1/45 26/03/2007 Gustavo Conesa High pT physics at LHC workshop Prompt photon physics in ALICE:  -jet &  -hadron correlations A feasibility and performance study Gustavo Conesa Balbastre

2/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Outlook Motivation: Photons in heavy-ion collisions Motivation: Photons in heavy-ion collisions Photons sources Photons sources RHIC measurements RHIC measurements ALICE experiment: Calorimeters ALICE experiment: Calorimeters Prompt photon identification Prompt photon identification Prompt photon correlations Prompt photon correlations Conclusions Conclusions

3/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Why  ? Study the properties of matter at high density and temperature with: Jets Jets Partons (jets) suffer energy loss traversing the medium  Jet multiplicity and energy redistribution  Jet-Quenching Partons (jets) suffer energy loss traversing the medium  Jet multiplicity and energy redistribution  Jet-Quenching Photons Photons Production unperturbed by the medium Production unperturbed by the medium Prompt photons: Test QCD,  -jet events  Jet-Quenching Prompt photons: Test QCD,  -jet events  Jet-Quenching Production modified or created in the medium Production modified or created in the medium Fragmentation photons  Quenching Fragmentation photons  Quenching Bremstrahlung, Jet-conversion  Enhancement Bremstrahlung, Jet-conversion  Enhancement Decay photons (neutral mesons)  Observation of hadron suppression  Jet-Quenching Decay photons (neutral mesons)  Observation of hadron suppression  Jet-Quenching Fragmentation  Jet Prompt  00

4/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Direct prompt  O  S )]: g+q   +q (Compton) q+q   +g (Annihilation) Parton in-medium-modification imprinted in the final hadronic state (jet-quenching). Prompt photons are not perturbed by the medium. Direct thermal photons Equilibrium: QGP and hadron gas. Thermal emission from the medium. Photon sources Pre-equilibrium Equilibrium Freeze-out 00 Prompt  AB Colliding ions

5/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Fragmentation prompt   O   S )]: Bremsstrahlung production modified by the medium Jet re-interaction q+g medium   +q q+q medium   +g Photon sources Prompt  AB Fragmentation  Pre-equilibrium Equilibrium Freeze-out Colliding ions 00

6/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Photon sources Photons carry unperturbed information on the hot and dense medium (direct photon), and reveal medium induced modifications (decay photons). Photon sources in the initial stage of the collision when the system is hottest (pQCD prompt, jet re-interaction, QGP thermal). Hadron gas + decay: later phase of the collision  Background EE Rate Hadron Gas Thermal T f QGP Thermal T i Jet Re-interaction √(Ti x √s) Bremsstrahlung (jet - quenching) pQCD LO (Compton) + NLO (fragmentation)

7/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Jet AB 00  Decay Photons : Neutral mesons,  0 and , decay mainly into 2 . Main photon source in heavy-ion collisions, background for direct . Mesons production suppressed (RHIC) by medium effects (jet-quenching). Only identified hadronic probe measurable up to very high p T Photon sources Pre-equilibrium Equilibrium Freeze-out Colliding ions

8/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Decay  vs Direct  p+p collisions: p+p collisions: mainly  0 mainly  0 A+A collisions: A+A collisions: Jet-Quenching Jet-Quenching RHIC: RHIC: N  > N  for p T > 10 GeV/c N  > N  for p T > 10 GeV/c LHC: LHC: N  > N  for p T > 100 GeV/c N  > N  for p T > 100 GeV/c PID: Shower shape + Isolation cut. PID: Shower shape + Isolation cut.  0 = 0,01-0,1 Photon Yellow Report hep-ph/

9/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Jet-quenching at RHIC  s = 200A GeV R AA reference: pQCD calculation Yesterday R AA reference: fit to p+p measurements Today Jet Hadrons suppression factor 5! No suppression of , as expected? CERN Heavy Ion Forum, March 6, G. David, BNL

10/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop CERN Heavy Ion Forum, March 6, G. David, BNL R AA with pQCD R AA with p+p data S. Turbide, Phys. Rev. C72 (2005) F. Arleo, JHEP09 (2006) O15 W. Vogelsang, NLO pQCD + isospin Direct  R AA in Au+Au – Theory and Experiment

11/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Outlook Motivation: Photons in heavy-ion collisions Motivation: Photons in heavy-ion collisions ALICE experiment: Calorimeters ALICE experiment: Calorimeters Prompt photon identification Prompt photon identification Prompt photon correlations Prompt photon correlations Conclusions Conclusions

