Heavy ion physics with the atlas detector for the atlas collaboration
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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

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Heavy Ion Physics with the ATLAS Detector for the ATLAS Collaboration

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Heavy ion physics with the atlas detector for the atlas collaboration

Heavy Ion Physics with the ATLAS Detectorforthe ATLAS Collaboration

Sebastian White

Brookhaven National Lab

Winter Workshop on Nuclear Dynamics


Jet physics with atlas

Jet Physics with ATLAS

Strikman,Vogt &SNW

-Gyulassy & Vitev

Winter Workshop on Nuclear Dynamics


Heavy ion physics with the atlas detector for the atlas collaboration

Studies of the Detector Performance

  • Using existing ATLAS detector and (mostly) algorithms

    developed for pp @L=1034 (~24 interactions @40Mhz)

  • Simulations:HIJING event generator, dNch/dh = 3200

  • Full GEANT simulations of the detector response

  • Large event samples:

  • |h|< 3.2 impact parameter range: b = 0 - 15fm (27,000 events)

  • |h|< 5.1 impact parameter range: b = 10 - 30fm (5,000 events)

Winter Workshop on Nuclear Dynamics


Simulation dataflow

Simulation DataFlow

Winter Workshop on Nuclear Dynamics


Heavy ion physics with the atlas detector for the atlas collaboration

ATLAS Inner Tracking (to |h|<2.5 )

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

TRT=39 layers

Winter Workshop on Nuclear Dynamics


Tracking reconstruction

Tracking Reconstruction

Full ATLAS Simulation

-2.5<h<2.5

Tile Calorimeter threshold cut will have excellent rejection.

Detailed reconstruction with pTthr = 300 MeV/c

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

Winter Workshop on Nuclear Dynamics


Tracking resolution

Tracking Resolution

Full ATLAS Simulation

Plot shows the average reconstruction resolution.

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

-2.5<h<2.5

Winter Workshop on Nuclear Dynamics


Heavy ion physics with the atlas detector for the atlas collaboration

State of the art

EM+Had calorimeter!

-Highly segmented.

-4 depth segments

-200k EM channels.

-LAr to |h|<4.9

Winter Workshop on Nuclear Dynamics


Em calorimeter segmentation

EM Calorimeter Segmentation

Winter Workshop on Nuclear Dynamics


Jet reconstruction

Jet Reconstruction

Energy in 0.1x0.1 tower in the EM and HAD calorimeter for |h|<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 h.

Full ATLAS Simulation

Winter Workshop on Nuclear Dynamics


55 gev jet

55 GeV Jet

PYTHIA + HIJING overlayed event.

PYTHIA only

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.

The Result !

Winter Workshop on Nuclear Dynamics

Full ATLAS Simulation


Jet reconstruction efficiency

Jet Reconstruction Efficiency

Full ATLAS Simulation

Very promising results with high 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.

Winter Workshop on Nuclear Dynamics


Jet reconstruction1

Jet Reconstruction

sh,f=.045,.035

Winter Workshop on Nuclear Dynamics


Jet energy resolution

Jet Energy Resolution

Excellent 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.

Winter Workshop on Nuclear Dynamics

Full ATLAS Simulation


Heavy ion physics with the atlas detector for the atlas collaboration

Weight=7000T

diameter=22m

Width=44m

Winter Workshop on Nuclear Dynamics


Heavy ion physics with the atlas detector for the atlas collaboration

Quarkonia Suppression

Color screening prevents formation of various  states when T>Tcfor the phase transition to QGP

(color screening length < size of resonance)

QGP thermometer

Upsilon family(1s) (2s) (3s)

Binding energies (GeV) 1.1 0.54 0.2

Dissociation at the temperature ~2.5Tc ~0.9Tc ~0.7Tc

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

Winter Workshop on Nuclear Dynamics


Heavy ion physics with the atlas detector for the atlas collaboration

Upsilon Reconstruction

  +–

  • Overlay  decays on top of HIJING events.

  • Use combined info from ID and m-Spectrometer

  • Single Upsilons

  • HIJING background

  • Half ’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.

Winter Workshop on Nuclear Dynamics


Heavy ion physics with the atlas detector for the atlas collaboration

Upsilon Reconstruction

Barrel only (|| <1)

A compromise has to be found

between acceptance and mass

resolution to clearly separate

upsilon states.

|| <1 || <2.5

Acceptance 4.9% 14.1% +efficiency

Resolution 123 MeV147 MeV

S/B 1.30.5

Purity 94-99%91-95%

For a 106s run with Pb+Pb at L=41026 cm-2 s-1

we expect 104 events in |h| < 1.2 (6% acc+eff).

- a study is under way (mass =53 MeV).

J/  +–

Winter Workshop on Nuclear Dynamics


Diffractive physics with atlas

Diffractive Physics with ATLAS

  • ATLAS Coverage

  • Forward Instrumentation

  • ATLAS reach in jj and gj

Pro-E model of ZDC

for ATLAS and

full simulation of

Energy response


Heavy ion physics with the atlas detector for the atlas collaboration

Lessons from Run IV:PHENIX J/y 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)

Winter Workshop on Nuclear Dynamics


Heavy ion physics with the atlas detector for the atlas collaboration

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

di-jet photoproduction-> parton distributions,x2

by g with momentum fraction, x1

4pt2/s=x1*x2

<y>~ -1/2*ln(x1/x2)

Signature: rapidity gap in g direction(FCAL veto)

x1

x2

ATLAS coverage to

|h|<5 units. Pt ~2 Gev

“rapidity gap” threshold

Analogous upc interactions and gap structure

diffractive

Non-diffractive

Winter Workshop on Nuclear Dynamics


Heavy ion physics with the atlas detector for the atlas collaboration

Event yields from a

1 month

HI (Pb-Pb) run at

Nominal Luminosity.

Counts per bin of

dpt=2 GeV

dx2/x2=+/- 0.25

M.Strikman,

R.Vogt, SNW

Winter Workshop on Nuclear Dynamics


Collision hall at start of installation feb 04

Collision Hall at start of installation( Feb. 04)

Winter Workshop on Nuclear Dynamics


Heavy ion physics with the atlas detector for the atlas collaboration

Location,location,location

Winter Workshop on Nuclear Dynamics


Heavy ion physics with the atlas detector for the atlas collaboration

US-ATLAS Heavy Ion Group

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

S. White

Brookhaven National Laboratory

J. Nagle-University of Colorado

B. 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

Winter Workshop on Nuclear Dynamics


280 gev event

280 GeV event

Preliminary 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.

Winter Workshop on Nuclear Dynamics

Full ATLAS Simulation


Heavy ion physics with the atlas detector for the atlas collaboration

c

a

b

d

Motivation:

High-pT Results from RHIC

Jet quenching observed in AuAu as predicted by pQCD:

(unquenching in dAu)

Hard processes:

excellent probes to test QCD!

PRL91, (2003)

Winter Workshop on Nuclear Dynamics


Heavy ion physics with the atlas detector for the atlas collaboration

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.

Winter Workshop on Nuclear Dynamics


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