BigCal Calibration E04-108

1
BigCal Calibration
E04-10804-019

• January 2008 Hall C Users Meeting

• Wei Luo
• Lanzhou University, China

2
Outline

• 1. Introduction
• 2. Calibration method
• 3. Calibration
• 4. Radiation damage
• 5. Energy resolution
• 6. Summary

3
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

4
Kinematics table
Kin Ebeam(Gev) Ee(Gev) Distance(cm) Angle() Absorber(cm)
1 2.717 1.102 960 60.3 10.0
2 1.032 0.662 960 60.3 10.0
3 2.533 1.072 960 60.3 10.0
4 4.045 1.274 605 60.3 10.0
5 1.867 0.535 493.2 105.1 2.5
6 2.839 1.507 1200.0 44.9 10.0
7 3.680 2.207 1116.0 32.6 10.0
5
2. Calibration Method
Eelectron energy (e_hms) AADC
value Ccalibration coefficient ievent
number jblock number
(1) (2) (3)

• where
• k1,1744
• Solve 1744 linear equations (3) for calibration
  coefficients Cj,
• Use Cj to calculate new High Voltage.
• 1ADC channel1Mev

(4)
6
3. Calibration

• Use HMS information to select elastic electrons
• HMS predicted energy
• HMS predicted BigCal Position correlation
• Max energy cluster.

7
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
8
Example
Kinematics 6, electron energy1.507Gev, BigCal
theta 44.9o, 10cm Al absorber
ADC mean1459 GainADC/E_hms0.957 Energy
resolution12
9
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)
10
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
11
4. Radiation damage

• The radiation damage of lead glass makes the
  energy resolution increased.
• The gain of cluster ADC keep decreasing as beam
  on.

12
Gain VS. Time
13
Gain VS. Beam Charge
1 Al
14
5. Energy resolution

• The relation of energy resolution and electron
  energy is defined as
• Where s 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)
15
Energy resolution VS. Beam Charge
16
Energy resolution VS. Time
17
Kin Ee(Gev) Distance(cm) Angle() Absorber(cm) Energy resolution
1 1.102 960 60.3 10.0 10.4
2 0.662 960 60.3 10.0
3 1.072 960 60.3 10.0 10.6
3 1.072 960 60.3 2.5 7.1
4 1.274 605 60.3 10.0 11.2
5 0.535 493.2 105.1 2.5 11.5
6 1.507 1200.0 44.9 10.0 10.7
7 2.207 1116.0 32.6 10.0 11.7
18
Energy resolutionE1/2 VS. Elastic electron
energy
Red points -10 cm absorber Blue points -2.5 cm
absorber
19
kine 5 energy resolution
Nov 28 2007
Jan 17 2008
20
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.

21

• Thank you!