Wounded Nucleons, Wounded Quarks, and Relativistic Ion Collisions

Wounded Nucleons,Wounded Quarks,and Relativistic Ion CollisionsHelena BiakowskaInstitute for Nuclear StudiesWarsaw

Zakopane, June 06, HB

What is a wounded nucleon?Classic definition, given by Biaas, Beszyski & Czy in 1976:

It is a nucleon that underwent at least one inelastic collision


The WNM (1976!) as usual started from experimental observation:Series of Fermilab expt`s on h-Aalso European NA5and lots of emulsion dataAverage multiplicity and increases more slowly than the number of collisions


Observation: ratio of multiplicities (hA/hp) behaves asAnd this is just the ratio of participants in p-A(1 from p and n from nucleus A) and in p-p (2 protons)


The Model:

Particle production in a nuclear collision -a superposition of independent contributionsfrom the wounded nucleons in the projectileand the targetThus you can:1 just measure NN2 count the participants in h - A3 and you have particle multiplicity in h A!


For p-A:works surprisingly well.from AGS energiesup to RHIC!Notice:we check here both Npart scalingand pp scaling


New idea: not wounded nucleons but wounded quarksAndrzej Biaas et al., 1977, Vladimir Anisovitch et al., 1978


Additive Quark Model1982 Biaas et al.:Specific predictions for nuclear collisions on the basis ofthe Additive Quark Model - with particle production fromthree sources:Breaking of the color strings between quarks fromthe projectile and the targetFragmentation of wounded quarks Fragmentation of spectator quarks


Pre-history: 1980P,d,,C on Ta, 4.2 GeV/NJINR DUBNAModel: 3.0Model 1.6AQM


First real high energy nuclear beams:200 GeV/c O and S from SPSK. Kadija et al., ZPhysC66,393(1995) consistent parametrization of production rates of negatives proportional to the No of wounded nucleonsand of kaons proportional to wounded quarks More history: NA35


WNAB works for negatives and it does not for K0s


For kaons - need Wq


Now for RHIC A A data:Notice: AuAuscaled by ppat twice the energy!(to account for leading baryon)PHOBOSWhite Paper


Here it looks better

but read the fine print!AuAu normalizedto e+e-Almost the same plot


Look more closely at total multiplicity per NpartProportionality,but higher than for ppat the same energypp systematically lowerWNM does not workfor Au - Au


Still, the scaling with Npartis surprisingand not only for total multiplicities ::


PHOBOS Au+Au PRL 94,082304(2005) PLB578,297(2004) Cu+Cu PRL(2006) acceptedThis geometric scaling with Npart worksnot only for soft (low pt) data!(courtesy ofBarbara Wosiek)


A very specific come-back of WNMA.Biaas & W.Czy, first presented in Zakopane in 2004:a two-component WNM to describe d-Au at 200 GeV/cBasic assumption:Superposition of independent contributionsfrom WN in the projectile and the targetApplies not only to the total charged multiplicitybut longitudinal spectra also


Density of particles in A B collision:The model requiresAnd the first consequence is(F is a contribution from a singlewounded nucleon)


A. Biaas, W. Czy, Acta Phys. Pol. B36, 905(2005)PHOBOSdAu 200 GeV


For full (pseudo)rapidity range: construct symmetric and antisymmetric componentAnd compare to data:


Symmetric and antisymmetric part for several centralities dAu:centrality


Two step particle production:Multiple color exchanges between partons from projectileand targetParticle emission from color sources created in step 1(AB+Marek Jeabek, Phys.Lett.B590,233 (2004))

Interpretation by the authors:

The contribution from one wounded nucleonextends over full rapidity rangeThere is a big difference between its symmetricand antisymmetric part


Revival of wounded quarks concept for A - AS. Eremin & S.Voloshin, Phys.Rev.C67, 064905 (2003)As Recall:at midrapidity increase of dN/dhper participantwith Npart


Try Nq-part instead of NNpartTo calculate: use same Nuclear Overlap Calculation(K.J.Eskola et al.,Nucl.Phys.B323,37(1989))as for N-N, but change density and s


Calculating Nn-part and Nq-partMass numbers of collidingnuclei are 3 times larger,but their size is the same.For pp the same procedurewith A=B=3, hard sphere R=0.8fm.


Compare NN, Nqtwo versions of


Eremin & VoloshinScale bynucleon participantsScale byquark participantsincreaseperhaps slight decrease(full vs empty: different s)


How does it work at SPS?Netrakanti & Mohanty, PRC70(2004)027901

look at WA98 data 158 GeV/n Pb-PbNucleon participantsQuark participants


Same trick at RHIC:


Bhaskar De & S.Bhattacharyya PRC 71(2005) 024903look at NA49 data (SPS) Noticelog scalenucleonsquarks


Caveat:

D & B write about integrated yields in figure caption, but show integrated yields for p, Kand midrapidity values for pbar, d(plots to be re-done by NA49)


Moreover...When you put together light and heavy nuclei,you see that Npart is not a good scaling variablefor strange particles


Now for the energy dependence:R.Nouicer, nucl-ex/051244,2005One step further: energy dependenceR.Nouicer nucl-ex/0512044Midrapidity charged particle density normalized to:Nucleon participants Quark participants


Again: CaveatThe author normalizes pp data by the number of quark participants for most central pp collisionsIs this a correct procedue?


p+p 200 GeV(Nq-part)inclusive 2.4 (Nq-part)central 3.5(plot stolen from Barbara Wosiek,who noticed the problem)


An attempt at a summary:Wounded nucleons remarkably successful in parametrization of global characteristics of particle productionNobody expects everything to be just a multiplication of N-N but the proportionalitylooks intriguingWounded quarks - perhaps better scaling?


DisclaimerI 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


Wounded Nucleons, Wounded Quarks, and Relativistic Ion Collisions

Documents

wounded quarksandrzej

hbfor p

wq zakopane

nuclear collisions

particle multiplicity

hbthe model

total multiplicity

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