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Asymmetry of QADC signals in single PbWO 4 crystal

Asymmetry of QADC signals in single PbWO 4 crystal. Cosenza INFN Group ( L. La Rotonda, E. Meoni, A. Policicchio, G. Susinno, T. Venturelli). Summary. Pb.

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Asymmetry of QADC signals in single PbWO 4 crystal

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  1. Asymmetry of QADC signals in single PbWO4 crystal Cosenza INFN Group ( L. La Rotonda, E. Meoni, A. Policicchio, G. Susinno, T. Venturelli)

  2. Summary Pb GOAL: The goal of this work is to measure the left-right asymmetry of QADC signals from single PbWO4 crystal and then estimate the (average) Cerenkov contribution both for showers at different depths and for mips. This study is related to the paper :“Separation of crystal signals into Cerenkov and scintillation components”. DATA SETS: we have studied QADC data taken at different angles with: electrons of 50 GeV both without Pb in front to the crystal and with different Pb layers in front to the crystal; Pions of 70 GeV without Pb in front to the crystal. The data are collected at room temperature. METHOD: We have computed asymmetry versus angle both from the mean of QADC spectra and event by event OBSERVATION: Since asymmetry depends on beam impact point position, we have tried to study also this dependence for showers in the early stage using electron of 50 GeV at different impact point positions

  3. Data sets Showers in the early stage Showers in different stages Pions Showers in the early stage at different impact points

  4. =2.2cm=2.5 X0 50 GeV electron showers in the early stage (CH 25) >0° (CH 24) ADC spectra after pedestal subtraction Applied a cut to suppress the pedestal and eventually the mip background in the beam 0° - 15° - 30° - 60° 0° - 15° - 30° - 60° Channel 25 Channel 25 (ADC counts) (ADC counts)

  5. We have equalized ADC signals of the two channels at 00 ADC Mean ADC CH25 ADC CH24 (CH 25) (CH 24) The ADC signal increases with the angle, because increases the track length. For positive angles the CH25 signal is larger than CH24 one because CH25 collects a larger Cerenkov component (vice versa for negative ones). But at fixed positive and negative corresponding angles, the difference between the signal of the 2 CHs is not equal, this is evident also in asymmetry slope.

  6. The first method (asymmetry from mean of ADC spectra) ADCmean is the mean of the ADC spectra shown before

  7. The second method (asymmetry event by event) We have computed asymmetry also event by event at a fixed angle 00 150 300450 Asymm Taken mean value of the asymmetry distribution for each angle Errors of the plot are RMS of asymmetry distributions

  8. The two methods give the same results Asy comp. evt by evt Asy comp. from ADC spectra

  9. =0.4Pb cm->3.5 Pb cm =0.7 X0-> 6.25 X0 Pb 50 GeV electron showers at different stages 10mm of Pb 4mm of Pb ADC spectra after pedestal subtraction and after a cut to suppress the pedestal and eventually the mip background in the beam 0°-15°-30° Channel 25 (ADC counts) (ADC counts) (ADC counts) 20mm of Pb 35mm of Pb 25mm of Pb (ADC counts) (ADC counts) (ADC counts)

  10. Asymmetry computed with mean of ADC spectra Asymmetry computed event by event

  11. Asymmetry difference between positive and negative angles Differences in asymmetry observed for corresponding positive and negative angles Setup without Pb From asymmetry results seems that there is a shift between the “real zero angle” and the “nominal zero angle” We tried to fix this angle: Equalized the 2 ADC channel data at -2°(-5°) fixed_angle= nominal_angle +2° (fixed_angle=nominal_angle+5°) Negative angles Positive angles The shift is close to 2° (no data taken at -1° -3°,-4° to perform other checks) Shift of 5° Shift of 2°

  12. First method First method Before angle correction After angle correction Second method Second method Before angle correction After angle correction

  13. Cerenkov component estimation Negative angles Positive angles Positive & negative angles Asy(30°)= 7.5% Asymax(26°)= 7.6% Asymax(30°)=7.0% Asymax(30°)=7.2% Asymmetry at 30° (from the global fit) Asymmetry at 30° (mean between positive & negative) Fit performed with a second-degree polynomial Cerenkov comp at 30° from asymm Error computed from event by event Asymmetry width

  14. =2.2cm=2.5 X0 70 GeV pions (CH 25) >0° (CH 24) ADC spectra after pedestal subtraction 0° - 15° - 30° - 60°- 75° Channel 25 (ADC counts) (ADC counts)

  15. Computed asymmetry event by event applying different cut of large ADC counts After angle correction Before angle correction Cut on 200 counts Cut on 300 counts Cut on 500 counts

  16. 2°32° 47°67° Asymmetry distribution event by event Asymm 00 150 300450 Asymm Taken mean value of the asymmetry distribution for each angle Errors of the plot are RMS of asymmetry distributions Angle (deg)

  17. Cerenkov component estimation Positive angles Negative angles Asymax(33°)= 11.9% Asy(30°)= 11.8% Asymax(38°)= 12.1% Asy(30°)= 11.5% Positive & Negative angles Cerenkov fraction is about 20% at 30° Asymax(33°)= 11.7% Asy(30°)= 11.7%

  18. (CH 25) (CH 24) L R x 9 0 -9 (cm) Asymmetry versus beam impact potision Taken a data set with electron of 50 GeV with a beam horizontal scan position from one crystal end to the other at step of 1 cm ADC spectra after pedestal subtraction CH25 Beam at 8 cm Beam at 3 cm Beam at 0 cm Beam at -3 cm Beam at -6 cm CH24 (ADC counts) (ADC counts) Effect due to ADC saturation We tried in any case to compute Asymmetry event by event

  19. (CH 25) (CH 24) L R x 9 0 -9 (cm) The asymmetry variation is  0.55%/cm

  20. Conclusions We have computed asymmetry with QADC data: For electron showers in the early stage we obtained a maximum asymmetry of (7± 3)% around 30°corresponding to Cerenkov fraction of (13± 5)%. As expected, the asymmetry as a function of the shower depth decreases. For mips (pions) we obtained a maximum asymmetry of 12% corresponding to Cerenkov fraction of 20% The results are compatible with the ones of the previous testbeam

  21. Asymmetry with cut on beam position We have repeated event by event analysis applying some cuts on the beam position The beam is all contained in x (horizontal coordinate) and is larger than the crystal in y (vertical coordinate) Selected only events that cross crystal around x_crystal_center ± 0.5 cm (assumed x_crystal_center=x_DREAM_center true with a precision of 1 cm) y_crystal_center ± 0.25 cm (y_crystal_center determinated by the beam profile) y (CH 25) (CH 24) L R x Without cut on beam position With cut on beam position

  22. Third method We have also computed asymmetry using only data at 30° and -30° ADC(CH) is the mean of ADC spectrum

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