Calibration of CMS Electromagnetic Calorimeter at LHC startup Riccardo Paramatti (INFN Rome & Cern) on behalf of CMS ECAL Collaboration CALOR2010 Conference
Calibration of CMS Electromagnetic Calorimeter at LHC startup
Riccardo Paramatti (INFN Rome & Cern)on behalf of CMS ECAL Collaboration
CALOR2010 Conference
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OutlineThe CMS Electromagnetic CalorimeterPre-calibration at the LHC startupResults with very first collisionsCalibration streams2010 plans
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CMS Electromagnetic Calorimeter
Excellent energy (and position) resolution for photons and electrons (H→γγ, H→ZZ →4e)Lead Tungstate (PbWO4) homogenous crystalBarrel (EB):
36 Supermodules (SM), each 1700 crystals |η|
Test Beam: Cern electron beams.
From 15 GeVto 250 GeV.(2004-2007)
Pre-calibration Campaign
Laboratory measurements during crystal qualification phase.(2000-2006)
Beam Splash:In September 2008
and November 2009, beam was circulated in LHC, stopped in collimators 150m away from CMS red = ECAL, green=ES, blue=HCAL
beam
Channel intercalibrationwith cosmic muons (only Barrel SMs)
(2006-2007)
cosmic muons
A very intense 10 years long pre-calibration campaign. Several orders of magnitude in energy: from 1 MeV of Co60 source to 120 GeV electron beam.
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Barrel Pre-calibration
Test Beam at Cern10 Supermodules on electron beam (intercalibration accuracy ~0.3%)
Cosmics Calibration36 SMs (~1.4-2.2%)
Light Yield Measurements36 SMs (~4.5-6.0%)
Combination strategy:Select best calibration availableCombine when comparable precision from two sources
Cosmics Calibration
η=0 η=1.48Supermodule
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Endcap Pre-calibration
Test Beam at Cern460 crystals (
Achievement with pre-calibrationIn the Barrel:
from inhomogeneity at the construction of 11.2% (RMS of constant distribution)to a pre-calibration precision of 0.3%-2.2%
In the Endcaps:from inhomogeneity at the construction of 27.2% (RMS of constant distribution)to a pre-calibration precision of ~5%
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Energy Scale
ECAL energy scale (the ADC to GeV conversion factor) fixed by Test Beam data in Barrel and Endcap separately.Confirmed later in dE/dxanalysis with cosmics (*) and in collisions with π0/η mass peak.Waiting for higher mass resonances to check the scale in-situ at high energy.
(*) presented by Andrea Benaglia
Distribution of 5x5 amplitude sum (S25) with and without intercalib. for EE crystals exposed to 120 GeV electron beam.
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In-situ CalibrationIntercalibration precision goal is 0.5%. Main contribution to the constant term of energy resolution.Several methods to calibrate (and follow-up) in-situ:
Laser monitoring: correction for crystal transparency changes (*). Due to very low radiation damage, negligible variation is expected at the startup.φ-symmetry calibration: invariance around the beam axis of energy flow in minimum bias events. Intercalibrate crystals at the same pseudorapidity, other methods are needed to intercalibrate regions at different pseudorapidity.π0 and η calibration: mass constraint on photon energy,use unconverted γ’s reconstructed in 3x3 matrices of crystals.High energy electron from W and Z decays (E/p with single electrons and invariant mass with double electrons). High luminosity required. Helpful at the startup only for energy scale. Testing also J/ψ.
(*) presented by Federico Ferri
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Supermodule relative scaleThe relative energy scale of the Barrel Supermodules is the first calibration with collisions. Results already with ~0.01 nb-1. With ~0.4 nb-1 stat. error negligible w.r.t. syst. (= 0.5% see next slide)
CMS Preliminary
φ-symmetry results for 2009 and 2010 collisions
CMS 2010 Preliminary
φ-symmetry and π0 results for 2010 collisions. Arrows point SMs tested with beam.
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Supermodule relative scaleDistribution of the relative scale of 10 Supermodules calibrated with test beam electrons.
The rms of 0.5%±0.1% estimates the current precision of the combined in-situ regional scale calibration.
CMS Preliminary
Distribution of the relative scale of 26 Supermodules calibrated only with cosmic rays.
The rms is 1.2%±0.2% with all SMs. Consistent with the expected precision of cosmic ray scale.
CMS Preliminary
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Reconstructed π0→γγ peakL = 0.43 nb-1. P⊥(γ) > 0.4 GeV, P⊥(γγ pair) > 1.0 GeV (pure ECAL selection)Good agreement observed for the fitted peak width and Signal/Background. The fitted mass agrees with the expectation to within 1%.
Number of π0 from the fit: 1.46▪106
DATA MC
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Reconstructed η→γγ peakL = 0.43 nb-1. P⊥(γ) > 0.5 GeV, P⊥(γγ pair) > 2.5 GeV (pure ECAL selection)Good agreement observed for the fitted peak width and mass Number of η from the fit: 2.55▪104
DATA MC
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Calibration streamsIn CMS dedicated streams are implemented for calibration.Use events accepted by Level 1 triggers in order to accumulate millions of events for a quick channel intercalibration.
In π0/η and φ-symmetry streams, only few tens of “useful” crystal hits are stored for each accepted event.The output rate is close to 1kHz per stream.
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Performance of Calibration streamCalibration stream commissioned with collision data.Higher transverse energy cuts in calibration stream, better S/B.~1000 π0/(crystal▪pb-1) at L=2▪1030 cm-2 s-1
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2010 plans
Improve crystal calibration down to 1% in the whole EB with few pb-1.Reach the goal of 0.5% precision in EB by the end of the year with ~10 pb-1Improve EE crystal calibration down from 5% to 1-2%.Set the absolute scale to few permille.
Integrated luminosity required to achieve a crystal intercalibration precision of 1% and 0.5% for Barrel crystals with different pseudorapidity, assuming L=2▪1030 cm-2 s-1
η=0 η=1.48Barrel
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ECAL crystal intercalibration in very good shape.0.3%-2% in EB, 5% in EEZ width already almost insensitive to residual mis-calibration even in EE. ~3.5 (3.0) GeV with 5% (0.5%) precision in EE.
First calibration result with collision data is SM relative scale in EB. π0 and φ-symmetry in agreement.Collected statistics (~3 nb-1 at 12th May) good for regional intercalibration (e.g. matrices of 5x5 crystals).Calibration streams commissioned.2010 goals: reach the 0.5% calibration precision in EB and improve EE calibration.
Summary
Backup
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EB calibration at the startupIntercalibration constants spread: 11.2%Intercalibration constants precision: 0.3%-2.2%
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EE calibration at the startupIntercalibration constants spread: 27.2%Intercalibration constants precision: 5%
Calibration of CMS Electromagnetic Calorimeter at LHC startupOutlineCMS Electromagnetic CalorimeterPre-calibration CampaignBarrel Pre-calibrationEndcap Pre-calibrationAchievement with pre-calibrationEnergy ScaleIn-situ CalibrationSupermodule relative scaleSupermodule relative scaleReconstructed p0 → peakReconstructed h → peakCalibration streamsPerformance of Calibration stream2010 plansSummaryBackupEB calibration at the startupEE calibration at the startup