Multiplicity Distributions and Percolation of Strings

J. Dias de Deus and C. PajaresCENTRA,Instituto Superior Tecnico,Lisboa

IGFAE,Universidade de Santiago de Compostela

• Clustering of color sources

• Fragmentation of clusters

• Results

• Conclusions

CERN, May 14th June 8th 2007

• Color strings are stretched between the projectile and target

• Strings = Particle sources: particles are created via sea qq production inthe field of the string

• Color strings = Small areas in the transverse space filled with color fieldcreated by the colliding partons

• With growing energy and/or atomic number of colliding particles, thenumber of sources grows

• So the elementary color sources start to overlap, forming clusters, verymuch like disk in the 2-dimensional percolation theory

• In particular, at a certain critical density, a macroscopic cluster appears,which marks the percolation phase transition

CLUSTERING OF COLOR SOURCES

(N. Armesto et al., PRL77 (96); J.Dias de Deus et al., PLB491 (00); M. Nardi and H. Satz(98).

• How?: Strings fuse forming clusters. At a certain critical density ηc(central PbPb at SPS, central AgAg at RHIC, central SS at LHC ) amacroscopic cluster appears which marks the percolation phase transition(second order, non thermal).

• Hypothesis: clusters of overlapping strings are the sources ofparticle production, and central multiplicities and transverse momentumdistributions are little affected by rescattering.

Energy-momentum of the cluster is the sum of the energy-momemtum ofeach string.

As the individual color field of the individual string may be oriented inan arbitrary manner respective to one another, 2 2

1nQ nQ

2 211 1

1

; nn T n T

n

nS nSp p

S S

less than parton saturation (9.5-10), HIJING, …more than extrapolation from SPS and RHIC (6.5) or applying limiting fragmentation (5.5).D.Kharzeev et al (6.8)

RESULTS

CONCLUSIONS

• Violation of limiting fragmentation

• 1500-1600 charged particles per unit rapidity at y=0

(less than most dynamical models)