12/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Solenoid magnet 0.5 T MUON Spectrometer PHOS HMPID ALICE: A Large Ion Collider Experiment ITS TPC TRD TOF Central tracking system

13/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop E > 10 GeV   E/E < 1.5%,  x =[0.5,2.5] mm Detectors to be used  =120º  |  | < 0.7  =100º  |  | < 0.12  =360º  |  | < 0.9 PHOS TPC EMCal  p/p = 2%,  =1.1º

14/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop PHOton Spectrometer: PHOS High granularity detector: High granularity detector: 17,920 lead-tungstate crystals (PbWO 4 ), 5 modules (56  64) 17,920 lead-tungstate crystals (PbWO 4 ), 5 modules (56  64) crystal size: 22  22  180 mm 3 crystal size: 22  22  180 mm 3 depth in radiation length: 20 depth in radiation length: 20 Distance to IP: 4.4 m Distance to IP: 4.4 m Acceptance: Acceptance: pseudo-rapidity [-0.12,0.12] pseudo-rapidity [-0.12,0.12] azimuthal angle 100 o azimuthal angle 100 o Charged Particle Veto, CPV Charged Particle Veto, CPV multi-wire particle gas chamber multi-wire particle gas chamber High Resolution spectrometer CPV Crystals EMC ALICE PPR chapter 5

15/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop ElectroMagnetic Calorimeter: EMCal Description: Description: 12,672 towers (scintilator-Pb), 12,672 towers (scintilator-Pb), 10 modules (24  48) + 10 modules (24  48) + 2 half size modules (12  48) 2 half size modules (12  48) tower size: 60  60  250 mm 3 tower size: 60  60  250 mm 3 depth in radiation length: 22 depth in radiation length: 22 Distance to IP: 4.28 m Distance to IP: 4.28 m Acceptance: Acceptance: pseudo-rapidity [-0.7,0.7] pseudo-rapidity [-0.7,0.7] azimuthal angle 110 o azimuthal angle 110 o EMCal is 7 times larger than PHOS but it is a moderate energy resolution calorimeter EMCal is 7 times larger than PHOS but it is a moderate energy resolution calorimeter

16/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop PHOS beam-test and simulations Energy resolutionPosition resolution E > 10 GeV   E/E < 1.5% E > 10 GeV   x =[0.5,2.5] mm Heavy-ion environment worsens the resolution by less than 2% ALICE PPR chapters 5

17/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop PHOS beam-test and simulations Fixed target experiment  C  0 (  )+X, E  - = 6 GeV Inv. Mass Resolution is 3-5% in 0.5 < E < 30 GeV in PHOS simulations ALICE PPR chapters 5

18/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop EMCal beam-test E > 10 GeV   E/E < 3% E > 10 GeV   x < 3.5 mm

19/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Outlook Motivation: Photons in heavy-ion collisions Motivation: Photons in heavy-ion collisions ALICE experiment: Calorimeters ALICE experiment: Calorimeters Prompt photon identification Prompt photon identification Isolation cut method Isolation cut method Prompt photon correlations Prompt photon correlations Conclusions Conclusions

20/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Photon identification We can discriminate  e  and   from anything else : “PCA” or “Bayesian”, based on: CPV : Charged particle rejection TOF : Rejection of massive low p T particles EMC : Hadron rejection via shower topology Algorithms tuned with simulations: Few % hadron contamination in HI environment. Designed to distinguish high-energy  and  0.  0 decay  overlaps in PHOS from 30 GeV (15 GeV in EMCal) High  identification efficiency, ~ 60%, and misidentification smaller than 10 % for 30 GeV < E  < 100 GeV. Not enough for Prompt  identification: We need Isolation Cut Method ALICE PPR chapters 5 and 6, photon sections

21/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Prompt  identification: Event generation p-p collisions: PYTHIA 6.2 as event generator, p-p 5.5 TeV: p-p collisions: PYTHIA 6.2 as event generator, p-p 5.5 TeV:  +jet in final state   – jet.  +jet in final state   – jet.  is the signal under study: 20 GeV < E  < 100 GeV. Prompt  is the signal under study: 20 GeV < E  < 100 GeV. 2 jets in final state  jet – jet. 2 jets in final state  jet – jet. These events constitute the background: These events constitute the background: and : 30 GeV < E jet < 300 GeV. high-p T  0  O  S )] and bremsstrahlung  O   S )] : 30 GeV < E jet < 300 GeV. Pb-Pb collisions: p-p collisions + underlying event for Pb-Pb 5.5 TeV, HIJING, dN/dy~6000. Pb-Pb collisions: p-p collisions + underlying event for Pb-Pb 5.5 TeV, HIJING, dN/dy~6000. Binary scaling from p-p collisions, minimum bias. Binary scaling from p-p collisions, minimum bias. No medium effects ! No medium effects ! ALICE-INT

