسنده , , J.-P. Chen، نويسنده , , E. Chudakov، نويسنده , , E. Cisbani، نويسنده , , M. Coman، نويسنده , , D. Dale، نويسنده , , A. Deur، نويسنده , , P. Djawotho، نويسنده , , M.B. Epstein، نويسنده , , S. Escoffier، نويسنده , , et al.، نويسنده ,
Abstract :
We have measured the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from the proton. The result is A=−15.05±0.98(stat)±0.56(syst) ppm at the kinematic point 〈θlab〉=12.3° and 〈Q2〉=0.477 (GeV/c)2. Both errors are a factor of two smaller than those of the result reported previously. The value for the strange form factor extracted from the data is (GsE+0.392 GsM)=0.025±0.020±0.014, where the first error is experimental and the second arises from the uncertainties in electromagnetic form factors. This measurement is the first fixed-target parity violation experiment that used either a “strained” GaAs photocathode to produce highly polarized electrons or a Compton polarimeter to continuously monitor the electron beam polarization.
