69 research outputs found
Nonperturbative transverse-momentum-dependent effects in dihadron and direct photon-hadron angular correlations in collisions at GeV
International audienceDihadron and isolated direct photon-hadron angular correlations are measured in p+p collisions at s=200ââGeV. The correlations are sensitive to nonperturbative initial-state and final-state transverse momenta kT and jT in the azimuthal nearly back-to-back region ÎÏâŒÏ. To have sensitivity to small transverse momentum scales, nonperturbative momentum widths of pout, the out-of-plane transverse-momentum component perpendicular to the trigger particle, are measured. In this region, the evolution of pout can be studied when several different hard scales are measured. These widths are used to investigate possible effects from transverse-momentum-dependent factorization breaking. When accounting for the longitudinal-momentum fraction of the away-side hadron with respect to the near-side trigger particle, the widths are found to increase with the hard scale; this is qualitatively similar to the observed behavior in Drell-Yan and semi-inclusive deep-inelastic scattering interactions, where factorization is predicted to hold. The momentum widths are also studied as a function of center-of-mass energy by comparing to previous measurements at s=510ââGeV. The nonperturbative jet widths also appear to increase with s at a similar xT, which is qualitatively consistent to similar measurements in Drell-Yan interactions. Future detailed global comparisons between measurements of processes where transverse-momentum-dependent factorization is predicted to hold and be broken will provide further insight into the role of color in hadronic interactions
Measurements of pairs from open heavy flavor and Drell-Yan in collisions at GeV
International audiencePHENIX reports differential cross sections of ΌΌ pairs from semileptonic heavy-flavor decays and the Drell-Yan production mechanism measured in p+p collisions at s=200ââGeV at forward and backward rapidity (1.2<|η|<2.2). The ΌΌ pairs from ccÂŻ, bbÂŻ, and Drell-Yan are separated using a template fit to unlike- and like-sign muon pair spectra in mass and pT. The azimuthal opening angle correlation between the muons from ccÂŻ and bbÂŻ decays and the pair-pT distributions are compared to distributions generated using pythia and powheg models, which both include next-to-leading order processes. The measured distributions for pairs from ccÂŻ are consistent with pythia calculations. The ccÂŻ data present narrower azimuthal correlations and softer pT distributions compared to distributions generated from powheg. The bbÂŻ data are well described by both models. The extrapolated total cross section for bottom production is 3.75±0.24(stat)±0.500.35(syst)±0.45(global)ââ[ÎŒb], which is consistent with previous measurements at the Relativistic Heavy Ion Collider in the same system at the same collision energy and is approximately a factor of 2 higher than the central value calculated with theoretical models. The measured Drell-Yan cross section is in good agreement with next-to-leading-order quantum-chromodynamics calculations
Correlations of , , and pairs in + collisions at GeV and implications for and production mechanisms
PHENIX has measured the azimuthal correlations of muon pairs from charm and bottom semi-leptonic decays in + collisions at GeV, using a novel analysis technique utilizing both unlike- and like-sign muon pairs to separate charm, bottom and Drell-Yan contributions. The dimuon measurements combined with the previous electron-muon and dielectron measurements span a wide range in rapidity, and are well described by PYTHIA Tune A. Through a Bayesian analysis based on PYTHIA Tune A, we show that leading order pair creation is the dominant contribution for production, whereas the data favor the scenario in which next-to-leading-order processes dominate production. The small contribution of next-to-leading-order processes in production at the collision energies of the Relativistic Heavy Ion Collider contrasts with the case at Large-Hadron-Collider energies, where next-to-leading-order processes are expected to dominate
Single-spin asymmetry of production in , Al, and Au collisions with transversely polarized proton beams at GeV
International audienceWe report the transverse single-spin asymmetries of J/Ï production at forward and backward rapidity, 1.2<|y|<2.2, as a function of J/Ï transverse momentum (pT) and Feynman-x (xF). The data analyzed were recorded by the PHENIX experiment at the Relativistic Heavy Ion Collider in 2015 from p+p, p+Al, and p+Au collisions with transversely polarized proton beams at sNN=200ââGeV. At this collision energy, single-spin asymmetries for heavy-flavor particle production of p+p collisions provide access to the spin-dependent gluon distribution and higher-twist correlation functions inside the nucleon, such as the gluon Qiu-Sterman and trigluon correlation functions. Proton+nucleus collisions offer an excellent opportunity to study nuclear effects on the correlation functions. The data indicate a positive asymmetry at the two-standard-deviation level in the p+p data for 2ââGeV/c<pT<10ââGeV/c at backward rapidity and negative asymmetries at the two-standard-deviation level in the p+Au data for pT<2ââGeV/c at both forward and backward rapidity, while in p+Al collisions the asymmetries are consistent with zero within the range of experimental uncertainties
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