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Elliptic flow of  meson in Pb-Pb

Elliptic flow of  meson in Pb-Pb. Paola Pagano. Elliptic flow. z. y. x. spectators. The flow is a collective motion of the particles produced in the ultrarelativistic nuclear reaction. . A non central collision produces an anisotropic flow in the transverse plane. participants.

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Elliptic flow of  meson in Pb-Pb

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  1. Elliptic flow of  meson in Pb-Pb Paola Pagano Paola Pagano Università di Salerno & INFN

  2. Elliptic flow z y x spectators The flow is a collective motion of the particles produced in the ultrarelativistic nuclear reaction. A non central collision produces an anisotropic flow in the transverse plane participants spectators The anisotropic transverse flow, i.e. elliptic flow, springs from the initial azimuthal asymmetry of the interaction region Paola Pagano Università di Salerno & INFN

  3. Elliptic flow It has origin from the anisotropic nature of the overlap region in the plane x-y with impact parameter b>0 The secondary interaction of particles converts the initial spatial anisotropy in an observed momentum anisotropy in the final state b=0 Paola Pagano Università di Salerno & INFN

  4. Elliptic Flow To measure the elliptic flow, we need first to estimate the reaction plane. Then the coefficients of the Fourierexpansion of the azimuthal distribution of particles with respect to the reaction plane are evaluated. j y Y2 x Poskanzer and Voloshin, Phys. Rev. C58, 1998 Elliptic flow coefficient Paola Pagano Università di Salerno & INFN

  5. Elliptic flow measurement: recent results at RHIC A scaling of the elliptic flow parameter v2 with the number of quarks is observed • To describe the observed scaling, two different models have been used: • Quark recombination models • Hadronic transport models. • In the context of both models, the observed v2 values seem to indicate that elliptic flow is built up prior to hadronization, in the partonic phase. 2007 Paola Pagano Università di Salerno & INFN

  6. fmeson’s elliptic flow measurement : recent results at RHIC (I) 2007 v2ofmeson increases with the eccentricity of the central region of overlap (i.e. the reduction of the centrality) Paola Pagano Università di Salerno & INFN

  7. NQ-scaling fit phi meson NQ = 2.3 ± 0.4 f meson’s elliptic flow measurement: recent results at RHIC (II) 2007 -mesons are produced via coalescence of seemingly thermalized quarks in central Au+Au collisions. This observation implies that hot and dense matter with partonic collectivity has been formed at RHIC Paola Pagano Università di Salerno & INFN

  8. How can we perform this measurement in ALICE? Mass invariant method • Mass invariant histogram for phi meson 2) Estimation of Signal and Background: fit with Breit-Wigner + polynomial 3) Estimation of reaction plane angle for each event: wi e i for the l’ith particle of a given event Paola Pagano Università di Salerno & INFN

  9. How can we perform this measurement in ALICE? Mass invariant method (cont’d) • Estimate of the opening angle for all K+K-pairs for each event • Histogram of v2(minv)= <cos2(KK-y2)> 6) Fit of the last histogram with the function: v2(minv) = a(minv)v2S+[1-a(minv)]v2B(minv) where v2(minv) = <cos2(KK-2)> v2S is thev2we are looking for v2B is the v2 of combinatorial background a(minv) = N(minv) / NK+ K_ (minv) Paola Pagano Università di Salerno & INFN

  10. Status of the analysis • The analysis tools are ready. • We are still producing a sufficient number of events  Estimation: approximately 106 events. • Two Productions: - one official, managed by the collaboration, for the production of the background, now I’m generating the signal - one private, containing only the generated particles without recostruction-> ongoing on the Salerno computer cluster • The time and space needed to perform this analysis, make essential the use of the world computing Grid facility. • Here we show some preliminary results for the estimation of: - reaction plane angle - v2 for all particles Paola Pagano Università di Salerno & INFN

  11. Reaction Plane Angle estimation: checking the algorithm Generated Particles Reconstructed Particles Paola Pagano Università di Salerno & INFN

  12. v2 estimation: checking the generator v2: 0.02794± 0.0011 v2: 0.03163± 0.0011 Generated Particles φ-Ψ2 (degree) Reconstructed Particles φ-Ψ2 (degree) After the determination of reaction plane angle Ψ2 , it’s possible to build a global distribution dN/d(φ-Ψ2) using events with same multiplicity and centrality. This distribution can be interpolated with the function: dN/dφ = cost.(1/2π) + 2 v2 cos2(φ-Ψ2)

  13. The End Paola Pagano Università di Salerno & INFN

  14. Back up

  15. Metodo della matrice di sfericità trasversa (I) • Diagonalizzazione della matrice di sfericità trasversa

  16. Metodo della matrice di sfericità trasversa (II) Il rapporto è proporzionale a v2 Dagli autovettori si ricava l’angolo del piano di reazione 2 :

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