Hard Scattering and Jets in Heavy-Ion Collisions
Naturwissenschaftlich-Mathematisches Kollegder Studienstiftung des deutschen Volkes
Kaiserslautern 30.9. – 5.10.2007
PD Dr. Klaus ReygersInstitut für Kernphysik Universität Münster
2 Hard Scattering and Jets in Heavy-Ion Collisions
Content
1 Introduction1.1 Quark-Gluon Plasma
1.2 Kinematic Variables
2 Lepton-Nucleon, e+e-, and Nucleon-Nucleon Collisions2.1 Deep-Inelastic Scattering and the Quark-Parton Model
2.2 Jets in e+e--Collisions
2.3 Jets and High-pT Particle Production in Nucleon-Nucleon Collisions
2.4 Direct Photons
3 Nucleus-Nucleus Collisions3.1 Parton Energy Loss
3.2 Point-like Scaling
3.3 Particle Yields and Direct Photons at High-pT
3.4 Further Tests of Parton Energy Loss
3.5 Two-Particle Correlations
3.6 Jets in Pb+Pb Collisions at the LHC
3 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss
3.1 Parton Energy Loss
4 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss
Jet Tomography in A+A Collisions
Hard parton-parton scatterings take place in initial phase, prior to the formation of a QGP
Scattered quarks und gluons sensitive to medium properties: „jet tomography“
5 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss
Parton energy loss in a finite, static medium consisting of colorcharge carriers
22
2
2ln ...
4s E
E C LL
a ml m
æ öç ÷D =- +ç ÷ç ÷ç ÷è ø
Energy loss for gluon jets larger than for quark jets:
3 for gluon jets
4 / 3 for quark jetsC
ìïï=íïïî
Energy loss due to gluon radiation dominant:
rad colld / d d / dE x E x
2
:
:
:
L
m
l
Parton Energy Loss
Typical momentum transfer frommedium to parton Mean free path of the radiated gluons in the medium
Path length of the parton in the medium
2~E LD
Total energy loss in the medium:
Detailed numerical calculation shows:
/ const.
for 20 GeV
E E
E
D »
<
(effect of quantummech. interference)
6 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss
Parton Energy Loss: Why E L2 ?
Probability for radiating a gluon: Lµ
Number of scatterings with momentum transfer kT until it decoheres: Lµ
Total energy loss: 2E LD µ
7 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss
Relation between Transport Coefficient andEnergy Density of the Medium
increases smoothly with energy density
Nuclear matter
ideal qgp
hot, massless pion gas
cold pion gas
q̂
2nuclear matter
ˆ 0.5 1 GeV / fmq < -
QGP (and hot hadron gas):
qgp nuclear matterˆ ˆq q
2ˆ /q Medium characterized by
(Momentum transfer per mean free path)
8 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss
Parton Energy Loss in Expanding Medium
3 Gluon2
d9 1 2ln ...
