Strangeness analysis in ALICE

1. Strangeness analysis in ALICE K0s and hyperons Ludovic Gaudichet, INFN Torino Vietri sul Mare 30/05/2006 genuine p+p physics PbPb physics analysis status, studies in PPR2 prospects

2. p+p analysis

3. p+p collisions at LHC p+p analysis Yields and pt spectra at mid-rapidity of K0s, Λ, Ξ and Ω and their anti-particles • Baryon asymmetry : • Is the baryon number carried by gluons also ? (comparison to gluonic baryon junction models) • Particle production mechanisms, in soft / intermediate / hard regimes • Beside gluons, u and d, strange quark is the only component of low pt multiparticle interaction which is statistically significant • comparison with pythia, HERWIG, ... • minimum bias / underlying events • Λ/Λbar and jets • Feed-down corrections : needed to determine yield of proton ! • Comparison to thermal models, interesting by itself and will serve heavy ion analysis • Baseline for the analysis of heavy ion collisions Ludovic Gaudichet INFN, Torino

4. “day one” analysis p+p analysis 104 events • Provided that we understand our detector, we could publish : • K0s yield and spectrum at mid-rapidity • Rough yields of Λ and Λbar Estimation with pythia 6.2 and ATLAS tuning. Could be more ! 130 Λ Already interesting for constraining pythia and understanding baryons production mechanisms Ludovic Gaudichet INFN, Torino

5. Results of first run p+p analysis 7.107 events (200h at 100Hz) • K0s yield and spectrum at mid-rapidity • Λ and Λbar yields and pt spectra up to pt = 8 GeV/c • Ξ and Ξbar yields and pt spectra up to pt = 4 GeV/c • 190 Omegas ... or hopefully more ! 926k Λ 19k Ξ Ludovic Gaudichet INFN, Torino

6. PbPb analysis

7. Strangeness enhancement PbPb analysis Tounsi et al. B. Hippolyte, Moriond 2004 Ludovic Gaudichet INFN, Torino

8. Strangeness enhancement PbPb analysis Statistical Equilibrium / non-equilibrium ? Difficult to know at RHIC, but big difference at LHC : • However : • Hard processes will compete with soft processes. 2 sources of strangeness, one equivalent to p+p ! • In p+p an increase of the volume could also gives some more phase space for strangeness production ! • Canonical to Grand Canonical transition still have to be there !? • Scaling with Nbin ? J. Rafelski Ludovic Gaudichet INFN, Torino

9. Intermediate transverse momentum PbPb analysis What : Why : between soft (hydrodynamics) and hard (pQCD) regimes 2-3 GeV/c and 6-7 GeV/c at RHIC Little known, between collective effects and hard scattering a lot to learn about hadronisation and its dynamics Ludovic Gaudichet INFN, Torino

10. Intermediate pt PbPb analysis Constituent quark scaling : P.R. Sorensen QM05 talk Ludovic Gaudichet INFN, Torino

11. Rcp in heavy ion collisions PbPb analysis Ludovic Gaudichet INFN, Torino

12. K0s and hyperons in ALICE

13. V0 cuts, selecting Λ DCA to primary vertex Daughter DCA DCA V0-Bachelor Angle between cascade momentum and primary vertex Angle between V0 momentum and primary vertex Bachelor DCA to primary vertex 2nd vertex reconstruction  -  K0s -  4 parameters + vertex radius + 5 parameters Ludovic Gaudichet INFN, Torino

14. Performance of topology reconstruction in PPR2 : p+p collisions Even without charged track PID ! No limit in pt other than statistic ! Ludovic Gaudichet INFN, Torino

15. Effect of event multiplicity in PPR2 : p+p collisions In p+p collisions the reconstruction rate is a function of the multiplicity : Small dependence from the primary vertex resolution + pt hardening of hyperon spectra Ludovic Gaudichet INFN, Torino

16. Reconstruction factors & raw spectra in PPR2 : p+p collisions 109 events Ludovic Gaudichet INFN, Torino

17. Reconstruction in PbPb collisions in PPR2 : PbPb collisions Ξ Λ Ω Ludovic Gaudichet INFN, Torino

18. Raw spectra in PbPb at 5.5 TeV in PPR2 : PbPb collisions Ξ Λ Ω Ludovic Gaudichet INFN, Torino

19. Classical cuts Neural net LDA Signal selection by the LDA Linear Discriminant Analysis + succession of cuts in the n-dim space of parameters Λ Ξ • LDA is : • Faster than anything else, more reliable than neural networks • Significance increases by 20% • Amount of selected signal increases by 60% Ludovic Gaudichet INFN, Torino

20. Conclusion p+p • Hadron production at LHC energy • Baseline for the analysis of heavy ion collisions • Soft physics : thermal production, hydrodynamics • a perfect fluid at LHC ? • Strangeness is a good probe • Intermediate transverse momentum : • key regime for the understanding of the collision dynamics • large portion of produced particle at LHC • striking advantage of Strangeness PbPb • Analysis of K0s and hyperons tested in p+p and PbPb collisions • Strange objects (V0 and cascades) available for any analysis like tracks • Room for improvement : Linear Discriminant Analysis • Next Data Challenge on the way : preparing analysis of p+p ! • Analysis code within the PWG2 of ALICE : to be discussed ... Ludovic Gaudichet INFN, Torino

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23. Ludovic Gaudichet INFN, Torino

24. Backup slides

25. To do next : Physics Data Challenge 06 • systematic from the primary vertex resolution • full study of Omega reconstruction efficiency Lacks in PPR2 : Ξ reconstruction rate, scaled by the difference seen in PbPb • 108 events • More realistic simulations • calibration (dead channels, mis-alignment, ...) • Trigger simulation What PDC 06 will provide : Last Data Challenge : test of the analysis speed and the CPU requirement ! Ludovic Gaudichet INFN, Torino

26. Pythia Pythia L+Lbar K0s 6.3 6.3 6.2 6.2 UA5 UA5 CDF STAR STAR SPS SPS √s √s Event cocktail for PDC 06 PDC 06 • Minimum bias events, as defined by pythia 6.2, ATLAS tuning • Events enriched with Ω and Ωbar • Have enough statistic • Compensate for pythia possible underestimation of strangeness 75000 enriched events with Ω, 75000 withΩbar dN/dy (-0.5<y<0.5) Ludovic Gaudichet INFN, Torino

27. Event cocktail for PDC 06 PDC 06 • Minimum bias events, as defined by pythia 6.2, ATLAS tuning • Events enriched with Ω and Ωbar • Have enough statistic • Compensate for pythia possible underestimation of strangeness 75000 enriched events with Ω, 75000 withΩbar Pythia X 6.3 K0s, Λ and Ξ estimation are acceptable, but Ω 6.2 RHIC SPS √s Ludovic Gaudichet INFN, Torino

28. Baryon excess : Λ/K0s PbPb analysis • Low pt limit can be define by the validity range of Hydro. • At high pt limit, the baryon and meson should merge again. • BUT seen in p+p too ! (UA1 & CDF) Ludovic Gaudichet INFN, Torino

29. Λ/K0s in pythia Ludovic Gaudichet INFN, Torino

30. <pT> versus mass in p+p at RHIC Ludovic Gaudichet INFN, Torino

31. thermal particle production Ludovic Gaudichet INFN, Torino

32. RAA in heavy ion collisions PbPb analysis We can also do RAA • Several effects here : • shadowing at low pt • Cronin effect • strangeness enhancement • jet quenching H. Caines, STAR Ludovic Gaudichet INFN, Torino

33. Azimuthal correlation at high pT Ludovic Gaudichet INFN, Torino