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Status of LAr EM performance and measurements for CTB

Status of LAr EM performance and measurements for CTB. Overview Data - MC comparison Uniformity and energy resolution 3x3 c luster corrections Longitudinal weights Linearity Different amounts of material VLE electrons ID – LAr alignment Conclusions and perspectives. Marco Delmastr o.

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Status of LAr EM performance and measurements for CTB

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  1. Status of LAr EM performance and measurements for CTB • Overview • Data - MC comparison • Uniformity and energy resolution • 3x3 cluster corrections • Longitudinal weights • Linearity • Different amounts of material • VLE electrons • ID – LAr alignment • Conclusions and perspectives Marco Delmastro on behalf of the LAr EM CTB Group Status of LAr EM performance andmeasurements fro CTB

  2. Overview • The preliminary calibration of the LAr detector (Pedestals, Ramps, OFC) has been completed, the analysis has entered the interesting stage where detailed physics effects and combined performances are studied… • Full list of analysis topics can be found at: • http://atlas.web.cern.ch/Atlas/GROUPS/LIQARGON/Comb_TB/CBT_Barrel/Analysis/summer2005.html • The LAr EM CTB Group meets regularly, please find the details of the analysis in: • http://agenda.cern.ch/displayLevel.php?fid=65 • A list of foreseen CTB e-gamma papers can be found at • https://uimon.cern.ch/twiki/bin/view/Atlas/EgammaCombinedTestBeam Status of LAr EM performance andmeasurements fro CTB

  3. Electrons Data-MC comparison:Configurations Yellow: MC Points: data Note: used one overall scale factor for MC and X-talk correction • Several MC configurations… • 13.35 mm of Al far upstream (beam line)… • Additional material in fron of the calorimeter: • 15mm of Al • 0mm of Al • Runs with/without charge corrections • 6 Energies: • 9, 20, 50, 100, 180, 250 GeV • Throughout the PS energy in the MC was scaled with 11/13 • X-talk between strips is still under study, affects strip normalisation... Status of LAr EM performance andmeasurements fro CTB

  4. Electrons Data-MC comparison:Total energy • 15mm of Al in front of calo… • Agreement is good at all energies… 50 Gev 20 Gev 100 Gev 180 Gev Status of LAr EM performance andmeasurements fro CTB

  5. Electrons Data-MC comparison:Sampling layers 50 GeV Status of LAr EM performance andmeasurements fro CTB

  6. Electrons Data-MC comparison:Presampler and Strips • MC with extra material need a more reasonable x-talk correction; L1/L2 is then better, but PS is off... • MC without extra material would require 10% x-talk to get good agreement... too much? • Can the effect be explained by material between PS and Strips? • ... or does it really come from X-talk? No material added on top of 13.35mm of Al far upstream + PS scaled in data by 0.89 (cross talk correction usually 0.93) + MC scale overall 0.957 Status of LAr EM performance andmeasurements fro CTB

  7. Electrons Data-MC comparison:Sensitivity on material between Presampler and Strips • Very strong sensitivity on the amount of material between the PS and the strips • Approximately 5%X0 between PS and strips raise signal in strips by 2-3% • with less than 10%X0 more material between PS and strips our material problem could be solved… • … but also cross-talk stil needs to be measured for CTB2004! (work is ongoing…) 5% more X0 between PS and strips nominal Beam energy (GeV) • Possible candidates for explanations are… • Cross-talk • Material in front of PS • Material between PS and strips • Description of energy collection in electrodes fold in MC? Difference: ~20% increase in energy loss Status of LAr EM performance andmeasurements fro CTB

