Do p+p Collisions Flow at RHIC? Understanding One-Particle Distributions, Multiplicity Evolution, and Conservation Laws

Abstract

Collective, explosive flow in central heavy ion collisions manifests itself in the mass dependence of $p_T$ distributions and femtoscopic length scales, measured in the soft sector ($p_T\lesssim 1$ GeV/c). Measured $p_T$ distributions from proton-proton collisions differ significantly from those from heavy ion collisions. This has been taken as evidence that p+p collisions generate little collective flow, a conclusion in line with naive expectations. We point out possible hazards of ignoring phase-space restrictions due to conservation laws when comparing high- and low-multiplicity final states. Already in two-particle correlation functions, we see clear signals of such phase-space restrictions in low-multiplicity collisions at RHIC. We discuss how these same effects, then, {\it must} appear in the single particle spectra. We argue that the effects of energy and momentum conservation actually dominate the observed systematics, and that $p+p$ collisions may be much more similar to heavy ion collisions than generally thought.

4 pages, 3 figures - To appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee

References in corpus (4)

• Viscosity in Strongly Interacting Quantum Field Theories from Black Hole Physics
• Recent results in relativistic heavy ion collisions: from ``a new state of matter'' to "the perfect fluid"
• Global Conservation Laws and Femtoscopy of Small Systems
• Conservation Laws and the Multiplicity Evolution of Spectra at the Relativistic Heavy Ion Collider

Cited by in corpus (6)

• Eccentricity and elliptic flow in proton-proton collisions from parton evolution
• Elliptic flow ($v_2$) in pp collisions at energies available at the CERN Large Hadron Collider: A hydrodynamical approach
• Flavoring the Quark-Gluon Plasma with Charm
• Large elliptic flow in low multiplicity pp collisions at LHC energy $\sqrt{s}$=14 TeV
• Extracting the hadronization timescale in sqrt{s}=7 TeV proton-proton collisions from pion and kaon femtoscopy
• Observation of the collective flow in proton-proton collisions