Evidence for Nonlinear Gluon Effects in QCD and their $A$ Dependence at STAR

Abstract

The STAR Collaboration reports measurements of back-to-back azimuthal correlations of di-${\pi }^0$s produced at forward pseudorapidities ($2.6<\eta <4.0$) in $p$+$p$, $p+$Al, and $p+$Au collisions at a center-of-mass energy of 200 GeV. We observe a clear suppression of the correlated yields of back-to-back ${\pi }^0$ pairs in $p+$Al and $p+$Au collisions compared to the $p$+$p$ data. The observed suppression of back-to-back pairs as a function of transverse momentum suggests nonlinear gluon dynamics arising at high parton densities. The larger suppression found in $p+$Au relative to $p+$Al collisions exhibits a dependence of the saturation scale, $Q_s^2$, on the mass number, $A$. A linear scaling of the suppression with $A^{1/3}$ is observed with a slope of $-0.09$ $\pm$ $0.01$.

arXiv comment7 pages,3 figures, 1 supplemental material

References in corpus (35)

• Computing Quark and Gluon Distribution Functions for Very Large Nuclei
• Operator expansion for high-energy scattering
• Gluon Distribution Functions for Very Large Nuclei at Small Transverse Momentum
• Small-x F_2 Structure Function of a Nucleus Including Multiple Pomeron Exchanges
• Saturation Effects in Deep Inelastic Scattering at low $Q^2$ and its Implications on Diffraction
• The Color Glass Condensate
• Evolution of the nuclear modification factors with rapidity and centrality in d+Au collisions at $\sqrt{s_{NN}} = 200 GeV
• Transverse Momentum Spectra in Au+Au and d+Au Collisions at $\sqrt{s_{NN}}$=200 GeV and the Pseudorapidity Dependence of High p${}_T$ Suppression
• Gluon saturation and initial conditions for relativistic heavy ion collisions
• Forward inclusive dijet production and azimuthal correlations in pA collisions
• Relating high-energy lepton-hadron, proton-nucleus and nucleus-nucleus collisions through geometric scaling
• Azimuthal correlations of forward di-hadrons in d+Au collisions at RHIC in the Color Glass Condensate
• Forward Neutral Pion Production in p+p and d+Au Collisions at sqrt(s_NN)=200 GeV
• Non-Abelian energy loss in cold nuclear matter
• Mining for Gluon Saturation at Colliders
• Suppression of back-to-back hadron pairs at forward rapidity in d+Au Collisions at sqrt(s_NN)=200 GeV
• Forward dihadron correlations in deuteron-gold collisions with a Gaussian approximation of JIMWLK
• Initial State Parton Broadening and Energy Loss Probed in d+Au at RHIC
• Back-to-Back Correlations of Di-hadrons in dAu Collisions at RHIC
• Jet Azimuthal Correlations and Parton Saturation in the Color Glass Condensate
• Nuclear Modification Factors for Hadrons At Forward and Backward Rapidities in Deuteron-Gold Collisions at sqrt(s_NN) = 200 GeV
• Observations on dA scattering at forward rapidities
• High Gluon Densities in Heavy Ions Collisions
• Probing Gluon Saturation through Dihadron Correlations at an Electron-Ion Collider
• Forward di-hadron back-to-back correlations in $\mathbf{pA}$ collisions from rcBK evolution
• Dihadron momentum imbalance and correlations in d+Au collisions
• Multiple parton interactions and forward double pion production in pp and dA scattering
• On the Dihadron Angular Correlations in Forward $pA$ collisions
• Forward Production in d+Au Collisions by Parton Recombination
• Energy losses in the black disc regime and correlation effects in the STAR forward pion production in dAu collisions
• Measurement of transverse single-spin asymmetries of ${\pi }^0$ and electromagnetic jets at forward rapidity in 200 and 500 GeV transversely polarized proton-proton collisions
• Dijet azimuthal correlations and conditional yields in $pp$ and $p$+Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV with the ATLAS detector
• Rapidity and centrality dependence of azimuthal correlations in Deuteron-Gold collisions at RHIC
• Comparison of transverse single-spin asymmetries for forward ${\pi }^0$ production in polarized $pp$, $p\mathrm{Al}$ and $p\mathrm{Au}$ collisions at nucleon pair c.m. energy $\sqrt{s_{\mathrm{NN}}}=200$ GeV
• Longitudinal Double-Spin Asymmetries for ${\pi }^0$s in the Forward Direction for 510 GeV Polarized $pp$ Collisions

Cited by in corpus (11)

• The Present and Future of QCD
• Tomography of Ultra-relativistic Nuclei with Polarized Photon-gluon Collisions
• Gluon Saturation Effects in Exclusive Heavy Vector Meson Photoproduction
• Novel Cross Section Ratios as Possible Signals of Saturation in UPCs
• Investigating the broadening phenomenon in two-particle correlations induced by gluon saturation
• Color Glass Condensate meets High Twist Expansion
• Description of di-hadron saturation signals within a universal nuclear parton distribution function approach
• Physics with high-luminosity proton-nucleus collisions at the LHC
• Hard processes in multi-TeV ion collisions
• Predictions for photon-jet correlations at forward rapidities in heavy-ion collisions
• Influence of the residual magnetic field on the azimuthal distribution of final-state particles in photon-nuclear processes