Moments of the spin structure functions and for 0.05<Q

Author:

CLAS Collaboration   Y. Prok   P. Bosted   V.D. Burkert   A. Deur   K.V. Dharmawardane   G.E. Dodge   K.A. Griffioen   S.E. Kuhn   R. Minehart   G. Adams   M.J. Amaryan   M. Anghinolfi   G. Asryan   G. Audit   H. Av  

Journal:

Physics Letters B

Issue Date:

2009

Abstract(summary):

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 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 data and Chiral Perturbation calculations for , even at the lowest Q².

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