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High pT Charged Hadron Suppression at s =200 GeV

Introduction Detectors Charged hadron analysis

Background Correction

High pT Results and Discussion Charged Hadron Spectra and Suppression d-Au results: Suppression is Final State Effect Details of the Suppression Patterns Collision Geometry and Jet absorption

Summary and outlook

Jiangyong JiaState University of New York at Stony Brook

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Quark Gluon Plasma

QCD coupling constant is “asymptotically free” s 0 as r 0

Lattice QCD predicts a deconfined phase Quarks and gluons are freed Quark Gluon Plasma TC ~ 155-175 MeV C ~ 0.3-1.0 GeV/fm3

Achieve in the laboratory by colliding heavy-ions Relativistic Heavy Ion Collider at BNL Estimate from measured transverse energy ET

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1~ TdEEV dycR

Formation time = 0.3-1fm/c

i ~ 5 - 15 GeV/fm3 Tc ~ 250-350 MeV

2%

Tnn

y 0

dE580GeV at s 200GeV

dy

RHIC

How can we confirm the existence and study the properties of QGP?

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The Experimental Probe for QGP

Use Hard Scattering or “Jets” as the probe Example : p—p collisions

proton

proton

q

q

hadronsleadingparticle

leading particle

schematic view of jet production

hadrons

p+p->0 + X s= 200 GeV

Jet dominate pT>2 GeV/c

Calibrated probe: Jet cross section can be calculated in pQCD for nucleon-nucleon collisions

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Calibrated probe

Incoming quarks and gluons (a,b) described by Parton Distribution Function PDF deduced from experimental data

Scatter with large momentum transfer “Hard scattering”and create c,d Early in the collision (t ~ 1/Q2) With large momentum (jets) Calculable in pQCD

c,d fragment and create hadrons Fragmentation functions from data

Fragmentation Theorem

AB hX fa/A(xa,Q

2a) fb/B(xb,Q

2b) a b cd

Dh/c(zc,Q2

c)

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Medium Modification of Jets

Initial production rate is proportional to the number of independent binary nucleon nucleon collisions Nbinary

Participants

hard hardAA NNbinaryN A

A

spectators

q

q

hadrons

hadrons

leadingparticle

jet production in quark matter

leadingparticle

Created early 0~1/E~0.2fm/c for 1 GeV parton

Experience the full time scale of the medium Strongly interact and lose significant amount of energy (~ GeV/fm)

Attenuation or absorption of jets

“jet quenching”

dydpNdN

dydpNdR

TNN

binary

TAA

AA 2

2:factor onmodificatiNuclear

Suppression of high pT hadrons

By definition, processes that scale with Nbinary will produce RAA=1.

q

q

hadronsleadingparticle

jet production in quark matter

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High pT suppression at s=130 GeV

First observation of high pT hadron suppression in Au-Au at s = 130 GeV PHENIX collaboration PRL

88 (2002) 22301

130GeV

Detailed pT and centrality dependence of charged hadrons PLB 561 (2003) 82 Peripheral RAA 1 Central RAA saturates ~ 0.6 at

pT >2GeV/C

PHENIX

More statistics from RUN-2. Higher in pT and more detailed centrality dependence

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Pioneering High Energy Nuclear Interaction eXperiment (PHENIX)@Relativistic Heavy Ion Collider (RHIC)

2 counter-circulating rings, 3.8 km circumference

Any nucleus on any other. Top energies (each beam):

100 GeV/nucleon Au-Au. 250 GeV polarized p-p.

Maximal Set of Observables Photons, Electrons, Muons, ID-hadrons

Highly Selective Triggering High Rate Capability. Rare Processes.

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PHENIX Setup for Au-Au at s = 200 GeV in Year 2001

Background Rejection and Subtraction Pad Chamber 2:PC2

RPC1 = 4.2 m

Pad Chamber 3:PC3RPC1 = 4.9 m

Ring Image Cerenkov Detector:RICHRRICH = 2.5-4.1 m

Charged particle Tracking||<0.35, =

Drift Chamber :DCRDC = 2-2.4 m

Pad Chamber 1:PC1RPC1 = 2.4 m

Trigger and CentralityBeam-Beam Counters:BBC3.0<||<3.9, = 2

Zero-Degree Calorimeters: ZDC|| > 6, |Z|=18.25 m

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Centrality Selection

BBC charge is participants ZDC energy is sensitive to

spectators.

