Neutral pion cross section and spin asymmetries at intermediate pseudorapidity in polarized proton collisions at $\sqrt{s} = 200$ GeV - INSPIRE

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Neutral pion cross section and spin asymmetries at intermediate pseudorapidity in polarized proton collisions at $\sqrt{s} = 200$ GeV

STAR

Collaboration

Sep 6, 2013

11 pages

Published in:

Phys.Rev.D 89 (2014) 1, 012001

Published: Jan 15, 2014

e-Print:

1309.1800 [nucl-ex]

DOI:

10.1103/PhysRevD.89.012001

Experiments:

BNL-RHIC-STAR

View in:

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Abstract: (APS)

The differential cross section and spin asymmetries for neutral pions produced within the intermediate pseudorapidity range

0.8 < η < 2.0

in polarized proton-proton collisions at

\sqrt{s} = 200 GeV

are presented. Neutral pions were detected using the end cap electromagnetic calorimeter in the STAR detector at RHIC. The cross section was measured over a transverse momentum range of

5 < p_{T} < 16 GeV / c

and is found to agree with a next-to-leading order perturbative QCD calculation. The longitudinal double-spin asymmetry

A_{L L}

is measured in the same pseudorapidity range and spans a range of Bjorken-

x

down to

x \approx 0.01

. The measured

A_{L L}

is consistent with model predictions for varying degrees of gluon polarization. The parity-violating asymmetry

A_{L}

is also measured and found to be consistent with zero. The transverse single-spin asymmetry

A_{N}

is measured over a previously unexplored kinematic range in Feynman-

x

and

p_{T}

. Such measurements may aid our understanding of the onset and kinematic dependence of the large asymmetries observed at more forward pseudorapidity (

η \approx 3

) and their underlying mechanisms. The

A_{N}

results presented are consistent with a twist-3 model prediction of a small asymmetry over the present kinematic range.

Note:

11 pages, 9 figures, REVTeX 4.1, Submitted to Phys. Rev. D. Changes for version 2: minor textual updates, modified discussion of gluonic polarization, clarified description of Fig. 4, and corrected sign convention in Fig. 8

21.10.Gv
13.87.Ce
13.88.+e
14.20.Dh
spin: asymmetry
p: spin
calorimeter: electromagnetic
quantum chromodynamics: perturbation theory
p p: inclusive reaction
higher-order: 1

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