PREDICTIONS for the HIGH DENSITY PROGRAMME at the LHC Carlos Pajares Dept Fisica de Particulas and IGFAE Universidad de Santiago de Compostela XII Mexican workshop on particles and fields Mazatlan,MEXICO 9-14 Nov 2009

Outline Multiplicity Parton Saturation Elliptic Flow. Transverse Momentum Suppression Charm, J/Ψ suppression Long Range correlations,Ridge structure Conclusions

SATURATION OF PARTONS Number of gluons. Size gluons Total Area New Scale QS

The whole gluon cascade, (ordered in longitudinal momenta) gives

A more detailed treatment, is the BFKL eq Grows as a power of the energy (Violation unitarity) Diffusive behaviour, gluons can go inside non-perturbative region

Small x, interaction among gluon sources BK equation

Solution At lower x (higher energy) N is large but lower than 1 (solving the unitarity problem) At small rT, N is small (color transparency) BFKL is OK. The transition between small rT takes place at a characteristic value rT~1/QS(τ). (solving the infrared diffusion problem) NEW SCALE QS (depends on y an A) dN/dy per participant does not depend on number of participants

MULTIPLICITY Extrapolation From lepton-Nucleon and p-A scaling on At LHC energy gives 9.5, i.e. 1800 charged particles per unit rapidity Other evaluations using CGC predicts 8.o,1500 Linear energy data extrapolation gives 6.5, 1200 charged particles String percolation around 1500 Most of the models over 2000before RHIC.Now they are below

ELLIPTIC FLOW

We expect Hydrodynamics perfect fluid result is for full thermalized system and a soft EoS Reynolds number Re=eLv/viscosity; Mach number Ma=v/cs, compresibility; Knudsen number Kn=lambda/L Viscosity=ecslambda Ma=Re x Kn Ma=1 ; Re=1/Kn

Perfect fluid should have scaling properties Limiting fragmentation Centrality dependence

This scaling suggests that the collective flow is at the partonic stage OK with coalescence models

Transverse Momentum Suppression Photons in agreement with perturbative QCD Energy loss by medium induced gluon radiation

Energy loss dependence on Npart O.K. with Energy loss dependence on Npart Non photonic electrons Problems: Equally supressed as charged hadrons contrary to predictions (less supressed) Q=14 GeV2/fm

J/Ψ SUPPRESSION hA

Data requires smaller σabs at most 3mb (usually σabs= 4.2 mb) Low x2 ~ 0.003 (shadowing region) Data requires smaller σabs at most 3mb (usually σabs= 4.2 mb) No additional suppression seen at RHIC σab=1mb 3 4

Grandchamp, Rapp, Brown PRL 92, 212301 (2004) Thews Eur.Phys.J C43, 97 (2005) Regeneration models fit the data. They predict, an increase of J/Ψ at LHC. Lattice studies indicate no suppression of J/Ψ at T=TC, only at T≥2TC. Ψ’ and are supressed at Defining SJ/Ψ,Ψ’ the survival probabilities once is substracted the absorption, as 60% J/Ψ are directly produced and 40% J/Ψ come from decays of Ψ’ and

The prediction for LHC is a large suppression of J/Ψ corresponding to the directly produced J/ Ψ. Clear difference at LHC between regeneration and sequential models

LONG RANGE CORRELATIONS A measurement of such correlations is the backward–forward dispersion D2FB=<nB nF> - <nB> <nF> where nB(nF ) is the number of particles in a backward (forward) rapidity <N> number of collisions: <n1B>,<n1F> F and B multiplicities in one collision In a superposition of independent sources model, is proportional to the fluctuations on the number of independent sources (It is assumed that Forward and backward are defined in such a way that there is a rapidity window to eliminate short range correlations). B F

Sometimes, it is measured with b in pp increases with energy. In hA increases with A also in AA,increases with centrality The dependence of b with rapidity gap is quite interesting, remaining flat for large values of the rapidity window. Existence of long rapidity correlations at high density

STAR Preliminary Data

Color Glass Condensate As the centrality increases, Qs increases, αs decreases and b increases (N.Armesto,L.McLerran and C.P NPA781,201(2007)

