IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)1/39
Jet quenching au RHIC:Jet quenching au RHIC:résultats expérimentauxrésultats expérimentaux
Journée thématique “Jet quenching”IPN-Orsay, November 14th, 2005
David d’EnterriaLLR – Ecole Polytechnique, IN2P3, Paris
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)2/39
OverviewOverview “Jet physics” results @ RHIC (w/o full jet reco): (1) Inclusive high pT spectra, (2) di-hadron φ,η high-pT triggered correlations.
confronted to non-Abelian radiative energy loss in QGP “paradigm”.
High pT (leading) hadron suppression data in central AA: 1. Magnitude ÞVery dense medium: dNg/dy ~ 1000 (~ dNch/dη). OK 2. Transverse momentum dependence: flat pT . OK 3. Centrality dependence. OK 4. Light-meson species dependence (π0 vs. η). OK 5. Center-of-mass energy dependence (SPS-20 GeV, RHIC-62,200 GeV). OK 6. Non-Abelian radiation. OK 7. Path-length dependence. OK ? 8. System-size (CuCu vs. AuAu) dependence. OK ? 9. Heavy vs. light quark suppression. OK ?
Modified high pT di-hadron (φ,η) correlations in central AA: 1. Disappeareance of away-side azimuthal dijet peak. OK 2. Enhanced (“volcano”-like) away-side associated yield at lower pT. (?) 3. Broadening of near-side pseudo-rapidity correlations. OK
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)
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“Jet quenching” as a QGP signal
Multiple final-state non-Abelian (gluon) radiation off the produced hard parton induced by the dense QCD medium
Parton energy loss µmedium properties:
Flavor dependent energy losses:
Energy is carried away by gluons emittted inside (broader) jet cone:
“gluonsstrahlung”
Prediction I: Suppression of high pT leading hadrons: dN/dpT
Prediction II: Modification of (di)jet correlations: d2Npair/dφdη Predition III: Modified energy- & particle- flow within full jet
dE/dx ~ s k2T
DEloss(g) > DEloss(q) > DEloss(Q) (color factor) (mass effect)
SPS,RHIC,LHC
RHIC,LHC
LHC
µ(g density, L)
µ (q coeffic., L2)
GLV:
BDMPSWiedemann: ˆ
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)4/39
Jet physics at RHIC: experimental limitsJet physics at RHIC: experimental limits
Full jet reconstruction w/ standard algorithms is unpractical at RHIC due to huge soft background (large “underlying event”):
Feasible at LHC for Ejet >~ 50 GeV
p+p ®jet+jet [Ös = 200 GeV] Au+Au ® X [ÖsNN = 200 GeV]
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)5/39
““Jet physics” at RHIC (I): Single inclusive high pJet physics” at RHIC (I): Single inclusive high pTT spectra spectra
Alternative I : Study the energy modifications suffered by the highest pT hadron in the event (“leading” hadron of the jet) in AA (compared to pp):
Many interesting results obtained from this “first-order” approach !
p+p ® h+ X [Ös = 200 GeV] Au+Au ® h+X [ÖsNN = 200 GeV]
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)6/39
““Jet physics” at RHIC (II): Di-hadron azimuthal correlationsJet physics” at RHIC (II): Di-hadron azimuthal correlations
Alternative II : Study the azimuthal correlations in AA relative to pp between highest pT hadron (“trigger”) & any other “associated” hadron:
Many interesting results obtained from this “2nd-order” approach !
p+p ® h1+h2+ X [Ös = 200 GeV] Au+Au ® h1+h2+ X [ÖsNN = 200 GeV]
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)7/39
““Jet physics” at RHIC (II): Di-hadron azimuthal correlationsJet physics” at RHIC (II): Di-hadron azimuthal correlations
Alternative II : Study the azimuthal correlations in AA relative to pp between highest pT hadron (“trigger”) & any other “associated” hadron:
Many interesting results also obtained from this “2nd-order” approach !
Many interesting results obtained from this “2nd-order” approach !
p+p ® h1+h2+ X [Ös = 200 GeV] Au+Au ® h1+h2+ X [ÖsNN = 200 GeV]
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)8/39
High pT leading hadron spectra at RHIC & jet-quenching models:
Good agreement data theory
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)9/39
Inclusive single spectra at high pT (AA, dA, pp)
High quality large-pT data (up to ~20 GeV/c) available in pp, dA and AA collisions:
Au+Au – 200 GeV
d+Au – 200 GeV
p+p – 200 GeV
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)10/39
Leading hadron spectra in free space: pp Leading hadron spectra in free space: pp @ @ 200 GeV200 GeVHigh pT p0,h± spectra up to ~15 GeV/c. Good theoret. (NLO pQCD) description
KKP FF
Kretzer FF
(PDF: CTEQ6M)
PHENIX Collab.PRL 91, 241803hep-ex/0304038
High quality data: sensitive to different parametrizations of gluon FF
p+p p0 X p+p h± X
Well calibrated (experimentally & theoret.) p+p baseline spectra at hand.
