STAR André Mischke for the STAR Collaboration ICPAQGP, Kolkata, India, February 8-12, 2005 Recent “high-p T ” measurements in STAR

STARSTAR

AndrAndréé Mischke Mischke

for the STAR Collaborationfor the STAR Collaboration

ICPAQGP, Kolkata, India, February 8-12, 2005

Recent Recent “high-p“high-pTT” measurements ” measurements

in STAR in STAR

Andre Mischke, Utrecht University CINPP 2005 2

STARSTAR

modified

modified

• High incident energy opens up hard scattering regime where High incident energy opens up hard scattering regime where pQCD pQCD is applicable in theoryis applicable in theory

• Hard scattered partons to probe the properties of the produced Hard scattered partons to probe the properties of the produced densedense colored mediumcolored medium

• High-pHigh-pTT (> 2 GeV/c) particle production (> 2 GeV/c) particle production p-p:p-p: - parton distribution function (PDF)- parton distribution function (PDF)

- hard scattering cross section- hard scattering cross section - fragmentation function (FF)- fragmentation function (FF)

A-A:A-A: - - modifiedmodified PDF PDF (e.g. shadowing)(e.g. shadowing) -- Cronin effect Cronin effect - hard scattering cross section- hard scattering cross section

-- partonic energy losspartonic energy loss (gluon radiation)(gluon radiation) - FF - FF softenedsoftened

• Measurable effects: medium-induced modification of jet FF Measurable effects: medium-induced modification of jet FF - suppression of high-p- suppression of high-pTT hadron production hadron production - jet broadening- jet broadening

High-pHigh-pTT probes at RHIC probes at RHIC

q q

q

qhadronic

partonic

q ?


STARSTAR

Central TriggerBarrel (CTB)

ZDC

Time Projection Chamber(TPC)

Barrel EMCal (BEMC)

Silicon Vertex Tracker (SVT)

Forward-TPC

Endcap EMCal (EEMC)

Time-of-Flight (TOF)

The STAR detectorThe STAR detectorNIM 499, 624 (2003)Solenoidal Tracker at RHIC

0


STARSTAR STAR results so farSTAR results so far

v2 {2-particle}v2 {AuAu – pp}v2 {4-particle}

• Au-Au collisions at Au-Au collisions at s=s=200 GeV:200 GeV:

- strong high-pstrong high-pTT particle particle

suppressionsuppression- disappearance of the away-side disappearance of the away-side

jetjet - large and saturated elliptic flowlarge and saturated elliptic flow

Consistent with the picture of Consistent with the picture of

parton parton

energy loss in the dense medium energy loss in the dense medium

(jet-quenching)(jet-quenching)

• d-Au measurementsd-Au measurements

Jet-quenching is an effect happens Jet-quenching is an effect happens

in in

the final state of the collisionthe final state of the collisionAndre Mischke, Utrecht University CINPP 2005 4

STARSTAR

PRL 91, 172302 PRL 91, 172302 (2003)(2003)PRL 91, 072304 PRL 91, 072304 (2003)(2003)PRL 90, 082302 PRL 90, 082302 (2003)(2003)PRL 93, 252301 PRL 93, 252301 (2004)(2004)


STARSTAR

00 ~2~2 ~6~6 ppTT(GeV/c)(GeV/c)

low-plow-pTT intermediate pintermediate pTT high-phigh-pTT

OutlineOutline• soft particle soft particle production:production: bulk matterbulk matter

• nuclear effectsnuclear effects• probe-mediumprobe-medium interplayinterplay

• “ “clean” jet fragmentationclean” jet fragmentation regime (pQCD)regime (pQCD)

VariablesVariables

• Incl. particle spectra (RIncl. particle spectra (RCPCP)) asymmetry in d-Au

identified particle

• Two-particle azimuthalTwo-particle azimuthal away-side hadrons

correlationcorrelation identified particle triggered

near-side

• Incident energy (62 GeV)Incident energy (62 GeV) charged hadron spectra


STARSTAR

• d-Au (p-p): pQCD works at high-pd-Au (p-p): pQCD works at high-pTT at RHIC at RHIC

