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

p+p analysis

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 3 p+p collisions at LHC Yields and pt spectra at mid-rapidity of K 0 s, 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 p+p analysis

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 4 “day one” analysis Provided that we understand our detector, we could publish :  K 0 s yield and spectrum at mid-rapidity  Rough yields of Λ and Λbar 130 Λ Already interesting for constraining pythia and understanding baryons production mechanisms Estimation with pythia 6.2 and ATLAS tuning. Could be more ! 10 4 events p+p analysis

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 5 Results of first run events (200h at 100Hz)  K 0 s 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 Λ19k Ξ p+p analysis

PbPb analysis

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 7 Strangeness enhancement Tounsi et al. PbPb analysis B. Hippolyte, Moriond 2004

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 8 Strangeness enhancement J. Rafelski 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 ? PbPb analysis

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 9 Intermediate transverse momentum 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 What : Why : PbPb analysis

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 10 Intermediate pt PbPb analysis Constituent quark scaling : P.R. Sorensen QM05 talk

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 11 R cp in heavy ion collisions PbPb analysis

K 0 s and hyperons in ALICE

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 13 2 nd vertex reconstruction K 0 s -  DCA to primary vertex Daughter DCA Angle between V0 momentum and primary vertex  -   V0 cuts, selecting Λ Bachelor DCA to primary vertex DCA V0- Bachelor 4 parameters5 parameters Angle between cascade momentum and primary vertex + vertex radius +

29/05/ Vietri sul Mare 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 !

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 15 Effect of event multiplicity 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 in PPR2 : p+p collisions

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 16 Reconstruction factors & raw spectra 10 9 events in PPR2 : p+p collisions

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 17 Reconstruction in PbPb collisions Λ Ξ Ω in PPR2 : PbPb collisions

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 18 Raw spectra in PbPb at 5.5 TeV in PPR2 : PbPb collisions Λ Ξ Ω

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 19 Signal selection by the LDA LDA Neural netClassical cuts LDA is :  Faster than anything else, more reliable than neural networks  Significance increases by 20%  Amount of selected signal increases by 60% ΛΞ Linear Discriminant Analysis + succession of cuts in the n-dim space of parameters

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 20 Conclusion  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  Analysis of K 0 s and hyperons tested in p+p and PbPb collisions  Strange objects (V 0 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... p+p PbPb

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Backup slides

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 25 To do next : Physics Data Challenge 06 Lacks in PPR2 :  systematic from the primary vertex resolution  full study of Omega reconstruction efficiency What PDC 06 will provide : 10 8 events More realistic simulations calibration (dead channels, mis-alignment,...) Trigger simulation Ξ reconstruction rate, scaled by the difference seen in PbPb Last Data Challenge : test of the analysis speed and the CPU requirement !

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 26 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 enriched events with Ω, with Ωbar STAR UA5 SPS Pythia  bar √s√s dN/dy (-0.5<y<0.5) K0sK0s SPS CDF STAR UA5 Pythia √s√s

29/05/ Vietri sul Mare 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 enriched events with Ω, with Ωbar  SPS RHIC Pythia √s√s K 0 s, Λ and Ξ estimation are acceptable, but Ω

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 28 Baryon excess : Λ/K 0 s 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) PbPb analysis

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 29 Λ/K 0 s in pythia

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 30 versus mass in p+p at RHIC

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 31 thermal particle production

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 32 R AA in heavy ion collisions We can also do R AA Several effects here : shadowing at low pt Cronin effect strangeness enhancement jet quenching H. Caines, STAR PbPb analysis

29/05/ Vietri sul Mare Ludovic Gaudichet INFN, Torino 33 Azimuthal correlation at high p T