Single transverse-spin asymmetries in forward pion production at high energy: Incorporating small-x effects in the target

Journal Article · Sun Oct 01 00:00:00 EDT 2006 · Physical Review. D, Particles Fields

DOI:https://doi.org/10.1103/PHYSREVD.74.074018· OSTI ID:20871317

Boer, Danieel; Dumitru, Adrian; Hayashigaki, Arata ^[1]

---

1. Dept. of Physics and Astronomy, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam (Netherlands)

We consider single-inclusive forward pion production in high-energy proton-proton collisions at RHIC energies. A good baseline description of the transverse momentum distributions at high rapidity is obtained within Mueller's dipole formalism with an anomalous dimension incorporating an 'extended geometric scaling' window between the saturation and DGLAP regimes. We then formulate pion production for transversely polarized projectiles within the same approach. We assume that an azimuthal, spin-dependent asymmetry arises from the so-called Sivers effect and investigate the single transverse-spin asymmetry A{sub N} at 200 GeV and 500 GeV center-of-mass energy. A simple parametrization of the Sivers functions from the literature compares reasonably well with the high-energy STAR data if the overall normalization is scaled up by at least a factor of 2. The STAR data might therefore indicate that the Sivers effect is significantly stronger than thought so far. We also analyze higher-twist contributions to A{sub N} and find that they largely cancel.

• OSTI ID: 20871317
• Journal Information: Physical Review. D, Particles Fields, Vol. 74, Issue 7; Other Information: DOI: 10.1103/PhysRevD.74.074018; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ANOMALOUS DIMENSION
ASYMMETRY
BROOKHAVEN RHIC
CENTER-OF-MASS SYSTEM
COMPARATIVE EVALUATIONS
DIPOLES
DISTRIBUTION
GEV RANGE
MULTIPARTICLE SPECTROMETERS
PARTICLE IDENTIFICATION
PARTICLE PRODUCTION
PARTICLE RAPIDITY
PIONS
PROTON-PROTON INTERACTIONS
SPIN
TRANSVERSE MOMENTUM