• Study nuclear effects like Cronin and shadowing Study nuclear effects like Cronin and shadowing baseline baseline

for Au-Au for Au-Au • Significant Significant dependence at highest centrality bin dependence at highest centrality bin• Yields are well described by AMPT and saturation modelYields are well described by AMPT and saturation model

Pseudo-rapidity asymmetry andPseudo-rapidity asymmetry andcentrality dependence in d-Aucentrality dependence in d-Au

Pt spectra

AuAudd

PRC 70, 064907 PRC 70, 064907 (2004)(2004)h±


STARSTARCharged hadron yield asymmetry Charged hadron yield asymmetry in d-Auin d-Au

• Back(Au)-forward(d) asymmetry ratio for two Back(Au)-forward(d) asymmetry ratio for two

rangesranges

• Cronin effect more pronounced in Au-direction Cronin effect more pronounced in Au-direction

• In qualitatively agreement with predictions from In qualitatively agreement with predictions from

saturation and coalescencesaturation and coalescence

• Different trend for initial parton scattering model Different trend for initial parton scattering model

(Hijing)(Hijing)

PRC 70, 064907 PRC 70, 064907 (2004)(2004)

ppTT

-1-1 -0.5-0.5 0.50.5 1100

open symbolsopen symbolssolid symbolssolid symbols

off mid-rapidityoff mid-rapidity

at mid-rapidityat mid-rapidity


STARSTAR RRCPCP for for and K and K00ss in d-Au in d-Au

• Yields enhanced for pYields enhanced for pTT > 1 GeV/c > 1 GeV/c• Not dominated by jet fragmentation (expectation: one Not dominated by jet fragmentation (expectation: one curve curve for all particles)for all particles)• Different behavior for mesons and baryons Different behavior for mesons and baryons Cronin effect depending on quark content; initial or Cronin effect depending on quark content; initial or final ?final ?

STAR preliminary

peripheralbinperipheral

centralbincentral

CPNyield

NyieldR

/

/


STARSTAR Flavor dependence of Flavor dependence of particle spectra in Au-Auparticle spectra in Au-Au

• Suppression at high-pSuppression at high-pTT

• More significant meson-baryon pattern in More significant meson-baryon pattern in Au-Au Au-Au • Collective hadron production mechanism: Collective hadron production mechanism: quark quark recombination/coalescence recombination/coalescence

RCP

PRL 92, 052302 (2004)PRL 92, 052302 (2004)J.Phys. G30, S963 (2004)J.Phys. G30, S963 (2004)

expectations from expectations from jet fragmentationjet fragmentation


STARSTAR

• Correlate high-pCorrelate high-pTT trigger particlestrigger particles with with associated associated

particlesparticles above a certain kinematical threshold above a certain kinematical threshold• Define correlation function: probability to find Define correlation function: probability to find

another particle in (another particle in (, , ))• Advantage of the Advantage of the STAR detectorSTAR detector: large acceptance : large acceptance • Corrections for flow (v2) and non-flow Corrections for flow (v2) and non-flow

contributionscontributions

• Correlation variables: Correlation variables: - peak width (- peak width (,,))

- N- Nchch(asso.)(asso.)

• Method favored the selection of high-pMethod favored the selection of high-pTT trigger trigger

particle near the medium surfaceparticle near the medium surface

Jetlike correlations: Jetlike correlations: study two-particle angular study two-particle angular

distributiondistribution

Trigger: leading hadron

ppzz

pp

ppxx

ppyy

Trigger: leading hadron


STARSTAR

• Parton energy loss dependsParton energy loss depends on the path length traversedon the path length traversed

• Consistent with jet-quenching Consistent with jet-quenching picture: picture: E E ss½qL½qL22

• Crosscheck at higher pCrosscheck at higher pTT

in-plane

out-of-plane

PRL 93, 252301 (2004)

correlation distribution wrt. to correlation distribution wrt. to the reaction plane in Au-Authe reaction plane in Au-Au

4 < pT(trig.) < 6 GeV/c 2 GeV/c< pT(asso.) < pT(trig.)


