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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High-pt probes of the quark-gluon plasma: STAR/PHENIX results at RHIC
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 Presentation
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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.
hard-scattered parton: calc. with perturbative QCD
high pt
jet of hadrons
p p
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
Sep 22, 2008 Craig Ogilvie 5
√s=200 GeV, p+p => x NLO QCD agrees well with data
D. d’Enterrianucl-ex/0611012
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
Sep 22, 2008 Craig Ogilvie 7
Au+Au 0 RAAS
uppressed
Enh
ance
d
)(/)(/
ppdpdNNAuAudpdNR
collAA
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
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
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
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
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)
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
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 ……
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
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)
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
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)
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
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)
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
Sep 22, 2008 Craig Ogilvie 28
Backup
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
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
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
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?
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
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 ?