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)11/39
Leading hadron spectra in AuAuLeading hadron spectra in AuAu @ 200 GeV@ 200 GeV
Au+Au p0 X (peripheral) Au+Au p0 X (central)
Peripheral data agree well with Strong suppression in p+p (data & pQCD) plus “Ncoll-scaling” central Au+Au collisions !
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)12/39
Suppressed high pSuppressed high pTT hadroproduction in central AuAu hadroproduction in central AuAu
Discovery of
high pT suppression(one of most significant results @ RHIC so far)
Ncoll scaling(“hard” production)
x5 suppression
Npart scaling (surface emission)
Very strong suppression (RAA ~ 0.2 !) up to pT ~ 10 GeV/c for π0 h±, well below incoherent scattering expectations for hard cross-sections
PHENIX Collab.PRL 88, 022301 (2002)nucl-ex/0109003[Run-2 data]
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)
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Hadrons are suppressed. Photons are not.Hadrons are suppressed. Photons are not.
Colorless hard probes (direct g insensitive to final-state) are unsuppressed.
Confirms that AuAu collision = incoherent sum of pp collisions (i.e. “Ncoll scaling” expectation is valid) for perturbative probes.
D.d'E, HP'04EJP C 43 (2005)295
PHENIX.PRL 94, 232301
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)
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Hadrons are suppressed in AuAu. Not in dAu.Hadrons are suppressed in AuAu. Not in dAu.
Initial-state cold nuclear matter effects (shadowing, Cronin) are small at RHIC mid-rapidity.
High pT suppression in central AuAu is due to final-state effects (absent in “control” dAu experiment)
D.d'E.,nucl-ex/0401001
PHENIX.PRL 91, 072303 (2003)
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)15/39
High pHigh pT T suppression: “Universal” for all light mesonssuppression: “Universal” for all light mesons
Common suppression pattern (magnitude, pT, centrality, ... dependence) for p0 and :
Same flat RAA ~ 0.2 up to 10 GeV/c
Universal suppression for light mesons indicates it is at partonic level prior to q,g fragmentation into leading meson according to vacuum FFs.
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)16/39
Magnitude of the suppression: medium propertiesMagnitude of the suppression: medium propertiesData vs. models (pQCD+ non-Abelian parton energy loss) comparison:
Initial gluon densities:
Opacities: <n> = L/ ≈ 3 – 4 [Levai et al.]
Transport coefficients:
Medium-induced radiative energy losses:
dE/dx ≈ 0.25 GeV/fm (expanding) dE/dx|eff ≈ 14 GeV/fm (static source) [X.N.Wang]
Very large gluon densities: dNg/dy~1000 consistent w/ measured dNch/dη ~700All medium properties imply energy densities >> ecrit QCD (assuming thermalizat.)
[BDMPS ] [Salgado-Wiedemann] [Dainese, Loizides ...] [Arleo]
dNg/dy ~ 1000 [Vitev & Gyulassy]
<q 0> ~ 14 GeV2/fm
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)17/39
High pHigh pT T suppression: psuppression: pTT-dependence-dependence
Flat pT- dependence described by parton energy loss models:
Underlying LPM interference for single gluon bremsstrahlung would give: DEloss ~ log(pT)
Combination of different effects (convolution w/ realistic gluon energy distribution, local parton pT slope, ...) yields constant suppression factor.
PQM – A. Dainese, C. Loizides, G. PaicEPJ C 38, 461(2005)
GLV – I. Vitev 2005
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)18/39
High pHigh pT T suppression: suppression: ÖÖs-dependences-dependence
Ös- dependence in agreement with parton energy loss in increasingly dense (expanding) medium:
D.d'E., HP'04EJP C 43 (2005)295
RAA ~ 1 @ Ös ~ 20 GeV Þ dNg/dy ~ 400 , <q0> ~ 3.5 GeV/fm2
RAA ~ 0.3 @ Ös = 62 GeV Þ dNg/dy ~ 650 , <q0> ~ 7 GeV/fm2
RAA ~ 0.2 @ Ös = 200 GeV Þ dNg/dy ~ 1100 , <q0> ~ 14 GeV/fm2
[Note: RAA @ SPS uses “revised” pp ref.]
