[Primexd] [GlueX] Target installation plan

Thu Feb 28 16:49:40 EST 2019

Matt,

If we project the electron and photon from a Compton event to the same plane perpendicular to the beam direction and draw a line through them. The intersections of those lines during the run will tell us the beam center position.

Liping 

-----Original Message-----
From: Primexd <primexd-bounces at jlab.org> On Behalf Of Shepherd, Matthew
Sent: Thursday, February 28, 2019 4:37 PM
To: Ashot Gasparian <gasparan at jlab.org>
Cc: primexd at jlab.org; andrsmit at jlab.org; Simon Taylor <staylor at jlab.org>; Mark Stevens <stevensm at jlab.org>
Subject: Re: [Primexd] [GlueX] Target installation plan

Ashot,

This whole discussion motivates another question.  Of course the Compton process itself is symmetric about the beam axis (not the detector axis).  Without tracking, how do you plan to control/monitor the beam axis?  We have seen throughout GlueX a consistent transverse displacement of the beam at the level of a few mm, but we get this through tracking.  We have seen it change occasionally in a run, presumably to changes in machine setup of the beam.

If such a change happens during the run, the acceptance for Compton will also change, and significantly on the scales you care about I think.

How do you plan to quantify this potential systematic uncertainty?

Matt

> On Feb 28, 2019, at 4:10 PM, Shepherd, Matthew <mashephe at indiana.edu> wrote:
> 
> Ashot,
> 
>> What we have is a Large asymetry.
>> I think we have to understand how to solve it to go forward with the 
>> data taking process.
> 
> 
> You solve the asymmetry by aligning your detector not with the beam line as you have done now but instead the FCAL beam hole.
> 
> Unfortunately, doing so means that you significantly change the acceptance of your detector.  And because of that you may want to reconsider taking the data you have collected already.
> 
> The cause seems pretty clear -- you just need a strategy that let's you make the measurement with acceptable systematic uncertainties.
> 
> I suspect you'll see the same effect in your December data also.
> 
> Matt
> 
> 
>> On Feb 28, 2019, at 4:06 PM, gasparan at jlab.org wrote:
>> 
>> 
>> Matt, before I go through your email and try to discuss, one thing we 
>> have to take care of is the real data.
>> We probably agree that in order to have better and usable data the 
>> acceptances need to be symmetrical. What we have is a Large asymetry.
>> I think we have to understand how to solve it to go forward with the 
>> data taking process.
>> 
>> let's discuss this in today's meeting.
>> 
>> Thanks,
>> Ashot
>> 
>>> 
>>> Ashot,
>>> 
>>> I don't think a survey of the beam line is needed.  I think you just 
>>> need to use the existing survey.
>>> 
>>> I realized that it completely explains your asymmetry.
>>> 
>>> As Justin noted, the Compton image on the CCAL is exactly as you 
>>> predict, just shifted by 2 cm.  What I neglected in my previous 
>>> message is that if you make a shift of CCAL by 1 cm you effectively shift the image by 2 cm.
>>> In your reconstruction, shifting CCAL to +x by 1 cm will make the 
>>> Compton occupancy go from -9 cm to +9 cm on the CCAL (instead of -8 
>>> cm to + 10 cm).
>>> 
>>> Now, if you need to shift CCAL by 1 cm, it means that, because of 
>>> the lever arm, the FCAL is shifted about 5 mm to +X.  This is 
>>> exactly as reported by Simon.  And there is no vertical offset, also 
>>> as reported by Simon.
>>> 
>>> Seems the conclusion is straightforward:
>>> 
>>> Your asymmetry of Compton events is not related to excess material 
>>> in the beam line, or bugs in reconstruction, it is byproduct of the 
>>> already known alignment of the FCAL with respect to the beam line.  
>>> Again, working with simulation done in the Hall D framework will demonstrate these effects.
>>> 
>>> Seems like you have two choices now:
>>> 
>>> * Align CCAL not on beam center but on FCAL hole center.  But then 
>>> you may want to retake Be data.
>>> * Live with existing alignment and explore systematics.
>>> 
>>> Matt
>>> 
>>> 
>>>> On Feb 28, 2019, at 3:48 PM, gasparan at jlab.org wrote:
>>>> 
>>>> 
>>>> Dear Matt and All,
>>>> 
>>>> At this stage it is clear that we should survey entire beam line, 
>>>> for sure including the FCAL (not only CCAL).
>>>> 
>>>> The question is what to do next.
>>>> 
>>>> Ashot
>>>> 
>>>> 
>>>>> 
>>>>> Liping,
>>>>> 
>>>>> Without survey I cannot definitively assert that it did not move, 
>>>>> but it would be really really really hard for the FCAL to make a 
>>>>> significant horizontal movement.  I just isn't that mobile.
>>>>> 
>>>>> Matt
>>>>> 
>>>>> 
>>>>>> On Feb 28, 2019, at 3:35 PM, Gan, Liping <ganl at uncw.edu> wrote:
>>>>>> 
