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