1. Two particle correlations: from RHIC to LHC Francesco Noferini Bologna University INFN – sez. Bologna ALICE-TOF Tuesday, May 16th Villasimius (Italy) HOT QUARK 2006

2. Tuesday, May 16th Francesco Noferini 2 OUTLINE  Results from RHIC on two particle correlation studies;  Quenching effect interpretation;  Monte Carlo Simulation of quenching effects (pythia, hijing);  Prediction at LHC;  Conclusions.

3. Tuesday, May 16th Francesco Noferini 3 STAR results on two particle correlations Phys.Rev.Lett.91:072304,2003 [STAR Collaboration] arXiv:nucl-ex/0604018 Increasing the value of the p T trigger cut the back-to-back correlation is visible again. In this p T range, only for central AA collisions, the back-to-back correlation is suppressed. 4 < p T trig < 6 GeV/c 2 GeV/c < p T corr < p T trig

4. Tuesday, May 16th Francesco Noferini 4 Geometry of collision L1L1 L2L2 Properties: L 1 ≠L 2 Strong dependence on the impact parameter (b) ΔE i enhancement with L i Jet pair production

5. Tuesday, May 16th Francesco Noferini 5 Quenching Mechanism The quenching mechanism proposed by Wiedeman & Salgado is parameterized as follows (Quenching Weight): characteristic scale for the radiation mean squared momentum for unity length The spectrum emission of gluons depends only on  c and R : C.A. Salgado and U.A. Wiedemann, Phys. Rev. D 588, 303 (2000) The avarage energy loss in this prediction is proportional to L 2 = path length squared through the medium.

6. Tuesday, May 16th Francesco Noferini 6 Quenching in Aliroot Quenching Weight (class in Aliroot framework) based on the Wiedemann-Salgado model, takes in account the Nuclear Geometry. An effective transport coefficient is calculated starting from the formula: If we define: Then: depends on b All information Nuclear Geometry Procedure is described in ref. A.Morsch J.Phys. G31 (2005) s597.

7. Tuesday, May 16th Francesco Noferini 7 Energy loss and radiated gluons In the code implementation (AliPythia::Quench method) the number of radiated gluons (multiple soft) are = 1 / (1-z*), in this way the energy of radiated gluons is always lower than that of the final leading parton. * z = fraction of energy loss ALICE PPR Vol. II Chapter 6

8. Tuesday, May 16th Francesco Noferini 8 Some results expected from Jet Quenching N. Borghini and U. A. Wiedemann, hep-ph/0506218 & ALICE PPR Vol. II, Chapter 6

9. Tuesday, May 16th Francesco Noferini 9 Dependence of q from centrality * A. Dainese, C. Loizides and G. Paic, Eur. Phys. J. C 38, 461-474 (2005) Dainese, Loizides and Paic results show* that a good agreement with RHIC data is reached with q ~ 14 GeV 2 /fm for: ^ ^

10. Tuesday, May 16th Francesco Noferini 10 Standard HIJING results at RHIC energy Results for two particle correlation obtained from HIJING with the quenching model implemented in the original code. The partial suppression affects both the peaks (near correlation, back correlation) so it is not fine when compared with RHIC data. Energy loss in HIJING quenching model is proportional to L = path length through the medium.

11. Tuesday, May 16th Francesco Noferini 11 Simulation strategy

12. Tuesday, May 16th Francesco Noferini 12 PYTHIA simulation @ 200 GeV eff in central collisions ~ 5 GeV 2 /fm Suppression vs. centrality qualitatively described by the model (factor 5 suppression wrt peripheral collisions, although the away side peak does not disappear completely). ^

13. Tuesday, May 16th Francesco Noferini 13 Some parameters in HIJING simulation  N gluon (emitted gluons) = 1 / (1-z);  k T lead leading parton momentum from the medium = ;  k T rad of the radiated gluons = k T lead /sqrt(N gluon );  Max. fraction of energy loss = 0.7, N gluon max = 4. eff in central collisions ~ 14 GeV 2 /fm ^ z = fraction of energy loss

14. Tuesday, May 16th Francesco Noferini 14 Hijing also without background  For statistics reasons some simulations are obtained for events with a single Nucleon- Nucleon collision. However, the quenching effect is simulated assuming the Glauber geometry and the Quenching Weight scheme (as for full simulations).  Results with hijing are consistent with those from PYTHIA. The advantage in using HIJING is that is possible to simulate signal and background together.

