Heavy Ion Physics with the ATLAS Detector for the ATLAS Collaboration

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Feb 11, 2005 Winter Workshop on Nuclear Dynamics Heavy Ion Physics with the ATLAS Detector for the ATLAS Collaboration Sebastian White Brookhaven National Lab

description

Heavy Ion Physics with the ATLAS Detector for the ATLAS Collaboration. Sebastian White Brookhaven National Lab. Jet Physics with ATLAS. Strikman,Vogt &SNW. -Gyulassy & Vitev. Studies of the Detector Performance. Using existing ATLAS detector and (mostly) algorithms - PowerPoint PPT Presentation

Transcript of Heavy Ion Physics with the ATLAS Detector for the ATLAS Collaboration

Page 1: Heavy Ion Physics  with the ATLAS Detector for the  ATLAS Collaboration

Feb 11, 2005 Winter Workshop on Nuclear Dynamics

Heavy Ion Physics with the ATLAS Detector

forthe ATLAS Collaboration

Sebastian WhiteBrookhaven National Lab

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Jet Physics with ATLAS

Strikman,Vogt &SNW-Gyulassy & Vitev

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Using existing ATLAS detector and (mostly) algorithmsdeveloped for pp @L=1034 (~24 interactions @40Mhz)

Studies of the Detector Performance

Simulations: HIJING event generator, dNch/d = 3200 Full GEANT simulations of the detector response

Large event samples: ||< 3.2 impact parameter range: b = 0 - 15fm (27,000 events) ||< 5.1 impact parameter range: b = 10 - 30fm (5,000 events)

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Simulation DataFlow

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ATLAS Inner Tracking (to ||<2.5 )

Pixel+SCT=11 layers(2-3+8)TRT=39 layers

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Tracking Reconstruction

-2.5<<2.5

Tile Calorimeter threshold cut will have excellent rejection.

Detailed reconstruction with pT

thr = 300 MeV/c

Track 10 of 11 planes. Most fakes in forward directions.

Full ATLAS Simulation

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Tracking Resolution

-2.5<<2.5Plot shows the average reconstruction resolution.

pt/pt=2% in barrel, larger in endcaps

Full ATLAS Simulation

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State of the art EM+Had calorimeter!-Highly segmented.-4 depth segments-200k EM channels.-LAr to ||<4.9

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EM Calorimeter Segmentation

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Jet ReconstructionEnergy in 0.1x0.1 tower in the EM and HAD calorimeter for ||<3.2. Most of the energy is in the EM calorimeter due to soft particles ranging out.

Hadronic calorimeter is relatively quiet even in b=0 HIJING events!

Energy in 0.1x0.1 tower as function of .

Full ATLAS Simulation

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55 GeV Jet

PYTHIA only

The Result !

PYTHIA + HIJING overlayed event.

After average background subtraction

For lower jet energies we found that it is easier to find jets if the first EM compartment is not included. Later the energy from the 1st compartment is recovered.

Full ATLAS Simulation

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Jet Reconstruction Efficiency

A “good” jet is defined as the one that finds a match in the generated event within a cone radius of 0.2. Fakes are the ones that do not fulfill the requirement.

Fakes include HIJING jets. Track matching may reduce the number of “real” fakes.

Full ATLAS Simulation

Very promising results with high jet reconstruction efficiency!

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Jet Reconstruction=.045,.035

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Jet Energy ResolutionExcellent jet energy resolution.

Energy resolution is close to a high luminosity L~1034 proton-proton run. This fact also means that large contingent of high energy ATLAS participants are interested in working on these issues.

Full ATLAS Simulation

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Weight=7000Tdiameter=22mWidth=44m

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Quarkonia SuppressionColor screening prevents formation of various states

when T>Tc for the phase transition to QGP

(color screening length < size of resonance)

Upsilon family (1s) (2s) (3s) Binding energies (GeV) 1.1 0.54 0.2Dissociation at the temperature ~2.5Tc ~0.9Tc ~0.7Tc

Important to separate (1s) and (2s)!

