Evidence for Strange-Quark Contributions to the Nucleon's Form Factors at Q2=0.108 (GeV/c)2
Abstract
We report on a measurement of the parity violating asymmetry in the elastic scattering of polarized electrons off unpolarized protons with the A4 apparatus at MAMI in Mainz at a four momentum transfer value of Q2=0.108 (GeV/c)2 and at a forward electron scattering angle of 30°<θe<40°. The measured asymmetry is ALR(e→p)=[-1.36±0.29(stat)±0.13(syst)]×10-6. The expectation from the standard model assuming no strangeness contribution to the vector current is A0=(-2.06±0.14)×10-6. We have improved the statistical accuracy by a factor of 3 as compared to our previous measurements at a higher Q2. We have extracted the strangeness contribution to the electromagnetic form factors from our data to be GsE+0.106GsM=0.071±0.036 at Q2=0.108 (GeV/c)2. We again find the value for GsE+0.106GsM to be positive, this time at an improved significance level of two σ.
- Publication:
-
Physical Review Letters
- Pub Date:
- April 2005
- DOI:
- 10.1103/PhysRevLett.94.152001
- arXiv:
- arXiv:nucl-ex/0412030
- Bibcode:
- 2005PhRvL..94o2001M
- Keywords:
-
- 13.60.Fz;
- 11.30.Er;
- 12.15.-y;
- 13.40.Gp;
- Elastic and Compton scattering;
- Charge conjugation parity time reversal and other discrete symmetries;
- Electroweak interactions;
- Electromagnetic form factors;
- Nuclear Experiment
- E-Print:
- 4 pages, 3 figures