ATLAS heavy-ion physics What is heavy-ion physics What was done at RHIC What to do at What about us. 1 Jiangyong Jia Stony Brook University & BNL

SB seminar Heavy-ion physics Study Non-Abelian QCD matter. Origin of mass, Confinement, Chiral symmetry restoration. Properties manifested through many body interactions and self interactions (complication leads to simplification). Implication to other fields (e.g. Cosmology) 2 Solid state physics with a force of different color s.vigdor

SB seminar Phases of QCD matter Nuclear matter Heat to 170 MeV or 2x10 12 QuarkGluonPlasma Strong QCD field Map out the phase diagram and properties of QCD matter Equation Of State

SB seminar 4 Heavy-Ion collision Form a matter in the overlap region. Matter expands under pressure. Matter interact with hard probes. Matter hadronize and freeze out. initial state pre-equilibrium QGP and hydrodynamic expansion hadronization hadronic phase and freeze-out

SB seminar How to extract properties? Bulk properties: Thermal and collective expansion. Dynamic properties: Interaction with Hard probes x z y 5

SB seminar Discoveries at RHIC Collective expansion: Discovery of perfect fluid, smallest Probe the medium: Discovery of jet quenching Discovery of collective medium response Mach cone ridge 6 v2v2 p T (GeV/c)

SB seminar Discoveries at RHIC Collective expansion: Discovery of perfect fluid, smallest 7 Medium response Jet quenching Probe the medium: Discovery of jet quenching Discovery of collective medium response Mach cone ridge

SB seminar Connection to string theory ADS/CFT. The limit of infinitely strong coupled CFT = classical super-gravity theory in ADS. Allows calculate non-perturbative quantities in field theory. Predict an universal lower bound on  /s =1/4 . First principle calculation of jet energy loss, medium response: Jet in our world is the tail end of the string dangling down to event horizon. J. Maldacena

SB seminar Why we want to go to LHC? Interaction is very strong that much information is lost. Would like to use probes with different coupling (quarks, gluons, photons, Z, heavy quarks) to understand flow, jet quenching and medium response Currently limited by rate at RHIC (E<20 GeV) 9 Supersonic: probe Energy loss/medium response Stationary: probe Collective flow

SB seminar 10 A different medium. Large rate and increased p T reach for hard-probes. What Can Do? Excellent calorimetry, large acceptance, triggering capability of ATLAS

SB seminar 11 HI Physics Program Overview “Day-1” measurements to probe bulk properties Multiplicity, collective flow, spectra. Jet and photon measurement to probe the jet quenching & medium response. Jet reco., jet multiplicity and shape, dijet, ,  -jet,  -tagged jet. Upsilon and J/  to probe Debye screening. Low x physics at forward  to probe the initial condition. Jet, spectra, correlation at forward 

SB seminar 12 ATLAS HI Physics Potentials Jets Direct   Collision Geometry Charged hadrons

SB seminar Challenges Need to understand the tracking, clustering, egamma performance beyond current pileup study (25 vs 1000 pp collisions) Need to handle huge background subtraction in jet reconstruction (400 GeV bg in R=0.7 cone). Physics is different from p+p: Jets, quarkonium are modified by medium. Current study relies on embedding various signals in Pb+Pb events 13

SB seminar 14 p+p Hard-scattering + Underlying event.

SB seminar 15 Au+Au: Initial and final state interactions Modified jet + flowing medium flow jet Jet+flow Strong interaction between jet and Underlying event (nuclear matter) Modified PDF (shadowing/saturation) Initial MPI, ISR/FSR different from pp

SB seminar Tracking xKalman is used. >=10 hits, cut on x2/NDF, perigee, etc Acceptable efficiency of 70%, with low fakes 16 b=2fm

SB seminar 17 Jet Reco. in Central Pb+Pb Embed PYTHIA dijet in HIJING HIJING: No quenching

SB seminar 18 Jet Reco. in Central Pb+Pb Embed PYTHIA dijet in HIJING HIJING: No quenching Subtract  -dependent average background

SB seminar 19 Jet Reco. in Central Pb+Pb Excellent jet reconstruction in densest environment. Embed PYTHIA dijet in HIJING HIJING: No quenching Subtract  -dependent average background Cone-jet reconstruction R=0.4, seed E T >5 GeV. Complementary kT algorithm (Cacciari and Salam) also studied

SB seminar 20 Jet reco. Performance in b=2fm Pb+Pb Energy resolution improves towards higher p T. Energy resolution has no strong dependence on . Excellent energy high p T and all  E T >70 GeV

SB seminar 21 Study Jet Modification Jet multiplicity, D(z), and jet shape, j T Reflect energy loss and medium response (eg. the ridge) Sensitive to 20% level modification. Jet jTjT 

SB seminar 22  -jet as Probe for the Medium  tagged jets do not suffer geometrical bias, direct handle on jet energy loss process  -id using the fine segmentation of strip layer Jet 

SB seminar 23 Single particle photon 00     -ID in central Pb+Pb

SB seminar 24 Single particle photon 00    Embedded in dN/d  = 2700    Very little background (<50MeV/strip in b=2fm Pb+Pb) Can separate single  from    in central event Photon identification without isolation in |  |<2.4  -ID in central Pb+Pb

SB seminar 25 Performance of  -ID Cuts Using the standard egamma variables, but selected for HI environment Rejection up to factor of 3 with efficiency of 90% (medium cut) Rejection up to factor of 5-6 with efficiency of 50% Study final state  : Fragmentation, conversion, bremsstrahlung Carry detailed information about the jet-medium interaction Dominate/important at p T <30-50 GeV, not isolated Turbide et al. Phys. Rev. C72 (2005)

SB seminar 26 Combining  -id and Isolation Cuts Combined relative rejection: S/N ~ 1 at 100 GeV assuming hadrons not suppressed S/N ~ 1 at 30 GeV assuming factor of 5 suppression on hadrons.

