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January 2008 Hall C Users Meeting. BigCal Calibration E04-108&04-019. Wei Luo Lanzhou University, China. Outline. 1. Introduction 2. Calibration method 3. Calibration 4. Radiation damage 5. Energy resolution 6. Summary. 1. Introduction.
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January 2008 Hall C Users Meeting BigCal Calibration E04-108&04-019 Wei Luo Lanzhou University, China
Outline • 1. Introduction • 2. Calibration method • 3. Calibration • 4. Radiation damage • 5. Energy resolution • 6. Summary
1. Introduction • TF1-0 type lead glass, 12-stage Russian FEU-84 PMT, coupled by 1cm soft optical ‘cookie’. • Protovino part: 1024 bars of 3.8x3.8x45cm3 lead glass • RCS part: 720 bars of 4.0x4.0x40cm3 lead glass • BigCal goal: identify elastic event, reduce high background rate
2. Calibration Method (1) (2) (3) E—electron energy (e_hms) A—ADC value C—calibration coefficient i—event number j—block number where • k=1,1744 • Solve 1744 linear equations (3) for calibration coefficients Cj, • Use Cj to calculate new High Voltage. • 1ADC channel=1Mev (4)
3. Calibration Use HMS information to select elastic electrons: • HMS predicted energy; • HMS predicted & BigCal Position correlation; • Max energy cluster.
Position Correlation BigCal cluster position VS. HMS predicted position Assuming elastic scattering, use HMS track to calculate elastic electron hit position. Reconstructed cluster HMS predicted position
Cluster ADC ADC/E_hms ADC/E_hms/gain Example Kinematics 6, electron energy:1.507Gev, BigCal theta: 44.9o, 10cm Al absorber ADC mean=1459 Gain=ADC/E_hms=0.957 Energy resolution=12%
HV ratio Amplitude Calculated Calibration coefficient HV difference HV calculation After solving formula (3) we can get calibration coefficient shown below. The mean calibration coefficient greater than 1, demands increase HV of BigCal. With formula (4), we can calculate new HV based the current HV. (note: negative HV)
After loading new HV • The gain of ADC shifted to1 after loading new HV • The energy resolution improved by 0.5% Cluster ADC ADC/E_hms
4. Radiation damage • The radiation damage of lead glass makes the energy resolution increased. • The gain of cluster ADC keep decreasing as beam on.
Gain VS. Beam Charge 1’’ Al
5. Energy resolution • The relation of energy resolution and electron energy is defined as: • Where σ is the energy resolution, E is electron energy, The first term includes all systematic block-to-block differences and calibration errors; the the second term contains the effect of photoelectron statistics; the third term represent the fluctuation in pedestal due to electronics noise. The effect of 10cm Al absorber on energy resolution is significant. (5)
Energy resolution*E1/2 VS. Elastic electron energy Red points -10 cm absorber Blue points -2.5 cm absorber
kine 5 energy resolution Nov 28 2007 Jan 17 2008
6. Summary • The BigCal calibration has been done at start of each kinematics (except 7). • Al absorber has strong effect on the energy resolution of BigCal. • The HV of BigCal increase approximately 86V comparing to the beginning of experiment. • The lead glass blocks cured itself partially when the beam is off for a long time.
