Medium information from harmonic flow Medium information from harmonic flow & jet quenching in relativistic HI collisions& jet quenching in relativistic HI collisions

Subrata PalSubrata PalTata Institute of Fundamental Research, Mumbai, IndiaTata Institute of Fundamental Research, Mumbai, India

Outline A brief history of jet quenching in HI collision

AMPT model updated with jets & new PDF

AMPT predictions versus RHIC & LHC data:

Particle yield, Anisotropic flow, Jet quenching

Conclusions

Jet quenchingJet quenching

hadrons

N

N

hadrons

Leading hadron

Balancing hadron

schematic view of jet production

+ pT

- pT

High pT > 2 GeV back-to-back partons (jets) produced from initial hard NN collision

Fragmentation of the jets produce a cluster of high pT hadrons (also called jets!)

p+p or d+A: no QGP formed, both the back-to-back jets survive

Central A+A: If QGP formed, one or both jets in the dense partonic medium suffer energy loss – jet quenching

pp

AAbinaryAA

Yield

NYield)(

/ TAA pR

RAA(pT) =1: Particle yield in A+A collision is simply superposition of independent p+p collisions.

RAA(pT) 1 at high pT : Deviation from this simple superposition concept (viz final-state effects).

PHENIX: PRL 88 (2002) 022301. STAR: PRL 91 (2003) 172302.

High pT hadron yield in central Au+Au suppressed compared to p+p collision in-medium jet energy

loss

Jet quenching: pQCD energy loss ΔE of partons by gluon bremsstrahlung

(1) R s

3(1)

2

2g

g

2R s

2CE Log ... ,

4

Static medium

9 C 1E Log ... ,

4 A

(L)

dNdy (L

1+1D

)

L 2E

Bjo

L

2EL

L

rken

Gyulassy, Levai, Vitev NPB 594 (2001) 371

p+p colln:

Inclusive hadron distribution – calculable in pQCD

Parton distribution fnsFragmentation

fnPerturbative cross section

),(),(),( 22/

2/ QzDdQxfQxfdN chccXabbNbaNah

zc = ph/pq

),(),(),( 22/

2/ QzDdQxfQxfdN chccXabbAbaAah ΔEA+A colln:

zc=ph/(pq-ΔE)

Jet formalismJet formalism

Jet quenching also sensitive to: Initial spatial parton distribution; Nuclear shadowing of PDF; Collective flow

sQGP + large soft particle production nonperturbative physics systematic model study

reqd.

AA MMultiultiPPhase hase TTransport model (ransport model (AMPTAMPT))

),(),(),( 22/

2/ QzDdQxfQxfdN chccXabbAbaAah ΔE

Inclusive hadron distribution – calculable in pQCD

Energy lossLin, Ko, Li, Zhang, SP, PRC72 (2005) 064901

Hard jets & its energy loss in AMPTHard jets & its energy loss in AMPT

ba

abbbaabTaTbTaTba

ppj

pd

dEQxfQxfggdddxdxK

pd

dE

,3

22223

),(),()k()k(kk

L

EdCE As 20

3 2log)()),((2

0

r

Momentum distribution of hard partons from LO pQCD in p+p collision

Total energy loss by a jet of energy E via gluon radiation

Number of gluons emitted from ΔE is related to entropy increase ΔS

),r(

),r(

4

1

4

1),r(

T

ESN g

T = ε(r,τ)/3ρ(r,τ)

From parton cascade

Radiated gluons scatter in medium with

Parton hadron duality: Ng →

Nπ

GRV94GaussianNLO

Parton density

SP, PRC 80 (2009) 041901(R)SP, Pratt, PLB 574 (2003) 14

σ ≈ 9s2/2μ2

AMPT with updated HIJING 2.0AMPT with updated HIJING 2.0• GRV parametrization of parton distribution function

PDF in nucleus:

sq = 0.1 (fixed) from deep-inelastic-scattering data off nuclear targets.

sg fitted to centrality dependence

of measured dNch/dy in A+A collision.

Deng,Wang, Xu, PLB 701 (2011) 133

Impact parameter dependent shadowing

p0 = 2 GeV/c

Parameters in AMPT

dNdNchch/dy in HIC at RHIC & LHC/dy in HIC at RHIC & LHC

In string fragmentation function, )/exp()1()( 21 zbmzzzf a

Default HIJING: a=0.9, b=0.5 GeV-2.

s=0.33, =3.226 fm-1 = 1.5 mb

Parton scatterings lead to 15% decrease in dNch/dy at RHIC & LHC!!

Hadron scattering insensitive to dN/dη.

