ATLAS heavyion physics Jiangyong Jia Stony Brook University

ATLAS heavy-ion physics Jiangyong Jia Stony Brook University & BNL Jiangyong Jia, Wuhan, H-I Physics @LHC 1

Study the QGP matter initial state hadronic phase and freeze-out QGP and hydrodynamic expansion pre-equilibrium hadronization Form a matter in the overlap region. Matter expands under pressure. Matter interact with probes. Matter hadronize and freeze out. Jiangyong Jia, Wuhan, H-I Physics @LHC 2

Properties to be studied z y x n Bulk properties (soft physics) n n n Energy density, Temperature, Chemical potential hydrodynamic behavior: radial flow, elliptic flow, viscosity, etc Dynamical properties (hard physics) n n Opacity, transport coefficient Debye screening Jiangyong Jia, Wuhan, H-I Physics @LHC 3

* Why LHC? n RHIC physics has been a fantastic success n n n But the rate of progress is slowing down. n n Discovery of “jet-quenching” and “perfect fluid” -> s. QGP + ADS/CFT -> revolution for string theory. Run out of easy knobs to turn. Upgrade and RHIC II And lack of quantitative constraints, especially for hard sector – intrinsic limitations on hard probes at RHIC. LHC provide a different medium + fantastically rich set of probes. Jiangyong Jia, Wuhan, H-I Physics @LHC 4

* A different medium? n n Day 1 physics will help us to understand the initial condition, thermalization, collectivity. Detailed measurements of multiplicity and elliptic flow n n Color Glass condensate? Strongly coupled QGP? Viscosity? EOS? ? ? n Bulk observables used are similar to RHIC. Jiangyong Jia, Wuhan, H-I Physics @LHC 5

* Probe the medium Study the absorption/scattering pattern N 1 n n QGP N 2 How various probes, quarks, gluons and photons, interact with medium? This quest is just started at RHIC. n n So far limited to leading particle and two-particle correlations. Momentum limited to <20 Ge. V/c Jiangyong Jia, Wuhan, H-I Physics @LHC 6

Status of jet quenching n Energy loss bias due to lack of full jet reconstruction n Transport coefficients from models differ by a factor of 10 n GLV, ASW, HTL, TE. Jiangyong Jia, Wuhan, H-I Physics @LHC 7

Status of jet quenching n n -jet D(z), limited by rate. Heavy quark jet measurements disentangle radiative/collisional eloss. n limited by low rate, and c/b separation. c, b D, B + others e + others Jiangyong Jia, Wuhan, H-I Physics @LHC 8

Status of medium response Suppressed Jet + shoulder Jet + ridge Dissipation of lost energy in medium n n Complicated modification patterns at low and intermediate p. T. Interpretation hampered by many effects. jet-hadron correlation is more revealing. Jiangyong Jia, Wuhan, H-I Physics @LHC 9

Sequential melting of quarkonia n n Why the suppression pattern show no s dependence? Focus on bottomonium measurement in ATLAS Not covered in this talk Jiangyong Jia, Wuhan, H-I Physics @LHC 10

Handles for QCD plasma at ATLAS Transport properties: Jets, photons, heavy quarks Bulk properties: Collectivity QGP Thermometer: Bound states, i. e. Quarkonium Synergies between RHIC and LHC Jiangyong Jia, Wuhan, H-I Physics @LHC 11

* ATLAS potentials n n n Full jet reconstruction in -5<h<5, excellent -id using highly segmented strip layer (0. 003) in 2. 5<h<2. 5 Excellent charged hadron tracking in -2. 5<h<2. 5. Muon in -2. 5<h<2. 5, for upsilon reconstruction. Jiangyong Jia, Wuhan, H-I Physics @LHC 12

Event centrality n n Many variables (Ncoll, Npart, b) are correlated with centrality. High multiplicity give resolution better than 10% in most bins. n Redundant measurement in many detectors, better systematics. FCAL EM HAD Jiangyong Jia, Wuhan, H-I Physics @LHC 13

Charged hadron tracking n Tracking n n n 3 pixel layers 4 double-sided strips 2 T solenoidal field. Track reconstruction Single hadron suppression to high p. T Fragmentation function. Jiangyong Jia, Wuhan, H-I Physics @LHC 14

