Measurements of Transverse Spin Effects with the Forward Pion Detector of STAR

Journal Article · Wed Jun 13 04:00:00 EDT 2007 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.2750839· OSTI ID:21063977

Nogach, L ^[1]

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1. Institute of High Energy Physics, 1 Pobeda street, Protvino, Moscow region 142281 (Russian Federation)

Measurements by the STAR collaboration of neutral pion production at large Feynman x (xF) in the first polarized proton collisions at {radical}(s) = 200 GeV were reported previously. Cross sections measured at {eta} = 3.3, 3.8 and 4.0 are found to be consistent with next-to-leading order perturbative QCD calculations. The analyzing power is consistent with zero at negative xF and at positive xF up to 0.3, then grows more positive with increasing xF. This behavior can be described by phenomenological models including the Sivers effect, the Collins effect or higher twist contributions in the initial and final states. Forward calorimetry at STAR has been extended, and there are plans for further expansion. An integrated luminosity of 6.8 pb-1 with average beam polarization of 60% from online polarimetry measurements was sampled with the upgraded FPD in the 2006 RHIC run. This data sample will allow for a detailed map of the {pi}0 analyzing power over kinematic variables bounded by 0.3 < xF < 0.6 and 1.2 < pT < 5.0 GeV/c at {radical}(s) = 200 GeV. The expanded FPD has observed multi-photon final states expected to have 'jet-like' characteristics. The transverse spin dependence of jet-like events can discriminate between the Collins and Sivers effects and lead to further progress in understanding the origin of single spin asymmetries in forward particle production. Data were also obtained at {radical}(s) = 62.4 GeV for xF {yields} 1 to test predictions based on phenomenological fits to earlier STAR results. Recent results, the status of the analysis of 2006 run data and near-term plans will be discussed.

• OSTI ID: 21063977
• Journal Information: AIP Conference Proceedings, Journal Name: AIP Conference Proceedings Journal Issue: 1 Vol. 915; ISSN APCPCS; ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ASYMMETRY
BROOKHAVEN RHIC
CROSS SECTIONS
GEV RANGE
INCLUSIVE INTERACTIONS
JET MODEL
MULTI-PHOTON PROCESSES
MULTIPARTICLE SPECTROMETERS
PARTICLE IDENTIFICATION
PARTICLE PRODUCTION
PIONS NEUTRAL
POLARIMETRY
POLARIZATION
POLARIZATION-ASYMMETRY RATIO
PROTON-PROTON INTERACTIONS
PROTONS
QUANTUM CHROMODYNAMICS
SPIN