22/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Prompt  identification: Generated signal and background Background Factor 5 suppression Direct results from PYTHIA, no detector response function, corrected for detector acceptance. Background =  decay + bremsstrahlung PHOS identifies  efficiently through Shower Topology: Not enough to tag them as prompt. Signal ALICE-INT

23/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Overlapped Clusters Rejection Signal/Background:  as     as  Too much  0 background ! New ID criteria to be found Pb-Pb collisions 1-d shower shape analysis ALICE-INT

24/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop 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. Prompt  are likely to be produced isolated. Prompt  identification: Isolation cut method PHOS TPC candidate IP Pb-Pb collisions R = 0.2, p T thres = 2 GeV/c Identification Probability 50 % Misidentification 7 % Signal/Background 4.2 pp collisions R = 0.2,  T thres = 0.7 GeV/c Identification Probability 100 % Misidentification 4.5 % Signal/Background 13ALICE-INT

25/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Final identified prompt  spectrum Annual statistics Particles identified as  (medium purity) IC: R =0.2, p T >2 GeV/c Factor 5 suppression Signal Background Statistics limits to ~ 100 GeV Corrected spectrum, systematic errors ALICE-INT

26/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Quality of data Systematic error suppressed a factor 5 by quenchingALICE-INT

27/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Outlook Motivation: Photons in heavy-ion collisions Motivation: Photons in heavy-ion collisions ALICE experiment: PHOS ALICE experiment: PHOS Prompt photon identification Prompt photon identification Prompt photon correlations Prompt photon correlations  -jet  -jet  -hadron  -hadron Conclusions Conclusions

28/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop  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 ).^

29/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Tagging jet with photon  Search identified prompt photon (PHOS) with largest p T (E  > 20 GeV). Strategy (event by event) : Strategy (event by event) :  min  max leading Search leading particle :   -  leading  180º E leading > 0.1 E  R Reconstruct the jet: Particles around the leading with p T > 0.5 GeV/c, inside a cone of R = configurations: charged and neutral hadrons (TPC+EMCAL) and charged only (TPC). IP PHOS EMCal TPC ALICE-INT

30/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Pb-Pb collisions, p T, part > 0.5 GeV/c Reconstructed jet selection 40 GeV jets TPC alone TPC+EMCAL p-p collisions, p T, part > 0.5 GeV/c TPC alone TPC+EMCAL Pb-Pb collisions, p T, part > 2 GeV/cALICE-INT

31/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Fragmentation function E  > 20 GeV/c; TPC+EMCal detect jet particles, PHOS  Pb-Pb collisions Background Signal HIC background Any neutral signal in PHOS z = p T, jet particle /E  Prompt  identified in PHOS If signal is quenched ALICE-INT

32/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Charged + EM  -tagged FF R AA  -tagged FF R AA With quenched  0 Systematic errors due to jet(  0 )-jet background Sensitive to medium modifications at low z if larger than ~5% in both configurations. ALICE-INT

33/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop  -hadron correlations We could do the same study in a simpler way: tagging hadrons opposite to the isolated . We could do the same study in a simpler way: tagging hadrons opposite to the isolated . Suggested by F. Arleo et al. in : Suggested by F. Arleo et al. in : JHEP 0609:015,2006, hep-ph/ JHEP 0609:015,2006, hep-ph/ JHEP 0411:009,2004, hep-ph/ JHEP 0411:009,2004, hep-ph/ hep-ph/ hep-ph/

34/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop F.Arleo et al. hep-ph/ = E parton  -hadron correlations

35/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Requirements for good measurement: Requirements for good measurement: Perturbative direct photons. Perturbative direct photons. At LHC p T  > GeV/c At LHC p T  > GeV/c Perturbative hadron, no medium residues. Perturbative hadron, no medium residues. At LHC p T  > 10 GeV/c At LHC p T  > 10 GeV/c Wide z range, ideally 0  z    Wide z range, ideally 0  z    Thus ideally : minimum p T  >> minimum p T  Thus ideally : minimum p T  >> minimum p T  Reasonable counting rates Reasonable counting rates At LHC p T  < 100 GeV/c At LHC p T  < 100 GeV/c Study made for p T  >20 GeV/c and p T  >70 GeV/c. Study made for p T  >20 GeV/c and p T  >70 GeV/c. F.Arleo et al. hep-ph/  -hadron correlations

36/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop  -hadron correlation p T  > 70 GeV/c – p T  >10 GeV/c Most of the z interval... but limited counting rate. F.Arleo et al. hep-ph/ Theoretical FF

37/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop  -hadron correlation p T  > 20 GeV/c – p T  >10 GeV/c F.Arleo et al. hep-ph/ Theoretical FF No match with real FF... but good counting rate.

