production @

WWND 2013 1Robert Pak (BNL)

production @

Ro

Robert Pak

for PHENIX Collaboration

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)

WWND 2013 3

p0 invariant mass

Robert Pak (BNL)

PRC 80, 054907 (2009)

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

WWND 2013 5

p0 invariant yields

Robert Pak (BNL)

PRL 101, 232301 (2008)

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)

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)

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.

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

WWND 2013 10

arXiv:1208.2254v2

more recent p0 invariant yields

Robert Pak (BNL)

WWND 2013 11Robert Pak (BNL)

RAA @ 200 GeV

arXiv:1208.2254v2

WWND 2013 12

fit the data

Robert Pak (BNL)

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

WWND 2013 13

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

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

WWND 2013 15

Sloss (= dpT/pT) vs. centrality

Robert Pak (BNL)

WWND 2013 16

Sloss @ PHENIX, cf., ALICE

Robert Pak (BNL)

arXiv:1208.2254v2

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

Robert Pak (BNL) WWND 2013 18

pseudorapidity

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:

WWND 2013 20

RAA vs. event plane

Robert Pak (BNL)

arXiv:1208.2254v2

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)

WWND 2013 22

RAA vs. event plane, cf., hydro models

Robert Pak (BNL)

arXiv:1208.2254v2Greater sensitivity in-plane:

cubic L dependence

WWND 2013 23

in-medium path length dependence

Robert Pak (BNL)

PRL 105, 142301 (2010)

WWND 2013 24

more hydro comparisons

Robert Pak (BNL)

Majumder & C. ShenPRL 109, 202301 (2012)

Progress extracting q̂ for comparison to LHC

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

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

WWND 2013 27

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

WWND 2013 28

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)

WWND 2013 29Robert Pak (BNL)