* n n Flow measurement Excellent reaction plane resolution Redundancy help to suppress the non-flow effect Allow jet-tomography studies! Jiangyong Jia, Wuhan, H-I Physics @LHC 15

Jet reconstruction in central Pb+Pb n Embed PYTHIA dijet in HIJING: No quenching, Q 2<100 Ge. V 2 Jiangyong Jia, Wuhan, H-I Physics @LHC 16

Jet reconstruction in central Pb+Pb n Embed PYTHIA dijet in HIJING n n HIJING: No quenching, Q 2<100 Ge. V 2 Subtract h-dependent average background Jiangyong Jia, Wuhan, H-I Physics @LHC 17

Jet reconstruction in central Pb+Pb n Embed PYTHIA dijet in HIJING n n n HIJING: No quenching, Q 2<100 Ge. V 2 Subtract h-dependent average background Cone-jet reconstruction n R=0. 4, seed ET>5 Ge. V. Excellent jet reconstruction in densest environment. Jiangyong Jia, Wuhan, H-I Physics @LHC 18

Jet reconstruction performance n n Energy resolution improves towards higher p. T. Energy resolution has no strong dependence on h. Excellent energy resolution @ high p. T and all h Jiangyong Jia, Wuhan, H-I Physics @LHC 19

* Inclusive jet spectra n n Reconstruction is fully efficient above 100 Ge. V in most central Pb+Pb event A few 107 jets > 50 Ge. V in 0. 5 pb Pb+Pb events Jiangyong Jia, Wuhan, H-I Physics @LHC 20

* Energy loss/medium response: jet multiplicity n n D(z) sensitive to energy loss and energy feedback Can recover D(z) in most central Pb+Pb environment. Medium response Energy loss p. T>1 Ge. V/c Jiangyong Jia, Wuhan, H-I Physics @LHC 21

* n n Energy loss/medium response: jet shape j. T distribution sensitive to jet shape modifications. Such as angular distribution of hard-radiations (they are still contained in a narrow cone). hep-ph/0310079 Jiangyong Jia, Wuhan, H-I Physics @LHC 22

* n Di-jet correlation Large signal evident with little background n n Given a jet>100 Ge. V, 60% probability to detect the associated >60 Ge. V jet. Benefit from large acceptance + high resolution Jet energy asymmetry and acoplanarity studies. Jiangyong Jia, Wuhan, H-I Physics @LHC 23

Direct -jet as probe for the medium n -tagged jets do not suffer eloss bias, direct handle on jet energy loss process Jet g Jet Jiangyong Jia, Wuhan, H-I Physics @LHC 24

How to identify a direct n n n Background for : p 0 and h. identification cuts ( -ID): distinguish from p 0/h on a particle-by-particle level. Isolation cuts: The p 0/h has other associated hadrons in jet cone. n n Similarly used in CMS and ALICE. Again, we can benefit from large acceptance. Jiangyong Jia, Wuhan, H-I Physics @LHC 25

* Unique ATLAS feature: ID For 50 Ge. V p 0, smallest open angle is about 0. 003 rad 0. 17 degree 0 photon Single particle p 0 Jiangyong Jia, Wuhan, H-I Physics @LHC 26

* Unique ATLAS feature: ID For 50 Ge. V p 0, smallest open angle is about 0. 003 rad 0. 17 degree Low occupancy from background in strips even in high multiplicity Embedded in d. N/d = 2700 (0. 5% AA) 0 photon Single particle p 0 Jiangyong Jia, Wuhan, H-I Physics @LHC p 0 27

Performance of -ID cuts n Rejection up to factor of 3 with efficiency of 90% Rejection up to factor of 5 -6 with efficiency of 50% (in backup) n Final state : Fragmentation, conversion, bremsstrahlung photons n n n Carry detailed information about the jet-medium interaction Dominate/important at p. T<30 -50 Ge. V, not isolated Turbide et al. Phys. Rev. C 72 (2005) 014906 Jiangyong Jia, Wuhan, H-I Physics @LHC 28

* Combining -id and isolation cut n S/N from p. QCD is <0. 1 below 100 Ge. V. Jiangyong Jia, Wuhan, H-I Physics @LHC 29

