[Olympus] Talk on Monday

[Michael Kohl]

Dear Norik,

at large theta_e the yield is expected to go down fast, but I agree that 
you might cut into the signal at large angle if is a constant cut tuned 
with the yield at forward angles where the statistics is high.

For the polar angle cut it would be good to plot the difference
\theta_pr - f(E_0,\theta_e^{WC}), where f provides the proton angle from 
the electron angle using elastic kinematics.
This angular resolution likely varies a lot with the angle because the 
protons at large angles correspond to low momentum hence suffer more 
multiple scattering and energy loss. So in principle the angular 
resolution should become better at large theta_e. However the lepton also 
becomes softer and this may make the resolution actually worse.

I recommend to plot the measured and calculated angle difference for each 
theta_e bin like your *_resol.pdf, but for the angle difference, then 
parametrize the cut ...

It would also be worthwhile to monitor the difference in lepton and proton 
vertex for each of these bins.

Best regards
   Michael


On Wed, 12 Feb 2014, Norair Akopov wrote:

>
> Dear Michael,
>
> I added the polar angles correlation cut and produced new plots, which are 
> located again on:
>
> http://www.desy.de/~akopov/Olympus_Monday_Meeting
>
> you can compare the old plots with the momentum resolution at different 
> \theta_e angular bins: electron(positron)_resol.pdf done W/O applied polar 
> angles correlation cut with the new plots: electron(positron)_resol_new.pdf 
> where this cut is applied. On the lower right panel (\theta_e&\theta_pr 
> double plot) you can see that this wide background area seen on old plots is 
> now almost removed.
> The meaning of applied cut should be clear from the plots: 
> electron(positron)_theta_q2.pdf,
> where the comparison of \theta_e and \theta_pr distribution as well the Q2 
> dsitributions are plotted with and W/O this additional cut applied.
> At any place I'm writing e.g  \theta_pr=f(E_0,\theta_e^{WC}) I mean that f() 
> is just expression based on elastic kinematics conditions.
>
> You can see that background clearly seen for angular distributions (at high 
> angles for lepton and at low angles for proton) W/O this cut applied is 
> essentially suppressed after the cut was applied.
>
> Then I estimated the rate of expected selected (close to elastic) events 
> sample with all cuts described in my talk W/O polar angle correlatrion cut 
> and with. This is effi.pdf file, where you can see, that unfortunately with 
> this additional cut the expected staistics at high \theta_e angles, where we 
> should reach the smallnest values of \epsilon is essentially decreased..
>
> I'm now thinking on another form to introduce the polar angles correlation 
> cut to select the data. It seems the used ratio of 
> sin(\theta_pr^{WC})/sin(\theta_pr=f((E_0,\theta_e^{WC}) to be close to unity 
> within 3 \sigma is too strong.
>
> Best regards,
>
> Norik
>
>
>

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