Upload
laurence-gilbert
View
217
Download
0
Tags:
Embed Size (px)
Citation preview
BigCal Calibration E04-108&04-019
Wei Luo
Lanzhou University, China
January 2008 Hall C Users Meeting
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
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
2. Calibration Method
where k=1,1744 Solve 1744 linear equations (3) for calibration coefficients Cj,
Use Cj to calculate new High Voltage. 1ADC channel=1Mev
VeA
1744
1
1744
1
jkjj
iiki
jijji
ijjij
XCAE
ACE
ACE
i
ikijjk AAX
E—electron energy (e_hms)
A—ADC value
C—calibration coefficient
i—event number
j—block number
(1)
(2)
(3)
(4)
3. Calibration
Use HMS information to select elastic electrons:
HMS predicted energy; HMS predicted & BigCal Position correlation; Max energy cluster.
Position Correlation
HMS predicted position
BigCal cluster position VS. HMS predicted position
Assuming elastic scattering, use HMS track to calculate elastic electron hit position.
Reconstructed cluster
Example Kinematics 6, electron energy:1.507Gev, BigCal theta: 44.9o, 10cm Al absorber
Cluster ADC ADC/E_hms ADC/E_hms/gain
ADC mean=1459
Gain=ADC/E_hms=0.957
Energy resolution=12%
Calculated Calibration coefficient
HV calculationAfter 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)
HV differenceAmplitude
HV ratio
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. Time
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.
E
C
E
BA
E
(5)
Energy resolution VS. Beam Charge
Energy resolution VS. Time
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
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
Energy resolution*E1/2 VS. Elastic electron energy
E
CBEA
E
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.
Thank you!