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Multi-Strange Baryon Analysis in High-Energy Collisions

Explore yield extraction and azimuthal correlations of multi-strange baryons (Ξ, Ω) in ALICE experiment. Investigate collective effects and particle identification in collision data.

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Multi-Strange Baryon Analysis in High-Energy Collisions

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  1. Antonin.MAIRE@cern.ch – IPHC Strasbourg Antonin MAIRE – PhD student / IPHC Strasbourg Tuesday, September 22nd 2009 – PWG2 meeting Multi-strange baryon (Ξ-/+,Ω-/+) analyses : Yield extraction, Azimuthal correlations.

  2. Antonin.MAIRE@cern.ch – IPHC Strasbourg Outline • Introduction : Ξ±, Ω± and ALICE • Analysis 1 : Yield extraction • Particle IDentification • Analysis 2 :Correlations Ξ±- h± or Ω±- h± • Conclusions and perspectives

  3. Antonin.MAIRE@cern.ch – IPHC Strasbourg → Charged multi-stranges baryons : Ξ- (dss) Ξ+ (dss) Ω- (sss) Ω+ (sss) I.1 – Intro. : multi-strange baryons

  4. Antonin.MAIRE@cern.ch – IPHC Strasbourg ITS : SPD (rtransv = 4cm & 7cm) π- → Charged multi-strange baryons : Ξ- (dss) Ξ+ (dss) Ω- (sss) Ω+ (sss) Ξ- ITS : SDD (rtransv = 15 cm & 24 cm) Λ0 ITS : SSD (rtransv = 39 cm & 44 cm) π- p TPC (rtransv = 85 cm) I.2– Intro. : multi-strange baryons & ALICE Sub-detectors needed for cascades : 1. Inner Tracking System 2. Time Projection Chamber What we detect from Ξ-, Ξ+, Ω-, Ω+ : - bachelor, - both V0 daughters. PPR Vol. II, p.1303

  5. Antonin.MAIRE@cern.ch – IPHC Strasbourg II – Yield extraction

  6. Antonin.MAIRE@cern.ch – IPHC Strasbourg Au-Au βradial ≠ 0 II.1 – Incentives : collective effects • « Radial flow » : → shape of the 1/pt. d2N/dptdy spectrum Flow seen in Au-Au RHIC data Example of a Tsallis Blast-Wave fit Blast-Wave (constraint at low Pt) + Power law (constraint at high Pt) Radial flow in p-p collisions at LHC ? → test with huge statistic, this, until high pt ... Tang et al. / arXiv:0812.1609 • Why using Ω, Ξ for this ? “… 2. small cross section for hadronic interactions • 3. decay mode in cascade • → identification possible over a large energy range”

  7. Antonin.MAIRE@cern.ch – IPHC Strasbourg II.2 – Analysis : current status • Raw material → 4 x TH3F within an analysis task : EffectiveInvariant MassVs PtCasc VsYCasc with different alternatives for PID (see Twiki page) : • without PID, • with PID : bachelor kaon, proton + kaon, proton … • Around histograms … → Efficiency Map in 2D en (Pt, Y) • → Post-treatment Root macro : • extraction of signal, of noise … per bin in pt • → Set of Root macros for the Blast-Wave fit • (Boltzmann-Gibbs Blast-Wave so far …)

  8. Antonin.MAIRE@cern.ch – IPHC Strasbourg II.3 – Yield extraction : example of Ξ- Example of Pt bin Pythia p-p at 10 TeV – 94 Mevts No PID Yield (without efficiency corrections) Overall signal (integrated in Pt)

  9. Antonin.MAIRE@cern.ch – IPHC Strasbourg II.4 – Needed stat. : 2 cases (for Ξ) • Foreword • Assessments made for Ξ- for p-p at 10 TeV, • based on Pythia • NB : a priori = underestimates • (Pythia is known to underestimate strangeness prod…) 94 Mevts → http://arxiv.org/abs/nucl-ex/0607033 Same estimations for Ω? – not yet, but … → http://arxiv.org/abs/0907.1509 • Needed statistic 1. Comfortable case = 100 Mevts … : Spectrum in1/pt. d2N/dptdy, > 15 points with good uncert., up to 7- 8 GeV/c 1,76 Mevts 2.« Bare Minimum » case : = spectrum made of 4 points, with 10% uncert. in each bin up to 4-5 GeV/c ? 2.1 – Need in min bias evts = 1,76 M min bias evts 2.2 – Need in High Multiplicity evts (extrapolation from min. bias) 640 k Hgh Mutliplicity evts (see Twiki page)

  10. Antonin.MAIRE@cern.ch – IPHC Strasbourg III – Particle ID Ω- Care : LHC09a4 data = Ω enhanced ! Priors (π =1; K=1; p=1) MC prod LHC09a4 (100 Mevts analysed)

