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

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 2 CMS Detector Crystal ECAL  General purpose detector  p-p collision at CM energy of 14 TeV  Goals: Discover the Higgs, new physics beyond standard model, …

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 3 State of the Higgs: 2007  Electroweak fit (w/ quantum corrections) to m H : depends on m W, m TOP  Best-fit value (2007): m H = –23 GeV using m TOP = ± 1.8, m W = ±.025 GeV  Direct search limit: m H > GeV  95% CL upper limit: m H < 144 GeV Low M H < 150 GeV

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 4 ECAL layoutbarrel Super Module (1700 crystals) endcapsupercystals (5x5 crystals) Pb/Si preshower barrel cystals EndCap “Dee” 3662 crystals Barrel: |  | < Super Modules crystals ( 2x2x23cm 3 ) EndCaps: 1.48 < |  | < Dees crystals (3x3x22cm 3 ) PWO: PbWO 4

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 5 CMS ECAL Test Beams 2006  H4 ECAL Test Beam  10 SM calibrated (1 twice, 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 H4 H2

May 1, 2007 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

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 7 Cluster Containment Corrections Example: 3x3 matrix 5x53x3 Containment effect decreases with the matrix size  3% Hodoscope Resolution: Uniform impact  Uniform impact  containment corrections needed Measurement in fixed size matrix of NxN crystals  position dependence of E REC e 1

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 8 Energy Resolution Energy resolution ≤ 0.5% at 120 GeV for any electron impact. Same shower containment correction applied (for all E and all Xtals). 0.5% Central impact “Uniform” impact

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 9 Caltech ECAL test beams  Caltech leadership in two important test beam tasks:  Operation of the online laser monitoring system  Improving π 0 inter-calibration technique using test beam data

May 1, 2007 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.  PbWO 4 Crystals change transparency under radiation  Correct using the observations of laser monitoring system 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). Resolution design goal: ~0.5% Calibrating and maintaining the calibration of this device will be very challenging. Hadronic environment makes physics calibration more challenging

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 11 Laser Monitoring System  Lasers at two different wavelengths: 1 = 440 nm 2 = 796 nm

May 1, 2007 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

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 13 Irradiation Crystal Response Monte Carlo with a ~12 hour LHC fill cycle

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 14 Irradiation Crystal Response

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 15 Laser H4  Test Beam at CERN from June to November 2006  One ECAL supermodule in beam at time  GeV electrons  Intensity: Up to 50K events / 60s, Approx. 15 rad/hour  Online monitoring system was implemented to reconstruct laser runs and log values Moveable stand ECAL SM 22 Beam line

May 1, 2007 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

May 1, 2007 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

May 1, 2007 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 Runs >13064 SM 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

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 19 Online Monitoring Stability  APD/PN All channels, all modules : Stability 1.4 % from gauss fit to peak. Overall stability good, even at this basic level without any further corrections.  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 APD/PNStability: Raw stability

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 20 Offline Monitoring Stability Mean before and after correction : % % Peak before and after correction : ~0.170 % ~0.05 %  Small systematic change in reconstructed APD value related to Peak timing.  Correct APD/PN ratios with a simple linear function of peak timing Example for one SM (22)

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 21 Raw Monitoring Stability at H2 APD/PN vs. Time, 100 Channels (1040 – 1140, center Module 3). Hardware intervention around t=2150 h, stability reasonable. Black : APD/PN, averaged over 100 channels. Red :  T/20+1 Anti-correlation between temperature and APD/PN – as expected.  APD/PN shows ~ -2%/C 0 temperature dependences – as expected. Temperature correction based on thermistors Raw APD/PN stability at reasonable level

May 1, 2007 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

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 23 Pulse Width Measurement  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 error bars blown up by a factor of 10 normalizatio n value Example Sigma / |Mean| = 6.9(1)% A total of 6 SMs have been measured. Pulse Width Non-Linearity has little channel to channel variation ! All slope for one SM

