Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /1 Performance of BIL tracking chambers for the ATLAS muon spectrometer A.Baroncelli, P.Branchini, F.Ceradini, E.Graziani, M.Iodice, D.Orestano, A.Passeri, F.Pastore, F.Petrucci, E.Spiriti, S.Tagliaventi and A.Tonazzo Università Roma Tre and INFN Sez. Roma IIII

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /2 Outline Description of ATLAS MDT chambers Equipment and tests in Roma Tre Calibration and resolution Effects of varying operational conditions –Temperature –Gas composition Use of charge information to improve the spatial resolution

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /3 The ATLAS muon system MDT chambers Air-core toroidal spectrometer (4 T/m) with 3 measurement stations  good momentum resolution 6GeV/c-1TeV/c + Dedicated trigger detectors BIL chambers: 2 MultiLayers x 4 Layers x 36 (or 30 or 24) MDTs Length=2.6m

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /4 MDT (Monitored Drift Tube) Gas mixture: Ar-CO % Absolute pressure 3 bar Gain 2x10 4 (HV=3080 V) Discriminator threshold: 20 primary e start stop Anode wire 50  m W TDC ADC electron drift time signal amplitude Al tube R=15mm 400  m thick Max drift time 700 ns Single point resolution ~80  m

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /5 MDT chamber equipment and tests StepACTIONMEASUREATLAS LIMIT 1Gas distribution systemLeak rate 2x10 -8 barl/s per tube 1 mbar/day per chamber 2HV distribution and signal readout cards Current 5 nA per tube 0.1  A per ML 3ElectronicsNoise rate 1 kHz per tube 4Cosmics dataPerformance RomaTre total 62 chambers, 32 done

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /6 Cosmic ray hodoscope Simultaneous test of up to 3 chambers Trigger = 3 planes of RPCs 6 segments along tube CHAMBER 1 CHAMBER 2 CHAMBER 3

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /7 Data acquisition system VME architecture 3 Chamber Service Modules (CSM0) read the events from front- end level-1 buffer of chamber TDCs and perform single chamber event building Digitization performed on the chamber by mezzanine boards hosting 3 ASD circuits and an Atlas Muon TDC (AMT) integrated circuit, that digitize the drift time and sampled charge The CSM0 also distribute the trigger and the main clock (40 MHz) and initializes the ASD and AMT parameter via a JTAG interface

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /8 Cosmics data 1.3 M events in 24 h Occupancy distributions: spot dead/hot channels Check response of each tube Chamber RM012: central position

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /9 Single tube response TDC counts Drift time spectrum T0T0 T max noise Distribution of drift time spectrum fit parameters for all tubes in one chamber

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /10 Autocalibration: space-time relation Iterative procedure: Straight line tangent to drift circles Evaluate residuals Compute mean value of residuals in each time slice Use it as correction to r-t relation

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /11 Resolution Select “good” events (single track, n≥8 hits) Cut on  2 (a tight cut selects hard  s, reducing contributions from MS) Compute residuals and extrapolation error for each point with track constructed with n-1 points Width of residuals distribution is  r)=  [Resolution(r)] 2 +[ (r)] 2  r)

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /12 Temperature effects Variations of r-t relations scale linearly with T Effect of temperature variations: Increase/decrease drift spectrum length Modify r-t relations R-t variations on cosmic samples at different temperatures:  T=1.1°C  T=3.1°C  T=5.1°C  T=2.1°C In ATLAS: measure T and apply corrections to r-t relations Systematic error not included

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /13 Effects of varying gas composition Effect of gas mixture variations: Increase/decrease drift spectrum length Modify r-t relations r-t variations on cosmic samples with precisely known Ar-CO 2 mixtures: 93-7% and %  CO 2 =-0.3%  T=7.1°C ….  T=0.2°C In ATLAS: Control gas composition stability at % level

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /14 Charge information 8-bit Wilkinson ADC to measure the charge collected in a given time gate after threshold crossing Charge→ADC conversion is non-linear Spread ~10% Width vs peak Equalize channels

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /15 Charge information: noise rejection TDC counts ADC counts ADC vs TDC counts cut

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /16 Charge information Average signal amplitude vs drift time (t) in the 6 trigger zones along the wire Average signal amplitude vs position along the wire Signal attenuation length ~30 m consistent with estimate from impedance value

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /17 Charge information: slewing corrections Charge information can be used to improve the spatial resolution Estimate  t from track residuals Use local linear correction for  t vs ADC- in each r interval

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /18 Slewing corrections Improvement on resolution most relevant at small radii Average resolution 90  m 80  m = ATLAS design The method is based solely on the data from the chamber itself ~50  m

Siena, May A.Tonazzo –Performance of ATLAS MDT chambers /19 Summary 32/62 MDT chambers for the ATLAS muon system have been equipped and tested at the Roma Tre site Cosmic ray data is used for calibration and resolution measurement Effects of varying operational conditions have been studied –Temperature –Gas composition A method to improve the spatial resolution using charge information has been developed