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Event-by-Event Fluctuations of the Mean Transverse Momentum at SPS Energy. … and their scale dependence in Dh-Df space. Georgios Tsiledakis for the CERES Collaboration GSI, Darmstadt, Germany. 2005 RHIC & AGS Annual Users' Meeting Tuesday, June 21, 2005. Outline. - PowerPoint PPT Presentation
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Event-by-Event Fluctuations of the Mean Transverse Momentum at SPS
Energy
Georgios Tsiledakis
for the CERES Collaboration
GSI, Darmstadt, Germany
… and their scale dependence in space
2005 RHIC & AGS Annual Users' Meeting Tuesday, June 21, 2005
Outline
• <pT> Fluctuations: Probing for Signs of a Phase Transition
• CERES experiment at the SPS
• Measure of mean pt fluctuations
• Previous results from SPS
• Recent results from run2000 at 158AGeV/c Pb-Au
• Scale dependence of the fluctuation strength as a function of and
• Two-particle correlation plots (cumulant pT variable )
• Centrality dependence
• Conclusions and outlook
<pT>EbE Fluctuations: Search for signatures of the QCD phase transition
• 1st order Phase Transition– Formation of QGP droplets
• 2nd order phase transitions – Location of Critical Point of
QCD phase diagram
They might be sensitive to…
… but also to…
• HBT and Coulomb correlations• Collective flow• Resonance decays• (Mini-) jet production• …
S. Mrowczynski (Phys. Lett. B314 (1993) 118) M. Stephanov, et al. (Phys. Rev. Lett. 81 (1998) 4816)
• Lattice QCD : There is a critical point...but uncertainty in location is large.
M. Stephanov (hep-ph/0402115)
• Experiments : Can contribute...
• Observables : <pT>EbE fluctuations
Event-by-event mean pT distributions(CERES collaboration, Nucl. Phys. A727(2003)97-119)
Event-by-event MpT distributions in real events are slightly wider than those in mixed eventsEvidence for the
non-statistical (dynamical) mean pT fluctuations
event per particles charged all of Mean Tp pMT
:
Real/mixed
6.5% central, 2.2<<2.7, 0.1<pT<1.5GeV/c
Realmixed
CERES Experiment
radial TPCtrack/momentumRICHes
Silicon DriftDetectorsPrimary vertex
acceptance:8 < < 15 deg2.2 < < 2.7
RUN2000 : 30M Pb-Au events at 158 AGeV/c, 8 % centrality 3M Pb-Au events at 158 AGeV/c, 20 % centrality
7M events analyzed for the present analysis
Hadron measurement near mid-rapidity in Pb+Au collisions
Multiplicity Counter
T
dynp
dynpp pT
TT
||sgn
2,2
,
N
pM T
pdynp TT
222
,
Measure of mean pt fluctuations
• normalized dynamical fluctuation
222TTT ppp
MpT : r.m.s. of MpT dist.
p2T : r.m.s. of inclusive pT dist.
<N> : mean multiplicity
pT : inclusive mean pT
Dimensionless measure
= 0 for purely statistical fluctuation > 0(< 0) with positive/negative two-
particle correlation or dynamical EbyE fluctuation
TTT ppp FΣN 2
pT
Proportional to mean covarianceof all particle pairs / eventRobust under change of multiplicity due to changes in beam energy and acceptance
Previous results on Event-by-Event fluctuations of Mpt
Dynamical fluctuations of ~ 1 % are observed at SPS, which are similar to RHIC data.
No indication for the critical point or phase transition is observed.
(CERES collaboration, Nucl. Phys. A727(2003)97, J.Phys.G30(2004)S1376)
Collision energy dependence
Centrality dependence
• Baseline:extrapolation from p+p measurement
12% measured in p+p@ISR(Braune, PLB123(1983)467)
• Non-monotonic dependence of NpartpT
2
– Little collision energy dependence
– Maximum in semi-central events
– Consistent with the p+p extrapolation in central and peripheral
2/12/%12
partAAp NT
NpartpT2 = 0.03(const)
(CERES collaboration, Nucl. Phys. A727(2003)97, J.Phys.G30(2004)S1376)
Comparison to STAR and NA49 data
– Similar fluctuations at each centrality at SPS and RHIC energies
G. Westfall, QM2004
STAR preliminary
NA49 (158AGeV/c)hep-ex/0311009
similar non-monotonic dependence
CERES
Rapidity range dependence of Mean pT fluctuations
• Monotonic increase in pT, decrease and saturation in pT • pT agrees at each bin at 3 beam energies• We use pT to compare data with different
pT dependent on multiplicity, acceptance size, beam energy.
