Performance and Physics Workshop Summary:

Top and Muons

Sarah Allwood-Spiers

Glasgow ATLAS meeting

June 2008

Top Summary

• Standard Model and Top groups are the important physics groups for first data – should be involved in at least one (as well as in performance groups).

• With this in mind, top group is also reorganising subgroups slightly.• “top reconstruction group” will deal with all issues relating to top

reconstruction: if top is your background you should be in this group.

• There will also be joint meetings between top and SM for W+jets.• Top Group is concentrating on studies for “Early data” – defined as

100pb-1 (or for “pre-commissioning” 15pb-1).• Top reconstruction depends on all the performance groups: electrons,

muons, jets, etmiss, btagging.• But a clean top sample can also provide measurements for all the

performance groups: trigger efficiencies, etmiss scale, Jet Energy Scale, b-tag efficiency.

• Day 1: – top properties: cross section (~20% with 100pb-1), mass, tune MonteCarlo.

– W+jets background: estimate from Z+jet events – detector performance: light jet energy scale (W->jj) ~1%, b tag efficiency ~5%, Etmiss

from W->lnu.– resonances, SUSY, differential cross sections dsigma/dpt, dsigma/dmww

100pb-1 semileptonic: errors on cross section 100pb-1 dileptonic errors:

Early AnalysesConsiderations for semileptonic and dileptonic analyses for 15pb-1:

• Leptons: influence of high jet multiplicity environment on isolated leptons and fake isolated leptons

• Jets: semileptonic cross section extracted from jet multiplicity. Sensitive to JES (+-5% JES -> +-10% cross section).

• Etmiss: to reject QCD events

For 100pb-1:

• B-tagging: important gain in signal purity.

Top for Calibration• W->jj from w-mass constraint, get light jet energy scale: global JES factor

~2% with 50pb-1.• Etmiss scale from W->lnu transverse mass, or from fits of dpt of

reconstructed tops, or mass of top: ~2% with 200pb-1.• b-tagging efficiency: count events with n-tagged jets. likelihood for cross

section and btag efficiency. ~5% with 100pb-1 for semileptonic and dileptonic.

The Muon Spectrometer

Muon Summary• Expected Performance: Most potential problems with the muon system in first

data will only affect trigger efficiencies / reco efficiencies / acceptance <~ few percent. The biggest unknowns are

– the TGC gas system (untested in final mixture)– the power supplies (high failure rate of power supplies from CAEN, and no access to

UX15)

• Data quality monitoring: online DQA and fast-offline DQA well advanced. Much work still to do on calibration stream.

• There are studies of performance determination from data from 3GeV-1TeV. Efficiencies, fake rates, energy loss and linearities studied, but a strategy to understand combined performance of MS and ID needed.

• Calibration: system tested in FDR2. Much work still to do.

• Trigger: Performance of muon trigger slice stable, pileup studied, trigger robustness wrt misalignment studied (more work needed). Trigger menu defined for 1031 and 1032, but min bias pileup needs to be accounted for.

• Alignment: installation and commissioning of optical alignment system well advanced. Determination of initial geometry with no B-field is not fully covered and barrel vs end-cap alignment for calibration stream hasn’t yet started.

• Reconstruction: showed efficiencies and fake rates for different muon reconstruction algorithms, looked at robustness of algorithms when faced with dead channels (but effect of fake rate not studied?) or with cavern background. Tested reconstruction algs with cosmics. AOD size & CPU ok.

Expected Performance of Muon Spectrometer• Commissioning almost complete for cabling/electronics, and the gas

systems for MDT, CSC, RPC. Most MDT, RPC and TGC sectors tested with cosmics.

• Successful P5 / M7 (standalone / all subsystems) runs. 6.5 million events.

• Monitored Drift Tubes: – 72 EOL chambers missing, tight schedule to install – but only minor loss of

efficiency.– Gas leaks. Worst case: disconnect multilayer of MDT chamber

• Resistive Plate Chambers– some inverted chambers – loss of acceptance ~1%.– Gas leaks 20/768 single gas gaps disconnected

-minor effect on trigger efficiency.

• Thin Gap Chambers: – Accident on side A small wheel / EIL4– 13* operating pressure. Exchanged most

affected TGCs but possible small reduction of reconstruction efficiency due to geometrical distortion.

• Alignment system good, EO alignment bars installation and commissioning still to be done.

• Magnet System: ECT C and barrel tested at nominal field. ECT A helium leak – 2 months to fix.

Measuring performance from data:

• Use resonances (J/psi (3GeV – 1pb-1 ), upsilon (10GeV), Z(90GeV- 100pb-

1)) to measure efficiencies, fake rates, energy scale/resolution, energy loss in calorimeters, linearity, alignment.

• tag and probe for tracking and trigger efficiencies. Tracking efficiencies can be measured to <1% precision for low and high pt

• Fakes: non-prompt muons from well known processes. First study to quantify data-MC (Ks->pipi) agreement on fake rates. Still preliminary

• Energy loss before MS: compare momenta in ID and muon system. 1pb-1.

• Energy scale and resolution: fit mz in Z->mumu. With 20pb-1, 0.1% stat error. Global energy scale can be measured at permill level, or 1% misaligned

• Alignment: mz constraint to redetermine muon momenta.

• Momentum linearity can be checked within ~1%/100GeV

• Need strategy for understanding combined MS and ID performance – disentangling reconstruction effects and intercalibration of two subdetectors.

Calibration• Need

– Online calibration of the time measurement for RPC and TGC– Offline calibration of the position measurement for MDT and CSC

• CSC: electronic calibration, no absolute calibration needed. Athena-based software 90% ready

• MDT: new calibration constants needed each day. more complicated, studied in FDR2.

• Calibration loop almost completed.

• System succesfully tested in FDR2.

• Lot of work is still required:– General software development– Algorithms robustness and optimization– Implementation and test of the corrections – Database optimization

Trigger• trigger menus are defined for 1031 and 1032.• Careful validation of releases for LVL1, LVL2 and EF.• LVL1:

– Cavern background increases efficiency at low pt – validation ongoing.– Cabling service inconsistency – loss in efficiency in forward region.

• LVL2:– isolation: in 14.0.x muon isolation has changed:

• calorimeter isolation: EM and Had energy in ring around muon• ID tracks (SumPtRing/MuonPt) (SiTrack)• showed eff vs rejection for Calo isolation and Calo+ID isolation

• EF:– TrigMuonEF – new package (14.2.0) under validation for muon EF code. Wrappers for

offline tools doing MS and combined reco.

• Pileup studies: Used ttbar events. Average EF eff wrt LVL2 reduced by 1%. Also looked at fake rates of tracks

• Misalignment of inner detector (realistic) and muon system (unrealistic) studied. LVL1 and LVL2 unaffected by ID misalignment. EF efficiencies deteriorate significantly, resolution in pt gets worse above 50-100Gev.

Muon Reconstruction• StandAlone: Muons reconstructed with the spectrometer, backTracked to

the IP and corrected for energy loss in the calorimeters =>Moore(MuidStandAlone) and Muonboy

• Combined muons: Combination of the StandAlone muons with an inner detector track : Muid (Moore) and Staco (Muonboy)

• Tagged muons: – Tag of inner detector tracks by segment(s) in the spectrometer : MuGirl and

MuTag– Tag of inner detector tracks with calo measurement : CaloTag and CaloLR

• Three containers in the AOD:

• Staco = (Muonboy/Staco/MuTag)

• Muid = (Moore/Muid/MuGirl)

• Calo = (CaloTag/CaloLR)

Online and Fast Offline Data Quality Monitoring

at tier 0 on express stream