1. 13/11/2007G. Conesa Balbastre @ ALICE-Italy workshop 1/20 Jet and direct photon physics with ALICE EMCal Gustavo Conesa Balbastre

2. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 2/20 Why jets and photons? Study the properties of matter at high density and temperature with: Jets Partons (jets) suffer energy loss traversing the new medium  Jet multiplicity and energy redistribution  Jet-Quenching Photons Production unperturbed by the medium  Thermal photons: Temperature reached by the medium.  Prompt photons: Test QCD,  -jet events  Jet-Quenching Production perturbed by the medium  Fragmentation photons  Jet-Quenching  Decay photons (neutral mesons)  Observation of hadron suppression  Jet-Quenching Fragmentation  00  Jet Prompt 

3. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 3/20 Nuclear Modification Factor What has been learned at RHIC? Jet-Quenching at  s = 200A GeV Factor 5 hadron suppression! well described by pQCD+partonic energy loss  jets lose energy in dense matter  qL 2 No prompt  suppression! Ratio of particle distributions in p-p and N A -N B collisions

4. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 4/20 Fragmentation function Jet quenching  fragmentation strongly modified at p T hadron ~1-5 GeV Jet quenching Thanks to Letizia C. Medium modification included in PYTHIA changing the splitting functions by the vacuum+medium ones

5. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 5/20 Decay  vs Direct   p+p collisions: mainly  0  A+A collisions: Jet-Quenching RHIC: N  > N  for p T > 10 GeV/c LHC: N  > N  for p T > 100 GeV/c  PID: Shower shape + Isolation cut.  0 = 0,01-0,1 Photon Yellow Report hep-ph/0311131

6. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 6/20 Major physics capabilities of EMCal The EMCal significantly extends the scope of the ALICE experiment for Jet- Quenching and photon measurements in Heavy-Ion Collisions: 1.The EMCal provides a fast, efficient trigger for high p T jets,  (   ), electrons  recorded yields enhanced by factor ~10-60 2.The EMCal markedly improves jet reconstruction through measurement of EM fraction of jet energy 3.The EMCal provides good   discrimination, augmenting ALICE direct photon capabilities at high p T   -jet analysis 4.The EMCal provides good electron/hadron discrimination, augmenting and extending to high p T the ALICE capabilities for heavy quark jet quenching measurements See tomorrow Delia’s and Cythia’s talks for more information about EMCal geometry and PID

7. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 7/20 Basic yields for 5.5A TeV Pb+Pb collisions Inclusive jet rates very high Heavy flavours copiously produced  +jet, Z+jet: precision measurements, but limited dynamic range 10k/year

8. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 8/20 Jets: Role of EMCal in jet reconstruction Charged Charged + neutral RMS [GeV]2115 E cone /E T 0.500.77 Efficiency67%80% R 2 GeV/c Jets can be found in Pb-Pb collisions and measured accurately for energies larger than 40 GeV R=0.3, p T > 2 GeV/c Magali

9. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 9/20 Jets: Reconstructed energy Avoid possible reconstruction with the leading in the TPC Simulate 100 GeV @ 14TeV jets inside the EMCal acceptance (jets with R=0.4 totally included in the detector) Reconstruct jets inside the EMCal acceptance Parameters: - R = 0.4 - E seed = 4. GeV - E min = 10. GeV - p Tcut = 0. GeV/ c 28.6%39.3%Resolution 21.7+/-0.616.9+/-0.5RMS (GeV) 75.9+/-0.743.0+/-0.6E mean (GeV) TPC+EMCalTPC Thanks to Magali E.

10. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 10/20 Jets: EMCal acceptance effects |  | < 0.3 For a jet of R=0.4: limit for a jet to be totally included in the calorimeter limit at which the leading (here center) of the jet is still in the detector acceptance 100 GeV Jets Full simulation R=0.4 TPC only TPC+EMCal Thanks to Magali E.

11. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 11/20 Jets: R CP (  ) for 125 GeV jets Nuclear modification will be observed with great accuracy combining the Central Tracking System and EMCal Central to Peripheral Pb-Pb collisions Thanks to Joern P.

12. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 12/20 Photons:  -  0 discrimination Three regions of analysis well separated clusters  invariant mass analysis <~ 10 GeV/c (30 GeV in PHOS) Opening angle << 1 cell all  0 ’s at this energy are in jets  isolation cut > 40 GeV/c merged clusters not spherical  shower shape analysis+ isolation cut ~10 - 40 GeV/c (30-100 GeV/c in PHOS) increasing p T See tomorrow Cythia’s talk for more details

13. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 13/20 p T threshold candidate isolated if: no particle in cone with p T > p T thres p T sum in cone,  pT <  pT thres Our signal Bremsstrahlung (Background!) Two parameters define  isolation: Cone size   R Prompt  are likely to be produced isolated. Isolation cut method EMCal TPC candidate IP G. Conesa et al. NIM A 580 (2007) 1446-1459

14. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 14/20 Isolation Cut in EMCal  Preliminary study at the generator level (PYTHIA) with EMCal. pp @ √ s=14 TeV PbPb @ √ s=5.5A TeV Study done with Amaya Casanova Díaz

15. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 15/20  Hadron redistribution can be best measured in the Fragmentation Function... If we know E parton.  HI environment limits the precision on the energy of the reconstructed jet/parton: Measure E prompt   E parton Fragmentation  Jet Prompt  Why  -hadron/jet correlations?  Study medium modification in fragmentation function (R AA of FF) from isolated  -jet and isolated  -hadron correlations. 00  Medium effects redistribute (  qL) the parton energy, E parton, inside the hadron jet (multiplicity, k T ).^

16. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 16/20  Requirements for good measurement: Perturbative direct photons. At LHC p T  > 20-30 GeV/c Perturbative hadron, no medium residues. At LHC p T  > 10 GeV/c Wide z range, ideally 0  z   1 Thus ideally : minimum p T  >> minimum p T  Reasonable counting rates At LHC p T  < 100 GeV/c  François A. made a study for p T  >20 GeV/c and p T  >70 GeV/c. F.Arleo et al. hep-ph/0701207  -hadron correlations

17. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 17/20  -hadron correlation Most of the z interval... but limited counting rate. F.Arleo et al. hep-ph/0701207 Theoretical FF p T  > 70 GeV/c – p T  >10 GeV/c p T  > 20 GeV/c – p T  >10 GeV/c No match with real FF... but good counting rate. Decrease of p T  is needed

18. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 18/20 Photon-Jet correlations Case 1: Study already performed with fast reconstruction in my thesis. Redo with full reconstruction PHOS measures prompt photon. CTS and EMCal measure jet. Good statistics in 15-25 GeV jets. Charged + EM G. Conesa et al., NIM A (2007) In press

19. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 19/20 Photon-Jet correlations Case 2: To be studied EMCal measures prompt photon CTS measures jet Measure events up to 15-45 GeV  Study quenching dependence as a function of the parton energy.

20. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 20/20 Conclusions ALICE+EMCal provides unique capabilities for jet studies at the LHC ALICE+EMCal provides unique capabilities for jet studies at the LHC Trigger enhancement of jet yields Major improvement in jet reconstruction performance ~ unbiased jet measurement over large jet energy range (~200 GeV)  evolution of energy loss excellent tracking at p T ~1 GeV/c  softening of fragmentation, response of the medium to the jet excellent PID: medium modification of jet hadronization (see Cynthia’s talk) EMCal contributes to the study of  at high p T EMCal contributes to the study of  at high p T Efficient separation  /  0 with shower shapes in EMCal up to p T <~ 40 GeV/c (see Cynthia’s talk). For higher energies we need Isolation cut, also used in lower energies to subtract remaining background after shower shape.  -jet/hadron studies feasible  evolution of energy loss from 20 to 45 GeV

21. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 21/20 Back-up

22. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 22/20 kT effect Outgoing partons carries transverse momentum k T. - momentum imbalance (partons pt are not equal ) due to k Tx component - acoplanarity (the transverse momentum of one jet doesn’t lie in the plane determined by the transverse momentum of the second jet and the beam axes) due to k Ty component R. P. Feynman, R. D Field, and G. C. Fox, Phys Rev D18 1978 J. Rak and M. Tannenbaum hep-ex/0605039 v1 Intrinsic : fermi motion of the confined partons inside the proton. NLO: hard gluon radiation Soft: initial and final state radiation /resummation techniques (hep- ph/9808467). p Ta p Tt p Tpair √2k Ty √2k Tx ΔΦ Thanks to Rafa D. and Jan R.

23. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 23/20 Momentum imbalance (at parton level) Intrinsic k T with similar behavior Average differences between the photon and jet transverse momenta Thanks to Rafa D. and Jan R.

24. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 24/20 ΔΦ distributions (at parton level) Acoplanarity decreases with the gamma trigger energy For a fixed photon energy there is more acoplanarity at 14 TeV than at 200 GeV Thanks to Rafa D. and Jan R.

25. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 25/20

26. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 26/20 EMCal PHOS http://aliceinfo.cern.ch/Collaboration/Documents/EMCal.html Placed at 4.5 m from the interaction point 12 Super Modules 2 SM per 20 o sector 2304 towers per sector Acceptance  = 1.4  = 110 o More details in Cynthia’s and Delia’s talks, tomorrow

27. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 27/20 Jets: EMCal trigger ALICE Rate to tape limited by DAQ and TPC gating (<500 Hz) Level 1 trigger (level 0 in p+p) needed to utilize luminosity EMCal enhances recorded yields of triggered hard probes by factors 10-60, depending on collision system 1.0  10 5