Balance functions fromAu+Au,d+Au, andp

Abstract

Balance functions have been measured for charged-particle pairs, identified charged-pion pairs, and identified charged-kaon pairs in Au + Au, d + Au, and p + p collisions at √ s NN = 200 GeV at the Relativistic Heavy IonCollider using the STAR detector. These balance functions are presented in terms of relative pseudorapidity, η, relative rapidity, y, relative azimuthal angle, φ, and invariant relative momentum, q inv . For charged-particle pairs, the width of the balance function in terms of η scales smoothly with the number of participating nucleons, while HIJING and UrQMD model calculations show no dependence on centrality or system size. For charged-particle and charged-pion pairs, the balance functions widths in terms of η and y are narrower in central Au + Au collisions than in peripheral collisions. The width for central collisions is consistent with thermal blast-wave models where the balancing charges are highly correlated in coordinate space at breakup. This strong correlation might be explained by either delayed hadronization or limited diffusion during the reaction. Furthermore, the narrowing trend is consistent with the lower kinetic temperatures inherent to more central collisions. In contrast, the width of the balance function for charged-kaon pairs in terms of y shows little centrality dependence, which 024905-2 BALANCE FUNCTIONS FROM Au + Au, d + Au, AND . . . 82, 024905 (2010) may signal a different production mechanism for kaons. The widths of the balance functions for charged pions and kaons in terms of q inv narrow in central collisions compared to peripheral collisions, which may be driven by the change in the kinetic temperature. PHYSICAL REVIEW C

Collective dynamics in high-energy proton-nucleus collisions

“…Sizable correlations among opposite-charge particles result from the local charge conservation [53]. There are indications that this effect is generated at hadronization [20,54], i.e., at the late stage of the reaction. Our implementation of the charge balancing is based on the assumption that the particle-antiparticle pairs of charged hadrons are emitted locally at freeze-out, carrying thermal distribution.…”

Charge Conservation and the Shape of the Ridge of Two-Particle Correlations in Relativistic Heavy-Ion Collisions

“…Thus we explain the ridge puzzle in a natural way, amending the (eventby-event, 3+1-dimensional, viscous) hydrodynamics with the local charge-conservation mechanism in the statistical hadronization occurring after the hydrodynamic evolution. This important charge balancing [5][6][7][8], simply stating that the hadron production conserves locally the charge, is an otherwise well-known and measured feature.…”

A Heavy Ion Fireball freeze-out Dipion Cocktail for Au-Au Collisions at root s=200 GeV pt dependence (Part 3).

“…The T 11 amplitude comes from a fit to of Ref [3] using three K-matrix poles for the σ, f 0 and some background from higher mass poles. pairs mass (GeV) Figure 3: The fit to the p-p balance function STAR data [8], where the solid line is the fit and dashed line is the ρ(770). The exponential is amplitude A and the dotted line is A plus A times the re-scattering of pions through the Pwave phase shift.…”

“…We turn to the central Au-Au balance function measured by STAR [8]. Again using the same functions that we used above we fit the data.…”