high-pt probes of the quark-gluon plasma: star/phenix results at rhic
DESCRIPTION
High-pt probes of the quark-gluon plasma: STAR/PHENIX results at RHIC. Craig Ogilvie, Iowa State University. What happens to a high-pt parton as it travels through a quark-gluon plasma (QGP)? What does this tell us about the QGP? Not much time on how QGP responds to the hard parton. - PowerPoint PPT PresentationTRANSCRIPT
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High-pt probes of the quark-gluon plasma: STAR/PHENIX results at RHIC
Craig Ogilvie, Iowa State University
1. What happens to a high-pt parton as it travels through a quark-gluon plasma (QGP)?
2. What does this tell us about the QGP? 3. Not much time on how QGP responds to the hard parton.
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Craig Ogilvie [email protected] 2
QCD Phase Diagram
Within sQGP, momentum transfers ~ T ~ few 100 MeV/c => coupling large
Non-peturbatively interacting plasma of quarks and gluonsfar from an ideal gas
strongly coupled QGP
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Sep 22, 2008 Craig Ogilvie 3
One way to probe the sQGPhard-scattered
parton during Au+AuHadron distribution changed
- singles spectra-2-particle correlations- jet-structure
Information on the plasma?
parton loses energywithin plasma
hard-scattered parton: calc. with perturbative QCD
high pt
jet of hadrons
p p
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Hard-scattering as a calibrated probe
Large scale that makes perturbative QCD applicable: high momentum transfer Q2
Assume factorization between perturbative hard part universal, non-perturbative
parton distribution functions (fA, fB) fragmentation (Dh/c) functions
from e++e-, p+p….
Sep 22, 2008 Craig Ogilvie 4
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Sep 22, 2008 Craig Ogilvie 5
√s=200 GeV, p+p => x NLO QCD agrees well with data
D. d’Enterrianucl-ex/0611012
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Sep 22, 2008 Craig Ogilvie 6
Partons lose energy as they travel through QGP 0 spectra at √s=200 GeV
Phys.Rev.C76:034904,2007PHENIX
p+p cross-section scaled by # of nucleon collisions in Au+Au Fewer high-pt 0 in Au+Au
Energy-lost by parton => info on opacity, density of QGP
Eloss
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Sep 22, 2008 Craig Ogilvie 7
Au+Au 0 RAAS
uppressed
Enh
ance
d
)(/)(/
ppdpdNNAuAudpdNR
collAA
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Elliptic asymmetry at high-pt
Sep 22, 2008 Craig Ogilvie 8
ddn
2v2
Asymmetry, v2, dN/d=A(1+2v2*cos(2))
Overlap zone is elliptical:
More energy-lost if parton travels through long-direction of ellipse
Fewer high-pt hadrons out-of-plane
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Sep 22, 2008 Craig Ogilvie 9
Particles correlated with high-pt trigger
A+A
Correlation survives high-multiplicity environment of A+A
p+p, PHENIXPRD, 74 072202 (06).
STAR PRL 97 (2006) 162301 = 1-2
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Suppression of far-side hadrons
Sep 22, 2008 Craig Ogilvie 10
Trigger particle
Far-side particle
Far-side yield per triggersensitive to relative energy lost by both partons=> Alphabet of observables, D(zT), IAA, JAA, …
STAR PRL 97 (2006) 162301
8 < ptrig <15 GeV/c
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Use measurements to learn about QGP
Wiedermann: models of gluon radiation, transport parameter Note
Hard-scattering takes place throughout collision volume Data and models average over wide range pathlengths…
Medium expands rapidly Parton travels through a medium whose density decreases
Sep 22, 2008 Craig Ogilvie 11
Scattering power of the QCD medium:path freemean
ed transferrmomentumˆ2
q
q̂
q̂
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Sep 22, 2008 Craig Ogilvie 12
Comparison data + models (e.g. PQM)
fm
2 GeV1.22.3 2.13ˆ q But no model uncertainty yet
Vary transport parameter q̂
PRC 77, 064907 (2008)
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Sep 22, 2008 Craig Ogilvie 13
Strong energy-loss
Experimentalist’s reaction:
1) Reduce averaging over path-length
2) Other observables to check understanding of energy-loss
RHIC data
Pion gas
perturbative
interacting QGP
Cold nuclear matter
R. Baier NPA715 209c
Large <q>
=> high momentum transfer => strong QGP coupling
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Change average over path-length: RAA versus reaction plane
Sep 22, 2008 Craig Ogilvie 14
