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CMS ECAL 2006 Test Beams Effort

CMS ECAL 2006 Test Beams Effort. Caltech HEP Seminar Christopher Rogan California Institute of Technology May 1, 2007. CMS Detector. General purpose detector p-p collision at CM energy of 14 TeV Goals: Discover the Higgs, new physics beyond standard model, …. Crystal ECAL.

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CMS ECAL 2006 Test Beams Effort

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  1. CMS ECAL 2006 Test Beams Effort Caltech HEP Seminar Christopher Rogan California Institute of Technology May 1, 2007

  2. CMS Detector • General purpose detector • p-p collision at CM energy of 14 TeV • Goals: Discover the Higgs, new physics beyond standard model, … Crystal ECAL Christopher Rogan - Caltech HEP Seminar

  3. State of the Higgs: 2007 • Electroweak fit (w/ quantum corrections) to mH : depends on mW, mTOP • Best-fit value (2007): mH = 76+34–23 GeVusing mTOP = 170.9 ± 1.8, mW = 80.396 ± .025 GeV • Direct search limit: mH> 114.4 GeV • 95% CL upper limit: mH < 144 GeV Low MH < 150 GeV Christopher Rogan - Caltech HEP Seminar

  4. ECAL layout barrel cystals Pb/Si preshower endcap supercystals (5x5 crystals) barrel Super Module (1700 crystals) EndCap “Dee” 3662 crystals PWO: PbWO4 Barrel: || < 1.48 36 Super Modules 61200 crystals (2x2x23cm3) EndCaps: 1.48 < || < 3.0 4 Dees 14648 crystals (3x3x22cm3) Christopher Rogan - Caltech HEP Seminar

  5. CMS ECAL Test Beams 2006 H4 H2 • H4 ECAL Test Beam • 10 SM calibrated (1 twice, 13600 xtals) • Detailed studies of E,  behaviour • Irradiation studies • Energy linearity studies • H2 ECAL+HCAL Test Beam • 1 ECAL SM • Two subdetector DAQ • Wide beam calibration • 0 data Christopher Rogan - Caltech HEP Seminar

  6. CMS ECAL Test Beams 2006 • A wide array of important studies were completed: • Electron, 0 and cosmic muon inter-calibrations • Energy linearity studies • Crystal containment corrections • Energy resolution studies • Amplitude reconstruction optimization • Noise studies • DAQ, Monte Carlo and software studies • Online laser monitoring • Crystal irradiation Christopher Rogan - Caltech HEP Seminar

  7. Cluster Containment Corrections 1 Measurement in fixed size matrix of NxN crystals  position dependence of EREC Containment effect decreases with the matrix size Example: 3x3 matrix 5x5 3x3 3% e Hodoscope Resolution: Uniform impact  containment corrections needed Christopher Rogan - Caltech HEP Seminar

  8. Energy Resolution “Uniform” impact Central impact 0.5% 0.5% • Energy resolution ≤0.5% at 120 GeV for any electron impact. • Same shower containment correction applied (for all E and all Xtals). Christopher Rogan - Caltech HEP Seminar

  9. Caltech CMS @ ECAL test beams • Caltech leadership in two important test beam tasks: • Operation of the online laser monitoring system • Improving π0 inter-calibration technique using test beam data Christopher Rogan - Caltech HEP Seminar

  10. ECAL Laser Monitoring Introduction • CMS is building a high resolution Crystal Calorimeter (ECAL) to be operated at LHC in a very harsh radiation environment. • PbWO4 Crystals change transparency under radiation • Correct using the observations of laser monitoring system Resolution design goal: ~0.5% Calibrating and maintaining the calibration of this device will be very challenging. Hadronic environment makes physics calibration more challenging The damage is significant (few % - up to ~5 % for CMS ECAL barrel radiation levels) at high luminosity The dynamics of the transparency change is fast (few hours) compared to the time scale needed for a calibration with physics events (weeks - month). Christopher Rogan - Caltech HEP Seminar

  11. Laser Monitoring System • Lasers at two different wavelengths: 1 = 440 nm 2 = 796 nm Christopher Rogan - Caltech HEP Seminar

  12. Laser Monitoring System • Laser light is injected into the crystals via fiber-optic cables • Avalanche photodiode response is measured (APD) • Light is also injected in reference PN diodes • Ratio of APD and PN responses is used to monitor crystal transparency changes Christopher Rogan - Caltech HEP Seminar

  13. Irradiation Crystal Response Monte Carlo with a ~12 hour LHC fill cycle Christopher Rogan - Caltech HEP Seminar

  14. Irradiation Crystal Response Christopher Rogan - Caltech HEP Seminar

  15. Laser Monitoring @ H4 Beam line • Test Beam at CERN from June to November 2006 • One ECAL supermodule in beam at time • 15-250 GeV electrons • Intensity: Up to 50K events / 60s, Approx. 15 rad/hour • Online monitoring system was implemented to reconstruct laser runs and log values ECAL SM 22 Moveable stand Christopher Rogan - Caltech HEP Seminar

