1 / 44

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.

lyn
Download Presentation

CMS ECAL 2006 Test Beams Effort

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related