1. Are Flow Measurements at RHIC reliable?
Arkadiy Taranenko
National Research Nuclear University MEPhI
(Moscow Engineering Physics Institute)
STRANGENESS IN QUARK MATTER (SQM 2015), July 6-11 , 2011, JINR, Dubna, Russia

2. 2015: 10 years of the “perfect fluid” found at RHIC
2005
2015
2015: 15 years of famous article: “Are flow measurements at SPS reliable?” , Nicolas Borghini , Phuong Mai Dinh, Jean-Yves Ollitrault . Phys.Rev. C62 (2000)

3. Are flow measurements at SPS reliable?
PHENIX: Phys. Rev. Lett. 94 (2005)
STAR, Phys. Rev. C75 (2007)
PHENIX (RHIC ) GeV CERES (SPS) 17.3 GeV : 50% difference
STAR (RHIC) GeV NA49 (SPS) GeV: % difference :

4. RHIC BES 1: Results vs SPS
STAR: Phys. Rev. C 86 (2012) 54908
STAR, Phys.Rev. C75 (2007)
STAR (RHIC) GeV NA49 (SPS) GeV: % difference : NA49 flow results were correct

5. Elliptic Flow Measurements V2 (pT , centrality) in PHOBOS/STAR/PHENIX
FTPC
TPC
FTPC
ZDC/SMD
ZDC/SMD η
|η| < 1.3
2.5 <|η|< 4.0
|η| > 6.3
STAR
Central Arms
BBC/MPC
ZDC/SMD
ZDC/SMD
BBC/MPC
RXN
RXN
1.0<|η|<2.8
|η| > 6.6
PHENIX
|η|<0.35
3.1<|η|<3.7 η
3.1<|η|<3.9 EP EP
PHOBOS η
η = 0-1.6
2.05<|η|<3.2

6. PHENIX Flow Measurements : Methods
Central Arms (CA) |η’| < 0.35
(particle detection)
ψn RXN (|h|=1.0~2.8)
MPC (|h|=3.1~3.7)
BBC (|h|=3.1~3.9)
From 2012:
- FVTX (1.5<|h|<3)
Correlate hadrons in central Arms
with event plane (RXN, etc)
∆φ correlation function for EPN - EPS
(II)
(I)
∆φ correlation function for EP - CA

7. PHENIX Flow Measurements : Methods
Vn (EP): Phys.Rev.Lett. 107 (2011)   
Phys. Rev. Lett. 105, (2010)
Good agreement between Vn results obtained by event plane (EP) and two-particle correlation method (2PC)
No evidence for significant η-dependent non-flow contributions from di-jets for pT= GeV/c. Systematic uncertainty : event plane: 2-5% for v2 and 5-12% for v3.
ψn RXN (|h|=1.0~2.8)
MPC (|h|=3.1~3.7)
BBC (|h|=3.1~3.9)
 arXiv:  , arXiv:

8. Comparison of differential v2(pT, centrality): PHOBOS/PHENIX
EP: 1.0<|η|<2.8
from PHOBOS QM06 proc. J. Phys. G34 S887 (2007)‏ η
EP{1}
EP{2}
EP: 3.1<|η|<3.7
PHOBOS EP: 2.05<|η|<3.2
Overall good agreement between differential flow measurements

9. 2015 Summary: PHENIX vs PHOBOS
There is good qualitative agreement between PHOBOS/PHENIX for v2 (pt) in Au+Au collisions at 200 GeV, but:
1) PHOBOS QM06 proc. J. Phys. G34 S887 (2007)‏ results are not published:
2) Different rapidity intervals: η = for PHOBOS and |η| < 0.35 for PHENIX
3) Wide centrality bins for comparison: 0-20%, 20-40%, 35-50% -
Event plane resolution correction for azimuthal anisotropy in wide centrality bins
Hiroshi Masui, Alexander Schmah, : arXiv: (2012) up to 15% effect
Conclusion: up to 60-70% of all flow measurements at RHIC are still preliminary data – Do you trust them ?
2018/9/14 9

10. Elliptic Flow Measurements V2 (pT , centrality) in STAR/PHENIX
FTPC
TPC
FTPC
ZDC/SMD
ZDC/SMD η
|η| < 1.3
2.5 <|η|< 4.0
|η| > 6.3
STAR
comparison
Central Arms
BBC/MPC
ZDC/SMD
ZDC/SMD
BBC/MPC
RXN
RXN η
1.0<|η|<2.8
|η| > 6.6
PHENIX
|η|<0.35
3.1<|η|<3.7
3.1<|η|<3.9

