ATLAS commissioning and early physics - resonance and jet production -

　 K. Hara (University of Tsukuba)　 on behalf of the ATLAS Collaboration

QNP2009, Sep.24 Beijing

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Cosmic events for ATLAS commissioningCosmic events for ATLAS commissioning

20092 weeks

20085 months

Cosmic events (~300M events) are very useful for detector calibration. The data taking was valuable experiences for coordinated detector operation, including all the detector components, trigger and DAQ system, monitoring, offline analysis, …

Another cosmic run is scheduled for final checkout for the collision

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Pickups from cosmic resultsPickups from cosmic resultsTrack impact point resolution vs. track pT

- requires overall understanding of detector alignment.

Track p difference between ID and MUONunderstanding the calorimeter material Measured calorimeter ET for muons

With early data (10-100 pb-1 integrated luminosity), quarkonium is first physics to measure including:1. prompt to indirect J/ cross-section ratio2. prompt J/→ and prompt ϒ→ differential production cross-sections3. spin alignment of J/ and ϒ as a function of quarkonium transverse momentum4. c cross-section→ J/b cross-section→ J/ J/… and others

Predicted rates$ @ 10TeV : require pT> 4 GeV for both muons

17k ev/ pb-1 @10 TeV (we expect ~100pb-1 @7 TeV)

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(pp→ Ｑ [44] X) @10TeV J/ ϒ(1S)

ϒ(2S)

ϒ(3S)

DY* bb*

generator-level cross section (nb) 27 18.5 10.2 8.8 0.24 16.2

rate after trig/reco/bg subtraction (nb) 17 12.1 5.5 4.1 0.14 9.5*8-12GeV mass range$color-octet model adopted in PYTHIA

The rest of the ATLAS simulation is @14TeV

Large predicted cross-sections and range of transverse momenta accessible at LHC, ATLAS can give new insight into quarkonium production and tests of QCD production mechanism of quarkonium has many features still unexplained large predicted quarkonia rates: J/ and ϒ will play a central role for calibrations of the ATLAS detector and software

Quarkonium physics with early dataQuarkonium physics with early data

color singlet

5QNP2009, Sep.24 Beijing

Color Octet Model can not explain everythingColor Octet Model can not explain everything

CDF: Phys.Rev.Lett.99:132001,2007

NRQCD: Braaten et al.,PRD61,094005(1995); Cho et al.,PLB346(1995)129.kT factorization: Baranov, PRD66,114003(2002)

CDF

+color octet

Angle of m+

*: helicity angle between + in rest frame and direction in lab frame

Kraemer: Prog.Part.Nucl.Phys.47:141-201,2001

polarization parameter =0 (un-polarized) =+1 100% transverse =1 100% longitudinal

J/

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NNLO* Color Singlet ModelNNLO* Color Singlet Model Artoisenet et al, Phys.Rev.Lett 101:152001 (2008)

　

LHC prediction

Precise and Xsec measurements to high PT are interesting at LHC

ϒ Xsec (CDF) is explained by CSM alone with NNLO*Negaitve is predicted (~D0 Run2)

Separation of prompt and indirect productionSeparation of prompt and indirect production

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Use decay time difference between prompt and indirect

B decay length~1mm, typically

Proper time for prompt/indirect separationProper time for prompt/indirect separation

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Proper time ~0: prompt J/ψ (spread=resolution) >0: secondary from B decay

no misalignment

~93% purity~92%@0.2ps

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Two different trigger strategies: di–muon trigger 4(or 44) single muon 10 (2nd ‘’ in offline)

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Quarkonium mass distributionsQuarkonium mass distributions

ϒ(1S) only

single trigger (2nd track pT >0.5 GeV) is to rescue small acceptance of di-muon trigger for forward J/ψ charge opposite to triggered no other candidate track in R<3 of |d0|<0.04mm(), 0.10mm(track)

larger bkg, but mass resolution not degraded

10 pb-1

signal+bkg before vertexing

before decay time cut

J/ψ

This method is not justified for ϒ (low S/N~0.25) at 10 pb-1

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with single 10 (+track) trigger, wider cosθ* range is covered : more reliable spin alignment measurement should be possible. events generated flat in cos θ*(acceptance shape depends on PT range: more flat for high PT )

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Acceptance for spin alignment measurementAcceptance for spin alignment measurement

CDF J/ acceptance

TeV14s

restricted cosθ* coverage (CDF) is a major source of systematics.

