John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec In QCD Medium Additional k T Significant energy loss?  high p T suppression Sensitive to color properties of medium High p T Physics in ALICE Hard probes  early times Calculable: pQCD Abundant at RHIC, LHC k T “radiative corrections” pre- and post-scattering di-jet:  Fragmentation: p(hadron) p (parton) z = Induced Gluon Radiation  ~collinear  gluons in cone  “Softened” fragmentation Gyulassy et al., nucl-th/

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec Highlights of High p T Physics Results from RHIC Suppression at High p T of Light Quark Hadrons ( , K, p, , …) Non-photonic e’s from Heavy Quarks (D+B) Quenching of Away-side Jet Disappearance of the Away-side Jet in Most Central Collisions Appearance of Away-side Jet Energy in Low p T Particles Re-emergence of the Away-side Jet at Much Larger Trigger Jet p T Appearance of a “Ridge” on the Near-side Large parton E-loss Large gluon density Strongly-coupled QGP Medium response and properties

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec The Start of Detailed “Tomography” of the QGP F QGP (  g QGP ) = f initial (√s, A 1 +A 2, b, x 1, x 2, Q 2 )  f QGP (p T ,y ,  ,p T jet,y jet,  jet, flavor jet,  flow ) “jet flow plane  /parton parton near-side Renk, hep-ph/ Di-hadrons penetrate core! Renk, hep-ph/ near-side Triggered jets come from near-side surface

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec Di-Hadron Correlations at RHIC “jet Data: STAR, nucl-ex/ ; pQCD E-loss Model + expansion: Renk, hep-ph/ No near-side sensitivity to medium Slight away-side sensitivity to medium More extensive di-hadron measurements from PHENIX (hep-ex/ ) and STAR (nucl-ex/ ): Di-hadron fragmentation functions exhibit only a weak sensitivity to medium!  - jet and better jet energy (full jet) measurements necessary

5 Extracting the medium density T. Renk, Hard Probes Singles Di-hadrons Box density Hydro profile Eskola et al., hep-ph/ Limited sensitivity to medium density Points of origin for detected high-p T particles Surface bias in single particle suppression Di-hadrons have smaller surface bias I.e. probe entire interaction zone: better for extracting medium density

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec High p T Physics with Heavy Ions at the LHC Real Jets! Role of LHC heavy ions? Larger  s Extend to much larger p T and “real” jets Abundant production of heavy quarks  increased statistics for differential studies

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec The Future of RHI‘s at the LHC: Dedicated HI experiment - ALICE Two pp experiments with HI program: ATLAS and CMS

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec ALICE Set-up HMPID Muon Arm TRD PHOS PMD ITS TOF TPC Size: 16 x 26 meters Weight: 10,000 tons

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec Simple Expectations - Heavy Ion Physics at the LHC  QGP (fm/c)  (GeV/fm 3 ) T / T c t form (fm/c) √ s NN (GeV) factor RHIC ≤ LHCSPS shorter hotter 15-60denser > 10 longer Significant increase in hard scattering yields at LHC: - jets & large p T processes -  bb (LHC ) ~ 100  bb (RHIC) -  cc (LHC) ~ 10  cc (RHIC)

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec Physics with the ALICE EMCal 10+1/2+1/2=11 super-modules 8 SM from US 3 SM from Europe Lead-scintillator sampling calorimeter  = 1.4,  =110 o Shashlik geometry, APD photosensor ~13K towers (  x  ~ x 0.014) EMCal Technical Proposal approved by LHCC 9/28/06!!

