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Re: A proposal for setting a BCAL threshold




Hi all,

Also note that given an amount of cross talk, you can calculate the effect
on the rms. See Section 5.3 of GlueX-doc-795. For 10% cross talk, the
pedesal sigma increases by 11%.

Elton.


Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton@jlab.org
(757) 269-7625

On Fri, 8 Jun 2007, Elke-Caroline Aschenauer wrote:

> 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                                +
> > >  ,&&&&&&&&:       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                              -
> > >             +=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-
> > > +=-+=-+
> > >
> >
> >
>
>  ( `,_' )+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=
>   )    `\                                                  -
>  /    '. |                                                  +
>  |       `,              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                              -
>             +=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+=-+
>
>