  8. Electrons Data-MC comparison:Summary of current situation with CTB material in front of ID and of LAr EM • EM sharing between Strips and layer 2 requires about 15% X0 additional just in front of PS… • 15% X0 just in front not really identified yet: • Rohacell LAr excluder? Recent measurements seem to exclude… • Material between Presampler and Strips? Sensitivity can be very high… • X-talk? Realistic treatment is needed, detailed measurement from data is ongoing… • … and about 15% X0 additional further upstream. • 15% X0 very far upstream identified… • but within magnetic part of beam, so unclear how much of it is relevant (was found to be relevant in 2002) • Detailed simulation of the beamline ongoing… • ID material itself understood to better than 10% from multiple scattering studies… • Tail of reconstructed momentum spectrum in ID for electrons of 9 GeV apparently does not support the hypothesis of 15% X0 additional material far upstream distorting the electron spectrum itself… • More studies in progress on all sides with next meeting foreseen in three weeks' time and progress on convergence reported by trigger/physics week… Status of LAr EM performance andmeasurements fro CTB

  9. From “raw” to “calibrated” energy:3x3 cluster corrections (1) • Position corrections – f(E, η) • S shape in the middle & strips • Cluster containment – f(E, η) • Lateral leakage • Longitudinal weights – f(E, η) • Tancredi’s style • Eta modulations – f(E) • Due to the finite size of the cluster • Phi modulations – no obvious dependence on E, dependence on η to be checked • Due to the accordion geometry • Three sets of the energy: single electrons at 50GeV, 180GeV and 250 GeV • Eta range 0-1.2 • Implementation in Athena… • CaloClusterCorrection Phi modulations a+b*X+c*X²+d*sin(16pX+e) Eta modulations Parabola fixed at 1 in the middle of the cell Status of LAr EM performance andmeasurements fro CTB

  10. From “raw” to “calibrated” energy:3x3 cluster corrections (2) Calibration formula in LArCTBLongWeights: a + b*Eps + c* sqrt(Eps*Estr) + d*Eacc + Eleak E=250GeV E=50GeV E upstream E upstream Eps Eps E=250GeV E lost between Eps-strips Sqrt(Eps.Estrips) Status of LAr EM performance andmeasurements fro CTB

  11. Uniformity RMS/<E> = O.52% 22 cells Global constant term: • total energy resolution: 0.7% Status of LAr EM performance andmeasurements fro CTB

  12. Energy resolution • Electronic noise in cluster subtracted • All corrections are applied: • S shape, Out of cone, • Longitudinal weights, eta and phi modulation • Different wrt Lar standalone TB because of • more material in front of calorimeter • beam spread Status of LAr EM performance andmeasurements fro CTB

  13. Linearity and resolution with different amounts of material • Errors on linearity comes from uncertainty of the beam energy • Noise term fixed to 200 MeV Status of LAr EM performance andmeasurements fro CTB

  14. VLE beam – Energy Measurement • A medium energy beam hits a secondary target about 50m upstream of our set-up • VLE spectrometer – Energy selection with the last magnets in the spectrometer B7, and B8 (deflection angle θ=120mrad), the currents are in the DB for each run • Calculated p=q*Bdl(I)/θ • Estimated momentum spread (defined by collimator C12) about 5% • Analysis to extend linearity study below 9 GeV has recently started… Status of LAr EM performance andmeasurements fro CTB

  15. Inner Detector – LAr alignment (1) • Track-cluster matching… • Phi-misalignment checked with 50GeV and 80GeV • Same results within 8% • In reality not all the LAr samplings will show the same offset… • Coming from the accordion shape – offset different in each layer Phi Status of LAr EM performance andmeasurements fro CTB

  16. Inner Detector – LAr alignment (2) • Same study done for Eta misalignment with 150 GeV muons • Tracker has worse resolution in eta… • It was found that the existing alignment correction overdoes the phi-correction and does rather well in eta • New corrections will be implemented… • But systematic in phi-measurement of LAr has to be understood better… Eta Status of LAr EM performance andmeasurements fro CTB

  17. Conclusions and perspectives • Energy reconstruction in LAr EM calorimeter for CTB is well advanced: • Cell calibration, cluster corrections, longitudinal weights, … • Data-MC agreement is good… • … but still no definite conclusions on material upstream, studies are ongoing • LAr realistic X-talk corrections are mandatory… • Uniformity, resolution and linearity studies show good performances… • Will be extended to… • Full eta range • VLE energy (<9 GeV) • Many physics studies are advancing, combined analysis started: • Combined tracking… • Photon conversion… Status of LAr EM performance andmeasurements fro CTB

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