1. Francesco Noferini Centro Studi e Ricerche “E. Fermi” (Roma) INFN – Sez. Bologna Roma, 29-11-2007 Particle correlations in heavy ion collisions for the ALICE experiment at the LHC

2. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 2 Summary Predictions for the QGP ; Results from RHIC ; The ALICE experiment; A new analysis method for particle correlations - Fourier Analysis -; Results from Monte Carlo simulations.

3. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 3 Predictions for the QGP

4. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 4 Predictions from lattice calculations Deconfinement is expected for high density over a critical temperature of  175 MeV. The strong coupling between two quarks is expected to vanish for T > T C. Heavy ion collisions are the suitable environment to probe it. Lattice calculations taken by: O.Kaczmarek and F.Zantow, Phys. Rev. D 71 (2005) 114510

5. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 5 Predictions from lattice calculations (II) Phase transition occurs at very high density and temperature. Chemical potential vanishes when the centre-of-mass energy of the colliding system increases. In this case the order of the transition changes from the FIRST to a CROSS OVER. RHIC & LHC

6. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 6 Observables for the QGP Chemical probes Kinetic probes Strangeness enhancement and vector-meson production Effects on J/  and B-production High p T probes Electromagnetic probes Statistical models. m s  T. Jet-medium interaction. Early stages of the interaction. Collective phenomena (flow) represent also a signature of the existence of a partonic medium and provide a way to probe the medium properties!

7. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 7 Results from RHIC

8. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 8 Strong QGP: elliptic flow Expansion is driven by a gradient of pressure There is a preferential direction for particle emission dN/dφ 2v22v2  Peripheral collision

9. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 9 RHIC results: elliptic flow Results for 2 at moderate p T are consistent with an ideal strong interacting fluid at  0 viscosity. The p T dependence of anisotropy scaled by the hadron quark content shows a universal behaviour (coalescence). RR J. Adams et al. [STAR Collaboration], Phys. Rev. C 72 (2005) 014904

10. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 10 RHIC results: jet quenching High p T hadron suppression as a signature of the jet-medium interaction. Medium seems to be transparent to photons. colored medium. T. Isobe [PHENIX Collaboration], AIP Conf. Proc. 842 (2006) 56

11. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 11 RHIC results: two-particle correlations The first RHIC result for jet quenching was the away side suppression of the jet correlation in AA collisions. For this reason the back-to-back correlation suppression showed a centrality dependence. D + Au AuAu central J. Adams et al. [STAR Collaboration], Phys. Rev. Lett. 91 (2003) 072304 J. Adams et al. [STAR Collaboration], Phys. Rev. Lett. 97 (2006) 162301 No centrality dependence Suppressed when centrality increases

12. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 12 The ALICE experiment

13. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 13 The charged multiplicity expected for PbPb collisions at LHC is 2000-8000 per unit rapidity. p T > 2 GeV/c p T > 1 GeV/c p T > 0.5 GeV/c 4 m PbPb HIJING events - b < 5 fm The ALICE environment

14. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 14 The ALICE detector Solenoid magnet 0.5 T PHOS ITS PMD HMPID TOF TRD Muon Arm TPC FMD T0,V0,ZDC

15. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 15 A new analysis method for particle correlations - Fourier Analysis -

16. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 16 N   The method idea N   corr peak FFT

17. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 17 Fourier analysis (I) Calculate the spectrum for each event. Average over all the events in order to select the most significant, loosing the phase information. Draw the function with the average spectrum. (FFT = Fast Fourier Transform)

18. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 18 Advantages of this kind of analysis w.r.t. the traditional one In principle it can reconstruct any kind of azimuthal and eta correlation. It doesn’t need any trigger contrarily to the two-particle correlation method. It works at intermediate p T, where the number of (mini)jets per event is very large. OTHER PROPERTIES It counts for all the correlations of any particle with each other. It works also in case of a superposition of many signals (jets), and in this case the amplitude of the reconstructed distribution follows a - dependence ( is the number of jets).

19. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 19 N jet dependence True distribution Reconstructed distribution True distribution Reconstructed distribution True distribution Reconstructed distribution True distribution Reconstructed distribution

20. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 20 Charge correlations The convolution of the jet shape with itself: SAME SIGN CORRELATIONS OPPOSITE SIGN CORRELATIONS

21. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 21 Results from Monte Carlo simulations

22. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 22 Jet correlations in PYTHIA MC pp hard processes generated with p T > 2 GeV/c @ ; Samples of events with a fixed number of jets ( N jet ) were created (overlap of PYTHIA events); The dependence of the reconstructed shape on the number of jets per event was tested. N jet =10 N jet =100 N jet =1

23. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 23 Jet correlations in PYTHIA MC PYTHIA (true) N jet = 1 PYTHIA N jet = 10 PYTHIA N jet = 1 PYTHIA N jet = 100

24. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 24 - 1 - Monte Carlo generation (PYTHIA, HIJING, …) - 2 - Track propagation (GEANT3) - 3 - Digitization Signal similar to reality - 4 - Final reconstruction Kinematics.root xxxHits.root xxx = for a single detector xxxSDigits.root xxxDigits.root xxx = for a single detector AliESDs.root Reconstruction with the ALICE detector for pp collisions Simulations of pp events and of the ALICE detector response showed a very good efficiency and precision in the final reconstructed shape with the FFT method. Analyses on 20k fully reconstructed events

25. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 25 Jet quenching effects in PYTHIA – an improved approach – Quenching effects are introduced in PYTHIA according to BDMPS- WS weights and Glauber geometry (Parton Quenching Model).BDMPS- WS low p T Enhancement at low p T due to radiated gluons Suppression at high p T only in the back-to-back correlation

26. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 26 Fully reconstructed HIJING events Comparison between the shape reconstructed with the information from MC ( blue line ) and that after the simulation of the whole detector response ( black line ). The analysis on the fully reconstructed data is not yet corrected for efficiency. Analyses on 200 fully reconstructed events

27. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 27 Resonances and Charge correlations The contribution due to several resonances in different channel is tested for: ρ 0 π + π -  π + π -  π + π -  K + K - K *0, K *0 K + π -,K - π +

28. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 28 Contribution from the resonances to oppostite sign correlations

29. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 29 Conclusions A new method addressing jet properties, complementary to two-particle correlations, was presented. The method works in a scenario of multiple production of jets in AA events. This feature is important to probe correlations at low p T at the LHC energy because of the big amount of mini-jets produced. The intrinsic capability of the method to reconstruct the original shape of the jet was also presented. This kind of analysis represents a major tool to investigate the production of QGP at LHC through measurements of jet energy loss (& elliptic flow). An improved model for the treatment of jet quenching was developed and tested. First significant results to demonstrate the sensitivity of the method in the ALICE experiment were shown.

30. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 30 Experimental: Two particle correlations same/opposite sign Opposite sign (+-) Same sign (++,- -) chain-like charge-ordering RHIC data at Nuclear Physics A715 (2003) 272

31. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 31 Time Of Flight (TOF) – MRPC system – 18 sectors covering the whole azimuthal angle, |  |<0.9; Granularity: 2.5x3.5 cm 2 at  4 m from the primary vertex;

32. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 32 Time Of Flight (TOF) – MRPC system – Standard gas mixture: C 2 H 2 F 4 (90%), SF 6 (5%), i-C 4 H 10 (5%) Time resolution: < 100 ps (overall) Efficiency: > 99%.

33. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 33 N jet dependence TOY MODEL E jet = 10 GeV A=1 GeV/c,  kT =0.3 GeV/c p T cut = 0.5 GeV/c

34. Sec 1Sec 2Sec 3Sec 4Sec 5backupConclusions Roma, 29-11-2007 34 Direct measurement of elliptic flow Reconstruction of the flow contribution from the spectrum. b  17508  500 2 = A 2 / (A 0 / 2) as a function of p T.