[Hps-ecal] HPS Ecal signals parametrization

[Andrea Celentano]

Dear all, I am sending again this e-mail.
I think was blocked by hps-ecal mailing list due to too big attachments.
Sorry If you are receiving this more than once.

Attachemnts are here:

http://www.ge.infn.it/~celentan/data/hps/

Regards

Andrea
----- Messaggio originale --------
Oggetto: 	HPS Ecal signals parametrization
Data: 	Tue, 01 Apr 2014 18:48:55 +0200
Mittente: 	Andrea Celentano <andrea.celentano at ge.infn.it>
A: 	hps-ecal at jlab.org



Dear all,
here are some results about HPS Ecal signals parametrization.
I took data with the crystal placed vertically, APD gain 150, room
temperature. I put a threshold ~ 20 mV to keep only big enough signals,
out of the noise.
I acquired data with a 2.5Gs/s oscilloscope, 1 GHz bandwidth, 50 Ohm
input impedance.

I used the same* configuration employed at JLab for cabling: 8m 3M cable
---> passive splitter ---> 3m lemo cable.

*actually I employed an 8 meters 3M cable instead of 7m because the
latter is not available here in Genova.

Attached you find a postcript file with the results. (outGood.ps shows
the fit results covering some parts of the signal, outGood1.ps no)

- Neglect first blank page
- Pages from 2 to 32 are the 31 signals I got, with superimposed the fit
performed with the two-gaussians parametrization. Each chi2 fit is
performed independently.
Signals are in mV and ns.
Note that near ~ 100 ns there is probably a reflection due to some
impedance mismatch in the cables chain.
However,  I am not using those points to fit. I am fitting the data in
between -200 ns and +80 ns. The function is then plotted in the full
time range.

- Last page is a summary of the fits performed. Two 1d-histograms are
the distributions of the two time constants used in the parametrization.
Then I am plotting also their correlation, as well as the correlation of
the rise-time (par[1]) with the signal amplitude (from the fit).

I noted that the fit parameters Trise, Tfall are not distributed as two
gaussians. In particular, for Trise there is an accumulation of events
at ~ 5 ns and ~ 7 ns, correlated with corresponding Tfall at ~ 15 and
~20 ns. Actually, I see that, other than the amplitude, signals do not
have always the same shape: look, for example, at signals n.5 and n.6
(ps pages n.5 and n.6).

Attached you find also the C implementation of the signal
parametrization, in form of a "double fun(double *x,double  *par)" used
by ROOT when fitting trough TF1.
Finally, I am attaching also the raw data for the 31 signals I got, so
if you're interested you can play with different signal parametrizations.

I am planning to take more data these days.


Bests,

Andrea



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