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Re: A proposal for setting a BCAL threshold
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
> >>>
> >>
> >
> >
>
>
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