Recent Results from STAR
Rene Bellwied, Wayne State, for the STAR Collaboration
Thermalization & Timescales
High pt physics
Fluctuations 130 to 200 GeV comparison
STAR’s strength
• STAR can map out the time, space and kinematic evolution of the colliding system by reconstructing hadronic probes over a large range of momentum and over 2in space. The coverage potentially allows to measure variables on an event-by-event basis.
STAR’s Physics in the first two years(i.e. the topics of my talk)
• The Evolution of the System (i.e. Thermalization, Expansion, Kinetic Freeze-Out, Time Scales)
•hadron production (strange and non-strange)
•flow (radial and elliptic) and HBT, balance functions
•The Critical Point
•Fluctuations
•The Early Conditions
•High pt physics
•Jet Quenching/Partonic Energy Loss
T = 190 MeV
T = 300 MeV
Tp = 565 MeV
mid-rapidity
Spectra via dE/dx and V0 topology
Will reach out to 5 GeV/c with Year-2 stats
Measuring yields and mt spectra up the
baryon
Preliminary
dN(-++) /dy = 0.64±0.14
dN-/dy = 0.32±0.09
dN+/dy = 0.34±0.09
Do yields (ratios) agree with the statistical model picture ?
Thermal fit prediction using all ratio except
/h-, /h-, /Thermal statistical model
fits particle ratios
ch =170±10 MeVB=48±10 MeVS=2.3±5.1 MeVS=0.99±0.11
/ (fit) = 0.96 0.07
M.Kaneta (LBNL)
STAR Preliminary
/ h(fit) = 0.00113 0.0007
/ (exp) = 0.95 0.15
/ h(exp) = 0.00127 + 0.0004
Wroblewski factor evolution(Strangeness Excitation
Function)
Wroblewski factordependent on T and B
dominated by Kaons
Peaks at 30 A GeV in AA collisions due to strong B dependence
mesons
baryons
hidden strangeness mesons
PBM et al., hep-ph/0106066
total
Preliminary
?
Multi-strangeness Excitation function
Preliminary
Temperature and collective behavior
Stronger radial flow at RHIC than SPS
Strange baryons freeze-out earlier
(stat. errors only)STAR Preliminary
What is the inverse slope parameter ?
T = 411±46MeV(stat.)Additional systematic error ~ 10%
Radial Flow at 200 GeV
K p
5% Central Events
60-80% Peripheral Events
p+p DataSTAR preliminary
Strangeness high pt spectra(Year-1)
Interesting agreementwith PHENIX result ofpbar vs. pion spectra
Simple hydrodynamicexplanation or more fundamental ?
In year-2:Lambdas out to 5 GeV/cCharged Kaons out to10 GeV/c via kinks
Ratio Comparison to pQCD (Y-2)
Done with 5% of totalstatistics.
With factor 20 more datathe ratio will go out to5.5 GeV/c with an errorbar comparable to the 2 GeV/c error bar in thisplot
Almond shape overlap region in coordinate space
y2 x2 y2 x2
2cos2 vx
y
p
patan
v2: 2nd harmonic Fourier coefficient in azimuthal distribution of particles with respect to the reaction plane
Origin: spatial anisotropy of the system when created and rescattering of evolving system. spatial anisotropy momentum anisotropy
Anisotropic (Elliptic) Flow – What is it ?
V2 pt dependence
v2(pt) - STAR Collaboration, PRL 87 (2001) 182301
v2 - STAR Collaboration, PRL 86 (2001) 402
Centrality dependence of v2(pt) at large pt
Inclusive pt distribution for negative hadrons
Hadron suppression factor = 2 relative to scaled NN (UA1) or peripheral
hadrons
q
q
hadrons leadingparticle
leading particle
Year-1 data
Two-Particle Azimuthal Correlations
Can’t fully reconstruct jets in Au+Au events Identify jet candidates using trigger particle with 4<pT<6 GeV/c. Associate with other charged tracks with 2<pT<pT(trig).= UA1 method (PLB 118, 173 (1982), pp @ √s = 540 GeV, Jet
Cone: <30˚ |y| < 0.5 Azimuthal correlation function:
Efficiency for finding the trigger particle cancels in definition of C2
No need for mixed events due to full azimuthal coverage
C2 ()1
N trigger
1
efficiencyd()N ( ,)
Jet analysis @ 130 GeV
130 GeV:= 0.27+-0.09 radArea = 4.9+-1.7 %
Area in agreementwith pp data(no statement about jet suppression)
Area = % of charged particles with pt>4 GeV/c that have an association
Effects of jet quenching and charge dependence
Quenching has negligible effect on angular correlations near = 0.
