1. Flow Measurement in PHENIX
Masahiro Konno
(Univ. of Tsukuba)
for the PHENIX Collaboration

2. Outline Physics Motivation Method, PHENIX detector
Single Particle Spectra:
- p/ ratios
- Npart Scaling of p/ in Au+Au, Cu+Cu
- RAA in Au+Au, Cu+Cu
Elliptic Flow:
- Scaling properties of v2
Summary

3. Single Particle Spectra

4. Physics Motivation - Baryon Enhancement - RAA p/ ratio Au+Au 200 GeV
PRC 74, (2006)
PRL 91, (2003)
p/ ratio
Au+Au 200 GeV .
- p/ ratio ~1 for central Au+Au at intermediate pT (2-4 GeV/c).
- Larger than expected from jet fragmentation (measured in pp, e+e-). - Baryon / Meson difference at intermediate pT.
- Several models try to reproduce the data.
What is the origin of (anti-)proton
enhancement at intermediate pT(2~5 GeV/c) ?
A systematic study at intermediate pT is
necessary over different collisions systems.
High-pT suppression due to parton energy loss
in the medium (jet quenching).
The suppression patterns depend on particle type.
Protons are enhanced, while pions and kaons are suppressed.

5. PHENIX detector - - EM Calorimeter (PID) TOF (PID)
- Central Arm Detectors
Centrality and Reaction Plane
determined on an E-by-E basis.
PID (particle identification) is
a powerful tool to study hadron
production.
Aerogel Cherenkov (PID)
Aerogel Cherenkov (ACC)
Time of Flight (TOF)
p (p) ID up to 7 GeV/c -
p (p) ID up to 4 GeV/c -
Drift Chamber
(momentum meas.) p K+
Tracking detectors
(PC1,PC2,PC3) π+
Veto for proton ID

6. pT spectra (Cu+Cu √sNN = 200 GeV)
Phenix preliminary
(Anti-) protons
ACC
- Cu+Cu is a smaller system compared to Au+Au.
pT reach extended for (anti-)protons with fine centrality bins.
<= (1) Aerogel Cherenkov, (2) Enough statistics in Au+Au/Cu+Cu
NOTE: No weak decay feed-down correction applied.

7. pT spectra (p+p √s = 200 GeV)
Phenix preliminary
TOF
High statistics 200 GeV p+p data.
More than10 times statistics used compared to previous Run3 p+p analysis.
The p+p data provides baseline spectra to heavy ion data, and it is
important to quantify in-medium nuclear effects in heavy ion collisions at RHIC.
NOTE: No weak decay feed-down correction applied.

8. p/ vs. pT Au+Au 200 GeV ACC p/ p/
- p/ (pbar/) ratios seem to turn over at intermediate pT,
and be close to the value of fragmentation at higher pT.
- Clear peak in central events than that in peripheral.
- Indicating a transition from soft to hard at intermediate pT.
NOTE: - No weak decay feed-down correction applied.
- p+p data (PRC 74, (2006))

9. p/ vs. pT Cu+Cu 200 GeV ACC p/ p/
Phenix preliminary
p/
p/
Baryon enhancement observed in Cu+Cu at 200 GeV.
- pT dependence in Cu+Cu is similar to that in Au+Au.
=> How about the magnitude as a function of centrality? see Next.
NOTE: No weak decay feed-down correction applied.

10. p/ vs. Npart1/3 3.0 - 4.0 GeV/c 4.0 - 5.0 GeV/c 2.0 - 3.0 GeV/c
Cu+Cu 200 GeV
vs. Au+Au 200 GeV
p/ vs. Npart1/3 pT
Phenix preliminary
GeV/c
GeV/c
GeV/c
GeV/c
GeV/c
Phenix
preliminary
- Centrality dependence in Cu+Cu looks similar to
that in Au+Au (Npart scaling at same sqrt(sNN)!).
- Even though overlap region has a different geometrical shape.
- Slight difference in the magnitude seen.
TOF (<3 GeV/c)
ACC (>3 GeV/c)
NOTE: No weak decay
feed-down correction
applied.

11. p/ vs. pT (Low pT) - Radial flow - TOF (Anti-)protons
Phenix preliminary
Phenix preliminary
- Radial flow: transverse expansion of the system
- At low pT, p/ shows weak and decreasing Npart dependence because inverse slope (from mT exponential fitting) also shows it.
NOTE: No weak decay feed-down correction applied.

12. p/ vs. pT (Intermediate pT)
TOF, ACC
- Radial flow (ex. blast-wave fit) -
Au+Au 200 GeV
Spectra for heavier particles has
a convex shape due to radial flow.
Using Blast-wave fitting, try to
estimate p/ ratio as a function of pT.
NOTE: No weak decay feed-down correction applied.
(hydro p)/(hydro )
(hydro p)/(real )
Hydrodynamic contribution for protons is one of
the explanations (baryon enhancement).
- Other contribution is also needed: Recombination, Jet fragmentation
Central
Peripheral

13. p/ vs. pT (Intermediate pT)
ACC
- Quark Recombination -
p/
Phenix preliminary
Now, we find a similar trend.
ACC
TOF
At intermediate pT, recombination of
partons may be a more efficient mechanism
of hadron production than fragmentation.
A number of models predicted a turnover
in the B/M ratio at pT just above where
the available data finished…
Fries, R et al PRC 68 (2003)
Greco, V et al PRL 90 (2003)
Hwa, R et al PRC 70(2004) etc.
NOTE: No weak decay feed-down correction applied.