Define centrality classes: ZDC vs BBC

bEZDC

QBBC

0-5%

15-20%10-15%

0-5%

5-10%

Centrality classes defined by cut on the BBC_Q and ZDC_E

Extract Npart, Ncoll from Glauber model simulation

27 million minimum bias events used

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Track reconstruction by DC-PC1

Drift Chamber measure trajectory in (x,y) plane Give the bending angle after magnetic field

T

Kp

pP

δp%1%7.0

Measured momentum resolution is

x

y

r

PC1 hits combined with the collision vertex fix the polar angle .

sin( )Tpp

z

r

0

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Backgrounds include

1. e+/e- from conversion of in materials

2. Weak decays, mostly K±

These tracks have small , consequently large apparent pT

Backgrounds in Charged Hadron measurement

Tracks with matching cut at PC2 and PC3

Overwhelmed by background at high pT

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Background under the matching distribution

Matching in r-plane at PC Plot the residual distribution Tails are the background Asymmetric shape due to residual bend

Different charge bend in opposite direction

e produce Cerenkov light in RICH, and detected by PMT.

Tracks can be divided into two categories according to RICH response:

NPMT >0 ( e background and high pT )NPMT <0 (decay background and high pT k,p )

a) Define the shape from a sample of background

b) Normalize the background outside the matching window

c) Subtract to get the signal

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6<pT<7GeV/c

Conversion Background Estimate

Tracks with RICH hit contains both electron background and primary pions e NPMT follows Poisson distribution with mean of 4.5 Pions begin to fire RICH at pT >4.8 GeV/c, <NPMT> < 3 at pT <10 GeV/c

e background subtraction from the matching distribution Require NPMT>4 to tag pure electron backgrounds Normalize electron background and subtract it Monte-Carlo reproduce the conversion background matching distribution.

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Decay Background Estimate

Tracks do not fire RICH (NPMT<0)contains decay background and

primary K±,P± Tracks at pT >10 GeV/c are dominated by decay background This sample of tracks gives the background matching distribution For each pT bin, normalize to background in 3-9 region and subtract Monte-Carlo reproduce the decay background matching distribution

6<pT<7GeV/c

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Signal/background ratio

Signal/All-bg ~ 1 at 7 GeV/c and ~0.3 at 10GeV/c.

SignalConversionDecay

Signal/bg

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Corrections

Monte-Carlo simulation of single particles through PHENIX detector

Plateau is given by geometrical acceptance and efficiency yellow band show the systematic

error At high pT dominated by

background subtraction

Embed single particle into real events to estimate occupancy correction correction for most central collision is

1.35 ± 6%

pT and centrality dependence factorize

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Charged hadron spectra and evolution

pT spectra out to 10 GeV/c Characteristic power-law tail

“Peripheral”

Particle

Physics

“Central”

Nuclear

Physics

Ratio of each centrality to minimum bias spectra Peripheral central Concave Convex High pT shape is almost centrality independent

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Suppression of charged hadron in Central collisions

Central RAA suppressed by factor of 4.5

Peripheral RAA ~ 1

Consistent with hard-scattering

*

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Suppression: An Initial State Effect?

Multiple elastic scatterings (Cronin effect) Wang, Kopeliovich, Levai, Accardi Nuclear enhancement observed in pA and

AA at lower energies

Nuclear shadowing Relevant for x<0.01 Not reached at RHIC

Gluon Saturation (CGC) Wavefunction of low x gluons overlap;

Gluon fusion ggg saturates the density of gluons in the initial state. (gets Nch right!)

Gribov, Levin, Ryshkin, Mueller,

Qiu, Kharzeev, McLerran,

Venugopalan, Balitsky,

Kovchegov, Kovner, Iancu …

1AAR

1AAR

Broaden pT :

xG(x,Q2)

QSx

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Jet Quenching: A Final State Effect?

Hadronic absorption of fragments: Gallmeister, et al. PRC67,044905(2003) Fragments formed inside hadronic medium

Energy loss of partons in dense matter Gyulassy, Wang, Vitev, Baier, Wiedemann…

PCM & clust. hadronization

NFD

NFD & hadronic TM

PCM & hadronic TM

CYM & LGT

string & hadronic TM

Hadron gas

1AuAuR d+Au is the “control” experimentFinal state effect: no suppressionInitial state effect: suppression dAu AuAuR R RdAu~ 0.7

D.Kharzeev et al., hep-ph/0210033

Gluon saturation model::

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First d-Au Results from RHIC

d-Au control experiment:

Initial state effects present in Au nucleusMedium volume too small for jet quenching

d-Au Result:

No suppression of high pt hadron yieldsPronounced “Cronin enhancement”

RHIC at too high x for shadowing and gluon saturation!

