Scaling properties of direct photon yields in heavy ion collisions

Abstract

A recent analysis from the PHENIX collaboration of available direct photon measurement results in collisions of various systems such as Au+Au, Cu+Cu, and Pb+Pb, at different beam energies ranging from 39 to 2760 GeV, has shown a universal, within experimental uncertainties, $multiplicity$ scaling, in which direct photon $p_T$-spectra for transverse momenta up to 2 GeV/$c$ are scaled with charged hadron pseudorapidity density at midrapidity raised to power $\alpha =1.25$. On the other hand, those direct photon $p_T$-spectra also exhibit $geometrical$ scaling in the similar $p_T$ range. Assuming power-law dependence of the scaled photon spectra for both scaling laws, we formulate two independent conditions for the power $\alpha$, which overshoot experimental data by $\sim 10\%$ on average. We discuss possible sources that might improve this estimate.

arXiv comment8 pages, 5 figures. The paper has been rewritten, title has been changed, new material and references added. Version accepted for publication in EPJ C. In v3 references updated, minor typos corrected

References in corpus (48)

• 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
• Green's Functions in the Color Field of a Large Nucleus
• Unitarization of the BFKL Pomeron on a Nucleus
• Saturation in Diffractive Deep Inelastic Scattering
• Hadron production in nuclear collisions at RHIC and high density QCD
• An Impact Parameter Dipole Saturation Model
• Geometric scaling for the total gamma^* p cross section in the low x region
• The production of photons in relativistic heavy-ion collisions
• The Energy Dependence of the Saturation Momentum
• Geometric Scaling above the Saturation Scale
• Geometric scaling as traveling waves
• Traveling wave fronts and the transition to saturation
• How Protons Shatter Colored Glass
• Thermal Photons and Collective Flow at the Relativistic Heavy-Ion Collider
• Thermal photons as a quark-gluon plasma thermometer revisited
• Pseudo-Critical Enhancement of Thermal Photons in Relativistic Heavy-Ion Collisions
• Viscous photons in relativistic heavy ion collisions
• Saturation models of HERA DIS data and inclusive hadron distributions in p+p collisions at the LHC
• Centrality dependence of the direct photon yield and elliptic flow in heavy-ion collisions at sqrt(s)=200 GeV
• Hadronic and partonic sources of direct photons in relativistic heavy-ion collisions
• Anisotropic flow of thermal photons as a quark-gluon plasma viscometer
• Direct real photons in relativistic heavy ion collisions
• Saturation and Scaling of Multiplicity, Mean p_T and p_T Distributions from 200 GeV < sqrt{s} < 7 TeV - Addendum
• The Glasma, Photons and the Implications of Anisotropy
• Parametric estimate of the relative photon yields from the Glasma and the Quark-Gluon Plasma in heavy-ion collisions
• Production of Photons and Dileptons in the Glasma
• Thermal photons from heavy ion collisions: A spectral function approach
• Geometric Scaling from GLAP evolution
• Geometrical Scaling of Direct-Photon Production in Hadron Collisions from RHIC to the LHC
• A Tale of Tails: Photon Rates and Flow in Ultra-Relativistic Heavy Ion Collisions
• Direct photon production from hadronic sources in high-energy heavy-ion collisions
• Electromagnetic Radiation in Hot QCD Matter: Rates, Electric Conductivity, Flavor Susceptibility and Diffusion
• Geometrical scaling in hadronic collisions
• Quantitative Study of Geometrical Scaling in Deep Inelastic Scattering at HERA
• Geometrical Scaling in Inelastic Inclusive Particle Production at the LHC
• Direct Photon Elliptic Flow at BNL Relativistic Heavy Ion Collider (RHIC) and CERN Large Hadron Collider (LHC)
• Properties of Thermal Photons at RHIC and LHC
• Phenomenology of photon and di-lepton production in relativistic nuclear collisions
• PHENIX measurements of low momentum direct photon radiation
• Photons from thermalizing matter in heavy ion collisions
• A Phenomenological Model of the Glasma and Photon Production
• Geometrical scaling of prompt photons in heavy ion collisions
• Hydrodynamic Description of Dilepton Production

Cited by in corpus (3)

• Prompt photon production in high-energy $pA$ collisions at forward rapidity
• Universality of scaled particle spectra in ultrarelativistic heavy-ion collisions
• Geometrical Scaling of Direct Photons in Relativistic Heavy Ion and d+Au Collisions