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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
>>>>>
>>>>
>>>
>>>
>>
>>
>
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