Mean chisq/DOF is 0.56 for 3-pole, 0.68 for double-Gaussian. http://www.slac.stanford.edu/~meeg/ecalpulsefit/3pole/rchisq.png http://www.slac.stanford.edu/~meeg/ecalpulsefit/2gaus/rchisq.png I think that in every fit the 2-Gaussian shape overestimates the rising edge; 3-pole looks better. As Andrea says, the pulse peak is definitely better fit by 3-pole. On Thu, 3 Apr 2014, Sho Uemura wrote: > chisq/dof plot attached - I'm using TGraph to fit, which assumes errors of 1 > mV per data point. I use the time range (-200, 60). > > On Thu, 3 Apr 2014, Gabriel CHARLES wrote: > >> Could you both provide an average value of chi square that the different >> parametrization can be compared easily, please ? >> >> Also, from the simulation it appears that the rising edge could be present. >> In attachment you will find a picture with two plots. The top one >> corresponds to the signal after the crystal and the APD, that is the input >> of the preamplifier. >> It is obtained by the convolution of the signal of the crystal and the APD. >> The crystal response is composed of the sum of two decreasing exponential >> governed by different time constants. The APD transfert function is given >> by the bottom plot (sorry for the wrong Y axis units). >> >> There is no reason for the preamplifier to reduce the tail. >> >> I think that if there is no huge difference between the chi square it would >> be better to keep the two gaussian function. >> >> --- >> Gabriel CHARLES >> Institut de Physique NuclĂ©aire d'Orsay >> >> On Thu, 3 Apr 2014 13:15:00 -0700 (PDT), Sho Uemura wrote: >>> I tried two more parametrizations. These are parametrizations >>> commonly used for the APV25 preamp that we use in the SVT. >>> >>> CR-RC: t*exp(-t/tp) >>> 3-pole, or CR-RC-RC: t^2*exp(-t/tp) >>> >>> 3-pole seems to fit well, I think better than the asymmetric >>> Gaussian. CR-RC seems no better than the Gaussian. Other >>> parametrizations I tried (variations on CR-RC or 3-pole using more >>> than one time constant) were degenerate with CR-RC or 3-pole, so I >>> didn't include those plots. >>> >>> Plots attached are for 3-pole function. All plots for 3-pole and >>> CR-RC, and the pyroot scripts I used, are online: >>> >>> http://www.slac.stanford.edu/~meeg/ecalpulsefit/ >>> >>> I also see what you see, where there are 2 clusters in the >>> distribution of shape parameters. I chose the center of the larger >>> cluster (with the faster time constant) and refit all the events with >>> this time constant fixed; those plots are named "fit2" and as expected >>> they fit the faster pulses well and the slower pulses poorly. >>> >>> More data will help. >>> >>> I plotted the three parametrizations we have, see plot4.pdf attached. >>> If we agree that the Gaussian has an unphysical rising edge, I think >>> we should use 3-pole. >>> >>> On Tue, 1 Apr 2014, Andrea Celentano wrote: >>> >>>> 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 >>>> >> >> ######################################################################## >> Use REPLY-ALL to reply to list >> >> To unsubscribe from the HPS-SOFTWARE list, click the following link: >> https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=HPS-SOFTWARE&A=1 > ######################################################################## Use REPLY-ALL to reply to list To unsubscribe from the HPS-SOFTWARE list, click the following link: https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=HPS-SOFTWARE&A=1