Qualitatively is rigth with exp data.Above a density b does not depends on rapidity gap .b increases with energy and centrality (through α) Ridge:(Dumitru,Gelis,McLerran,Venugopalan) Radial flow+correlations

CLUSTERING OF COLOR SOURCES Color strings are stretched between the projectile and target Strings = Particle sources: particles are created via sea qq production in the field of the string Color strings = Small areas in the transverse space filled with color field created by the colliding partons With growing energy and/or atomic number of colliding particles, the number of sources grows So the elementary color sources start to overlap, forming clusters, very much 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

How?: Strings fuse forming clusters. At a certain critical density ηc (N. Armesto et al., PRL77 (96); J.Dias de Deus et al., PLB491 (00); M. Nardi and H. Satz). How?: Strings fuse forming clusters. At a certain critical density ηc (central PbPb at SPS, central AgAg at RHIC, central SS at LHC ) a macroscopic cluster appears which marks the percolation phase transition (second order, non thermal).The energy momentum of the cluster is the sum of the corresponding for each string.Therefore there is a longitudinal expansion Hypothesis: clusters of overlapping strings are the sources of particle production, and central multiplicities and transverse momentum distributions are little affected by rescattering.

In the two steps scenario,it is obtained : b=1/(1+k/<nf>) 1/K is the normalized strings fluctuations As <nf> increases with centrality(saturates) and energy,b increases ( the K behaviour with centrality depends on the kinematical cuts,this can make that b can decrease) Qualitative agreement with data N.Armesto,M.A.Braun,P.Brogueira,J.Dias de Deus,E.G.Ferreiro,Kolevatov,C.Pajares V.V.Vechernin

b for Pb-Pb at LHC will not be much larger than at RHIC but extended several units of rapidity. In pp at LHC will appear large long range rapidity correlations extended over several units of rapidity Ridge structure at LHC more extended in rapidity.Also in pp

CONCLUSIONS Experiments at LHC can shed ligth to many questions formulated previously at RHIC and SPS on high density matter The nature and properties of the highly coherent object formed should be clarified

If you can not get rid of the noise…. study the noise Penzias and Wilson

Narrowing of the Balance function with Centrality number of identified charged pion pairs in The width sensitive to hadronization time. Delayed hadronization narrow balance function (stronger correlation in rapidity for the charged particles) Caveat: In PyTHIA and other models with short hadronization time are able to describe data. The narrowing is only observed at midrapidity

Different Extreme Reaction Scenarios MULTIPLICITY FLUCTUATIONS Different Extreme Reaction Scenarios NPTarg fluctuations contribute in target hemisphere (most string hadronic models) NPTarg fluctuations contribute in both hemispheres (most statistical models) NPTarg fluctuations contribute in Projectile hemisphere M. Bleicher M. Gazkzicki, M. Gorenstein arXiv:hep-ph/0511058 Multiplicity fluctuations sensitive to reaction scenario

Reflection, Mixing and Transparency Significant amount of mixing of particles projectile and target sources

String Hadronic Models Projectile hemisphere HSD, UrQMD: V. Konchakovskyi et al. Phys. Rev. C 73 (2006) 034902 HIJING: M. Gyulassy, X. N. Wang Comput. Phys. Commun. 83 (1994) 307 Simulation performed by: M. Rybczynski String hadronic models shown (UrQMD, HSD, HIJING) belong to transparency class They do not reproduce data on multiplicity fluctuations

PERCOLATION COLOR SOURCES L.Cunqueiro,E.G.Ferreiro,F del Moral,C.P. Results for the scaled variance of negatively charged particles in Pb+Pb collisions at Plab=158 AGeV/c compared to NA49 experimental data. The dashed line corresponds to our results when clustering formation is not included, the continuous line takes into account clustering.

FLUCTUATIONS AT RHIC %

(N. Armesto et al. , PRL77 (96); J. Dias de Deus et al (N. Armesto et al., PRL77 (96); J.Dias de Deus et al., PLB491 (00); M. Nardi and H. Satz). How?: Strings fuse forming clusters. At a certain critical density ηc (central PbPb at SPS, central AgAg at RHIC, central SS at LHC ) a macroscopic cluster appears which marks the percolation phase transition (second order, non thermal). Hypothesis: clusters of overlapping strings are the sources of particle production, and central multiplicities and transverse momentum distributions are little affected by rescattering.