Jet studies in preparation for ATLAS: from pp to heavy ion collisions

Jet studies in preparation for Jet studies in preparation for ATLAS: from pp to heavy ion ATLAS: from pp to heavy ion

collisionscollisions

Arthur M. MoraesArthur M. MoraesBrookhaven National LaboratoryBrookhaven National Laboratory

(on behalf of the ATLAS Collaboration)(on behalf of the ATLAS Collaboration)

APS – April Meeting 2006 Dallas, April 22nd – 25th 2006.

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APS 2006 – April 25th 2006Arthur Moraes 2

Outline:Outline:

II. Jet studies at the LHC: Measuring jets in pp collisions

I. LHC and ATLAS

IV. Summary

III. Heavy ion collisions & jet physics From RHIC to the LHC Jets in LHC heavy ion collisions Finding jets in central Pb-Pb events Reconstruction performance

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• p-p collisions at √s = 14TeV

• bunch crossing every 25 ns (40 MHz)

low-luminosity: L ≈ 2 x 1033cm-

2s-1 (L ≈ 20 fb-1/year)

LHC (LHC (LLarge arge HHadron adron CCollider):ollider):

• Pb-Pb collisions at √s = 5.5TeV (per colliding nucleon pair)

Pb-Pb luminosity: L ≈ 1027cm-2s-1

(limited by the quenching of the magnets)

• bunch crossing every 100 ns (10 MHz)

• p-Pb and lighter ion collisions are also foreseen.

More info: CERN/LHCC/2004-009

first runs with heavy-ion collisions are expected in 2008.

LHC heavy ion programme: one month of running per year of operation.

high-luminosity: L ≈ 1034cm-2s-1

(L ≈ 100 fb-1/year)

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Muon DetectorsMuon Detectors Tile CalorimeterTile CalorimeterLiquid Argon CalorimeterLiquid Argon Calorimeter

Toroid MagnetsToroid MagnetsSolenoid MagnetSolenoid Magnet

SCT TrackerSCT TrackerPixel DetectorPixel Detector

TRT TrackerTRT Tracker

ATLAS: AATLAS: A TToroidal oroidal LLHC HC AAparatuparatuSS

• Multi-purpose detectorscoverage up to |η| = 5;design to operate at L= 1034cm-2s-1

• Most of the detector subsystems will be operational for the study of heavy ion collisions.

• Inner Detector: Pixel & SCT will be able to provide track measurements. TRT is unusable for nucleus-nucleus (Pb-Pb) studies due to high occupancy.

• Calorimetry: well suited for jet quenching studies. Best granularity and hadronic energy resolution compared to other LHC detectors.

• Muon System: quieter than in pp collisions at high-luminosity. Can be used for efficient μ identification and b-jet tagging.

ATLAS is well adapted to ATLAS is well adapted to perform perform high-pT high-pT measurements in LHC pp measurements in LHC pp collisioncollision as well as as well as physics physics studies in heavy ion studies in heavy ion collisions.collisions.

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Jet physics at the LHCJet physics at the LHC

p

p Essentially all physics at LHC are connected to the interactions of Essentially all physics at LHC are connected to the interactions of quarks and gluons (small & large transferred momentum). quarks and gluons (small & large transferred momentum).

Expect multi-jet final states.Expect multi-jet final states. This requires a solid understanding of QCD.This requires a solid understanding of QCD.

Large event rate reduces statistical errors Large event rate reduces statistical errors quickly. quickly.

SM candles (W, Z, SM candles (W, Z, γγ-jet and top production) -jet and top production) will be used to calibrate the detector.will be used to calibrate the detector.

Inclusive Jet Inclusive Jet ProductionProduction

~10~101.31.3××1010-6-6pptt > 3 TeV > 3 TeV

~10~10331010-4-4pptt > 2 TeV > 2 TeV

~10~10660.10.1pptt > 1 TeV > 1 TeV

~10~1099100100ppt t > 200 GeV> 200 GeV

Events/year Events/year ((LL=10 fb=10 fb-1-1)) σσ (nb) (nb)

pp collisions at pp collisions at √s=14TeV√s=14TeV

Systematic errors are expected Systematic errors are expected to dominate.to dominate.

