production @
DESCRIPTION
production @. Ro. Robert Pak. f or PHENIX Collaboration. Knobs to turn: Centrality, N part Collision energy, √ s NN In-medium path length, L, using event plane Observables: x T scaling of invariant yield Nuclear modification factor, R AA Fractional momentum loss, S loss - PowerPoint PPT PresentationTRANSCRIPT
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WWND 2013 1Robert Pak (BNL)
production @
Ro
Robert Pak
for PHENIX Collaboration
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WWND 2013 2
• Knobs to turn:– Centrality, Npart
– Collision energy, √sNN – In-medium path length, L, using event plane
• Observables:– xT scaling of invariant yield– Nuclear modification factor, RAA
– Fractional momentum loss, Sloss
– Elliptical flow, v2
• Model comparisons• Summary• Acknowledgements
Robert Pak (BNL)
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WWND 2013 3
p0 invariant mass
Robert Pak (BNL)
PRC 80, 054907 (2009)
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WWND 2013 4
h-meson to p0 ratio
Robert Pak (BNL)
arXiv:1208.2254v2
• For constant fit to min. bias data: h/p0 = 0.45 +/- 0.01
• Similar to d+Au (0.47 +/- 0.03) and p+p (0.48 +/- 0.03)
• Lack of nuclear effects at high pT indicates fragmentation occurs outside the medium
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WWND 2013 5
p0 invariant yields
Robert Pak (BNL)
PRL 101, 232301 (2008)
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WWND 2013 6
xT = 2pT/√s scaling
Robert Pak (BNL)
In hard scattering region:
universal scaling function
For isolated photons from p+p collisions in Bjorken’s parton model:
neff = constant = 4.0
PRD 86, 072008 (2012)
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WWND 2013
xT scaling (cont)
Robert Pak (BNL) 7
In pQCD contributions from:• running as(Q2) • PDF (and FF) evolutionOther effects:• kT smearing• higher-twist phenomena
So neff not constant, rather:
Largest deviation for 39 and 200 GeV Au+Au comparison hard scattering not dominant source of high pT p0 in 39 GeV Au+Au collisions
to compare different beam energies.
PRL 109, 152301 (2012)
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WWND 2013 8
nuclear modification factor - RAA
Robert Pak (BNL)
PRL 101, 162301 (2008)
n.b., RAA requires p+p reference data at corresponding √s.
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WWND 2013 9
q̂ from PQM
Robert Pak (BNL)
PRC 77, 064907 (2008)
Early attempt to extract transport coefficient q̂ using a parton quenching model
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WWND 2013 10
arXiv:1208.2254v2
more recent p0 invariant yields
Robert Pak (BNL)
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WWND 2013 11Robert Pak (BNL)
RAA @ 200 GeV
arXiv:1208.2254v2
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WWND 2013 12
fit the data
Robert Pak (BNL)
Above Npart = 167 slope of linear fit is significantly different from zero
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cf., ALICE
Robert Pak (BNL)
• Similar suppression for 14x increase in colliding energy at LHC ~2x increase in parton density at LHC
• Slope in PHENIX data comes as no surprise
arXiv:1208.2711v1
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WWND 2013 14
fractional momentum shift
Robert Pak (BNL)
Partons in 200 GeV collisions suffer largest average momentum loss
PRL 109, 152301 (2012)
arXiv:1208.2254v2
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WWND 2013 15
Sloss (= dpT/pT) vs. centrality
Robert Pak (BNL)
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WWND 2013 16
Sloss @ PHENIX, cf., ALICE
Robert Pak (BNL)
arXiv:1208.2254v2
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WWND 2013 17
model comparisons
Robert Pak (BNL)
• AMY: Arnold, Moore & Yaffe, JHEP 0206, 030 (2006)
• HT: X.N. Wang & X. Guo,NPA 696, 788 (2001)
• ASW: Salgado & Wiedemann,PRD 68, 014008 (2003)
• Parton energy loss models incorporated into same 3D hydro calculation
• No distinguishing power despite differences in q̂
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Robert Pak (BNL) WWND 2013 18
pseudorapidity
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Robert Pak (BNL) WWND 2013 19
flowparticipants
spectators
• More recently, generalized eccentricities for higher flow moments:
• Measured values must be corrected by event plane resolution:
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WWND 2013 20
RAA vs. event plane
Robert Pak (BNL)
arXiv:1208.2254v2
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WWND 2013 21
centrality dependence
Robert Pak (BNL)
3.4 fm
6.1 fm
6.7 fm
5.9 fm• Suppression increases
with centrality• In-plane suppression
less than out-of-plane• Average path length in
medium changes more in-plane than out-of-plane difference in RAA becomes larger as centrality decreases
• All in agreement with: PRC 80, 054907 (2009)
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WWND 2013 22
RAA vs. event plane, cf., hydro models
Robert Pak (BNL)
arXiv:1208.2254v2Greater sensitivity in-plane:
cubic L dependence
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WWND 2013 23
in-medium path length dependence
Robert Pak (BNL)
PRL 105, 142301 (2010)
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WWND 2013 24
more hydro comparisons
Robert Pak (BNL)
Majumder & C. ShenPRL 109, 202301 (2012)
Progress extracting q̂ for comparison to LHC
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WWND 2013 25
mesons
baryons
Robert Pak (BNL)
PRL 98, 162301 (2007)
same mass scaling pattern as seen in 200 GeV Au+Au collisions
√sNN dependence of PID v2
preliminary preliminary
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WWND 2013 26Robert Pak (BNL)
quark number (nq) scaling indicates partonic collective flow down to 39 GeV
Phys. Rev. Lett. 98, 162301 (2007)
mesons
baryons
PID v2/nq
preliminary preliminary
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more recent PID v2
Robert Pak (BNL)
PRC 85, 064914 (2012)
• New TOF patch installed to extend PID
• quark number scaling breaks down at higher pT
Au+Au √sNN = 200 GeV
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Summary
• Onset of hard processes at high pT from xT scaling • Onset of suppression from RAA vs √sNN
– PHENIX data provides a bridge to RAA @ LHC
• Sloss (= dpT/pT) increases with Npart and √sNN
• In-medium path length dependence > L2 for parton energy loss
• Progress to extract q̂ through model comparisons• From PID collective flow in Au+Au collisions:
– partonic flow (with perfect fluidity) down to 39 GeV– quark number scaling breaks down at higher pT
Robert Pak (BNL)
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WWND 2013 29Robert Pak (BNL)