Initial gluon density: Medium transport coeff.:
SPSRHICRHIC
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)19/39
High pHigh pTT meson suppression in AA meson suppression in AA @@ 17.3 GeV ? 17.3 GeV ?Revised pp reference: high pT π
0 production in (0-10%) central PbPb at SPS is slighted suppressed or consistent w/ “Ncoll-scaling” :
D.d'E. PLB 596, 32 (2004)
NA57, PLB62, 317 (2005)
Confirmed by NA57 (& NA49) recent high pT results in central PbPb at SPS:
NA49 (A. Lazslo, QM'05)
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)20/39
High pHigh pT T suppression: non-Abelian naturesuppression: non-Abelian nature
Excitation function (Ös-dependence) & non-Abelian nature of energy loss in agreement w/ parton energy loss calculations: (i) rising initial parton density with Ös (ii) increasing relative fraction of hard-scattered gluons (at fixed pT) with Ös
“Jet quenching” model + 2-D longitudinal plasma expansion
D.d'E. EJP C 43 (2005)295
Gluon: CA = Nc = 3Quark: CF =(Nc
2-1)/2Nc = 4/3
Relative fraction of q,g at pT = 5 GeV/c:
QCD radiation probability:
CA /CF=2.25}
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High pHigh pT T suppression: centrality dependencesuppression: centrality dependence
Increasing centrality (Npart) Þ increased L, r Þ increased suppression
Agreement data models as expected for diff. suppressions at different (geometrical) parton production points.
PQM – A. Dainese, C. Loizides, G. PaicEPJ C 38, 461(2005)X.N. Wang, PLB 2003
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High pT leading hadron spectra at RHIC & jet-quenching models:
Less good agreement data theory ?
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)23/39
High pHigh pT T suppression: ssuppression: system-size dependenceystem-size dependence
Smaller CuCu system adds significant precision at intermediate Npart~100:Theory predicts: ln(RAA) µNpart
-2/3
Both PHENIX & STAR preliminary data seem to exclude = -2/3Fit to STAR Npart
prefers ~ -1/3 (circumf./area ~ A-1/3 ~ Npart-1/3 ?)
PHENIX data seems to indicate a “steeper” slope at low Npart.Differences STAR PHENIX and PQM GLV still unclear at this point.
M. van Leeuwen, QM'05
C.Klein-Boesing, QM'05
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)24/39
High pHigh pT T suppression: path-length dependencesuppression: path-length dependence
2 times more suppression out-of-plane (“long” direction)
than in-plane (“short” direction).
Glauber parton energy loss model predicts only ~50% increased “out-of-plane” vs “in-plane” π0 emission
Azimuthal anisotropy stronger than “canonical” L2 (or L) path-length dependence.Source of extra azim. anisotropy above pT ~ 4 GeV/c ?
D = 0°
D = 90°
PRELIMINARY[B. Cole, S. Mioduszewski HP'04][D.d'E, EJP C 43 (2005) 295]
RAA vs φ w/ respect to reaction plane :
PQM – Dainese, Loizides, Paic EPJ C 38, 461(2005)
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)25/39
Heavy quark suppression viaHeavy quark suppression via non-photonic electrons (I)non-photonic electrons (I)
Semi-leptonic decays of open charm and bottom mesons = main source of high pT (“non-photonic”) electrons.
proton-proton baseline: Au+Au suppression
(Note: state-of-the-art theory underpredicts data)
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Heavy quark suppression viaHeavy quark suppression via non-photonic electrons (II)non-photonic electrons (II)
Latest single e± RAA indicates large suppression in central AuAu:
Note: STAR – PHENIX RAA agrees, but the pp refs are different by ~ 50%.
