[Olympus] momentum spectrum

[Brian S. Henderson]

Hello all,

To clarify, I would expect the MC for MWPCs only to look more like what 
is shown on the second slide of the document Stan sent around (and the 
addition of external bremsstrahlung would help to fill in the low 
momentum tail, as has been seen in the past).  On the first slide of 
what Stan sent around, you can see some results I ran yesterday for 
MWPC-only tracking.  As you can see, the real data momentum distribution 
looks more like we would expect than MC.  While the broadness is due to 
the low resolution of the MWPCs alone,  there is a shift in the 
peak/shape/broadening that indicates a problem in the MC for the MWPCs, 
most likely in the digitization stage.  While the MC I ran yesterday 
agrees with the distributions show by Kirril yesterday, I think the 
appropriate conclusion to draw is that the MWPCs are still not well 
modeled in the MC.

Since the agreement between data and MC used to be better (as I alluded 
to yesterday and as shown by the plot included from Yuri on slide 2 of 
what Stan sent), my main guess is that I introduced some sort of bug 
into the MWPC digitization when I changed things to account for the 
recent geometry changes.  I am currently re-examining the MWPC 
digitization and testing for possible problems.

Brian

On 05/13/2014 09:26 AM, Belostotski, Stanislav wrote:
> Dear Brian and colleagues,
> Thanks a lot for your plot.  In view of our Monday discussion, the 
> result is as expected.
> The broad Kirill's distribution is due to reconstruction done without 
> GEMs with MWPC only. The MWPC spatial resolution is about 0.5mm while 
> the total deflection of the lepton in the magnetic field  is 2. to 
> 2.5mm, i.e. momentum resolution (without GEMs) must be very poor.
> This has also been demonstrated by Yuri in his MC studies.
> I included Brian's plot in a the attached file where various variants 
> (with or without GEMs reconstruction) are presented.
> A good cross check is made.
> With best regards, StanB
>
> On 13.05.2014 14:43, Brian S. Henderson wrote:
>> Hello again,
>>
>> I have attached a set of plots that looks at the various reconstruction
>> parameters for MWPC only tracking for two combined electron runs (7909
>> and 7910) and two combined positron runs (7950 and 7951) with the
>> corresponding MC data sets.  The only thing like a cut applied was to
>> accept only the single best fit track per event (with very loose cuts on
>> the max chi^2 and number of iterations).
>>
>> As you can see, the momentum distributions from the MC look similar to
>> what you showed yesterday.  It looks like something has definitely
>> changed in the MC since I last used MWPC only tracking, so I apologize
>> for questioning your momentum distributions yesterday.  Oddly, the data
>> looks more like what I would expect than the MC (at least for the first
>> 10 plots which are left arm), especially the missing energy distribution
>> which peaks at around 250 MeV for the MC.  This makes me think that
>> there could be an issue in the way the MWPC digitization was changed to
>> correspond with the GDML changes made to fix the coordinate system
>> issues. It also could be that the estimate of the MWPC resolution
>> currently used in the digitization is not a good model.  I will take a
>> look at this right away this morning to see if I can figure anything 
>> out.
>>
>> Brian
>>
>> On 05/12/2014 12:59 PM, Suvorov, Kirill wrote:
>>> Hi Brian,
>>>
>>> Could you please send pictures of reconstructed momentum distribution
>>> for radiative generator (without GEM digitization) and tell what cuts
>>> did you use?
>>>
>>> best regards, Kirill
>>>
>>> p.s. We trying to understand why my pictures of momentum distribution
>>> are worse.