[Olympus] Status of results and timeline

[Norair Akopov]

On Thu, 11 Aug 2016, Alexander Kiselev wrote:

>   Dear Norik,
Dear Alexander,
>
>>  Now concerning the Q2 quality plot, which has a very clear interpretation,
>>  and it puzzles me that nobody could understand it, because it is basic
>>  relativistic kinematics from third year college physics, but I will
>>  explain it in more detail:
>>  If you have already selected the elastic events (full set of cuts,
>>  including the PID applied), then by making a binning over the lepton angle
>>  you can define the average Q2 (<Q2>) (also stat. uncertainty for <Q2>) for
>>  a certain angular bin. Here you have two opportunities how to define the
>>  Q2: with the only lepton/proton measured angles (in our case preferable
>>  due to good angular resolution) - Q^2_{exp}; with the measured angles and
>>  momentum (worse due to bad momentum resolution) - Q^2{obs}.
>>  I also defined Q^2_{TH} using well known expressions for a scattered
>>  lepton energy expressed via angle, with the beam energy  E_b=2010 MeV.
>>  Then I introduced the ratios: <Q^2_{obs}>/Q^2_{TH}(<\theta>), also
>>  <Q^2_{exp}>/Q^2_{TH}(<\theta>). I assumed that in case we are really
>>  selected the elastic events both ratios should be very close to unity,
>>  this is, again basic physics.
>
>  I believe I understand what is plotted, but I have difficulty to interpret 
> this. Am I right, that background contribution in each theta bin is properly 
> subtracted when you calculate Q^2 of "true" ep-elastic events by either of 
> the two methods?
I supposed to make this subtraction bin per bin (now I have no enthusiasm 
to continue with any studies..), BUT even W/O the 
background subtraction just based on central limiting theorem we have 
quite stable values for averaged over the angular bin for both: Q^2_{obs} 
and Q^2_{exp}, in fact what is Q^2_{obs}:
Q^2_{obs} = (P_z^{lep}+P_z^{pr})*P^{lep}*sin^2(\theta_{lep}/2)
note on this stage we already know (PID is applied) who is who, this is 
important due to the formulae we used is not symmetric in respect to angle/momentum of 
lepton/proton (BTW as well the definition of Q^2_{exp} is also assumees to 
know who is who in sense of the angles used)

  Then (since there is obviously no bin-to-bin 
migration in > theta at this point) the message is that momentum
> measurement accounting screws up Q^2 calculation? And the screw up is
> different for e+ and e- samples? If so, is this of any significance, given 
> that Q^2 is calculated using proton theta only in both Brian's (thesis p.235)
> and Rebecca's (thesis p.150) analyses (and both red and blue open circles on 
> your plot indeed show sort of constant and very similar behaviour over theta 
> within errors)?

Now what we can conclude from destroied ratio of 
Q^2_{TH}(<\theta_{lep}>)/<Q^2_{obs}> ?

Just a trivial fact, that we still have not ideal TTD algorithm, which has 
been essentially improved, I would say before the last improvement P_z 
momentum balance has a bias on the order of 100 MeV, now it's just ~30-40 
MeV (depending on angular bin), which 
is much better, BUT still not enough to satisfy the strong elastic 
kinematics.. I never beleived for a statements like "any bias in p_z 
momentum is due to bad momentum resolution", bad resolution can caused 
larger \sigma for a P-z momentum balance spectra, BUT not shift the 
central value..

Unfortunately, I did not recognized things related to our discussion on 
pages 235 (Brian) and 150 (Rebecca) in their theses?

My general comment remains the same: we should not expect that all 
potential co-authors will read in details all theses, instead we have to 
provide much shorter release report with all important analysis issues:

- used cuts/binnings
-PID scheme
-description of the cross check procedure and results
- detailed description of the systematics estimation

collected in ONE document.


Best regards,
Norik










>
>   Best regards,
>     Alexander.
>
>