Model T. Renk, vary Eloss PHENIX prelim centrality 20-30% 0 6<pt<7 GeV/c
Overlap zone is elliptical:
More energy-lost as parton travels through long-direction of ellipse
RAA smaller out-of-plane
This and other models fail, yet reproduce RAA vs pt1.Need stronger variation of Eloss for different paths, or2.Sharper early spatial distribution of energy density, or3.More rapid variation of q with , or ……
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Test for other mechanisms of energy-loss:
Sep 22, 2008 Craig Ogilvie 15
S.Wicks, W. Horowitz, M. Djordjevic M. Gyulassy (WHDG) nucl-th/0512076
Radiationdue to scattering
Elastic collision,energy re-distribution
Many calcs on relative importance
Probe via high-pt heavy-quarks• smaller energy loss after elastic collision• gluon radiation also reduced
interference during radiationdead-cone effect
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Heavy-Quark Energy-loss
Sep 22, 2008 Craig Ogilvie 16
Semi-leptonic decays of charm beauty mesons, R. Averbeck
Strong suppression of high-pt charm
PRL98, 172301 (2007)
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Radiative+collisional energy-loss models struggle
Sep 22, 2008 Craig Ogilvie 17
STAR Phys. Rev. Lett. 98 (2007) 192301
Note, BDMPs charm only, may not be realistic to remove beauty
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Strong resonance interaction in-medium
Sep 22, 2008 Craig Ogilvie 18
Heavy-quarks may form resonances in sQGP near Tc
H. van Hees et al, PRL 100, 192301 (2008)
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Oct 3, 2007 Craig Ogilvie 19
Separation charm/beautyPHENIX VTX, STAR HFT
silicon pixel+strip detectorsTracks extrapolate back to collision
Displaced vertices => charm (D), beauty (B)
Requires ~ 50 m precision
De+X Au
e
Au
X
B e+X
X e
Great hardware opportunity for post-docs
Next Steps Conclusion
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Medium Response: Low-pt far-side
Sep 22, 2008 Craig Ogilvie 20
Hard-scattering
Energy-loss
Medium response
trigger
STAR arXiv:0805.0622v1, PHENIX PRL 98, 232302 (2007)
Trigger: 3 < pT < 4 GeV/c Assoc: 1 < pT < 2 GeV/c,
Growing evidence for conical medium responseSTAR: 3-particle correlationsPHENIX :angle of conical emission independent of pt
=> not bremstrahlung
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No clean separation between medium-response and fragmentation?
Sep 22, 2008 Craig Ogilvie 21
Shocked medium contributesto fragmentation
e.g. coalescence of protons from shower+medium partons
=> Additional high-pt protonsR. Hwa
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Protons
Fragmentation to protons enhanced by combining with shocked medium?
and/or As parton propagates in medium it can change flavor
=> energy-loss comparable for gluons and quarks,
Sep 22, 2008 Craig Ogilvie 22
RA
A Au+
Au
cent
ral 0
-12%
More protons than pions at high-pt, even out to 10 GeV/c
Liu, W. and R.J. Fries, PRC 2008. 77 054902
Conclusion
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Next Steps (I/III): Excitation Function
Does q return to perturbative QCD at LHC?
Evaluate q at SPS (in progress)
Low-E RHIC, onset of strong opacity?
Sep 22, 2008 Craig Ogilvie 23
Pion gas
perturbative
interacting QGP
Cold nuclear matter
RHIC LHC?
SPS?
Conclusion
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sNN Dependence: pT Dependence of 0 RAA in Cu+Cu
62.4, 200 GeV: Suppression consistent with
parton energy loss for pT > 3 GeV/c
22.4 GeV: No suppression Enhancement consistent with
calculation that describes Cronin enhancement in p+A
Parton energy loss starts to prevail over Cronin enhancement between 22.4 and 62.4 GeV
PHENIX, arXiv:0801.4555 [nucl-ex]
ConclusionSep 22, 2008 24Craig Ogilvie
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Next Steps (II/III) Measure E directly
Sep 22, 2008 Craig Ogilvie 25
q
qg
γ q
q g
γ
Compton Annihilation
Direct to tag energy
RHIC-II, LHC
Conclusion
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Next Steps (III/III): Fragmentation within jet Jets with pt-cut off
Higher-pt => LHC, RHIC-II
Sep 22, 2008 Craig Ogilvie 26
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Conclusion Energy-loss as high-pt parton travels through QGP
Opaqueness parameter, momentum transferred/length larger than expected pQCD, => strongly coupled QGP
Puzzles RAA vs , modeled Eloss too flat => stronger spatial variation? Large heavy-flavor Eloss => quasi-resonances near Tc? Proton RAA closer to 1 => shocked medium recombining?