STARSTAR Identified particle Identified particle correlations: correlations: and K and K00

s s in d-Auin d-Au

• Integrated yields of correlation Integrated yields of correlation peakspeaks

• Comparable to PHENIX Comparable to PHENIX

measurements measurements

• Associated charged hadron Associated charged hadron

multiplicity similar for meson multiplicity similar for meson

and baryon triggersand baryon triggers

• No significant flavor dependence No significant flavor dependence

at intermediate pat intermediate pTT

||ηη|<0.7|<0.7

preliminary

<Npart>


STARSTAR Away-side associate charged Away-side associate charged hadrons: low-phadrons: low-pTT part part

• Observation so far: back–to-back jets Observation so far: back–to-back jets

disappear for pdisappear for pTT(asso.) > 2 GeV/c(asso.) > 2 GeV/c

• For lower pFor lower pTT(asso.) threshold: (asso.) threshold:

- correlation widely dispersed- correlation widely dispersed

- momentum balance shape- momentum balance shape

- higher fragmentation multiplicity- higher fragmentation multiplicity

- p- pTT distribution softened distribution softened

• Indication for thermal equilibrationIndication for thermal equilibration

of the away-side fragmentation of the away-side fragmentation

products with the bulk mediumproducts with the bulk medium

nucl-ex/0501016

STAR preliminary

4 < pT(trig.) < 6 GeV/c

0.15<pT(asso.)<4 GeV/c


STARSTAR near-side correlationsnear-side correlations

• In central Au-Au: In central Au-Au:

- jet-like correlation (short range) - jet-like correlation (short range)

sits on top of a wide, nearly flat sits on top of a wide, nearly flat

correlation (long range)correlation (long range)

- evidence for near-side jet - evidence for near-side jet

broadening in broadening in direction direction

d+Au, 40-100%

Au+Au, 0-5%

STAR preliminary

3 < pT(trig.) < 6 GeV/c2 < pT(asso.) < pT(trig.)


STARSTAR near-side correlations (cont’d)near-side correlations (cont’d)

• Significant broadening at low pSignificant broadening at low pTT(trig.), (trig.),

disappears with increasing pdisappears with increasing pTT(trig.)(trig.)

• NNchch(asso.) invariant with collision system (asso.) invariant with collision system • Interpretation: - Recombination effects ?Interpretation: - Recombination effects ?

- Interplay of - Interplay of medium-induced medium-induced gluon radiation gluon radiation and collective and collective longitudinal flow ?longitudinal flow ?

correlation width

Armesto et al., Armesto et al., PRL93, 242301 PRL93, 242301 (2004) (2004) S.A. Voloshin, nucl-th/0312065S.A. Voloshin, nucl-th/0312065

STAR preliminarySTAR preliminary correlated yield

3 < pT(trig.) < 4 GeV/c2 < pT(asso.) < pT(trig.)

|| < 1.0


STARSTARInclusive charged hadron spectra Inclusive charged hadron spectra in 62 GeV Au-Au in 62 GeV Au-Au

• High-pHigh-pTT absolute yield one order absolute yield one order

of magnitude lowerof magnitude lower

• Spectrum shapes similar to 200GeVSpectrum shapes similar to 200GeV

• RRAAAA~1 at SPS. What happens ~1 at SPS. What happens

at at

intermediate energies ? intermediate energies ?

• More quark jets expected at More quark jets expected at

62 GeV62 GeV less suppression less suppression

• Energy dependence of the Energy dependence of the

suppression factorsuppression factor


STARSTAR RRCPCP in 62 GeV Au-Au in 62 GeV Au-Au

• Same pSame pTT threshold for both threshold for both

energiesenergies

• Splitting at intermediate pSplitting at intermediate pTT

(due to Cronin effect ?)(due to Cronin effect ?)

