FLC Group Test-beam Studies of the Laser-Wire Detector 13 September 2006 Maximilian Micheler Supervisor: Freddy Poirier

Introduction The goal of the Test-Beam Studies is to measure the performance of the lead-tungstate detector used at the Laser-Wire experiment at PETRA II: →Calibration, for the use of the detector at the Laser-Wire experiment →Resolution, mainly for simulation purposes

Experimental setup Detector is placed in line with the electron beam as to achieve an EM shower in the centre of the lead-tungstate crystal. (achieved by mounting the detector on an adjustable table) Hamamatsu R6236 photomultiplier tube (54mmx54mm active photo cathode surface) for detection of the energy dissipation in the crystal Two scintillators (one horizontal and one vertical scintillator) were placed in front of the detector and connected to a coincidence unit to only record signals for electrons which entered the crystal in the centre The electron beam energies were selected by changing the currents in the magnets using a computer with a provided software in the Test-beam 24 control room.

Electronics Scintillator signal processed using: Amplifier Discriminator Coincidence unit TTL signal converter TTL signal used for triggering integration of PMT output signal. Using a Computer (ADC Break-out box in the figure) and an integrator card to integrate the PMT signal and to record the area. The setup of the test-beam studies was chosen to have the same conditions as in the Laser-Wire Hut: Identical electronics for the read-out system, i.e. ADC box and integrator card Similar timing for read-out system

Data Acquisition Signal from PMT is a negative voltage peak. Integrator card integrates this peak and outputs the area as a positive voltage which is recorded by the computer. For every single beam energy and PMT supply voltage around 1000 integrator card voltages have been measured. The 1000 area measurements were plotted on a histogram and fitted with a Gaussian function The two graphs are taken for a PMT supply voltage of 1115V at a beam energy of 3.6GeV Mean, Standard deviation, and Errors on the Standard deviation from Gaussian function

Calibration plot: the mean of the integrated signal against the corresponding beam energy for the 4 different PMT supply voltages This calibration plot was expected to show a linear dependence of the integrated signal on the beam energy Linear fittings of the individual data sets show a non-linear behaviour Detector Performance Resolution plot: the PMT normalised resolution (Gaussian width/integrated signal) against the beam energy Resolution is expected to decrease with increasing beam energy. At a PMT supply voltage of 1300V this is not the case Calibration plot Resolution plot

Control Tests Possible reasons why the results differ from expectation: Saturation of PMT Cutting the signal → Incorrect delay →Incorrect integration width Saturation of the read-out system Investigation of the raw PMT output signal recorded from the oscilloscope (as shown). The following quantities were directly calculated from the raw signal: Signal amplitude (difference between constant base line and minimum voltage) Signal area (sum of the relative signal w.r.t. the base line within the integration range)

Control Tests – PMT saturation effects Plot of signal amplitude against signal area shows a linear dependence: Fit: y = x where y represents the signal amplitude and x the signal area. Plot of signal amplitude against beam energy shows a linear dependence: Fit: y = 0.404x where y represents the signal amplitude and x the beam energy. Therefore the signal area also shows a linear dependence on the beam energy → No detector saturation while increasing the beam energy

Control Tests – Cut-off effects 1μs integration delay w.r.t. the TTL trigger, 2.4μs integration width The two graphs show a integration with an asymmetric cut-off of the signal from the tail and the front of the PMT raw signal, respectively. Signal area decreases due to cut-off. However, the plots of the signal area against the beam energy for the different cut-off points are still linear. → Cut-off effects do not seem to be responsible for the non-linear characteristics of the integrated signal →No cut-off effects due to integration width as width is sufficiently long enough to detect entire signal (width approx. 110ns) tail front

Control Tests – Read-out system saturation Resolution plot and Calibration plot achieved for the Laser-Wire detector Results used for calibration of the signal at the Laser-Wire experiment After the calibration the data from the Laser-Wire experiment will be compared with previous simulations At the present time, the read-out system is under study to check how it performs with voltages higher than it is designed for. Conclusions