PHENIX

*

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Centrality Dependence

Different and opposite centrality evolution of Au+Au experiment from d+Au control

Centrality dependence is consistent with Cronin effect

Au + Au Experiment d + Au Control Experiment

Preliminary Datanucl-ex/0308006

Jet suppression is clearly a final state effect

A.Accardi

*

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Beam Energy Dependence

Expect xT scaling for hard processes: Spectrum shape depends only on

Normalization by

Empirically n=6.3

( )n T

dE G xdp s

3

3

1

TT

px

s

2

n

s

Compilation of neutral pion data

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Test xT Scaling for Au-Au

Compare data from 130 and 200 GeV beam energy Central & peripheral 0 data consistent with n=6.3 Peripheral h data consistent with n=6.3 Small deviation for central h data consistent with proton enhancement

Expected s dependence for hard scattering processes

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Particle Composition: Charged-to-Pion Ratio

Intermediate pT region h/ centrality dependent ~ 1.6 for peripheral collisions Reaches ~ 2.5 for central events

Proton enhancement in central collisions

High pT region (pT > 4.5 GeV/c) h/ ~ 1.6 Independent of centrality Same value as found in pp

Particle composition likeJet fragmentation

hard

protons

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Centrality Dependence of Jet Quenching

Hard region: pT > 4.5 GeV/c Suppression depends on centrality but not on pT Characteristic features of

jet fragmentation independent of centrality

xT scaling h/0 constantpQCD spectral shape

softhard

Soft and intermediate region: pT < 4.5 GeV/c Extends > 2 GeV/c into pQCD region Changing particle composition unlike jet

fragmentation pT dependent suppression

Have jet quenching but

particle production from

jet fragmentation

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Centrality Dependence of Suppression(I)

High pT yield per binary collision: pT > 4.5 GeV/c continuous decrease with centrality Identical for charged hadrons and 0

peripheral to central factor ~ 4

High pT yield per participant pT > 4.5 GeV/c Initially increases like collision scaling Decreases above Npart~100 by ~1.5

Approximate participant scaling???

*

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Centrality Dependence of Suppression(II)

Surface emission givesapproximate Npart scaling:

part

part part

part

NyieldN N

event N

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Jet absorption + nuclear geometry

suggested by Bjorken 1982

Energy loss (B.Mueller, nucl-th/0208038)Energy loss (X.N.Wang,nucl-th/0307036)jet absorption with Woods-Saxon geometry (next)

STAR data from nucl-ex/0305015

Hadron yield above 4.5 GeV/c peripheral data scale with Ncoll deviation for Npart > 50

*

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max~17/fm2

Central collisions (0-5%)

Ncoll ~ 1000

Peripheral collisions (75-80%)

Ncoll ~ 10

max<1/fm2

very dilute surface

Modeling the Hard Scattering

Number of hard scattering proportional to collision density Ncoll (x,y)

Number of collisions determined from the nuclear overlap Woods-Saxon nuclear density distribution Project into plane transverse to beam and divide by transverse area

probability of hard scattering Ncoll (x,y)

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max~4/fm2

Central collisions (0-5%)

Npart ~ 350

Peripheral collisions (75-80%)

Npart ~ 10

max<0.7/fm2

Modeling the Matter Density Matter density proportional to participant density Npart (x,y)

Number of participants calculated from collision geometry Participant density related to energy density

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2 3

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2~ 2.5 / ~ 5 15 /central

Npart Bjorken

Afm GeV fm

r A

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Jet Absorption Picture

Npart(x,y)

Ncoll(x,y)

Generate dijet isotropicly according to binary collision profile

Density of matter in transverse plane determined by participant density

dl

f e Interpretation: - static source absorption l

Jets are absorbed in dense reaction volume according to:

is the absorption parameter (only free parameter)fix to give f = 0.22 for central collisions

in static limit corresponds to absorption length ~ 2.9 fm

Neglect any pT dependence and jet fragmentation

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I = dl ρ (x,y)

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I = dl l ρ (x,y)

03

00

lI = dl ρ (x,y)

l +l

Centrality Dependence of High pT Yields

Compare to jet absorption picture describes centrality

dependence of yield Not very sensitive to

absorption pattern used

1. Centrality dependence consistent with jet absorption in extremely opaque medium

2. Centrality dependence of yield reflects mostly collision geometry

- static source absorption l- static source absorption l2

- expanding source absorption l

*

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Jet-Jet Azimuthal Correlations(I)

Di-jet are correlated in azimuth direction Leading particle + angular correlation Strong near side and far side correlation in p-p collisions

