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Systematic investigation of partonic collectivity through centrality dependence of elliptic flow

Systematic investigation of partonic collectivity through centrality dependence of elliptic flow of multi-strange hadron in Au+Au collision at  s NN =200 GeV in STAR. Md. Nasim (for the STAR Collaboration) Variable Energy Cyclotron Centre Kolkata , India.

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Systematic investigation of partonic collectivity through centrality dependence of elliptic flow

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  1. Systematic investigation of partonic collectivity through centrality dependence of elliptic flow of multi-strange hadron in Au+Au collision at sNN=200 GeV in STAR • Md. Nasim • (for the STAR Collaboration) • Variable Energy Cyclotron Centre • Kolkata , India • Outline • Introduction & motivation • STAR experiment at RHIC • Results • Summary Quark Matter Washington D.C August 12-18, 2012 VECC Md Nasim

  2. Elliptic Flow (v2) Initial spatial anisotropy ( ε2 ) Momentum anisotropy( v2) y Py Pressure gradient Interactions Px Pz x Reaction plane P. Klob, U. W. Heinz Nucl. Phys. A715, (2003) 653c • Interactions among constituents transform the initial spatial anisotropy into momentum anisotropy • Process quenches itself → sensitive to early times in the evolution of the system • Sensitive to the equation of state Md Nasim

  3. Motivation • Low interaction cross-section • with other hadrons • BW Model results support • early freeze out of multi-strange • hadrons • Tk ~ Tch ~ Tc( Lattice QCD) • v2( ϕ, Ξ, Ω) is a good probe • of partonic collectivity STAR Collaboration : Nuclear Physics A 757 (2005) Partonic collectivity : Centrality dependence of NCQ scaling Partonic collectivity vs. System size. Hadronic re-scattering effect : v2(p)/v2(ϕ) > 1 ~ mass ordering of v2(hydro-like) < 1 ~ hadronic re-scattering effect STAR Collaboration: Phys.Rev.Lett. 99 (2007) 112301 Comparison of v2(ϕ) with v2(p) can be used to study the effect of hadronic re-scattering. T Hirano et.al Phys. Rev. C 77, 044909 (2008) Md Nasim

  4. STAR Detectors p • Full 2π coverage • Excellent particle identification • capabilities (Using TOF and TPC) K p Data Set: Au+Au 200 GeV, collected in 2010 Total # of analyzed events = 240 M dE/dx clean PID: pion/kaon: pT ~ 0.6 GeV/c and proton pT~ 1.0 GeV/c With TOF : pion/kaon: pT ~ 1.6 GeV/c and proton pT~ 3.0 GeV/c Md Nasim

  5. Multi-strange hadron & v2 measurement Ω -> Λ + K Ξ -> Λ + π ϕ -> K+ +K- • Ω and Ξ are reconstructed by decay topology method + invariant mass method • f-mesons are reconstructed by invariant mass method v2 vs. invariant mass method: Md Nasim

  6. Centrality Dependence Au+Au 200 GeV, η sub EP , Δη = 0.1 unit |y | < 1.0 STAR Preliminary Note : Only statistical errors • Centrality dependence for multi-strange hadrons v2 observed Md Nasim

  7. v2 vs. mT-m0 Au+Au 200 GeV, η sub EP • Centrality 0-30% : • Baryon–meson splitting at intermediate mT-m0. • Centrality 30-80% : • Deviations of multi-strange hadrons from baryons and mesons • groups at intermediate mT-m0. • Multi-strange hadron v2 smaller than other strange hadrons • v2 at mT-m0>1 GeV/c2 (v2(Ξ)<v2(Λ), v2(ϕ)<v2(K0S)) Ref: v2 of π, K , p, K0s and Λ – Poster Presentation by Hiroshi Masui (poster #145) Md Nasim

  8. Number-of-Constituent-Quark Scaling: pT/nq Au+Au 200 GeV, η sub EP • Centrality 0-30% : • f-meson is below from fit line 4 ± 7 % for pT/nq > 1 GeV/c. • Centrality 30-80%: • f-meson is below from fit line 14 ± 5 % for pT/nq > 1GeV/c Md Nasim

  9. (mT-m0)/nq scaling Au+Au 200 GeV, η sub EP • Centrality 0-30% : • f-meson below from fit line 4 ± 6 % for (mT-m0)/nq > 0.6 GeV/c2. • Centrality 30-80%: • f-meson below from fit line 11 ± 4 % for (mT-m0)/nq > 0.6 GeV/c2. Md Nasim

  10. Deviation from K0s STAR Preliminary • f–meson seems to show larger deviation in 30-80% than 0-30% Md Nasim

  11. Mass ordering of elliptic flow Au+Au 200 GeV, η sub EP STAR Preliminary • Mass ordering observed in 0-80%, except between proton and • f-meson for pT < 1.0 GeV/c • Similar trend is observed for 0-30% and 30-80% centrality. Md Nasim

  12. v2(f)/v2(p) vs. pT Au+Au 200 GeV, η sub EP Hydro+Cascade T Hirano, Phys. Rev. C 77, 044909 (2008) • At low pT the v2(f) tends to be higher than v2(p) • for central collisions. This trend is consistent • with the hadronic re-scattering scenario as • proposed in Phys. Rev. C 77, 044909 (2008). • The effect is stronger in central collisions Md Nasim

  13. Summary • First systematic measurement of centrality dependence of multi- • strange hadrons ( ϕ(ssbar),Ξ(dss), and Ω (sss)) at mid-rapidity in • Au+Au collisions at √sNN=200 GeV. • Multi-strange hadron v2 at 30-80% centrality is • smaller than other strange hadrons v2 at • mT-m0>1 GeV/c2 (v2(Ξ)<v2(Λ), v2(ϕ)<v2(K0S)) • f–meson seems to show larger deviation • in 30-80% than 0-30% in NCQ scaling. May indicate smaller contribution to the collectivity from partonic phase in peripheral collisions. • v2(f)/v2(p) tends to be greater than unity • at low pT. • Consistent with hadronic re-scattering • effect as proposed in theoretical model. Md Nasim

  14. Back-up Md Nasim

  15. Md Nasim

  16. Number-of-Constituent-Quark Scaling: pT/nq Au+Au 200 GeV, η sub EP Md Nasim

  17. (mT-m0)/nq scaling Au+Au 200 GeV, η sub EP Md Nasim

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