1. Marco Delmastro 23/02/2006 Status of LAr EM performance andmeasurements fro CTB1 Status of LAr EM performance and measurements for CTB Overview Data - MC comparison Uniformity and energy resolution 3x3 c luster corrections Longitudinal weightsLinearity Different amounts of material VLE electrons ID – LAr alignment Conclusions and perspectives on behalf of the LAr EM CTB Group Marco Delmastro

2. Marco Delmastro 23/02/2006 Status of LAr EM performance andmeasurements fro CTB2 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/CB T_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/EgammaCombinedTes tBeam

3. Marco Delmastro 23/02/2006 Status of LAr EM performance andmeasurements fro CTB3 Electrons Data-MC comparison: Configurations 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... Yellow: MC Points: data Note: used one overall scale factor for MC and X-talk correction

4. Marco Delmastro 23/02/2006 Status of LAr EM performance andmeasurements fro CTB4 Electrons Data-MC comparison: Total energy 20 Gev 50 Gev 100 Gev180 Gev 15mm of Al in front of calo… Agreement is good at all energies…

5. Marco Delmastro 23/02/2006 Status of LAr EM performance andmeasurements fro CTB5 Electrons Data-MC comparison: Sampling layers 50 GeV

6. Marco Delmastro 23/02/2006 Status of LAr EM performance andmeasurements fro CTB6 Electrons Data-MC comparison: Presampler and Strips 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 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?

7. Marco Delmastro 23/02/2006 Status of LAr EM performance andmeasurements fro CTB7 Electrons Data-MC comparison: Sensitivity on material between Presampler and Strips nominal 5% more X0 between PS and strips Difference: ~20% increase in energy loss Beam energy (GeV) Very strong sensitivity on the amount of material between the PS and the strips Approximately 5%X 0 between PS and strips raise signal in strips by 2-3% with less than 10%X 0 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…) 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?

8. Marco Delmastro 23/02/2006 Status of LAr EM performance andmeasurements fro CTB8 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% X 0 additional just in front of PS… 15% X 0 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% X 0 additional further upstream. 15% X 0 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% X 0 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…

9. Marco Delmastro 23/02/2006 Status of LAr EM performance andmeasurements fro CTB9 From “raw” to “calibrated” energy: 3x3 cluster corrections (1) 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

10. Marco Delmastro 23/02/2006 Status of LAr EM performance andmeasurements fro CTB10 E=250GeV E=50GeV E upstream Eps Calibration formula in LArCTBLongWeights: a + b*Eps + c* sqrt(Eps*Estr) + d*Eacc + Eleak Eps E upstream E=250GeV E lost between Eps-strips Sqrt(Eps.Estrips) From “raw” to “calibrated” energy: 3x3 cluster corrections (2)

11. Marco Delmastro 23/02/2006 Status of LAr EM performance andmeasurements fro CTB11Uniformity Global constant term: total energy resolution: 0.7% RMS/ = O.52% 22 cells

12. Marco Delmastro 23/02/2006 Status of LAr EM performance andmeasurements fro CTB12 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

13. Marco Delmastro 23/02/2006 Status of LAr EM performance andmeasurements fro CTB13 Linearity and resolution with different amounts of material Errors on linearity comes from uncertainty of the beam energy Noise term fixed to 200 MeV

14. Marco Delmastro 23/02/2006 Status of LAr EM performance andmeasurements fro CTB14 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…

15. Marco Delmastro 23/02/2006 Status of LAr EM performance andmeasurements fro CTB15 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

16. Marco Delmastro 23/02/2006 Status of LAr EM performance andmeasurements fro CTB16 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

17. Marco Delmastro 23/02/2006 Status of LAr EM performance andmeasurements fro CTB17 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…