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!