Next steps Excitation function of , LHC, SPS, low-E RHIC Eloss via -h and reconstructed jets
Sep 22, 2008 Craig Ogilvie 27
q̂
q̂
q̂
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Sep 22, 2008 Craig Ogilvie 28
Backup
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Protons in jets
For each proton trigger, number of mesons starts to decrease Additional source of protons, e.g. from medium response
Sep 22, 2008 Craig Ogilvie 29
proton trigger particlewith N mesons on near side
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Sep 22, 2008 Craig Ogilvie 30
Ratio of (Au+Au)/(scaled p+p spectra)
Mesons suppressed 5 → energy-lost in QGP scale with parton flux
Drop possibly due to isospin difference p+p and A+A
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RAA 0, , , J/, Mesons and Direct
Same suppression pattern for 0 and : parton energy loss and fragmentation in the vacuum
RAA for ‘s larger than 0 RAA for 2 < pT < 5 GeV/c
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Sep 22, 2008 Craig Ogilvie 32
Fate of Gluons
Nathan Grau, Hua Pei
Do radiated gluons produce broader jet?
parton loses energywithin plasma
Jets broader in Cu+Cu than p+p Fragmentation of induced gluon radiation?
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Sep 22, 2008 Craig Ogilvie 33
Far-side Production of Particles
Observation of particles produced~1 radian away from back-to-back!
Fit with 2 Gaussians, each D radians away from D scales with system size => emission consistent with medium’s response to jet
centrality
PHENIX preliminarynucl-ex/0611019
1<pt,ass<2.5<pt,trig<4 GeV/c
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Sep 22, 2008 Craig Ogilvie 34
Response of medium to passage of high-pt parton
Near-side, generation of ridge => strength large (STAR talk) Far-side: does super-sonic parton generate a mach-cone ?
3 < pt,trigger < 4 GeVpt,assoc. > 2 GeVAu+Au 0-10%
preliminary
hep-ph/0410067; H.Stocker…Jorge Casalderry-Solana
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Conical? flow – QM08: B. Cole
Cone? angle does not change appreciably as a function of pT of trigger or associated hadron. Or centrality, or angle wrt reaction plane
STAR Preliminary
Con
e an
gle
(rad
ians
)
pT (GeV/c)
Beware: PHENIX measurement from 2 particle, STAR 3 particle
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Sep 22, 2008 Craig Ogilvie 36
Baseline p+p 0 spectra compared to pQCD
•parton distribution functions, for partons a and b•measured in DIS, universality
•perturbative cross-section (NLO)•requires hard scale•factorization between pdf and cross section
•fragmentation function•measured in e+e-
),(
)(ˆ
),(),(
2/
2/
2/
zD
dcba
xfxfd
c
bAbaAa
Phys. Rev. Lett. 91, 241803 (2003)
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Fragmentation within jet: J. Putschke
Sep 22, 2008 Craig Ogilvie 37
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Strongly Interacting QGP
Sep 22, 2008 Craig Ogilvie 38
S. Gupta QM08
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LHC predictions: Xin-Nian Wang
Sep 22, 2008 Craig Ogilvie 39
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Steffen A. BassJet Energy-Loss in a 3D
Hydrodynamic Medium #40
Quantitative Comparison: Stefan Bass
öq öq0 with
TT0
3
,0
3/ 4
,ss0
define local transport coefficient along trajectory for all three approaches and compare initial maximum value q0:
for ASW, use Baier formula:
For AMY use: öq0 2K 0
34
q0 [GeV2/fm]
ASW HT AMY
T 10 2.3 5.5 20 4.5 Xs 3.4 X
(all values quoted for a gluon jet)
different medium scaling can affect q by a factor of 2need higher precision data and theory advances to provide guidance for proper
medium scaling
öq0 C
g 2
4
T0
3 8 169