QGP thermometer

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Upsilon Reconstruction- Overlay decays on top of HIJING events.- Use combined info from ID and -Spectrometer

+–

Single Upsilons

HIJING backgroundHalf ’s from c, b decays, half from π, K decays for pT>3 GeV.

Background rejection:- 2 cut - geometrical cut - pT cut.

,: differences between ID and µ-spectrometer tracks after back-extrapolation to the vertex for the best 2 association.

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Upsilon ReconstructionBarrel only (|| <1)

|| <1 || <2.5

Acceptance 4.9% 14.1% +efficiency

Resolution 123 MeV 147 MeV

S/B 1.3 0.5

Purity 94-99% 91-95%

For a 106s run with Pb+Pb at L=41026 cm-2 s-1 we expect 104 events in || < 1.2 (6% acc+eff).

J/ +– - a study is under way (mass =53 MeV).

A compromise has to be found between acceptance and mass resolution to clearly separate upsilon states.

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Diffractive Physics with ATLAS

•ATLAS Coverage

•Forward Instrumentation

•ATLAS reach in jj and j

Pro-E model of ZDC for ATLAS andfull simulation of Energy response

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Lessons from Run IV:PHENIX J/ and high mass e+e- Photoproduction

PHENIX implemented trigger for small cross section UPC physics

~10 M events collected

(seeG.Baur et al. Nucl-th/03070310)

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di-jet photoproduction-> parton distributions,x2by with momentum fraction, x14pt

2/s=x1*x2<y>~ -1/2*ln(x1/x2)Signature: rapidity gap in direction(FCAL veto)

x1

x2

Analogous upc interactions and gap structure

diffractive Non-diffractive

Probing small x structure in the Nucleus with N->jets, heavy flavor.

ATLAS coverage to||<5 units. Pt ~2 Gev“rapidity gap” threshold

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Event yields from a 1 monthHI (Pb-Pb) run at Nominal Luminosity.Counts per bin of pt=2 GeVx2/x2=+/- 0.25

M.Strikman,R.Vogt, SNW

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Collision Hall at start of installation( Feb. 04)

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Location,location,location

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US-ATLAS Heavy Ion Group

S. Aronson, K. Assamagan, M.Baker,H. Gordon, M. Levine, P. Nevski, H. Takai, P.Steinberg, S. WhiteBrookhaven National Laboratory

J. Nagle-University of ColoradoB. Cole-Columbia University

+Bern, CERN, Geneva, Prague,Cracow…

-LOI submitted to LHCC by the full ATLAS collaboration in May ‘04

-Broad range of physics and simulation activities now under way

Atlas.ch/standardmodel/HeavyIons

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280 GeV eventPreliminary efficiency numbers show that jet reconstruction efficiency is larger than 90% above 50 GeV.

Below 50 GeV the efficiency lowers to approximately 75% with an increase in the number of “ghosts”.

Remember we are using b=0 HIJING events as our test case.

Full ATLAS Simulation

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Motivation: High-pT Results from RHIC

Jet quenching observed in AuAu as predicted by pQCD:(unquenching in dAu)

PRL91, (2003)PRL91, (2003)

Hard processes:excellent probes to test QCD!

c

d

ab

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Heavy ion Physics with the ATLAS Detector

-Introductory- we come from a program at RHIC which has been productive beyond our expectations. Much of the physics has been driven by experimental opportunities due to large multi-purpose detectors. Key experimental tools have been excellent tracking coverage with particle identification, powerful calorimetry (electromagnetic in the central region-PHENIX,STAR EMC; Hadronic in the forward region ZDC/SMD and Pcal in the forward region). Many aspects of Heavy Ion physics evolving now; heavy flavors, UPC, jet studies at the highest pt.