  11. Antonin.MAIRE@cern.ch – IPHC Strasbourg III.1 – Comb. PID: significance = f(pt) No PID Kaon+Proton PID Kaon PID Ω- Significance extraction

  12. Antonin.MAIRE@cern.ch – IPHC Strasbourg III.2 – Comb. PID: summary plot 1. Kaon PID = efficient at low Pt, → up to 3 GeV (where the bckgnd is the highest = contribution of Ξ to the combinatorial bckgnd of Ω) 2. The complementary use of proton PID - on top of Kaon PID - does not help, at any Pt. 3. Starting from 3 GeV for PtCasc, the use of Kaon PID becomes counter-productive. Priors (π =1; K=1; p=1) Care : LHC09a4 data = Ω enhanced ! MC prod LHC09a4 (40 Mevts analysed) → See Twiki page

  13. Antonin.MAIRE@cern.ch – IPHC Strasbourg IV – Azimuthal Correlations

  14. Antonin.MAIRE@cern.ch – IPHC Strasbourg IV.1 – Incentives : hadronisation mechan. Soft or hard hadronisation ? (→ in Pb-Pb, coalescence Vs fragmentation ?) Tool : azimuthal correlations with 2 particles, as a 1st step → Correlation study led at RHIC in Au-Au, for Ξ±- h± et Ω±- h± in d-Au, for Ξ±- h± in p-p, … missing stat … See also the jumping-off point : - J. Bielcikova (STAR) / arXiv :0701047 - R. Hwa / arXiv: nucl-th/0602024 B.Abelev (STAR) / arXiv:0705.3371 Question : correlation in p-p at LHC ?

  15. Antonin.MAIRE@cern.ch – IPHC Strasbourg IV.2 – Analysis : current status • Raw material → 4 x THnSparseF with 5 dimensions, within an analysis task : Δφ(Casc,Track) VsΔη (Casc,Track)VsPtCasc VsPttrack VsEff. Inv. Mass → Macro for post-treatment : selections + projection of THnSparse • Principles of the analysis • 1. Restriction to ±10 MeV around the nominal mass, Mpdg, • 2. Cascade = leading particle in each retained event, • 3. Exclusion of the 3 tracks that build the cascade.

  16. Antonin.MAIRE@cern.ch – IPHC Strasbourg IV.3 – Illustration : example of Ξ- 94 Mevts analysed • Comment + open question : - we guess a fragmentation mechanism … - Why the away-side peak = flatter + wider ?! whereas we are in p-p … (→ Tri-jets ? No back-to-back in ηdir ?)

  17. Antonin.MAIRE@cern.ch – IPHC Strasbourg IV.4 – Analysis : perspectives • Next improvements → re-think some simplifying hypotheses, → for h±, restrain track selection to primary tracks, → correct in efficiency = f(pt, φ, η ), for the cascade and for tracks h± ? • Needed statistic → no figures available with this respect … What is clear, though : need of statistic ! (Correlation h± - h± = appeared in STAR in 2003-04 Correlation Ξ ± or Ω± - h± = appeared in STAR in 2005-06) • Foreseen requirements : → need of purity for cascades → tighter selections + PID ! → understanding of the simulations →Simulation with another generator (EPOS) → Difficulty in Pb-Pb : subtraction of v2 … (I couldn’t go for such a correlation analysis in Pb-Pb) • Hypotheses : • 1. no interaction of Xi with matter (beam pipe, ITS, …) • 2. straight trajectory within the field. → φ(Xi) at emission = φ(Xi) found by reconstruction at the Xi decay vertex → introduction of a syst. error (1-4o)

  18. Antonin.MAIRE@cern.ch – IPHC Strasbourg Perspectives • Developments linked with the yield analysis • → applications of the efficiency corrections, → implementation of the Tsallis Blast-Wave fit. - Embedding, - Simulation with another generator (EPOS). • Developments linked with the PID tool - test PID on Pb-Pb simulated data, - play with priors. • Developments linked with the correlation analysis → control of the systematic error sources, → control of the background, → understanding of the hard/soft interplay at the level of simulation.

  19. Antonin.MAIRE@cern.ch – IPHC Strasbourg Conclusion 1. Question of the similarities between p-p (at LHC) and A-A (at RHIC…) : - hadronisation mechanisms ? - radial flow ? 6. Angular Correlation study Ξ±-h± and Ω±-h±, • in p-p collision. 2. Appropriate probe : multi-strange baryons (identifiable from low to high pt) 3. Topological reconstruction of cascades 5. Test a Tsallis Blast-Wave fit on 1/pt. d2N/dptdy spectrum • in p-p collision, • in Pb-Pb collision. 4.Control tools for reconstruction - QA task (ESD/AOD) - visualisation, AliEVE - ...

