August 11, [email protected] - ISMD05 Kromeriz1 ENERGY AND RAPIDITY DEPENDENCE OF ELECTRIC CHARGE CORRELATIONS AT 20 – 158 GeV BEAM ENERGIES

August 11, 2005 [email protected] - ISMD05 Kromeriz 1

ENERGY AND RAPIDITY DEPENDENCE OF ELECTRIC CHARGE CORRELATIONS

AT 20 – 158 GeV BEAM ENERGIES AT THE CERN SPS (NA49)

P. Christakoglou, A. Petridis, M. Vassiliou

University of Athens,

for the NA49 collaboration.


OUTLINE

The NA49 experimental setup.

The Balance Function:Motivation.

Definition.

Analysis scenarios.

System size and centrality dependence at 158 AGeV and 40 AGeV:Published results – Comparison NA49/STAR – Interpretations.

New results – Mid-rapidity region.

New results – Forward rapidity region.

Preliminary results on the energy dependence study:Central Pb+Pb collisions at 20-158 AGeV.

UrQMD and HSD results.

Comparison with STAR.

Summary.


THE NA49 EXPERIMENT

Large acceptance hadron spectrometer at the CERN-SPS

particle identification

• dE/dx and momentum

• TOF around midrapidity

• invariant mass + topology

• energy of projectile spectators measured for centrality selection

• fragmentation beam for smaller nuclei

13m


BALANCE FUNCTION


MOTIVATION

Oppositely charged particles are created at the same location of space – time.

Charge – anticharge particles that were created earlier (early stage hadronization) are separated further in rapidity.

Particle pairs that were created later (late stage hadronization) are correlated at small Δy.

The Balance Function quantifies the degree of this separation and relates it with the time of hadronization.


DEFINITION

The Balance function is defined as a correlation in y of oppositely charged particles, minus the correlation of same charged particles, normalized to the total number of particles.

where P1: any rapidity interval in the detector

P2: relative rapidity interval

• Bass-Danielewicz-Pratt, Phys.Rev.Lett.85, 2000• D. Drijard et al, Nucl. Phys. B(155), 1979

N

NN

N

NNB

)()()()(

2

1)(

)1,(

)1,|2,()1,|2,(

)1,(

)1,|2,()1,|2,(

2

1)|( 12 PN

PPNPPN

PN

PPNPPNPPB


BALANCE FUNCTIONS – HOW DO THEY WORK

The Balance Function is constructed in such way that can identify correlated pairs of oppositely charged particles on a statistical basis.

This term is the conditional probability of detecting a particle of type b in the bin P2 whilst there is a particle of type a in the bin P1.

The numerator counts the pairs that satisfy both criteria within an event and then is summed over all events. The denominator counts particles that were used for the creation of pairs within an event. It is then summed over all events.

)1,(

)1,|2,()1,|2,(

PaN

PaPbNPaPb


Due to cooling the width falls with time (σtherm).

THE WIDTH OF THE BALANCE FUNCTION

The overall width of the Balance Function (BF) in relative rapidity is a combination of the thermal spread and the effect of diffusion.

The effect of diffusion stretches the BF (σδn).

If the hadronization occurred at early times then the effect of collisions is to broaden the BF.

On the other hand late stage hadronization suggests narrower BF.

k

ii

k

iii

B

B

0

0


DIFFERENT ANALYSIS SCENARIOS

The Balance Function can be studied as a function of the relative pseudo-rapidity interval:

S. Bass et al. , Phys. Rev. Lett. 85, 2689 (2000).

J. Adams et al. (STAR collaboration), Phys. Rev. Lett. 90, 172301 (2003).

C. Alt et al. (NA49 collaboration), Phys. Rev. C 71, 034903 (2005).

Insight about the time of hadronization.

Study of the BF for different species (pions, kaons, protons) as a function of the relative rapidity interval:

S. Bass et al., Phys. Rev. Lett. 85, 2689 (2000).

G. Westfall et al. (STAR collaboration), J. Phys. G 30, S345 (2004).

Insight about the different hadronization processes for the different species.

Study of the BF as a function of the azimuthal angle:P. Bozek, Phys. Lett. B 609, 247 (2005).

Quantify the transverse flow for different centralities/energies.

Study of the BF as a function of Qinv:S. Pratt and S. Cheng, Phys. Rev. C 68, 014907 (2003).

