Performance of the ATLAS muon spectrometer

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PERFORMANCE OF THE ATLAS MUON SPECTROMETER

Marcello Bindi, on behalf of ATLAS Collaboration

KRUGER 2010:Workshop on Discovery Physics at the LHC 06/12/2010

Marcello Bindi - University and INFN of Bologna - Kruger2010

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ATLAS Muon Spectrometer

25 meter of diameter, 44 meter length including also the End-caps

Three large super-conducting air-core toroidal magnets(2~6 T· m)

Weight : 7000 tonsx

y

z

06/12/2010

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Muons for ATLAS physicsMuon : promising probe for new physics - clean signature of final states with muons over largest possible solid angle is crucial for physics at LHC - HZZ*μμll, A μμ, Z’μμ… - required mass resolution: Δm/m < few %


H ZZ* μ+μ−μ+μ−

Challenging issues for Muon Spectrometer Trigger Selectivity: – select muons (pT > 6 GeV) from interaction point – identify interesting events with 25 ns accuracy PT resolution: 3~4% up to pT = 100 GeV, 10% for pT ~

TeV. Charge identification for pT ~ TeV.06/12/2010


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~

~

p

p

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4 detectors with different purposes

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Monitored drift tubes MDT (barrel + end-cap)|η| < 2.7, 370k ch, 6 multi layer

Thin Gap Chambers TGC (end-cap)1.1 < | η | < 2.4,440k ch, 7 layers

Cathodes Strip Chambers CSC (forward)

Resistive Plate Chambers RPC (barrel)| η | < 1.1, 360k ch, 6 layers

Precise spatial measurements Trigger and Readout

2.0 < | η | < 2.7, 31k ch, 4 layers


06/12/2010


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Muon detectors and the B-fieldFast trigger chambers: • RPC(barrel)

• TGC (end-cap)

Precision chambers:• MDT (barrel and end-cap)

• CSC (forward region)

Toroidal magnetic field of 0.5 T:• barrel and two end-cap toroids • complex field ATLAS

06/12/2010


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Muon detection in ATLASTrigger: RPC + TGC Bunch crossing period: 25 ns @ LHC Trigger chamber time resolution < 10 ns pT is estimated by on-detector electronics, according to ΔR w.r.t infinite momentum line. pT thresholds cab be adjusted: from 6 to ~ 40 GeVPrecise PT measurement (MDT+CSC) Measure magnetic deflection by toroidal field 3 planes of precision chambers:• Barrel: 3 point sagitta measurement• Endcap: point-angle measurement pT = 1 TeV ; 500 μm sagitta 50 μm point resolution needed

06/12/2010


Monitored Drift Tubed

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99.7% of channels working during pp data taking (out of 341K tubes) 0.2% lost forever (i.e. broken wire or not accessible anymore) 0.1% to be fixed in X-mas 2011 or later shutdowns

Detector coverage : 100%

06/12/2010

Drift time spectrum in the ATLAS MDT chambers.

Space time relationship of the ATLAS MDT chambers.


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Resistive Plate Chambers Status of non active Gas Gaps unchanged since several months: 1% (out of 3592) disconnected from HV due to broken gas inlets; not accessible

anymore 0.6 % disconnected from HV due to excessive gap currents; recoverable during winter

shutdown HV connectors:

About 1 failure/10 days (quickly replaced) ; anyway no holes thanks to trigger redundancy replacement of all connectors already planned

Trigger coverage : 99.7 % 1 trigger tower (out of 404)

06/12/2010

The plots show the Eta and Phi view coincidence of Low/High Pt RPC trigger hits.


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Thin Gap Chambers Detector : 98.4% fully operational

50KHz max Level1 (L1) trigger rate (100KHz after Dec.)

HV Trips when Luminosity steps up (most recovered within 24h)

Maintenance foreseen during next winter shutdown.

TGC, timing optimization

Trigger coverage : 100.0 %

06/12/2010


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CSC Detector operational the entire year at

98.5%

Maximum output rate sustainable ~ 70 kHz

1% data loss due to errors (it will be fixed in December)

06/12/2010

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Detector operation and stability


Stable running conditions during 2010:

Muon detectors “running efficiency”almost 100% during STABLE beam periods with DAQ running .

