Hi Nevzat,
What seems strange to me is that when you apply my patch
correction and re-fit your coeefficients, is that bith the
W peak and EBeam for ep events shift noticeably, even for
inbending runs like 5.7in. Since I assume you are only
using the patch corr. for outbending particles, it means
that only the proton momentum would have shifted. But
since W only uses the electron momentum, it means your
new corrections are affecting the electron momentum to
somehow compensate for a change in proton momentum?
Could you try applying the patch corr. ONLY to
outbending electrons (since it probably does things we
don't want to large angle outbending protons and pions),
and see if things are more sensible then?
Another idea would be to include Ebeam in your
Chi2 definition (I suppose it is not in now, or your
peaks wouldn't be off so much...). I think this would
help, as you have so many parameters that just fitting
Emiss and Pmiss allows multiple very similar solutions,
with varying effects on W and Ebeam.
Two other observations:
1) even without the Patch correction, often Ebeam is
quite noticeably off. It is VERY sensitive to slight
changes in angle.
2) Your W distributions look surprisingly square (not
Gaussian).
3) Most of these ep elastic e p pi pi events involve
a fairly large angle, low momentum proton. They have
relatively large energy loss in each layer of the DC,
which presently is not taken into account properly.
So it might well be that it is impossible to simultanously
correcto for large angle low momentum pion, electrons,
and protons, due the difference in energy loss (that
affects the radius of curvature and hence momentum).
I think Harut has been working on this problem?
Ideally, the tracking code should know the mass of
the particle it is tracking, and take the dedx into
account. But for simplificy, maybe there could be a
formula or look-up table that accounts for the effect.
Peter
Prof. Peter Bosted
email: bosted@jlab.org
phone: (757) 269-5851
address: Jefferson Lab Suite 6, 12000 Jefferson Ave, Newport News VA 23606
On Fri, 28 Mar 2008 nguler@jlab.org wrote:
> This is about latest fits for momentum corrections and effect of Peter's Patch
> Correction to correct specifically small angles. Since we did not have much
> time in the meeting to look at these plots together, I created a small Readme
> file that explains some details and includes links to relevant directories
> with plots. The site is still being developed but it now has enough
> information now for finding around your way with some effort.
> So, please visit the site:
> http://www.jlab.org/Hall-B/secure/eg1/EG2000/nevzat/MOMCORR/Readme.html
>
> And I specifically want to draw your attention to a paragraph that says
> following (This came up in the meeting and I tested it):
>
> MoniData_NoPatch: I obtained the old parameters again just to see if I can
> obtain a similar set of parameters as the ones that I already have. This is to
> test if something changed in the fitting program or if there is and
> mulfunction. Our main concern here is the source of the shift in calculated
> beam energy after Patch correction applied. Both columns of plots in this case
> represents the old (original with no patch correction) parameters. They should
> look very similar. The left column is old parameters, the right column is with
> newly obtained old parameters. These plots actually concludes that the shift
> in the calculation of beam energy is not due to some fitting mulfunction but
> it is real effect of Patch correction.
>
>
>