[Frost] tagger sag
Michael Dugger
dugger at jlab.org
Wed Jun 9 16:34:54 EDT 2010
Sung,
I really hate to be a bother. From what I can tell, the plots you show are
from the kinematic fitter. The FSU kinematic fitter showed the exact same
kind of agreement for g8b. I do not know why. There were many
discussions regarding this. Please see
http://www.jlab.org/~dugger/tmp/meanValues_048326.A10.gif (this plot goes
along with the email I got from Charles Hanretty shown at the bottom of
this email). Charles and I had the exact same conversations regarding the
tagger sag for g8b.
The pull parameters for the photon energy are a much better gauge of how
well the measured photon energy compares to the calculated when using a
kinematic fitter. A kinematic fitter can not be relied upon to give
accurate results when the pulls are not close to optimal. This appears to
very much the case for the calculated photon energy using the FSU
kinematic fitter for g8b (and probably for g9a as well).
You can see the difference in the pull parameters before and after the
tagger sag correction for g8b data in Fig. 7 on page 8 of
http://www1.jlab.org/ul/Physics/Hall-B/clas/public/2009-030.pdf
Your photon pulls shown on your web page at:
http://www.jlab.org/Hall-B/secure/g9/sungkyun/6-1-10.html
Give the following parameters:
Carbon->
mean 0.122
sigma 1.124
CH2->
mean 0.251
sigma 1.235
For Chuck using g8b data:
Before tagger sag correction->
mean 0.3027
sigma 1.219
After tagger sag correction->
mean 0.0049
sigma 1.040
At first glance, it looks entirely reasonable to suspect that you have the
same sort of photon energy problems that Chuck had.
I also want to make it clear that the sag correction was supposed to be
included in the g8b data and it was never determined what went wrong. Why
should we assume that the tagger sag is fixed when it has not been
verified?
One more thing that might be of interest: It appears that the
[E_calculated - E_measured] is nearly perfect for the comparisons
done by the kinematic fitter. However, it would be very surprising to get
this same type of result from your most recent study at:
http://www.jlab.org/Hall-B/secure/g9/sungkyun/6-9-10.html
I only propose that you find out [E_calculated -
E_measured]/E_measured using your most current study (without kinematic
fitter) and include enough statistics to get the numbers to the 0.1%
level. This would serve as a way to verify that the tagger sag is
correctly included in g9a.
No matter what, you are going to have to get your photon pulls to be much
better before you can reliably use the kinematic fitter in your analysis.
That is the price you pay for using such a powerful technique.
************************
Date: Wed, 19 Aug 2009 15:18:41 -0400 (EDT)
From: Charles Hanretty <hanretty at hadron.physics.fsu.edu>
To: Michael Dugger <dugger at jlab.org>
Subject: Re: E(true) and E(meas)
Parts/Attachments:
1 Shown 161 lines Text
2 OK 12 KB Image
----------------------------------------
Mike,
Attached is a plot I have of the mean values generated from just 1
1.3GeV file
(cooked_048326.A10.B00). I fit each slice of the (Etrue/Emeas)vEmeas plot
by using the function
TH2::FitSlicesY (168 slices). Looking at this, one could see the
similarity between this plot and
the one you showed at the meeting. I've made this final plot
(Etrue-Emeas v Emeas) but it does not look how I expect it to or want it
to
so I'm trying to figure out if I made an error somewhere. One thing to
note
is that the differences between Etrue and Emeas (for me) seem to be
smaller
than the differences you are dealing with. This might flatten out some of
the bumps we're looking
for. For example, your Etrue/Emeas v Emeas plot has a
y-range of 0.95-1.05. I started off with this range but had a lot of
empty
space and therefore have changed my y-range to 0.998-1.002. Anyway, this
is an update; there is
still work to be done.
-Chuck
*************************************88
-Michael
On Wed, 9 Jun 2010, Sungkyun Park wrote:
> Hi Michael,
>
> My understanding is that we do not worry about the problem of the tagger sag in FROST data.
> When we make the cooking file, that problem is corrected.
>
> I make a same plot made at g8b.
> The first plot is about E-id vs E{true photon beam} - E{measured photon beam}
> The second plot is about E{measured photon beam} vs E{true photon beam} - E{measured photon beam}
>
> These plots are made in topology #gamma p -> p #pi+ #pi- (all detected) and the updated eloss correction is applied.
> E{measured photon beam} is the initial photon energy.
> E{true photon beam} is the photon energy after kinematic fitting.
> I used 0.05 as the confidence level cut. I used only a run 55570 in period 3. The electron beam energy of period 3 is 1.645 GeV. So The energy range of E{measured photon beam} is from 0.33 GeV to 1.56 GeV.
> When we compare plots in CLAS-NOTE with plots attached with this email, FROST data do not have any problem of the tagger sag.
>
> Sung
> Florida State University
>
>
> ----- Original Message -----
> From: Michael Dugger <dugger at jlab.org>
> Date: Wednesday, June 9, 2010 1:04
> Subject: [Frost] tagger sag
> To: frost at jlab.org
>
>>
>> Hi,
>>
>> I know that the study Sungkyun performed was to help verify the
>> eloss
>> momentum corrections, and I think that this is a reasonable way to
>> look at
>> his study. However, this sort of study is also very useful in
>> determining
>> the tagger sag. Since the eloss correction is not as pronounced for
>> the
>> Carbon and CH2 targets, these targets can give us a good picture on
>> the
>> tagger sag situation.
>>
>> If you look at the CLAS note:
>> http://www1.jlab.org/ul/Physics/Hall-B/clas/public/2009-030.pdf
>>
>> Fig. 5 on page 6 shows the tagger sag correction to be on the order
>> of
>> 0.5% for g1c data. For g8b data, the sag correction was between 0.2
>> to
>> 1.0% (Fig. 6 page 7). This means that we need to look for energy
>> effects
>> on the order of 0.1% to be sure that the tagger sag is not an issue.
>>
>> For g8b it was found that the tagger sag correction was important
>> in
>> obtaining reasonable pulls for the FSU kinematic fitter (see table
>> 1 on
>> page 7).
>>
>> One way to get a better look at the energy study is to use:
>> [E_calculated - E_measured]/E_measured
>> instead of
>> E_calculated/E_measured.
>>
>> Since Mike Williams used this sort of parametrization for g1c (and
>> I
>> did the same for g8b), we can more easily compare results between
>> the
>> different run periods to see if the shape of the energy correction
>> distributions look similar. The tagger sag has a "signature" three
>> bump
>> pattern that should be clearly visible once we get to the 0.1% level.
>>
>> -Michael
>> _______________________________________________
>> Frost mailing list
>> Frost at jlab.org
>> https://mailman.jlab.org/mailman/listinfo/frost
>>
>
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