Kistenev

Slide1: 

Exploring the saturation in cold nuclear matter at RHIC E.Kistenev, BNL Introduction to RHIC; Legacy of the first three years; Hints of the nontrivial initial state effects; Outlooks for the not so distant future Summary

RHIC’s Experiments: 

3.83 km circumference Two independent rings 120 bunches/ring 106 ns crossing time Any nuclear species on ~any other species Energy: 500 GeV for p-p 200 GeV for Au-Au (per N-N collision) Luminosity Au-Au: 2 x 1026 cm-2 s-1 p-p : 2 x 1032 cm-2 s-1 (polarized) RHIC’s Experiments

RHIC is special : 

Ideal enviroment to study partonic structure functions and evolution Compared to fixed target heavy ion facilities ECM increased by order-of-magnitude Accessible x (parton momentum fraction) decreases by ~ same factor Access to perturbative phenomena Direct photons Jets Non-linear dE/dx RHIC is special Atomic number A introduces new scale Q2 ~ A1/3 Q02 Gluon density is increased relative to the proton by A1/3 ;

Slide4: 

gluons overlap and fuse -> saturating gluon density in the initial state (scale Qs) Color dipole interacts with saturated nuclear glue PDS in x->0 limit: discovery or just measurement Implications for Qs2<Q2< Qs4/2QCD - Npart scaling of minijet production, “monojets”-- 21 gluon fusion Kharzeev, Levin, McLerrean Nuclear dijet decorrelation Nikolaev, Zakharov 1/Q

Slide5: 

In the saturation limit (McLerran et al.) linear factorization breaks down and one can describe the proton or nucleus in terms of classical gluon fields Color Glass Condensate CGC is not a state of matter like QGP, it is a Fock state of the wavefunction. The factorization breakdown does not affect suppression in the central rapidity region but may contribute to the total multiplicity.

The signs of DGLAP breakdown due to saturation effects should be relatively easy to identify in hard processes: : 

The signs of DGLAP breakdown due to saturation effects should be relatively easy to identify in hard processes: large scale in calculations makes perturbative QCD applicable to establish a base line: high momentum transfer (Q2), high invariant mass (M), high transverse momentum (pT) It is calculable DIS at HERA x In the limit x2<<x1 Q2=sx1x2 nA collisions to reach very low x values in nuclei

Legacy of the first three years: 

Legacy of the first three years

Further clues from dAu: 

Further clues from dAu Dramatically different and opposite centrality evolution of Au+Au experiment from d+Au control allows to claim that suppression observed in central region is clearly a final state effect. Au + Au Experiment d + Au Control Experiment Preliminary Data Final Data

BRAMS: 

BRAMS

As of today: 

As of today Physics at low x is being explored by all four RHIC experiments BRAHMS charged hadrons; STAR charged hadrons, 0 ‘s; PHENIX hadrons, muons, J/Y; PHOBOS charged particles; All four experiments have plans for major upgrades related to low x physics (via Forward Studies)

Slide11: 

PHOBOS 2003 – near complete h-coverage dN/dh N Rings P Rings Octagon Spectrometer

Related observables in PHENIX: 

Related observables in PHENIX Charged and neutral multiplicity Transverse Energy in EMCal Collision Region (not to scale) Hit multiplicity in BBC Muons and hadrons in muon spectrometers

Slide13: 

J/Y dA from PHENIX Suppression in deuteron direction consistent with some shadowing but can’t distinguish among various models Anti-shadowing in Au direction Overall absorption *Centrality dependence unique measurement from RHIC R. Granier ”J/Psi Production and Nuclear Effects for dAu and pp Collisions at RHIC” d Au

Rapidity dependence of the high Pt hadron yield suppression (compilation): 

Rapidity dependence of the high Pt hadron yield suppression (compilation)

Heavy quarks and shadowing(PHENIX): 

Heavy quarks and shadowing (PHENIX) probing gluon field in the initial state measuring total yield; - probing media effects measuring inv. s Yield of is consistent with binary scaling in d+Au and Au+Au collisions. Scaled down by ncoll

pQCD vs CGC(*).: 

pQCD vs CGC(*). We got hints of what to come. The goal now is to answer a fundamental question if those hints point to the breakdown of DGLAP evolution and advent of “dynamic shadowing” : CGC . The NLO DGLAP must be further tuned (NNLO) to describe transverse energy flow; forward (Mueller-Navelet) jets; jet azimuthal correlations; forward particles and energy flow together (measure of the range of compensation for forward partons) in pp interactions. Establish base-line for dynamical effects in the high Pt yields in dAu collisions. Use hard-scattering processes, the cleanest is g q->g J to find if DGLAP really breaks down. (*) see A.Accardi talk at QM2004

Can it be done at RHIC: 

Can it be done at RHIC Kinematics x yield restrict such measurements to h ~ 3.5 and pT ~ 6 GeV/c Dream detector…… Large solid angle Momenta in the range 20-60 GeV/c (photons, hadrons, jets) PID in the range 20-60 GeV/c Typical cross section at pT~5-6 GeV/c is d2N/dptdh~ 10-6

BRAMS – aiming to increase acceptance: 

Magnet Tracking Rich Calorimeter 1.5 4 8 Such a design can probably give a factor 10 in solid angle and improved rates but ……. philosophy is unchanged measuring forward jets would require radically different design. BRAMS – aiming to increase acceptance

STAR and PHENIX – similar goals, different constrains: 

STAR and PHENIX – similar goals, different constrains

Summary: 

Summary first hints of saturated gluon partonic density in fast moving nuclei are observed in dAu collisions at 200 GeV at RHIC. All four experiments reported new data on related observables to Quark-Matter 2004 Conference in January 2004; the suppression of the forward yields is found consistent in value for J/Y, charged hadrons, inclusive muons and p0’s measured by different experiments; presently running RHIC experiments able to see only tip of the iceberg, further progress requires dedicated upgrades; by chance central particle production at RHIC is largely unaffected by saturation so the matter effects potentially related to QGP are really pronounced. At LHC CGC will (may) become a dominant player even in y=0 region. Just be aware.    

Particle production at RHIC: 

Particle production at RHIC is the realization of “pre-existing” (dense) gluon fields F(x); In the low x limit Parton Saturation (~Extreme shadowing ~ Extreme kT ) results in F(x) described as coherent Yang-Mills field (Color Glass Condensate); Saturation scale QS2 increases with nuclear size and/or overlap Saturation condition r s ~ 1 here  =  s(Q2) / Q2   xG(x, Q2) nucleon  QS2 ~ aS A xG(x,Q2) / R2 ~ A1/3 F = F (x, Q/QS)