Hard Scattering and Jets
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Hard Scattering and Jets in Heavy-Ion Collisions Naturwissenschaftlich-Mathematisches Kolleg der Studienstiftung des deutschen Volkes Kaiserslautern 30.9. – 5.10.2007. PD Dr. Klaus Reygers Institut für Kernphysik Universität Münster. Content. 1 Introduction 1.1 Quark-Gluon Plasma

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Pd dr klaus reygers institut f r kernphysik universit t m nster

Hard Scattering and Jets in Heavy-Ion CollisionsNaturwissenschaftlich-Mathematisches Kollegder Studienstiftung des deutschen VolkesKaiserslautern 30.9. – 5.10.2007

PD Dr. Klaus ReygersInstitut für Kernphysik Universität Münster


Content

Content

1 Introduction

1.1 Quark-Gluon Plasma

1.2 Kinematic Variables

2 Lepton-Nucleon, e+e-, and Nucleon-Nucleon Collisions

2.1 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 Collisions

3.1 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

2 Hard Scattering and Jets in Heavy-Ion Collisions


Pd dr klaus reygers institut f r kernphysik universit t m nster

3.1 Parton Energy Loss

3 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss


Jet tomography in a a collisions

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“

4 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss


Parton energy loss

Parton Energy Loss

  • Detailed numerical calculation shows:

  • Energy loss for gluon jets larger than for quark jets:

  • Energy loss due to gluon radiation dominant:

  • Parton energy loss in a finite, static medium consisting of colorcharge carriers

  • Total energy loss in the medium:

(effect of quantummech. interference)

Path length of the parton in the medium

Typical momentum transfer frommedium to parton

Mean free path of the radiated gluons in the medium

5 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss


Parton energy loss why d e l 2

Parton Energy Loss: Why DE L2 ?

Probability for radiating a gluon:

Number of scatterings with momentum transfer kT until it decoheres:

Total energy loss:

6 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss


Relation between transport coefficient and energy density of the medium

increases smoothly with energy density

Nuclear matter

Relation between Transport Coefficient andEnergy Density of the Medium

ideal qgp

hot, massless pion gas

  • QGP (and hot hadron gas):

cold pion gas

Medium characterized by

(Momentum transfer per mean free path)

7 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss


Parton energy loss in expanding medium

Parton Energy Loss in Expanding Medium

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

8 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss


Medium modified fragmentation functions i

Medium-Modified Fragmentation Functions (I)

hadron h, energy

energyloss

parton

Prob. Distr. for parton energy loss e (“Quenching weight”)

Consider fixed parton energy loss e:

Average over energy loss probability:

Hadrons resultingfrom gluon bremsstrahlungneglected

9 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss


Medium modified fragmentation functions ii

Medium-Modified Fragmentation Functions (II)

Fragmentation functionu →p for a medium with L = 7 fm and various gluon densities

10 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss


Quenching weights i

Quenching Weights (I)

quenching weight

continuous quenching weight

Note that P(DE) is a generalized probability which can take negative values as long as this equation holds

probability to have no induced gluon radiation

taken from PhD thesis of C. Loizides

11 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss


Quenching weights ii continuous weight

Quenching Weights (II): Continuous Weight

taken from PhD thesis of C. Loizides

These quenching weights hold for parton energies E→ 

12 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss


Parton energy loss in the limit e

Parton Energy Loss in the Limit E→ 

More realistic models need to take finite parton energies into account

13 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 in the GLV Formalism for Cu+Cu, Au+Au, and Pb+Pb

I. Vitev, Phys.Lett.B639:38-45,2006

energy loss

# radiated gluons

Calculated 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

14 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss


Simple estimate of the relative energy loss

Simple Estimate of the Relative Energy Loss

pT independence of RAA implies constant fractional energy loss

p0 spectrum without energy loss:

Sloss from p0RAA

Constant fractional energy loss:

This leads to:

PHENIX, nucl-ex/0611007

p0 spectra at RHIC energy (sNN = 200 GeV) described with n 8

15 Hard Scattering and Jets in Heavy-Ion Collisions – 3.1 Parton Energy Loss


Pd dr klaus reygers institut f r kernphysik universit t m nster

3.2 Point-like Scaling

16 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling


Expectation for particle yields from hard scattering processes in a a collisions

Expectation for Particle Yields from Hard Scattering Processes in A+A collisions

Only changecompared to p+p

  • 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

17 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling


Digression luminosity of a collider

Digression: Luminosity of a Collider

Rate of event for a given physics process:

Cross section [cm2]

Event rate [s-1]

Luminosity [(scm2)-1]

