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ATLAS commissioning and early physics - resonance and jet production -

K. Hara (University of Tsukuba) on behalf of the ATLAS Collaboration. ATLAS commissioning and early physics - resonance and jet production -. QNP2009, Sep.24 Beijing. Cosmic events for ATLAS commissioning. 2009 2 weeks. 2008 5 months.

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ATLAS commissioning and early physics - resonance and jet production -

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  1. K. Hara (University of Tsukuba) on behalf of the ATLAS Collaboration QNP2009, Sep.24 Beijing ATLAS commissioning and early physics - resonance and jet production -

  2. QNP2009, Sep.24 Beijing Cosmic events for ATLAS commissioning 2009 2 weeks 2008 5 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 2

  3. QNP2009, Sep.24 Beijing Pickups from cosmic results Track impact point resolution vs. track pT - requires overall understanding of detector alignment. Track p difference between ID and MUON understanding the calorimeter material Measured calorimeter ET for muons 3

  4. QNP2009, Sep.24 Beijing Quarkonium physics with early data With early data (10-100 pb-1 integrated luminosity), quarkonium is first physics to measure including: prompt to indirect J/y cross-section ratio prompt J/y →mm and prompt ϒ→mm differential production cross-sections spin alignment of J/y and ϒ as a function of quarkonium transverse momentum cccross-section→ J/y g ; cbcross-section→ J/y J/y… and others 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/y and ϒ will play a central role for calibrations of the ATLAS detector and software Predicted rates$ @ 10TeV : require pT> 4 GeV for both muons $color-octet model adopted in PYTHIA *8-12GeV mass range 17k ev/ pb-1 @10 TeV (we expect ~100pb-1 @7 TeV) The rest of the ATLAS simulation is @14TeV 4

  5. Color Octet Model can not explain everything CDF: Phys.Rev.Lett.99:132001,2007 CDF J/y Kraemer: Prog.Part.Nucl.Phys.47:141-201,2001 color singlet NRQCD: Braaten et al.,PRD61,094005(1995); Cho et al.,PLB346(1995)129. kT factorization: Baranov, PRD66,114003(2002) q*: helicity angle between m+ in rest frame and y direction in lab frame polarization parameter a =0 (un-polarized) a=+1 100%transverse a =-1 100% longitudinal +color octet Angle of m+ QNP2009, Sep.24 Beijing

  6. QNP2009, Sep.24 Beijing NNLO* Color Singlet Model Artoisenet et al, Phys.Rev.Lett 101:152001 (2008) ϒ Xsec (CDF) is explained by CSM alone with NNLO* Negaitve a is predicted (~D0 Run2) LHC prediction Precise a and Xsec measurements to high PT are interesting at LHC 6

  7. Separation of prompt and indirect production m+ Use decay time difference between prompt and indirect y m- y y B B decay length ~1mm, typically QNP2009, Sep.24 Beijing

  8. Proper time for prompt/indirect separation Proper time ~0: prompt J/ψ (spread=resolution) >0: secondary from B decay m+ m- CERN-OPEN-2008-020 CERN-OPEN-2008-020 no misalignment y y B e~93% purity~92% @0.2ps CERN-OPEN-2008-020 QNP2009, Sep.24 Beijing

  9. Quarkonium mass distributions signal+bkg before vertexing • Two different trigger strategies: • di–muon trigger m6m4(or m4m4) • single muon m10 (2nd ‘m’ in offline) before decay time cut ϒ(1S) only CERN-OPEN-2008-020 CERN-OPEN-2008-020 single m trigger (2nd track pT >0.5 GeV)is to rescue small acceptance of di-muon trigger for forward J/ψ charge opposite to triggered m no other candidate track in DR<3 of m |d0|<0.04mm(m), 0.10mm(track) 10 pb-1 larger bkg, but mass resolution not degraded m This method is not justified for ϒ (low S/N~0.25) at 10 pb-1 J/ψ QNP2009, Sep.24 Beijing

  10. Acceptance for spin alignment measurement CDF J/y acceptance restricted cosθ* coverage (CDF) is a major source of systematics. D0 Run2 ϒ polarization data disagree with theoretical models and CDF Run1 data with single m10 (+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) QNP2009, Sep.24 Beijing CERN-OPEN-2008-020

