Physics Perspectives with ALICE EMCAL q Physics Motivations

Physics Perspectives with ALICE EMCAL q Physics Motivations q Jet reconstruction performances q Jet fragmentation functions q -Jet capabilities q B-Jet q Conclusions International Workshop on Heavy Ion Physics at LHC, Wuhan, China, 21 -24 May 2008 1 M Germain

What have we learned about energy loss & jet quenching at RHIC ? From single particle q Charged hadron and 0 are suppressed in Au+Au q Direct photons seems not affected except at very high p. T q No suppression in d. Au -> final state effect But: RAA do not give strong constraint on energy loss model parameters Eskola et al. NPA 747, 511 (2005) T Renk, K. J Escola, hep-ph 0706. 4380 From hadron correlations q. Away side peak suppression not so clear in Au+Au data q. High p. T region compatible to jet quenching scenario : Phenix, PRC 77(2008)011901(R) q Lower p. T region modifications and structures in away side jet q Conical emission in away side peak, J. Ulery (STAR), ar. Xiv: 0704. 0220 q ……. Medium modification of the away side jet in central Au Au @ 200 Ge. V/c M Germain 2

Jet Physics at LHC Jet Reconstruction Ø increase the sensibility to medium modification via the jet fragmentation function measurement Jets in Medium: Jet(E) →Jet(E- E) + soft gluons ( E) d. N/dz= FF(z, q) Armesto et al. ar. Xiv: 0710. 3073 p. T~ 10 Ge. V M Germain z=ph/Ejet p. T~ 1 Ge. V = ln (1/z)z=ln(Ejet/ph) 3

Jet Reconstruction in ALICE • ITS+TPC+(TOF, TRD) – Charged particles |h| < 0. 9 – Excellent momentum resolution up to 100 Ge. V/c ( p/p from 1% to 6% at 100 Ge. V/c) – Tracking down to 100 Me. V/c – Excellent Particle ID and heavy flavor tagging • • EMCal – Energy from neutral particles – Pb-scintillator, 13 k towers – = 110 , | | < 0. 7 – Granulatity 0. 0143 x 0. 0143 – Energy resolution ~7 -10%/√E – Trigger capabilities PHOS – High resolution electromagnetic spectrometer (Pb. WO 4 crystals) – -Trigger – | | < 0. 12 – 220 < < 320 – Granularity: 0. 004 x 0. 004 – Energy resolution: E /E = 3%/ E – Position resolution: x/x = 23%/ E 4 M Germain

Expected Jet rates in ALICE 1 year running Charged + neutral pp (14 Te. V) 50 pb-1 Pb. Pb (5. 5 Te. V) 0. 5 nb-1 Charged : 109 evts pp 107 evts. Pb ET > Njets (Charged) (Charged+Neutral) 50 Ge. V 2. 0 107 5. 8 × 106 100 Ge. V 1. 1 106 3. 1 × 105 150 Ge. V 1. 6 105 200 Ge. V 4. 0 104 4. 8 × 104 1. 2 × 104 q Extended energy range (200 Ge. V with EMCal) q Some important reference measurements only possible with EMCal trigger. 5 M Germain

Jet Reconstruction in ALICE Pb Pb M. Estienne ET [Ge. V] pp Important bias in Pb Pb (Underlying Event) - Jet identification - Energy resolution - Low p. T contribution Iterative jet cone finder algorithm based on the UA 1 cone method. Ø Charged tracks + neutral digits/clusters in EMCal Ø Analyses performed on a ( , ) grid of size EMCal granularity in EMCal acceptance 6 M Germain

Background from Underlying event in Pb Pb E(R) [Ge. V] ALICE, PPR, Vol II J. Phys. G: Nucl. Part. Phys. 32 1295 -2040 E Bg in R cone Cone algorithm modifications — no p. T cut — p. T>1 Ge. V/c — p. T>2 Ge. V/c ETjet 150 Ge. V 100 Ge. V 50 Ge. V 30 Ge. V - look at domains Emean >> Ebg - reduce the cone size. 80% of the jet energy is included in a cone of Rc ~ 0. 3 BG and BG fluctuation scale as Rc 2 and Rc reducing them to 170 Ge. V and 12 Ge. V. - apply a low p. T cut R 7 M Germain

Jet Resolution from full simulations M. Estienne q E/E (Charged+neutral) 30 -35% (Charged only) ~ 45% q Better resolution with smaller p. T cut on charged particles q Accurate jet direction recontruction in p+p and Pb+Pb 8 M Germain

