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24/6/2007 P.Ganoti, 1 Study of Λ(1520) production in pp TeV with the ALICE detector Paraskevi Ganoti University.

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Presentation on theme: "24/6/2007 P.Ganoti, 1 Study of Λ(1520) production in pp TeV with the ALICE detector Paraskevi Ganoti University."— Presentation transcript:

1 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 1 Study of Λ(1520) production in pp interactions @14 TeV with the ALICE detector Paraskevi Ganoti University of Athens for the ALICE Collaboration

2 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 2 Outline  Introduction and Physics Motivation  The kinematic properties of the produced Λ(1520) by Simulation  The Geometrical Acceptance and the Reconstruction Efficiency of Λ(1520) in pp interactions inside the ALICE detector  Invariant mass spectra of K-p pairs  Conclusion and future plans

3 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 3 Introduction-Physics Motivation The production of Resonances is a method to study the dynamics of QGP hadronization. The idea is to use unstable resonances with varying lifetime (typical lifetimes comparable to that of the hot and dense matter created in heavy ion collisions) and to determine the effect of rescattering and regeneration on the Resonances yields. After hadronization of the QGP, but before the interactions of the hadrons cease, the physical properties of resonances, such as their masses and widths, might be modified by the density of the surrounding medium. In addition, the yield might change. Resonance Life-time [fm/c]  1.3  ++ 1.7 f 0 (980) 2.6 K*(892) 4.0   (1520) 13 ω(783) 23  (1020) 45 The overall net effect of rescattering and regeneration on the total observed yields depends on the time interval between chemical and thermal freeze- out, the lifetime of the resonances and the magnitudes of the interaction cross- sections of the decay particles

4 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 4 Signal measured Pb-Pb Hadronization: Hadrons are formed from quarks Chemical freeze-out: end of inelastic interactions (particle yields) Thermal freeze-out: end of elastic interactions (particle spectra) Λ(1520)  p π K-K- Rescattering Κ-Κ- p Λ(1520) K- K- p Regeneration Signal lost space time Resonances may probe the timescale between chemical and kinetic freeze-out

5 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 5 Λ(1520) is a resonance with: m = 1519.5 MeV/c Width = 15.6MeV/c, τ = 13fm/c, BR(NK)=45% In this analysis 1.08M min bias pp simulated events @14TeV have been used. In these events, 18200 Λ(1520) are generated in |η| < 0.9 and with p T > 0.2GeV/c -> 0.017/event. Glossary Perfect PID : we know exactly the kind of a reconstructed particle from comparison with generation Detectors PID : the PID that the combination of the central ALICE detectors give. In this analysis only the PID information from TPC and TOF are used. Λ(1520) : Both Λ * + Λ *. Similarly, K: Both K + + K -, p: Both p + p Event Sample for Λ(1520) study

6 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 6 Λ(1520):Kinematic Properties Generated Λ(1520) 241265 generated Λ(1520) with = 0.82GeV/c Λ(1520) = 0.82GeV/c = 0.57GeV/c = 0.37GeV/c

7 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 7 Generated in |η| 0.2GeV/c 18200 generated Λ(1520) with = 1.28GeV/c = 1.28GeV/c = 0.87GeV/c = 0.53GeV/c

8 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 8 Geometrical Acceptance # Λ(1520) in |η| 0.2GeV/c # Λ(1520) generated in |η| 0.2GeV/c Mean Geometrical Acceptance : ~73%

9 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 9 K, p interactions with the detector material Reconstruction Efficiency I p K - (all) K - interactions K - decays ITSTPCTRDTOF

10 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 10 Reconstruction Efficiency II 3623 Λ(1520) (out of 13248 that are geometrically accepted) are lost due to interactions/decay of K/p in a radius R < 100cm. p K + (all) K + interactions K + decays The numbers in the above plots reflect the different cross sections of K +, K -, p and p. σ(K - ) ~ 2σ(K + ) and σ( p ) ~ 6σ(p) around 1GeV.

