1 / 36

Anisotropic Flow @ RHIC

Anisotropic Flow @ RHIC. Hiroshi Masui / Univ. of Tsukuba Feb./11/2007 RHIC 高エネルギー原子核反応の物理研究会、 RHIC 現象論松本合宿. Outline. Introduction Anisotropic flow, eccentricity Results Several scaling relations have been observed especially for elliptic flow Eccentricity scaling

lexi
Download Presentation

Anisotropic Flow @ RHIC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Anisotropic Flow@ RHIC Hiroshi Masui / Univ. of Tsukuba Feb./11/2007 RHIC高エネルギー原子核反応の物理研究会、RHIC現象論松本合宿

  2. Outline • Introduction • Anisotropic flow, eccentricity • Results • Several scaling relations have been observed especially for elliptic flow • Eccentricity scaling • Scaling of higher order anisotropy • mT and NCQ scaling of elliptic flow • Summary H. Masui / Univ. of Tsukuba

  3. Definition& Terminology H. Masui / Univ. of Tsukuba

  4. Anisotropic Flow Z • What ? • Azimuthally anisotropic emission of particles with respect to the reaction plane • Why ? • The probe for early time • Driven by • initial eccentricity of overlap zone • Re-interactions among the particles (pressure gradient) • Initial eccentricity --> Final momentum anisotropy Reaction plane Y X Pz Py Px H. Masui / Univ. of Tsukuba

  5. Observables • Particle azimuthal distributions by Fourier expansion • Odd harmonics (v1, v3, …) vanish at mid-rapidity in symmetric collision • v2 = “Elliptic Flow” S. Voloshin and Y. Zhang, Z. Phys. C70, 665 (1996) A. M. Poskanzer and S. A. Voloshin, Phys. Rev. C58, 1671 (1998) H. Masui / Univ. of Tsukuba

  6. Methods Two main types of methods H. Masui / Univ. of Tsukuba

  7. Event plane method • Brackets denote average over all events and all particles, kn is “event plane resolution” • w (weight) is chosen to maximize the event plane resolution (ex. pT, multiplicity etc) • The best weight is vn itself  H. Masui / Univ. of Tsukuba

  8. Event plane @ PHENIX • Event plane determination @ Beam-Beam Counter (BBC), || ~ 3 - 4 • Large rapidity gap between measured particles ( ~ 0) and event plane  Reduce non-flow effects • di-jet contribution is negligible (nucl-ex/0609009) H. Masui / Univ. of Tsukuba

  9. Multi-particle correlation 2-particle correlation • Non-flow effects contribute order • 1/N in 2-particle correlation • 1/N3 in 4-particle correlation 4-particle correlation H. Masui / Univ. of Tsukuba

  10. Terminology • std : standard eccentricity • Spatial anisotropy in coordinate space • part : Participant eccentricity • Effect from the fluctuations in the positions of participant nucleons • v2{EP2} : v2 with respect to the 2nd harmonic Event Plane • v2{BBC} : v2{EP2} by BBC in PHENIX • v2{FTPC} : v2{EP2} by Forward-TPC in STAR • v2{EP}(AA-pp) : Modified event plane method • v2{n} : v2 from n-th particle cumulants • v4{n} : v4 from n-th particle cumulants H. Masui / Univ. of Tsukuba

  11. Eccentricity : definition • Participant eccentricity in a given event is defined by the axes (x’, y’) • … denote average over all participant nucleons and events in the same impact parameter • {…} denote the average over all participants in one collision event H. Masui / Univ. of Tsukuba

  12. Eccentricity vs centrality • Fluctuations lead significant increase of eccentricity at most central and peripheral H. Masui / Univ. of Tsukuba

