(N2 laser run: Root file with charge histograms and summed waveforms
for all channels, nd3.0 = dimmest)
run_5334_wavehisto.root (N2 laser run: Root file with charge histograms and summed waveforms for all channels, nd2.0 )
run_5335_wavehisto.root (N2 laser run: Root file with charge histograms and summed waveforms for all channels, nd1.0 )
run_5337_wavehisto.root (N2 laser run: Root file with charge histograms and summed waveforms for all channels, nd0.0 = brightest)
ch542_nd00_qhist.gif charge histogram for OM542, brightest N2 run
ch542_nd30_qhist.gif charge histogram for OM542, dimmest N2 run
wavesum_om542_nd00.gif sum of waveforms to form a composite from brightest run (OM542)
wavesum_om542_nd20.gif sum of waveforms to form a composite waveform for next to dimmest run (OM542)
This study was done using OM542 as the receiver at a distance of 100m. Its depth is approximately the same as the N2 laser module. OM542 (LED-aom) represented a compromise between too few photons for more distant OMs (although the photons are spread over a a greater amount of time) and too close, where too many photons arrive within a short time span. For more waveforms from OM542 and others, see sample waveforms.
|Npe = 180
OM 542, ND00
x-axis = 10ns/bin
Notice wide TOT for first LE
|Npe = 18
OM 542, ND01
x-axis = 10ns/bin
Notice that you can count the individual PE hits.
|Npe = 1.8
OM 542, ND20
x-axis = 10ns/bin
Not typical, most waveforms have only 1 or 2 pulses i n them.
Integrated Dynamic Range (IDR)
We investigated two approaches to estimate the integrate dynamic range of the TWR system: visual inspection of the composite waveforms and plotting the histogram of the sum of the negative voltage over the complete waveform (ie, we summed only those bins in the waveform with a voltage less than the baseline value). These estimates provide a lower limit to the true capabilities. First, we had limited control over the gain of the prompt output from the ORBs since they were also being used by the muon DAQ. Also, the TO crew has already calibrated the time delay for the muon DAQ so we felt it was not prudent to lower the gain of the prompt channel. Second: the maximum output from the prompt ORB channels is only 1.2V, which is much smaller than typical for the delayed output. Typically, our instanteneous dynamic range was less than 10 pe and often only a few pe.
This study was done using OM542 as the receiver at a distance of 100m. Its depth is approximately the same as the N2 laser module. OM542 (LED-aom) represented a compromise between too few photons for more distant OMs (although the photons are spread over a a greater amount of time) and too close, where too many photons arrive within a short time span.
IDR (Method 1): estimate from composite waveforms
Run 5334: ND2.0, Composite of 138
The jitter is due to the relatively few waveforms in the compositie. The overshoot is clearly visible.
Run 5335: ND1.0, Composite of 1228
Notice the strong overshoot on the right side of the pulse. Clearly some of the signal is shifted to positive values, but the simple estimate of charge ignores this contribution.
Run 5335: ND0.0, Composite of 531
Notice that pulse shape is slightly rounded near bottom, suggesting that saturation of the instanteneous signal is beginning.
Table 1: Summary of results from composite waveform
|Npe (laser)||Q_est||Ratio||Expect. Ratio|
So this estimate shows that the charge measured is almost linearly proportional to the known brightness variation by the laser. Clearly, we need to find a better estimator of the charge contained in the pulse.
We also computed the "charge histogram" of the individual waveforms for OM542.
IDR (method 2): Charge integration
Npe = 0.18
Npe = 1.8
T. Feser implemented the FFTW subroutine to remove baseline shifts and slow overshoots of the waveform. It works well for waveforms with individual pulses, but does not work so well for complex waveforms. For example, we show a waveform from OM 542 for the brightest N2 laser run.
ch542_fft_before_and_after_filtering.gif (OM 542 waveform before (top black line) and after FFT filtering (red line))
The filtered wavefom is highly distorted. Clearly, the FFT filtering
scheme does not work well with a pulse width close to 0.5us wide.