AA

yield(AuAu) backgroundI =

expected

Back jet are easier to be quenched in medium

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Jet-Jet Azimuthal Correlations (II)

Compare STAR data 4 < pT < 6 GeV/c to absorption picture by construction, same side jet (~0) will always give unity Away side jet () suppression by factor ~ 7 well described by jet

absorption and collision geometry Away side jet have almost factor of 2 more suppression than single

hadron suppression, consistent with surface emission

Near side

Away side

centrality dependence of yield reflects mostly collision geometry

*

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Azimuthal Anisotropy(I)

Different direction have different energy loss Jet are more likely to be emitted in plane than

out of planeIn plane

Out plane

Centrality dependence of v2 at pT > 4 GeV/c from data Measured v2 for different methods are quite different v2

2-particle-cumulant>= v2BBC-reaction-plane> v2

4-particle-cumulant

The difference comes from contributions that do not correlate with reaction plane

4 particle cumulant method is less affected by non-flow contribution

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Azimuthal Anisotropy(II)

Comparing to jet absorption calculation largest v2 from jet absorption picture 5-10% 1 from v2

4-particle-cumulant

Sensitive to the energy loss assumption and dynamic evolution of the medium

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Nuclear profile dependence

Woods-Saxon matter density has defuse surface

v2 increase by using hard sphere or cylindrical nuclear geometry May imply that the medium has a different shape other than Woods-Saxon

However, it misses the centrality dependence of the suppression

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Summary

Charged hadron pT spectra measured out to 10 GeV/c with bg rejection

Rich high pT phenomena observed at RHIC

Jet quenching well established experimentally Suppression of high pT hadron yields d-Au data indicate it is an final state effect Consistent with jet quenching and surface emission

xT scaling of pion production similar to pp

Particle composition at high pT are like pp

pT >4-5 GeV/c, suppression is ~ constant, spectra shape like pp

Jet absorption picture and collision geometry works reasonably well Describe general features of jet quenching

Consistent with suppression of hadron yieldsConsistent with back-to-back jet correlation

Azimuthal anisotropy described qualitatively

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Outlook

Suppression is a well established effect. What is future of high pT physics?

s dependenceSPS s = 17.2 GeV i =3 GeV/fm3 RHIC s = 200 GeV i ~ 5 GeV/fm3

where the jet quenching set in? or does it already happen in SPS? Hadron pT>20 GeV/c

At certain pT, jet should penetrate the medium again. More details on the Jet modification pattern:

RAA for baryon at high pT back-to-back correlation High pT v2 for identified particle

Jet absorption

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Track reconstruction by DC-PC1

Drift Chamber provides 12 hits in (x,y) plane. Give the bending angle after magnetic field,

which provide the initial momentum measurement

TT

R

rRq

pcGeVmrad

p

dLBr /087.0

PC1 hits combined with the collision vertex fix the polar angle .

pP

δp%1%7.0

Measured momentum resolution is

)sin(Tpp

41DC

PC1 PC2PC3

r-BVe

x

y

r-at PC2 and PC3 are correlated Define optimized matching variables:

D+ and D-

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Nucleon-Nucleon Reference

PHENIX p-p data at 200 GeV 0 data out to 14 GeV/c consistent with NLO pQCD

calculation charged hadron results not available

yet

Comparison to fit of UA1 data UA1 data at 200GeV PHENIX 0 spectra scaled by

1.6(ISR result)

Charged hadron N-N reference Use 0 data to constrain fit systematic uncertainty ~ 20%

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xT-scaling in pp

Charged hadrons s = 23-1800 GeV Approximate xT scaling with n = 6.3

Deviation from xT scaling for pT < 1-2 GeV/c

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3 ( , )

1( )

T

pTxT sn x s

dE Gdp s

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Neutral pions s = 39-540 GeV Approximate xT scaling with n = 6.3

No data for pT < 1-2 GeV/c

xT-scaling in pp (II)

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Testing xT scaling with 130 and 200 GeV Au-Au

xT scaling can be used to test pQCD in heavy-ion collisions Shadowing and gluon saturation is basically a scaling effect Partonic final state medium effect may or may not scale Hadron absorption and parton coalesce probably does not scale

Scaled by6.3( / 200)s

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xT scaling power n from 200/130 ratio

)130log()200log())200(/log())130(/log( 3333

)( GeVpdEdGeVpdEd

Txn

n=6.410.250.49

n=7.530.180.4

n=6.330.390.37

n=6.120.330.36

n= ncent-nperi = 1.410.43proton “enhancement” up to 4 GeV