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Calibration of the CMS Electromagnetic Calorimeter with first LHC data

IPRD10 Siena, June 7-10 2010. Calibration of the CMS Electromagnetic Calorimeter with first LHC data. Maria Margherita Obertino ( Universita ’ del Piemonte Orientale – INFN Torino) On behalf of the CMS Collaboration. OUTLINE. The CMS Electromagnetic Calorimeter (ECAL)

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Calibration of the CMS Electromagnetic Calorimeter with first LHC data

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  1. IPRD10 Siena, June 7-10 2010 Calibration of the CMS Electromagnetic Calorimeter with first LHC data Maria MargheritaObertino (Universita’ del Piemonte Orientale – INFN Torino) On behalf of the CMS Collaboration

  2. OUTLINE • The CMS Electromagnetic Calorimeter (ECAL) • Pre-calibration: crystal intercalibration before the LHC startup • In situ calibration: crystal intercalibration with collision data • Results with very first collisions • Calibration data streams • 2010 plans M.M.Obertino – IPRD10

  3. ECAL • Hermetic homogeneous calorimeter made of PbWO4 • Crystals • Barrel (EB) [|h|<1.48 ] • 36 Supermodules (SM) with 1700 crystals each • Photodetectors: APD • Endcaps (EE) [1.48<|h|<3.0 ] • 2 Dees each side, 14648 crystals in total • Photodetectors: VPT • Preshower (ES) [1.65<|h|<2.6 ] • Sampling calorimeter (lead, silicon strips) EE Supermodule ES EE M.M.Obertino – IPRD10

  4. ECAL ENERGY RESOLUTION Excellent energy (and position) resolution for photons and electronscrucial for studying interesting physics channel (Hgg, HZZ4e, …) • Constant term depends on: • channel intercalibration accuracy • non uniformity of the longitudinal light collection • rear leakage • Target value: 0.5 % set by H channel High precision in the channel to channel intercalibration crucial. Hγγ width Zee width M.M.Obertino – IPRD10

  5. PRE-CALIBRATION Extensive10 years long pre-calibration program carried out before ECAL installation in CMS. Test Beam at CERN 90-120 GeV electrons (2004-2007) [ Intercalibration of the barrel electromagnetic calorimeter of the CMS experiment at start-up - 2008 JINST 3 P10007 ] Beam • 10 EB SMs • 460/14648 EE crystals Intercalibration reproducibility Number of crystals From repeated measurements: iIntercalibrationprecision ~0.3% dominated by statistical uncertainty, determined comparing two independent data samples (A and B) collected in the same conditions. M.M.Obertino – IPRD10

  6. PRE-CALIBRATION Light yield (LY) measurements with 60Co (1MeV g) during crystal qualification (2000-2006) • EB: LY Measurements • Intercalibration precision ~4.5-6.0% • EE: LY + VPT gain Measurements • Intercalibration precision ~8% M.M.Obertino – IPRD10

  7. PRE-CALIBRATION Light yield (LY) measurements with 60Co (1MeV g) during crystal qualification (2000-2006) • EB: LY Measurements • Intercalibration precision ~4.5-6.0% • EE: LY + VPT gain Measurements • Intercalibration precision ~8% • 36 EB SMsoperated on a cosmic ray stand for a period of ~1 week/SM • Deposited energy per crystal ~ 250 MeV Cosmic muons Channel intercalibration with cosmic muons (2006-2007) Mean intercalibration precision ~1.5% EB SM h=0 h=1.48 M.M.Obertino – IPRD10

  8. PRE-CALIBRATION Beam splash: in September 2008 and November 2009 beam was circulated in LHC, stopped in collimators 150 m away from CMS • All Endcap crystals Intercalibration precision ~6% BEAM CLOSED COLLIMATOR Combination of LY and beam splash gives ~5% intercalibration precision over the entire EE M.M.Obertino – IPRD10

  9. PRE-CALIBRATION CONSTANTS • EB • LY, cosmic, test beam. • Combination strategy: • Select best calibration available • Combine when comparable precision from two sources • EE • Test beam (460 crytals) • Combination of LY and beam splash Intercalibration precision achieved with these constants: 5% Intercalibration precision achieved with these constants: 0.3-2.2% M.M.Obertino – IPRD10

  10. ENERGY SCALE: ADC to GeV • ECAL energy scale fixed by Test Beam data in Barrel and Endcap separately • ~63 MeV/ADC in EE • ~39 MeV/ADC for EB Distribution of 5x5 amplitude sum (S25) with and without intercalibration for EE crystals exposed to 90 GeV electron beam . • Confirmed later in dE/dx • analysis with cosmics(*) and in collisions withp0 and h mass peak. • Waiting for higher mass resonances to check the scale • in-situ at high energy. 90 GeV INTERCALIBRATION (*) presented by F.DeGuio M.M.Obertino – IPRD10

