marcello bindi, on behalf of atlas collaboration kruger 2010 : workshop on discovery physics at the...
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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
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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 %
Marcello Bindi - University and INFN of Bologna - Kruger2010
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
Marcello Bindi - University and INFN of Bologna - Kruger2010
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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
Marcello Bindi - University and INFN of Bologna - Kruger2010
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Marcello Bindi - University and INFN of Bologna - Kruger2010
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Muon detectors and the B-field
Fast 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 GeV
Precise 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
Marcello Bindi - University and INFN of Bologna - Kruger2010
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.
Marcello Bindi - University and INFN of Bologna - Kruger2010
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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.
Marcello Bindi - University and INFN of Bologna - Kruger2010
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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
Marcello Bindi - University and INFN of Bologna - Kruger2010
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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
Marcello Bindi - University and INFN of Bologna - Kruger2010
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
Marcello Bindi - University and INFN of Bologna - Kruger2010
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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.
Marcello Bindi - University and INFN of Bologna - Kruger2010
Allocated rate
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Marcello Bindi - University and INFN of Bologna - Kruger2010
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Reconstruction performance
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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
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Di-muon mass
Marcello Bindi - University and INFN of Bologna - Kruger2010
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
Marcello Bindi - University and INFN of Bologna - Kruger201006/12/2010
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Reconstruction Efficiency from 2010 beam data
Marcello Bindi - University and INFN of Bologna - Kruger2010
06/12/2010
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
Marcello Bindi - University and INFN of Bologna - Kruger2010
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Momentum resolution
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Momentum resolution preformance from 2009 Cosmics
Marcello Bindi - University and INFN of Bologna - Kruger2010
Muons from Barrel Region
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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 map
Results analyses from J/ψ, W and Z
Work in progress on resolution preformance from 2010 Data
06/12/2010
Marcello Bindi - University and INFN of Bologna - Kruger2010
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
Marcello Bindi - University and INFN of Bologna - Kruger2010
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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
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Z resolution with combined MUON-ID
Marcello Bindi - University and INFN of Bologna - Kruger2010
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
pTµ
|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
Marcello Bindi - University and INFN of Bologna - Kruger2010
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Improvements after November reprocessing on first 6 pb-1
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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
Marcello Bindi - University and INFN of Bologna - Kruger2010
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Back-u
p
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Rpc trigger coverage Eta vs Phi (Strip)
Marcello Bindi - University and INFN of Bologna - Kruger2010
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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.
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Marcello Bindi - University and INFN of Bologna - Kruger2010
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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
Marcello Bindi - University and INFN of Bologna - Kruger2010
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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.