Jet and direct photon physics with ALICE EMCal

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

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

What has been learned at RHIC? Jet-Quenching at s = 200 A Ge. V Nuclear Modification Factor Ratio of particle No prompt g suppression! distributions q. L 2 in p-p and NA-NB collisions 13/11/2007 Factor 5 hadron suppression! well described by p. QCD+partonic energy loss jets lose energy in dense matter G. Conesa Balbastre @ ALICE-Italy workshop 3

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

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

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, ( 0), 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 / 0 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 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 6

Basic yields for 5. 5 A Te. V Pb+Pb collisions Inclusive jet rates very high Heavy flavours copiously produced +jet, Z+jet: precision measurements, but limited dynamic range 13/11/2007 10 k/year G. Conesa Balbastre @ ALICE-Italy workshop 7

Jets: Role of EMCal in jet reconstruction Magali R<0. 5, pt>2 Ge. V/c Charged + neutral RMS [Ge. V] 21 15 Econe/ET 0. 50 0. 77 67% 80% Efficiency 13/11/2007 R=0. 3, p. T > 2 Ge. V/c Jets can be found in Pb-Pb collisions and measured accurately for energies larger than 40 Ge. V G. Conesa Balbastre @ ALICE-Italy workshop 8

Thanks to Magali E. Jets: Reconstructed energy Avoid possible reconstruction with the leading in the TPC Simulate 100 Ge. V @ 14 Te. V 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 - Eseed = 4. Ge. V - Emin = 10. Ge. V - p. Tcut = 0. Ge. V/c TPC (Ge. V) 43. 0+/-0. 6 TPC+EMCal 75. 9+/-0. 7 RMS (Ge. V) 16. 9+/-0. 5 Resolution 39. 3% 21. 7+/-0. 6 28. 6% Emean 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 9

Thanks to Magali E. Jets: EMCal acceptance effects | | < 0. 3 TPC+EMCal TPC only 100 Ge. V Jets Full simulation R=0. 4 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 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 10

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

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

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

Isolation Cut in EMCal Pb. Pb Te. V pp@@√ √s=5. 5 A s=14 Te. V w Preliminary study at the generator level (PYTHIA) with EMCal. Study done with Amaya Casanova Díaz 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 14

Why -hadron/jet correlations? p 0 Jet Fragmentation ^ Medium effects redistribute ( q. L) the parton energy, Eparton, inside the hadron jet (multiplicity, k. T). Ø Hadron redistribution can be best measured in the Fragmentation Function. . . If we know Eparton. Ø Prompt g HI environment limits the precision on the energy of the reconstructed jet/parton: Ø Measure Eprompt g Eparton Ø Study medium modification in fragmentation function (RAA of FF) from isolated -jet and isolated -hadron correlations. 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 15

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

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

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

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

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

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

Thanks to Rafa D. and Jan R. P. Feynman, R. D Field, and G. C. Fox, Phys Rev D 18 1978 J. Rak and M. Tannenbaum hep-ex/0605039 v 1 k. T effect p. Ta √ 2 k. Ty p. Tpair Outgoing partons carries transverse momentum k. T. ΔΦ p. Tt √ 2 k. Tx - momentum imbalance (partons pt are not equal ) due to k. Tx component Intrinsic : fermi motion of the confined partons inside the proton. NLO: hard gluon radiation Soft: initial and final state radiation /resummation techniques (hepph/9808467) 13/11/2007 . - 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 G. Conesa Balbastre @ ALICE-Italy workshop 22

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

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

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

More details in Cynthia’s and Delia’s talks, tomorrow EMCal http: //aliceinfo. cern. ch/Collaboration/Documents/EMCal. html Acceptance D = 1. 4 DF = 110 o 12 Super Modules 2 SM per 20 o sector 2304 towers per sector Placed interaction point 13/11/2007 at 4. 5 m from G. Conesathe Balbastre @ ALICE-Italy workshop PHOS 26

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 1. 0 105 EMCal enhances recorded yields of triggered hard probes by factors 10 -60, depending on collision system 13/11/2007 G. Conesa Balbastre @ ALICE-Italy workshop 27