Sources of systematic errors:Sources of systematic errors: jet algorithm,jet algorithm, calorimeter response (jet energy scale),calorimeter response (jet energy scale), jet trigger efficiency,jet trigger efficiency, luminosity (dominant uncertainty 5% -10% ),luminosity (dominant uncertainty 5% -10% ), the underlying event.the underlying event.

Jets in pp collisions at Jets in pp collisions at √s=14TeV√s=14TeV

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Reconstructed jet event (pp Reconstructed jet event (pp collisions):collisions): Atlantis event displayAtlantis event display

Jets in pp collisions at Jets in pp collisions at √s=14TeV√s=14TeV

EETT jet #2jet #2 = 1.16TeV = 1.16TeV

EETT jet #1jet #1 = 1.63TeV = 1.63TeV

• Test of pQCD in an energy Test of pQCD in an energy regime never probed!regime never probed!

• The measurement of di-jets The measurement of di-jets and their properties (Eand their properties (ETT and and ηη1,21,2) ) can be used to can be used to constrain constrain p.d.f.’sp.d.f.’s..

• Multi-jet production is important for Multi-jet production is important for several physics studies: several physics studies: a)a) tt production with hadronic final tt production with hadronic final

statesstatesb)b) Higgs production in association Higgs production in association

with tt and bb with tt and bb c)c) Search for R-parity violating SUSY Search for R-parity violating SUSY

(8 – 12 jets).(8 – 12 jets).

• Inclusive jet cross section: Inclusive jet cross section: ααSS(M(MZZ)) measurement with measurement with 10% accuracy10% accuracy..

( can be reduced by using the 3-jet to 2-jet production )

Some applications Some applications of jet of jet measurements in measurements in pp collisions:pp collisions:

--

-- --

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Results from RHIC experiments suggest that a hot and dense Results from RHIC experiments suggest that a hot and dense QCD matter, which may be the QCD matter, which may be the quark-gluon plasma (QGP)quark-gluon plasma (QGP), is , is formed in Au-Au collisions at √s=200GeV per colliding nucleon formed in Au-Au collisions at √s=200GeV per colliding nucleon pair.pair.

Jets in heavy ion collisionsJets in heavy ion collisions

STAR, PRL 91 (2003) 072304 The LHC will collide heavy nuclei such as Pb at The LHC will collide heavy nuclei such as Pb at √s=5.5TeV/nucleon pair. At these energies it will be possible to √s=5.5TeV/nucleon pair. At these energies it will be possible to produce an even higher temperature QCD matter.produce an even higher temperature QCD matter.

Hard scattering cross-sections will increase Hard scattering cross-sections will increase significantlysignificantly and the resulting jets could be used as probes and the resulting jets could be used as probes of the QCD matter. of the QCD matter.

RHIC experiments also show that RHIC experiments also show that hard scattered quarks hard scattered quarks inside the QGP radiate gluonsinside the QGP radiate gluons and therefore modify the jet and therefore modify the jet properties such as energy angular distribution and suppression properties such as energy angular distribution and suppression of high-pof high-pTT hadrons (jet quenching). hadrons (jet quenching).

From RHIC to the LHCFrom RHIC to the LHC

The parton energy loss is directly related to the initial gluon The parton energy loss is directly related to the initial gluon density of the system, which is expected to be over a density of the system, which is expected to be over a factor of factor of ten higher at the LHC than at RHICten higher at the LHC than at RHIC..

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Pb-Pb at √s = 5.5TeV (per colliding nucleon pair) One month (~10One month (~1066s) run with Pb-Pb at L=4s) run with Pb-Pb at L=410102626 cm cm-2-2 s s-1-1

Expected numbers of jet events at ATLAS for |Expected numbers of jet events at ATLAS for |ηη| < 4.9:| < 4.9:

Jets in heavy ion collisions at the LHCJets in heavy ion collisions at the LHC

Jet ET threshold Number of events

50 GeV 30 106

100 GeV 1.5 106

150 GeV 1.9 105

200 GeV 4.4 104

And also: ~106 + jet events ~500 Z0() + jets with ET > 40 GeV

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Finding jets in central Pb-Pb eventFinding jets in central Pb-Pb event

