[Halld-physics] draft text of the eta-Primakoff proposal update

[Matthew Shepherd]

Hi Ashot,

I'm not too concerned about comp-cal radiation damage since we know lead tungstate is tuff stuff.

It seems like there is about 5-6 orders of magnitude difference between my rate estimate and yours.  Maybe the high energy showers are really this rare, but it should be checked.  I imagine GlueX design has a lot more conversion material between the target and the FCAL than was present in PrimEx.

One other question:  am I correct that that your cross section measurement depends on measuring the Compton scattering rate to the 1% level.  This means that you need to know the both the acceptance (through the FCAL beam hole) and the absolute detection efficiency of these Compton events at the 1% level.  Is it foreseen how to do this?  This seems like an extraordinary challenge to calibrate -- especially the electron efficiency as the electron will be going through a region of the GlueX detector (with the field off) that is not very well understood.

Cheers,

Matt


On Nov 30, 2010, at 11:29 AM, Ashot Gasparian wrote:

> 
>  Hi Matt,
> 
>  I probably forgot in my previous email that that number
> (1-3 KHz) is for upper energy cut, (total energy deposition)
> > than ~3 GeV. For sure, the rate will go up as we make this
> threshold lower, but we are also planning to have a higher
> energy region for the trigger.
> Other than that I think your numbers are correct. As much as
> the radiation is concerns, we do monitor each detector cell by
> light monitoring system and also by the pion mass. We did not see
> any sizable shift in gains during our experiments where we had
> rather intensive photon beams.
> 
> Thanks,
> Ashot
> 
> 
> .............................................................
> Ashot Gasparian                    Phone:(336)285-2112 (NC A&T)
> Professor of Physics
> Physics Department                       (757)-269-7914 JLab
> NC A&T State University              Fax:(757)-269-6273 JLab
> Greensboro, NC 27411               email: gasparan at jlab.org
> .............................................................
> 
> 
> On Tue, 30 Nov 2010, Matthew Shepherd wrote:
> 
>> 
>> Hi Ashot,
>> 
>> It seems that the total count rates you cite 1-3 kHz are orders of magnitude away from what we are used to thinking about.
>> 
>> Take a look at the first plot on this page:
>> 
>> http://www.jlab.org/Hall-D/software/wiki/index.php/FCAL_Backgrounds
>> 
>> It is a bit dated, but should still be approximately correct.  There you can see count rates *per block* in the region next to the beam hole of 3 MHz.  It is significantly higher inside the beam hole and will probably be higher yet behind the calorimeter where you will get beam interactions with the walls of the hole in the FCAL.
>> 
>> One very important note in this:  we are counting energy deposition all the way down to 2 MeV.  This is relevant for radiation damage, but not for tagging high energy particles like you would like.  We need to check the rates at high energy.
>> 
>> My naive estimate based on these numbers would be a total count rate in the CompCal of a couple hundred megahertz.
>> 
>> -Matt
>> 
>> On Nov 29, 2010, at 7:00 PM, Ashot Gasparian wrote:
>> 
>>> 
>>> Hi Matt,
>>> 
>>> Thanks for raising good questions. Let me try to come up with
>>> my thoughts on your questions:
>>> 
>>> 1) the suggested CompCal detector is actually a very small copy
>>>   of existing HyCal. It will have 16x16 PbWO4 crystal detectos
>>>   (with a size: 32x32 cm^2) and central 2x2 crystals removed
>>>   (that makes a 4x4 cm^2 hole in the center, like the HyCal is)
>>> 2) the expected count rates: we had some MC results done in last
>>>   year for the CompCal detector also. My recollection is that we
>>>   did not finish it on the level to estimate the count rate. It is
>>>   in plan for the December, but we have a direct experimental data
>>>   from the two PromEx-I and PrimEx-II experiment. There we had a
>>>   similar detector with the similar beam hole and in intencive
>>>   photon beam: Ie=110 nA, on 10^4 r.l. radiator, no collimator on
>>>   beam, gives ~ 7x10^7 eq. photons/sec., 5 to 10 r.l. physics targets
>>>   in beam and the calorimeter located on ~7.5 m down from the targets.
>>>   Our rates in the proposal are also calculated for a similar beam
>>>   conditions. The total HyCal rate (for the sum) was from 1 KHZ to
>>>   3 KHz depending on beam tune. With these rates we had it as the
>>>   primary trigger in the experiment with a good physics results.
>>>   The CompCal will be all the same only the outer dimension much
>>>   smaller. Based on our experimental reasults, I do not expect any rate
>>>   problem with this design. Though, we will try to finish the MC
>>>   simulations left from the last year.
>>> 3) for the document for CompCal: I agree with you we need a draft of
>>>    technical design report for this detector. I will try to do that in
>>>    the comming weeks and post it in the GlueX wiki.
>>> 
>>> Hope these are answering to your questions in some ways. Please let
>>> me know if some of them needs more discussions.
>>> 
>>> Thanks,
>>> Ashot
>>> 
>>> 
>>> .............................................................
>>> Ashot Gasparian                    Phone:(336)285-2112 (NC A&T)
>>> Professor of Physics
>>> Physics Department                       (757)-269-7914 JLab
>>> NC A&T State University              Fax:(757)-269-6273 JLab
>>> Greensboro, NC 27411               email: gasparan at jlab.org
>>> .............................................................
>>> 
>>> 
>>> On Mon, 29 Nov 2010, Matthew Shepherd wrote:
>>> 
>>>> 
>>>> Hi Ashot,
>>>> 
>>>> Do you have a document that outlines the details of CompCal
>>> including simulations of the background?  Has such a technique
>>> been used for other experiments?  What is the geometry of this
>>> detector -- does it have a beam hole?  I imagine count rates
>>> for this detector must be incredibly high.
>>>> 
>>>> -Matt
>>>> 
>>>> On Nov 29, 2010, at 5:53 AM, Ashot Gasparian wrote:
>>>> 
>>>>> 
>>>>> Dear Hall D Collaborators,
>>>>> 
>>>>> We are required to submit a short update for the eta-Primakoff
>>>>> proposal to this upcoming PAC37 for the beam time assignment and
>>>>> scientific rating.
>>>>> The proposal was approved a year ago by PAC35.
>>>>> 
>>>>> The first draft of the suggested update is in the attachment of
>>>>> this email. The submission deadline is on this Wednesday, so you
>>>>> will have a few days to send your critical suggestions and questions
>>>>> to us to make this document better for the submission.
>>>>> 
>>>>> Thank you for your participation and valuable support,
>>>>> Ashot, Liping
>>>>> 
>>>>> 
>>>>> 
>>>>> .............................................................
>>>>> Ashot Gasparian                    Phone:(336)285-2112 (NC A&T)
>>>>> Professor of Physics
>>>>> Physics Department                       (757)-269-7914 JLab
>>>>> NC A&T State University              Fax:(757)-269-6273 JLab
>>>>> Greensboro, NC 27411               email: gasparan at jlab.org
>>>>> .............................................................
>>>>> <eta_update_PAC37_v3.pdf>_______________________________________________
>>>>> Halld-physics mailing list
>>>>> Halld-physics at jlab.org
>>>>> https://mailman.jlab.org/mailman/listinfo/halld-physics
>>>> 
>>>> 
>> 
>>