Peripheral AuAu
Central AuAu
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Heavy quark suppression viaHeavy quark suppression via non-photonic electrons (III)non-photonic electrons (III)
Theory expectations :
Quantitative predictions:
Models need larger medium densities: dNg/dy=3500, <q> = 14 GeV2/fm than for light mesons RAA to reproduce data ! Unclear consistency w/ dNch/dy ~ 600
M. Djordjevic et al., nucl-th/0507019
Armesto, Salgado, Wiedemann, QM'05
• Charm RAA = 0.2 - 0.3• Beauty RAA = 0.4 - 0.6
DEloss(g) > DEloss(q) > DEloss(Q) (color factor) (mass effect)
22QQ
2 ])/([1Em
Gluonsstrahlung probability
“Dead cone”: g rad. suppressed at < mQ/EQ
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Heavy quark suppression viaHeavy quark suppression via non-photonic electrons (IV)non-photonic electrons (IV)
Models need too dense medium to account for observed suppression in data:
Possible resolutions of the disagreement (or a combination of them ?):(1) Larger suppression of beauty …or charm dominance up to electron pT ≈ 10 GeV?(2) Extra gluon-fragmentation production of charm affected by energy loss ? (would also
explain PHENIX proton-proton data ?)
(3) Hadronic (+ partonic) energy loss ?(4) Radiative + collisional energy loss ? Other ... ?
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High pT di-hadron φ,η correlations in high-energy AuAu collisions
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)30/39
““Jet physics” at RHIC (II): di-hadron azimuthal correlationsJet physics” at RHIC (II): di-hadron azimuthal correlations
Study the azimuthal correlations in AA relative to pp between the highest pT hadron (“trigger”) & any other “associated” hadron:
Many interesting results obtained from this “2nd-order” approach !
p+p ® h1+h2+ X [Ös = 200 GeV] Au+Au ® h1+h2+ X [ÖsNN = 200 GeV]
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)31/39
3-5 GeV/c d+Au
Near-side
away-side
Dijets via high pDijets via high pTT di-hadron di-hadron φφ correlations: pp, dAu correlations: pp, dAu
Two-particle correlations: h±- – h±, p0,± – h±. Trigger: highest pT (leading) hadron.
Associated D distribution (e.g. ”assorted”: 2 GeV/c < pTassoc < pT
trigger)
Normalized to number of triggers:
d+Au (cent, MB) p+p
2-3 GeV/c
p+p
Preliminary d+Au
p+p
pTassoc = 2-3 GeV/c pT
assoc = 3-5 GeV/c
Clear near- (D ~ 0) and away- (D ~ p) side jet signals
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)32/39
Dijets via high pDijets via high pTT di-hadron di-hadron φφ correlations: AuAu correlations: AuAu
Same dNpair/dφ analysis as in pp (dAu) but 2 extra “complications”: (1) Increased “underlying event” background (2) Collective elliptic flow (harmonic) contribution
Ajitanand, ICPAQGP'04and nucl-ex/0501025
Delicate subtraction procedure (esp. in finite acceptances).
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)33/39
Di-hadron AuAu Di-hadron AuAu ΔφΔφ correlations: Results at high p correlations: Results at high pTT
Centrality dependence of away-side disappearance globally described by parton energy loss models (increasing medium traversed):
STAR, PRL 90, 082302 (2003) pT trigg = 4 – 6 GeV/cpT assoc > 2 GeV/c
Away-side peak disappearance: “monojet”-like topologies in central AuAu.
Near-side jet-like Gaussian peak unmodified (AuAu ~ dAu ~ pp)
PQM – A. Dainese, C. Loizides, G. PaicEPJ C 38, 461(2005)
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Di-hadron AuAu Di-hadron AuAu ΔφΔφ correlations: Results at lower p correlations: Results at lower pTT
W.Holtzman, RIKEN-Corrs. Workshop '05
“Lost” away-side energy is recovered at lower pT values. Strongly modified away-side D correlations in central AuAu:
“peak”“dip”
Std. away-side Gaussian peak
Preliminary
Away-side (p) “dip” and excess of energy (“double peak”) at: PHENIX: p 1.3 rad STAR: p 1.1 rad
Au+Au periph
Au+Au central
PHENIX, PRLsubmitted, nucl-ex/0507004
“peaks”
pT trigg = 4 – 6 GeV/cpT assoc = 0.15 – 4 GeV/c
STAR, PRL95,152301(05)nucl-ex/0501016
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)35/39
33.0)(1
sf
avs cdc
““Double peak” = Mach wave cone ?Double peak” = Mach wave cone ?
Double peak structure at at p 1.2 rad reminiscent of Mach wave conical shock (“sonic boom”) Þ speed of sound accessible
Note: gluon Cerenkov-like emission also proposed [access to medium index refrac. n=1/cos(c)]
Caveats:
cos M sc
M Trigger
Stoecker, Satarov, Mishutin, hep-ph/0505245.Casalderrey, Shuryak, Teaney, hep-ph/0411315.
