event-by-event fluctuations of the mean transverse momentum at sps energy

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> (%)


pT

(%

)


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?


Overall fit

<pi,pj> for different charge combinations

• there are differences…


• 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 ?

(+) (+)(-) (-)

(+) (-)


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 %



• 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)



= 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


all pairs

Two-particle correlations ( dependence)

= 0 - 0.5

all pairs


= 0 - 0.5

+/+


= 0 - 0.5

- / -


= 0 - 0.5

+ / -


= 0 - 0.5


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 %



<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


<pt,ipt,j> = 32.23 +/- 1.82 MeV2<pt,ipt,j> = 24.05 +/- 1.28 MeV2



•peak structure enhances with centrality• could be elliptic flow, but only?

event-by-event fluctuations of the mean transverse momentum at sps energy

Documents

mean multiplicity pt

inclusive pt

ebe fluctuations event

p p extrapolation

p p measurement12

outlookebe fluctuations

outline fluctuations

mean transverse momentum