Studies of the ATLAS Tile Hadron Calorimeter Performance

1. Studies of the ATLAS Tile Hadron Calorimeter Performance Ilya Korolkov (IFAE) presented by Stanislav Němeček (FZU) • Outline • Tile Hadron Calorimeter (TileCal) Performance • Detector Geometry • Working Environment • Dynamic Range • R&D History of the TileCal • ’94, ’96 Performance for Pions • ’01 Performance for Electrons • ’01 Performance for Pions • Calibration Strategy • Monitoring Program • Summary

2. Detector Geometry. y z 5.6 degree azimuthal slice The TileCal, the barrel part of the hadron calorimeter in ATLAS, is a sampling device made of steel and scintillating tiles. Due to the LAR EM-calorimeter in front mainly the hadronic response is optimized. Some sensitivity to muons is used in the level-1 trigger. Hermeticity coverage 1.7 cracks at transition region Intermediate Tile Calorimeter + Gap Scintillators Segmentation Each 0.1 azimuthal slice has 73 cells arranged into projective towers with0.1. Each of 64X3 modules has three depth segmentations called samples A, B, and D. Sampling 18 mm period in z with radial tiles staggered in depth. local variations in sampling fraction for ||<0.1 Material budget to contain jets and to shield muon system. η=1.7

3. Working Environment. Energy deposition per BXing (MC) for a typical cell (A1) in the innermost sample Occupancy 15% Mean energy 9MeV 1/2 S =14TeV desired dynamic range from fraction of GeV to 2TeV (had) per cell L=(210 –10 ) cm s pile up -> on average (5-23) min bias events per BXing improved understanding of expected min bias signals in TileCal on average 30% less energy than it was expected in ’96 optimal filtering algorithm is well advanced applying to ’98 TB data -> reduction in noise RMS by 30% intension to use MB currents to monitor TileCal stability BXing=25nsec TB data with 25nsec beam structure (’01), timing everywhere in the module better than 1nsec which includes beam spread. For ATLAS timing ~0.5 nsec compatible to the bunch size. Radiation Hardness Tiles and fibers are expected to loose less then 5% of the light yield under 40kRad (10yeas of ATLAS) (’94-’96). This loss to be monitored with Cs during ATLAS shut-downs. Natural ageing of optics estimated to be at the same level. Dedicated QC of all the electronics components 33 34 -2 -1 GeV <4kRad/year ID only

4. Dynamic Range. Npe/GeV improves over the years due to the instrumentation experience. Current plan is to set PMT gains to 1.2pC/GeV of em energy at 90 degrees. This will require setting HVs down by (10-40)V from the nominal values -> non-linearity from PMTs rises up to 2%. Non-linearity can be recovered by LAS calibration or by weighting technique (less likely) Dynamic Range = 1.52GeV/cell (had scale) Proposal to enhance the dynamic range by recovering saturation.

5. Test Beams History of the TileCal. ‘94 ‘97 ’98-’99 ‘96 ’00-’01 ’93 first prototype ’94 combined with ’97 ExtB M0 full LAR prototypes size prototype ’95 five 1m prototypes ’98 Barrel Mod0 ’96 Barrel Mod0 full size reinstrumented prototype combined’99 Barrel Mod0 with LAR and standalone ’00 one production Barrel and two ExtB modules. ’01 one Barrel and two ExtB production modules with final electronics, start of calibration

6. Hadron Calorimeter Performance for s. ’94 ‘96 Two combined TBs with LAR ’94 – five 1m prototypes ’96 – +full size barrel Mod0 since than no combined TBs were done. Energy resolution (after weighting ) Punch-through probability fors Average Energy loss for evts with longitudinal leakage Response linearity (after weighting ) ’94 – within 1% ’96 – within 2%

7. ’01 Performance for electrons.  = 20 Sampling ‘a’ and constant ‘b’ terms of the electron energy resolution (’01) compared to those of the prototype Mod0. Two production EB modules (’01) Uniformity of (pC/GeV) in  is within few % Resolution /E