• High-pHigh-pTT suppression at 62 suppression at 62

GeV GeV similar to 200 GeVsimilar to 200 GeV

• High-pHigh-pTT part (>6 GeV) part (>6 GeV)

suggest suggest that suppression is driven that suppression is driven by by nuclear geometrynuclear geometry

RCP


STARSTAR correlations in 62 GeV Au-Aucorrelations in 62 GeV Au-Au

• Near-side associated yields are reduced (factor of ~3) at 62 GeV Near-side associated yields are reduced (factor of ~3) at 62 GeV

• Similar suppression of the away-side correlation Similar suppression of the away-side correlation

preliminary


STARSTAR Particle production rangesParticle production ranges

• soft particle soft particle production:production: bulk matterbulk matter

• nuclear effectsnuclear effects• probe mediumprobe medium interplayinterplay

• “ “clean” jet fragmentationclean” jet fragmentation regime (pQCD)regime (pQCD)

VariablesVariables

• Incl. particle spectra (RIncl. particle spectra (RCPCP) ) asymmetry in d-Au

identified particle

• Two-particle azimuthal Two-particle azimuthal away-side hadrons

correlationcorrelation identified particle triggered

near-side

• Incident energy (62 GeV)Incident energy (62 GeV) charged hadron spectra

00 ~2~2 ~6~6 ppTT(GeV/c)(GeV/c)

low-plow-pTT intermediate pintermediate pTT high-phigh-pTT


STARSTAR

• Barrel-EMCalBarrel-EMCal- ||||1 and full azimuthal coverage1 and full azimuthal coverage

- EETT spectra: PRC 70, 054907 (2004) spectra: PRC 70, 054907 (2004)

Neutral pions in d-AuNeutral pions in d-Aunucl-ex/nucl-ex/04100320410032

see poster by R. Sahoo

0

=pT/2, pT and 2pT

0<<1

• First hadron measurement First hadron measurement

with with

BEMCBEMC- 10% normalization uncertainty10% normalization uncertainty- NLO pQCD calculations, NLO pQCD calculations, W. W.

Vogelsang Vogelsang

- Reasonable agreement within Reasonable agreement within

errorserrors- Lower the systematic errors, Lower the systematic errors,

work in progress work in progress


STARSTAR

• Trigger on high-ETrigger on high-ETT photons measured in the Barrel-EMCal photons measured in the Barrel-EMCal

• EETT(trig.) up to 11 GeV (Au-Au: up to 20 GeV/c) (trig.) up to 11 GeV (Au-Au: up to 20 GeV/c)

Photon - charged hadron Photon - charged hadron azimuthal correlation in 200 GeV d-Au azimuthal correlation in 200 GeV d-Au

preliminary

see poster by S. Chattopadhyay


STARSTAR ““The overall picture”The overall picture”• d-Au provides essential information for deeper understanding d-Au provides essential information for deeper understanding of the underlying mechanismsof the underlying mechanisms in Au-Au in Au-Au

• Baryon-meson pattern present in d-Au and Au-Au (due to quark Baryon-meson pattern present in d-Au and Au-Au (due to quark coalescence ?)coalescence ?)

• Near-side correlations:Near-side correlations: - - : similar for p-p, d-Au and Au-Au: similar for p-p, d-Au and Au-Au - - : interplay between parton energy loss and collective flow: interplay between parton energy loss and collective flow

• Away-side correlation:Away-side correlation: - jets traverse through the produced dense medium - jets traverse through the produced dense medium - associate hadrons appear at low-p- associate hadrons appear at low-pTT

- first indications of thermal equilibration with the bulk matter- first indications of thermal equilibration with the bulk matter

• High-pHigh-pTT hadron suppression similar in 62 and 200 GeV hadron suppression similar in 62 and 200 GeV

Suppression seems to be driven by nuclear geometrySuppression seems to be driven by nuclear geometry


STARSTAR Future challengesFuture challengesSTAR white paper, STAR white paper, nucl-ex/0501009nucl-ex/0501009

• Identified particle spectra at still higher pIdentified particle spectra at still higher pTT to see where to see where pQCD pQCD becomes dominantbecomes dominant high statistic data set: run IV at 200 GeV, analysis high statistic data set: run IV at 200 GeV, analysis underwayunderway

• d-Au analysis at higher pd-Au analysis at higher pTT for deeper understanding of the for deeper understanding of the underlying mechanismsunderlying mechanisms (e.g. initial and final Cronin effect) (e.g. initial and final Cronin effect) identified particle spectra, e.g. neutral pions identified particle spectra, e.g. neutral pions • Evolution of jet quenching effectEvolution of jet quenching effect system size (geometric scaling uncertainties): Cu-Cu system size (geometric scaling uncertainties): Cu-Cu (run V, (run V, data taking right now) vs. peripheral Au-Audata taking right now) vs. peripheral Au-Au energy: range mapping between top SPS and 62 GeVenergy: range mapping between top SPS and 62 GeV