Mach cone:
= arccos(cavs) = 1.2 rad = 71º
c2s ¹ constant:
QGP (1/ Ö3) ® phase transition (0.) ® HRG (Ö0.2) :
~ exp
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d+Au, 40-100%
Au+Au, 0-5%
STAR preliminary
3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig)[D. Magestro, HP'04]
Di-hadron Di-hadron DD correlations: AuAu, dAu, pp (I) correlations: AuAu, dAu, pp (I)
Significant broadening of near-side pseudorapidity correlations in AuAu compared to pp, dAu. (“stretching” of jet cone along η).
STAR preliminary p+p
Au+Au, 0-5%
near-side width
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)37/39
d+Au, 40-100%
Au+Au, 0-5%
STAR preliminary
3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig)
Armesto, Salgado, WiedemannPRL 93, 242301 (2004)
Di-hadron Di-hadron DD correlations: AuAu, dAu, pp (II) correlations: AuAu, dAu, pp (II)
Significant broadening of near-side pseudorapidity correlations in AuAu compared to pp,dAu. (“stretching” of jet cone along η).
Coupling of g radiation w/ longitudinal expanding medium ?
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)38/39
““Cartoon” Summary: Jet-quenching at RHIC Cartoon” Summary: Jet-quenching at RHIC
Jet profile in pp (dAu) collisions: Jet profile in AuAu central collisions:
D
D ° D
D °
Near-side width: <jT> ~ 600 MeV/cunmodified in pp,dAu
Away-side width and acoplanarityunmodified in pp and dAu
Factor ~5 suppression of leading hadron(very large initial parton densities: dNg/dy~1000)
Disappearance of back-to-back peak (“monojets”)“Double peak” structure at lower pT in away-side(“sonic boom” in medium ?)
Dijet broadening in η (coupling of g radiation w/ expanding medium ?)
Strong QCD medium effects at work !
“QCD vacuum” & “cold QCD medium” “hot & dense QCD Medium”
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SummarySummary
Large amount of precision high-pT hadron production data after 5 years of operation at RHIC allows to quantitatively address jet physics in QCD
medium (w/o full jet reco).
Differential observ. of suppressed hadro-production in central Au+Au provide: - stringent constraints on underlying quenching mechanism. - direct access to the density & transport properties of QCD medium.
Are “jet quenching” data due to radiative energy loss in a QGP ?
Good agreement with calculations on: Leading hadrons: Magnitude, √s, pT, centrality, (light) species dependence Dihadron correlations: disappeareance of away-side azimuthal dijet peak,
Broadening of near-side pseudo-rapidity correlations. Some tests are weak at present:
Few details missing in system-size dependence No sharp test of L2 dependence yet. Heavy quark energy loss larger than expected
New insights of medium properties from new observables (cs via “Mach cone”) ?LHC = enormous reach, qualitatively new observ. (full jet reco, jet-jet, jet-g,Z ...)
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)40/39
backup slides ...
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Di-jet properties: experimental observablesDi-jet properties: experimental observables
Spread of hadrons around jet axis, relative orientation of the 2 jets: jT, kT, pout
Multiplicity of assoc. hadrons (area under peaks): “fragmentation function” D(z)
hadron
hadron
Δφ
Jet “width” jT
Di-jet acoplanarity kT
: total of parton pairTy Tk p
Tk : of hadron to jet axisTy Tj pTj
parton
parton
near-side away-sideD
nearfar
µTy nearj
2 2µ -T fary neark
[see e.g. J.Jia, nucl-ex/0409024]
D(z), z=p/ptot “Fragmentation function”
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““Fragmentation functions”: Central AuAuFragmentation functions”: Central AuAu
syst. errorAway side:
softening of spectra from pp to central Au+Au
energy from initial parton converted to
low pT particles.
energy loss inmedium!
Associated (pT assoc = 0.15 – 4 GeV/c) near- and away- side hadron pT spectra:
Associated near-side jet yields overall enhanced (enhanced underlying evt.)Associated away-side jet yields “shifted down” in pT: spectra closer to pure “soft” inclusive hadron production (“thermalized”)
Near-side Away-side
pT trigg = 4 – 6 GeV/cpT assoc = 0.15 – 4 GeV/c
STAR, submitted to PRLnucl-ex/0501016
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Jet production in AA : (a few) theoretical expectationsJet production in AA : (a few) theoretical expectations
Mono-jets:Jet broadening in η:
X.N.Wang&M.Gyulassy PRL 68, 1480 (1992)
Armesto et alhep-ph/0405301
Leading hadron suppression:
Valuable diagnostic tools of QCD medium properties (dNg/dy, <q0>, cs, ...)