  13. Results (i)non-identified hadrons H. Masui / Univ. of Tsukuba

  14. Integrated v2 • ~ 50 % increase from SPS to RHIC • Hadron cascade underestimate the magnitude of v2 at RHIC • Due to the small transverse pressure in early times QM2005, H. Masui RQMD FOPI : Phys. Lett. B612, 713 (2005). E895 : Phys. Rev. Lett. 83, 1295 (1999) CERES : Nucl. Phys. A698, 253c (2002). NA49 : Phys. Rev. C68, 034903 (2003) STAR : Nucl. Phys. A715, 45c, (2003). PHENIX : Preliminary. PHOBOS : nucl-ex/0610037 (2006) H. Masui / Univ. of Tsukuba

  15. Eccentricity scaling (i) • Assume  = k  v2 • A Glauber model estimate of  gives • k = 3.1  0.2 • v2 scales with  and the scaled v2 values are independent of the system size Scale invariance of ideal hydrodynamics nucl-ex/0608033 H. Masui / Univ. of Tsukuba

  16. Eccentricity scaling (ii) Statistical errors only • Scaling of v2/part in Cu+Cu and Au+Au • Participant eccentricity is relevant geometric quantity for generating elliptic flow Au+Au 200 GeV Cu+Cu 200 GeV PRL: nucl-ex/0610037 PHOBOS CollaborationPRL: nucl-ex/0610037 PRC C72, 051901R (2005) H. Masui / Univ. of Tsukuba

  17. Eccentricity scaling (iii) QM2006, S. A. Voloshin QM2006, R. Nouicer • Linear increase from SPS to RHIC • Eccentricity scaling of v2 reach hydro limit at most central H. Masui / Univ. of Tsukuba

  18. Differential v2, v2(pT) :PHENIX vs STAR (Au+Au) • Non-flow effects are under control • v2{4}  v2{BBC} ~ v2{FTPC} < v2{2} • Similar acceptance : BBC, FTPC STAR : Phys. Rev. Lett. 93, 252301 (2004) PHENIX : Preliminary QM2006, S. A. Voloshin H. Masui / Univ. of Tsukuba

  19. v2(pT) in Cu+Cu STAR preliminary (QM06, S. A. Voloshin) • Larger non-flow effects in smaller system • Dominant non-flow is ~ O(1/N) PHENIX v2{2} v2{FTPC} PHENIX : nucl-ex/0608033 H. Masui / Univ. of Tsukuba

  20. Higher order QM06, Y. Bai STAR preliminary || < 1.3 • Non-zero v4 at RHIC • v4 ~ (v2)2 (Ollitrault) • v4/(v2)2 is a probe of ideal hydro behavior • N. Borghini and J.-Y. Ollitrault, Phys. Lett. B642, 227 (2006) QM05, H. Masui H. Masui / Univ. of Tsukuba

  21. v4/(v2)2 vs pT • Experimentally, v4/(v2)2 ~ 1.2 - 1.5 • Ideal hydro prediction v4/(v2)2 = 0.5 • Maximum non-flow contribution Star Preliminary H. Masui / Univ. of Tsukuba

  22. Summary (i) • The magnitude of v2 is as large as that from perfect fluid hydrodynamics at RHIC • 50 % increase from SPS • Hadron cascade cannot reprduce the magnitude of v2 • Eccentricity scaling • Consistent description of Au+Au and Cu+Cu v2 systematics by participant eccentricity • Different conclusion from different experiments • Non-flow effects are under control via • Large rapidity gap (PHENIX, STAR) • Multi-particle correlation (STAR) • Higher order, v4 • Non-zero v4 is observed • v4/(v2)2 ~ 1 > 0.5 but systematic error is huge at high pT H. Masui / Univ. of Tsukuba

  23. Results (ii)identified hadrons H. Masui / Univ. of Tsukuba

  24. “mT scaling” of v2 • v2{BBC} for identified hadrons • At low pT, mT scaling of v2 • Radial flow leads mass ordering of v2 • Meson-Baryon grouping at intermediate pT • Quark coalescence, recombination H. Masui / Univ. of Tsukuba

