[Olympus] acceptance of MWPS lumi monitor

[Belostotski, Stanislav]

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