STAR 1 APS Spring Meeting - April 2002 - malisa Recent results from STAR M.A. Lisa, for the STAR Collaboration
Feb 02, 2016
STAR 1APS Spring Meeting - April 2002 - malisa
Recent results from STARM.A. Lisa, for the STAR Collaboration
STAR 2APS Spring Meeting - April 2002 - malisa
OutlineYear-1 data (Au+Au s=130 GeV)hadro-chemistry• driving dynamical physics and consistent picture @ low pT?
• central collisionsradial flow• two-particle correlations HBTK- correlations
balance functions• non-central collisionselliptical flowHBT vs reaction-plane
• low-pT summary• driving physics @ “high” pT?spectra compared to pp collisionselliptical flowtwo-particle correlations
• Summary
STAR 3APS Spring Meeting - April 2002 - malisa
Particle ID in STAR
pion
s
kaons
pro
tons
deute
rons
electrons
STAR
dE/dx
dE/dx PID range: (dE/dx) = .08]
p ~ 0.7 GeV/c for K/
~ 1.0 GeV/c for p/p
RICH PID range:
1 - 3 GeV/c for K/
1.5 - 5 GeV/c for p/p
RICH
“kinks”:
K +
Vo
Decay vertices
Ks + + - p + -
p + + - + -
+ + + + K -
Topology CombinatoricsKs + + - K + + K -
p + - p + +
+ + - p + -
from K+ K- pairs
K+ K- pairs
m inv
m inv
same event dist.mixed event dist.
background subtracted
dn/dm
dn/dm
STAR 4APS Spring Meeting - April 2002 - malisa
Vector meson production in Ultra-peripheral collisions
Signal region:
pT<0.15 GeV
0 PT
0
Au
Au
• b > 2R electromagnetic interactions• d/dpT consistent with predictions for
coherent 0 production
STAR 5APS Spring Meeting - April 2002 - malisa
Kaon Spectra at Mid-rapidity vs Centrality
Exponential fits to mT spectra: ⎟⎠
⎞⎜⎝
⎛−∝T
mA
dm
dN
mT
TT
exp1
K+ K- (K++K-)/2
Ks
STAR preliminary STAR preliminary STAR preliminary
0-6%
11-18%
26-34%
45-58%58-85%
Centralitycuts
0-6%
11-18%
26-34%
45-58%58-85%
Centralitycuts
0-6%
11-18%
26-34%
45-58%58-85%
Centralitycuts
Good agreement betweendifferent PID methods
STAR 6APS Spring Meeting - April 2002 - malisa
Statistical Thermal Model: Fit Results
• b driven by p/p, K-/K+
• T driven by p/
STAR 7APS Spring Meeting - April 2002 - malisa
Something different vs pT?Particle/Antiparticle Ratios
STAR Preliminary
Within the errors no or very small pT dependence(as one might expect from simply flow)
see talk by B. Norman
STAR 8APS Spring Meeting - April 2002 - malisa
pT spectra: Flavor Dependence
Enhancement at ~2 GeV is not specific to baryons mass effectsimplest explanation: radial flow)
STAR 9APS Spring Meeting - April 2002 - malisa
Thermal motion superimposed on radial flow
Fits by M. Kaneta
Hydro-inspired “blast-wave” thermal freeze-out fits to , K, p,
Tth = 107 ± 8 MeVhydro predictions reproduce early
pT spectra
preliminary
STAR 10APS Spring Meeting - April 2002 - malisa
Hydro attempts to reproduce data
Rout
Rside
Rlong: model waits too longbefore emitting
• KT dependence approximately reproduced correct amount of collective flow
• Right dynamic effect / wrong space-time evolution??? the “RHIC HBT Puzzle”
generichydro
model emission timescale too long
STAR 11APS Spring Meeting - April 2002 - malisa
Blastwave: radii vs pT
STAR data
blastwave: R=13.5 fm, freezeout=1.5 fm/c
Magnitude of flow and temperature from spectra can account for observed drop in HBT radii via x-p correlations, and Ro<Rs
…but emission duration must be small
Four parameters affect HBT radii
pT=0.4
pT=0.2
K
K
222s
2o RR β+=
STAR 12APS Spring Meeting - April 2002 - malisa
From Rlong: tkinetic = 8-10 fm/c
Simple Sinyukov formula (S. Johnson)
– RL2 = tkinetic2 T/mT
tkinetic = 10 fm/c (T=110 MeV)
B. Tomasik (~3D blast wave) tkinetic = 8-9 fm/c
STAR 13APS Spring Meeting - April 2002 - malisa
Kaon – pion correlation:dominated by Coulomb interaction
Smaller source stronger (anti)correlation
K-p correlation well-described by:
• Blast wave with same parameters as spectra, HBT
But with non-identical particles, we can access more information…
STAR preliminary
STAR 14APS Spring Meeting - April 2002 - malisa
Initial idea: probing emission-time ordering• Catching up: cos0
• long interaction time• strong correlation
• Ratio of both scenarios allow quantitative study of the emission asymmetry
• Moving away: cos0• short interaction time• weak correlation
Crucial point:kaon begins farther in “out” direction(in this case due to time-ordering)
purple K emitted firstgreen is faster
purple K emitted firstgreen is slower
STAR 15APS Spring Meeting - April 2002 - malisa
measured K- correlations - natural consequence of space-momentum correlations
• clear space-time asymmetry observed
• C+/C- ratio described by:– “standard” blastwave w/ no time shift
• Direct proof of radial flow-induced space-momentum correlations
Kaon <pt> = 0.42 GeV/c
Pion <pt> = 0.12 GeV/c
STAR preliminary
STAR 16APS Spring Meeting - April 2002 - malisa
Balance functions: How they work
For each charge +Q, there is one extra balancing charge –Q.