4 ds
N EE C L
A y L
pa
m
æ öç ÷D =- +ç ÷ç ÷ç ÷è ø
Taking into account the expansion of the fire ball (Bjorken Model):
Initial gluon density
Transverse area(A ~ R1/3 für b = 0)
Energy loss linear in L
Energy loss becomes linear in L for 1D Bjorken expansion
9 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss
Medium-Modified Fragmentation Functions (I)
energyloss
qE (1 ) qEe-
parton
hadron h, energy
hE
2/ ( , )h qD z Q( )P e
Prob. Distr. for parton energy loss (“Quenching weight”)
Consider fixed parton energy loss 2/
1( , )
1h q
dn dn dzD z Q
dx dz dx e= × = ×
-
,(1 )
(1 )
h h
q q
E Ez x
E E
x
e
e
= =-
=-
Average over energy loss probability
1
med 2 2/ /
0
1( , ) ( ) ( , )
1 1h q h q
xD x Q d P D Qe e
e e=
- -òHadrons resultingfrom gluon bremsstrahlungneglected
10 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss
Medium-Modified Fragmentation Functions (II)
Fragmentation functionu → for a medium with L = 7 fm and various gluon densities
11 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss
Quenching Weights (I)
quenching weight
probability to have no induced gluon radiation
continuous quenching weight
0ˆas function of in the limit :p q E® ¥
Note that P(E) is a generalized probability which can take negative values as long as this equation holds
taken from PhD thesis of C. Loizides
12 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss
Quenching Weights (II): Continuous Weight
taken from PhD thesis of C. Loizides
These quenching weights hold for parton energies E →
13 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss
Parton Energy Loss in the Limit E →
More realistic models need to take finite parton energies into account
14 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss
Energy loss in the GLV Formalism for Cu+Cu, Au+Au, and Pb+Pb
energy loss # radiated gluonsCalculated fractional energy loss and number of radiated gluons shown for three centralities in each figure:
Au+Au at sNN = 200 GeV:
Cu+Cu at sNN = 200 GeV:
Pb+Pb at sNN = 5500 GeV:
dNg/dy = 2000, 3000, 4000
I. Vitev, Phys.Lett.B639:38-45,2006
15 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss
Simple Estimate of the Relative Energy Loss
pT independence of RAA implies constant fractional energy loss
Loss Loss: , i.e., (1 )TT T
T
pS p S p
p
2
Loss
1/( 2)Loss
1
1
n
AA
nAA
R S
S R
0 spectra at RHIC energy (sNN = 200 GeV) described with n 8
Sloss from 0 RAA
PHENIX, nucl-ex/0611007
1T
d
dn
T
Np
p
0 spectrum without energy loss:
Constant fractional energy loss:
This leads to:
16 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling
3.2 Point-like Scaling
17 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling
Calculate increase of the effective luminosity of nucleons (and partons, respectively) based on known nuclear geometry
Result:Particle yields scale with the average number Ncoll of inelastic
nucleon-nucleon collisions in the absence of nuclear effects
hart hartAB
d d
d d
A B p p
T T
NT
p p
s+ +
= ×
unel.AB coll NN/T N s=
Only changecompared to p+p
Expectation for Particle Yields from Hard Scattering Processes in A+A collisions
18 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling
Digression: Luminosity of a Collider
Rate of event for a given physics process:
N L s= ×
Luminosity [(scm2)-1]
Cross section [cm2]
Event rate [s-1]
If two bunches of particles collide with frequency f then :
1 2 1 2
beam 4 x y
n n n nL f f
A ps s= =
Transverse area of the beam
ni: number of particles in bunch i
Example:Au+Au at RHIC: L = 2 x 1026 cm-2 s-1
19 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling
Effective Nucleon Luminosity: The Nuclear overlap function
A A( ) : ( , )dT s s z zr=ò
Nuclear thickness:
Normalization:
2A ( )dT s s A=ò
“nucleon luminosity” in area s 2
AB A Bd ( ) ( ) ( )dT s T s T s b s= × -
2AB A B( ) ( ) ( )dT b T s T s b s= × -ò
p+pcoll AB inel( ) ( )N b T b s= ×
unit: 1/area
2d s at :
“Total nucleon luminosity” for collisions at impact parameter b (nuclear overlap function):
Thus, number of interactions for process with cross section
int AB int( ) ( )N b T b s= × In particular:
20 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling
Impact Parameter Distribution of a A+A collisions
Au+Au at sNN = 200 GeV
500 000 Glauber MC collisions
slope: 2
Analytic approximation:A+B NNinel inel( ) 1 exp( ( ) )ABp b T b
Glauber MC:
A+Binel
d2 ( )
db p b
b
A+Binel
0
dd
db
b
Au+Au@200GeVinel 6.9 bs »Total cross section:
probability for an inelastic A+B collision at impact parameter b
21 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling
Averaging TAB(b) over an Impact Parameter Distribution
Observable: Hard process per inelastic A+A collisions, i.e.
