[Olympus] experiment MC comparison for MWPC lumi

Sun Aug 26 08:28:11 EDT 2012

Dear Michael, Jan, and all,
I agree that the  results are promising, however the numbers obtained 
are by far not the final ones.
To answer to Michael's question, there are some considerations below.
The detection efficiency is C=C_geom x C_trig x C_track,
here C_track is overall track  reconstruction efficiency including MWPC 
digitization. As Jurgen  mentioned last Friday, number of MWPC tracks 
surpasses those of GEM by some 30% same track reconstruction program 
being used. It is not yet certain that the ep elastic scattering tracks 
only were selected such that   C_track (exp) could have been both larger 
and less than 1.
  In the MC, to calculate the lumi count rate,  we find the C_geom and 
averaged over MWPC1-3 acceptance cross section,  assuming that within a 
MWPC sensitive volume detection efficiency is constant (=1), as well as 
   C_trig= C_track=1.
Next step in the MC is to include digitization and track reconstruction 
program  in the same way as the latter   treats an experimental data 
sample,   while  C_trig is  to be experimentally determined.
In the exp data analysis joint GEM/MWPC track reconstruction, associated 
  proton track inclusion  and additional kinematic cuts to make as clean 
as possible the final data sample  are soon to come.
Then we hopefully come to the final conclusion.
With best regards StanB

On 24.08.2012 17:36, Michael Kohl wrote:
> Dear Stan, all,
> indeed this is a milestone.
> I suppose the efficiencies were all assumed to be unity, which adds in
> some uncertainty, too?
> Best regards
>      Michael
>
>
> On Fri, 24 Aug 2012, Jan C. Bernauer wrote:
>
>> Dear Stan,
>>
>>   this is excellent news. If I understand correctly, it means that the
>> new target has very close to "full" density and that the luminosity
>> calculation from slow control works. The remaining discrepancy is
>> certainly realistic just from the uncertainty in the slow control lumi.
>>
>> Best,
>> Jan
>>
>>
>> On 24.08.12 08:51, Belostotski, Stanislav wrote:
>>> Dear collegues,
>>> I am glad to report on a good agreement between MC (see the message
>>> attached below) and experiment for  MWPC Lumi monitor track
>>>    count rates ( taken @ 1 inverse nb, one arm):
>>>
>>>            in bending   out bending
>>> MC        6.55           11.52
>>> EXP       7.37           13.82
>>>
>>> The EXP track numbers were obtained  using Jan's track reconstruction
>>> program applied to MWPC hits for runs 4162 (inbend.) and 4137(outbend.),
>>> respectively.
>>> Statistical errors are negligible in both cases. As for systematics,
>>> there is some room to better determine the experimental numbers (to
>>> attach the proton tracks) as well as to finalize the MC calculations.
>>> Proceeding from above, it can be at least stated that our estimation of
>>> luminosity/target density looks quite reasonable and extracted lumi
>>> track data sample can be really used for lumi monitoring.
>>> With best regards StanB
>>>
>>>>
>>>>
>>>> On 23.08.12 08:46, Belostotski, Stanislav wrote:
>>>>> Dear Jan and all,
>>>>> having analyzed the MC file I found out that MWPC sensitive area is
>>>>> wrongly described: the sensitive area  given in MC is 15.5x15.5cm**2
>>>>> while  it is  10.5x10.5cm**2. This results in  higher count rate
>>>>> obtained from MC using MWPC tracks. Also, electron scattering angle
>>>>> distribution is twice wider then expected.Could you (Jan)  please
>>>>> correct that by inserting 10.5x10.5cm**2.
>>>>> The latter number is good enough as taken proceeding from experimental
>>>>> hit distribution and corresponds to MWPC drawings.
>>>>> The distance from the I.P. (269cm) is correct.
>>>>> In ideal case (point like target, no secondary re-scattering, no
>>>>> magnetic field) we have
>>>>> solid angle=1.52x10**-3 sr (one arm),
>>>>> the cross section found from MC, no magnetic field,   is 6206nb/sr so we
>>>>> end up with the
>>>>> integrated cross section 6206nb/sr x 1.52x10**-3 sr = 9.43 nb
>>>>>      which is equal to the count rate at integrated luminosity of
>>>>> 1/nb. For
>>>>> the in bending /out bending magnetic field I have (preliminary) obtained
>>>>> 6.55nb and 11.52nb, respectively, the numbers close to that obtained by
>>>>> Axel (not forget a factor of 2 for two arms). For the final numbers we
>>>>> need to generate two MC files (magnetic field +-) with correct MWPC
>>>>> dimensions. However I believe that the above numbers are very close to
>>>>> reality.
>>>>> With best regards StanB
>>>>>
>>>>> _______________________________________________
>>>>> Olympus mailing list
>>>>> Olympus at mit.edu
>>>>> http://mailman.mit.edu/mailman/listinfo/olympus
>>>>>
>>>>
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>>>
>>
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>
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