8. ’01 Performance for s. Leakage in the transverse direction had not been controlled -> resolution looks larger than it is. Resolution /E Two production EB modules (’01) The pion Energy is calculated using: e – em calibration const Rπ - measured signal e/h = (1.36 ± 0.01), Measured on Mod0 fπ = 0.11*ln(Ebeam)  scan Longitudinal scan

9. Calibration Strategy. Jets in-situ calibration To correct for detector effects non-linearity from non-compensation, longitudinal leakage, pmts, energy lost in the dead material, (3-13)% depending on , noise from min bias and electronics, magnetic field effects, finite granularity depending on physics goals may go deeper into fragmentation, IRS, FRS … Recovery methods: Weighting Techniques (H1), Energy flow method (using tracker information) Golden channels: E/Pt for a single hadron (usually coming from ) with 10fb of data (320k signal evts) may reach .6% level in jet E calibration. Z/+jet Pt balance with 10fb of data may reach 1% level in jet E calibration and 1% linearity. t->W->jj with 10fb of data may reach 2% level in jet E calibration and 2% linearity. Concerns limited statistics and HUGE number of weights (usually both Energy and  dependent) analysis usually assumes no tails in Energy measurements. Requirements from the detector: (5-10)% accuracy on EM scale after transporting TB calibration to the ATLAS, stability. MC

10. Calibration Strategy (cont’d). TB -> ATLAS calibration What do we want? Accuracy, Stability, Uniformity, Simplicity. Procedure: All the modules to undergo Cs scans with the final electronics: Final QC and repairs Cs constants are produced HVs (gains) are set to 1.2pC/GeV of em energy at 90 degrees. except for the D sample (+20% gains to improve  trigger) minor impact on had trigger: 0.6% overestimation of tot had energy and ITCs for which expected signals are smaller (-> +20%) Target: gain setting to a better than 1% level. 8Barrels+8EBAs+8EBCs (12% of total) to be calibrated with the TB: electron constants (pC/GeV) for every reachable TR-segment, cell. muon constants (MOP, truncated mean) for every TR-segment, cell. e/h, uniformity, improve Cs-data correlation … TB constants to be transported to the cells (modules) not exposed to the beam using Cs constants: const = const x After the gains are set by Cs cell to cell variation in gains seen by muons is 1.8% (’01) Cs 2 2 1 Cs 1 RMS=2% Example of the accuracy of the Muon constants transportation From one EB module to other two (’01)

11. Monitoring Program. nA Simulation of the MB current from one of the cells 100BXings During the data-taking actually, during the empty bunches not to interfere with the data flow Monitoring of the Min Bias currents Unique opportunity to have on-line diagnostic of the beam (from inside of TileCal) and the optics inside of the cells. It’s been shown that depending on the cell position 5-500 measurements are enough to reach 1% level of accuracy. It uses “slow” electronics (RC~10msec) of the Cs system -> Challenge is to use “fast” triggers from the empty bunches to perform few switches which otherwise may affect data. Laser system (LAS) to monitor PMT block optics and PMT gains Charge Injection System (CIS) to monitor behavior of each read-out channel over its full dynamic range. During shut-downs Cs scans to monitor (and recalibrate if needed) optics inside of the cells on the deep level of individual tiles, fibers and couplings. One Barrel and two EB modules will be kept at TB area to monitor ageing and to be the “spares” if needed. An example of the CIS data (’01) Injected pulse on the top Leakage pedestals (effect of the switches) on the bottom.

12. Summary. The detector geometry and principles of the TileCal were optimized for the best hadronic performance in a combined operation with other ATLAS calorimeters. An extensive check of the stand-alone and combined performance was carried out during period from ’93 to ’99 on a set of prototypes mostly at the H8 test beam at CERN. The latest full size prototypes, called Mod0, complied to all the requirements set for the TileCal. The research efforts since than were concentrated on calibration of the production modules which started in ’01. From all the data collected during TBs ’00-’01 we conclude that the performance of the production modules is at the same level or better than the performance of Mod0 full size prototypes. Special efforts are applied toward future integration of the TileCal in ATLAS such as transportation of the calibration constants to the ATLAS environment and developing various monitoring systems.