# Presentation: 682267

## 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 MpT distributions in real events are slightly wider than those in mixed events

- Event-by-event mean pT distributions(CERES collaboration, *Nucl. Phys. A727(2003)97-119*)

-    Event-by-event *M**pT* distributions in real events are slightly wider than those in mixed events
- Evidence for the non-statistical (dynamical) mean pT fluctuations

- Real
- /mixed

- 6.5% central, 2.2<<2.7, 0.1<pT<1.5GeV/c

- Real
- mixed

## CERES Experiment

**acceptance****:**
**8 < ********< 15 deg**
**2.2 < ********< 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

## Measure of mean pt fluctuations

- normalized dynamical fluctuation

- 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

******p****T**

- Proportional to mean covariance
- of all particle pairs / event
- Robust 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

## NpartpT2 = 0.03(const)

- Baseline:extrapolation from p+p measurement
- 12% measured in p+p@ISR
- (*Braune, PLB123(1983)467*)
- Non-monotonic dependence of *N**part****pT**2*
- Little collision energy dependence
- Maximum in semi-central events
- Consistent with the p+p extrapolation in central and peripheral

*N**part****pT**2* = 0.03(const)

- (CERES collaboration, *Nucl. Phys. A727(2003)97,*
*	**	**        **J.Phys.G30(2004)S1376*)

## Similar fluctuations at each centrality at SPS and RHIC energies

- Comparison to STAR and NA49 data

- G. Westfall, QM2004

- STAR preliminary

- NA49 (158AGeV/c)
- hep-ex/0311009

- similar non-monotonic dependence

- CERES

## Rapidity range dependence of Mean pT fluctuations

- 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)*

## pt measure at NA49 data

- 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 =**((0.015****2****+(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 analysis
- 0.1 < pT < 1.5

## Centrality determination

| /geo | 0-5 % | 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 selection
- Multiplicity Counter (158 GeV)
- Number of participant nucleons is estimated with a geometric nuclear overlap (Glauber) model

- minb

- cental

- 50   40    30     20         10      5                             0 %

- 0%-100% of the total Pb+Au
-  inelastic cross section
- 0% -> impact parameter=0
_**Multiplicity Counter gain distribution**_

## Average momentum correlator 

- <pt,i pt,j>

- mean covariance of all
- particle pairs / event

- ... but <pt,i pt,j> allows to select pairs by charge sign,...

*S. Voloshin. V. Koch. H. Ritter, PRC60 (1999)*

## <pt,ipt,j> as function of  and 

- Peaks at and

**<pi,pj>  (MeV****2****)**

- CERES
- 158 AGeV/c Pb-Au
- Preliminary

***0.1 < p******T****** < 1.5 GeV/c***

- 7M events analyzed, 8% centrality

## Using mixing events

- 7M events analyzed, 8% centrality

- 2M mixed events analyzed

**<********pt,i********pt,j> = ****22.71****+/- 0.32 MeV****2**

**<********pt,i********pt,j> = ****-0.20****+/- 0.42 MeV****2**

## Normalized dynamical fluctuation

**On average : ********p****T**** ~ 1.04 % (agrees well with previous studies)**

******p****T**** = 100 * (<********p****t,i**** ********p****t,j****>)****1/2**** / p****T****<incl>****  ****(%)**

- CERES
- 158 AGeV/c Pb-Au
- Preliminary

******p****T****   (%)**

## <pt,ipt,j> as function of  and 

**0      -      180**

**0      -      180**

**0      -      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,i********pt,j> = ****22.71****+/- 0.32 MeV****2**
************p****T****,dyn= ****22.28**** +/- 0.48 MeV****2**

** ****average value consistent**
** ****rich structure in******
** ****origin?**

- CERES
- 158 AGeV/c Pb-Au
- Preliminary

- Overall fit

## <pi,pj> for different charge combinations

-  there are differences...

- CERES
- 158 AGeV/c Pb-Au
- Preliminary

-   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

**<pi,pj>  (MeV****2****)**

**N****part**

**CERES Pb-Au Preliminary**

-  similar centrality dependence at SPS and RHIC

## Centrality dependence

**10-20 % centrality**

**20-30 %**

**40-50 %**

**0-5 %**

- CERES
- 158 AGeV/c Pb-Au
- Preliminary

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

## Centrality dependence

- 

- <pi,pj>  (MeV2)

- CERES
- 158 AGeV/c Pb-Au
- Preliminary

- = 0 - 0.5

## <N><pt,i pt,j> vs Centrality

**non-monotonic centrality**
**dependence 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**

## Two-particle  correlations ( dependence)

- CERES
- 158 AGeV/c Pb-Au
- Preliminary

**all pairs**

- Two-particle  correlations (**** dependence)

- = 0 - 0.5

## Two-particle  correlations ( dependence)

**all pairs**

- Two-particle  correlations (**** dependence)

- = 0 - 0.5

## Two-particle  correlations ( dependence)

**+/+**

- Two-particle  correlations (**** dependence)

- = 0 - 0.5

## Two-particle  correlations ( dependence)

**- / -**

- Two-particle  correlations (**** dependence)

- = 0 - 0.5

## Two-particle  correlations ( dependence)

- Two-particle  correlations (**** dependence)

- = 0 - 0.5

## <pt,ipt,j> as function of  and 

## 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 Republic
- GSI Darmstadt, Germany
- Frankfurt University, Germany
- Heidelberg University, Germany
- JINR Dubna, Russia
- Weizmann Institute, Rehovot, Israel
- SUNY at Stony Brook, USA
- CERN, Switzerland
- BNL, Upton, USA
- Münster University, Germany
- MPI Heidelberg, Germany

## Slide 34

## Short-range correlations (SRC)

- 

- 

**q****inv**** (GeV/c)**

**q****inv**** (GeV/c)**

**C****2****(q****inv****)**

- 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

**q****inv**** (GeV/c)**

## Dependence on pT cuts

***0.1 < p******T****** < 2 GeV/c***

***0.6 < p******T****** < 2 GeV/c***

***0.1 < p******T****** < 1.5 GeV/c***

***0.1 < p******T****** < 0.8 GeV/c***

******p****T**** ~ 1.02 %**

******p****T**** ~ 1.14 %**

******p****T**** ~ 1.24 %**

******p****T**** ~ 0.46 %**

- CERES
- 158 AGeV/c Pb-Au
- Preliminary

## Centrality dependence

**<********pt,i********pt,j> = 41.39 +/- 7.12 MeV****2**

**<********pt,i********pt,j> = 87.34 +/- 10.93 MeV****2**

**<********pt,i********pt,j> = 134.54 +/- 20.12 MeV****2**

**<********pt,i********pt,j> = 294.76 +/- 40.24 MeV****2**

**10-20 % centrality**

**20-30 % centrality**

**30-40 % centrality**

**40-50 % centrality**

**<********pt,i********pt,j> = 32.23 +/- 1.82 MeV****2**

**<********pt,i********pt,j> = 24.05 +/- 1.28 MeV****2**

**0-5 % centrality**

**5-10 % centrality**

- CERES
- 158 AGeV/c Pb-Au
- Preliminary

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