Jet Correlations in ATLAS RHIC Correlations and High-pT Measurements with ATLAS Jet Correlations in ATLAS Nathan Grau Columbia University, Nevis Labs High-pT Physics at the LHC 3/25/2007

High-pT Physics at the LHC Outline A very brief review of some key RHIC data on high-pT (> 5 GeV trigger, mostly) correlations Questions rather than answers Move on to possibly finding answers: Need event-by-event data, not integral/average quantities i.e. LHC jet studies at ATLAS High-pT Physics at the LHC 3/25/2007

Jet Quenching at RHIC: Singles Dramatic quenching relative to binary-scaled p+p is observed How sensitive is RAA to the details of energy loss? T. Renk Hard Probes 2006 High-pT Physics at the LHC 3/25/2007

Jet Quenching at RHIC: Pairs Why are high-pT two-particle away-side correlation yields suppressed but their shape is not broadened? 8 < pT(trig) < 15 GeV/c 8 < pT(trig) < 15 GeV/c High-pT Physics at the LHC 3/25/2007

High-pT Physics at the LHC IAA vs RAA J. Jia, QM 2006 Cu+Cu D. Magestro, QM 2005 Why is IAA ~ RAA? High-pT Physics at the LHC 3/25/2007

IAA vs RAA : An Interesting Implication Is this “factorized” e-loss? RAA dominated by geometry, so is IAA? Pair suppression High-pT Physics at the LHC 3/25/2007

High-pT Physics at the LHC IAA vs RAA : Is It True? Chun Zhang, QM 2006 h-h Correlations from Au+Au 2-3 GeV/c trigger DAA 00-20% : RAAtrig=0.60, RAAassoc=0.30 20-40% : RAAtrig=0.75, RAAassoc=0.45 60-92% : RAAtrig=0.90, RAAassoc=0.80 High-pT Physics at the LHC 3/25/2007

Jet Medium Interactions: The Ridge in STAR J. Putschke, QM 2006 And it’s always there… pt,assoc. > 2 GeV STAR has measured a very pronounced ridge structure in Au+Au High-pT Physics at the LHC 3/25/2007

Jet Medium Interactions: The Ridge in PHENIX Chun Zhang, QM 2006 h-h Correlations from 0-20% Au+Au Near Side Seems at higher associated pT ridge even goes away? Where is the ridge the 4-5 GeV/c bin? High-pT Physics at the LHC 3/25/2007

Jet Medium Interactions: Near-side Energy Loss H Pei, QM2006 ~1/Ntrigg dN/djT jT Increased yield in radiative tail of jT distribution measured in Cu+Cu Not the ridge since this is hard (perturbatively calculable) radiation Near side jet loses energy: not surface emission. High-pT Physics at the LHC 3/25/2007

Jet Medium Interactions: The Mach Cone J. Jia, QM2005 30-40% Au+Au 2.5-4.0x1.0-2.5 h-h I think PHENIX has their v2 systematics under control. Is this just momentum conservation? Know v2 depending on trigger’s RP orientation. J. Bielcikova et al, Phys. Rev. C69:021901, 2004 High-pT Physics at the LHC 3/25/2007

Jet Medium Interactions: Cone or Bent Jet M. Horner, QM 2006 Two-particle can possibly rule out a bent-jet scenario: seems like dip is filled in by the jet. But this is not event-by-event information High-pT Physics at the LHC 3/25/2007

pT-Dependence of Jet Modification How do di-hadrons vary with pT: Conical  extinction  punch-through? NG QM2006, p0-h in Au+Au High-pT Physics at the LHC 3/25/2007

Summary of the Introduction Discovery of jet quenching occurred at RHIC! But that was in 2000-2001 What more can we say since then about Medium properties? Energy-dependence of energy loss? Path-length dependence of energy loss? To borrow a phrase from Mike: “We are still on a long learning curve.” What is missing: A clear event view of a ridge/mach cone/broadened jet etc. a la Paris 1982 Where can we do this: at the LHC with ATLAS High-pT Physics at the LHC (and CMS and ALICE) 3/25/2007

High-pT Physics at the LHC The ATLAS Detector High-pT Physics at the LHC 3/25/2007

High-pT Physics at the LHC The ATLAS Detector Full azimuthal acceptance in all detectors Unprecedented pseudorapidity coverage for A+A High-pT Physics at the LHC 3/25/2007

Tracking with the Inner Detector Inner detector has full azimuthal coverage within |h|<2.5 and consists of Pixel detector Silicon tracking detector Transition radiation tracker Results from p+p tracking algorithm optimized for HI environment. Reconstructed tracks with |h|<1 Tracking down to 500 MeV. Important for D(z) and v2. High-pT Physics at the LHC 3/25/2007

High-pT Physics at the LHC ATLAS Calorimetry Hadronic Barrel EM Barrel Forward EM EndCap Hadronic EndCap High-pT Physics at the LHC 3/25/2007

Longitudinal Segmentation: 3-d Jets Sampling of a 100 GeV jet (no background) 1 2 3 4 5 6 Note the h-f region is 0.8x0.8: a typical jet size Sampling aides in energy resolution. Important for EM vs. hadronic energy separation. High-pT Physics at the LHC 3/25/2007

Approach to Cone Jet Reconstruction Original cells Cloned cells Different background Techniques are possible: E-by-E cell level E-by-E tower level E-avg cell level E-avg tower level Iteration also possible. Original towers Background subtraction (exclude seeds) Subtracted cells Cells: single readout channel Tower: 0.1x0.1 h-f sums of constituent cells Need to understand the fluctuations in the different methods Inherent limitations on jet measurements. New towers Use standard ATLAS code, except for the background subtraction. Reconstructed jets High-pT Physics at the LHC 3/25/2007

