Nuclear modification of high transverse momentum particle production in p+A collisions at RHIC and LHC

TL;DR

This work develops a perturbative QCD framework that embeds cold nuclear matter effects—isospin, Cronin $k_T$ broadening, cold nuclear matter energy loss, and dynamical shadowing—into the LO pQCD baseline for single inclusive production. It demonstrates that this CNM-decomposed approach can describe RHIC $d+Au$ data for photons and light hadrons and delivers predictions for LHC $p+Pb$ at $\sqrt{s}=5$ TeV, with forward-rapidity suppression enhanced relative to mid-rapidity. The results span parameter variations that connect to the strength of multiple scattering and show that the predicted $R_{pPb}$ lies between EPS09-based shadowing and CGC expectations. Overall, the framework provides a transparent, process-dependent tool for constraining CNM effects and informing dense QCD-matter tomography with upcoming collider data.

Abstract

We present results and predictions for the nuclear modification of the differential cross sections for inclusive light hadron and prompt photon production in minimum bias d+Au collisions at $\sqrt{s} = 200$ GeV and minimum bias p+Pb collisions at $\sqrt{s} = 5$ TeV at RHIC and LHC, respectively. Our calculations combine the leading order perturbative QCD formalism with cold nuclear matter effects that arise from the elastic, inelastic and coherent multiple scattering of partons in large nuclei. We find that a theoretical approach that includes the isospin effect, Cronin effect, cold nuclear matter energy loss and dynamical shadowing can describe the RHIC d+Au data rather well. The LHC p+Pb predictions will soon be confronted by new experimental results to help clarify the magnitude and origin of cold nuclear matter effects and facilitate precision dense QCD matter tomography.

Figures (4)

• Figure 1: Left panel: our calculation at $\sqrt{s}=200$ GeV and rapidity $y=0$ is compared to RHIC photon data (top) Adare:2012yt and $\pi^0$ data (bottom) Adare:2007dg. We choose $K=1$ for $\pi^0$ and $K=1.8$ for photon production. Right panel: comparison to LHC photon data at $\sqrt{s}=7$ TeV and $|y|<0.9$Chatrchyan:2011ue and charged hadron data at $\sqrt{s}=2.76$ TeV and $|y|<1$CMS:2012aa. We choose $K=1.5$ for photon and $K=1$ for charged hadron production.
• Figure 2: The nuclear modification factor $R_{dAu}$ is plotted as a function of transverse momentum $p_T$ for photons (left panel) and $\pi^0$s (right panel) at RHIC energy of $\sqrt{s}=200$ GeV. Empty and filled circles are low-mss virtual photon and real photon experimental data at mid-rapidity from PHENIX Adare:2012yt. Filled squares are the minimum bias mid-rapidity $\pi^0$ data Adler:2006wg, filled triangles are the forward rapidity $y=4$ STAR $\pi^0$ data Adams:2006uz, and empty squares is the forward rapidity $3<y<3.8$ PHENIX $\pi^0$s Adare:2011sc. We have also presented predictions for rapidity $y=1.5$ (dashed curves) and $y=3$ (dotted curves) for both photon and hadron production.
• Figure 3: Predictions for the nuclear modification factor $R_{pPb}$ as a function of transverse momentum $p_T$ for $\pi^0$ (left panel) and charged hadron (right panel) production in minimum bias p+Pb collisions at the LHC energy of $\sqrt{s}=5$ TeV. Results for three rapidities $y=0$, $y=2$, and $y=4$ are shown.
• Figure 4: Predictions for the nuclear modification factor $R_{pPb}$ as a function of transverse momentum $p_T$ for photon production in minimum bias p+Pb collisions at the LHC energy of $\sqrt{s}=5$ TeV for rapidities $y=0$, $y=2$, and $y=4$.