Cross section and transverse single-spin asymmetry ofηmesons inp↑+pcollisions at

Abstract

We present a measurement of the cross section and transverse single-spin asymmetry (AN ) for η mesons at large pseudorapidity from √ s = 200 GeV p ↑ + p collisions. The measured cross section for 0.5 < pT < 5.0 GeV/c and 3.0 < |η| < 3.8 is well described by a next-to-leading-order perturbative-quantum-chromodynamics calculation. The asymmetries AN have been measured as a function of Feynman-x (xF ) from 0.2 < |xF | < 0.7, as well as transverse momentum (pT ) from 1.0 < pT < 4.5 GeV/c. The asymmetry averaged over positive xF is AN = 0.061±0.014. The results are consistent with prior transverse single-spin measurements of forward η and π 0 mesons at various energies in overlapping xF ranges. Comparison of different particle species can help to determine the origin of the large observed asymmetries in p ↑ + p collisions.

Cross section and transverse single-spin asymmetry of muons from open heavy-flavor decays in polarized p+p collisions at s=200 GeV

“…The large TSSA of pion production has been subsequently observed in hadronic collisions over a range of energies extending up to √ s = 500 GeV for π 0 ( √ s = 200 GeV for π ± ) [3][4][5][6][7][8][9][10][11][12]. Furthermore, TSSA in η meson production has also been studied at forward rapidity [13,14]. The results are consistent with the observed π 0 asymmetries at various energies in the overlapping x F regions.…”

Azimuthal asymmetries of back-to-back π±−(π0, η, π±)Li1, Vossen2, Aihara3 et al. 2019Phys. Rev. DSelf Cite151100View full textAdd to dashboardCite

“…This is in particular true for the transverse spin structure of the nucleon. The large single transverse spin asymmetries of π 0 and η mesons observed in pp collisions [3][4][5][6][7] were at odds with the expectation that they would vanish due to the suppression of spin-flip amplitudes in the hard scattering [8]. However, Collins showed [9] that spinflip amplitudes for soft components of the cross section, the PDFs and FFs, are not necessarily suppressed.…”

“…These results provide additional constraints on the Collins function in global fits. The final states including η mesons will provide sensitivity to the fragmentation of strange quarks and are also of interest since there are hints that the transverse spin asymmetries of π 0 and η mesons in pp collisions are different [6,7].…”

Nuclear Dependence of the Transverse Single-Spin Asymmetry in the Production of Charged Hadrons at Forward Rapidity in Polarized p+p , p+Al , and Aidala1, Akiba2, Alfred3 et al. 2019Phys. Rev. Lett.Self Cite

“…The first observations in pion production at large Feynmanx (x F ) [1] showed measured TSSAs that were considerably larger than early theoretical predictions (in collinear leading twist approach) [2]. Surprisingly large measured TSSAs continued to persist in hadronic collisions at high energies up to √ s = 500 GeV [3][4][5][6][7][8][9][10][11][12][13][14]. To explain these large TSSAs, two approaches were proposed within perturbative quantum chromodynamics (pQCD).…”