Hello and thanks a lot for your suggestions on this. I really appreciate for
not being alone in this thing.. My response is below:
> 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,
I am not aware that I need to apply patch correction to only outbending
particles. For the record, I am applying the patch correction to all
particles, electrons, protons, pions... ( Shortly whatever is in preselected
data goes through the patch correction..). And I use all parameters ( 3
parameters for each sector, and torus, in total 3*6*2 = 36 parameters..)
Moreover, applying sepecific corrections to specific particles selectively
does not exactly warm me up.
And I have tried putting Ebeam among the parameters at the very beginning of
momentum corrections studies. If I do that, minimization routine keeps
changing beam energy always in one direction, it keeps increasing it or
decreasing it and rearranges other parameters accordingly. As far as I
remember, that method was not working at all. I was giving exact starting
values but still the minimization was changing the value of beam energy and
giving out very off values sometimes..
For the minimization to work properly, one side of the equation should have a
fixed value so that the program can re-arrange the parameters on the other
side based on the fixed side of the equation. Beam energy represents the fixed
side of the equation and the parameters represent the other side. If I put the
beam energy to the parameter side, The program mainly prefers to play with the
beam energy to accomplish minimization because it is one parameter that has
effect on everything cumulative. I think it is easier for the program to keep
changing the beam energy value to accomplish its goal so it keeps changing it.
I remember I also tried to put strict limits and very small steps on the Ebeam
parameter but none of my trials were giving good results so I have concluded
that study by saying using beam energy as another parameter is not a working
method. But certainly I can try the same things again may be even more
carefully.
Best regards,
Nevzat
> 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.
>>
>>
>>
>