Hard Radiation in p+p Collisions Vacuum radiation is important Changes “typical” R-cut in cone and kT algorithms, i.e. R<0.7 Splitting/Merging of proto-jets is important in p+p Simulated pythia event with hard scattering from 140-280 GeV High-pT Physics at the LHC 3/25/2007

Radiation From E-Loss: More Subjets The distribution of radiated gluons related to Hard radiation in the tail subjets Requires a precise measure of the jet direction High-pT Physics at the LHC 3/25/2007

Cone Jet Position Resolutions Df Dh 70-140 GeV 35-70 GeV 140-280 GeV Very good position resolution of jets Position resolution not dominant error on jT 5% uncertainty in the angular measurement, pT is about 2% High-pT Physics at the LHC 3/25/2007

High-pT Physics at the LHC Energy Resolution Energy Resolution of jets necessary for Jet spectrum  show jet cross section binary scales Fragmentation functions since error in z is dominated by error on jet ET This is using the most brute force cell background subtraction Improvements on the method are being made Calibrations due to subtraction have not been applied. h High-pT Physics at the LHC 3/25/2007

Utilizing the kT Algorithm See W. Holzmann’s talk for all of the details Cacciari and Salam: Fast kT Not a new kT algorithm, just improved the algorithms speed Fast enough to run on HI events before subtracting the background event! Use background jets to discriminate real jets: i.e. their properties are different High-pT Physics at the LHC 3/25/2007

“Fast” kT Finder: Discriminating Jets and Background Real Jets appear as narrow towers “Fake” Jets appear flat and broad Each color is a different “jet” defined by the algorithm “Real” jets and “Background” jets look different. High-pT Physics at the LHC 3/25/2007

Advantages of kT Algorithm Not a fixed cone size Easier to handle the hard radiation from jets No seeds are required All the energy in a high multiplicity (central) heavy ion event results in a jet Changed the problem of subtracting a background to discrimination of clustered energy Could suffer less from background fluctuations High-pT Physics at the LHC 3/25/2007

The More Perfect Way: g-jet EM Layer 1 ET (GeV)  Single f slice 0.1 rad g-jet event embedded Jet Back ground All too wide for single photons Single f slice 0.1 rad Jet Background Single f slice 0.1 rad Barrel EMCal front layer finely segmented in h for vectoring H  gg events and p0 rejection. Example of jet embedded in central b=2 fm HIJING event. High-pT Physics at the LHC 3/25/2007

Separation from p0 Decay Fractional energy outside core Energy of a 2nd maximum Cuts to discriminate g/p0 before isolation Inverting these cuts results in p0 measurement High-pT Physics at the LHC 3/25/2007

High-pT Physics at the LHC g/p0 Separation Rejection of p0 with appropriate cuts on previous variables Efficiency in p+p is ~90%, flat with ET and h Some rejection prior to isolation from jet! High-pT Physics at the LHC 3/25/2007

High-pT Physics at the LHC Summary & Conclusion RHIC high-pT discoveries and measurements are interesting and the I don’t understand all of the measurements at the moment. ATLAS will provide useful and necessary measurements complimentary to the RHIC program and extend these results and, ideally, help to answer the questions I have. Single jet, di-jet, and g-jet Unfortunately I could not cover all aspects of ATLAS high-pT program: heavy flavor bound states, heavy flavor energy loss, v2, etc. Let’s have more than 1 ATLAS and 1 CMS talk next time? High-pT Physics at the LHC 3/25/2007

ATLAS Heavy Ion Working Group A. Ajitanand10, A. Angerami3, G. Atoian11, M. Baker1, P. Chung10, B. Cole3, R. Debbe1, A. Denisov5, J. Dolejsi2, N. Grau3, J. Hill7, W. Holzmann3, V. Issakov11, J. Jia10, H. Kasper11, R. Lacey10, A. Lebedev7, M. Leltchouk3, A. Moraes1, R. Nouicer1, A. Olszewski6, A. Poblaguev11, V. Pozdnyakov8, M. Rosati7, L. Rosselet4, M. Spousta2, P. Steinberg1, H. Takai1, S. Timoshenko9, B. Toczek6, A. Trzupek6, F. Videbaek1, S. White1, B. Wosiek6, K. Wozniak6, M. Zeller11 1 Brookhaven National Laboratory, USA 2 Charles University, Prague 3 Columbia Unversity, Nevis Laboratories, USA 4 University of Geneva, Switzerland 5 IHEP, Russia 6 IFJ PAN, Krakow, Poland 7 Iowa State University, USA 8 JINR, Dubna, Russia 9 MePHI, Moscow, Russia 10 Chemistry Department, Stony Brook University, USA 11 Yale University, USA High-pT Physics at the LHC 3/25/2007

High-pT Physics at the LHC Backup Slides High-pT Physics at the LHC 3/25/2007

IAA from xE distributions in Cu+Cu High-pT Physics at the LHC 3/25/2007

IAA from xE distributions in Cu+Cu High-pT Physics at the LHC 3/25/2007

High-pT Physics at the LHC Tracking to Lower pT Minimum bias p+p Preliminary Work extending pT reach important for p+p and A+A. dN/dh in both cases v2 in A+A Ongoing with high energy and heavy ion participation Efficiency: red/black Fake rate: red/green High-pT Physics at the LHC 3/25/2007