If two bunches of particles collide with frequency f then :

ni: number of particles in bunch i

Transverse area of the beam

Example:Au+Au at RHIC: L = 2 x 1026 cm-2 s-1

18 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling


Effective nucleon luminosity the nuclear overlap function

Effective Nucleon Luminosity: The Nuclear overlap function

Nuclear thickness:

Normalization:

“nucleon luminosity” in area

at

:

“Total nucleon luminosity” for collisions at impact parameter b(nuclear overlap function):

unit: 1/area

Thus, number of interactions for process with cross section

In particular:

19 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling


Impact parameter distribution of a a a collisions

Impact Parameter Distribution of a A+A collisions

Glauber MC:

Analytic approximation:

Au+Au at sNN = 200 GeV

500 000 Glauber MC collisions

probability for an inelastic A+B collision at impact parameter b

slope: 2p

Total cross section:

20 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling


Averaging t ab b over an impact parameter distribution

Averaging TAB(b) over an Impact Parameter Distribution

Observable: Hard process per inelastic A+A collisions, i.e.

Typical example: pT dependent pion yield per inelastic event:

Averaging over an impact parameter range f (say b1 b b2):

weighting factor:

Note that

21 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling


Nuclear modification factor i

Nuclear Modification Factor (I)

Consider special case b1 = 0, b2 = :

(holds for hard scattering in the absence of nuclear effects)

Definition of nuclear modification factor:

(in the absence of nuclear effects)

In practice:

where is determined with a GlauberMonte Carlo code

22 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling


Nuclear modification factor ii

Ncoll from Glauber Monte-Carlo calculation

In the absence of nuclear effects:RAB = 1 at high pT (pT > 2 GeV/c)

Nuclear Modification Factor (II)

RAB

“no medium effects”

RAB = 1

RAB < 1

pT (GeV)

23 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 ds/db = 2pb

Collision between two nucleons take place if their distance d in the transverse plane satisfies

Glauber Monte-Carlo Approach

Au+Au bei sNN = 200 GeV

  • Npart and Ncoll through simulation of many A+B collisions (typically ~ 106)

24 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling


Examples of glauber mc events i

Examples of Glauber-MC Events (I)

Au+Au bei sNN = 200 GeV

Side view:

Transverse plane:

25 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling


Examples of glauber mc events ii

Examples of Glauber-MC Events (II)

Au+Au at sNN = 200 GeV

Side view:

Transverse plane:

26 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling


N part und n coll vs impact parameter

Npart und Ncoll vs. Impact Parameter

Ncoll(b)

Npart(b)

Approximate relation between Npart and Ncoll:

27 Hard Scattering and Jets in Heavy-Ion Collisions – 3.2 Point-like Scaling


Pd dr klaus reygers institut f r kernphysik universit t m nster

3.3 Particle Yields at Direct Photons at High-pT

28 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


Cronin effect in p a collisions

Cronin-Effect in p+A Collisions

Proton-Nucleus Collisions:

p+A Collisions:

Nuclear modification factorRpA > 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

29 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


P 0 spectra in p p and au au collisionen

p0 spectra in p+p- and Au+Au Collisionen

peripheral:

Ncoll = 12.3  4.0

central

Ncoll = 955  94

Strong suppression of the p0 spectrum in central Au+Au collisions relative to Ncoll-scaled p+p spectrum

30 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


P 0 production in au au at s nn 200 gev

p0 production in Au+Au at sNN = 200 GeV

Ncoll = 5 ± 1

factor 4-5 suppression

Ncoll = 12 ± 4

Ncoll = 955 ± 94

Ncoll = 603 ± 59

Ncoll = 61 ± 10

Ncoll = 29 ± 8

Ncoll = 220 ± 23

Ncoll = 374 ± 40

Ncoll = 120 ± 14

  • No suppression in peripheral Au+Au collisions

  • Factor 4-5 suppression in central Au+Au collisions

31 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


Particle composition in a a

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 ?

32 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


What s going on at intermediate p t 2 p t 6 gev c

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

33 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

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)

34 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

Cold Nuclear Matter Effects studied at RHIC with d+Au

RdA 1: Cold nuclear matter effectsare small at sNN = 200 GeV

p0

d+Au

nucl-ex/0610036

35 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


Centrality dependence of r aa in d au and au au

Centrality Dependence of RAA in d+Au and Au+Au

Au + Au Experiment

d + Au Control Experiment

Final Data

Preliminary Data

36 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


Direct photons at high p t

Production of direct photons and hadrons at high pT sensitive to the same parton luminosity

Direct Photons at high pT

as

a

as

as

Example:

  • Direct photons escape the medium unscathed

37 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.p0 g+g,h  g+g

Method:gdirekt = gGesamt – gZerfall

Photon Sources in A+A Collisions

hard:

thermal:

Decay photons

38 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

Direct Photons in Au+Au

Au+Au bei sNN = 200 GeV

Phys.Rev.Lett.94:232301,2005

39 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


Nuclear modification factor for direct photons

Nuclear Modification factor for direct Photons

No energyloss for g‘s

Factor 5 suppression

energy lossfor q and g

Hadrons are suppressed whereas direct photons are not:Evidence for parton energy loss (as expected in the QGP)

40 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


Centrality dependence of p 0 and direct photon production in au au at s nn 200 gev

Centrality Dependence of p0 and Direct Photon Production in Au+Au at sNN = 200 GeV

41 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


More recent data with higher statistics

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

42 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


Reminder direct and fragmentation component

Reminder: Direct and Fragmentation Component

NLO pQCD calculation by W. Vogelsang (p+p at s=200 GeV)

direct

fragm.

43 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


Jet quenching data vs theory

Data imply

high initial gluon density

high energy density

Energy loss for a 10 GeV quark:

Jet Quenching: Data vs. Theory

Au+Au at sNN = 200 GeV

without parton energy loss

Levai

Wang

Wang

with parton energy loss

Vitev

Levai

44 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


Pd dr klaus reygers institut f r kernphysik universit t m nster

3.4 Further Tests of Parton Energy Loss

45 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

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

46 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


P 0 r aa in au au and cu cu at s nn 200 gev

p0RAA 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

47 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


S nn dependence of r aa i au au at 62 gev and 200 gev

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

48 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


S nn dependence of r aa ii r aa in cu cu at 22 4 62 4 and 200 gev

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

49 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


S nn dependence of r aa iii r aa in pb pb collisions at the cern sps

sNN Dependence of RAA (III): RAA in Pb+Pb Collisions at the CERN SPS

Suppression in very central Pb+Pb collisions (Npart > 300)

50 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


Path length dependence of r aa i

Path Length Dependence of RAA (I)

Out of Plane

In Plane

reaction plane

Dependence of RAA on angle with respect to reactionplane allows to study pathlength dependence of energyloss

3 < pT < 5 GeV/c

PHENIX, nucl-ex/0611007

51 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


Path length dependence of r aa ii

Path Length Dependence of RAA (II)

Out of Plane

In Plane

  • Approximate scaling in rLxyexpected in parton energy loss models

  • Experimental evidence weak

  • Path length dependence of jetquenching remains an open question

Averaged over jet productions points in (x,y) plane

52 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


Jet quenching and angular anisotropy i

Jet Quenching and Angular Anisotropy (I)

y

y

x

x

A. Drees

Anisotropy in particle production related to collision geometry

Common wisdom:low pT high pT

Jet Propagation

Bulk (Hydrodynamic) Matter

reaction plane

Energy loss results anisotropy based on location of hard scattering in collision volume

Pressure gradient converts position space anisotropy to momentum space anisotropy

v2: 2nd harmonic Fourier coefficient in dN/d with respect to the reaction plane

v2 at high pT should result from jet quenching

53 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


Jet quenching and angular anisotropy ii

Jet Quenching and Angular Anisotropy (II)

Charged hadron v2:

v2 {2-particle}

v2 {AuAu – pp}

v2 {4-particle}

STAR, Phys.Rev.Lett.93:252301, 2004

  • v2 remains large at high pT – too large to be explained by geometry of jet quenching?

  • Origin of v2 at high pT unclear

54 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 (g conversion, p0 Dalitz decay [p0→e+e-], …)

Electrons from decay of charm and bottom quarks dominant source of excess electrons

Measurement of Charm Production via Electrons

  • D meson reconstruction via Kp channel requires good secondary vertex reconstruction:

55 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

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

56 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


Excess electrons in au au at s nn 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 collisions

Excess Electrons in Au+Au at sNN = 200 GeV (I)

FONLL calculation scaled by TAB

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 s nn 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 models

Excess Electrons in Au+Au at sNN = 200 GeV (II)

PHENIX, Phys.Rev.Lett.98:172301,2007

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 s nn 200 gev iii

Excess Electrons in Au+Au at sNN = 200 GeV (III)

PHENIX

Parton energy loss calculation

Radiative energy loss +elastic scattering

Radiative energy loss

  • Radiative energy loss not sufficient to describe excess electron RAA

  • Inclusion of elastic scattering improves the situation only slightly

59 Hard Scattering and Jets in Heavy-Ion Collisions – 3.3 Particle Yields at Direct Photons at High-pT


Pd dr klaus reygers institut f r kernphysik universit t m nster

3.5 Two-Particle Azimuthal Correlations

60 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

Two-Particle Correlations

Expectation in jet quenching scenario:

61 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations


10 2 jet quenching two particle correlations in p p

10.2 Jet-Quenching Two-Particle Correlations in p+p

Triggerteilchen

  • Trigger particle: pT > 4 GeV/c

  • Associated particle: pT > 2 GeV/c

p+p 2 Jets

Triggerteilchen

62 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations


Two particle correlations in a a

Two-Particle Correlations in A+A

p+p

Trigger particle with high pT > pT cut 1

yield/trigger

0

Df to all other particles

with pT > pT cut-2



/2

0

Au+Au

yield/trigger

elliptic flow

random background

0



/2

0

Au+Au ???

statistical background subtraction

Au-Au

yield/trigger

pp jet+jet

STAR

suppression?

Jet correlations in Au-Au via

statistical background subtraction

0



/2

0

63 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations


Two particle correlations in au au at s nn 200 gev

Two-Particle Correlations in Au+Au at sNN = 200 GeV

Au+Au central

  • No jet correlation around 180 in central Au+Au

  • Consistent with jet quenching picture

Au+Au peripheral

background and ellip. flow subtracted

Trigger particle: pT > 4 GeV/cAssociated particle: pT > 2 GeV/c

PRL 90, 082302 (2003)

64 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

Dependence of the Away-side Peak on Angle w.r.t. The Reaction Plane

STAR

Stronger suppression at Df = 180° if jet axis is perpendicularto reaction plane, in line with jet quenching scenario.

PRL 93, 252301

20-60% central

Out-of-plane

In-plane

65 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations


Two particle correlations towards higher p t

Two-Particle Correlations: Towards higher pT

trigger particle

  • Trigger particle: pT > 8 GeV/c

  • Associated particle: pT > 6 GeV/c

For higher jet energies the correlation at Df = 180° in central Au+Au is not fully suppressed anymore

66 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

What happens to the jet energy ?

High pT

Low pT

67 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations


P t distributions of associated particles

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

68 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations


A so far unexplained phenomenon the ridge

A so-far Unexplained Phenomenon: The Ridge

Au+Au 0-10%

preliminary

3 < pt,trigger < 4 GeV

pt,assoc. > 2 GeV

Components

  • Near-side jet peak

  • Near-side ridge

  • Away-side (and v2)

hadron-hadron

“ridge” = broad correlation in Dh on the near side

69 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations


Near side yields per trigger particle

Near Side Yields per Trigger Particle

Jet + ridge

Ridge subtraced

After subtraction of the “ridge”:

jet-yield per trigger independent of centrality

70 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations


What s going on on the away side i

What’s going on on the Away Side? (I)

partner > 1 GeV

Trigger > 2.5 GeV

71 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations


What s going on on the away side ii

What’s going on on the Away Side? (II)

D

D

PHENIX preliminary

Mach cone?

  • Possible explanations of the splitting of the away-side peak include

  • Mach cones

  • flow induced jet deflection

  • and many more ….

72 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations


Three particle correlations principle

Three-Particle Correlations (Principle)

Example: PHENIX

73 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations


Three particle correlations phenix result consistent with mach cone scenario

Three-Particle Correlations: PHENIX Result Consistent with Mach Cone Scenario

74 Hard Scattering and Jets in Heavy-Ion Collisions - 3.5 Two-Particle Correlations


Pd dr klaus reygers institut f r kernphysik universit t m nster

3.6 Jets in Pb+Pb Collisions at the LHC

75 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

Single Particle Cross Section at the LHC

p+p

76 Hard Scattering and Jets in Heavy-Ion Collisions - 3.6 Jets in Pb+Pb Collisions at the LHC


Annual jet yield in alice acceptance

Annual Jet Yield in ALICE Acceptance

Pythia simulation (Pb+Pb, no jet quenching)

1 ALICE year = 1 month of runningluminosity L = 51026 cm-2 s-1

Rate of jets with ET > 100 GeV is greater than 1 Hz

77 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 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

Influence of background from the underlying event minimized withcone size R ~ 0.3 – 0.4

ALICE simulation

background

Cone size for jet reconstruction

78 Hard Scattering and Jets in Heavy-Ion Collisions - 3.6 Jets in Pb+Pb Collisions at the LHC


A prediction for r aa in pb pb at the lhc

A Prediction for RAA in Pb+Pb at the LHC

79 Hard Scattering and Jets in Heavy-Ion Collisions - 3.6 Jets in Pb+Pb Collisions at the LHC


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