Charges: electric, strangeness, baryon numberBass, Danielewicz, Pratt (2000)
STAR 17APS Spring Meeting - April 2002 - malisa
Balance functions - clocking the evolution
Model predictions Wide early creation of charges
nn, e+e- collisions Narrow late hadronization / (Q)GP
central collisions @ RHIC?
Pythia (wide)
Bjorken (narrow)
Bass, Danielewicz, Pratt (2000)
STAR 18APS Spring Meeting - April 2002 - malisa
Balance Functions in STAR
STAR Preliminary
0.550.60.650.7
Data0 0.20.40.60.81
<>y
/b bmax-HIJING GEANT
STAR Preliminary
Pairs
• Peripheral collisions approach Hijing (NN)• Clear narrowing for central collisions
• In Bass/Danielewicz/Pratt model, central data consistent with:Tchem ~ 175 MeV Tkinetic ~ 110 MeV
tchem = 10 fm/c tkinetic = 13 fm/c
STAR 19APS Spring Meeting - April 2002 - malisapT (GeV/c)
0.2
0.1
0
0 1 2 3
Noncentral collision dynamicshydro evolution
• hydro reproduces v2(pT,m) @ RHIC for pT < ~1.5 GeV/c• system response (pressure):
x-space p-space anisotropy
• again: correct p-space dynamical effect
• freezeout shape evolution duration?STAR preliminarysee talk of J. Fu
v2
flow of neutral strange particlesPID beyond pT=1 GeV/c
STAR 20APS Spring Meeting - April 2002 - malisa
Blast-wave fit to low-pT v2(pT,m)STAR, PRL 87 182301 (2001)
• spatial anisotropy indicated
• consistent with out-of-plane extended source(but ambiguity exists)
p=0°
p=90°
Rside (large)
Rside (small)
• possible to “see” via HBT relative to reaction plane?
• expect• large Rside at 0• small Rside at 90
2nd-orderoscillation
STAR 21APS Spring Meeting - April 2002 - malisa
Out-of-plane extended source~ short system evolution time
STAR preliminary
• Same blastwave parameters as required to describe v2(pT,m), plus two more:
– Ry = 10 fm = 2 fm/c
• Both p-space and x-space anisotropies contribute to R()
– mostly x-space: definitely out-of-plane
• calibrating with hydro, freezeout ~ 7 fm/c
Ros2 - new “radius” important for
azimuthally asymmetric sources
STAR 22APS Spring Meeting - April 2002 - malisa
RHIC 130 GeV Au+Au
Disclaimer: all numbers (especially time) are approximate
Low-pT dynamics — one (naïve?) interpretation:rapid evolution and a “flash”
K-
K* yield
STAR 23APS Spring Meeting - April 2002 - malisa
Physics at “high” pT (~6 GeV/c)
hadrons
q
q
hadrons
leadingparticle suppressed
leading particle suppressed
hadrons
q
q
hadrons
leadingparticle
leading particle
Jets modified in heavy ion collisions
-Parton Energy loss in dense nuclear medium
-Modification of fragmentation function
1) high-pT suppression relative to NN(especially in central collisions)
2) finite, non-hydro v2 due to energy loss(non-central collisions)
see talk of J. Klay
y
Jet 1
Jet 2x
STAR 24APS Spring Meeting - April 2002 - malisa
Inclusive spectra
preliminary
Statistical errors only
STAR 25APS Spring Meeting - April 2002 - malisa
Power law fits
• Power Law: “pQCD inspired”• Fits wide range of hadronic spectra: ISR Tevatron
• Good fits at all centralities (2/ndf~1) • Smooth dependence on centrality
• most peripheral converges to Nucleon-Nucleon reference (UA1)
n
TT p
pA
dp
dN
p−+= )1(
1
0
(p0, n highly correlated)
STAR preliminary
STAR 26APS Spring Meeting - April 2002 - malisa
• Central collisions: suppression of factor 3 (confirms PHENIX)• Peripheral collisions: “enhancement” consistent with zero
(uncertainties due to <Nbinary> and NN reference)
• Smooth transition central peripheral
preliminary
low pT scales as <Npart>
ηηddpdT
ddpNdpR
TNN
AA
TAA
TAA /
/)(
2
2
=
STAR 27APS Spring Meeting - April 2002 - malisa
Azimuthal anisotropy - theory and data
Preliminary
• pT<2 GeV: good description by hydrodynamics• pT>4 GeV: hydro fails but finite v2
• finite energy loss finite v2 at high pT
• sensitive to gluon density
y
Jet 1
Jet 2 x
model: Gyulassy, Vitev and Wang, (2001)
Low pT: parameterized hydro High pT: pQCD with GLV radiative energy loss
STAR 28APS Spring Meeting - April 2002 - malisa
V2 centrality dependence
Preliminary
all centralities: finite v2 at high pT
STAR 29APS Spring Meeting - April 2002 - malisa
But are we looking at jets? - 2 Particle Correlations
• Trigger particle pT>4 GeV/c, |η0• azimuthal correlations for pT>2 GeV/c• short range η correlation: jets + elliptic flow • long range η correlation: elliptic flow
subtract correlation at |η1η0• NB: also eliminates the away-side jet correlations
• extracted v2 consistent with reaction-plane method
• what remains has jet-like structure first indication of jets at RHIC!