>>>>>> Hi, Matt,
>>>>>> 
>>>>>> Do you know if FCAL position has been changed since 2015 survey?
>>>>>> 
>>>>>> Liping
>>>>>> 
>>>>>> From: GlueX-Collaboration <gluex-collaboration-bounces at jlab.org> 
>>>>>> On Behalf Of Simon Taylor
>>>>>> Sent: Thursday, February 28, 2019 3:23 PM
>>>>>> To: Ilya Larin <ilarin at jlab.org>; Shepherd, Matthew 
>>>>>> <mashephe at indiana.edu>; Ashot Gasparian <gasparan at jlab.org>
>>>>>> Cc: primexd at jlab.org; andrsmit at jlab.org; GlueX Collaboration 
>>>>>> <gluex-collaboration at jlab.org>; Mark Stevens <stevensm at jlab.org>
>>>>>> Subject: Re: [GlueX] Target installation plan
>>>>>> 
>>>>>> For what it's worth, according to the 2015 survey (I am not sure 
>>>>>> if the FCAL was resurveyed at a later date), the FCAL as a whole 
>>>>>> is off in x by about +5mm, but only a tiny amount off from zero 
>>>>>> in y.
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> In the attachment the highlighted numbers are z,x,y in meters.
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> Simon
>>>>>> 
>>>>>> From: GlueX-Collaboration <gluex-collaboration-bounces at jlab.org> 
>>>>>> on behalf of Ilya Larin <ilarin at jlab.org>
>>>>>> Sent: Thursday, February 28, 2019 2:58:38 PM
>>>>>> To: Shepherd, Matthew; Ashot Gasparian
>>>>>> Cc: primexd at jlab.org; andrsmit at jlab.org; GlueX Collaboration; 
>>>>>> Mark Stevens
>>>>>> Subject: Re: [GlueX] Target installation plan
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> Hi Matt,
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> according to the pictures the square pipe is asymmetrical vs beam 
>>>>>> line
>>>>>> 
>>>>>> and is most likely causing the "shade" on ComCal face.
>>>>>> 
>>>>>> Wondering if  FCAL is placed symmetrically vs beam,
>>>>>> 
>>>>>> that should mean that pipe doesn't exactly match FCAL hole.
>>>>>> 
>>>>>> The exact values from drawings would help and needed for MC
>>>>>> 
>>>>>> geometry db to get an exact acceptance.
>>>>>> 
>>>>>> If it is the case, that only mean we have to reduce ComCal
>>>>>> 
>>>>>> fiducial region for Compton events.
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> Thanks for pictures.
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> Ilya
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>> ÃzÃ',: GlueX-Collaboration 
>>>>>> <gluex-collaboration-bounces at jlab.org>
>>>>>> ÃÂ¾Ã',
>>>>>> ÃÂ¸ÃÂ¼ÃÂµÃÂ½ÃÂ¸ Shepherd, Matthew <mashephe at indiana.edu>
>>>>>> ÃzÃ',ÃÂ¿Ã'?ÃÂ°ÃÂ²ÃÂ»ÃÂµÃÂ½ÃÂ¾: 28 
>>>>>> Ã'"ÃÂµÃÂ²Ã'?ÃÂ°ÃÂ»Ã'Â
>>>>>> 2019 ÃÂ³. 12:49
>>>>>> ÃsÃÂ¾ÃÂ¼Ã'f: Ashot Gasparian
>>>>>> ÃsÃÂ¾ÃÂ¿ÃÂ¸Ã'Â: primexd at jlab.org; andrsmit at jlab.org; GlueX 
>>>>>> Collaboration; Mark Stevens
>>>>>> ÃÂ¢ÃÂµÃÂ¼ÃÂ°: Re: [GlueX] Target installation plan
>>>>>> 
>>>>>> 
>>>>>> Hi Ashot,
>>>>>> 
>>>>>>> On Feb 28, 2019, at 11:58 AM, gasparan at jlab.org wrote:
>>>>>> 
>>>>>>> Therefore, it would be extremely important to take pictures of 
>>>>>>> the
>>>>>> FCAL
>>>>>>> insertion part and post on some place to see, before our meeting 
>>>>>>> this evening.
>>>>>> 
>>>>>> 
>>>>>> I've posted pictures of the FCAL insert here:
>>>>>> 
>>>>>> https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2F
>>>>>> logbooks.jlab.org%2Fentry%2F3661206&data=01%7C01%7Cganl%40unc
>>>>>> w.edu%7Cb1a9771bc2594bbc311108d69dc4f3aa%7C2213678197534c75af2868
>>>>>> a078871ebf%7C1&sdata=zPHHfW6WpDrgP5OvWA7m5iHBL3q4kL1sq4HxWH1Q
>>>>>> pnE%3D&reserved=0
>>>>>> 
>>>>>> It looked today exactly as it did 5+ years ago when these were taken.
>>>>>> (I'm surprised you haven't taken a peek at it before as it 
>>>>>> defines the acceptance of your detector.)
>>>>>> 
>>>>>> The Plexiglas monitoring system is held in the groove on the 
>>>>>> upstream end.  Anything of any density should be clear of the 
>>>>>> inner opening in the tube.  From the darkroom all that is visible 
>>>>>> is what appears to be a thin tedlar cover on the upstream end.  
>>>>>> It is needed for a light seal or else there is light path from 
>>>>>> the hall into the darkroom via the beam pipe.
>>>>>> 
>>>>>> Matt
>>>>>> 
>>>>>> -----------------------------------------------------------------
>>>>>> ----
>>>>>> Matthew Shepherd, Professor
>>>>>> Department of Physics, Indiana University, Swain West 265
>>>>>> 727 East Third Street, Bloomington, IN 47405
>>>>>> 
>>>>>> Office Phone:  +1 812 856 5808
> 
> _______________________________________________
> Primexd mailing list
> Primexd at jlab.org
> https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmailm
> an.jlab.org%2Fmailman%2Flistinfo%2Fprimexd&data=01%7C01%7Cganl%40u
> ncw.edu%7Cb1a9771bc2594bbc311108d69dc4f3aa%7C2213678197534c75af2868a07
> 8871ebf%7C1&sdata=xnnkSinq3dw84FDXfhdY5bK8NLOctiXG6ga1p80jZRk%3D&a
> mp;reserved=0