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 24 Example Irradiation Cycle Normalized laser and electron responses Xtal 168 SM 22  For each electron response point an interpolated laser response value is calculated

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 25 Example Correlation Plot Relative electron response Relative Laser Response Xtal 168 SM 22

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 26 Example Corrected Resolution Xtal 168 SM GeV electrons, 3x3 crystal matrix

May 1, 2007 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

May 1, 2007 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

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 29 Continuing Irradiation Studies C. Rogan Xtal 168 SM 22

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 30 Continuing Irradiation Studies Still statistics limited in outer bins Can potentially be used for precision offline corrections

May 1, 2007 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

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 32 π 0 Calibration Concept  Level 1 trigger rate dominated by QCD: several π 0 ‘s/event  Useful π 0  γγ decays selected online from such events  Main advantage: high π 0 rate (nominal L1 rate is 100kHz !)  “Design” calibration precision  better than 0.5% Achieving it would be crucial for the H  γγ detection  Reporting on studies performed with about four million fully simulated QCD events. Results given for the scenario of L=2x10 33 cm -2 s -1 and L1 rate of 10 kHz (LHC start-up). Data after L1 Trigger Online Farm  0 Calibration >10 kHz ~1 kHz

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 33 π 0   Selection Based on local, crystal-level variables — suitable for online filter farm.  Kinematics: P T (  ) >1 GeV, P T (pair) > 3.5 GeV and η < 1.48 (barrel)  Photon shower-shape cuts: S 9 /S 25 > 0.9 and S 4 /S 9 > 0.9 defined with 2x2, 3x3, and 5x5 crystal matrices (S 9 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)

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 34 Selection Results  rate of 0.9 kHzor 1,250 π 0 /crystal/day with S/B ≈ 2.0 π 0   rate of 0.9 kHz or 1,250 π 0 /crystal/day with S/B ≈ 2.0 High-rapidity regions suffer both in rate and S/B (3  1)

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 35 A Calibration Algorithm (of many) Simple iterative algorithm (L3/RFQ Calibration) (w i  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 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 π 0 mass

May 1, 2007 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 π 0 /crystal

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 37 Calibration Studies in Test Beams π 0 decays produced through: π - +Al  π 0 +X (11/2006) Three different π - beam energies: 9, 20, and 50 GeV Consider only 9x8 crystal matrix: about 140 π 0 decays/crystal

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 38 Reconstruction of π 0  

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 39 Selection of π 0 using S1, S2 ADC

May 1, 2007 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. π 0   from upstream scintillators

May 1, 2007 Christopher Rogan - Caltech HEP Seminar GeV e - peaks with TBS1 9 GeV constants

May 1, 2007 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!

May 1, 2007 Christopher Rogan - Caltech HEP Seminar 43 π 0 Conclusions and Outlook with full detector  Proof-of-principle was achieved with full detector simulation: crystal-by-crystal intercalibration to 1% simulation: crystal-by-crystal intercalibration to 1% should be possible after a few days at L=2x10 33 cm -2 s -1 should be possible after a few days at L=2x10 33 cm -2 s -1 Other methods are much slower and tracker dependent. Other methods are much slower and tracker dependent.  Optimistic outlook for achieving and maintaining a ~0.5% precision. Many months of work on understanding ~0.5% precision. Many months of work on understanding the ECAL performance and non-uniformity at lower the ECAL performance and non-uniformity at lower energies (work of ~15 physicists from 4 teams). energies (work of ~15 physicists from 4 teams).  Test beam study demonstrated a 1% calibration precision with ~5 GeV photons: successfully used to reconstruct with ~5 GeV photons: successfully used to reconstruct 50 GeV electrons. No noticeable systematics. 50 GeV electrons. No noticeable systematics. (Many thanks to the entire H2 test beam team). (Many thanks to the entire H2 test beam team).  Currently a lot of work is being done on developing filter farm tools for collecting π 0   in situ at the LHC. Calibration of the endcaps is also being considered.

May 1, 2007 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