Jet reconstruction in heavy ion Jet reconstruction in heavy ion environment is more challenging than environment is more challenging than in pp collisions because of the in pp collisions because of the large large background of low-pbackground of low-pTT particles particles..

pp collisionspp collisions: jet E: jet ETT threshold threshold ~10(20)GeV for a jet of size ~10(20)GeV for a jet of size ΔΔR=0.4R=0.4

central Pb-Pbcentral Pb-Pb: jet E: jet ETT threshold ~50GeV threshold ~50GeV for a jet of size for a jet of size ΔΔR=0.4R=0.4

Jet energy calibration may be Jet energy calibration may be different for pp and heavy ion events.different for pp and heavy ion events.

Reconstruction:Reconstruction:

-background is estimated in rings background is estimated in rings xx=0.1=0.1xx22ππ and subtracted from and subtracted from calorimeter towers.calorimeter towers.

-sliding window algorithmsliding window algorithm is used to is used to find jet candidates, which are find jet candidates, which are reconstructed inside cones of size reconstructed inside cones of size ΔΔR=0.4.R=0.4.

- jet candidates are accepted if jet candidates are accepted if EETT

jetjet>40GeV.>40GeV.

- other methods are currently other methods are currently being investigated being investigated (e.g. cone fit (e.g. cone fit algorithm)algorithm)..

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Jet reconstruction performanceJet reconstruction performance

Jet reconstruction efficiency Pb-Pb (b=0 – 1 fm)Jet reconstruction efficiency Pb-Pb (b=0 – 1 fm)

The worsening in energy resolution introduced The worsening in energy resolution introduced by the background has nearly the same effect by the background has nearly the same effect when pile-up and electronic noise is added to high when pile-up and electronic noise is added to high luminosity proton-proton runs (see ATLAS-TDR).luminosity proton-proton runs (see ATLAS-TDR).

The efficiency of the reconstruction is The efficiency of the reconstruction is evaluated by counting reconstructed jets evaluated by counting reconstructed jets (PYTHIA+HIJING) matching the generated PYTHIA (PYTHIA+HIJING) matching the generated PYTHIA jets within a cone of size jets within a cone of size ΔΔR=0.2.R=0.2.

• Two jet finder algorithms testet up to now - Sliding Window and Cone Fit

for ET > 75GeV: efficiency > 95%, fake < 5% good energy and angular resolution

Fake jets: comparison between jets in HIJING Fake jets: comparison between jets in HIJING (background) matching the direction of jets on (background) matching the direction of jets on PYTHIA+HIJING.PYTHIA+HIJING.

EETT=75GeV=75GeV

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Summary:Summary:

Jet measurements are crucial to most LHC studies. This applies not only to Jet measurements are crucial to most LHC studies. This applies not only to physics from proton-proton collisions but also to the heavy ion programme.physics from proton-proton collisions but also to the heavy ion programme.

ATLAS ATLAS cancan mak makee a valuable and significant contribution to the LHC’s heavy a valuable and significant contribution to the LHC’s heavy ion ion physics programmephysics programme

Jet physics studies in LHC heavy ion collisions at ATLAS will contribute immensely to the Jet physics studies in LHC heavy ion collisions at ATLAS will contribute immensely to the understanding of jet quenching. understanding of jet quenching.

jet reconstruction is possible despite the additional backgroundjet reconstruction is possible despite the additional background jet energy resolution comparable to pp for jet Ejet energy resolution comparable to pp for jet ETT>>100 GeV100 GeV

Measuring jets in pp collisions: precision Measuring jets in pp collisions: precision limited by systematiclimited by systematic and not by and not by statistical uncertainties!statistical uncertainties!

Measuring jets in heavy ion collisions: challenging environment (low-pMeasuring jets in heavy ion collisions: challenging environment (low-pTT background), but ATLAS will be able to deliver precise measurements.background), but ATLAS will be able to deliver precise measurements.

Combining calorimeter measurements with tracking and muon system there is also the Combining calorimeter measurements with tracking and muon system there is also the possibility to study separately light and heavy-quark jetspossibility to study separately light and heavy-quark jets

Documents

Jet studies in preparation for ATLAS: from pp to heavy ion collisions