[Moller_pion_bg] MOLLER Pion Background Phone Meeting Friday 9 am

Mon Mar 20 17:34:53 EDT 2017

Hi KK,

Why do you think it looks "unusual" as a QE curve? That is, in fact, the QE
curve determined by Peiqing for the Electron Tube 9312WKB 5 inch PMTs used
by Qweak. There's no input from Cherenkov processes in that curve at all.

It is very similar to the Photonis XP4500 series (XP4572) 5 inch PMTs used
by G0, BLAST, and now the SHMS Gas Cherenkov. (What's missing is the
borosilicate glass in front of the cathode, which is modeled separately in
Qweak and lowers the cutoff to 250 nm. For the MOLLER pion detector I
didn't assume we'd get fancy PMTs windows, just lime glass, so the cut-off
is different in the figs below.)

Here's the ET brochure figure, the relevant line is (basically) W:

[image: Inline image 1]

Since QE = radiant sensitivity / wavelength, you should look at the angled
y-axis values. That introduces a sharper cut-off with increasing wavelength
(1/lambda).

Anyway, the QE(lambda) is probably the most justified choice in the entire
pion detector. Everything else, from size to angles to materials, is still
undetermined. Let's focus on that instead of the PMT QE curve.

Finally, I find that geant4 is somewhere on the continuum between "general
instincts" and data ;-) It's probably somewhere between geant3 and data :-)
It is the best collection of physics modeling we have, but it is still a
computer program: garbage in, garbage out. In my experience, the garbage is
more likely to come from the user, not from geant4 :-)

Cheers,
Wouter

On Mon, Mar 20, 2017 at 4:55 PM, Krishna Kumar <krishna.kumar at stonybrook.edu
> wrote:

> Okay, so the efficiency curve vs Lambda may or may not make sense. If it
> is the efficiency curve due to photocathode QE, then that curve is unusual.
> If it is the 1/lambda^2 cherenkov distribution, then there is a cutoff
> below 250 nm. Perhaps this is the product of the two? That would perhaps
> make sense, but then it would be good, as a cross-check, to look at both
> curves (QE curve and raw cherenkov distribution) individually.
>
> My general instinct is that if one doesn’t drill down into Geant and
> ensure that the physics makes sense, we are liable to get burned….
>
> Cheers, KK
>
> On Mar 20, 2017, at 4:47 PM, Wouter Deconinck <wdeconinck at wm.edu> wrote:
>
> Hi KK,
>
> Sorry, I may not have been very clear about this. This is the PMT
> efficiency curve that is an INPUT to the simulation. It has nothing to do
> with the lucite or air emission or absorption spectrum. But, it does mean
> that any photon energy spectrum at the photocathode will be convoluted with
> this (can be taken out trivially, of course, for any new simulations).
>
> The absorption spectrum for lucite is INPUTs as well (although to be fair
> all previous results were obtained with a fixed absorption length of 1 m to
> cut down on infinitely bouncing rays). Here's what we'd use for a more
> realistic lucite simulation.
>
> <image.png>
>
> I think technically this data is for quartz, not lucite, but it's
> qualitatively similar to lucite data I did find but didn't digitize (in
> particular sharp transmission cut-off below 350 nm).
>
> As for air, we do not include any optical absorption currently (though we
> do include Cherenkov radiation, n = 1.000292).
>
> Cheers,
> Wouter
>
> On Mon, Mar 20, 2017 at 4:19 PM, Krishna Kumar <
> krishna.kumar at stonybrook.edu> wrote:
>
>> Okay, this is pretty conservative. We can do better than this between 200
>> and 300 if it becomes an issue, but you might decide you don’t need it,
>> which will save us money. I wonder why it cuts off though? If you didn’t
>> explicitly put in a photocathode QE curve, what physics in G4 cuts it off?
>> If it is gas physics, it would start cutting off below 200, not below 250.
>> Is the scintillator material transparent below 250 or not? I don’t recall
>> this from my prior experience. KK
>>
>> On Mar 20, 2017, at 4:08 PM, Wouter Deconinck <wdeconinck at wm.edu> wrote:
>>
>> Hi all,
>>
>> Since it came up in MOLLER pion detector simulation discussions last
>> Friday, here is the efficiency curve of the photocathode in the pion
>> simulations. UV photons are definitely not registered below about 230 nm.
>>
>> <image.png>
>>
>> Since someone will ask: from the course code I think it uses linear
>> interpolation, constant value extrapolation outside the given range. So
>> it'd make sense to add a zero efficiency point on both sides of the range.
>>
>> Cheers,
>> Wouter
>>
>> On Tue, Mar 14, 2017 at 3:20 PM, Kurtis Bartlett <kdbartlett at email.wm.edu
>> > wrote:
>>
>>> Hello Everyone,
>>>
>>> As a reminder to the members of the MOLLER Pion Background/Detector
>>> working group, there will be a meeting this week on Friday at 9am.
>>>
>>> The agenda for the meeting can be found on the MOLLER wiki:
>>>
>>> https://hallaweb.jlab.org/wiki/index.php/MOLLER_Pion_Backgro
>>> und_Meeting_Friday%2C_March_17%2C_2017_9:00am_EST
>>>
>>> Feel free to add any other points of business to the wiki.
>>>
>>> Here is the Bluejeans call information:
>>>
>>> URL: https://bluejeans.com/624029893
>>>
>>> Phone Number: 1-888-240-2560
>>>
>>> Meeting ID: 624029893
>>>
>>> Hope to see everyone there.
>>>
>>> Cheers,
>>>
>>> Kurtis
>>>
>>>
>>> --
>>> Kurtis D. Bartlett
>>>
>>> PhD. Research Candidate
>>> College of William and Mary Physics Department
>>> kdbartlett at email.wm.edu
>>>
>>> _______________________________________________
>>> Moller_pion_bg mailing list
>>> Moller_pion_bg at jlab.org
>>> https://mailman.jlab.org/mailman/listinfo/moller_pion_bg
>>>
>>>
>>
>>
>> --
>> Wouter Deconinck
>> Assistant Professor of Physics
>> College of William & Mary
>> Office: Small Hall 343D
>> Phone: (757) 221-3539
>>
>> Emails sent to this address are subject to requests for public review
>> under the Virginia Freedom of Information Act.
>> _______________________________________________
>> Moller_pion_bg mailing list
>> Moller_pion_bg at jlab.org
>> https://mailman.jlab.org/mailman/listinfo/moller_pion_bg
>>
>>
>>
>
>
> --
> Wouter Deconinck
> Assistant Professor of Physics
> College of William & Mary
> Office: Small Hall 343D
> Phone: (757) 221-3539
>
> Emails sent to this address are subject to requests for public review
> under the Virginia Freedom of Information Act.
>
>
>
> _______________________________________________
> Moller_pion_bg mailing list
> Moller_pion_bg at jlab.org
> https://mailman.jlab.org/mailman/listinfo/moller_pion_bg
>
>

-- 
Wouter Deconinck
Assistant Professor of Physics
College of William & Mary
Office: Small Hall 343D
Phone: (757) 221-3539

Emails sent to this address are subject to requests for public review under
the Virginia Freedom of Information Act.
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