Angular decay coefficients of J/ψ mesons at forward rapidity from p+p collisions at s

Abstract

We report the first measurement of the full angular distribution for inclusive J/ψ → µ + µ − decays in p+p collisions at √ s = 510 GeV. The measurements are made for J/ψ transverse momentum 2 < pT < 10 GeV/c and rapidity 1.2 < y < 2.2 in the Helicity, Collins-Soper, and Gottfried-Jackson reference frames. In all frames the polar coefficient λ θ is strongly negative at low pT and becomes close to zero at high pT , while the azimuthal coefficient λ φ is close to zero at low pT , and becomes slightly negative at higher pT . The frame-independent coefficientλ is strongly negative at all pT in all frames. The data are compared to the theoretical predictions provided by nonrelativistic quantum chromodynamics models.

Polarization and cross section of midrapidity J/ψ production in p+p collisions at s=Acharya1, Adare2, Aidala3 et al. 2020Phys. Rev. DSelf Cite3010View full textAdd to dashboardCite

“…510 GeV in p þ p at forward rapidity showed largely longitudinal net polarization (negative angular coefficients) [13], while a prior midrapidity PHENIX measurement at ffiffi ffi s p ¼ 200 GeV was consistent with no strong polarization [12]. The present analysis for midrapidity J=ψ production in ffiffi ffi s p ¼ 510 GeV collisions is complementary to both previous measurements.…”

“…Results are also compared to previous PHENIX measurements at a different beam energy [12] and rapidity [13]. Figure 13 compares λ θ in the helicity frame for different collision energies.…”

“…This procedure closely follows methods described in Ref. [13] and additionally adopts the trigger emulator described in Sec. III B.…”

“…The spin alignment of a positively charged lepton from a J=ψ decay, commonly known as "polarization," has been measured at the Tevatron [11], RHIC [12,13], and the LHC [14][15][16][17]. Measuring spin alignment provides additional tests for the theory and understanding dominant quarkonium production mechanisms in different kinematic regimes.…”

An experimental review of open heavy flavor and quarkonium production at RHIC

“…Figure 13 shows the measurements of polarization parameters for inclusive J/ψ in various reference frames at forward rapidity in p+p collisions at √ s = 510 GeV [86]. In all frames, the polarization parameter λ θ is significantly negative at low p T and consistent with no polarization at high p T .…”