1. ECAL Digitization Rick Wilkinson May 25, 2006 1

2. ECAL Digitization CaloHitResponse CaloSamples (analog signal) EcalElectronicsSim EBDataFrame EEDataFrame SimHits 2 (EB ieta -17, iphi84 ; ism 23, ic 324) 10 samples ADC=198, gainId=2 ADC=199, gainId=2 ADC=195, gainId=2 ADC=358, gainId=2 ADC=409, gainId=2 ADC=376, gainId=2 ADC=317, gainId=2 ADC=260, gainId=2 ADC=220, gainId=2 ADC=198, gainId=2

3. Photostatistics Photoelectrons per GeV: ● Barrel: 2500 ● Endcap: 1800 ● Leads to a stochastic energy resolution of: Barrel: Endcap: 3

4. Shaping ● ECAL charge collection much slower than HCAL ● ECAL: 47.6 ns peaking time ● HCAL: 14 ns ● HF: 2 ns ● Requires more samples for reconstruction ● ECAL: uses 5 samples ● HCAL: 2 ● HF: 1 ● More sensitive to pileup ● No jitter effect added 4

5. Sources of Noise ● PEDESTAL NOISE: ● Barrel: 40 MeV ● Endcap: 150 MeV ● GAIN VARIATIONS: ● Intrinsic (light collection uniformity) ● 0.3% smearing in simulation ● Calibration uncertainty ● NOT simulated ● To be included by other methods ● Database? ● External smearing tools? ● Goal: 0.5% 5

7. SimHits Contains: ● Energy ● Time-of-flight ● SimTrack ID One SimHit is created for each: ● Generator particle ● Detector Unit ● Nanosecond of shower development Made by GEANT4 Simulation step

8. Encoding ● Energy encoded into 12 bits by Multi-Gain Preamplifier (MGPA) ● Gains of 1, 6, and 12 ● Gain 12: 1 ADC = 35 MeV (barrel), 60 MeV (endcap) ● Gain 6: 1 ADC = 70 MeV (barrel), 120 MeV (endcap) ● Gain 1: 1 ADC = 420 MeV (barrel), 720 MeV (endcap) ● Saturates at 1.7 TeV (barrel), 2.95 TeV (endcap) ● Hysteresis effect: once a gain is switched up, it stays up for 5 samples. 8

9. Calibration & Condition Databases ● ECAL digitization doesn't use these interfaces yet ● uses configurable parameters now ● The interfaces exist. We could retrieve, channel-by-channel: ● Pedestals & pedestal widths ● Intercalibration constant, mean and sigma ● Calibration: ADC to GeV ● Gain ratios: 12/6 and 6/1 ● Weights for reconstruction 9

10. Trigger Towers ● Barrel geometry is simple ● One ECAL trigger tower equals: ● 25 crystals ● One HCAL tower ● Endcap Geometry is not simple 10

11. Selective Readout Being implemented now ● High Interest EM Trigger Tower (> 5 GeV) ● Take all crystals from: ● This tower ● Neighboring towers ● Medium Interest EM trigger tower (> 2.5 GeV) Take all crystals in this tower ● Low Interest ● Barrel threshold: 90 MeV ● Endcap threshold: 450 MeV ● Remember, noises were 40 MeV and 150 MeV 11