qm2008 jaipur, india feb.4 feb. 10, 2008 1 star's measurement of long-range forward- backward...
DESCRIPTION
QM2008 Jaipur, India Feb.4– Feb. 10, Multiparticle production at high energies can be described in terms of color strings stretched between the projectile and target. These strings hadronize to produce the observed particles. The no. of strings grow with energy and the no. of participating nucleons. Interaction between the strings must be considered. This problem acquires even more importance considering that, at very high energies, collisions of heavy nuclei at RHIC may produce high density matter. A collective interaction between strings may be required to evolve the system towards a Quark-Gluon Plasma (QGP) state. Ref: M. A. Braun and C. Pajares, Nucl. Phys. B390, 542(1993). M. A. Braun et al., Inter. Jour. Mod. Phys. A14,2689, (1999). H. Satz, Rep. Prog. Phys., 63, 1511(2000). N. Armesto et al., Phys. Lett. B527, 92(2002). INTRODUCTIONTRANSCRIPT
Feb.4– Feb. 10, 2008
1 QM2008 Jaipur, India
STAR's Measurement of Long-range Forward-backward Multiplicity Correlations as the Signature of “Dense Partonic Matter” in
Heavy Ion Collisions at
Brijesh K Srivastava Purdue University
GeVsNN 200
Feb.4– Feb. 10, 2008
2 QM2008 Jaipur, India
INTRODUCTION
Correlations have always been expected to reflect the features ofmultiparticle production and the possibility of phase transitions.Simplistic, multipurpose picture of multiparticle production: first formation of sources, then coherent decay of the sources into particles.
Correlations in rapidity characterize, in principle, the process offormation and decay of such clusters: how many of them, which sizei. e. how many particles do they produce?
Particleemission
Feb.4– Feb. 10, 2008
3 QM2008 Jaipur, India
Multiparticle production at high energies can be describedin terms of color strings stretched between the projectile and target. These strings hadronize to produce the observed particles.
The no. of strings grow with energy and the no. of participating nucleons. Interaction between the strings must be considered.
This problem acquires even more importance considering that, at very high energies, collisions of heavy nuclei at RHIC may produce high density matter.A collective interaction between strings may be required to evolve the system towards a Quark-Gluon Plasma (QGP) state.
Ref: M. A. Braun and C. Pajares, Nucl. Phys. B390, 542(1993). M. A. Braun et al., Inter. Jour. Mod. Phys. A14,2689, (1999). H. Satz, Rep. Prog. Phys., 63, 1511(2000). N. Armesto et al., Phys. Lett. B527, 92(2002).
INTRODUCTION
Feb.4– Feb. 10, 2008
4 QM2008 Jaipur, India
FB Correlation• Predicted in context of Dual Parton Model (and Color Glass
Condensate/Glasma).• Test of multiple elementary [partonic] scattering.• Linear expression relating Nb and Nf (forward (and backward
multiplicity), found in hadron-hadron experiments (ex. UA5),
• “b” is the FB correlation strength.– Function of √s and A.– Coefficient can be expressed as,
fNb bNaNf
2
2
22ff
bf
ff
bfbf
DD
NNNNNN
b
N = # of hadrons
A. Capella et al., Phys. Rep. 236, 225(1994).Y. V. Kovchegov et al., Phys. ReV. C63, 024903(2001).
Feb.4– Feb. 10, 2008
5 QM2008 Jaipur, India
ηη1 η2- η1- η2 0
Forward NfBackward Nb
Rapidity Gap Rapidity interval
High Energy
Short + Long Range
Long Range Long Range
Low Energy
Strings
Feb.4– Feb. 10, 2008
6 QM2008 Jaipur, India
STAR Detector
– Used for centrality determination.5.0
0.15.0 6
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Analysis
1. Au+Au and pp MB data.2. For Au+Au, eight centrality bins as defined by STAR charged particle reference multiplicity: 0-10%, 10-20%, …, 70-80%.
- || < 0.5 (for intervals w/ | > 0.5) or 0.5 < || < 1.0 (for intervals w/ | < 0.5 or
| < 0.3 + 0.6 < || < 0.8 (for = 1.0)- pT > 0.15 - |vz| < 30
3. Backward and forward intervals are 0.2 units in . Intervals are separated by an increasing gap about midrapidity from = 0.2 - 1.8, measured from bin centers.
4. is measured in an absolute coordinate system, where = 0 is fixed at the primary collision vertex.