  16. Online Laser Monitoring • For each laser run: • APD and PN pulses reconstructed • APD, APD/PN and PN distributions for each channel (1700 per SM) are fit and used to extract mean values • Similar distributions are monitored in geometric groupings (half SM, light modules); used for potential corrections • Correlations between different values (APD - APD/PN - timing, Chi2, etc.) • 10 ECAL supermodules examined • Over 1,600 laser runs processed Christopher Rogan - Caltech HEP Seminar

  17. Online Laser Data Analysis ~15 min. to process each laser run Plots of various distributions are available online immediately after processing. APD/PN values (among other things) logged in database for higher level analysis Christopher Rogan - Caltech HEP Seminar

  18. Consecutive run monitoring Comparison plots between consecutive runs for the APD/PN and APD values are used to monitor short term stability and inter-run changes For example, this plot shows the relative difference in the APD/PN values, for each channel, between two consecutive runs. Almost all channels are stable to within .5 per mille between consecutive runs 00013061-00013064 .001 0.0 -.003 Runs 13061->13064 SM16 Christopher Rogan - Caltech HEP Seminar

  19. Online Monitoring Stability All channels, all modules : Stability 1.4 % from gauss fit to peak. APD/PNStability: • Get APD/PN ratios for each channel, each SM • Normalize average APD/PN to 1 for each SM • Fit gauss to normalized APD/PN for each channel • Sigma of these fits is the stability Raw stability D APD/PN Overall stability good, even at this basic level without any further corrections. Christopher Rogan - Caltech HEP Seminar

  20. Offline Monitoring Stability Example for one SM (22) • Small systematic change in reconstructed APD value related to Peak timing. • Correct APD/PN ratios with a simple linear function of peak timing Mean before and after correction : 0.180 % 0.088 % Peak before and after correction : ~0.170 % ~0.05 % Christopher Rogan - Caltech HEP Seminar

  21. Raw Monitoring Stability at H2 Black : APD/PN, averaged over 100 channels. Red : DT/20+1 Anti-correlation between temperature and APD/PN – as expected. APD/PN vs. Time, 100 Channels (1040 – 1140, center Module 3). Hardware intervention around t=2150 h, stability reasonable. Temperature correction based on thermistors Raw APD/PN stability at reasonable level • APD/PN shows ~ -2%/C0 temperature dependences – as expected. Christopher Rogan - Caltech HEP Seminar

  22. Laser Pulse Width Correction • Reconstructed APD/PN ratio sensitive to laser pulse width • For normalized APD/PN ratio, ~2%/ns • Long-term pulse width stability ~1-2 ns Christopher Rogan - Caltech HEP Seminar

  23. Pulse Width Measurement error bars blown up by a factor of 10 normalization value All slope for one SM Example • Linear fit of the APD/PN-width dependence for each channel of each SM • Normalize APD/PN by the fit value at width = 30 ns • Distributions and crystal maps for the slope, intercept, chi2, etc. of the linear fits for the normalized APD/PN values Sigma / |Mean| = 6.9(1)% A total of 6 SMs have been measured. Pulse Width Non-Linearity has little channel to channel variation ! Christopher Rogan - Caltech HEP Seminar

  24. Example Irradiation Cycle Xtal 168 SM 22 Normalized laser and electron responses • For each electron response point an interpolated laser response value is calculated Christopher Rogan - Caltech HEP Seminar

  25. Example Correlation Plot Xtal 168 SM 22 Relative electron response Relative Laser Response Christopher Rogan - Caltech HEP Seminar

  26. Example Corrected Resolution 120 GeV electrons, 3x3 crystal matrix Xtal 168 SM 22 Christopher Rogan - Caltech HEP Seminar

  27. Continuing Irradiation Studies Hodoscope hits - entire irradiation period • Beam events distributed throughout crystal • Sufficient statistics to explore variations in electron response within crystal Xtal 168 SM 22 Christopher Rogan - Caltech HEP Seminar

  28. Continuing Irradiation Studies Hodoscope hits - entire irradiation period • Reconstruct electron data for 25 different bins • Generate R-plot for each bin Xtal 168 SM 22 Christopher Rogan - Caltech HEP Seminar

  29. Continuing Irradiation Studies C. Rogan Xtal 168 SM 22 Christopher Rogan - Caltech HEP Seminar

  30. Continuing Irradiation Studies Still statistics limited in outer bins Can potentially be used for precision offline corrections Christopher Rogan - Caltech HEP Seminar