A clearer insight about the physics interpretations of the balancing charges and illumination of the different distorting effects.


SYSTEM SIZE AND CENTRALITY DEPENDENCE STUDY


PREVIOUS RESULTS @ √sNN = 17.2 GeV COMPARISON WITH RHIC - INTERPRETATIONS


EVENT AND TRACK SELECTION

EVENT SELECTION

Cut on the vertex position in x,y and z

direction.

TRACK SELECTION

Cut on the extrapolated distance of the

closest approach of the particle at the

vertex plane (dx and dy).

Azimuthal acceptance.

PHASE SPACE

2.6 ≤ η ≤ 5.0 (√s = 17.2 GeV)

0.005 ≤ Pt ≤ 1.5 GeV/c

Acceptance filter


SYSTEM SIZE DEPENDENCE - √sNN = 17.2 GeV

The width takes its maximum value for p+p interactions.

Data show a strong system size and centrality dependence.

Neither HIJING nor shuffled data show any sign of system size or centrality dependence.

C. Alt et al. [NA49 collaboration], Phys.Rev. C71, 034903 (2005).


COMPARISON NA49 – STAR

NA49 data show a strong centrality dependence of the order of (17 ± 3)%.

STAR data show also a strong centrality dependence of the order of (14 ± 2)%.

J. Adams et al., (STAR Collaboration) Phys. Rev. Lett. 90, 172301 (2003)


SUGGESTED INTERPRETATIONS

Delayed hadronization scenario of an initially deconfined phase.S.A. Bass, P. Danielewicz, S. Pratt, Phys. Rev. Lett. 85, 2689 (2000).

J. Adams et al. (STAR collaboration), Phys. Rev. Lett. 90, 172301 (2003).

C. Alt et al. (NA49 collaboration), Phys. Rev. C 71, 034903 (2005).

Part of the decrease could be attributed to the presence of the resonances’ decay products.

P. Bozek, W. Broniowski, W. Florkowski, nucl-th/0310062.

P. Bozek, W. Broniowski, W. Florkowski, nucl-th/0402028.

Statistical hadronization model with the addition of hydrodynamic expansion. Several smaller fireballs with individual charge conservation + blast wave model.

S. Cheng et al., Phys. Rev. C 69, 054906 (2004).

Quark coalescence model of an initially deconfined phase reproduced the values of the width from STAR.

A. Bialas, Phys. Lett. B31, 579 (2004).


RESULTS @ √sNN = 17.2 GeV


√sNN = 17.2 GeV – FORWARD REGION

Mid – rapidity (2.5 < η < 3.9) Forward rapidity (4.0 < η < 5.4)

Acceptance filter OFF

Acceptance filter ON


RESULTS @ √sNN = 8.8 GeV


SYSTEM SIZE DEPENDENCE - √sNN = 8.8 GeV

ACCEPTANCE FILTER OFF

Centrality dependence of the order of (14.9 ± 4.2)%

ACCEPTANCE FILTER ON

Centrality dependence of the order of (14.4 ± 5.8)%


√sNN = 8.8 GeV – FORWARD REGION

Mid – rapidity (1.8 < η < 3.2) Forward rapidity (3.3 < η < 4.7)

Acceptance filter OFF

Acceptance filter ON


ENERGY DEPENDENCE STUDY


ENERGY DEPENDENCE @ SPS

%100

shuffling

datashufflingW

ACCEPTANCE FILTER OFF ACCEPTANCE FILTER ON


COMPARISON NA49 – STAR

The results are not directly comparable yet, since STAR studies the BF in a different phase space window!!!

LHC???

%100

shuffling

datashufflingW


SUMMARY


SUMMARY

BF could give us insight about the time of hadronization.

Results @ √sNN =17.2 GeV show that:

The width of the BF takes its maximum value for p+p interactions. The width of the BF for shuffled and HIJING events doesn’t show any sign of system size or centrality dependence. The width decreases with increasing system size and centrality in Pb+Pb interactions. The centrality dependence is of the order of (17 ± 3)%.The effect is not apparent in the forward rapidity region.STAR experiment shows the same trend. The centrality dependence is of the order of (14 ± 2)%.

Preliminary results @ √sNN =8.8 GeV show that:The width of the BF behaves in a similar way as in the previous case for both real and shuffled data. The centrality dependence is of the order of (14.5 ± 5)%.The effect is not apparent in the forward rapidity region.