14. p/ vs. pT Cu+Cu 62 GeV vs. Au+Au 62 GeV TOF Phenix preliminary
- Again, look at centrality dependence of p/ ratios.
- Similar tendencies as at 200 GeV.

15. p/ vs. Npart1/3 Cu+Cu 62 GeV vs. Au+Au 62 GeV TOF Phenix preliminary
Npart scaling of p/ also at 62 GeV in Au+Au/Cu+Cu.
NOTE: No weak decay feed-down correction applied.

16. p/ vs. Npart1/3 ,(dET/dy)1/3
Au+Au 200 GeV
vs. Au+Au 62 GeV
TOF
Phenix preliminary
Phenix preliminary
No Npart scaling of p/ (pbar/) in Au+Au between 62 GeV and 200 GeV.
dET/dy scaling of pbar/ seen. => Proton production (at this pT range)
at 62 GeV is partly from baryon transport, not only pair production.
Nuclear stopping is still large at 62 GeV.
NOTE: No weak decay feed-down correction applied.

17. (dET/dy)/Npart vs. Npart
Phenix preliminary
R. Armendariz
(2006)
- Transverse energy density is a connection key.

18. * No weak decay feed-down correction applied.
Beam energy dependence of p/
T. Chujo
(QM ‘06)
- p/+ ratio : decreasing as a function of sNN.
p/- ratio : increasing as a function sNN.
Suggesting a significant contribution of baryon
transport at lower energies.
* No weak decay feed-down correction applied.

19. * No weak decay feed-down correction applied.
Beam energy dependence of p/
Antiproton is a good probe to study the excitation function.
* No weak decay feed-down correction applied.

20. RAA vs. pT TOF Phenix preliminary Similar Npart dependence
NOTE: Systematic errors (~10%)
for overall normalization not shown.
Similar Npart dependence
for Au+Au / Cu+Cu.
(Npart scaling of RAA)
- Cronin effect in peripheral
Proton, antiproton are enhanced at GeV/c
for all centralities. (enhancement > suppression)
- Suppression is seen for pions, kaons.
NOTE: No weak decay feed-down correction applied.

21. Elliptic Flow

22. Elliptic Flow Overlap region is like ellipsoid
at the beginning of collision.
Spatial anisotropy of the system
followed by multiple scattering of
particles (pressure gradient) in the
evolving system
- Spatial anisotropy => momentum anisotropy Z
Reaction plane Y X Py Pz
v2: 2nd harmonic Fourier coefficient in azimuthal distribution of particles with respect to the reaction plane Px

23. KET Scaling of v2 A. Taranenko (QM ‘06) Large elliptic flow observed.
nucl-ex/
KET ~ mT–m0
at y ~ 0
PHENIX preliminary
Large elliptic flow observed.
- Mass ordering seen at low pT (<1.5 GeV/c).
KET scaling (for hadronic flow) vanish this mass
dependence but give clear splitting of meson/baryon v2.

24. No.-of-Constituent-Quarks Scaling of v2
nucl-ex/
PHENIX preliminary
Species dependence of v2 well accounted for
by scaling v2 and pT (KET) with # of quarks.
Evidence of partonic flow! v2 is developed before
hadrons form.
v2q(pT) = v2h(pT/n)/n, v2q(KET) = v2h(KET/n)/n

25. Eccentricity Scaling of v2
At mid rapidity, v2 (pt,M,b,A)/n~ F(KET/n)*ε(b,A)?
ε(b,A): integral elliptic flow of charged hadrons
KET : transverse kinetic energy
n: number of quarks

26. Eccentricity Scaling of v2
M. Shimomura
(JPS ‘06)
GeV/c
GeV/c
GeV/c
- ε(b,A)/v2(b,A) ~ 3.1+/-0.2
v2/eccentricity vs. Npart has different slopes
for different pT.
Black: 200GeV
Red: GeV

27. Energy and System Size dependence of v2
Black AuAu 200GeV
Red AuAu 62.4GeV
Green CuCu 200GeV
Blue CuCu 62.4GeV
GeV/c
GeV/c
v2 is not scaled by Npart.

28. Energy and System Size dependence of v2
Black AuAu 200GeV
Red AuAu 62.4GeV
Green CuCu 200GeV
Blue CuCu 62.4GeV
GeV/c
GeV/c
GeV/c
v2 looks rather scaled by eccentricity.

29. Summary pT reach of PID (especially for p, pbar) extended with:
(1) High statistics Au+Au/Cu+Cu data
(2) New PID detector (Aerogel)
(Anti-)Proton enhancement is observed
in Au+Au/Cu+Cu collisions at 200/62 GeV.
p/ ratios:
(1) Indicating a transition from soft to hard production at intermediate pT.
(2) Npart scaling (dET/dy scaling) over different collision systems.
(3) Recombination + radial flow would explain the pT, Npart dependencies.
- PID v2:
(1) KET scaling, NCQ scaling
(2) Eccentricity scaling
- Systematic study of PID spectra, elliptic flow (and jet correlations)
for different collision systems can provide information
to understand the hadron production mechanisms.

30. Backup slides

31. Beam energy dependence of net protons
nucl-ex/
nucl-ex/
SPS
AGS
- The shape of net proton distribution change dramatically with beam energy.
- pbar/ ratio could be a good indicator of thermalization.

32. v2 of phi meson
v2 vs KET – is a good way to see if v2 for the φ follows
that for mesons or baryons
v2 /n vs KET/n scaling clearly works for φ mesons as well

33. No.-of-Constituent-Quarks Scaling of v2
PHENIX Preliminary
KET/n scaling works for the full measured range
with deviation less than 10% from the universal scaling curve