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Re: A proposal for setting a BCAL threshold
On Fri, 8 Jun 2007, Matthew Shepherd wrote:
Matt,
this depends highly on your rate and your fraction of cross talk.
I just thought if we now spend the effort to collect facts, it would be
one to be taken into account. Actually Carl is measuring this at them
moment to see what we see.
elke
> Date: Fri, 8 Jun 2007 16:51:43 -0400
> From: Matthew Shepherd <mashephe@indiana.edu>
> To: Elke-Caroline Aschenauer <elke@jlab.org>
> Cc: George Lolos <George.Lolos@uregina.ca>,
> Richard Jones <richard.t.jones@uconn.edu>, halld-cal@jlab.org
> Subject: Re: A proposal for setting a BCAL threshold
>
>
> Elke,
>
> Right -- but it looks like the rate for double PE equivalent hits is
> down by an order of magnitude. So it should be about a 10%
> correction. I think at the level we are trying to estimate this I'm
> happy to operate on the assumption that the single PE rate completely
> dominates the dark rate.
>
> Cheers,
>
> -Matt
>
> On Jun 8, 2007, at 4:00 PM, Elke-Caroline Aschenauer wrote:
>
> > On Fri, 8 Jun 2007, Matthew Shepherd wrote:
> >
> > Matt,
> >
> > just one remark the assumption that all of the dark rate will be one
> > photon electron is not really true for SiPMTs, please look to
> > /home/elke/public/070419_jlabs_presentation.pdf page 29 and 30
> > as a pixel can only be on or off, contrary to other devices.
> >
> > bye elke
> >
> >
> >> Date: Fri, 8 Jun 2007 15:38:09 -0400
> >> From: Matthew Shepherd <mashephe@indiana.edu>
> >> To: George Lolos <George.Lolos@uregina.ca>
> >> Cc: Richard Jones <richard.t.jones@uconn.edu>, halld-cal@jlab.org
> >> Subject: Re: A proposal for setting a BCAL threshold
> >>
> >>
> >> Richard and George,
> >>
> >> Thanks for the info. So 32 MHz was maybe a bit optimistic -- let's
> >> take then 60 MHz. At 60 MHz, the probability to have 11 or more dark
> >> pulses in a 100 ns window is 0.04 (less than 5%). So I will bump the
> >> threshold up to 11 photoelectrons or about 2.4 MeV.
> >>
> >> I propose a 1 MeV threshold coming out of HDGeant. Then in the BCAL
> >> response code in DANA I'll introduce some sampling fluctuations and
> >> make a second cut at 2.4 MeV.
> >>
> >> -Matt
> >>
> >>
> >> On Jun 8, 2007, at 1:12 PM, George Lolos wrote:
> >>
> >>> Hi Richard and Matt:
> >>>
> >>> We had a phone conference yesterday with SensL and they have just
> >>> tested the wafers for the arrays under Phase 1.
> >>> The 820L pixel type has demonstrated the following performance at
> >>> room temperature:
> >>>
> >>> Voltage above breakdown Pure PDE (no cross
> >>> talk or after pulsing) DR/pixel DR/
> >>> Array
> >>>
> >>> +
> >>> 1V
> >>> 7% 800
> >>> Hz 65 MHz
> >>> +
> >>> 2V
> >>> 11% 1700
> >>> Hz 137 MHz
> >>> +
> >>> 3V
> >>> 13% 3200 Hz
> >>> +
> >>> 4V
> >>> 17%
> >>> At a temperature of +5 C the dark rates are cut by a factor of
> >>> 2.6, so without an elaborate or expensive cooling we can bring this
> >>> down to around 53 MHz at 11% PDE. These then will be for Phase
> >>> 1. For Phase 2, the new Si process they have just implemented has
> >>> reduced the DR by a factor of just over 2 and they expect to
> >>> further improve and come down to that of the original Si treatment
> >>> that does not give good reproducibility of breakdown voltage.
