EHSNA22 Collaboration - PowerPoint PPT Presentation

Title: EHSNA22 Collaboration


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Boost Invariance and Multiplicity Dependence of
the charge balance function in pip and Kp
collisions at vsNN 22 GeV
Phys. Lett. B 637(2006)

• EHS/NA22 Collaboration
• Na Li
• Institute of Particle Physics

1. Introduction ? why BF ? current status
? motivation ? data 2. Main Results and
Discussions 3. Summary
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Introduction ? Why Balance Function
Charge compensation in hadronization in ee- ,
l-h, h-h!
old interest
D. Drijard et al., Nucl. Phys. B155, 269(1979)
B166, 233(1980) H. Aihara etal., Phys. Rev.
Lett. 53, 2199(1984) P. D. Acton et al., Phys.
Lett. B305, 415(1993).
is the conditional probability
BF measures how the conserved electric charges
compensate in the phase space, i.e., how the
surrounding net charges are rearranged if the
charges of selected point change from negative to
positive due to the charge conservation.
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new interest
Clocking hadronization in A-A!
S. A. Bass, P. Danielewicz, and S. Pratt, PRL 85,
2689(2000).
Relative rapidity
If QGP is formed in the early stage of
the collision, oppositely charged pairs are
expected to be created later and correlate
more tightly in momentum space, i.e., a
significant narrowing of BF is expected in A-A.
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Introduction ? Current status
Current status
Narrowing of the Balance Function with
centrality in AuAu Collisions at vsNN130GeV
J. Adams et al., (STAR Coll.), PRL90,
172301(2003)
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Introduction ? Current status
Current status
System size and centrality dependence of the
balance function in AA Collisions atvsNN17.2 GeV
C.Alt et al., (NA49 Coll.), PRC71, 034903(2005)
Narrowing of BF with increasing system size
and multiplicity
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Introduction ? Motivations
?
Central collision and heavy nuclear
Narrowing of BF QGP
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Introduction ? Data
p p and ? p Collisions at 22GeV
A total of 44 524 NSD events
0.001GeV/c lt pt lt 10 GeV/c full 4p
acceptance
M. Adamus, et al., (NA22 Coll.), Z. Phys. C32,
(1986)475 M. Adamus, et al., (NA22 Coll.), Eur.
Phys. J. C21, (2001)271
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Results and discussion ? A direct checking
of boost invariance of balance function
in full phase space
? Boost invariance of BF is valid over the whole
rapidity space, in contrast to the strong
dependence of the particle density on
rapidity ? Charge correlation is essentially
the same in any longitudinally-Lorentz-transformed
frame!
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Results and discussion ? BF for
different widths of rapidity windows
? BF becomes narrower with decreasing size of
rapidity window
? holds approximately,
thus BF for whole phase space can be obtained,
therefore, different experimental results are
comparable.
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Results and discussion ? BF for
different multiplicity intervals in full
phase space
? BF becomes narrower with increasing
multiplicity in h-h collisions. ?This
multiplicity effect should be properly accounted
if the narrowing of BF is used as a QGP signal.
? The hadronization scheme with string
fragmentation implemented in PYTHIA qualitatively
reproduces the multiplicity dependence of the
data.
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Results and discussion ? BF and charge
fluctuations
S. Jeon and Scott Pratt, PRC65,044902 (2002)
? D(Q) is independent of the position of the
rapidity window , same as BF.
? Limited acceptances will destroy the
boost-invariance
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Summary

• It is the first time to find that BF is invariant
  under a longitudinal boost over the whole
  rapidity region, in contrast to the strong
  dependence of the particle density on rapidity
• BF in a limited rapidity window is
  boost-invariantly related to that in the full
  rapidity range and the results from different
  collaborations are comparable
• BF becomes narrower for increasing multiplicity
  in h-h collision, therefore, this influence
  should be properly accounted for before using
  narrowing of BF as a QGP signal
• The charge fluctuations are boost invariant but
  depend on the size of the rapidity window.

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Thank you!
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Appendix I ? on the measure of charge balance
function
Associated particle density
the density of particles of charge Q at rapidity
y under the condition that a particle of charge
Qs is detected at the rapidity ys.
Associated net charge density
the net charge density at rapidity y under the
condition that there exists a particle of charge
Qs at the rapidity ys.
Associated charge density balance
A measure of the change of the associated net
charge density, when the charge of the selected
particle(s) is changed from negative to positive.
D. Drijard, et al., (ACCDHW Coll.) , Nucl. Phys.
B166(1980)233-242 D. Drijard, et al., (CCHK
Coll.) , Nucl. Phys. B155(1979)269.
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Monte Carlo ? PYTHIA
? The hadronization scheme with string
fragmentation implemented in PYTHIA qualitatively
reproduces the trend of the data