event-by-event particle ratio fluctuations in na49 and future cbm experiment

Event-by-event Particle Ratio Fluctuations in NA49 and future

CBM Experiment

D. Kresan for the NA49 and CBM Collaborations

GSI, Darmstadt

DPG Spring Meeting16-th – 20-th of March 2009

Bochum

19.03.2009 D. Kresan DPG Spring Meeting 2/14

Motivation

arXiv: 0808.1237 [nucl-ex]

Phys.Rev.D68:014507,2003 (hep-lat/0305007)

19.03.2009 D. Kresan DPG Spring Meeting 3/14

The NA49 Detector at CERN SPSLarge acceptance hadron spectrometer

, K, p

momentum ranges: 20, 30, 40A GeV: 3 – 40 GeV/c80, 158A GeV: 3 – 120 GeV/c

PID detector: TPC (dE/dx measurement)

19.03.2009 D. Kresan DPG Spring Meeting 4/14

Event-by-event Fit

Shape of the dE/dx distributions is obtained from the inclusive

dE/dx fit

Probability Density Functions (PDFs)

Particle yields are determined by fitting the relative yields to the dE/dx spectrum using Maximum

Likelihood Method

NO possibility for track-by-track PID

Minimization of 2 for one event will fail due to low statistics

19.03.2009 D. Kresan DPG Spring Meeting 5/14

Yield Ratio Distributions

Width of the distribution is dominated by the statistical fluctuations and dE/dx resolution

Event mixing for the background estimation

dyn2 = data

2 mixed2

central Pb + Pb at 20A GeV

19.03.2009 D. Kresan DPG Spring Meeting 6/14

Energy dependence

Increase towards lower SPS energies is confirmed by independent analysis

Low sensitivity to the acceptance cuts

As a first step, meant for validation of the software3.5% most central

arXiv: 0808.1237 [nucl-ex]

19.03.2009 D. Kresan DPG Spring Meeting 7/14

Centrality Bin Size Dependencemin-bias Pb + Pb at 158A GeV

Small difference between standard 3.5% and 5% centrality bin sizeUse bins of 5% for centrality dependence

3%

3.5%

5% 10%17.5%

15%

20%

19.03.2009 D. Kresan DPG Spring Meeting 8/14

Centrality Dependence

Enhancement of first bin for peripheral events.Starts at centrality of about 30% due to low multiplicity

min-bias Pb + Pb at 158A GeV

19.03.2009 D. Kresan DPG Spring Meeting 9/14

Centrality dependence (2)

K/ p/

Follow 1/Npart scaling

In case of K/ fluctuations saturation for peripheral events is observed

BN

ANf

partpart

Increase with decreasing centrality

Preliminary results! More understanding is needed

Resonance contribution?

min-bias Pb+Pb at 158A GeV

19.03.2009 D. Kresan DPG Spring Meeting 10/14

Future CBM ExperimentIntermediate energy regime critical point?

Check sensitivity and layout with respect to particle ratio fluctuations and difficulties in method experienced in NA49

19.03.2009 D. Kresan DPG Spring Meeting 11/14

Hadron Identification

Hadrons will be identified by TOF

Good kaon-pion separation up to 3.5 GeV/c

%100all

K

N

Npurity

identification track-by-track for e-b-e PID also works for low multiplicities and low K/ ratios

central Au + Au at 25 AGeV by UrQMD

19.03.2009 D. Kresan DPG Spring Meeting 12/14

K/ Dynamical Fluctuations from UrQMD

4RECO + PID

50% purity (p < 5 GeV/c)

No large acceptance bias

19.03.2009 D. Kresan DPG Spring Meeting 13/14

Purity Study

Fluctuations increase with increasing purity

In agreement with MC truth with momentum cut applied

Purity restriction implies a momentum cut off for kaons

19.03.2009 D. Kresan DPG Spring Meeting 14/14

Conclusion• NA49

– energy and centrality dependence of particle ratio fluctuations was measured by NA49

– energy dependence is in agreement with independent analysis

– fluctuations increase towards lower centralities

• CBM– feasibility of the measurement of event-by-event particle

ratio fluctuations shown– no strong bias from the acceptance, reconstruction and PID

procedures is introduced