HIJING: dNch/dη||η|0.5 = 705 (RHIC)

= 1775 (LHC)

AMPT hadron yield ratios at LHC

12.0/,05.1/,00.1 KKK

00.1/,96.0/,92.0/,82.0/ pp

(0-5)% Centrality

SP, Bleicher, PLB 709 (2012) 82

Au+Au collisions at RHIC: Measured charged hadron multiplicity density per participant pair constrains gluon shadowing parameter

sg = 0.10 - 0.17

Centrality dependence of dNCentrality dependence of dNchch/d/dηη

Pb+Pb collisions at LHC: Stronger centrality dependence in ALICE data due to large minijet production (at small x) gives a stringent constraint on

sg ≈ 0.17

[5]

HIJING2 (w/o FSI) fits with sg=0.20 - 0.23

Deng,Wang, Xu, PLB 701 (2011) 133ALICE Collab, PRL 106 (2011) 032301

Anisotropic flow vAnisotropic flow vnn in HI collision in HI collision

1

)](cos[v212

1)(

nRPn nf

d

dN

Ollitrault, PRD 46 (1992) 229

For smooth profile Odd harmonics = 0Odd harmonics = 0For "lumpy" profile Odd harmonics ≠ 0Odd harmonics ≠ 0

Borghini et al, PRC 64 (2001) 054901

...,)(cosv 4,3,2,1)( nne n

ninn

Event Plane angle: )cos(

)sin(arctan

1

np

np

n T

Tn

Origin of triangular flow v3: fluctuations in the position of participant nucleons Alver & Roland, PRC 81 (2010) 054905

Elliptic flow v2: initial spatial ellipticity converted to final momentum anisotropy by interaction among particles

vn are Fourier coeff in φ distribution of

particles relative to the Reaction Plane

nnven in }2{221

21)()(cos

2, 4 particle azimuthal correlations:2, 4 particle azimuthal correlations:

nonflow part44

4321 }4{2)(cos }2{ nn vvn

2

3

42 2

2 2

y x

y x

2x

yz

RP cannot be measured directly. Estimated by

Anisotropic flow @ RHICAnisotropic flow @ RHIC

v2 > v3 > v4 in AMPT (b0) describes RHIC data

Initial spatial asymmetry and matter flow in AMPT consistent with RHIC

SP, Bhalerao, in prep.

Ma, Wang, PRL 106 (2011) 162301

AMPT b=0

Anisotropic flow @ LHCAnisotropic flow @ LHCALICE, PRL 107 (2011) 032301

<vn> slightly larger at LHC due to large <pT>

Magnitude, pattern of vn(pT) at RHIC & LHC similar! At LHC larger density but faster expansion

Av. v2,v3,v4 described by AMPT over large centrality

0-5% centrality0-5% centrality 30-40% centrality30-40% centrality

RHICRHIC

p+p @ LHCAMPT spectra is less steep at high pT compared to the ALICE data obtained from interpolation between s = 0.9 and 7 TeV

Charged particle spectra @ RHIC & LHCCharged particle spectra @ RHIC & LHC

Pb+Pb @ LHC Peripheral collision: AMPT spectra agrees with ALICE data. 0-5% central collision: Enhanced energy loss in AMPT even with elastic parton-parton scattering.

p+p, Au+Au @ RHICAMPT spectra agrees with STAR data up to high pT for both peripheral & central collisions

SP, Bleicher, PLB 709 (2012) 82

STAR Collab, PRL 91 (2003) 0172302

ALICE Collab, PLB 696 (2011) 30

Jet quenching and lost jet remnantsJet quenching and lost jet remnantsAu+Au @ 200 GeV at b=0 fm

Momentum conservation

trigTxxx pdppp )(

4 <pTtrig <6 GeV/c

+ x

away

Trig

- x

)cos(tracksall

II trig

i

iTT pp

)()( 2,,2,, TtrigTTtrigTj ppppA

Overall momentum imbalance: projection of all track pT on pT,trig

Dijet asymmetry ratio

Balanced jet

Unbalanced jet

0-30% Pb+Pb @ 2.76 TeV

In-cone large mom. imbalance at high pT

Low pT, momentum balanced in an event

Out-of-cone low pT particles balance the event

Away side: energy lost by high pT partons is converted to soft particles with |px| < 600 GeV/c

SP, Pratt, PLB 574 (2003) 14

Trigger jet is surface biased

Zhang et al, PRL 98 (2006)

Trigger

Trigger

Trigger side Away sidedN/d

p x=

Dihadron azimuthal angle correlationDihadron azimuthal angle correlationSP, PRC 80 (2009) 041901(R)

Default: away-side hadrons peak → small rescatterings and dNg/dy

pT(trig)

pT(assoc)

= 3-4 GeV/cData: PHENIX, PRC 78 (2008) 014901

Low pT: away-side jet traverse into dense medium, scatter & thermalize → broad distribution around Δφ = π

High pT: Jets produced near surface

→ “conical flow” peaks at Δφ = π ± 1

String melting

SM with σ = 10 mb explains Au+Au data

p+p in pQCD agrees with data

p+p: peaks at near side & away-side (Δφ ≈ π)

