[Primexd] [GlueX] Target installation plan

Thu Feb 28 18:12:35 EST 2019

Liping,

Great to hear you have good resolution on the beam spot in the transverse plane.  Simon can clarify but I think there is also the potential for a mild z dependence:  true beam axis not parallel to the lab z axis.

It will be nice to have this in the online monitoring plots.  My understanding based on discussion after the meeting is that Drew has put this into the monitoring plugin.

Matt

> On Feb 28, 2019, at 4:49 PM, Gan, Liping <ganl at uncw.edu> wrote:
> 
> 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
>> 
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> 
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