(CERES collaboration, Nucl. Phys. A727(2003)97)
NA49 nucl-ex/0208020
pt measure at NA49 data
pt small and charge dependent
•Proposed by S. Mrowczynski, and M. Gazdzicki.
Recent results from run2000 at 158AGeV/c Pb-Au
• Scale dependence of the fluctuation strength as a function of and magnitude of fluctuations
• Two-particle correlation plots (cumulant pT variable )
origin of fluctuations ??
Tracking selection and parameters
• Track Selection– TPC tracks (no. of hits >= 12 out of 20)– Target cut (projection of TPC track on the primary vertex <
10cm)
• Momentum resolution p/p =((0.0152+(0.016p)2)1/ 2 at 158 AGeV
• Full Acceptance • Tracking efficiency
– Better than 85% at pT>0.05GeV/c
• 2-particle resolution– ~5 mrad in TPC
7M events analyzed for the present analysis0.1 < pT < 1.5
/geo0-5 % 5-10 % 10-20 % 20-30 % 30-40 % 40-50 %
<Npart> 347 287 220 153 102 64
<Ncol> 809 638 450 279 161 88
Centrality selectionMultiplicity Counter (158 GeV) Number of participant nucleons is estimated with a geometric nuclear overlap (Glauber) model
Centrality determination
minb
cental
50 40 30 20 10 5 0 %
0%-100% of the total Pb+Au inelastic cross section0% -> impact parameter=0
Multiplicity Counter gain distribution
Average momentum correlator <pt,i pt,j>
As a function of centrality and acceptance
pt pt i /Neventi1
Nevent
pt,ipt, j 1
Nevent
pt,i pt pt, j pt N(N 1)j1,ij
N
i1
N
Nevent = number of events
pt i = average pt for ith event
N = number of tracks for ith event
pt,i = pt for ith track in event
jtitdynp ppT
,,2
,
mean covariance of allparticle pairs / event
… but <pt,i pt,j> allows to select pairs by charge sign,...
S. Voloshin. V. Koch. H. Ritter, PRC60 (1999)
<pt,ipt,j> as function of and
• Peaks at and
<p
i,p
j>
(MeV
2 )
CERES 158 AGeV/c Pb-AuPreliminary
0.1 < pT < 1.5 GeV/c
7M events analyzed, 8% centrality
Using mixing events
7M events analyzed, 8% centrality
2M mixed events analyzed
<pt,ipt,j> = 22.71+/- 0.32 MeV2
<pt,ipt,j> = -0.20+/- 0.42 MeV2
Normalized dynamical fluctuation
On average : pT ~ 1.04 % (agrees well with previous studies)
pT = 100 * (<pt,i pt,j>)1/2 / pT<incl> (%)
CERES 158 AGeV/c Pb-AuPreliminary
pT
(%
)
<pt,ipt,j> as function of and
0 - 180 0 - 1800 - 180 0 - 180 0 - 180
(degrees)
0 < < 0.1
0.1 < < 0.2
0.2 < < 0.3
0.3 < < 0.4
0.4 < < 0.5
<pt,ipt,j> = 22.71+/- 0.32 MeV2
pT,dyn= 22.28 +/- 0.48 MeV2
• average value consistent• rich structure in• origin?
CERES 158 AGeV/c Pb-AuPreliminary
Overall fit
<pi,pj> for different charge combinations
• there are differences…
CERES 158 AGeV/c Pb-AuPreliminary
• at < 7.5 deg. and small (+) (+) and (-) (-) similar strength and shape origin could be the same (HBT, Coulomb?) • (+) (-) peak weaker and narrower Coulomb, resonances, e+e-?• away-side component (flow, minijets?) •What is the proton contribution ?
(+) (+)(-) (-)
(+) (-)
Centrality dependence
0 50 100 150 200 250 300 350 400
0
50
100
150
200
250
300
350
<p
i,p
j>
(MeV
2 )
Npart
CERES Pb-Au Preliminary
• similar centrality dependence at SPS and RHIC
GeV 17,3s
10-20 % centrality
20-30 %
40-50 %
0-5 %
Centrality dependence
CERES 158 AGeV/c Pb-AuPreliminary
• peak structure enhances with centrality• could be elliptic flow, but only?
