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Robert Pak (BNL) WWND 2013 0

production @

Ro

Robert Pak

for PHENIX Collabora0on

•  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


π0 invariant mass


PRC 80, 054907 (2009)

η-meson to π0 ratio


arXiv:1208.2254v2

•  For constant fit to min. bias data: η/π0 = 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

π0 invariant yields


PRL 101, 232301 (2008)

xT = 2pT/√s scaling


E d3!dp3

=1

sneff xT , s( )

G(xT )

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)

xT scaling (cont)


neff xT( ) =log Yield xT , s1( ) Yield xT , s2( )( )

log s2 s1( )

In pQCD contributions from: •  running αs(Q2) •  PDF (and FF) evolution Other 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 π0 in 39 GeV Au+Au collisions

to compare different beam energies.

PRL 109, 152301 (2012)

nuclear modification factor - RAA


PRL 101, 162301 (2008)

n.b., RAA requires p+p reference data at corresponding √s.

q ̂from PQM


PRC 77, 064907 (2008)

Early attempt to extract transport coefficient q ̂using a parton quenching model

arXiv:1208.2254v2

more recent π0 invariant yields


Robert Pak (BNL)

RAA @ 200 GeV

WWND 2013 10

arXiv:1208.2254v2

fit the data


Above Npart = 167 slope of linear fit is significantly different from zero

cf., ALICE


•  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

fractional momentum shift


Partons in 200 GeV collisions suffer largest average momentum loss

PRL 109, 152301 (2012)

arXiv:1208.2254v2

Sloss (= δpT/pT) vs. centrality


Sloss @ PHENIX, cf., ALICE


arXiv:1208.2254v2

model comparisons


•  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 q ̂


pseudorapidity


flow participants

spectators

•  More recently, generalized eccentricities for higher flow moments:

•  Measured values must be

corrected by event plane resolution:

RAA vs. event plane


arXiv:1208.2254v2

centrality dependence


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)

RAA vs. event plane, cf., hydro models


arXiv:1208.2254v2 Greater sensitivity in-plane:

cubic L dependence

in-medium path length dependence


PRL 105, 142301 (2010)

more hydro comparisons


Majumder & C. Shen PRL 109, 202301 (2012)

Progress extracting q ̂for comparison to LHC

mesons

baryons


PRL 98, 162301 (2007)

same mass scaling pattern as seen in 200 GeV Au+Au collisions

√sNN dependence of PID v2

preliminary preliminary


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

more recent PID v2


PRC 85, 064914 (2012)

•  New TOF patch installed to extend PID

•  quark number scaling breaks down at higher pT

Au+Au √sNN = 200 GeV

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 (= δpT/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


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