[Halld-physics] draft text of the eta-Primakoff proposal update
Ryan Mitchell
remitche at indiana.edu
Tue Nov 30 11:55:41 EST 2010
Hi,
To add just a little to Matt's question...
> 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.
Is it clear that one couldn't do better with just the FCAL, perhaps
with the magnetic field on? The acceptance for Compton events must
decrease using just the FCAL and there is probably more background
since you won't be able to cut as tightly on acoplanarity. But it
seems you would be able to almost completely cancel the detection
efficiency systematic errors by looking at the ratio of the eta
Primakoff to Compton rates. Anyway, it's not obvious to me which
route would result in the lowest overall systematic errors...
Ryan
> 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
>>>>>
>>>>>
>>>
>>>
>
>
> _______________________________________________
> Halld-physics mailing list
> Halld-physics at jlab.org
> https://mailman.jlab.org/mailman/listinfo/halld-physics
More information about the Halld-physics
mailing list