[Frost] tagger sag

[dugger at jlab.org]

Hi Park,

Unless the photon pulls are better than you have previously reported, the
energy differences shown can not be taken as accurate. This means that I
do not know what to say regarding your most recent plots.

Chuck had stated that the pull parameters are going to give you more
meaningful information than the corrected energy. He should know. Why
don't you do as he suggested, and show the center of the photon pulls as a
function of photon energy?

Of course you are free to feel confident in the corrected values of the
photon energy given by your kinematic fitter. It is up to you to find out
how best to make the photon pull parameters more reasonable. I would
concentrate on the easiest thing first: Make the Carbon and CH2 targets
have reasonable pulls, and then work on the Butanol target. That is just
me. It is your analysis.

Happy hunting.

Best wishes,
Michael






> Hi Dugger,
>
> I have made more updated histograms.
> The y-axis value has [E_calculated - E_measured] / [E_measured]
> The x-axis has [E_measured] or Z-vertex.
> You can check my results in the following web:
>
>    http://www.jlab.org/Hall-B/secure/g9/sungkyun/6-14-10.html
>
> I am sure that after applying the recent updated eloss correction, the
> ratio of {E(cal. photon) - E(cal. photon)} to E(cal. photon) has been
> located near zero more. I think the current eloss is improved more.
>
> I do not know about the tagger sag. After eloss correction, there are
> still structure. that is, In the low energy, measured photon energy is
> bigger than calculated photon energy. However, the difference is very
> small when we compare them with the histogram which are made before eloss.
> Do you think the reason of this difference is the tagger sag?
>
> Sung
>
> Florida State University
>
>
>
>
> ----- Original Message -----
> From: Michael Dugger <dugger at jlab.org>
> Date: Wednesday, June 9, 2010 4:34 pm
> Subject: Re: [Frost] tagger sag
> To: Sungkyun Park <sp06k at fsu.edu>
> Cc: frost at jlab.org
>
>>
>> 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
>> >>
>> >
>>
>