  31. Laser Monitoring Outlook • Measured the APD/PN stability for individual channels on a large scale • Demonstrated reasonable online APD/PN stability; could be used for online electron response corrections • Achieved offline APD/PN stability for majority of channels with simple corrections. Further corrections are currently being studied • Demonstrated the ability to maintain resolution during irradiation Christopher Rogan - Caltech HEP Seminar

  32. π0 Calibration Concept Data after L1 Trigger p0Calibration Online Farm • Level 1 trigger rate dominated by QCD: several π0‘s/event • Useful π0γγdecays selected online from such events • Main advantage: high π0 rate (nominal L1 rate is 100kHz !) • “Design” calibration precision  better than 0.5% Achieving it would be crucial for the Hγγdetection • Reporting on studies performed with about four million fully simulatedQCD events. Results given for the scenario of L=2x1033cm-2s-1 and L1 rate of 10 kHz (LHC start-up). ~1 kHz >10 kHz Christopher Rogan - Caltech HEP Seminar

  33. π0 Selection Based on local, crystal-level variables — suitable for online filter farm. • Kinematics: PT () >1 GeV, PT (pair) > 3.5 GeV and η < 1.48 (barrel) • Photon shower-shape cuts: S9/S25 > 0.9 and S4/S9 > 0.9 defined with 2x2, 3x3, and 5x5 crystal matrices (S9 is chosen as photon energy) • Additional isolation cut optimized to remove showers with significant bremsstrahlung radiation: want to select mainly unconverted photons Trigger Tower (5x5 crystals) Christopher Rogan - Caltech HEP Seminar

  34. Selection Results π0rate of 0.9 kHzor 1,250 π0/crystal/day with S/B ≈ 2.0 High-rapidity regions suffer both in rate and S/B (31) Christopher Rogan - Caltech HEP Seminar

  35. A Calibration Algorithm (of many) Simple iterative algorithm (L3/RFQ Calibration) (wi  fraction of shower energy deposited in this crystal) • Both photon energy and direction reconstructed using crystal level information (same as during selection). • After each iteration pairs are re-selected with new constants (typically 10-15 iterations to converge). • Miscalibration is done before selecting events (4%). • Calibration precision defined as R.M.S. of the product of the final and initial miscalibration constant. • Use only pairs from ±2σ window around fitted π0 mass Christopher Rogan - Caltech HEP Seminar

  36. Calibration Performance Precision is then fitted to N is the number a=27±1% and b=0.20±0.25% of π0/crystal Christopher Rogan - Caltech HEP Seminar

  37. Calibration Studies in Test Beams π0 decays produced through: π-+Al  π0+X (11/2006) Three different π- beam energies: 9, 20, and 50 GeV Consider only 9x8 crystal matrix: about 140 π0 decays/crystal Christopher Rogan - Caltech HEP Seminar

  38. Reconstruction of π0 Christopher Rogan - Caltech HEP Seminar

  39. Selection of π0 using S1, S2 ADC Christopher Rogan - Caltech HEP Seminar

  40. First Resonance Observed by CMS Clear improvement over the uncalibrated peak (L3 algorithm). For a precise estimate of the calibration precision: use the 50 GeV electron test beam data. π0from upstream scintillators Christopher Rogan - Caltech HEP Seminar

  41. 50 GeV e- peaks with TBS1 9 GeV constants Christopher Rogan - Caltech HEP Seminar

  42. Calibration Precision with 50 GeV Electrons For each crystal, electron energy spectra were fitted to a Gaussian. Distributions of the obtained peak positions for 9x8 crystal matrix: Precision: 1.0±0.1% with 0.9±0.1% expected. Calibration with ~5 GeV photon works well for higher-energy showers! Christopher Rogan - Caltech HEP Seminar

  43. π0 Conclusions and Outlook • Proof-of-principle was achieved with full detector simulation: crystal-by-crystal intercalibration to 1% should be possible after a few days at L=2x1033cm-2s-1 Other methods are much slower and tracker dependent. • Optimistic outlook for achieving and maintaining a ~0.5% precision. Many months of work on understanding the ECAL performance and non-uniformity at lower energies (work of ~15 physicists from 4 teams). • Test beam study demonstrated a 1% calibration precision with ~5 GeV photons: successfully used to reconstruct 50 GeV electrons. No noticeable systematics. (Many thanks to the entire H2 test beam team). • Currently a lot of work is being done on developing filter farm tools for collecting π0 in situ at the LHC. Calibration of the endcaps is also being considered. Christopher Rogan - Caltech HEP Seminar

  44. Test Beam 2006 Summary • Two successful ECAL test beam efforts (H4, H2) • Recorded invaluable data for upcoming LHC startup while demonstrating viability of ECAL performance expectations • Caltech continues its leadership roles in hardware/software development of the 0 inter-calibration and laser monitoring • Credit is due to the hard work of entire ECAL community Christopher Rogan - Caltech HEP Seminar

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