Data
HIJING
opposite sign/same sign ≈ 2.6+-0.7property of LUND fragmentation picture
Time scales of the collision
hadronization
initial state
pre-equilibrium
QGP andhydrodynamic expansion
hadronic phaseand freeze-out
PCM & clust. hadronization
NFD
NFD & hadronic TM
PCM & hadronic TM
CYM & LGT
string & hadronic TM1 fm/c 5 fm/c 10 fm/c 50 fm/c time
dN/dt
Chemical freeze outKinetic freeze out
Measurements:HBTBalance functionResonances
Year-1 pion HBT
Published STAR HBT data Hydro does not describe
the data Blast wave with “default”
parameters does Pt dependence of radii well
reproduced Thanks to space-momentum
correlations
Striking feature: short emission duration = 1.5 fm/c
STAR data
Blast wave
Year 1 -K correlation functions Fitting in pair rest frame
Pionsource
KaonSource
Separation between and K andBoost to pairRest frame
Pion <pt> = 0.12 GeV/c
Kaon <pt> = 0.42 GeV/c
Out ratio 1 and K
source are shifted
Side and Long ratio ~1 as they must be
r* = (r - t) tpion-tkaon < 5.6 fm/c rkaon-rpion < 4.2 fm
<r*pion-r*kaon> = -6.3 fm (in pair rest frame )
Data agree with blast wave
RQMD overestimates the shift
From Rlong: Kinetic = 8-10 fm/c
Simple Sinyukov formula (Steve Johnson) Rlong2 = 2 T/mT
= 10 fm/c (when T=110 MeV)
B. Tomasik fit (~3D blast wave = 8 fm/c (++) = 9.2 fm/c (--)
Balance function principle
For each charge +Q, there is one extra balancing charge –Q.
Charges: electric, strangeness, baryon number
Hadronization
Early =Large Delayed =Small
Preliminary data on +- pairs
Bjorken + thermal model to reproduce data f = 15 fm/c > from Rlong (8-
10) Extremely low Tf (Tf = 45
MeV)Poor agreement with other measured parameters Ti = 175 MeV
From particle ratios i = 9-10 fm/c Tf = 100-110 MeV
From spectra f-i = = 2-4 fm/c
Resonance survival rate
UrQMD: signal loss in invariant mass reconstruction
K*(892) (1520)
SPS (17 GeV) [1] 66% 50% 26%
RHIC (200GeV) [2] 55% 30% 23%
Strange resonances studied with STAR K*(892)
Lifetime = 3.9 fm/c (1520)
Lifetime = 12.8 fm/c Rescattering
between chemical and kinetic freeze-out may wash out the resonance signal Sensitive to = Kinetic - Chemical
K*0 K+ + -
multiplicity for |y| <0.5 K*0 |y|<0.5 = 10.0 0.8 25%
Upper limit estimation: dN/dy preliminary
(1520) |y|<1 < 1.2 at 95% C. L.
(1520) p + K-
Survival rate interpretation according to
Rafelski
Upper limit
Combining both K* and (1520) results ~ 0-3 fm/c
Caveats: thermal fits
reproduce K* yield with T ~ 175 MeV (not Tchem~100 MeV!)
No need to destroy K* Possible K*
regeneration
Time scales according to STAR data
1 fm/c 5 fm/c 10 fm/c 20 fm/ctime
dN/dt
Chemical freeze outKinetic freeze out
Balance function (require flow)
Resonance survival
Rlong (and HBT wrt reaction plane)Rout, Rside
Comparison of <pt> fluctuations in two acceptance bins
Fluctuations are multiplicity dependent. Construct variable pt that allows to fold out the N dependence
pt = ptpt
Inclusive varianceDeviation of event Pt from event average
Conclusions
Yields, slope parameters, and ratios for all measured hadrons are well described by statistical models
Time scale for emission seems short. Two particle correlations are best described by blast wave parametrization.
Non statistical fluctuations are small but not zero. Flow and particle production at high pt seems to indicate a
new regime and potentially partonic energy loss. Future: year-2 will determine negative hadron spectra out
to 10 GeV/c, strange baryon spectra out to 5 GeV/c. The interesting physics might lie at high pt and in rare
probes (, D-meson, J/)