A+Bhard hardA+B
inel
( )( )
( )ABT b
N bp b
Typical example: pT dependent pion yield per inelastic event:
A+Binel inel
( )1( )
( )
p pAB
A BT T
T bdN db
N dp p b dp
Averaging over an impact parameter range f (say b1 b b2):
2
1
2
1
inel A+Binel
2 ( )1
2 ( )
b
AB p pb
ABbA B fT T Tf
b
b T b dbdN d d
TN dp dp dp
b p b db
A+Binel ( )p b
weighting factor:
2
1
2d 2 db
f b
b b b Note that
22 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling
Nuclear Modification Factor (I)
Definition of nuclear modification factor:
Consider special case b1 = 0, b2 = :
0A+B
inel A+B inelinel
0
2 ( )1
2 ( )
AB A B p p
A BT T T T Tf
b T b dbdN d AB d d d
ABN dp dp dp dp dp
b p b db
(holds for hard scattering in the absence of nuclear effects)
inel
2
1
/( )
/( ) /
1
A BA BT fT
AB T p pAB Tfp p
AB T
f
dNN dpd dp
R pT d dp
d b T b d dp
In practice:
inelcoll NN/AB f f
T N where is determined with a GlauberMonte Carlo code
coll fN
(in the absence of nuclear effects)
23 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling
Ncoll from Glauber Monte-Carlo calculation
In the absence of nuclear effects:RAB = 1 at high pT (pT > 2 GeV/c)
2T
T 2coll T
d / d d( )
d / d dA B
AB
p p
N p yR p
N N p y+
+
=´
“no medium effects”
RAB
= 1R
AB
RAB
< 1
pT (GeV)
Nuclear Modification Factor (II)
24 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling
Glauber Monte-Carlo Approach
Nucleons of both nuclei randomly distributed in space according to Woods-Saxon distribution
Impact parameter b drawn from distribution d/db = 2b
Collision between two nucleons take place if their distance d in the transverse plane satisfies
NNinel /d
Npart and Ncoll through simulation of many A+B collisions (typically ~ 106)
Au+Au bei sNN = 200 GeV
NNinel 42 mb at 200 GeVNNs
25 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling
Examples of Glauber-MC Events (I)
Au+Au bei sNN = 200 GeV
Side view: Transverse plane:
26 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling
Examples of Glauber-MC Events (II)
Au+Au at sNN = 200 GeV
Side view: Transverse plane:
27 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling
Npart und Ncoll vs. Impact Parameter
Npart(b)
Ncoll(b)
4/ 3coll partN NµApproximate relation between Npart and Ncoll:
28 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
3.3 Particle Yields at Direct Photons at High-pT
29 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Cronin-Effect in p+A Collisions
Proton-Nucleus Collisions:
p+A Collisions:
Nuclear modification factor
RpA
> 1, at intermediate pT, before
RpA
= 1 is reached in the limit
of very high pT
Common explanation of the Cronin effect: Multiple soft scattering in p+A leads to additional transverse momentum kT
30 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
0 spectra in p+p- and Au+Au Collisionen
peripheral:N
coll = 12.3 4.0
centralN
coll = 955 94
Strong suppression of the 0 spectrum in central Au+Au collisions relative to Ncoll-scaled p+p spectrum
31 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
production in Au+Au at sNN = 200 GeV
factor 4-5 suppression
Ncoll = 5 ± 1Ncoll = 12 ± 4Ncoll = 29 ± 8Ncoll = 61 ± 10Ncoll = 120 ± 14Ncoll = 220 ± 23Ncoll = 374 ± 40Ncoll = 603 ± 59Ncoll = 955 ± 94
2
T 2coll
d / d d( )
d / d d
T A BAB
T p p
N p yR p
N N p y+
+
=´
No suppression in peripheral Au+Au collisions
Factor 4-5 suppression in central Au+Au collisions
32 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Particle Composition in A+A
For a parton that hadronizes in the vacuum after traversing the medium (A+A collision), particle ratios should be similar to those in d+Au or e++e-
This is indeed approximately true for pT > 6 GeV/c
2 < pT < 6 GeV/c: quark coalescence ?
33 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
What’s going on at Intermediate pT (~2 < pT < ~6 GeV/c) ?