> >>> Trenching will also reduce cross talk and keep the DR at the 1 P.E.
> >>> level.
> >>>
> >>> The bottom line is that Richard is correct that at the present time
> >>> 32 MHz at PDE values larger than have not been achieved. Are such
> >>> rates achievable for production? I believe they are but aiming at
> >>> a more realistic 50-60 MHz at PDE ~ 10-15% is the wiser route to go.
> >>>
> >>> I hope this helps,
> >>>
> >>> George
> >>>
> >>>
> >>> Richard Jones wrote:
> >>>
> >>>> Matt,
> >>>>
> >>>> The design goal of 32MHz may eventually be achieved, but this is
> >>>> not demonstrated. At the last meeting George agreed that 100MHz
> >>>> is achievable with what he has seen. I would believe something
> >>>> more like 150MHz @ 22C from what I have actually seen, but I am
> >>>> not working with Sensl modules. This depends a lot on
> >>>> temperature, but we agreed that we do not want to have to
> >>>> refrigerate the BCal readout very much.
> >>>>
> >>>> Richard J.
> >>>>
> >>>> Matthew Shepherd wrote:
> >>>>
> >>>>>
> >>>>> Hi All,
> >>>>>
> >>>>> Here's a proposal for setting a BCAL threshold so we can start to
> >>>>> refine the reconstruction a little bit.
> >>>>>
> >>>>> - take dark rate at 32 MHz (design goal from GlueX-doc-795) and
> >>>>> assume this is only single PE rate
> >>>>> - for a 100 ns window this means an average of 3.2 pulses per
> >>>>> window
> >>>>> - assume the fADC processing just generates a pedestal subtracted
> >>>>> mean and that dark rate (not electronics noise) dominates the
> >>>>> pedestal
> >>>>> - let's assume the DAQ can handle 5% occupancy in the BCAL
> >>>>> - if average is 3.2 dark pulses, the probability of having 7 or
> >>>>> more pulses in a window is 0.04
> >>>>>
> >>>>> --->> set threshold at 7 photoelectrons
> >>>>>
> >>>>> 7 photoelectrons * ( 26 keV_fiber / pe ) / 12% = 1.5 MeV energy
> >>>>> deposited in cell
> >>>>>
> >>>>> I propose we adjust the threshold to 1.5 MeV (down from 10 MeV)
> >>>>> and work from there. Of course this needs further study, and
> >>>>> validation through whatever bench studies, beam test, etc. etc..
> >>>>> My main goal is to get around the right order of magnitude so we
> >>>>> can make another pass at the reconstruction algorithm which will
> >>>>> behave very differently with this much lower threshold. Does
> >>>>> anyone see a serious flaw with this?
> >>>>>
> >>>>> -Matt
> >>>>>
> >>>>
> >>>
> >>>
> >>
> >>
> >
> > ( `,_' )+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=
> > ) `\ -
> > / '. | +
> > | `, Elke-Caroline Aschenauer =
> > \,_ `-/ -
> > ,&&&&&V Jefferson Lab +
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> > +=-+=-+
> >
>
>
( `,_' )+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=
) `\ -
/ '. | +
| `, Elke-Caroline Aschenauer =
\,_ `-/ -
,&&&&&V Jefferson Lab +
,&&&&&&&&: HALL-D 12C / F381 121-A Atlantic Avenue =
,&&&&&&&&&&; Mailstop: 12H5 Hampton, VA 23664 -
| |&&&&&&&;\ 12000 Jefferson Ave +
| | :_) _ Newport News, VA 23606 Tel.: 001-757-224-1216 =
| | ;--' | Mail: elke@jlab.org Mobil: 001-757-256-5224 -
'--' `-.--. | +
\_ | |---' Tel.: 001-757-269-5352 =
`-._\__/ Fax.: 001-757-269-6248 -
+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+