Reconstructed Jet Spectra 1 month Pb Pb running Charged only Charged +EMCAL 9 M Germain

Jet Fragmentation function reconstruction <Ejet> = 90 Ge. V M Germain Background subtraction 1/Njets. d. N/d Pb. Pb - 1/Njets. d. N/d PURE HIJING 10

Sensibility of the Fragmentation function to the medium Energy loss from PQM Ge. V 2/fm J. Putschke [AQM] Expected signal « strengh » : Ratio FF(ppquenched)/FF(pp) M. Estienne full simulation 11 M Germain

-jet physics with EMCAL • • Dominant processes in pp – g + q → + q Compton – q + q → + g Annihilation -jet correlations – E Ejet: no bias on jet energy reconstruction for FF – Direct photons are not perturbed by the medium Yaxian’s talk: precise measurement of isolated and -hadron correlation with phos Here: and -hadron correlation with EMCAL Motivated by yield improvement with EMCAL 12 M Germain

Direct detection with EMCAL Prompt are expected to be isolated (no hadronic activity around) Isolation cut method : G. Conesa et al. NIM A 580 (2007) 1446 -1459 Two parameters for isolation: q Cone size R = + q p. T threshold candidate isolated if: 2 2 ü no particle in cone with p. T > p. T thres ü p. T sum in cone, Sp. T < Sp. Tthres IP TPC R candidate EMCal Simulations: G. Conesa g – jet: Prompt is the signal under study. jet – jet: background: decay , fragmentation and hadrons. pp @ √ 14 Te. V pp @ √ 5. 5 Te. V, merged with HIJING Pb-Pb, no quenching in PYTHIA. pp @ √ 5. 5 Te. V, merged with HIJING Pb-Pb, quenching: qhat = 50 Ge. V 2/fm. 13 M Germain

Direct identification: Isolation efficiency • PID criteria based on shower shape (see Christelle’s talk)+ Isolation • Background (decay, fragmentation ) rejection inproved with PID+isolation p. Tthres = 0. 5 Ge. V/c R = 0. 2 o R = 0. 5 pp @ 14 Te. V G. Conesa p. Tthres = 2 Ge. V/c R = 0. 2 o R = 0. 5 Pb Pb @ 5. 5 Te. V ^ q=50 Ge. V 2/fm Prompt photons signal larger than background (fragmentation+ decay) for p. T larger than around 15 Ge. V/c for pp and quenched Pb. Pb events 14 M Germain

Isolated spectra in EMCAL pp @ 14 Te. V Pb Pb @ 5. 5 Te. V q=50 Ge. V 2/fm EMCAL prompt measurements allows –jet studies above 10 -20 Ge. V in pp and Pb Pb collisions. 15 M Germain

B-jet physics with EMCAL B-jets: pure sample of quark jets Measurement of B-jet fragmentation function: harder fragmentation of b quark higher z = ph/Ejet ~5000 e from B > 30 Ge. V/c Good efficiency (80%) of pion from electron rejection in EMCAL Will allow B-jet studies M Germain M. Heinz, J Putshke 16

Summary EMCAL especially devoted to high p. T and jet physics in ALICE: It will: q allow to trigger on: jets, , o, electrons q extand jet energy reaches to ~ 200 Ge. V in Pb Pb q allow to reconstruct jets and jet fragmentation functions in medium with a significant sensitivity with respect to pp q - jet physics above 20 Ge. V q B-jet physics up to ~ 80 Ge. V Study of medium properties and medium induced modifications of parton propagation through pp, p. Pb and Pb Pb collisions 17 M Germain

Backup 18 M Germain

High PT Physic Motivation Parton propagation in QCD Medium Jets, E Parton energy loss in Medium Important role of gluons Baier, Dokshitzer, Mueller, Peigné, Schiff (BDMPS): Phys. Lett. B 345(95)277 Medium Transport coefficient : ^q ; Quarkonia dissociaton medium exchanged momentum =1/( ): mean free path Medium expansion Prompt photons Gyulassi, Levai, Vitev & dilepton Nucl. Phys B 594(2001)371 Hierarchy of parton energy loss: Flavour dependance E(g) > E(q) > E(Q) color factor M Germain mass effect 19

What have we learned about medium modification at RHIC ? From hadron correlations Phenix, PRC 77(2008)011901(R) Medium modification of the away side jet in central Au Au @ 200 Ge. V/c M Germain 20

