Au Au vs. p p @ 200 GeV (p0)

1
AuAu vs. pp _at_ 200 GeV (p0)

• AuAu? p0 X (peripheral)
  AuAu? p0 X (central)
• Peripheral data agree well with
  Strong suppression in
• pp (datapQCD) plus Ncoll scaling
  central AuAu collisions

2
Nuclear modification factor (p0)
PHENIX Collab. PRL 91, 072303 (2003)
nucl-ex/0304022

RAA ltlt 1 well below pQCD (collinear
factorization) expectations for hard
scattering cross-section
3
Nuclear modification factor (p0) ?vsNN dependence

• CERN-SPS PbPb central (vsNN 17.3 GeV) no
  suppression() (within errors)
• CERN-ISR aa (vsNN 31 GeV) Cronin
  enhancement.
• RHIC AuAu (vsNN 130, 200 GeV) x 4-5
  suppression.

A.L.S.Angelis, PLB 185, 213 (1987) WA98, EPJ C
23, 225 (2002) () Reanalysis D.d'E.
nucl-ex/0403055 PHENIX, PRL 88 022301
(2002) PHENIX, PRL 91, 072303 (2003)
4
High pT azimuthal correlations jet signals in
AuAu pp

• dNpair/d?? for trigger (pT gt 4GeV/c)
  associated (pT 2- 4 GeV/c) charg. hadrons

Red histogram pp (flow) Black points
AuAu Blue curve flow contribution
Periph. Central

• Near-side peak AuAu pp.
• Trigger hadrons (pT gt 4GeV/c)
• from jet fragmentation.
• Away-side peak AuAu ltlt pp
• Back-to-back jets suppressed
• ("mono-jet") in central AuAu !

5
High pT azimuthal correlations AuAu dijet
signal disappearance

• Ratio of AuAu (- flow) over pp azimuthal
  correlation strengths

Near-side peak IAA 1 Away-side peak
IAA 0
6
Unquenched dAu production at high pT

• Suppression in central AuAu not due to
  initial-state effects

7
dAu nuclear modification factor (? 3.2)

• Factor 2 suppression
• pT 1-3 GeV/c hadron
• production at ? 3.2
• (x2 10-4 in Au).

• First time a large shadowing is seen at small-x
  and high pT in nuclear syst.
• So far unexplored perturbative region of nuclear
  (x,Q2) plane.

Perturbative
non-perturbative
8
Overview (Status of QGP CGC search)

• 1. Introduction
• The goal Study Quantum Chromo many-body
  Dynamics QGP, CGC.
• The means Compare hard scattering production in
  diff. colliding had. systems.
• 2. QCD vacuum reference results high pT in
  pp
• Baseline hard scattering data in free space.
• 3. Hot QCD medium highlights high pT in
  central AA
• ??dN/dpT light hadrons (u,d,s) suppressed
• ?s, pT, centrality, and meson-baryon
  dependence
• ??dNpair/df azimuthal anisotropies
• dissapearence of away-side dijet correlations
• ??dN/dpT colorless probes (g) unsuppressed
• 4. Cold QCD medium highlights high pT in dAu

CGC ?

9
The quest for gluon saturation effects _at_ RHIC ...

• RHIC kinematical regime
• High pT _at_ midrapidity
• y 0, Q2 1-100 GeV2/c2
• - pQCD collinear factorization
• - DGLAP evolution (g splitting)
• - small nuclear effects in PDFs
• (LT shadowing).
• Moderate pT, rapidities
• y 1-3, Q2 10 GeV2/c2
• - kT factorization
• - linear BFKL evolution (g splitt.)
• - moderate nuclear effects (LT
• shadowing).

(2 ? 2)
x small Look forward in rapidity !
10
AuAu collisions _at_ 200 GeV

600 charged particles per
unit rapidity at midrapidity (top 10 central)