production - wayne state universityrhic.physics.wayne.edu/~bellwied/wwnd2013/wwnd2013-pak.pdfsummary...

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

Robert Pak (BNL) WWND 2013 1

π0 invariant mass

Robert Pak (BNL) WWND 2013 2

PRC 80, 054907 (2009)

η-meson to π0 ratio

Robert Pak (BNL) WWND 2013 3

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  

Robert Pak (BNL) WWND 2013 4

PRL 101, 232301 (2008)

xT = 2pT/√s scaling

Robert Pak (BNL) WWND 2013 5

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)

Robert Pak (BNL) WWND 2013 6

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

Robert Pak (BNL) WWND 2013 7

PRL 101, 162301 (2008)

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

q ̂from PQM

Robert Pak (BNL) WWND 2013 8

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) WWND 2013 9

Robert Pak (BNL)

RAA @ 200 GeV

WWND 2013 10

arXiv:1208.2254v2

fit the data

Robert Pak (BNL) WWND 2013 11

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

cf., ALICE

Robert Pak (BNL) WWND 2013 12

•  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

Robert Pak (BNL) WWND 2013 13

Partons in 200 GeV collisions suffer largest average momentum loss

PRL 109, 152301 (2012)

arXiv:1208.2254v2

Sloss (= δpT/pT) vs. centrality

Robert Pak (BNL) WWND 2013 14

Sloss @ PHENIX, cf., ALICE

Robert Pak (BNL) WWND 2013 15

arXiv:1208.2254v2

model comparisons

Robert Pak (BNL) WWND 2013 16

•  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 ̂

Robert Pak (BNL) WWND 2013 17

pseudorapidity

Robert Pak (BNL) WWND 2013 18

flow participants

spectators

•  More recently, generalized eccentricities for higher flow moments:

•  Measured values must be

corrected by event plane resolution:

RAA vs. event plane

Robert Pak (BNL) WWND 2013 19

arXiv:1208.2254v2

centrality dependence

Robert Pak (BNL) WWND 2013 20

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

Robert Pak (BNL) WWND 2013 21

arXiv:1208.2254v2 Greater sensitivity in-plane:

cubic L dependence

in-medium path length dependence

Robert Pak (BNL) WWND 2013 22

PRL 105, 142301 (2010)

more hydro comparisons

Robert Pak (BNL) WWND 2013 23

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

Progress extracting q ̂for comparison to LHC

mesons

baryons

Robert Pak (BNL) WWND 2013 24

PRL 98, 162301 (2007)

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

√sNN dependence of PID v2

preliminary preliminary

Robert Pak (BNL) WWND 2013 25

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

Robert Pak (BNL) WWND 2013 26

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

Robert Pak (BNL) WWND 2013 27

Robert Pak (BNL) WWND 2013 28