preliminary0-11%
STAR 30APS Spring Meeting - April 2002 - malisa
STAR vs UA1
UA1: Phys. Lett. 118B, 173 (1982)(most events from high ET trigger data)
• UA1: very similar analysis (trigger pT>4 GeV/c)• But sqrt(s)=540 GeV, |η|<3.0
preliminary
STAR 31APS Spring Meeting - April 2002 - malisa
Brief Summary• chemistry:
• wide range of particle yields well-described by thermal model• Tchem ~ 170 MeV b ~ 45 MeV
• pT dependence of yields (e.g. baryon dominance) consistent with radial flow
• dynamics at pT < 2 GeV/c• “real” model (hydro) reproduces flow systematics, but not HBT• finger-physics analysis of probes sensitive to time:
• short system evolution, then emission in a flash• Tchem ~ 170 MeV Tkin ~ 110 MeV
• tchem ~ 10 fm/c tkin ~ 13 fm/c
• naïve? unphysical? useful feedback to modelers?
• dynamics at pT > 2 GeV/c• hydro picture breaks down• preliminary jet signal observed• evidence for medium effects at high pT
STAR 32APS Spring Meeting - April 2002 - malisa
THE END
STAR 33APS Spring Meeting - April 2002 - malisa
Ratios driving the thermal fits
Plots from D. Magestro, SQM2001
STAR 34APS Spring Meeting - April 2002 - malisa
Blast Wave Mach I - central collisions
)0 ,sinh ,(cosh )0,,( rezrtu ==
β= −tanh 1r )( rfst ββ =R
βs
Ref. : E.Schnedermann et al, PRC48 (1993) 2462
flow profile selected
(βt =βs (r/Rmax)n)
mt
1/m
t dN
/dm
t
TfoA
βt
2-parameter (Tfo, βt) fit to mT distributions
STAR 35APS Spring Meeting - April 2002 - malisa
Blastwave Mach II - Including asymmetries
R
βt
( )
( )
( )22
psT
/t
y222
cossinhT
p
T1
e
R/xy1
e
coshT
mKp,xf
τΔ−
φ−φρ
×η+−θ
×
×⎟⎠⎞
⎜⎝⎛ ρ=
rr
– Flow
• Space-momentum correlations
• <> = 0.6 (average flow rapidity)
• Assymetry (periph) : a = 0.05
– Temperature
• T = 110 MeV
– System geometry
• R = 13 fm (central events)
• Assymetry (periph event) s2 = 0.05
– Time: emission duration
• = emission duration
}}}
analytic description of freezeout distribution: exploding thermal source
STAR 36APS Spring Meeting - April 2002 - malisa
Comparison to Hijing
Ratio of integrals over correlation peak: 1.3
Hijing fragmentation is independent of quenching
STAR 37APS Spring Meeting - April 2002 - malisa
High-pT highlights
Qualitative change at 2 GeV
Jet-like structure
STAR 38APS Spring Meeting - April 2002 - malisa
measured K- correlations - natural consequence of space-momentum correlations
• clear space-time asymmetry observed
• C+/C- ratio described by:– static (no-flow) source w/ tK- t=4 fm/c
– “standard” blastwave w/ no time shift
• We “know” there is radial flow further evidence of very rapid freezeout
• Direct proof of radial flow-induced space-momentum correlations
Kaon <pt> = 0.42 GeV/c
Pion <pt> = 0.12 GeV/c
STAR preliminary