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

2. Cosmic events for ATLAS commissioning
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. Pickups from cosmic results
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. Quarkonium physics with early data
QNP2009, Sep.24 Beijing
Quarkonium physics with early data
With early data ( 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
cc cross-section→ J/y g ; cb cross-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 10TeV : require pT> 4 GeV for both muons
s(pp→Ｑ[m4m4]
J/y
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
$color-octet model adopted in PYTHIA
*8-12GeV mass range
17k ev/ TeV
(we expect TeV)
The rest of the ATLAS simulation 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: ,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
Alpha>0 for J/psi inherit gluon polarization, which is likely to be transverse for massless (pt>J/psi)
+color octet
Angle of m+
QNP2009, Sep.24 Beijing

6. NNLO* Color Singlet Model
QNP2009, Sep.24 Beijing
NNLO* Color Singlet Model
Artoisenet et al, Phys.Rev.Lett 101: (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 6

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

8. Proper time for prompt/indirect separation
QNP2009, Sep.24 Beijing
Proper time for prompt/indirect separation
Proper time
~0: prompt J/ψ (spread=resolution)
>0: secondary from B decay y m+ m-
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no misalignment
e~93% purity~92%
@0.2ps B
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9. Quarkonium mass distributions
QNP2009, Sep.24 Beijing
Quarkonium mass distributions
signal+bkg before vertexing
before decay time cut
Two different trigger strategies:
di–muon trigger m6m4 (or m4m4)
single muon m10 (2nd ‘m’ in offline)
ϒ(1S) only
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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

10. Acceptance for spin alignment measurement
QNP2009, Sep.24 Beijing
Acceptance for spin alignment measurement
CDF J/y acceptance
D0 Run2 ϒ polarization data disagree with
theoretical models and CDF Run1 data
restricted cosθ* coverage (CDF) is a major source of systematics.
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 )
Area normalized for single and di-muon triggers　#events are similar
CERN-OPEN

11. Quarkonium spin alignment sensitivity at 10 pb-1
QNP2009, Sep.24 Beijing
Quarkonium spin alignment sensitivity at 10 pb-1
ATLAS
agen is properly reconstructed
(Da~ in 10<PT<20 GeV for J/y, comparable to the Tevatron ~1 fb-1 data)
CERN-OPEN
Determination less precise for ϒ:
(single-muon + track is not reliable for S/N~0.05 at 10 pb-1 ) ϒ
10pb-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

12. QCD physics at ATLAS QCD Physics include, e.g.
QNP2009, Sep.24 Beijing
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
J.Stirling
Primary interest is to look for deviations in high
ET jet events from QCD due to new physics
O(100) jet ET > 1TeV for TeV

13. QNP2009, Sep.24 Beijing
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

14. Determination of jet-energy scale (JES)
QNP2009, Sep.24 Beijing
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
1. Z+jets events (10<ET< GeV)
1% stat. uncertainty on JES with 300 pb-1
syst.: ISR/FSR+UE ~5-10% at low ET % at ET~200 GeV Z

15. Determination of jet-energy scale (JES) cont’d
QNP2009, Sep.24 Beijing
Determination of jet-energy scale (JES) cont’d
3. Jet balance (ET>500 GeV) to low energy jets with calibrated JES
2% fb-1
7% syst.* from low energy jet JES
2. g+jets events ( <ET<500 GeV)
1-2% stat.uncertainty on JES with100 pb-1
syst.: ISR/FSR+UE ~ 1-2% g
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jets
*improvement expected using data, e.g.
understanding MinBias/UE (R. Kwee talk on Tuesday)
di-jet decorrelation

16. Azimuthal di-jet decorrelation
QNP2009, Sep.24 Beijing
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
MidPoint algorithm with R=0.7
D0 data prefer between
“low ISR” and “increased ISR”
D0 data are from
PRL 94, (2005)

17. QNP2009, Sep.24 Beijing
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

18. Quarkonia for detector calibration
QNP2009, Sep.24 Beijing
Quarkonia for detector calibration
Resonance peaks are clean and useful for detector calibration
6 pb–1
no misalignment
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
Quarkonia decays will also be used for online monitoring
(e.g. trigger efficiencies, detector calibration)

19. QNP2009, Sep.24 Beijing
CERN-OPEN

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