11. 15 Years of Elliptic Flow Measurements at RHIC
STAR FTPC
2.5 <|η|< 4.0
PHENIX BBC
3.1 <|η|< 3.9
Cu+Cu at 200 GeV – the only beam energy where PHENIX can make “apple to apple “ comparison with STAR.
STAR: Charged and strange hadron elliptic flow in Cu+Cu collisions at 62.4 and 200 GeV  Phys. Rev. C 81 (2010) 44902
PHENIX Scaling properties of azimuthal anisotropy in Au+Au and Cu+Cu collisions at s(NN) = 200-GeV,  Phys.Rev.Lett. 98 (2007)  
The difference in results 3-8% , systematic uncert. ~10%

12. Comparison v2(pT) PHENIX/STAR: BBC vs ZDC/SMD event plane
|η|<0.35
BBC
ZDC/SMD
Phys. Rev. C 80, (2009) η
|η|>6.6
3.1<|η|<3.9
PHENIX: V2{ZDC/SMD} < V2{BBC} and does not dependts on pT – different fluctuations
Good agreement with STAR preliminary data since 2009.
H. Masui, Eur.Phys.J.C62: ,2009

13. V2{EP} – standard event plane method
Au+Au at 200 GeV: Differential v2(pT, centrality): STAR [Central TPC |η|<1.0]
V2{EP} – standard event plane method
Phys.Rev. C72(2005) 14904‏
V2{EP2} – modified event plane method: all subevent particles in |Δη|<0.5 around highest pT particle in the event are excluded from event-plane determination. Ratio: V2{EP} / V2{EP2} > 1 at high pT
2005: The only published STAR data for Au+Au at 200 GeV (in the last 10 years )

14. Comparison v2(pT, centrality): STAR [Central TPC |η|<1.0] / PHENIX
V2{EP2} – modified EP method
For 0-20% central collisions STAR V2 > PHENIX V2 : do we have the same centrality definition between experiments?

15. STAR/PHENIX Au+Au at 39-200 GeV
Similar trends for central collisions in Au+Au collisions GeV
STAR: Inclusive charged hadron elliptic flow in Au + Au collisions at GeV  Phys. Rev. C 86 (2012) 54908, PHENIX QM2011 Preliminary

16. Differential v2(pT): STAR [Central TPC]: Multi-particle methods
Phys. Rev. Lett. 93 (2004)
Phys. Rev. C 77 (2008) 54901
V2{2}
V2{4}
V2{LYZ}
Question for STAR: Why V2/V2{EP} has pT dependence for 4p cumulant method, but it is flat as a function of pT for LYZ method ?
Question for PHENIX: where is your measurements using multi-particle methods ?
V2{4} – four particle cumulant method
V2{LYZ} – Lee Yang Zero method

17. V3 in Au+Au at 200 GeV (STAR/PHENIX)
STAR: Third Harmonic Flow of Charged Particles in Au+Au Collisions at 200 GeV  Phys. Rev. C 88 (2013) 14904
Do we understand the difference in v3 measurements between STAR and PHENIX ?

18. Effect of rapidity gap on Vn measurements at LHC
Significant bias from near-side jet for |Δη|<0.5
Consistent for larger Δη at pT<4 GeV
Deviation again for pT>4 GeV due to swing of recoil jet
EP method ( |Δη|< 2.5 with EP from full FCAL: 3.3<|Ƞ|<4.8 ) 5
ATLAS AN:

19. Effect of rapidity gap on Vn measurements at LHC5

20. Comparison with LHC ALICE Pb+Pb at 2.76 TeV : kaons
ALICE: CERN-PH-EP   e-Print: arXiv:  
PHENIX
 arXiv:  , arXiv:
Difference between charged and neutral kaons v2 at LHC is due to physics ?
Do we see the same difference at RHIC ( question to STAR) ?

21. Are Flow Measurements at RHIC reliable? Maybe !
The detailed and proper comparison between STAR and PHENIX results for v2 is not possible due to luck of published measurements. Up to 70% of all results are still preliminary.
The difference for V3 and higher harmonics need to be understood.
Sometimes we do not see full picture …..
A good measurement should be reproducible; in particular, it should be done in such a way that one can easily compare results from different experiments, using different detectors.
For the sake of comparison with theory, an ideal measurement is a well-defined quantity that corresponds to a generic property of the system, closely related to an interesting theoretical concept.
“Eliminating experimental bias in anisotropic-flow measurements of high-energy nuclear collisions”, Phys.Rev. C87 (2013) 4,
Matthew Luzum, Jean-Yves Ollitrault

22. Backup Slides 22