The US ATLAS Heavy Ion Program Summary Summary: US Ef as long as t & Impact
McCracken, Harry, Founder and Editor has reference to this Academic Journal, PHwiki organized this Journal The US ATLAS Heavy Ion Program Brian A. Cole, Columbia University January 12, 2007 Phases of QCD Matter Town Meeting LHC Heavy Ion Program: Key Questions What is the mechanism as long as initial particle production at the LHC Production from a saturated initial state How rapidly do produced particles thermalize or isotropize, what is the mechanism Faster than RHIC, slower How do high-energy quarks in addition to gluons interact in the quark gluon plasma What is the response of the medium What is the screening length of the QGP What are the quasi-particles of the QGP How does the QGP hadronize LHC Heavy Ions Program: Key Questions
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LHC Heavy Ions Program: Key Questions The ATLAS Central Detector Inner tracking, EM in addition to Hadronic calorimeters, external muon spectrometers ATLAS from the Inside
ATLAS Acceptance US ATLAS Heavy Ion: Primary Goals Measure dnchg/d, dET/d (total+EM) Characterize gross properties of initial state. Test saturation predictions Measure charged, inclusive , 0 elliptic flow Probe early collective motion of (s/t/w)QGP Measure jets, jet fragmentation, -Jet, di-jet, Precision tomography of QGP & its properties Medium response to passage of quenched jet Measure Upsilon production via +- Probe Debye screening in medium Study low x hard processes in p-p, p-A Study factorization violations, BFKL, saturation LHC Physics Summary Collectivity
Jet Tomography At RHIC, studied via leading hadrons Statistics suffer from frag. function rates Quenching geometric bias No direct measure of frag. function. At LHC: Full jets, high pT, large rates, b jets, di-jet, -jet Precision jet tomography Jet Tomography At RHIC, studied via leading hadrons Statistics suffer from frag. function rates Quenching geometric bias No direct measure of frag. function. At LHC: Full jets, high pT, large rates, b jets, di-jet, -jet Precision jet tomography Parton Showers, Hard Radiation @ LHC Copious hard radiation in high Q2 final-state parton showers, F ~ 1/kT Both an opportunity in addition to a challenge Underst in addition to ing jet quenching more difficult Potentially: time-dependent probe of medium Resolving hard radiation in jets a must!
ATLAS Calorimetery EM Long. Segmentation Hadronic Barrel Hadronic EndCap EM EndCap EM Barrel Forward EM Calorimeter Long. Segmentation Segmentation of first EM sampling layer so fine that heavy ion background is ~ negligible Nchg + N < 1, ET ~ 30 MeV Fine rejection of neutral hadron decays Clean 1st sampling prompt isolation x = 0.0028 x 0.1 Jets in A+A Jets from PYTHIA in 0.1x0.1 (logical) towers Jets in A+A merged with b = 2 fm Pb+Pb event (HIJING) Jets from PYTHIA in 0.1x0.1 (logical) towers Jet Energy Resolution Study of different event samples embedded into central Pb+Pb HIJING (b=0-2 fm) Results obtained from st in addition to ard p-p cone algorithm w/ background subtraction. Some re-calibration still needed. Jet Fragmentation Observables ATLAS: Gamma-Jet Pythia + jet (75 GeV) superimposed on b=4 fm HIJING Pb+Pb event, full GEANT Jet Gamma ATLAS: Gamma-Jet Pythia + jet (75 GeV) superimposed on b=4 fm HIJING Pb+Pb event, full GEANT ATLAS: Gamma-Jet, EM 1st Layer Gamma 1st layer unaffected by Pb+Pb background isolation w/ 1st layer ~ unaffected by Pb+Pb Zoom in on barrel EM calorimeter 1st sampling layer ATLAS: Gamma-Jet, EM 1st Layer Gamma EM Layer 1 ET (GeV) Isolated photon gives clean signal in EM first sampling layer Even in central Pb+Pb ! One (of 64) rows in barrel EM calorimeter 1st sampling layer ATLAS: Gamma-Jet, EM 1st Layer EM Layer 1 ET (GeV) Zoomed Width of high-energy shower in 1st sampling unaffected by bkgd 0, rejection retained Institutional Ef as long as ts/Strengths Brookhaven (Global, flow, jets, low-x) Expertise in global in addition to flow measurement (PHOBOS), high-multiplicity tracking in addition to low-x physics (BRAHMS) Columbia (Jets, Photons, low-x) Expertise in high-pT physics, jet correlations in addition to direct photon measurements (PHENIX) Expertise in p-A physics Iowa State (Di-muons) Expertise in di-muon measurements (PHENIX) SUNY Stony Brook (Chemistry) Expertise in flow, high-pT physics, jet correlations
Summary ATLAS-HI physics program addresses primary physics questions of interest @ LHC ATLAS provides unique capabilities with highly segmented EM calorimeters Especially as long as measuring isolated direct photons For separating jets from heavy ion background For measuring jet shapes, hard radiation ATLAS calorimeters provide best intrinsic (i.e. in p-p) jet resolution @ LHC Can US af as long as d NOT to participate in expt providing most precise jet measurements @ last energy frontier in heavy ion physics Summary: US Ef as long as t & Impact US ef as long as t (FY09 & beyond) ~30 physicists, 6 Ph.D students at current institutions. More desirable. More than ½ of full ATLAS-HI program. Highly leveraged ef as long as t with big impact Possible because of ATLAS collaboration Synergy with high-energy groups in US US provides co-convener of ATLAS HI WG BAC as of fall 2006 US Expertise developed @ RHIC US will provide highly visible leadership of ATLAS-HI program.
ATLAS Inner Tracker 3 layers Si pixel 8 layers Si strip TR tracker Pb+Pb b=2 fm Si tracking per as long as mance Charged Multiplicity from Pixels 1. Truth tracks (black) 2. B-Layer Hits 3. Layer 1 Hits 4. Matched Tracklets Good estimate of particle densities with subset of full detector ATLAS Zero Degree Calorimeter Test beam @ CERN 10.06 ZDC Prototype @ CERN 10.06 Experiment Simulation p+p events, w/ precision EM module TAN region, z=140m
ATLAS vs CMS Jet Resolution CMS Pb+Pb Jet resolution (Nov 2005) @ 75 GeV, CMS~16%, ATLAS~13% @ 125 GeV, CMS~15%, ATLAS~10% @ 175 GeV, CMS~12%, ATLAS~8% ATLAS better than CMS even in p-p Note: ATLAS numbers from 2003
McCracken, Harry Founder and Editor
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