Coalescence of quarks from the QGP is a conceivablemodel for hadronization at intermediate pT
34 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Alternative Explanation: Effects of Cold Nuclear Matter ?
Hadron suppression e.g. due to strong modification of parton distributions in heavy nuclei (initial state effects)?
Example: Color Glass Condensate Model
Fewer gluons in wavefunction of incoming Au nuclei
Result: Fewer hard parton-parton scatteringsand therefore fewer particles at high pT
Hadron suppression in Au+Au can be described!
Control Measurements
Hadron production in d+Au
High-pT direct photons in Au+Au
Kharzeev, Levin, McLerran,Phys.Lett. B 561, 93 (2003)
35 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Cold Nuclear Matter Effects studied at RHIC with d+Au
nucl-ex/0610036
d+Au 0
200 GeVNNs =
RdA 1: Cold nuclear matter effectsare small at sNN = 200 GeV
36 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Centrality Dependence of RAA in d+Au and Au+Au
Au + Au Experiment d + Au Control Experiment
Preliminary DataFinal Data
37 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Direct Photons at high pT
Production of direct photons and hadrons at high pT sensitive to the same parton luminosity
Direct photons escape the medium unscathed
s
s
s
Example:
38 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Photon Sources in A+A Collisions
Direct photons from hard scattering dominate at high pT
Experimental challenge: Background from hadron decays, e.g.,
Method:direkt = Gesamt – Zerfall T
1np
hard:
/ E Tethermal:
Decay photons
39 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Direct Photons in Au+Au
QCD + Ncoll scaling describes direct photon spectra in Au+Au
Au+Au bei sNN = 200 GeV
Phys.Rev.Lett.94:232301,2005
40 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Nuclear Modification factor for direct Photons
A+B
coll T p+p
d / d
d / dT
AB
N pR
N N p=
´
Factor 5 suppression
energy lossfor q and g
No energyloss for ‘s
Hadrons are suppressed whereas direct photons are not:Evidence for parton energy loss (as expected in the QGP)
41 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Centrality Dependence of 0 and Direct Photon Production in Au+Au at sNN = 200 GeV
42 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
More Recent Data with Higher Statistics
Possible Explanations for direct photon suppression at pT 18 GeV/c:
Proton/neutron difference
Modification of parton distribution (EMC effect?)
Quenching of fragmentation photons
43 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Reminder: Direct and Fragmentation Component
dir
ect
frag
m.
NLO pQCD calculation by W. Vogelsang (p+p at s=200 GeV)
44 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Jet Quenching: Data vs. Theory
without parton energy loss
Wang
Wang
Levai
Levai
Vitev
Au+Au at sNN
= 200 GeVq
q
q
q
q
q
q
q
Data imply
high initial gluon density
high energy density
Energy loss for a 10 GeV quark:
Gluonend / d 1000 200N y » ±
3c10 GeV/fme e>
1,5 2 GeVED = -
with parton energy loss
45 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
3.4 Further Tests of Parton Energy Loss
46 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
How to Learn More about Jet Quenching ?
