Download ppt - IASA

Energy Loss in Dense Media
“Jet Quenching”
Axel Drees, University Stony Brook
EINN, Milos Greece, Sep. 23 2005
One of the first discoveries at RHIC!
PHENIX
PRL 88 (2002) 22301
Outline of My Talk

Introduction
 Quark Gluon Plasma at RHIC
 Jets and how they probe the QGP
 Jet quenching in heavy ion collisions




pp baseline
High pt particle suppression in Au-Au
d-Au control experiment
Suppression of jet-jet correlations
 New experimental results


Medium modification of jet-correlations
Medium modifications of charm spectra
 Summary & Outlook
Axel Drees
The Phase Diagram of Nuclear Matter
 QGP in Astrophysics


RHIC
Relativistic
Heavy Ion
Collisions
170 MeV
1Gev/fm3
early universe:
time < 106 seconds
possibly in the interior
of neutron stars
 Quest of heavy ion collisions

Quark-Gluon Plasma
Critical
point


create QGP as transient
state in heavy ion collisions
verify existence of QGP
study properties of QGP
Early Universe
Hadron Gas
“frozen Quarks”
nuclei
Color superconductor
Color-flavor
locking
mbaryon or nucleon density Neutron Stars?
Overwhelming evidence for
strongly interacting plasma produced at RHIC
Axel Drees
Matter at RHIC has 15 GeV/fm3
III. Jet Quenching
I. Transverse Energy
PHENIX
130 GeV
V2
central 2%
1 1  dE T 
 Bj  2 
R ct0  dy 
PHENIX
Huovinen et al
Bjorken estimate:
t0 ~ 0.3 fm
dNg/dy ~ 1100
~15 GeV/fm3
II. Hydrodynamics
Initial conditions: ttherm ~ 0.6 -1.0 fm/c
~15-25 GeV/fm3
Pt GeV/c
Axel Drees
Ideal Experiment to Probe the QGP
 Rutherford experiment
SLAC electron scattering
a  atom
e  proton
discovery of nucleus
discovery of quarks
QGP
penetrating beam
(jets or heavy particles)
absorption or scattering pattern
Nature needs to provide penetrating beams and the QGP
in Au-Au collisions
 QGP created in Au-Au collisions as transient state for 10 fm
 penetrating beams created by parton scattering before QGP is formed


high transverse momentum particles  jets
Heavy particles  charm and bottom
Axel Drees
Jets: A Penetrating Probe for Dense Matter




leading particle
hadrons
schematic view of jet production
 What is a jet?
Incoming partons may carry large fraction x of
beam momentum
These partons can scatter with large
momentum transfer
Results in large pT of scattered partons
appears in laboratory as “jet” of particles
hadrons
leading
particle
q
 Jet production can be observed as


high pT leading particles
angular correlation
 In a gold gold collision


q
leading
particle
Scattered partons travel through dense matter
Expected to loose a lot of their energy
hadrons
hadrons
leading particle
 Energy loss observed as



suppression of high pT leading particles
reaction plane
suppression of angular correlation
Depending on path length, i.e. centrality and
angle to reaction plane
Axel Drees
Particle Spectra from p-p Collisions
 Jet production measured indirectly by
0 from
p-p collisions
transverse momentum (pT) spectrum


Identified particles (0)
Charged particles (h = , K, p, .. )
yield ( pT ) 
1 dN
Nevt pT dpT
 At RHIC energies different
mechanisms are responsible for
different regions of particle production


Thermally produced “soft” particles
“hard” particles from jet production
 Hard component can be calculated
QCD calculation
soft
hard
with QCD


Data agrees with QCD calculation
“calibrated” reference
Axel Drees
Scaling from p-p to Heavy Ion Collisions
 Hard-scattering processes in p-p



quarks and gluons are point-like objects
small probability for scattering in p-p
p-p independent superposition of partons
 Minimum bias A-A collision




assume small medium effects on parton density
superposition of independent p,n collisions
collision probability increases by A2
cross section scales by number of binary collisions
 Impact parameter selected A-A collisions



superposition of p,n collisions among participants
calculable analytically by nuclear overlap integral
or by MC simulation of geometry “Glauber Model”
Participants
NN hard
 hard AA  Nbinary  hard NN  TAA  inel
 NN
Axel Drees
Binary Scaling in Au-Au tested with Direct Photons
 pp collisions:


g
q
q
g
qg-Compton scattering
Direct g production described by NLO pQCD
 Au-Au collisions:


Direct g rates scale with Nbinary
Similar scaling observed for charm quark
production
Hard processes
in Au-Au
yield ( AuAu
)N
R p  
( pp)
scale withyield
Nbinary
coll
AA
T
Axel Drees
Suppression of 0 in Central AuAu Collisions
PRL 91 (2003) 72301
Nuclear modification factor:
yield ( AuAu ) Ncoll
RAA  pT  
yield ( pp)
PHENIX
PHENIX preliminary
High pT suppressed by factor ~ 5
pp to central AuAu and peripheral to central Au-Au
Axel Drees
Control Experiment with d-Au
deuteron gold
collision
gold-gold
collision
 Final state effect “jet quenching”



Medium created in d-Au has small volume
Jets easily penetrate short distance
No suppression of jet yield expected in d-Au
RdA  1
 Initial state saturation effect



Gluon density saturated in incoming gold nucleus
RdA
Deuteron shows no or little saturation
Expect suppression of jet yield, but with reduced magnitude
Final state effect: no suppression
Initial state effect: suppression
 RAA  0.7
Axel Drees
Suppression at Parton Level