7
Feb.4– Feb. 10, 2008
8 QM2008 Jaipur, India
Calculating Dispersion…• By calculating <Nf>, <Nb>, <Nf
2>, and <Nf Nb> as functions of STAR reference multiplicity Nch
chNf bNaNch
•Tracking efficiency and acceptance corrections applied in each event. •Method removes the dependence of the FB correlation strength on size of centrality bin.
• Obtained on event-wise basis as function of event multiplicity.
8
Nch
<Nf>
STAR Preliminary
Feb.4– Feb. 10, 2008
9 QM2008 Jaipur, India
Results corrected for tracking efficiency & detector acceptance.
STAR Preliminary
Results Au+Au at 200 GeV
2
2
22ff
bf
ff
bfbf
DD
NNNNNN
b
The correlationstrength is almostflat as a functionof Δη for all thethree centralities
All the errors are stat+sys.
Feb.4– Feb. 10, 2008
10 QM2008 Jaipur, India
STAR Preliminary
Results
Au+Au
Au+Au
Correlation strengthfor 30-40% centralityshows tendency to fall with Δη
For 40-50% the correlation strength decreases with theincrease in Δη
pp at 200 GeV has similar behavior as40-50% centrality in Au+Au. This is identified as short range correlation (SRC)
FB correlation strength beyond Δη > 1.0 is termed as long range correlation (LRC).
Feb.4– Feb. 10, 2008
11 QM2008 Jaipur, India
STAR Preliminary
Results
FB correlation strength b, is controlled by forward-backward dispersion .
Au+Au
pp
STAR Preliminary
2
2
22ff
bf
ff
bfbf
DD
NNNNNN
b
2bfD
Feb.4– Feb. 10, 2008
12 QM2008 Jaipur, India
STAR Preliminary
Energy and System size Dependence Au+Au
For details see poster P-176by Terence Tarnowsky
• Comparison of LRC in central Au+Au and Cu+Cu shows little difference.
• LRC still present in Cu+Cu collisions.
LRC decreases with energy
STAR Preliminary
Feb.4– Feb. 10, 2008
13 QM2008 Jaipur, India
STAR Preliminary
Energy and System size DependenceComparison ofFB correlationstrength from pp and Au+Au and Cu+Cu at 200 GeV.
The results for Au+Au and Cu+Cu are for mid peripheral collisions.
All of them showbehavior consistent with SRC.
Feb.4– Feb. 10, 2008
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STAR Preliminary
pp at 62, 200 and 400 GeV
?
Comparing correlation as function of
1. 200 and 400 GeV in close agreement: *Larger SRC at 400GeV *Plateau at same value of b at large Δη has 200 GeV
2. 62.4 GeV goes smoothly to b = 0.
Not even a small LRC.
NNs
SRC only
Feb.4– Feb. 10, 2008
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Interpretation of F-B Multiplicity Correlations in DPM
• DPM assumes short-range correlations confined to individual strings.
• A gap about midrapidity will eliminate effect of short-range correlations (e.g .from clustering, jets, …)– Long-range correlations due to superposition of
fluctuating number of strings.
bf
bfbf
bfbfbf
NNnn
NNNNn
NNNND
0022
0000
2
)(
bqqfqqbfbf NNnnNNNN 22
In nucleus-nucleus collisions at high energies:
A. Capella et al., Phys. Rep. 236, 225(1994).
Feb.4– Feb. 10, 2008
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Comparison with phenomenological models
HIJING has only SRCand predicts SRC with a large value of b near midrapidity in agreement with the data.
PSM has LRC built in theform of long strings and and is in qualitative agreement with the data.
STAR Preliminary
Feb.4– Feb. 10, 2008
17 QM2008 Jaipur, India
Partonic Core, Hadronic Corona?• If A+A collision can be
envisioned as a central core due to multiple partonic interactions, surrounded by a hadronic corona. The LRC is built up during partonic scattering:– In central collisions, larger
volume of the core implies larger LRC.
– In peripheral A+A, smaller (or no) core region decrease in correlation strength.
Feb.4– Feb. 10, 2008
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Summary Strong long range correlations are observed for central
Au+Au at
* Dual Parton Model has been explored to explain the
LRC observed in the data. * Both DPM and CGC considerations argue that the
long range correlations are due to multiple parton interactions. Mid-central and peripheral events show relatively weaker
long range correlations. This indicates that dense matter with multi-parton
interactions is formed in mid-central and central collisions at
GeVsNN 200
GeVsNN 200