* Combining -id and isolation cut n n S/N from p. QCD is <0. 1 below 100 Ge. V. Combined relative rejection : 20 -50 n n S/N ~ 1 at 100 Ge. V assuming hadrons not suppressed S/N ~ 1 at 30 Ge. V assuming factor of 5 suppression. Reasonable S/N is need for robust study of gamma-jet! Jiangyong Jia, Wuhan, H-I Physics @LHC 30

* n Given n n Direct Photon Rates NLO p. QCD (INCNLL) rates Reconstruction efficiency of 50 -60% Raa~0. 2 @ 30 Ge. V 3 weeks/year running at 60% uptime (0. 5 nb-1) We expect to measure 200 k above 30 Ge. V per LHC year with S/B>1 (10 K above 70 Ge. V) This allow us to do jet tomography with -jet correlation n Jiangyong Jia, Wuhan, H-I Physics @LHC 31

Muons in ATLAS has excellent muon detection capabilities for |h| < 2. 6 and PT > 2. 5 Ge. V/c MDT: Monitored drift tubes (barrel and endcaps) CSC: Cathode strip chambers (endcaps) c, b D, B + others m + others RPC: Resistive Plates Chambers (barrel trigger) TGC: Thin Gap Chambers (endcaps and barrel trigger) Jiangyong Jia, Wuhan, H-I Physics @LHC 32

* Muon-jet correlation n n Heavy quark jet (c, b) are produced in pairs They can be tagged by high p. T muons n n Require muon p. T>5 Ge. V and jet ET>35 Ge. V Run pythia event embedded into HIJING. 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 Jiangyong Jia, Wuhan 33

Summary n “Day 1” measurements to understand the bulk properties of the medium. n n Multiplicity, E_T, thermalization, flow. Probe the medium using quarks, gluons, and photons. n n Single jet fragmentation, di-jet acoplanarity, asymmetry, -jet, -tagged jet, b-tagged jet: full jet tomography. Understand “medium response” using jet tags n If there is a cone – see it as a cone not with 3 -particle mess. Jiangyong Jia, Wuhan, H-I Physics @LHC 34

ATLAS people n New institutes since last 6 months Jiangyong Jia, Wuhan 35

* Final state direct n Fragmentation, conversion, bremsstrahlung photons n n n Carry detailed information about the jet-medium interaction Dominate/important at p. T<30 -50 Ge. V, not isolated. Can be enriched via -ID cuts Strip layer provide unbiased/centrality-independent factor of 3 -6 background rejection Turbide et al. Phys. Rev. C 72 (2005) 014906 fragmentation conversion bremsstrahlung Jiangyong Jia, Wuhan 36

Isolation cut n Isolation requirement n n R=0. 2, track pt<2. 5 Ge. V R=0. 2, tower ET<31 Ge. V Efficiency ~65% Rejection ~ 10 Jiangyong Jia, Wuhan 37

* n Given n n Direct Photon Rates NLO p. QCD (INCNLL) rates Reconstruction efficiency of 50 -60% Raa~0. 2 @ 30 Ge. V 3 weeks/year running at 60% uptime (0. 5 nb-1) We expect to measure 200 k above 30 Ge. V per LHC year with S/B>1 (10 K above 70 Ge. V) This allow us to do jet tomography with -jet correlation n Jiangyong Jia, Wuhan 38

Signal/background n n n Original S/N from p. QCD is <0. 1 below 100 Ge. V. S/N ~ 1 at 100 Ge. V assuming hadrons not suppressed S/N ~ 1 at 30 Ge. V assuming factor of 5 suppression. Reasonable S/N is need for robust study of gamma-jet! Jiangyong Jia, Wuhan 39

Photon id – tight cut Jiangyong Jia, Wuhan 40

Jet reconstruction performance n n Energy resolution quite uniform across all h. Better energy resolution in low multiplicity. Excellent energy resolution @ high p. T and all h Jiangyong Jia, Wuhan 41

Upsilon identification Integrated (over p. T and h) mass resolution is 177 Me. V. n n n Resolution is 120 Me. V for |h|<1 Integrated acceptance times efficiency is ~0. 19 Pb. Pb singles Jiangyong Jia, Wuhan 42

Upsilon states from Muons in ATLAS n n Estimate of signal/background in |h|<1 only for typical LHC year. Separation of 3 states possible. ~15 k reconstructed U 1 S S/B ratio ~ 1 Jiangyong Jia, Wuhan 43