Medium-modified FFs:
"Mach cone":
X.N.Wang;A. Majumder,Salgado&Wiedem.Arleo, ...
Bjorken, 1982
dNpair/dφ dNpair/dη
dN/dpT
M Trigger
dN/dzT
cos M sc
Stoecker et al. hep-ph/0505245.Casalderrey, Shuryak, hep-ph/0411315
nucl-th/0302077
Nchjet increases
<zjet> decreases
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Intermediate pIntermediate pT T mesons suppressed. Baryons are notmesons suppressed. Baryons are not
Strongly enhanced baryon (p, L) production at pT ~ 2 – 4 GeV/c
Strong centrality dependent baryon/meson: ratio well above “perturbative” (pp) ratios.
Clear deviation from std. vacuum fragmentation functions (large non-pQCD effects) calls for extra baryon production mechanism: recombination.
Above pT ~ 6 GeV/c: Recovery of “vacuum” fragmentation ratio. Baryons suppressed too.
L/K
0 s
Au+Au 0-5%
p+p
Au+Au 0-10%
p+p
Lamont, QM'05
O.Barannikova, QM'05
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Baryon vs. meson “fragmentation functions”Baryon vs. meson “fragmentation functions”
However ... Associated yields similar for meson & baryon triggers.
Magnitude and centrality-dependence of associated (near- & away- side) hadron pT spectra for baryon & meson triggers show small differences.
Jet-like production but different suppression for leading baryons and mesons !?
PRC 71, 051902 (2005)
Near-side
Away-side
pT trigg= 2.5 – 4 GeV/cpTassoc = 1.7 – 2.5 GeV/c
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How to compare high pT spectra in AA and pp ?
High pT particles issue from hard scatterings describable by pQCD:
A
B
AB
dAB → hard = A·B·dpp → hard
dNAB → hard (b) = TAB(b)·dpp → hard
Nuclear Modification Factor:
ABAt impact parameter b:
geom. nuclear overlap at b production is “shadowed”TAB ~ # NN collisions (“Ncoll scaling”)
“Factorization theorem”:
Independent scattering of “free” partons:
A+B = “simple superposition of p+p collisions”
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High pHigh pT T suppression: ssuppression: system-size dependenceystem-size dependence
RAA for Cu+Cu @ √sNN = 200 GeV
• Suppression observed for central Cu+Cu• Models scale density from central Au+Au
All models show reasonable to good agreement
STAR preliminaryCharged hadrons
M. van Leeuwen (STAR), QM'05M. Shimomura (PHENIX), QM'05
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PHENIX Preliminary
Di-hadron AuAu: Di-hadron AuAu: ΔφΔφ correlations (III) correlations (III)
Same dNpair/dD result in polar coords. now:
Strongly non-Gaussian away-side “peak”.
Standard back-to-back di-jet topology.
Au+Au peripheral
Au+Au central
PHENIX Collab. PRL to be submitted
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)49/39
Jet production in the “QCD vacuum” (pp collisions)Jet production in the “QCD vacuum” (pp collisions)
Jet : Collimated spray of hadrons in a cone ( ~ 0.7) with 4-momentum of original fragmenting parton
Leading hadron takes away large fraction (<z> ~0.6 –0.8 @ RHIC) of parent parton pT
Jet balanced back-to-back by other hard-scattered "parton" (jet, direct g, ...) A (small) acoplanarity appears due to intrinsic kT (parton Fermi motion).
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Jet production in “QCD media” (pA, AA collisions)Jet production in “QCD media” (pA, AA collisions)
kT broadening (Cronin enhancement)
(Leading-twist) shadowing or gluon saturation (CGC)
Final-state effects
Parton energy loss due to medium-induced gluon-strahlung in hot & dense environment
Initial-state effects (accessible via pA colls.):
(accessible in AA colls.):
IPN-Orsay, Nov 14th, 2005 David d'Enterria (LLR, Paris)51/39
““Fragmentation functions”: xFragmentation functions”: xEE distributions pp,dAu distributions pp,dAu
Þ Dqp(z)~e-6z
• independent of pTt
<ztrig>=0.85 measured*Away-side associated hadron pT spectra:
xE ~ z/<ztrig> represents away jet fragmentation z
xE variable: Two-particle equivalent of fragmentation variable z
At high pT, i.e. when di-jets are nearly back-to-back.
)(1
assoctrigassoctrig
trig
Etrig
zDzdzdN
Nz
dxdN
N