No suppression for direct photons
Hadron suppression persists up to >20 GeV jets
Common suppression for 0 and h; it is at partonic level
Typical model calculation:  > 15 GeV/fm3; dNg/dy > 1100
Hot opaque partonic medium:  > 15 GeV/fm3
Axel Drees
Centrality Dependence of Suppression
 Hard region: pT > 7 GeV/c


Suppression depends on centrality but not on pT
Characteristic features of jet
fragmentation independent
of centrality
pQCD spectral shape
h/0 constant
xT scaling
Convolute jet absorption
or energy loss with nuclear geometry
(many publications)
Centrality dependence characteristic for jet
absorption in extremely opaque medium!
Insensitive to details of energy loss mechanism
Axel Drees
Azimuthal Correlations from Jets
p+p
Trigger particle with high pT > pT cut 1
0
Df to all other particles
with pT > pT cut-2
0
/2
Df

Au+Au
elliptic flow
random background
0
0
pp jet+jet
Au+Au
???
/2
Df

statistical background subtraction
STAR
Au-Au
suppression?
Jet correlations in Au-Au via
statistical background subtraction
0
0
/2

AxelDf
Drees
Disappearance of the “Away-Side” Jet
trigger 6 <pt< 8 GeV
partner 2 < pt < 6 GeV
Integrate yields in
some f window on
near and away side
pedestal and flow subtracted
Near-side: p+p, d+Au, Au+Au similar
Back-to-back: Au+Au strongly suppressed relative to p+p and d+Au
Suppression of the away side jet in central Au+Au
Axel Drees
Suppression of Back-to-Back Pairs
Near side
Jet correlation strength:
IAA =
Away side
yield(AuAu)  background
expected
Compared to jet absorption model
(J.Jia et al.)
Away side jets are suppressed
consistent with jet absorption in
opaque medium
“Mono jets”
point outward
Axel Drees
Remaining Jets from Matter Surface
“Mono jets”
point outward
Surviving “Di jets”
tangential
8 < pT(trig) < 15 GeV/c
pT(assoc)>6 GeV
D. Magestro, QM2005
STAR Preliminary
~factor 5
Qualitatively
consistent with
surface emission
Decreased surface/volume
Axel Drees
Where Does the Energy Go?
partner > 1 GeV
Trigger > 2.5 GeV
Axel Drees
Modification of Jet Shape at Lower pT
Near side
Away side
PHENIX preliminary
Can jet shape be related to
properties of matter?
Axel Drees
Theoretical Speculation:
 Energy loss of jet results in conical
shock wave in strongly interacting
plasma



Hydrodynamic mach cone?
Longitudinal modes ?
Cherenkov radiation ?
 Momentum conservation
Wake effect or “sonic boom”
Shuryak et al.
“multiple scattering” with
meduium
 Medium evolution of radiated
gluons
Sound velocity? Dielectric Constant?
Jet Tomography will be power tool to probe matter!
Axel Drees
How opaque is the medium? Check Charm Production!
e,m
p+p
X
 Signal:
p
D
p
 Background:
0
e
g e
background subtracted electron spectrum



Default PYTHIA parameterization

PDF – CTEQ5L; mC = 1.25 GeV; mB = 4.1 GeV

<kT> = 1.5 GeV; K = 3.5
Parameterization tuned to describe s < 63 GeV p+N world data
Spectral shape is “harder” than PYTHIA expectation
pp PHENIX preliminary
Axel Drees
Open Charm in Au+Au at sNN=200 GeV

Total yield scales with
number of binary
collisions
No indication of strong
medium modification of
charm production
Axel Drees
Heavy Quark Energy Loss: Nuclear Modification Factor
R AA
 d3N 


3 
 dp  AA

 d 3σ 
TAA   3 
 dp  pp
 Strong modification of the
spectral shape
 Suppression by factor 2-5,
similar to pion suppression
 Large bottom contribution
above 4 GeV?
Production of charm scales
like hard process
Spectral shape modified
while propagating in medium
Axel Drees
Elliptic Flow: A Collective Effect
f
z
y
x
dn/df ~ 1 + 2 v2(pT) cos (2 f) + ...
Initial spatial anisotropy is converted
into momentum anisotropy
Axel Drees
Charm Quarks flow with light quarks

Greco,Ko,Rapp: PLB595(2004)202
Charm flows, strength ~ 60% of
light quarks (0)
 Drop of the flow strength at high pT
due to b-quark contribution?
 The data favor the model that
charm quark itself flows at low pT.
High parton density and
strong coupling in the matter
Axel Drees
Summary & Outlook
Strongly interacting QGP produced at RHIC
State of unprecedented energy density ~ 15 GeV/fm3
Opaque to colored “hard” probes, jets and heavy flavor
Hard probes will be critical to study properties of QGP
On tape; analysis ongoing
2004
2001
4x larger Au-Au
data sample in 2006
2002
Factor 10
luminosity increase
with electron cooling
after 2010
Discovery of jet quenching
Most data seen today
Axel Drees
Backup Slides
Axel Drees
Outlook into the “Away” Future
g-jet: the golden channel for jet tomography
Quark gluon Compton scattering:
g
q
q
g
PHENIX Preliminary
pQCD direct g
+ jet quenching
AuAu 200 GeV 0-10%
g-energy fixes jet energy
g & Jet direction fix kinematics
measure DE as function of:
E, “L”, flavor
pQCD direct g
70% of photons are prompt photons
Promising measurement at RHIC:
every low cross section; pT< 8-10 GeV on tape
luminosity and detector upgrades:
extend range to pT~25 GeV and |y|<3
Axel Drees