A Student’s Guide to Hard Scattering at RHIC. Thomas K Hemmick Stony Brook University. Helmut Satz. A Defining Moment for Me. In 1988, Brookhaven National Lab held a school for the students in the fledgling field of Relativistic Heavy Ions.
Thomas K Hemmick
Stony Brook University
100% Centrality 0%
J/Y & U
The importance of the control measurement(s) cannot be overstated!
NOTE: Only the pQCD cross sections are fundamental. PDF and Fragmentation are
based upon measurementFactorization Theorem:
Collins, Soper, Sterman, Nucl. Phys. B263 (1986) 37
leading particleq/g jets as probe of hot medium
Jets from hard scattered
quarks observed via fast
leading particles or
between the leading
If no “effects”:
RAA < 1 in regime of soft physics
RAA = 1 at high-pT where hard
RAA < 1 at high-pT
1. Compare Au+Au to nucleon-nucleon cross sections
2. Compare Au+Au central/peripheral
Effect is real…seen by ALL 4 experiments…Final or Initial State Effect?
gluons in Pb / gluons in p
xMore than just a bunch of nucleons
Au + Au Experiment
d + Au Control Experiment
PRL 94, 232301
p0 suppression caused by medium created in Au+Au collisions
Expectation for Ncoll scaling of direct photons
holds for all centrality classes
Empirical energy loss from data
Fractional energy loss
Quantify the Energy Loss
M. Djordjevic, et. al. nucl-th/0507019
X-ray pictures areshadows of bones
Can Jet Absorption be Used to“Take an X-ray” of our Medium?
STAR PRL 90, 082302 (2003)
Peripheral Au + Au
Central Au + Au
d + Au
0 3 Df (radians)
Emergence of a Volcano Shape
“split” of away side jet!
peripheral: normal jet pattern
Wake Effect or “sonic boom”
Cherenkov Gluon Radiation
nucl-th/0503028A. K. Chaudhuri
Renk & Ruppert Phys. Rev. C73 011901 (2006)
nucl-th/0507063 Koch, Majumder, X.-N. Wang
nucl-th/0601012 Ma, Zhang, Ma, Huang, Cai, Chen, He, Long, Shen, Shi
nucl-th/0605054 Chiu & Hwa
Jets and Flow couple
Experimental Handle:3-particle correlations
flow components, jet-related two-particle correlation
clear elongation (jet deflection)
off-diagonal signal related to mach cone?Three-Particle Correlations
Au+Au Central 0-12% Triggered
Raw – Jet x Bkgd – Bkgd x Bkgd
(Soft-Soft incl. Flow)
Some of both patterns
jet-like yield consistent in and and independent of centrality
ridge yield increases with centrality
3 < pt,trigger < 4 GeV and pt,assoc. > 2 GeV
Centrality Dependence of the Ridge
xPressure? “elliptic flow” barometer
Almond shape overlap region incoordinate space
Origin:spatial anisotropy of the system when created, followed by multiple scattering of particles in the evolving system
spatial anisotropy momentum anisotropy
v2:2nd harmonic Fourier coefficient in azimuthal distribution of particles with respect to the reaction plane
Can microscopic models work as well?
Flow is sensitive to thermalization time since expanding system loses spatial asymmetry over time.
Hydro models require thermalization in less than t=1 fm/cLarge v2
Adler et al., nucl-ex/0206006
Huge cross sections!!
T0ave ~ 300-400 MeV !?
≤ħ/<mT>final = 0.35 fm/c
≤ 2 fm/c (conservative)
e(form) > 15 GeV/fm3 (0.35 fm/c)
e(therm) > 2.8 GeV/fm3 (2.0 fm/c)
Stat. model fit:Tch~ 160MeV, gs~1.0
Strangeness saturation at RHIC?
p/K/p measurement in a
Broad pt range
stronger radial flow at RHIC?
Tkin ~ 100 MeV
<vT/c> ~ 0.5