Asymmetry of QADC signals in single PbWO 4 crystal
description
Transcript of Asymmetry of QADC signals in single PbWO 4 crystal
Asymmetry of QADC signals in single PbWO4 crystal
Cosenza INFN Group( L. La Rotonda, E. Meoni, A. Policicchio, G.
Susinno,T. Venturelli)
2
Summary
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 triedto study also this dependence for showers in the early stage using electron of 50 GeV atdifferent impact point positions
Pb
3
Showers in the early stage
Showers in differentstages
Pions
Showers in the early stageat different impact points
Data sets
4
50 GeV electron showers in the early stage
(ADC counts)
(CH 25)
(CH 24)
ADC spectra after pedestal subtraction
(ADC counts)
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
>0°
=2.2cm=2.5 X0
5
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.
We have equalized ADC signals of the two channels at 00
ADC CH25ADC CH24 (CH 25)
(CH 24)
AD
C M
ean
6
(CH25)ADC(CH24)ADC(CH24)ADC(CH25)ADC
Asymmetrymeanmean
meanmean
ADCmean is the mean of the ADC spectra shown before
The first method (asymmetry from mean of ADC spectra)
7
We have computed asymmetry also
event by event at a fixed angle
H25)ADCcount(CH24)ADCcount(C
H24)ADCcount(CH25)ADCcount(CAsymmetry
00 150 300 450
Taken mean value of the asymmetry distribution for each angle
Errors of the plot are RMS of asymmetry distributions
The second method (asymmetry event by event)
Asymm
8
The two methods give the same results
Asy comp. evt by evtAsy comp. from ADC spectra
9
10mm of Pb
35mm of Pb(ADC counts)
(ADC counts)
(ADC counts)
0°-15°-30°
4mm of Pb
20mm of Pb
50 GeV electron showers at different stages
25mm of Pb
(ADC counts)
(ADC counts) (ADC counts)
ADC spectra after pedestal subtraction and after a cut to suppress the pedestal and eventually the mip background in the beam
Pb
Channel 25
=0.4Pb cm->3.5 Pb cm =0.7 X0-> 6.25 X0
10
Asymmetry computed event by event
Asymmetry computed with mean of ADC spectra
11
Asymmetry difference between positive and negative angles
From asymmetry results seems that thereis a shift between the “real zero angle” and the “nominal zero angle”
Shift of 2°Shift of 5°
The shift is close to 2° (no data taken at -1° -3°,-4°to perform other checks)
Differences in asymmetry observed for corresponding positive and negative angles
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 anglesPositive angles
Setup without Pb
12
Before angle correctionAfter angle correction
Before angle correction After angle correction
First method
Second method
First method
Second method
13
Positive angles Negative angles
Cerenkov component estimation
Asymax(30°)=7.0%
Asy(30°)= 7.5%
Asymax(26°)= 7.6%
Error computed from event by event Asymmetry width 5)%(13)(30
SignalCerenkov
3)%(7Asym
Asym)(1
2Asym)(30
SignalCerenkov
stage early the In
10GeV of ele of testbeam previuos of result 6)%(13)(30Signal
Cerenkov
Fit performed with a second-degree polynomial
Asymmetry at 30° (mean between positive & negative)
Cerenkov comp at30° from asymm
Positive & negative angles
Asymax(30°)=7.2%
Asymmetry at 30° (from the global fit)
14
70 GeV pions
(ADC counts) (ADC counts)
ADC spectra after pedestal subtraction
Channel 25
(CH 25)
(CH 24)>0°
=2.2cm=2.5 X0
0° - 15° - 30° - 60°-75°
15
Computed asymmetry event by event applying different cut of large ADC counts
Before angle correction After angle correction
Cut on 200 countsCut on 300 countsCut on 500 counts
16
Taken mean value of the asymmetry distribution for each angle
Errors of the plot are RMS of asymmetry distributions
00 150 300 450
Asymmetry distribution event by event
Asymm
Angle (deg)
Asy
mm
2° 32° 47° 67°
17
Positive angles Negative angles
Positive & Negative angles
Cerenkov component estimation
Asymax(38°)= 12.1% Asy(30°)= 11.5%
Asymax(33°)= 11.9% Asy(30°)= 11.8%
Asymax(33°)= 11.7% Asy(30°)= 11.7%
Cerenkov fraction is about 20% at 30°
18
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
CH24CH25
Beam at 8 cmBeam at 3 cm Beam at 0 cmBeam at -3 cmBeam at -6 cm
ADC spectra after pedestal subtraction
Effect due to ADC saturation
(CH 25)
9 0 -9 (cm)
(CH 24)
xRL
We tried in any case to compute Asymmetry event by event
(ADC counts) (ADC counts)
19
(CH 25)
9 0 -9 (cm)
(CH 24)
xRL
The asymmetry variation is 0.55%/cm
(CH25)ADC(CH24)ADC(CH24)ADC(CH25)ADC
Asymmetrycountcount
countcount
20
Conclusions
We have computed asymmetry with QADC data:
For electron showers in the early stage we obtained a maximumasymmetry of (7± 3)% around 30°corresponding to Cerenkovfraction of (13± 5)%.As expected, the asymmetry as a function of the shower depthdecreases.
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
We have repeated event by event analysis applying some cuts on the beam position
(CH 25)(CH 24)
x
RL
y
The beam is all contained in x (horizontal coordinate) and is larger than the crystal in y (vertical coordinate)Selected only events that cross crystalaround x_crystal_center ± 0.5 cm(assumed x_crystal_center=x_DREAM_centertrue with a precision of 1 cm) y_crystal_center ± 0.25 cm(y_crystal_center determinated by the beamprofile)
Asymmetry with cut on beam position
Without cut on beam positionWith cut on beam position
22
Third method
30-(CH25)(CH24)30(CH25)(CH24)
30-(CH24)(CH25)30(CH24)(CH25)
]ADCADC]ADC[ADC]ADC[ADC]ADC[ADC
Asy[
We have also computed asymmetry using only data at 30° and -30°
ADC(CH) is the mean of ADC spectrum
)%.()( 51430Signal
Cerenkov stage early the In