[Halld-physics] draft text of the eta-Primakoff proposal update
Ryan Mitchell
remitche at indiana.edu
Tue Nov 30 13:45:51 EST 2010
OK. I see. Thanks, Ryan
On Nov 30, 2010, at 1:41 PM, Gan, Liping wrote:
> Hi, Ryan,
>
> We did not see visible changes in the theta distribution with the
> magnet on, only the resolution become worse. Since those scattering
> electrons
> are almost parallel to the solenoid magnetic field, they will spiral
> through the center hole of the FCAL even with the magnet on.
>
> Liping
>
>
> ________________________________________
> From: Ryan Mitchell [remitche at indiana.edu]
> Sent: Tuesday, November 30, 2010 1:27 PM
> To: Gan, Liping
> Cc: Matthew Shepherd; GlueX Physics
> Subject: Re: [Halld-physics] draft text of the eta-Primakoff
> proposal update
>
> Thanks Liping,
>
> I see from figure 5 in the proposal update that the electrons are very
> forward. But doesn't that distribution change significantly if the
> magnetic field is on? Are the electrons still too forward to be seen
> by the FCAL?
>
> Ryan
>
>
> On Nov 30, 2010, at 1:18 PM, Gan, Liping wrote:
>
>> Hi, Ryan,
>>
>> Thanks for your suggestions. I Just want to comment on your question
>> "Is it clear that one couldn't do better with just the FCAL, perhaps
>> with the magnetic field on? "
>>
>> It would be a great idea if we could use FCAL alone to measure the
>> Compton cross section. The scattering electrons from the Compton
>> events are extremely forward at high energy (less than 1 degree at
>> experimentally accessible rate), however, the GlueX detector will
>> not have acceptance for those electrons. We detect the Compton
>> events by requiring the coincidence of scattering electron and
>> photon in order to measure the cross section at percentage level.
>> Therefore, it can not be done by using FCAL alone unfortunately.
>> With additional small ComCal calorimeter located further downstram
>> of the beamline, will help us resolve this problem without changing
>> the experimental setting.
>>
>>
>> Liping
>>
>>
>> ________________________________________
>> From: halld-physics-bounces at jlab.org [halld-physics-
>> bounces at jlab.org] On Behalf Of Ryan Mitchell [remitche at indiana.edu]
>> Sent: Tuesday, November 30, 2010 11:55 AM
>> To: Matthew Shepherd
>> Cc: GlueX Physics
>> Subject: Re: [Halld-physics] draft text of the eta-Primakoff
>> proposal update
>>
>> 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
>>>>>>>
>>>>>>>
>>>>>
>>>>>
>>>
>>>
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