  25. NCQ scaling of v2 • NCQ scaling indicate the collective flow evolves in quark level • Number of Constituent Quark scaling by quark coalescence / recombination model • Assumption • Exponential pT spectra • Narrow momentum spread (-function) • Common v2 for light quarks (u, d, s) R. J. Fries, et., al, Phys. Rev. C68, 044902 (2003) V. Greco, et., al, Phys. Rev. C68, 034904 (2003) H. Masui / Univ. of Tsukuba

  26. Multi-strange hadrons J. H. Chen et., al, Phys. Rev. C74, 064902 (2006) • Why ? •  and  are less affected by hadronic interactions • Hadronic interactions at a later stage do not produce enough v2 Y. Liu et., al, J. Phys. G32, 1121 (2006) H. Masui / Univ. of Tsukuba

  27. Multi-strange hadrons QM06, A. Taranenko •  meson v2 is more consistent with meson v2 than baryon v2 • Show sizable v2 • Collectivity at pre-hadronic stage, s-quark flow STAR preliminary 200 GeV Au+Au SQM06, M. Oldenburg H. Masui / Univ. of Tsukuba

  28. Universal scaling of v2 • Substantial elliptic flow signals are observed for a variety of particles species at RHIC H. Masui / Univ. of Tsukuba

  29. Universal scaling of v2 At mid-rapidity H. Masui / Univ. of Tsukuba

  30. Summary (ii) • Mass ordering at low pT • Predicted by hydrodynamics (radial flow effect) • At intermediate pT, NCQ scaling holds a variety of particles species • Indication of light quark (u, d, s) collectivity at pre-hadronic stage • Universal v2 motivated by perfect fulid hydrodynamics is observed for both mesons and baryons over a broad range of kinetic energy, centrality via NCQ scaling H. Masui / Univ. of Tsukuba

  31. Back up H. Masui / Univ. of Tsukuba

  32. Flow measurements • 2 main types of methods • “Event plane” method • J.-Y. Ollitrault, Phys. Rev. D48, 1132 (1993) • A. M. Poskanzer and S. A. Voloshin, Phys. Rev. C58, 1671 (1998) • Multi-particle correlation method • N. Borghini, P. M. Dinh, J.-Y. Ollitrault, Phys. Rev. C63 054906 (2000); Phys. Rev. C64, 054901 (2001) • R. S. Bhalerao, N. Borghini, J.-Y. Ollitrault, Nucl. Phys. A727, 373 (2003); Phys. Lett. B580, 157 (2004) • Different sensitivity to “non-flow” effects • Correlations unrelated to the reaction plane, ex. jets, resonance decays etc … H. Masui / Univ. of Tsukuba

  33. Non-flow effects from Jets (i) • Nucl-ex/0609009 • “Trigger” pT : 2.5 < pT < 4 GeV/c • “Associated” pT : 1 < pT < 2 GeV/c • Background Au+Au events from HIJING • Checked to reproduce the charged hadron multiplicity in  from PHOBOS • v2 is implemented according to the PHENIX v2 measurement (nucl-ex/0608033) • Di-jet pairs are generated from PYTHIA H. Masui / Univ. of Tsukuba

  34. Non-flow effects from Jets (ii) • Fake v2 for leading particles • Fake v2 is negligible in BBC acceptance (3 <  < 4) • NOTE • Results are not corrected event plane resolution H. Masui / Univ. of Tsukuba

  35. Non-flow effect on v4 • Consider 3-particle correlation • Maximum non-flow contribute if (i, k) correlate non-flow and (j, k) correlate flow Non-flow flow H. Masui / Univ. of Tsukuba

  36. Clear  signal •   K+K- • Typical S/N ~ 0.3 • Centrality 20 – 60 % • S/N is good • Event plane resolution is good • Separation of v2 between meson and baryon is good • Magnitude of v2 do not vary very much Before subtraction Signal + Background Background After subtraction H. Masui / Univ. of Tsukuba

More Related