[Halld-physics] draft text of the eta-Primakoff proposal update
Ashot Gasparian
gasparan at jlab.org
Tue Nov 30 12:30:16 EST 2010
Hi Matt,
The total energy cut in HyCal was > 3 GeV, under this condition
the rate in HyCal was from 1 to 3 KHz and it made the trigger in the
past experiment. For sure, if we go down to 3 MeV this rate will be
many orders of magnitude higher.
About the material between the target and FCAL/ComCal: that is right,
here in my calculations I assumed it is just a He gas (like in PrimEx).
I am putting some realistic number of material in my GEANT code now
to run it again. The expected result is that the co-planarity resolution
in Fig. 3 will go up for a few more degrees (not more). We can live with
that in the experiment.
About the Compton Cross section and the accepatnce: Yes that is right,
since this process is for the verification (not for normalization) of
the primakoff cross section, we need it on the same accuracy level.
That is to say that we will need to know the acceptances on the same
level. Yes, there are difficulties on this measurements, but they are
all solvable. For the geometrical acceptances, the design of the CompCal
is to cover the central hole of the FCAL. That is we will have the
coordinates measured with a ~1 mm level. With that we would be able to
cut the more sensitive areas off from the geometrical acceptance. This
is how we do in our PrimEx experiment and we are in process of Compton
cross section publication.
There was one more good question about the possible reflection of
electrons from the FCAL hole structure. Yes, we agree there is an issue
here to look, but there are several ways to come up with solutions also.
In our experiment, with this configuration, we will have several very
strong cuts for the Compton event selection: the energy conservation
is already a strong selections for those type of events (delta energy is
~ 120 MeV). Further, the angle/energy correlation is another one.
From the other hand, This kind of situation we have in many places in our
experimental setup also. I agree, here it is more emphasized.
About the electron detection efficiency: yes, agree it is not solved yet.
We do that in the PrimEx experiment by moving the HyCal in 3d ways around
the low intensity beam. There are some other ways we can do it with the
GlueX, we need to work on this part. You are right.
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,
>
> 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
>>>>>
>>>>>
>>>
>>>
>
>
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