SB seminar 27 Detailed Control on Collision Geometry High precision measurement on event centrality. High multiplicity give resolution better than 10% in most bins. Redundant measurement in many detectors. Excellent reaction plane resolution Redundancy help to suppress the non-flow effect Detailed jet-tomography studies!

SB seminar Zero Degree Calorimter Primary hardware contribution by ATLAS HI group Located 140m away in TAN absorber.  8. Pb+Pb Min-bias trigger, centrality selection, reaction plane determination and UPC trigger. 28

SB seminar 29 Summary & future plan ATLAS Heavy-ion program provide unprecedented capability in probing the QCD matter via jets, photons, and heavy quark. Large rate, large acceptance and triggering capability. ~Data-ready jet and photon measurement; Quantitative evaluation of physics performance (details see HI PPR) BNL and SB-chem interest: Pb+Pb: Global physics and photon-jet physics. p+p : mininum bias and egamma Effort growth

SB seminar 30 ATLAS Heavy Ion Institutions

SB seminar 31 ATLAS Heavy Ion Physics Program ETET Jetdi-jet Photon Jet and photon measurement: Jet quenching & medium response. Spectra HIJING b=2fm v2v2 “Day-1” measurements: Bulk properties Upsilon Upsilon, J/  : Debye screening Low x Low x physics at forward  : Initial condition ZDC YY’ Y’’

SB seminar Entropy production: 400  6000 in second 32

SB seminar Collectivity: anisotropic flow azimuthal asymmetry Less matter, easy to expand More matter, difficult to expand Large v2 : v2 ~0.15 => yield in plane and out of plane differ by 50%! In plane Out of plane Implies very little viscosity, hence strong coupling

SB seminar 34 Discovery of perfect fluid D. Teaney, PRC68, (2003) *viscosity = resistance of liquid to shear forces (and hence to flow) Thermalization time  <1 fm/c and  =20 GeV/fm3 And small viscosity Can be described by classical relativistic hydrodynamic equations

SB seminar 35 Inclusive Jet Spectra Reconstruction is fully efficient above 100 GeV in most central Pb+Pb event Expect >10 6 jets with 100 GeV in 0.5 nb -1 Pb+Pb events Sensitive to >20% level suppression. dN/d  =2700

SB seminar 36 Energy and position resolution for Cone jet

SB seminar 37 Di-jet Correlation Large signal with little background from unrelated jet pairs Sensitive to radiative energy loss and broadening. Correlation of away-side hadrons with triggering jet may help understand the origin of Mach cone. Benefit from large acceptance + high resolution Mach cone

SB seminar Cluster resolution 38 ATLAS Preliminary

SB seminar Six cut variables 39 |  |<0.75, 45 GeV<E T < 70 GeV

SB seminar 40 Photon id – tight cut

SB seminar 41 Direct Photon Spectra Expected direct photon spectra for 0.5 nb -1 in |  |<2.4 Assuming neutral hadron R AA =1 (worst case).  rate for 1 year LHC run of 0.5 nb k at E>30 GeV, 10 k at E>70 GeV Measurement  -jet correlation and fragmentation function

SB seminar 42 Final state direct  Fragmentation, conversion, bremsstrahlung photons Carry detailed information about the jet-medium interaction Dominate/important at pT<30-50 GeV, not isolated. Can be enriched via  -ID cuts Turbide et al. Phys. Rev. C72 (2005) fragmentationconversionbremsstrahlung Strip layer provide unbiased/centrality-independent factor of 3-6 background rejection

SB seminar 43  -jet Correlation Clean  -jet  distribution in central Pb+Pb Tail comes from pQCD radiation Measure in-medium jet fragmentation function Can help jet analysis at low E T. Tune jet reco. algorithms. Reject fake jets. dN ch /d  =2700 (HIJING)

SB seminar 44 Sequential melting of quarkonia Why the suppression pattern show no  s dependence? Focus on bottomonium measurement in ATLAS

SB seminar 45 Muons in ATLAS Muon detection capabilities for |  | 2.5 GeV/c MDT: Monitored drift tubes (barrel and endcaps) CSC: Cathode strip chambers (endcaps) RPC: Resistive Plates Chambers (barrel trigger) TGC: Thin Gap Chambers (endcaps and barrel trigger) c,b  D,B + others   + others

SB seminar 46 Muon-jet Correlation Tag heavy quark jet (c,b) by high p T muons Require muon p T >5 GeV and jet E T >35 GeV Low p T : 1/3 of away-side jet each from b,c, light quarks+gluons. High p T : dominated by bottom quark. Heavy quark energy loss