D0 Run2 ϒ polarization data disagree withtheoretical models and CDF Run1 data

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Quarkonium spin alignment sensitivity at 10 pbQuarkonium spin alignment sensitivity at 10 pb-1-1

At 7 TeV, sensitivity is not much degraded for J/need more luminosity (at least 100 pb-1) for ϒ

TeV14s

ϒ

ATLASATLAS

10pb-1

gen is properly reconstructed~0.02-0.06 in 10<PT<20 GeV for

J/comparable to the Tevatron ~1 fb-1 data)

Determination less precise for ϒ:(single-muon + track is not reliable for S/N~0.05 at 10 pb-1 )

produced from published ATLAS MC results

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QCD physics at ATLASQCD physics at ATLAS

QCD Physics include, e.g.• PDF measurements (proton

structure)• Jet studies (reconstruction, rates,

cross sections…)• Fragmentation studies• Diffractive physics s measurements…

Tevatron ETmax~0.7TeV

O(100) jet ET > 1TeV for 10 pb-1 @ 14 TeV

Primary interest is to look for deviations in high

ET jet events from QCD due to new physics

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J.Stirling

PDF uncertainty• uncertainty evaluation using CTEQ6, 6.1• largest uncertainty: high x gluons• at pT 1 TeV around 15% uncertainty

Jet cross sectionJet cross section

Jet energy scale uncertainty (largest in exp.)• 1% uncertainty →10% error on • 5% uncertainty → 30% error on • 10% uncertainty → 70% error on control to 1-2% (c.f. PDF uncertainty) is our target

Scale uncertainty• variation of F and R within pT

max/2<<2pTmax

• ~10% uncertainty at 1TeV

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Steeply falling pT spectrum: control of systematics necessary

1. Z+jets events (10<ET<100-200 GeV) 1% stat. uncertainty on JES with 300 pb-1

syst.: ISR/FSR+UE ~5-10% at low ET 1-2% at ET~200 GeV

Determination of jet-energy scale (JES) Determination of jet-energy scale (JES)

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Z

Many effects from detector (non compensation, noise, cracks….) and from physics (clustering, fragmentation, ISR and FSR, UE….) are to be understood

Use in-situ calibration with physics processes (in divided ET ranges)

CERN-OPEN-2008-020

Jet energy calibration is a complex task, including calorimeter cluster reconstruction (each tower needs to be equalized beforehand) cluster to jet assignment jet calibration from calorimeter to particle scale jet calibration from particle to parton scale

3. Jet balance (ET>500 GeV) to low energy jets with calibrated JES 2% statistical @1 fb-1

7% syst.* from low energy jet JES

Determination of jet-energy scale (JES) Determination of jet-energy scale (JES) cont’dcont’d

jets

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*improvement expected using data, e.g. understanding MinBias/UE (R. Kwee talk on Tuesday)di-jet decorrelation

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2. +jets events (100-200<ET<500 GeV) 1-2% stat.uncertainty on JES with100 pb-1

syst.: ISR/FSR+UE ~ 1-2%

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Azimuthal di-jet decorrelationAzimuthal di-jet decorrelation

Di-jet production result in:Δφ(di-jet) = ｜ φ(jet1) – φ(jet2) ｜ = πin the absence of radiative effects

Di-jet events with smaller angle are sensitive to radiative effects, multi-parton interactions, soft-QCD processes

D0 data prefer between“low ISR” and “increased ISR” D0 data are from

PRL 94, 221801 (2005)

MidPoint algorithm with R=0.7

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A. Moraes et al., ATL-PHYS-PUB-2006-013

SummarySummary Resonances are first objects to study for detector performance Resonances are first objects to study for detector performance evaluation and calibration evaluation and calibration With 10 pbWith 10 pb-1-1, J/, J/cross-section will be measured precisely (around cross-section will be measured precisely (around 1% accuracy excluding e.g. luminosity uncertainty) with prompt and 1% accuracy excluding e.g. luminosity uncertainty) with prompt and indirect processes well separated. indirect processes well separated. Quarkonium spin alignment measurements will have the capability to Quarkonium spin alignment measurements will have the capability to distinguish quarkonium production models:distinguish quarkonium production models:

with reduced systematics ATLAS will provide competitive with reduced systematics ATLAS will provide competitive measurement to Tevatron with 10 pbmeasurement to Tevatron with 10 pb-1-1 (J/ (J/)- and >100 )- and >100 pbpb-1-1

((ϒϒ ATLAS will investigate high EATLAS will investigate high ETT jets to look for deviations from QCD. jets to look for deviations from QCD.

Jet energy scale calibration is a crucial experimental uncertainty and Jet energy scale calibration is a crucial experimental uncertainty and various methods are under study to cover wide jet energy range.various methods are under study to cover wide jet energy range. Di-jet azimuthal angle decorrelation will examine the PDFs and Di-jet azimuthal angle decorrelation will examine the PDFs and modeling of soft components. modeling of soft components. 17


ATLAS IS READY FOR TAKING DATAATLAS IS READY FOR TAKING DATA

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Quarkonia for detector calibrationQuarkonia for detector calibration

6 pb–1

no misalignment

e.g.,Look at mass shifts in m vs. pT: check tracker momentum scale energy loss corrections in calorimetervs. and : check correct implementation of material effects, magnetic field uniformity and stabilityvs. 1/pT(+) – 1/pT(-): check detector misalignment (→ ）

Resonance peaks are clean and useful for detector calibration

Quarkonia decays will also be used for online monitoring(e.g. trigger efficiencies, detector calibration)

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CDF: Phys.Rev.Lett.99:132001,2007

J/

CDFPhys.Rev.Lett.85:2886-2891,2000

ATLAS commissioning and early physics - resonance and jet production -

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