The spin structure functions g1 for the proton and the deuteron have been measured over a wide kinematic range in x and Q2 using 1.6 and 5.7 GeV longitudinally polarized electrons incident upon polarized NH3 and ND3 targets at Jefferson Lab. Scattered electrons were detected in the CEBAF Large Acceptance Spectrometer, for 0.05 < Q2 < 5 GeV2 and W < 3 GeV. The first moments of g1 for the proton and deuteron are presented - both have a negative slope at low Q2, as predicted by the extended Gerasimov-Drell-Hearn sum rule. The first extraction of the generalized forward spin polarizability of the proton γ0p is also reported. This quantity shows strong Q2 dependence at low Q2. Our analysis of the Q2 evolution of the first moment of g1 shows agreement in leading order with Heavy Baryon Chiral Perturbation Theory. However, a significant discrepancy is observed between the γ0p data and Chiral Perturbation calculations for γ0p, even at the lowest Q2.
|Number of pages
|Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
|Published - Feb 9 2009
Bibliographical noteFunding Information:
We would like to acknowledge the outstanding efforts of the staff of the Accelerator and the Physics Divisions at Jefferson Lab that made this experiment possible. This work was supported in part by the US Department of Energy and National Science Foundation, the Italian Istituto Nazionale di Fisica Nucleare, the French Centre National de la Recherche Scientifique, the French Commissariat à l'Energie Atomique and the Korean Science and Engineering Foundation. Jefferson Science Associates operates the Thomas Jefferson National Accelerator Facility for the United States Department of Energy under contract DE-AC05-84ER-40150. We would also like to thank M. Vanderhaeghen for helpful discussions.
- Chiral Perturbation Theory
- Nucleon structure
- Spin structure functions
ASJC Scopus subject areas
- Nuclear and High Energy Physics