  20. Antonin.MAIRE@cern.ch – IPHC Strasbourg Appendices • Topological identification • Efficiency = f(pt) or … = f(pt, y) • Boltzmann Blast-Wave fit • Extrapolation from Min. Bias to Hgh Multipl. evts • Status of both analyses within AliRoot

  21. Antonin.MAIRE@cern.ch – IPHC Strasbourg A.1 – Topological Identification Default selections in AliCascadeVertexer = the same since Dec. 2006 → = cuts adapted to p+p events 1.χ2 < 33 2. | Eff. V0 Mass – m(Λ0) | < 10 MeV 3.Cos(«Xi» Pointing Angle) > 0.9985 4.+ 5. Fiducial volume : 0.2 cm < transverse pos. of «Xi» vertex < 100 cm

  22. Antonin.MAIRE@cern.ch – IPHC Strasbourg A.2 – Topological Identification 7. DCA of the bachelor track at the 1ry vertex > 0.035 cm 6. DCA of the V0 at the 1ry vertex > 0.05 cm 8. DCA between “Xi” daughters < 0.10 cm

  23. Antonin.MAIRE@cern.ch – IPHC Strasbourg Reconstructed Ξ - : 22 868 Ξ - generated. at mid-rapidity : 932 995 2,45 % Overall efficiency for Ξ - = B.1 – Efficiency = f(pt ) Ξ- Hypotheses : No PID 1. Pythia p-p at 10 TeV, Here, 98.8 Mevts analysed with MC 2. Considered channel = Ξ - 0 +π - - )+π - (B.R. = 99,88% * 63,9% = 63,8 % ) Used definition Nb of MC part. effectively reco. Eff. = __________________________________________ Nb of gen. at |y| < 1

  24. Antonin.MAIRE@cern.ch – IPHC Strasbourg B.2 – Efficiency in 2D = f(pt ,y) Ξ-associés au MC = Ξ-générés

  25. Antonin.MAIRE@cern.ch – IPHC Strasbourg (GeV/c2)2 C – Boltzmann Blast-wave fit • Exercise : Boltzmann Blast-Wave fit on some STAR data : Au+Au at √SNN = 62.4 GeV Following : Retiere, Lisa :arXiv:nucl-th/0312024v3 Schnedermann et al : arXiv:nucl-th/9307020v1 • Next step : Tsallis Blast-Wave fit ...

  26. Antonin.MAIRE@cern.ch – IPHC Strasbourg D – Extrapolation for Hgh Multi. evt Bare minimum stat in Min bias events To extract a 1/pt. d2N/dptdy spectrum with : - 4 points, - 10% uncert. in each bin, - up to 4-5 GeV/c. MB → basis for extrapolating the needed stat. to get the same accuracy in Hgh Multiplicity evts. 1,76 Mevts

  27. Antonin.MAIRE@cern.ch – IPHC Strasbourg E.1 – Analysis Status : CheckCasc. Description of the task : AliAnalysisTaskCheckCascade 1. performs basic cross-checks prior to full Cascade analysis (advanced QA task) = Validation of the cascade vertexer selections = Info for extra selections (Armenteros, Λ mass Vs Ξ- mass…) 2. provides TH3F Inv Mass Vs Pt Vs Y = raw material for yield extraction, = wi/wo combined PID, under different mass hyp. (Ξ-/+, Ω-/+ ) ... 3. provides THnSparseFΔφ(Casc,Tr) Vs Δη (Casc,Tr) Vs … = correlation study Output : TList of 44 TH1F, 11 TH2F, 10 TH3F and 4 THnSparseF Readiness of the code : - code is in SVN ($ALICE_ROOT/PWG2/SPECTRA), - class in compliance with ALICE Analysis Framework, - tested on local, CAF, GRID with latest aliroot trunk, - able to process ESD ... or ~ AOD, pp or PbPb.

  28. Antonin.MAIRE@cern.ch – IPHC Strasbourg E.2 – Analysis Status : CheckPerf. Description of the task : AliAnalysisTaskCheckPerformanceCascade →Performs study of performance with MC info = look for any primary generated cascades, = look for generated cascades which are findable, = Inv Mass distribution of the candidates under different mass hypotheses (Ξ-/+, Ω-/+ ), = Association of reconstructed cascade candidate to MC cascade, = tap MC PID info, Output : TList of 59 TH1F and 27 TH2F Readiness of the code : - code is in SVN ($ALICE_ROOT/PWG2/SPECTRA), - class in compliance with ALICE Analysis Framework, - tested on local, CAF, GRID with latest aliroot trunk, - able to process ESD ... + ~AOD, pp or PbPb.

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