Very good working fractions.

Operational developments:• 4 sub-detectors have unified their procedures, user interfaces and shifters• since the begin of September the HV operations related to LHC beam conditions (injection …) are automatic. From February one single shifter will supervise the 4 sub-detectors.06/12/2010


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Trigger performance

06/12/2010

Muon trigger status L1 custom hardware

Require coincidence in eta phi view. PT estimation based on geometrical

roads. Road definition and time alignment

commissioned.

HLT software L2: Pattern recognition

EF: Full muon reconstruction available

L1, L2 and EF commissioned and used for

active rejection.

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RPC

TGC

Marcello Bindi - University and INFN of Bologna - Kruger201006/12/2010

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Muon Trigger Efficiencies Efficiency determined by looking at

Inclusive muons relative to offline. Tag & Probe method on

J/Psi and Z events. Trigger Efficiencies at L1

barrel 75% end-cap 95%

Rel. Trigger efficiencies at HLT L2 >98% EF >98%

L1 efficiency, T&P with J/Psi Barrel + End-caps

L1 efficiency, inclusive muon BarrelEF efficiency, inclusive muon Barrel + End-caps

Marcello Bindi - University and INFN of Bologna - Kruger2010pT> 4 GeV06/12/2010

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Muon Trigger vs Luminosity Measured L1 trigger rates as a function of the

instantaneous luminosity for different L1 thresholds. Extrapolation to higher luminosity based on rates

measured with data fundamental for the trigger strategy.

The steps are due to different filling schemes changing the contribution of cosmic radiation to the trigger rate.


Allocated rate

06/12/2010


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Reconstruction performance

06/12/2010


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Muon reconstructionObjective: Muon identification in a wide momentum range from GeV to TeV. Make use of all detector components and use different strategies: Muon Spectrometer Standalone (MS) reconstruction

MS and Inner Detector (ID) combined fit

Outside-in Inside-out Statistical combination

Taggers ID track is matched to MS segments ID track is matched to a MIP in calorimeter

06/12/2010

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Di-muon mass


Di-muon invariant mass spectrum for 2010 full data, from fully combined opposite sign muons.Event Filter applies a pT cut at ~15 GeV, which for consistency is reconfirmed offline for one of the two inner detector-muon spectrometer combined tracks (the other one is required to pass a pT threshold of 2.5 GeV). 06/12/2010

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Reconstruction Efficiency from 2009 cosmics data

Select events with ID tracks traversing MS barrel.

Look for MS track in top hemisphere

(pID > 5 GeV) bottom hemisphere

(pID > 9 GeV) Measures

reconstruction efficiency of MS conditional to a L1 trigger.

Turn on curve:Good agreement between Data and MC

Average efficiency:97.4 ±0.1 %95.2 ±0.1 %

ATLAS Preliminary2009 Cosmic Data

ATLAS Preliminary2009 Cosmic Data


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Reconstruction Efficiency from 2010 beam data


Use independent algorithms to assess reconstruction efficiency.

Tag and Probe studies are under preparation with J/Psi and Z.

First results from Z will be available soon.

(Non-)Prompt MuonsMuons from light hadrons (“non-prompt”)Decay within the ID volume Hadron and the secondary muon are reconstructed as one trackmomentum mismatch of ID and MS PT

Muons from heavy flavour (“prompt”)Secondary muon produced close to IPID and MS measure the muon track.

Discriminate by “loss momentum” fraction between MS and ID pT measurement:

Use templates derived from MC to determine fractions of “prompt” and “non-prompt” secondary muons. 22

K0s -> p+p-J/Y -> m+m-

ID barrel

06/12/2010 Marcello Bindi - University and INFN of Bologna - Kruger2010

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(Non-)Prompt Muons Fraction of prompt muons determined in bins of pT and

eta. MC and data agree within uncertainties Dominant systematic uncertainties:

template shape at low pT MC flavor content at high pT ID barrel

ID end-cap

06/12/2010 Marcello Bindi - University and INFN of Bologna - Kruger2010


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Momentum resolution

06/12/2010

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Momentum resolution preformance from 2009 Cosmics