  11. ϒ Quarkonium spin alignment sensitivity at 10 pb-1 agen is properly reconstructed (Da~0.02-0.06 in 10<PT<20 GeV for J/y, comparable to the Tevatron ~1 fb-1 data) ATLAS ATLAS CERN-OPEN-2008-020 10pb-1 Determination less precise for ϒ: (single-muon +track is not reliable for S/N~0.05 at 10 pb-1 ) At 7 TeV, sensitivity is not much degraded for J/y need more luminosity (at least 100 pb-1) for ϒ produced from published ATLAS MC results QNP2009, Sep.24 Beijing

  12. QCD 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 • Primary interest is to look for deviations in high • ET jet events from QCD due to new physics • O(100) jet ET > 1TeV for 10 pb-1 @ 14 TeV J.Stirling QNP2009, Sep.24 Beijing

  13. Jet cross section Steeply falling pT spectrum: control of systematics necessary • Scale uncertainty • variation of F and R within pTmax/2<<2pTmax • ~10% uncertainty at 1TeV • PDF uncertainty • uncertainty evaluation using CTEQ6, 6.1 • largest uncertainty: high x gluons • at pT  1 TeV around 15% uncertainty • 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 QNP2009, Sep.24 Beijing

  14. Determination of jet-energy scale (JES) 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 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 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 Z QNP2009, Sep.24 Beijing

  15. Determination of jet-energy scale (JES) cont’d 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 2. g+jets events (100-200<ET<500 GeV) 1-2% stat.uncertainty on JES with100 pb-1 syst.: ISR/FSR+UE ~ 1-2% g CERN-OPEN-2008-020 CERN-OPEN-2008-020 CERN-OPEN-2008-020 CERN-OPEN-2008-020 *improvement expected using data, e.g. understanding MinBias/UE(R. Kwee talk on Tuesday) di-jet decorrelation jets QNP2009, Sep.24 Beijing

  16. Azimuthal di-jet decorrelation Di-jet production result in: Δφ(di-jet) = ｜φ(jet1) – φ(jet2)｜ = π in the absence of radiative effects Di-jet events with smaller angle are sensitive to radiative effects, multi-parton interactions, soft-QCD processes A. Moraes et al., ATL-PHYS-PUB-2006-013 MidPoint algorithm with R=0.7 D0 data prefer between “low ISR” and “increased ISR” D0 data are from PRL 94, 221801 (2005) QNP2009, Sep.24 Beijing

  17. Summary • Resonances are first objects to study for detector performance evaluation and calibration • With 10 pb-1, J/y cross-section will be measured precisely (around 1% accuracy excluding e.g. luminosity uncertainty) with prompt and indirect processes well separated. • Quarkonium spin alignment measurements will have the capability to distinguish quarkonium production models: with reduced systematics ATLAS will provide competitive measurement to Tevatron with 10 pb-1 (J/y)- and >100 pb-1 (ϒ) • ATLAS will investigate high ET jets to look for deviations from QCD. Jet energy scale calibration is a crucial experimental uncertainty and various methods are under study to cover wide jet energy range. • Di-jet azimuthal angle decorrelation will examine the PDFs and modeling of soft components. ATLAS IS READY FOR TAKING DATA QNP2009, Sep.24 Beijing

  18. Quarkonia for detector calibration Resonance peaks are clean and useful for detector calibration e.g., Look at mass shifts in mmm vs. pT: check tracker momentum scale energy loss corrections in calorimeter vs.  and : check correct implementation of material effects, magnetic field uniformity and stability vs. 1/pT(+) – 1/pT(-): check detector misalignment (→） CERN-OPEN-2008-020 6 pb–1 no misalignment Quarkonia decays will also be used for online monitoring (e.g. trigger efficiencies, detector calibration) QNP2009, Sep.24 Beijing

  19. CERN-OPEN-2008-020 QNP2009, Sep.24 Beijing

  20. QNP2009, Sep.24 Beijing CERN-OPEN-2008-020 20

  21. QNP2009, Sep.24 Beijing CERN-OPEN-2008-020 CDF: Phys.Rev.Lett.99:132001,2007 J/y CDF Phys.Rev.Lett.85:2886-2891,2000 21

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