• More details on the modification of the FF are needed, e.g. More details on the modification of the FF are needed, e.g. quantification of partonic energy lossquantification of partonic energy loss direct photon tag direct photon tag heavy quark tag (discrimination between quark and heavy quark tag (discrimination between quark and gluon jets)gluon jets)


STARSTAR

49 institutes from 13 countries, 522 49 institutes from 13 countries, 522 participantsparticipants

The STAR CollaborationThe STAR Collaboration


STARSTAR

Back-up slidesBack-up slides


STARSTAR

• Neutral pion pNeutral pion pTT

measurement up measurement up to 13-16 GeV/cto 13-16 GeV/c

• Agreement with Agreement with

PHENIX PHENIX measurementmeasurement

within 10%within 10%

PHENIX data: PRL 91, 072303 (2003)PHENIX data: PRL 91, 072303 (2003)

0 0 transverse masstransverse mass spectrum spectrum


STARSTAR Nuclear modification factor RNuclear modification factor RAAAA

in 62 GeV Au-Au in 62 GeV Au-Au

• p-p reference data from p-p reference data from ISRISR (25-30% uncertainties)(25-30% uncertainties)

• Same pSame pTT threshold for threshold for bothboth energiesenergies


STARSTARInclusive hadron spectra in Au-Au Inclusive hadron spectra in Au-Au


STARSTAR

Compiled references: π0, h±

62 GeV data: p-p reference62 GeV data: p-p reference


STARSTAR Azimuthal anisotropy at 62 GeV Azimuthal anisotropy at 62 GeV publication in preparationpublication in preparation

Similar pSimilar pTT dependence v dependence v22

for 62 GeV to 200GeVfor 62 GeV to 200GeV

solid colored symbols: 62 GeVopen symbols: 200 GeV

two- (squares) and four- particle (triangles) culumant method


STARSTAR

Away

syst. error

Near

4 < pT(trig.) < 6 GeV/c0.15 < pT(asso.) < 4 GeV/c


STARSTARIdentified strange particles in d-AuIdentified strange particles in d-Au

STAR preliminary

Yields measured up to (mYields measured up to (mTT-m-m00) ~ 5 GeV/c vs. centrality) ~ 5 GeV/c vs. centrality


STARSTAR

• Systematic studies underway with , K0s as trig, assoc. particles

h-Λh-Λ

pt (trig

)

K0s-hh-h

STAR preliminary

d+Au200 GeV


STARSTAR

1.5 < pT(trig) < 3 GeV1.5 < pT(assoc) < 3 GeV

(0-5)% (10-30)%

(30-50)% (50-70)% p+p

(5-10)%

Au+Au200 GeV

STAR preliminary

h-Λ

Andre Mischke, Utrecht University ICPAQGP 2005 35

STARSTAR

~ jet cone width

~ jet co-planarity

• Width of near- and away-side peak decreases slightly with EWidth of near- and away-side peak decreases slightly with ETT(trig.)(trig.)

• <j<jTT> stays constant; > stays constant; <k<kTT22> saturates at high-E> saturates at high-ETT

Photon- and charged-charged Photon- and charged-charged azimuthal correlation in 200 GeV d-Au azimuthal correlation in 200 GeV d-Au

STAR preliminary


STARSTARAzimuthal anisotropy in 200GeV Au-AuAzimuthal anisotropy in 200GeV Au-Au

In central Au-Au collisions, azimuthal In central Au-Au collisions, azimuthal anisotropy at high-panisotropy at high-pTT (>5 GeV/c) dominated (>5 GeV/c) dominated

by non-flow effectsby non-flow effects

Multiplicity independent quantity

PRL 93, 252301 (2004)

Documents

STAR André Mischke for the STAR Collaboration ICPAQGP, Kolkata, India, February 8-12, 2005 Recent “high-p T ” measurements in STAR