Muons from Barrel Region06/12/2010

26Marcello Bindi - University and INFN of Bologna - Kruger2010

Calibration Precise r-t relations Precise t0 values B field corrections to r-t relations Objective to reach a MDT hit resolution < 100 μm Alignment Improved alignment in few chamber (End-cap) Use of Toroid off data Cross checks using high PT tracks Magnetic Field - Use of Asymmetric B field mapResults analyses from J/ψ, W and Z

Work in progress on resolution preformance from 2010 Data

06/12/2010


Alignment and Calibration status

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barrel alignment±50 mm (large sectors)±100 mm (small sectors)

end-cap alignment±45 mm

Goal of the alignment: < 50μm ; dominant contribution to the pT resolution for pT>300 GeV

Optical alignment systemBarrel: relativeEnd-caps: absolute

Data with toroidal B-field off. Momentum from inner detector

Measure alignment with straight tracks.

06/12/2010


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Momentum Z resolution performance

Zµµ in the Barrel region Using the Muon Spectrometer and Inner detectorFit using the following function: Z Breit-Wigner with

γ-interference convoluted with one single gaussian resolution function with σZ

06/12/2010

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Z resolution with combined MUON-ID


Oppositely charged Muon pairs with pT>20 GeV Track isolation cut: Σ(pTtracks) in a cone (η,Ф) of radius < 0.4 is < 0.2 pT

µ |η1, η2|<1.05. EF triggers used: 10 GeV threshold and 13 GeV for higher luminosity. Monte Carlo prediction using Pythia-generated Z->µµ events.

06/12/2010


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Improvements after November reprocessing on first 6 pb-1

06/12/2010


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Conclusions and outlook Muon detectors have been very stable and fully

operational during the whole 2010 data taking. Performance of detector, trigger and reconstruction

have been studied with first data and cosmic events. Overall performance very close to detector design! Good agreement between data and MC. Some

improvements will be following soon, specially in resolution studies.

Many more results soon to come with the full amount of available data set.

Big expectations from 2011 data taking with higher luminosity!

06/12/2010


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Back-up

06/12/2010


3306/12/2010

Rpc trigger coverage Eta vs Phi (Strip)


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L1 trigger efficiency

Trigger efficiency of L1 muon for the lowest threshold MU0 as a function of the offline muon pT obtained with a tag and probe method on Jpsi candidates using combined muons for both the tag and probe tracks. Events are required to have passed the L1 MinBias trigger and a muon EventFilter confirmation. A reconstructed primary vertex with at least 3 Inner Detector (ID) track is required in each event. Muon combined tracks in the eta range [-2.4,2.4] are required to match with a reconstructed primary vertex with z < 10 mm. Only muons associated with ID tracks that have at least one hit in the pixels and six in the SCT are accepted.

The Jpsi candidates have been selected asking for two opposite sign muons and with angular distance 0.4<DR<2.0 and with an invariant mass window between 2860 MeV and 3340 MeV. The tag and probe method has been applied matching the combined muons to muon trigger RoIs using the geometrical criteria DR<0.4. L1 triggers found within +- 3 BCs are included in the efficiency calculation as the RPC L1 timing is not yet fully commissioned. The used data sample corresponds to an integrated luminosity of about 210 nb-1.

06/12/2010

https://twiki.cern.ch/twiki/bin/edit/Atlas/MinBias?topicparent=Atlas.TriggerPublicResults;nowysiwyg=1

https://twiki.cern.ch/twiki/bin/view/Atlas/EventFilter

https://twiki.cern.ch/twiki/bin/view/Atlas/MeV

https://twiki.cern.ch/twiki/bin/view/Atlas/MeV

https://twiki.cern.ch/twiki/bin/view/Atlas/RoI


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L2 relative efficiency

Efficiency of the L2 muon trigger combining muon spectrometer and inner detector information wrt to the L1 muon trigger as a function of the transverse momentum pT from offline reconstructed combined muons. A cut at L2 is applied to retain muons with pt>4GeV. 06/12/2010


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Timing for RPC and TGC

06/12/2010

• Big improvement with first few pb-1 in RPC timing• RPC is now close to have 100% events in right BC on both, Low and High pT trigger.• TGC almost there since the beginning of 2010 data taking.

Documents

Performance of the ATLAS muon spectrometer