Au+Au: away side peak shifts to Δφ ≈ π ± 1.2

Data

Background v2 subtracted

Flow contribution to dihadron correlationFlow contribution to dihadron correlation

Ma & Wang, PRL 106 (2011) 162301

PHENIX, PRC 78 (2008) 014901

Au+Au: away side peaks at Δφ ≈ π ±1.2

only v2 contribution subtracted

AMPT : On subtraction of harmonic flows vn (n=2-6), away side peaks suppressed

v3 contributes most to double peak

PHENIX data:

Jet quenching data in HI CollisionJet quenching data in HI Collision

SPS energy: rising/flat RAA≈ 1 with pT little/no jet energy loss

RAA(LHC) < RAA(RHIC) at pT < 6 GeV/c: Enhanced energy loss as the medium is denser at LHC than at RHIC

Rise of RAA at pT > 7 GeV/c due to slow fall with increasing pT of primary jet spectra (pQCD physics)

Medium effects at high pT quantified by nuclear modification factor:

Jet quenching at RHIC & LHCJet quenching at RHIC & LHC

Stronger suppression in AMPT for 0-5% centrality due to significant jet energy loss in a dense matter: c: [ c(LHC) ≈ 2c(RHIC) ] Recombination of hard partons in AMPT not enough to enhance RAA.

Medium at LHC less opaque??

Smaller RAA in AMPT leaves no room for model study of energy loss by gluon radiation??

Pb+Pb @ 2076 GeV

Au+Au @ 200 GeV RAA in AMPT describes RHIC data Model parton energy loss consistent with that of the evolving medium

ALICE: PLB 696 (2011) 30

(RAA)ch > (RAA)0 Larger (anti)baryon

yield than 0 from parton coalescence

Is large E-loss in models generic at LHC?Is large E-loss in models generic at LHC?

Further experimental results andtheoretical investigations required

Control d+Pb expt required to get sg.

Decrease in saturation parameter

sg enhance RAA but destroys dNch/dy

fit.

Understanding the medium

opacity.

Coupling of geometry to flow.

Approximations in E-loss

equation.

Horowitz, Gyulassy, NPA 872(2011) 265

Suggestions:

Gyulassy, Matsui, PRD 29 (1984) 419SP, Pratt, PLB 578 (2004) 310

Modification of jet-medium coupling Modification of jet-medium coupling ss

Scaling reln (~10% viscous entropy production)

dy

dN

Ady

dS

As ch

iii 85.7

11

pQCD screening mass (T dependent) sTgT 4

Parton elastic scattering cross section 22

2

8

9

2

9

Tss

Estimate initial Ti at RHIC &

LHC:

QGP with massless gas of light q, q-bar42)3021(with34 iiiii TTs

Alternative: =3.22 fm-1 is constant at RHIC & LHC To get = 0.76 mb at LHC requires s = 0.24

Quenching at LHC suggest thermal suppression of QCD coupling s by ~30%

≈ 320 MeV ≈ 1.4 mb (RHIC) ≈ 436 MeV ≈ 0.76 mb (LHC)

i = 1fm/c

Ti s= 0.33

(0-5)% expt dNch/dyy≈0 ≈ 687 (RHIC), 1601(LHC)

SummarySummary

dNch/dy at RHIC and LHC quite sensitive to parton scattering

dNch/dy versus Centrality data at LHC strongly constrains sg = 0.17

AMPT fluctuations and matter flow agree with measured v2 > v3 > v4

AMPT jet quenching consistent with RHIC data at all centralities

Quenching data at LHC suggests thermal decrease in s by ~30%

Lost jet energy & its medium excitations re-appear as soft particles

RESERVE SLIDES

Measured charged hadron spectra well described in AMPT model up to high pT

AMPT comparison with p+p collision dataAMPT comparison with p+p collision data

pT in AMPT underpredict data Hadron production by recombination is not efficient in p+p collision

Elliptic flow (vElliptic flow (v22) in AMPT model) in AMPT model

String melting enhances parton density v2 well explained with string melting & parton recombination v2 sensitive to parton elastic σqq→qq (= 6 mb best fit)

→ dense partonic medium required to explain v2

Charged hadrons

Lin, Ko, PRC 65 (2002) 034904

Lin, Ko, Li, Zhang, SP, PRC72 (2005) 064901

Origin of vOrigin of v22, v, v33 in AMPT in AMPT

<v2> 2: Final elliptic flow proportional to initial eccentricity

<v3> 3: Final triangular flow proportional to initial triangularity

Alver & Roland, PRC 81 (2010) 054905

,)(cos RPn nnv ...,,

)sin()cos(43,2,1

22

n

n

nn

n r

nrnr

hh spectra in pp spectra in pp and and RAA @ LHCRAA @ LHC

• charged particle spectra in pp at √s = 0.9, 2.76, 7 TeV

H. Appelshäuser, Talk at Quark Matter 2011