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Title: Impact of CLAS and COMPASS data on polarized parton densities and higher twist

Abstract

We have reanalyzed the world data on inclusive polarized deep inelastic scattering (DIS) including the very precise CLAS proton and deuteron data, as well as the latest COMPASS data on the asymmetry A{sub 1}{sup d}, and have studied the impact of these data on polarized parton densities and higher twist effects. We demonstrate that the low Q{sup 2} CLAS data improve essentially our knowledge of higher twist corrections to the spin structure function g{sub 1}, while the large Q{sup 2} COMPASS data influence mainly the strange quark density. In our new analysis we find that a negative polarized gluon density, or one that changes sign as a function of x, cannot be ruled out on the basis of the present DIS data.

Authors:
; ;  [1];  [2];  [3]
  1. Imperial College, Prince Consort Road, London SW7 2BW (United Kingdom)
  2. (Russian Federation)
  3. (Bulgaria)
Publication Date:
OSTI Identifier:
21020287
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. D, Particles Fields; Journal Volume: 75; Journal Issue: 7; Other Information: DOI: 10.1103/PhysRevD.75.074027; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ASYMMETRY; CORRECTIONS; DEEP INELASTIC SCATTERING; DENSITY; DEUTERIUM TARGET; FOUR MOMENTUM TRANSFER; GLUONS; HYDROGEN 1 TARGET; MULTIPARTICLE SPECTROMETERS; PARTICLE IDENTIFICATION; PROTONS; S QUARKS; SPIN; STRUCTURE FUNCTIONS

Citation Formats

Leader, Elliot, Sidorov, Aleksander V., Stamenov, Dimiter B., Bogoliubov Theoretical Laboratory Joint Institute for Nuclear Research, 141980 Dubna,, and Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Boulevard, Tsarigradsko Chaussee 72, Sofia 1784. Impact of CLAS and COMPASS data on polarized parton densities and higher twist. United States: N. p., 2007. Web. doi:10.1103/PHYSREVD.75.074027.
Leader, Elliot, Sidorov, Aleksander V., Stamenov, Dimiter B., Bogoliubov Theoretical Laboratory Joint Institute for Nuclear Research, 141980 Dubna,, & Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Boulevard, Tsarigradsko Chaussee 72, Sofia 1784. Impact of CLAS and COMPASS data on polarized parton densities and higher twist. United States. doi:10.1103/PHYSREVD.75.074027.
Leader, Elliot, Sidorov, Aleksander V., Stamenov, Dimiter B., Bogoliubov Theoretical Laboratory Joint Institute for Nuclear Research, 141980 Dubna,, and Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Boulevard, Tsarigradsko Chaussee 72, Sofia 1784. Sun . "Impact of CLAS and COMPASS data on polarized parton densities and higher twist". United States. doi:10.1103/PHYSREVD.75.074027.
@article{osti_21020287,
title = {Impact of CLAS and COMPASS data on polarized parton densities and higher twist},
author = {Leader, Elliot and Sidorov, Aleksander V. and Stamenov, Dimiter B. and Bogoliubov Theoretical Laboratory Joint Institute for Nuclear Research, 141980 Dubna, and Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Boulevard, Tsarigradsko Chaussee 72, Sofia 1784},
abstractNote = {We have reanalyzed the world data on inclusive polarized deep inelastic scattering (DIS) including the very precise CLAS proton and deuteron data, as well as the latest COMPASS data on the asymmetry A{sub 1}{sup d}, and have studied the impact of these data on polarized parton densities and higher twist effects. We demonstrate that the low Q{sup 2} CLAS data improve essentially our knowledge of higher twist corrections to the spin structure function g{sub 1}, while the large Q{sup 2} COMPASS data influence mainly the strange quark density. In our new analysis we find that a negative polarized gluon density, or one that changes sign as a function of x, cannot be ruled out on the basis of the present DIS data.},
doi = {10.1103/PHYSREVD.75.074027},
journal = {Physical Review. D, Particles Fields},
number = 7,
volume = 75,
place = {United States},
year = {Sun Apr 01 00:00:00 EDT 2007},
month = {Sun Apr 01 00:00:00 EDT 2007}
}
  • The impact of the recent very precise CLAS and COMPASS g{sub 1}/F{sub 1} data on polarized parton densities and higher twist effects is discussed. It is demonstrated that the low Q{sup 2} CLAS data improve essentially our knowledge of higher twist corrections to the spin structure function g{sub 1}, while the large Q{sup 2} COMPASS dala influence mainly the strange quark and gluon polarizations which slightly decrease. It is shown that the uncertainties in the determination of the polarized parlon densities are significantly reduced. We find also that the present inclusive DIS data cannot rule out a negative polarized andmore » changing in sign gluon densities.« less
  • The present status of the longitudinal polarized parton densities (PDFs) and the contribution of their first moments to the nucleon spin is discussed. Special attention is paid to the role of higher twist effects in determining the PDFs and to the polarized strange quark and gluon densities, which are still not well determined from the present data.
  • Precise measurements of polarized electroproduction and Drell-Yan processes in the deep inelastic limit will soon provide the first information on the higher-twist parton distributions {ital g}{sub {ital T}}({ital x}) and {ital h}{sub {ital L}}({ital x}). Sum rules for higher-twist structure functions are only valid provided the corresponding Compton amplitudes satisfy unsubtracted dispersion relations. Subtracted dispersion relations have to be used when the (real part of the) forward scattering amplitudes do not fall off rapidly enough for {nu}{r_arrow}{infinity} (fixed {ital Q}{sup 2}). Formally, such subtractions lead to {delta} functions at the origin in the parton distributions, which are not accessible tomore » experiment, and the integral over the data fails to satisfy the sum rule. The {delta} functions in the parton distributions can be identified with the zero modes that appear in light-front quantization. An explicit {ital infinite} {ital momentum} {ital boost} identifies these soft quark modes with low momentum contributions arising from self-energy-type interactions.« less
  • In a recent Letter Yang and Bodek presented results of a new analysis of proton and deuteron structure functions in which the free neutron structure function F{sub 2}{sup n}, was extracted at large x. Knowledge of F{sub 2}{sup n} is crucial for determining the neutron/proton structure function ratio, whose x {r_arrow} 1 limit is sensitive to mechanisms of SU(6) spin-flavor symmetry breaking, and provides one of the fundamental tests of the x dependence of parton distributions in perturbative QCD. Relating nuclear structure functions to those of free nucleons is, however, not straightforward because at large x nuclear effects become quitemore » sizeable. In particular, omitting nuclear binding or off-shell corrections can introduce errors of up to 50% in F{sub 2}{sup n}/F{sub 2}{sup p} already at x {approximately} 0.75. Rather than follow the conventional procedure of subtracting Fermi motion and binding effects in the deuteron via standard two-body wave function, Yang and Bodek instead extract F {sub 2}{sup n} by extrapolating the density dependence of the nuclear corrections to the case of the deuteron. Here the authors point out why this approach is likely to be misleading for light nuclei, and correctly applied predicts that the nuclear correction in the deuteron should be zero.« less
  • The quark and gluon higher-twist contributions to hard processes are obtained very simply for leptoproduction in lowest order from on-shell parton diagrams, and used for the phenomenology of R = sigma/sub L//sigma/sub T/. .AE