0 30 60 90 120 150 180
-400
-200
0
200
400
600
800
1000
1200 0-5 % centrality 5-10 % centrality 10-20 % centrality 20-30 % centrality 30-40 % centrality 40-50 % centrality
<pi
,pj>
(M
eV2)
Centrality dependence
CERES 158 AGeV/c Pb-AuPreliminary
= 0 - 0.5
<N><pt,i pt,j> vs Centrality
0 50 100 150 200 250 300 350 400-20000
0
20000
40000
60000
80000
100000
<N
part>
<pi
,pj>
(M
eV2 )
<Npart
>
0 < < 15 15 < < 30 30 < < 45 45 < < 60 60 < < 75 75 < < 90 90 < < 105 105 < < 120 120 < < 135 135 < < 150 150 < < 165 165 < < 180
non-monotonic centralitydependence is related to back-to-back structure (?)
Two-particle correlations (cumulant pT variable )
NA49 nucl-ex/0208020
No structure characteristic of event-by-event temperature fluctuations is observed
CERES 158 AGeV/c Pb-AuPreliminary
all pairs
Two-particle correlations ( dependence)
= 0 - 0.5
all pairs
Two-particle correlations ( dependence)
= 0 - 0.5
+/+
Two-particle correlations ( dependence)
= 0 - 0.5
- / -
Two-particle correlations ( dependence)
= 0 - 0.5
+ / -
Two-particle correlations ( dependence)
= 0 - 0.5
<pt,ipt,j> as function of and
0 20 40 60 80 100 120 140 160 180
0
200
400
600
800
0.0 < < 0.1
<P
t ,
i ,
P t
, j>
(
MeV
2)
= |i-
j|( degrees)
all charged +/+ pairs -/- pairs +/- pairs
Summary and conclusions
• <pt,i pt,j> as a function of and have been presented
• strong dependence on and + +, - -, + - has been observed
• integrated pT is mainly given by small angle correlations
• there are hints of an away-side structure• correction should be applied for detector effects
(using mixing events)• conclusive results require full statistics + comparison to models
CERES Collaboration
D. Adamova, G. Agakichiev, D. Antonczyk, A. Andronic, H. Appelshäuser, V. Belaga, J. Bielcikova, P. Braun-Munzinger, O. Busch, A. Castillo, A. Cherlin,
S. Damjanovic, T. Dietel, L. Dietrich, A. Drees, S. Esumi, K. Filimonov, K. Fomenko,Z. Fraenkel, C. Garabatos, P. Glässel, G. Hering, J. Holeczek, V. Kushpil, B. Lenkeit,
W. Ludolphs, A. Maas, A. Marin, J. Milosevic, A. Milov, D. Miskowiec, R. Ortega, Yu. Panebrattsev, O. Petchenova, V. Petracek, A. Pfeiffer, S. Radomski, J. Rak,
Ravinovich, P. Rehak, W. Schmitz, J. Schukraft, H. Sako, S. Shimansky, S. Sedykh, J. Stachel, M. Sumbera, H. Tilsner, I. Tserruya, G. Tsiledakis, T. Wienold, B. Windelband, J.P. Wessels, J.P. Wurm, W. Xie, S. Yurevich, V. Yurevitch
NPI ASCR, Rez, Czech RepublicGSI Darmstadt, Germany
Frankfurt University, GermanyHeidelberg University, Germany
JINR Dubna, RussiaWeizmann Institute, Rehovot, Israel
SUNY at Stony Brook, USACERN, SwitzerlandBNL, Upton, USA
Münster University, GermanyMPI Heidelberg, Germany
Short-range correlations (SRC)
qinv (GeV/c)
qinv (GeV/c)
C2(qinv)
HBT + Coulomb
Coulomb + resonances
D.Antonczyk - correlations for CERES
1
1
•The peak at the origin is probably contaminated
by HBT+Coulomb
all acceptance
0 < < 7.5 deg. , 0 < < 0.1
qinv (GeV/c)
Dependence on pT cuts
0.1 < pT < 2 GeV/c 0.6 < pT < 2 GeV/c
0.1 < pT < 1.5 GeV/c0.1 < pT < 0.8 GeV/c
pT ~ 1.02 % pT ~ 1.14 %
pT ~ 1.24 % pT ~ 0.46 %
CERES 158 AGeV/c Pb-AuPreliminary
Centrality dependence
<pt,ipt,j> = 41.39 +/- 7.12 MeV2 <pt,ipt,j> = 87.34 +/- 10.93 MeV2
<pt,ipt,j> = 134.54 +/- 20.12 MeV2 <pt,ipt,j> = 294.76 +/- 40.24 MeV2
10-20 % centrality 20-30 % centrality
30-40 % centrality 40-50 % centrality
<pt,ipt,j> = 32.23 +/- 1.82 MeV2<pt,ipt,j> = 24.05 +/- 1.28 MeV2
0-5 % centrality 5-10 % centrality
CERES 158 AGeV/c Pb-AuPreliminary
•peak structure enhances with centrality• could be elliptic flow, but only?
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