Wounded Nucleons, Wounded Quarks, and Relativistic Ion Collisions

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Wounded Nucleons,Wounded Quarks,and
Relativistic Ion Collisions

• Helena Bialkowska
• Institute for Nuclear Studies
• Warsaw

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What is a wounded nucleon?

• Classic definition, given by Bialas, Bleszynski
  Czyz in 1976
• It is a nucleon that underwent at least one
  inelastic collision

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The WNM (1976!) as usual started from
experimental observation

• Series of Fermilab expts on h-A
• also European NA5
• and lots of emulsion data
• Average multiplicity and
• increases more slowly than the
  number of collisions

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Observation ratio of multiplicities (hA/hp)
behaves as
And this is just the ratio of participants in
p-A (1 from p and n from nucleus A) and in p-p
(2 protons)
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The Model
Particle production in a nuclear collision - a
superposition of independent contributions from
the wounded nucleons in the projectile and the
target
Thus you can 1 just measure NN 2 count the
participants in h - A 3 and you have particle
multiplicity in h A!
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Notice we check here both Npart scaling and pp
scaling
For p-A works surprisingly well. from AGS
energies up to RHIC!
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New idea not wounded nucleons but wounded quarks
Andrzej Bialas et al., 1977, Vladimir Anisovitch
et al., 1978
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Additive Quark Model
1982 Bialas et al. Specific predictions for
nuclear collisions on the basis of the Additive
Quark Model - with particle production from three
sources Breaking of the color strings between
quarks from the projectile and the
target Fragmentation of wounded quarks
Fragmentation of spectator quarks
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Pre-history 1980
AQM
Model 3.0
Model 1.6
P,d,?,C on Ta, 4.2 GeV/N JINR DUBNA
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More history NA35
First real high energy nuclear beams 200 GeV/c
O and S from SPS
K. Kadija et al., ZPhysC66,393(1995) consistent
parametrization of production rates of negatives
proportional to the No of wounded nucleons and
of kaons proportional to wounded quarks
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WNAB works for negatives
and it does not for K0s
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For kaons - need Wq
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Now for RHIC A A data
PHOBOS White Paper
Notice AuAu scaled by pp at twice the energy!
(to account for leading baryon)
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Almost the same plot
Here it looks better but read the fine print!
AuAu normalized to ee-
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Look more closely at total multiplicity per Npart
for Au - Au
Proportionality, but higher than for pp at the
same energy
pp systematically lower
WNM does not work
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Still, the scaling with Npartis surprising
and not only for total multiplicities
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This geometric scaling with Npart works not
only for soft (low pt) data!
PHOBOS AuAu PRL 94,082304(2005)
PLB578,297(2004) CuCu
PRL(2006) accepted
(courtesy of Barbara Wosiek)
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A very specific come-back of WNM
A.Bialas W.Czyz, first presented in Zakopane
in 2004 a two-component WNM to describe d-Au at
200 GeV/c
Basic assumption Superposition of independent
contributions from WN in the projectile and the
target Applies not only to the total charged
multiplicity but longitudinal spectra also
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Density of particles in A B collision
The model requires
(F is a contribution from a single wounded
nucleon)
And the first consequence is
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PHOBOS dAu 200 GeV
A. Bialas, W. Czyz, Acta Phys. Pol. B36,
905(2005)
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For full (pseudo)rapidity range construct
symmetric and antisymmetric component
And compare to data
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Symmetric and antisymmetric part for several
centralities dAu
centrality
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Interpretation by the authors The contribution
from one wounded nucleon extends over full
rapidity range There is a big difference between
its symmetric and antisymmetric part

• Two step particle production
• Multiple color exchanges between partons from
  projectile
• and target
• Particle emission from color sources created in
  step 1
• (ABMarek Jezabek, Phys.Lett.B590,233 (2004))

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Revival of wounded quarks concept for A - A
S. Eremin S.Voloshin, Phys.Rev.C67, 064905
(2003)
Recall at midrapidity increase of dN/dh per
participant with Npart
As
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Try Nq-part instead of NNpart
To calculate use same Nuclear Overlap
Calculation (K.J.Eskola et al.,Nucl.Phys.B323,37(1
989)) as for N-N, but change density and s
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Calculating Nn-part and Nq-part
Mass numbers of colliding nuclei are 3 times
larger, but their size is the same.
For pp the same procedure with AB3, hard sphere
R0.8fm.
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Compare NN, Nq
two versions of
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(No Transcript)
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Eremin Voloshin
Scale by nucleon participants
increase
Scale by quark participants
perhaps slight decrease
(full vs empty different s)
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How does it work at SPS?
Nucleon participants
Netrakanti Mohanty, PRC70(2004)027901 look at
WA98 data 158 GeV/n Pb-Pb
Quark participants
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Same trick at RHIC
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Bhaskar De S.Bhattacharyya PRC 71(2005)
024903 look at NA49 data (SPS)
nucleons
Notice log scale
quarks
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Caveat D B write about integrated yields in
figure caption, but show integrated yields for
p, K and midrapidity values for pbar, d
(plots to be re-done by NA49)
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Moreover...
When you put together light and heavy nuclei, you
see that Npart is not a good scaling variable for
strange particles
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Now for the energy dependence
One step further energy dependence R.Nouicer
nucl-ex/0512044
Midrapidity charged particle density normalized
to
R.Nouicer, nucl-ex/051244,2005
Nucleon participants Quark
participants
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Again Caveat
The author normalizes pp data by the number of
quark participants for most central pp
collisions
Is this a correct procedue?
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pp 200 GeV (Nq-part)inclusive ?2.4
(Nq-part)central ?3.5
(plot stolen from Barbara Wosiek, who noticed
the problem)
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An attempt at a summary

• Wounded nucleons remarkably successful in
  parametrization of global characteristics of
  particle production
• Nobody expects everything to be just a
  multiplication of N-N but the proportionality
• looks intriguing
• Wounded quarks - perhaps better scaling?

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Disclaimer

• I am fully aware that A-A collisions at high
  energy produce something that can not be fully
  described in terms of simple hadronic degrees of
  freedom and/or nuclear geometry