T.M. Cormier Wayne State University for the ALICE – USA Collaboration

1. Jet Physics in ALICE and a Proposed Electromagnetic Calorimeter T.M. Cormier Wayne State University for the ALICE – USA Collaboration

2. Creighton University Kent State University Lawrence Berkeley National Laboratory Michigan State University Oak Ridge National Laboratory Purdue University The Ohio State University University of California, Berkeley University of California, Davis University of California, Los Angeles University of Houston University of Tennessee University of Texas at Austin University of Washington Wayne State University

3. Why Jets in Heavy Ion Collisions? or Isn’t there a better way to make a living?

4. Why Jets in Heavy Ion Collisions? • Jets in Heavy Ion Collisions Provide …… • A unique look at the QCD Radiation length of Dense, • Strongly Interacting (Colored) matter (QGP). • A tomographic tool to quantitatively study the QGP medium when benched marked with pp running or peripheral heavy ion collisions.

5. The basic physics ….. Parton energy loss via induced gluon radiation in the dense medium

6. Collision Centrality Scaling of Inclusive hadron Spectra at RHIC Central Peripheral

7. Baryons versus Mesons

8. Recent data from STAR at RHIC: Away-side Jet Absorbed in Central Collisions! Central Collisions Peripheral Collisions

9. How will this physics look in ALICE? Inclusive po prediction Vitev and Gyulassy Data: SPS: WA98 RHIC: PHENIX Range of initial state gluon Density dN/dy = 2000 - 3500 Perhaps as little as a few % of hadrons from hard collisions will survive in this PT range

10. away side jet signal ALICE TPC is the perfect tool for this Physics STAR TPC data AuAu Simulation of f-correlation due to mini jets in central PbPb

11. Low PT jets and mini-jets 1/R dN/dR correlation of high PT hadrons Fragmentation Function of Correlated Particles Background of uncorrelated Particles

12. TPC and inner tracker allow flavor tagging in low PT jets Hadronic Charm reconstruction

13. What about jets at high PT in ALICE? • Rates / Signal to Background? • What can be measured? • Trigger? • TPC at high PT? • Reconstruction in the presence of • complex underlying event?

14. Opportunity at the LHC to go beyond inclusive measurements 100 and 200 GeV Jets imbedded in Central PbPb Event Underlying Event dominates jet energy resolution at lower PT

15. Jet energy resolution is not a significant issue because there is no significant jet energy loss to be measured….. 100 GeV PYTHIA Compared to Wiedeman et al for 20 GeV parton energy loss Jet energy loss is apparent only for limited cone radii.

16. Primary jet quenching effect is thus redistribution of energy along and perpendicular to the jet axis. The goal of the ALICE jet physics program is to measure this energy redistribution, it’s dependence on centrality and flavor.

17. Pb/Sci EMCal Dh x Df = 1.4 x 2p/3 (Trigger, h, po, direct and thermal g) RICH TPC TRD TOF PHOS ITS

18. Trigger with EMCal = electromagnetic energy + ~40 - 50% hadronic energy Trigger bias independent of PT Of charged hadrons within ~10% Trigger turn-on versus Ejet

19. DPT/PT (%) ITS+TPC+TRD long tracking lever arm in ALICE 9% at 100 GeV/c

20. 100 GeV/c jets in pp Jet reconstruction: Poor man’s energy flow analysis: Ejet =A*SPTch + B*SEMCal 16%

21. Resolution for 100 GeV jets in pp and PbPb versus cell ET cut pp 16% PbPb Central 25% PbPb events include full mini jet background from HIJING

22. . The bottom line …. The distribution of energy parallel to (PL ), and perpendicular to ( jT), the jet axis….. Reconstructed PL distributions for 50 and 100 GeV jets in central PbPb collisions.

23. Reconstructed jT distributions for 50 and 100 GeV jets in central PbPb collisions. These distributions are particularly interesting to search for “transverse heating in the fragmentation process should it proceed within the dense medium

24. Flavor dependence of jet quenching – two examples of many Leading particle spectrum for K and L lead jets with PT > 75 GeV/c, baryon versus meson quenching Baryon/anti-Baryon led jets With PT > 75 GeV/c - distinction of quark / gluon quenching

25. The Detector: Pb/Scintillator with mega-tile technology ~ 20k towers in Df x Dh = 2p/3 x 1.4 Towers exactly projective with tiles ~ 5cm x 5cm Resolution (simulated) (sE/E )2= (12.2%/E)2 + (0.4%)2 Photo Detectors: 5mm x 5mm APD’s Modular design permitting “late” installation

26. Technical issues: Optical studies with 5cm x 5cm tiles and WLS readout via 0.5mm fiber Achieve ~1.5 % RMS spatial uniformity

27. Summary: • ALICE-USA collaboration is in the process of proposing • a modest investment in instrumentation* for an EMCal to better • enable high PT jet physics in ALICE. • The combined power of the EMCal and the ALICE TPC and • other detectors permit a complete measurement of the redistribution • of jet energy parallel to and perpendicular to the jet axis. Medium • modification of the parton fragmentation process including it’s • dependence on energy and flavor (s,c,b) will be measured. These • measurements constitute an important extension of on going RHIC • measurements to a to a much hotter, denser and longer lived plasma. * ~$200k per ALICE-USA institution per year for three years

28. Summary: • All of the above can be studied separately for baryon • and meson led jets. Early RHIC data suggests there are • significant differences in the quenching in these two cases. • The calorimeter permits the study of exclusive hard scattering • processes such as g + jet and Zo + jet.

31. Figure 5. Comparison for ideal jet resolution of the quenched and unquenched fragmentation functions of 100 GeV jets in a schematic model in which a 20 GeV primary parton energy loss is modeled as the production of a 20 GeV jet in consort with an 80 GeV jet. The Statistics correspond to only 1000 events. The properly normalized background for central HIJING PbPb events is shown.