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

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Motivation

arXiv: 0808.1237 [nucl-ex]

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

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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)

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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

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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

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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]

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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%

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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

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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

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Future CBM ExperimentIntermediate energy regime critical point?

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

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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

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K/ Dynamical Fluctuations from UrQMD

4RECO + PID

50% purity (p < 5 GeV/c)

No large acceptance bias

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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

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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