Suppression of high pT hadron yields
Dependence on colliding system
Dependence on center-of-mass energy
Dependence on path length L in the medium
Difference between energy loss for light (up, down) and heavy quarks (charm)
Study modification of di-hadron correlations in Au+Au with respect to p+p
47 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
0 RAA in Au+Au and Cu+Cu at sNN = 200 GeV
Approximately same RAA in Au+Au and Cu+Cu for similar Npart values in accordance with jet quenching models
48 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
sNN Dependence of RAA (I):Au+Au at 62 GeV and 200 GeV
Similar RAA for pT > 6 GeV in Au+Au at 62 and 200 GeV
49 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
sNN Dependence of RAA (II):RAA in Cu+Cu at 22.4, 62.4 and 200 GeV
Cronin enhancement appears to win over parton energy loss in central Cu+Cu collisions at 22 GeV
50 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
sNN Dependence of RAA (III): RAA in Pb+Pb Collisions at the CERN SPS
Suppression in very central Pb+Pb collisions (Npart > 300)
51 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Path Length Dependence of RAA (I)
In Plane
Out of Plane
fD
Dependence of RAA on angle with respect to reactionplane allows to study pathlength dependence of energyloss
reaction plane
3 < pT < 5 GeV/c
PHENIX, nucl-ex/0611007
52 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Path Length Dependence of RAA (II)
In Plane
Out of Plane fD
Averaged over jet productions points in (x,y) plane
Approximate scaling in Lxy expected in parton energy loss
models
Experimental evidence weak
Path length dependence of jetquenching remains an open question
53 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Jet Quenching and Angular Anisotropy (I)
Bulk (Hydrodynamic) Matter
Pressure gradient converts position space anisotropy to momentum space anisotropy
Jet Propagation
Energy loss results anisotropy based on location of hard scattering in collision volume
y
x
y
x
Common wisdom: low pT high pT
v2 at high pT should result from jet quenching
Anisotropy in particle production related to collision geometry
2 cos 2v f= atan y
x
p
pf =( )( )
3 2
31
11 2 cos
2 n rnt t
d N d NE v nd p p dp dy
jp
¥
=
æ öç ÷= + - Yç ÷ç ÷ç ÷è øå
v2: 2nd harmonic Fourier coefficient in dN/d with respect to the reaction plane
reaction plane
A. Drees
54 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Jet Quenching and Angular Anisotropy (II)
Charged hadron v2:v2 {2-particle}
v2 {AuAu – pp}
v2 {4-particle}
v2 remains large at high pT – too large to be explained by geometry of jet quenching?
Origin of v2 at high pT unclear
STAR, Phys.Rev.Lett.93:252301, 2004
55 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Measurement of Charm Production via Electrons
Observable:Excess electrons after subtraction of trivial sources ( conversion, 0 Dalitz decay [0→e+e-], …)
Electrons from decay of charm and bottom quarks dominant source of excess electrons
0( ) ( ) eD cu K su e n- +® + +
D meson reconstruction via K channel requires good secondary vertex reconstruction:
/
0
D : 312 m
D : 123 m
c
c
lab
pL v c c
mc
1 3GeV/c:
dominated by c decay
4GeV/c:
dominated by c and
b decays
T
T
p
p
< <
>
56 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Excess Electrons in p+p at s = 200 GeV
Perturbative QCD calculation (FONLL = Fix-order-next-to-leading-log) in agreement with measurement within systematic uncertainties
57 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Excess Electrons in Au+Au at sNN = 200 GeV (I)
Total charm yield (i.e. pT > 0.3 GeV/c) scales with TAB as expected for charm production in hard processes
High pT > 4 GeV/c charm yields appear to be suppressed in central Au+Au collisionsFONLL calculation scaled by TAB
58 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Excess Electrons in Au+Au at sNN = 200 GeV (II)
Models based on radiative parton energy loss predict
Thus, electrons from charm and bottom quarks should be less suppressed than pions
Experimental observation:Electrons from charm (and bottom) decays as strongly suppressed as pions
Simultaneous measurement of electron flow further constrains energy loss modelsPHENIX, Phys.Rev.Lett.98:172301,2007
gluon quark , 0 quark , 0m mE E E= ¹D > D > D
59 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT
Excess Electrons in Au+Au at sNN = 200 GeV (III)
PHENIX
Parton energy loss calculation
Radiative energy loss not sufficient to describe excess electron RAA
Inclusion of elastic scattering improves the situation only slightly
Radiative energy loss
Radiative energy loss +elastic scattering
60 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations
3.5 Two-Particle Azimuthal Correlations
61 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations
Two-Particle Correlations
Angular correlations around 0 as in p+p
Suppression of angular correlations around 180
Expectation in jet quenching scenario:
62 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations
10.2 Jet-Quenching Two-Particle Correlations in p+p
Trigger particle: pT > 4 GeV/c
Associated particle: pT > 2 GeV/c
p+p 2 Jets
Triggerteilchen
Triggerteilchen
63 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations
Two-Particle Correlations in A+A
pp jet+jet STAR
Trigger particle with high pT > pT cut 1
to all other particles with pT > pT cut-2
Au+Au ???