38/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop  -hadron correlation fragmentation  contribution Much larger fragmentation  component with p T  >20 GeV/c. Decay photons will contribute much more. Isolation of direct photons will reject both.

39/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop  -hadron correlation Quenching Don’t see expected suppression in all region. Weaker energy loss, but see larger z region.

40/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop The study claims that better concentrate in p T  >70 GeV/c direct , and p T  >10 GeV/c, but our calorimeters acceptance reduce  counting rate:  PHOS  20< p T  < 40 GeV/c  EMCal  20< p T  < 60 GeV/c We have to investigate results at lower p T cuts. Basic yields for 5.5A TeV Pb+Pb collisions 1k/year

41/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop  -hadron correlation in ALICE  Search identified prompt photon (PHOS or EMCal) with largest p T (E  > 20 GeV).  Strategy following François Arleo studies (event by event) : hadron Search for all charged hadrons (TPC+ITS) or neutral  0 (EMCal or PHOS): 90º<   -  hadron < 280º p T hadron > 10 GeV/c IP PHOS/EMCal EMCal/PHOS TPC+ITS

42/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Outlook Motivation: Photons in heavy-ion collisions Motivation: Photons in heavy-ion collisions ALICE experiment: Calorimeters ALICE experiment: Calorimeters Prompt photon identification Prompt photon identification Prompt photon correlations Prompt photon correlations Conclusions Conclusions

43/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Conclusions 1/3 Identification of 2  2 pQCD processes with  Identification of 2  2 pQCD processes with  Prompt photon identification: Isolation cut method. Prompt photon identification: Isolation cut method. Efficiently rejects background. Efficiently rejects background. 20% of systematic error from left over background. 20% of systematic error from left over background. Assuming quenching, systematic errors dramatically reduced in Pb-Pb collisions. Assuming quenching, systematic errors dramatically reduced in Pb-Pb collisions. Statistics (PHOS acceptance) limits the measurement to energies below 100 GeV. Statistics (PHOS acceptance) limits the measurement to energies below 100 GeV. Photon-tagged algorithm to measure jet properties. Photon-tagged algorithm to measure jet properties. To measure the redistribution of fragmentation hadrons inside the jet (jet multiplicity, jet heating). To measure the redistribution of fragmentation hadrons inside the jet (jet multiplicity, jet heating). EMCal helps to improve the background rejection. EMCal helps to improve the background rejection. R FF shows a sensitivity of medium induced modification at the level of 5%. R FF shows a sensitivity of medium induced modification at the level of 5%.

44/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Conclusions 2/3 Within its present configuration and the developed methods, ALICE can measure photon (PHOS) tagged jets (TPC) with energy ~20 GeV. Within its present configuration and the developed methods, ALICE can measure photon (PHOS) tagged jets (TPC) with energy ~20 GeV. Adding EMCal, due to the increased acceptance, measurements of photon (EMCal) tagged jets (TPC) extended to ~ 40 GeV. Adding EMCal, due to the increased acceptance, measurements of photon (EMCal) tagged jets (TPC) extended to ~ 40 GeV. Study of the jet-quenching over a broader energy range. Study of the jet-quenching over a broader energy range. In both cases the sensitivity to medium effects is of about 5 %. In both cases the sensitivity to medium effects is of about 5 %.

45/45 26/03/2007Gustavo Conesa High pT physics at LHC workshop Conclusions 3/3  -hadron correlation provides new insight in the study of medium modifications  -hadron correlation provides new insight in the study of medium modifications Optimum conditions would be at p T  > 70 GeV/c and p T  >10 GeV/c, but small statistics, p T  > GeV/c and smaller p T  cut might be OK, to be investigated. Optimum conditions would be at p T  > 70 GeV/c and p T  >10 GeV/c, but small statistics, p T  > GeV/c and smaller p T  cut might be OK, to be investigated. Event production with the GRID started. Study  -jet/hadron correlations with new more realistic simulations. Event production with the GRID started. Study  -jet/hadron correlations with new more realistic simulations.