11 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 11 Reconstruction Efficiency III Reconstructed Λ(1520) in |η| 0.2GeV/c assuming perfect pid # Λ(1520) generated in |η| 0.2GeV/c after accounting for K, p interactions/decay Mean Reconstruction Efficiency : 57%

12 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 12 Perfect PID Count 5441 reconstructed Λ(1520) if only the K-p pairs becoming from a true generated Λ(1520) are accepted. B.W. fit results χ 2 /ndf =15.17/9 M Λ(1520) = (1.52  0.00)GeV/c 2 Γ = (0.01644  0.00039) True Signal

13 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 13 All pairs from the same event and the mixed-event background

14 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 14 B.W.+polynomial fit results χ 2 /ndf =199.2/6 M Λ(1520) = (1.52  0.00)GeV/c 2 Γ = (0.01968  0.00051) Extracted Signal 4533  162 reconstructed Λ(1520) inside 2σ (in comparison with the 5441). S/B = 0.42 and S/  (S+B) = 36.5

15 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 15 Comparison of True - Extracted signals

16 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 16 B.W. fit results χ 2 /ndf =15.25/9 M Λ(1520) = (1.52  0.00)GeV/c 2 Γ = (0.01661  0.00065) True Signal 2026 reconstructed Λ(1520) if only the K-p pairs becoming from a true generated Λ(1520) are accepted. Detectors PID (TPC + TOF)

17 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 17 All pairs from the same event and the mixed-event background

18 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 18 Extracted Signal B.W.+polynomial fit results χ 2 /ndf =130.8/5 M Λ(1520) = (1.523  0.000)GeV/c 2 Γ = (0.0392  0.0012) 1951  162 reconstructed Λ(1520) inside 2σ. S/B = 0.16 and S/  (S+B) = 16.4

19 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 19 Comparison of True - Extracted signals

20 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 20 Generated Total 241265 Generated in |η| 0.2GeV/c 18200(100%) Both decay products are geometrically accepted 13248(72.8%) No K/p interaction nor K decay 9625(52.9%) Reconstructed Λ * (true pairs) Perfect PID case 5441(29.9%) Reconstructed Λ * (true pairs) Real PID case 2026(11.1%) Summarizing the numbers… Geometrical Acceptance Reconstruction Efficiency

21 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 21 Conclusions and Future Plans  The number of reconstructed Λ(1520) in the Detectors PID case is about 63% lower than in the Perfect PID case. This means that we need better particle identification and the corresponding groups in ALICE work towards this direction. Detectors like ITS, TRD and HMPID will be included in the next data production. In addition, from a preliminary study we expect an increase of the Λ(1520) signal of ~15% from kaon identification through their kink decays.  Study of other observables concerning Resonances Study such as - Transverse momentum and transverse mass spectra - Particle Ratios (Resonant over no Resonant particles)

22 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 22 Especially for the last observable, particle ratios in pp collisions will be the reference point for the corresponding ones in Heavy Ion collisions where we expect a decrease (or increase depending on the resonance lifetime) due to the stronger influence of the hot dense matter to the reconstruction of resonances. The project is co-funded by the European Social Fund and National Resources (EPEAEK II, PYTHAGORAS II)

23 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 23 Backup

24 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 24 Particle ratio pp STAR Au-Au STAR Thermal model Δ(1232)/p 0.72 ± 0.108 0.96 ± 0.148 0.68 K(892)/K 0.389 ± 0.029 0.228 ± 0.044 0.32 Λ(1520)/Λ 0.104 ± 0.03 0.033 ± 0.017 0.071 Φ(1020)/Κ 0.124 ± 0.025 0.1556 ± 0.0311 0.13 The K(892)/K and the Λ(1520)/Λ suggest that rescattering is larger than regeneration. The φ(1020)/Κ ratio is consistent with the thermal model predictions The Δ(1232)/p suggests regenaration. Results from STAR experiment

25 24/6/2007 P.Ganoti, SQM2007@Levoca-Slovakia 25 Theoretical Models Some models have been written, trying to explain the yield of the various resonances “seen” by the experiments:  Rescattering of the decay products - Regenaration of the resonance [UrQMD: Marcus Bleicher and Jörg Aichelin Phys. Lett. B530 (2002) 81. M. Bleicher and H. Stöcker.Phys.G30 (2004) 111].  Rescattering of the decay products no Regeneration of the resonance [Torrieri G and Rafelski J 2001 Phys.Lett.B 509 239-45]  Broadening of the width of the resonance and mass modification [Shuryak E V and Brown G E 2003 Nucl.Phys.A 717 322-35]

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