  11. IN-SITU CALIBRATION • Several methods to calibrate in-situ: • f-symmetry method: intercalibration for crystals at the • same pseudorapidity. • Based on invariance around the beam axis of the energy flow in minimum • bias events. • Calibration performed comparing the total energy deposited in each • crystal with the mean of the distribution of the total energies for all crystals • at the same pseudorapidity M.M.Obertino – IPRD10

  12. IN-SITU CALIBRATION • Several methods to calibrate in-situ: • f-symmetry method: intercalibration for crystals at the • same pseudorapidity. • Based on invariance around the beam axis of the energy flow in minimum • bias events. • Calibration performed comparing the total energy deposited in each • crystal with the mean of the distribution of the total energies for all crystals • at the same pseudorapidity • p0 and h method: single crystal intercalibration • Constants derived using unconverted g’s from p0 and h decay reconstructed • in 3x3 matrices • The reconstructed mass is used to determine the photon energy M.M.Obertino – IPRD10

  13. IN-SITU CALIBRATION • Several methods to calibrate in-situ: • f-symmetry method: intercalibration for crystals at the • same pseudorapidity. • Based on invariance around the beam axis of the energy flow in minimum • bias events. • Calibration performed comparing the total energy deposited in each • crystal with the mean of the distribution of the total energies for all crystals • at the same pseudorapidity • p0 and h method: single crystal intercalibration • Constants derived using unconverted g’s from p0 and h decay reconstructed • in 3x3 matrices • The reconstructed mass is used to determine the photon energy • High energy electrons fromWenand Zeedecays (J/y under study) • Higher integrated luminosity required. Helpful at the startup only for energy • scale. M.M.Obertino – IPRD10

  14. SUPERMODULE RELATIVE SCALE First calibration with collisions of the barrel. • First results in 2009 with ~0.01 nb-1 collected at • Scale derived in 2010 with ~0.4 nb-1 collected at • Systematic error: 0.5% (see next slide) • Statistical error negligible w.r.t. systematic one CMS Preliminary CMS Preliminary Tested with beam • f-symmetry data • p0 data M.M.Obertino – IPRD10

  15. SUPERMODULE RELATIVE SCALE In-situ SM relative scale defined as the weighted average of p0 andf-symmetry results. Distribution of the relative scale of 10 SMscalibrated with test beam electrons. Distribution of the relative scale of 26 SMs calibrated only with cosmic rays. CMS Preliminary CMS Preliminary The RMS is 1.2%±0.2% is consistent with the expected precision of cosmic ray scale. The RMS of 0.5%±0.1% estimates the current precision of the combined in-situ SM relative scale calibration. M.M.Obertino – IPRD10

  16. RECONSTRUCTED p0 gg PEAK • L = 0.43 nb-1 • PT (g) > 0.4 GeV, PT(ggpair) > 1.0 GeV(pure ECAL selection) • Good agreement between data and MC. • Number ofp0 from the fit: 1.46 106 MC DATA The fitted mass agrees with the expectation to within 1% (first in situ validation of absolute energy scale) M.M.Obertino – IPRD10

  17. RECONSTRUCTED hgg PEAK • L = 0.43 nb-1 • PT (g) > 0.5 GeV, PT(ggpair) > 2.5 GeV(pure ECAL selection) • Good agreement between data and MC • Number ofh from the fit: 2.55 104 DATA MC M.M.Obertino – IPRD10

  18. CALIBRATION DATA STREAM In CMS dedicated paths of data acquisition (streams) are implemented for calibration. In p0 and f-symmetry streams, only few tens of “useful”crystal hits are stored for each accepted event (output limited to 1kHz per stream). Calibration stream commissioned with collision data. p0 peak from dedicated calibration stream (better S/B because of higher transverse energy cuts in calibration stream) M.M.Obertino – IPRD10

  19. PLANS FOR 2010 In the Barrel • improve crystal calibration down to 1% in the whole EB with few pb-1. • reach the goal of 0.5% precision in EB with ~10pb-1, expected by the end of the year. Fluctuation due to material in front of ECAL • Improve Endcap crystal calibration from 5% to 1-2%. • Set the absolute scale to few permille. M.M.Obertino – IPRD10

  20. SUMMARY • ECAL crystal intercalibration in very good shape. 0.3%-2% in EB 5% in EE • Z width already almost insensitive to residual mis-calibration. • First calibration result with collision data: SM relative scale in EB. • p0and f-symmetry in agreement. • Calibration streams commissioned. • Collected statistics (~17 nb-1 at 26th May) good for regional • intercalibration (5x5 matrix). • 2010 goals: 0.5% intercalibration precision in EB • 1-2% intercalibration precision in EE M.M.Obertino – IPRD10

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