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec Capabilities of ALICE Extended by EMCal EMCal improves detector capabilities: - Fast trigger ~ enhancement of jets - Improves jet reconstruction (plus TPC) - Good   discrimination increases coverage - Good electron/hadron discrimination EMCal extends the physics of ALICE: 10 4 /year in minbias Pb+Pb: inclusive jets: E T ~ 200 GeV dijets: E T ~ 170 GeV   : p T ~ 75 GeV inclusive  : p T ~ 45 GeV inclusive e: p T ~ 30 GeV Thanks – Peter Jacobs

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec New and Extended ALICE Physics from EMCal Pb + Pb collisions: medium-induced modification of jets response of medium to large energy deposition from parton energy loss mechanisms photon physics and photon-tagged jets heavy flavor physics using semi-leptonic decays into electrons measured in the EMCal and b-tagged jets. Also important to understand reference data in p + p, p + A and light A + A collisions

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec Jet Reconstruction Fragmentation: p(hadron) p (parton) z = =  (  2 +  2 ) Large background in RHI Collisions – must limit jet cone radius R, track p T cut  only measure fraction of parton energy - calibrate

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec Medium Modification of Fragmentation from Jets Fragmentation along jet axis: z = p hadron / p parton Introduce  = ln(E jet / p hadron ) ~ ln (1/z):  = ln( E jet / p hadron ) p T hadron ~2 GeV “Jet quenching” modifies spectrum for p T (hadron) ~ 1-5 GeV jet direction z - MLLA vacuum fragmentation (basis of PYTHIA) - Medium effects at parton splitting Borghini and Wiedemann, hep-ph/ Thanks – Joern Putschke

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec Simulations on Jet Quenching Measured in ALICE E jet ~175 GeV Solid: unquenched (p+p) Dashed: quenched jet (Pb+Pb) Pythia-based simulation with quenching Measure dashed / solid Ratio = PbPb (central) / pp Thanks – Joern Putschke

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec Reminder - Gluon versus Quark Jets LHC  Gluon jets Top energy RHIC p T < 20 GeV  Gluon jets p T > 20 GeV  Quark jets Lower RHIC energy transition from gluon to quark jets Utilize RHIC versatility in √s!  -jet and di-hadrons     correlations  x  x  correlations qg, gg, qq scattering 3-jet events?

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec Use b-jets to Tag Quark Jets Radiative quark energy loss different for heavy and light quarks - Y.L.Dokshitzer and D.E. Kharzeev, hep-ph/ Reconstruct jets, tag heavy quark (c,b) - jets via Hadronic decay: secondary vertices from charged tracks Leptonic decay: muons with displaced vertices Compare jet shapes / properties of heavy quark jets and light quark jets. Exploit parton mass dependence to study parton energy loss mechanism. b b B D 

Photon-tagged jets Why  -jet ? Why  -jet ? Medium effects redistribute (  qL) the parton energy, E jet, inside the hadron jet (multiplicity, k T ). Medium effects redistribute (  qL) the parton energy, E jet, inside the hadron jet (multiplicity, k T ). Jet Measure E  = E jet. Prompt  ^ Redistribution can be best measured in the Fragmentation Function... If we know E jet. Redistribution can be best measured in the Fragmentation Function... If we know E jet. HI environment hinders precise reconstruction of E jet. AB ALICE-INT Thanks - Gustavo Conesa Balbastre – INFN Frascati

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 Thanks - Gustavo Conesa Balbastre – INFN Frascati

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec Special thanks for contributors: Marco Leeuwen Joern Putschke Gustavo Conesa Balbastre Peter Jacobs

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec Summary and Future Hard pQCD probes require for in-depth, differential studies better statistics better jet energy determination Still a lot to understand with present and upcoming RHIC data Significant high p T physics still to be done at upgraded RHIC (& detectors) luminosity at LHC

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec Back-up Slides

 -distribution: qhat variation Need ~10% resolution at large 

Reference systems Jet trigger Compare central Pb+Pb to reference measurements Pb+Pb peripheral: vary system size and shape p+A: cold nuclear matter effects p+p (14 TeV): no nuclear effects, but different energy p+p (5.5 TeV): ideal reference, but limited statistics Includes acceptance, efficiency, dead time, energy resolution All reference systems are required for a complete systematic study

Jet yields: one LHC year Jet yield in 20 GeV bin Large gains due to jet trigger Large variation in statistical reach for different reference systems

John Harris (Yale) HEP Workshop, Valparaiso, Chile, Dec Di-hadron Correlations and Fragmentation Function 8 < p T,trig < 15 GeV Near-side – no modification Away-side quenched by factor 4 – 5, but no shape modification Near-sideAway-side STAR nucl-ex/ X.N. Wang nucl-th/