First Determination of the Weak Charge of the Proton
Abstract
The Qweak experiment has measured the parity-violating asymmetry in polarized e-p elastic scattering at Q^2 = 0.025(GeV/c)^2, employing 145 microamps of 89% longitudinally polarized electrons on a 34.4cm long liquid hydrogen target at Jefferson Lab. The results of the experiment's commissioning run are reported here, constituting approximately 4% of the data collected in the experiment. From these initial results the measured asymmetry is Aep = -279 +- 35 (statistics) +- 31 (systematics) ppb, which is the smallest and most precise asymmetry ever measured in polarized e-p scattering. The small Q^2 of this experiment has made possible the first determination of the weak charge of the proton, QpW, by incorporating earlier parity-violating electron scattering (PVES) data at higher Q^2 to constrain hadronic corrections. The value of QpW obtained in this way is QpW(PVES) = 0.064 +- 0.012, in good agreement with the Standard Model prediction of QpW(SM) = 0.0710 +- 0.0007. When this result is further combined with the Cs atomic parity violation (APV) measurement, significant constraints on the weak charges of the up and down quarks can also be extracted. That PVES+APV analysis reveals the neutron's weak charge to be QnW(PVES+APV) = -0.975 +- 0.010.
Keywords
Cite
@article{arxiv.1307.5275,
title = {First Determination of the Weak Charge of the Proton},
author = {Qweak Collaboration and D. Androic and D. S. Armstrong and A. Asaturyan and T. Averett and J. Balewski and J. Beaufait and R. S. Beminiwattha and J. Benesch and F. Benmokhtar and J. Birchall and R. D. Carlini and G. D. Cates and J. C. Cornejo and S. Covrig and M. M. Dalton and C. A. Davis and W. Deconinck and J. Diefenbach and J. F. Dowd and J. A. Dunne and D. Dutta and W. S. Duvall and M. Elaasar and W. R. Falk and J. M. Finn and T. Forest and D. Gaskell and M. T. W. Gericke and J. Grames and V. M. Gray and K. Grimm and F. Guo and J. R. Hoskins and K. Johnston and D. Jones and M. Jones and R. Jones and M. Kargiantoulakis and P. M. King and E. Korkmaz and S. Kowalski and J. Leacock and J. Leckey and A. R. Lee and J. H. Lee and L. Lee and S. MacEwan and D. Mack and J. A. Magee and R. Mahurin and J. Mammei and J. W. Martin and M. J. McHugh and D. Meekins and J. Mei and R. Michaels and A. Micherdzinska and A. Mkrtchyan and H. Mkrtchyan and N. Morgan and K. E. Myers and A. Narayan and L. Z. Ndukum and V. Nelyubin and Nuruzzaman and W. T. H van Oers and A. K. Opper and S. A. Page and J. Pan and K. D. Paschke and S. K. Phillips and M. L. Pitt and M. Poelker and J. F. Rajotte and W. D. Ramsay and J. Roche and B. Sawatzky and T. Seva and M. H. Shabestari and R. Silwal and N. Simicevic and G. R. Smith and P. Solvignon and D. T. Spayde and A. Subedi and R. Subedi and R. Suleiman and V. Tadevosyan and W. A. Tobias and V. Tvaskis and B. Waidyawansa and P. Wang and S. P. Wells and S. A. Wood and S. Yang and R. D. Young and S. Zhamkochyan},
journal= {arXiv preprint arXiv:1307.5275},
year = {2013}
}
Comments
7 pages, 3 figures