Abstract
We presented measurements of the transverse single spin asymmetries ([Formula: see text]) for neutral [Formula: see text] and [Formula: see text] meson at forward rapidities and central rapidity with the PHENIX detector at RHIC at 62.4 GeV and 200 GeV. At mid-rapidity, [Formula: see text] and [Formula: see text] are reconstructed from di-photon decay. At forward rapidities, [Formula: see text] and [Formula: see text] meson are measured using di-photons decays and electromagnetic clusters due to the photon merging effects are significant for energy [Formula: see text]. The neutral-pion measurement of [Formula: see text] at mid-rapidity is consistent with zero with uncertainties a factor of 20 smaller than previous publications, which will lead to improved constraints on the gluon Sivers function. At higher rapidities, both neutral [Formula: see text] and [Formula: see text] [Formula: see text] exhibit sizable asymmetries. The origin of the forward [Formula: see text] is presently not understood quantitatively. We also measured [Formula: see text] meson cross section for [Formula: see text] GeV/c and [Formula: see text]. It is well described by a NLO pQCD calculation.
Highlights
The measurement of transverse single-spin asymmetries (TSSAs) gives us the opportunity to probe the quark and gluon structure of transversely polarized nucleons
Transverse-single-spin asymmetries AN of hadrons produced in transverse polarized p + p collisions were expected to be small,1 but large azimuthal transverse single-spin asymmetry of up to about 40% were first observed at larg√e Feynman-x in π meson production from transversely polarized p + p collisions at s = 4.9GeV
Wang in 1976.2 and extending up stuob√sesqu=en2tl0y0GobesVer.3veIdn in hadronic collisions over a order to describe the large range of energies transverse SSAs observed, two theoretical frameworks have been developed over the past two decades to understand the origin of these large asymmetries; the transverse momentum dependent (TMD) framework, and the collinear twist-3 factorization framework
Summary
The measurement of transverse single-spin asymmetries (TSSAs) gives us the opportunity to probe the quark and gluon structure of transversely polarized nucleons. Another effect is Collins effect, which describes the coupling of a quark transversity and a transfers spin dependent fragmentation function Another framework requires higher-twist contributions in the collinear factorization scheme, the exchange of a gluon between one of the partons taking part in the hard scattering and the color field of either an initial- or final-state hadron. This was first proposed by Qiu and Sterman for gluon exchange in the initial state[4] and by Kanazawa and Koike for exchange in the final state.[5] Gluon exchange in either the initial or final state leads to terms including multiparton correlation functions, which can generate a non-zero TSSA. The comparison of π and η meson can help our understanding of the large transverse single spin asymmetries observed in forward rapidity
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