New results on the proton spin-dependent structure function g1p at COMPASS with E=200 GeV

Abstract The gluon polarization contribution to the proton spin is an integral part to solve the longstanding proton spin puzzle. At the Relativistic Heavy Ion Collider (RHIC), the STAR experiment has measured jets produced in mid-pseudo-rapidity, |η| < 1.0, and full azimuth, ϕ, from longitudinally polarized pp collisions to study the gluon polarization in the proton. At center of mass energies s = 200 and 510 GeV, jet production is dominated by hard QCD scattering processes such as gluon-gluon (gg) and quark-gluon (qg), thus making the longitudinal double-spin asymmetry (ALL ) sensitive to the gluon polarization. Early STAR inclusive jet ALL results at s = 200 GeV provided the first evidence of the non-zero gluon polarization at momentum fraction x > 0.05. The higher center of mass energy s = 510 GeV allows to explore the gluon polarization as low as x ∼ 0.015. In this talk we will present the recent STAR inclusive jet and dijet ALL results at s = 510 GeV, and discuss the relevant new analysis techniques for the estimation of trigger bias and reconstruction uncertainty, the underlying event correction on the jet energy and its effect on jet ALL . Dijet results are shown for different topologies in regions of pseudo-rapidity, effectively scanning the x-dependence of the gluon polarization.

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Polarized Deep Inelastic Scattering

Australian Journal of Physics ◽

10.1071/p96044 ◽

1997 ◽

Vol 50 (1) ◽

pp. 71

Author(s):

F. M. Steffens ◽

A. W. Thomas

Keyword(s):

Inelastic Scattering ◽

Structure Function ◽

Spin Structure ◽

Good Description ◽

Proton Spin ◽

Spin Structure Function ◽

Sum Rule ◽

Axial Anomaly ◽

Proton Spin Structure ◽

Polarized Deep Inelastic Scattering

We give an overview of present calculations involving the proton spin structure function. It is shown that a significant part of the discepancy between the data and the Ellis–Jaffe sum-rule may arise through the axial anomaly if the gluons within the proton are strongly polarized. While a quark model, such as the MIT bag, does not include the anomaly, and therefore cannot be expected to reproduce the spin structure function, it does give a rather good description of recent data which is anomaly free, such as the distribution of polarized, valence up-quarks in the proton.

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