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

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) 034902

Are flow measurements at SPS reliable? PHENIX: Phys. Rev. Lett. 94 (2005) 232302 STAR, Phys. Rev. C75 (2007) 054906 PHENIX (RHIC ) 62.4-200 GeV - CERES (SPS) 17.3 GeV : 50% difference STAR (RHIC) 62.4-200 GeV - NA49 (SPS) 17.3 GeV: 10-25% difference :

RHIC BES 1: Results vs SPS STAR: Phys. Rev. C 86 (2012) 54908 STAR, Phys.Rev. C75 (2007) 054906 STAR (RHIC) 62.4-200 GeV - NA49 (SPS) 17.3 GeV: 10-25% difference : NA49 flow results were correct

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

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

PHENIX Flow Measurements : Methods Vn (EP): Phys.Rev.Lett. 107 (2011) 252301   Phys. Rev. Lett. 105, 062301 (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=0.3-3.5 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:1412.1038 , arXiv:1412.1043

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

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: 2007-2015 2) Different rapidity intervals: η = 0-1.6 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:1212.3650 (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

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

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) 162301  The difference in results 3-8% , systematic uncert. ~10%

Comparison v2(pT) PHENIX/STAR: BBC vs ZDC/SMD event plane |η|<0.35 BBC ZDC/SMD Phys. Rev. C 80, 024909 (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.C62:169-173,2009

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 )

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?

STAR/PHENIX Au+Au at 39-200 GeV Similar trends for central collisions in Au+Au collisions 39-200 GeV STAR: Inclusive charged hadron elliptic flow in Au + Au collisions at 7.7 - 39 GeV  Phys. Rev. C 86 (2012) 54908, PHENIX QM2011 Preliminary

Differential v2(pT): STAR [Central TPC]: Multi-particle methods Phys. Rev. Lett. 93 (2004) 252301 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

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 ?

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: http://cdsweb.cern.ch/record/1352458

Effect of rapidity gap on Vn measurements at LHC 5

Comparison with LHC ALICE Pb+Pb at 2.76 TeV : kaons ALICE: CERN-PH-EP-2014-104  e-Print: arXiv:1405.4632  PHENIX  arXiv:1412.1038 , arXiv:1412.1043 Difference between charged and neutral kaons v2 at LHC is due to physics ? Do we see the same difference at RHIC ( question to STAR) ?

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, 044907 Matthew Luzum, Jean-Yves Ollitrault

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