Re: comment on simulation section

["Kornicer, Mihajlo" <mikornic@indiana.edu>]

Hi all,

just one comment regarding the pi0 mass resolution from eta-pi0 events:
- the pi0 width when two photons are in the BCAL is ~9 MeV,
   which is close to what Alex reported. The width is different than
   when one generates pi0 flat in momentum-angle space.
- the pi0 width with two photons in the FCAL is 5.5 Mev
   because current FCAL simulation lacks the 3.6% floor term, which is
   dominant for high energy photons.

Regards,
Mihajlo

>
> Hi Elton,
>
> Thanks much for the comments.  I have also earlier this evening
> talked  with Elke on the phone about her comments and we agreed on
> places  where clarity can be improved.  In making revisions, I will
> try to  incorporate your other comments on the text.
>
> I want to quickly try to address a few of the substantial ones:
>
>> page 11, bottom line, vertex errors
>> Assuming the vertex position error is the 'size of the target  (30cm)' for
>> reconstruction seems to be very pessimistic. Does this uncertainty  in the
>> vertex position influence all the invariant mass plots? Should it be
>> updated (even artificially) by assuming a charged particle z-position
>> resolutions?
>
> What matters for the sake of the invariant mass plots is whether the
> true vertices are spread in z throughout the target.  Maybe Mihajlo
> can provide a quantitative answer to how much, if any, broadening of
> the peak, gets induced by the spread in actual vertex position.
>
> To clarify what we did:  In reconstruction all vertices are assumed
> to  originate from the center of the target (of course this will be
> refined once an event vertex can be better determined from charged
> particles).  The uncertainty assumptions are needed to construct the
> error matrix which is important for kinematically fitting the the
> event -- here we went with what was the actual uncertainty currently
> in the simulation, i.e. the physical size of the target.
>
>> page 15, figure 11, question
>> Do we understand why the resolutions in the FCAL are much better  than the
>> resolutions in the BCAL? In the introduction Alex plots pi0 and eta  widths
>> and there seems to be little difference between FCAL and BCAL. What is
>> different? If we know this we should add a note to the text. (Could  it be
>> the vertex resolution? see above).
>
> This is a fascinating question that we picked up on late last week
> and  Mihajlo has worked on to sort out.  We think this is actually
> just due  to the kinematic "bias" for the types of events FCAL and
> BCAL accept.   While both have comparable energy resolution, and Alex
> has shown this  is the key factor in determining pi^0 and eta width,
> the BCAL is  biased towards catching softer more forward particles.
> In that front  part of the BCAL leakage is an issue and the energy
> resolution in  probably worse.  The FCAL typically gets nice high
> energy photons that  can be well measured.
>
> The term that drives the mass resolution goes like:  A*sqrt( 1/E1 +
> 1/ E2 ) where E1 and E2 are photon energies and A is the statistical
> term  in energy resolution (the number that is roughly the same for
> BCAL and  FCAL).  For this eta pi^0 channel Mihajlo made a plot of
> this term in  the BCAL and FCAL for etas and pi0s:
>
> http://dustbunny.physics.indiana.edu/~mikornic/GlueX/CalRew08/sigmaM_Afactor_pi0.eps
> http://dustbunny.physics.indiana.edu/~mikornic/GlueX/CalRew08/sigmaM_Afactor_eta.eps
>
> In both cases the BCAL with comparable energy resolution to FCAL is
> biased towards more poorly measured pi^0's and eta^'s.  So, I think
> the interesting bottom line is that one doesn't get comparable eta
> and  pi^0 widths in the BCAL and FCAL by simply matching their
> average  energy resolutions.  One has to consider several other
> things like:   position dependence of energy resolution in BCAL and
> the fact that  BCAL is biased towards softer photons.  When these are
> considers one  would like a much better energy resolution in the BCAL
> to match  reconstructed pi^0 width in the FCAL.  Of course this
> statement  probably also depends somewhat on the physics channel.
>
> Mihajlo's results are rather fresh and we should compare also with
> Alex's parametric studies to try to understand  exactly what
> differences are (after all Alex is likely simulating real event
> kinematics also).  We will talk tomorrow and try to address this
> somewhat softly in the text.  It is clear we will want to have a
> prepared answer since this is kind of an obvious question.
>
>> page 23, figure 20 (right)
>> It is hard to see the data symbols. If I read them correctly there  seems
>> to be substantial false P-wave found for masses around 0.9 GeV  (about 20%)
>> which seems to be quite large. Symbols in different colors would  help see
>> what is plotted, but there should be a comment on the amount of  false
>> resonant P-wave.
>
> Noted, this plot was meant to be "proof of principle" that we
> actually  have amplitude fitting code in such a shape to begin to
> look at these  things.  I agree there appears to be some P-wave
> leakage and all of  this needs further study.  I was hoping to just
> demonstrate that our  technology (both in generating and fitting
> amplitudes) has matured  enough to be at a stage to begin to do these
> types of tests.  I can't  say anything more substantive about P-wave
> leakage other than really  what is in the caption and text: that this
> is the type of thing we are  going to be looking at.  If you feel
> this plot is a distraction, I'm  happy to remove it.
>
> Cheers,
>
> -Matt
>
>
>