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

ALICE-USA Collaboration 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

ALICE-USA Collaboration Why Jets in Heavy Ion Collisions? or Isn’t there a better way to make a living?

ALICE-USA Collaboration 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.

ALICE-USA Collaboration The basic physics ….. Parton energy loss via induced gluon radiation in the dense medium

ALICE-USA Collaboration Collision Centrality Scaling of Inclusive hadron Spectra at RHIC Central Peripheral

ALICE-USA Collaboration Baryons versus Mesons

ALICE-USA Collaboration Recent data from STAR at RHIC: Away-side Jet Absorbed in Central Collisions! Central Collisions Peripheral Collisions

ALICE-USA Collaboration How will this physics look in ALICE? Vitev and Gyulassy SPS: WA98 RHIC: PHENIX Inclusive  o prediction Data: Range of initial state gluon Density dN/dy = Perhaps as little as a few % of hadrons from hard collisions will survive in this P T range

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

ALICE-USA Collaboration 1/R dN/dR correlation of high P T hadrons Fragmentation Function of Correlated Particles Background of uncorrelated Particles Low P T jets and mini-jets

ALICE-USA Collaboration TPC and inner tracker allow flavor tagging in low P T jets Hadronic Charm reconstruction

ALICE-USA Collaboration What about jets at high P T in ALICE? Rates / Signal to Background? What can be measured? Trigger? TPC at high P T ? Reconstruction in the presence of complex underlying event?

ALICE-USA Collaboration 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 P T

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

ALICE-USA Collaboration 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.

ALICE-USA Collaboration Pb/Sci EMCal  x  = 1.4 x 2  /3 (Trigger, ,  o, direct and thermal  TPC TRD TOF PHOS RICH ITS

ALICE-USA Collaboration Trigger with EMCal = electromagnetic energy + ~ % hadronic energy Trigger turn-on versus E jet Trigger bias independent of P T Of charged hadrons within ~10%

ALICE-USA Collaboration ITS+TPC+TRD long tracking lever arm in ALICE 9% at 100 GeV/c  P T /P T (%)

ALICE-USA Collaboration 100 GeV/c jets in pp 16% Jet reconstruction: Poor man’s energy flow analysis: E jet =A*  P T ch + B*  EMCal

ALICE-USA Collaboration PbPb Central 25% pp 16% Resolution for 100 GeV jets in pp and PbPb versus cell E T cut PbPb events include full mini jet background from HIJING

ALICE-USA Collaboration. The bottom line …. The distribution of energy parallel to (P L ), and perpendicular to ( j T ), the jet axis….. Reconstructed P L distributions for 50 and 100 GeV jets in central PbPb collisions.

ALICE-USA Collaboration Reconstructed j T 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

ALICE-USA Collaboration Flavor dependence of jet quenching – two examples of many Leading particle spectrum for K and  lead jets with P T > 75 GeV/c, baryon versus meson quenching Baryon/anti-Baryon led jets With P T > 75 GeV/c - distinction of quark / gluon quenching

ALICE-USA Collaboration The Detector: Pb/Scintillator with mega-tile technology ~ 20k towers in  x  = 2  /3 x 1.4 Towers exactly projective with tiles ~ 5cm x 5cm Resolution (simulated)  E /E ) 2 = (12.2%/  E) 2 + (0.4%) 2 Photo Detectors: 5mm x 5mm APD’s Modular design permitting “late” installation

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

ALICE-USA Collaboration Summary: ALICE-USA collaboration is in the process of proposing a modest investment in instrumentation* for an EMCal to better enable high P T 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

ALICE-USA Collaboration 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  + jet and Z o + jet. Summary:

ALICE-USA Collaboration

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.

ALICE-USA Collaboration