15. Tuesday, May 16th Francesco Noferini 15 HIJING results @ 200 GeV HIJING single collision HIJING full event Like in PYTHIA+quech. simulations the back side correlation is strongly suppressed. The full HIJING+quench. simulations (preliminary results N trig = 2700) confirm this effect. Background doesn’t correspond exaclty to RHIC data but the Monte Carlo is not tuned yet.

16. Tuesday, May 16th Francesco Noferini 16 What happens at higher trigger p T ? N trig = 4493 HIJING single collision Increasing the value of the p T trigger cut the back-to-back correlation is clearly visible again as in RHIC data.

17. Tuesday, May 16th Francesco Noferini 17 Radiation effects at low p T with radiation effects (WR) without radiation effects (WoR) N trig = 1713(WR)/150(WoR) In the kinematic region of low pT, for central collisions, the contribution to back-to-back correlations could be due to the radiated gluons. HIJING single collision

18. Tuesday, May 16th Francesco Noferini 18 HIJING simulation @ 5.5 TeV HIJING single collision HIJING full event Simulation at LHC energy with the quenching strength used for the simulation @ 200 GeV shown a clear signal with this choice for p T cut. It is possible to test the di-hadron correllation for different p T cuts. 5.5 TeV 8 < p T trig < 15 4 < p T corr < 6 5.5 TeV 8 < p T trig < 15 4 < p T corr < 6 |η| < 1

19. Tuesday, May 16th Francesco Noferini 19 Conclusions  Quenching Weight implementation in HIJING seems to work in the kinematical regions investigated @ RHIC and it is more realistic than the standard quenching effect simulated in the HIJING original code;  In this way is possible to study the scenario could happen @ LHC for the observables presented herein;  Implementation of radiated gluons is still not complete but the analysis seems to be sensible at their contribution.

20. Tuesday, May 16th Francesco Noferini 20 Backup

21. Tuesday, May 16th Francesco Noferini 21 Some results expected from Jet Quenching -II A.Morsch J.Phys. G31 (2005) s597. No quenched Quenched Energy distribution around a jet axis for a jet of 100 GeV. Background:

22. Tuesday, May 16th Francesco Noferini 22 Other plots from STAR [STAR Collaboration] arXiv:nucl-ex/0604018 8 < p T trig < 15 GeV/c

23. Tuesday, May 16th Francesco Noferini 23 [PHENIX Collaboration] arXiv:nucl-ex/0511044 At lower value of p T some new effects come out.

24. Tuesday, May 16th Francesco Noferini 24 Impact Parameter vs. Centrality calculated in Glauber Geometry (class $ALICE/FASTGEN/AliFastGlauber.h)

25. Tuesday, May 16th Francesco Noferini 25 Quenching Weights in HIJING Monte Carlo THijing class AliQuenchingWeights AliFastGlauber classes HIJING Monte Carlo Fortran Call to HIJING code: Generation of partons scattering Quenching of the hard partons: call to Quenching Weight class Call to HIJING code: Fragmentation

26. Tuesday, May 16th Francesco Noferini 26 Pythia without quenching Rate: 60k events over 10M nucleon-nucleon collisions In the Transverse Plane (x,y) pp

27. Tuesday, May 16th Francesco Noferini 27 Pythia + Quenching  L (HIJING) Rate: 5k events over 10M nucleon-nucleon collisions b = 0 fm AuAu E loss = 2 GeV/fm

28. Tuesday, May 16th Francesco Noferini 28 Pythia + Quenching  L 2 Rate: 6k events over 10M nucleon-nucleon collisions b = 0 fm AuAu q = 1.5 GeV 2 /fm ^

29. Tuesday, May 16th Francesco Noferini 29 Suppression vs. Impact Parameter (b) Quenching  L Quenching  L 2 [suppression ΔΦ = π]

30. Tuesday, May 16th Francesco Noferini 30 Region of jet production External Region in Central Collisions AuAu b = 0 fm r