Direct Photons : Models/Generators Is there a good agreement between theoritical predictions (NLO p. QCD) and event generators? Pythia, http: //home. thep. lu. se/~torbjorn/Pythia. html | | < 0. 5 NLO calculs, L. Benhabib with INCNLO P. Aurenche et al, http: //lappweb. in 2 p 3. fr/lapth/PHOX_FAMIL Y/main. html Event Generator for pp collisions Partonic processes: q Prompt photons: Compton and annihilation q Fragmentation photon: FSR Ø Parton radiation and fragmentation Bremhstrahlung and fragmentation photons pp collisions √s=14 Te. V | | < 0. 5 M Germain Good agreement on cross sections & spectra shapes. 21

Direct photon RAA at high p. T PHENIX preliminary & JHEP 0609 (2006) 015 22 M Germain

ALICE Discrimination - 0 G. Bourdaud, C. Hadjidakis Three regions of analysis increasing p. T well separated clusters invariant mass analysis merged clusters not spherical shower shape analysis Opening angle << 1 cell all 0’s at this energy are in jets isolation cut < 10 Ge. V/c in EMCal < 30 Ge. V/c in PHOS 10 - 30 Ge. V/c in EMCal 30 - 100 Ge. V/c in PHOS > 30 Ge. V/c only method in EMCal 23 M Germain

Jet Trigger Efficiency ALICE Rate to tape limited by DAQ and TPC gating (<500 Hz) Level 1 trigger (level 0 in p+p) needed pp 3000 Pb-Pb 14 P. Jacobs, A. Pavlinov M Germain 24

Jet Reconstruction Resolution in pp M. Estienne Resolution = RMS/Erec = mean energy inside a cone of radius R Almost flat resolution with jet energy (R=0. 4) ~ 40% (charged only) ~ 30% (charged + EMCal) 25 M Germain

Background fluctuations 26 M Germain

Direct identification (II) G. Conesa pp @ √ 14 Te. V Pb. Pb @ 5. 5 Te. V, ^q = 50 Ge. V 2/fm PID criteria based on shower shape (see Christelle’s talk) Clusters from bkg rejection inproved with PID 27 M Germain

Improvement of jet energy reconstruction with EMCAL M. Estienne Pythia simulations: 100 Ge. V @ 14 Te. V jets inside the EMCal acceptance (jets with R=0. 4 totally included in the detector) M Germain TPC+EMCal Emean (Ge. V) 43. 0+/-0. 6 75. 9+/-0. 7 RMS (Ge. V) 16. 9+/-0. 5 21. 7+/-0. 6 Resolution 39. 3%* 28. 6%* 28

/ 0 discrimination Ndirect /N from 0 C. Haddjidakis, G. Bourdaud o o o 2 (shower shape) cut • No cut p+p 14 Te. V o • No cut p+p 14 Te. V central Pb+Pb 5. 5 Te. V p. T(Ge. V) Ø 0 suppression factor = 5 -10 for p. T =[10 -30] Ge. V/c in p+p Ø 0 suppression factor > 5 for p. T =[15 -30] Ge. V/c in Pb+Pb Ø Ndirect / N from 0 ~ 1 in Pb+Pb for p. T =[20 -30] Ge. V/c Ø Invariant mass analysis for 0 for p. T<20 Ge. V/c M Germain o 2 (shower shape) cut p. T(Ge. V) 29

EMCAL Pb scintillator sampling calorimeter - r. M ~ 2 cm - 22. 1 X 0 - Acc: 80 < < 190°, | | < 0. 7 Shashlik geometry – 11 SM - ~13000 towers ( x = 0. 014 x 0. 014) E/E ~15%/ E(Ge. V) Energy from neutral particles: 0/ discrimination to ~ 30 Ge. V/c Trigger capabilities 30 M Germain

Expected Rates with ALICE EMCAL Extended rates due to EMCAL triggering • • • First jet physics with TPC up to ET 100 Ge. V. Already possible with low luminosity Pb. Pb run (50 mb-1) Extended energy range (200 Ge. V with EMCal) Some important reference measurements only possible with EMCal trigger. Jet yield in 20 Ge. V bin 31 M Germain

Electron identification in EMCAL q Matching between track (TPC) – cluster EMCAL q Electron ID based on p/E variable ( p from TPC; E from EMCAL) M. Heinz, J Putshke p/E pion rejection > 100 with efficiency of 80 % 32 M Germain

Pion from electron rejection with emcal 33 M Germain

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