Preliminary results from the energy scan show that:We have a plateau of the parameter W in the energy range 30-80AGeV.Then this parameter rises towards RHIC (LHC?) energies.


BACKUP


THE NA49 COLLABORATION

C. Alt, T. Anticic, B. Baatar, D. Barna, J. Bartke, L. Betev, H. Bialkowska, C. Blume, B. Boimska, M. Botje, J. Bracinik, R. Bramm, P. Buncic, V. Cerny, P. Christakoglou, O. Chvala , J.G. Cramer, P. Csató, P. Dinkelaker, V. Eckardt, D. Flierl, Z. Fodor, P. Foka, V. Friese, J. Gál, M. Gazdzicki, V. Genchev , G. Georgopoulos, E. Gladysz, K. Grebieszkow, S. Hegyi, C. Höhne, K. Kadija, A. Karev, M. Kliemant, S. Kniege, V.I. Kolesnikov, E. Kornas, R. Korus, M. Kowalski, I. Kraus, M. Kreps, A. Laszlo, M. van Leeuwen, P. Lévai, L. Litov, B. Lungwitz, M. Makariev, A.I. Malakhov, M. Mateev, G.L. Melkumov, M. Mitrovski, J. Molnár, St. Mrówczynski, V. Nicolic, G. Pálla, A.D. Panagiotou, D. Panayotov, A. Petridis, M. Pikna, D. Prindle, F. Pühlhofer, R. Renfordt, C. Roland, G. Roland, M. Rybczynski, A. Rybicki, A. Sandoval, N. Schmitz, T. Schuster, P. Seyboth, F. Siklér, B. Sitar, E. Skrzypczak, G. Stefanek , R. Stock, C. Strabel, H. Ströbele, T. Susa, I. Szentpétery, J. Sziklai, P. Szymanski, V. Trubnikov, D. Varga, M. Vassiliou, G.I. Veres, G. Vesztergombi, D. Vranic, A. Wetzler, Z. Wlodarczyk, I.K. Yoo, J. Zimányi

NIKHEF, Amsterdam, Netherlands.Department of Physics, University of Athens, Athens, Greece.Comenius University, Bratislava, Slovakia.KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary.MIT, Cambridge, USA.Institute of Nuclear Physics, Cracow, Poland.Gesellschaft für Schwerionenforschung (GSI), Darmstadt, Germany.Joint Institute for Nuclear Research, Dubna, Russia.Fachbereich Physik der Universität, Frankfurt, Germany.CERN, Geneva, Switzerland.Institute of Physics Swietokrzyska Academy, Kielce, Poland.Fachbereich Physik der Universität, Marburg, Germany.Max-Planck-Institut für Physik, Munich, Germany.Institute of Particle and Nuclear Physics, Charles University, Prague, Czech Republic.Department of Physics, Pusan National University, Pusan, Republic of Korea.Nuclear Physics Laboratory, University of Washington, Seattle, WA, USA.Atomic Physics Department, Sofia University St. Kliment Ohridski, Sofia, Bulgaria.Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria.Institute for Nuclear Studies, Warsaw, Poland.Institute for Experimental Physics, University of Warsaw, Warsaw, Poland.Rudjer Boskovic Institute, Zagreb, Croatia.


TPC – NA49

CHARACTERISTICS OF NA49 TPC

TPC : VTPC MTPC

HEIGHT (cm) 72 129

LENGTH (cm) 260 384

WIDTH (cm) 200 384

DRIFT LENGTH (cm) 66 115


ENERGY DEPENDENCE STUDY


ENERGY DEPENDENCE @ SPS - HSD

%100

shuffling

datashufflingW



ENERGY DEPENDENCE @ SPS - UrQMD

%100

shuffling

datashufflingW



MULTIPLICITY DEPENDENCE STUDY


MULTIPLICITY DEPENDENCE @ 160GeV - pp


This study was motivated by a new paper by the NA22 collaboration: hep-ex 0506027

The multiplicity distribution of the p+p data sample was divided in 3 bins:

1 < Ntracks < 7

1 < Ntracks

7 < Ntracks

Documents

August 11, [email protected] - ISMD05 Kromeriz1 ENERGY AND RAPIDITY DEPENDENCE OF ELECTRIC CHARGE CORRELATIONS AT 20 – 158 GeV BEAM ENERGIES