09/12/2009Paola Pagano Università di Salerno & INFN 1 Elliptic flow of meson in Pb-Pb Paola Pagano

09/12/2009Paola Pagano Università di Salerno & INFN 2 Elliptic flow x z y participants 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 The anisotropic transverse flow, i.e. elliptic flow, springs from the initial azimuthal asymmetry of the interaction region

09/12/2009Paola Pagano Università di Salerno & INFN 3 Elliptic flow b=0 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

09/12/2009Paola Pagano Università di Salerno & INFN 4 Elliptic Flow Elliptic flow coefficient x y 2 Poskanzer and Voloshin, Phys. Rev. C58, 1998 To measure the elliptic flow, we need first to estimate the reaction plane. Then the coefficients of the Fourier expansion of the azimuthal distribution of particles with respect to the reaction plane are evaluated.

09/12/2009Paola Pagano Università di Salerno & INFN 5 Elliptic flow measurement: recent results at RHIC 2007 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 v 2 values seem to indicate that elliptic flow is built up prior to hadronization, in the partonic phase. A scaling of the elliptic flow parameter v 2 with the number of quarks is observed

09/12/2009Paola Pagano Università di Salerno & INFN 6 mesons elliptic flow measurement : recent results at RHIC (I) v 2 of meson increases with the eccentricity of the central region of overlap (i.e. the reduction of the centrality) 2007

09/12/2009Paola Pagano Università di Salerno & INFN 7 mesons elliptic flow measurement : recent results at RHIC (II) -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 NQ-scaling fit phi meson NQ = 2.3 ±

09/12/2009Paola Pagano Università di Salerno & INFN 8 How can we perform this measurement in ALICE? Mass invariant method 1)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: w i e i for the li th particle of a given event

09/12/2009Paola Pagano Università di Salerno & INFN 9 4)Estimate of the opening angle for all K + K - pairs for each event 5)Histogram of v 2 (m inv )= 6) Fit of the last histogram with the function: v 2 (m inv ) = a(m inv )v 2S +[1-a(m inv )]v 2B (m inv ) where v 2 (m inv ) = v 2S is the v 2 we are looking for v 2B is the v 2 of combinatorial background a(m inv ) = N (m inv ) / N K+ K _ (m inv ) How can we perform this measurement in ALICE? Mass invariant method (contd)

09/12/2009Paola 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 10 6 events. Two Productions: - one official, managed by the collaboration, for the production of the background, now Im 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 - v 2 for all particles

09/12/2009Paola Pagano Università di Salerno & INFN 11 Reaction Plane Angle estimation: checking the algorithm Reconstructed Particles Generated Particles

22/02/ v 2 estimation: checking the generator After the determination of reaction plane angle Ψ 2, its possible to build a global distribution dN/d(φ-Ψ 2 ) using events with same multiplicity and centrality. This distribution can be interpolated with the function: dN/dφ = cost.(1/2π) + 2 v 2 cos2(φ -Ψ 2 ) v 2 : ± Generated Particles φ-Ψ 2 (degree) v 2 : ± Reconstructed Particles φ-Ψ 2 (degree)

09/12/2009Paola Pagano Università di Salerno & INFN 13 The End

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Metodo della matrice di sfericità trasversa (I) Diagonalizzazione della matrice di sfericità trasversa

Metodo della matrice di sfericità trasversa (II) Il rapporto è proporzionale a v 2 Dagli autovettori si ricava langolo del piano di reazione 2 :