0 /2 0
yiel
d/t
rig
ger
p+p
yiel
d/t
rig
ger
0 /2 0
Au+Au
random backgroundelliptic flow
0 /2
0
yiel
d/t
rig
ger
Au-Au
statistical background subtraction
suppression?
Jet correlations in Au-Au viastatistical background subtraction
64 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations
Two-Particle Correlations in Au+Au at sNN = 200 GeV
No jet correlation around 180 in central Au+Au
Consistent with jet quenching picture
Au+Au peripheral Au+Au central
background and ellip. flow subtracted
PRL 90, 082302 (2003) Trigger particle: pT > 4 GeV/cAssociated particle: pT > 2 GeV/c
65 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations
Dependence of the Away-side Peak on Angle w.r.t. The Reaction Plane
Stronger suppression at = 180° if jet axis is perpendicularto reaction plane, in line with jet quenching scenario.
STARSTAR PRL 93, 25230120-60% central
In-plane
Out-of-plane
66 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations
Two-Particle Correlations: Towards higher pT
Trigger particle: pT > 8 GeV/c
Associated particle: pT > 6 GeV/c
trigger particle
For higher jet energies the correlation at = 180° in central Au+Au is not fully suppressed anymore
67 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations
What happens to the jet energy ?
Jet suppression at high pT accompanied by multiplicity enhancement at lower pT
High pT
Low pT
68 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations
pT Distributions of Associated Particles
Associated charged hadron pT distribution(4 < pT,trigger < 6 GeV/c)
pT distribution on away side in central Au+Au similar to inclusive distribution:hint of thermalization of hadrons on away side
69 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations
A so-far Unexplained Phenomenon: The Ridge
Components
Near-side jet peak
Near-side ridge
Away-side (and v2)
3 < pt,trigger < 4 GeV
pt,assoc. > 2 GeV
Au+Au 0-10%
preliminary
hadron-hadron
“ridge” = broad correlation in on the near side
70 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations
Near Side Yields per Trigger Particle
After subtraction of the “ridge”: jet-yield per trigger independent of centrality
Jet + rid
ge
Ridge subtraced
71 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations
What’s going on on the Away Side? (I)
Trigger > 2.5 GeVpartner > 1 GeV
72 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations
What’s going on on the Away Side? (II)
D D
PHENIX preliminary
Possible explanations of the splitting of the away-side peak include Mach cones flow induced jet deflection and many more ….
Mach cone?
73 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations
Three-Particle Correlations (Principle)
Example: PHENIX
74 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations
Three-Particle Correlations: PHENIX Result Consistent with Mach Cone Scenario
75 Hard Scattering and Jets in Heavy-Ion Collisions - 3.6 Jets in Pb+Pb Collisions at the LHC
3.6 Jets in Pb+Pb Collisions at the LHC
76 Hard Scattering and Jets in Heavy-Ion Collisions - 3.6 Jets in Pb+Pb Collisions at the LHC
Single Particle Cross Section at the LHC
p+p
77 Hard Scattering and Jets in Heavy-Ion Collisions - 3.6 Jets in Pb+Pb Collisions at the LHC
Annual Jet Yield in ALICE Acceptance
1 ALICE year = 1 month of runningluminosity L = 51026 cm-2 s-1
Pythia simulation (Pb+Pb, no jet quenching)
Rate of jets with ET > 100 GeV is greater than 1 Hz
78 Hard Scattering and Jets in Heavy-Ion Collisions - 3.6 Jets in Pb+Pb Collisions at the LHC
Jets in Pb+Pb at the LHC
Jets with ET > ~ 50 GeV in Pb+Pb at s = 5500 GeV at the LHC can be identified above the background on an event-by-event basis
ALICE simulation
Cone size for jet reconstruction
bac
kgro
un
d
Influence of background from the underlying event minimized withcone size R ~ 0.3 – 0.4
79 Hard Scattering and Jets in Heavy-Ion Collisions - 3.6 Jets in Pb+Pb Collisions at the LHC
A Prediction for RAA in Pb+Pb at the LHC