[G12] urgent help needed please
Lei Guo
lguo at jlab.org
Mon Oct 11 16:03:20 EDT 2010
Sure.
On Oct 11, 2010, at 3:41 PM, Johann Goetz wrote:
> which is why i did not use the trigger bits in my analysis. However,
> I do believe that there is some inefficiency in the lower part of
> the tagger due solely to the trigger configuration. I can measure
> this to be about 35% by looking at the triggered flux plot that
> craig shows here:
>
> http://clasweb.jlab.org/rungroups/g12/wiki/index.php/Image:G12_omega_gflux_tid30.png
>
> If I correct the flux (reduce the estimated flux below 3.6 GeV by
> 35% I get the following comparison which I am quite happy with. The
> shape of the g12 excitation function is extremely reliable here. But
> there still may be an overall systematic shift and I quote a
> systematic error of 12% here.
>
> <xi1320_xfncomp.png>
>
> On Mon, Oct 11, 2010 at 11:16 AM, Craig Bookwalter <craigb at jlab.org>
> wrote:
> I believe we had some kind of discussion a while back that the
> trigger bits in TGBI are not reliable, ie sometimes events are
> written out with no trigger bits set, or perhaps even the wrong bits
> set...
>
> Lei Guo wrote:
> Hi, Johann,
>
> I would think there is inefficiency for your two prong events below
> 3.6 (or is it 3.8?) GeV. I'd love to be proven wrong though. I
> assume you got your events from the two prong trigger, correct? Then
> in your Xi events below 3.6 GeV, you would have to have another
> higher energy photon (>3.6GeV) in the same time window for this
> event to have triggered the event, otherwise, your real event would
> not have been included in the two prong triggered events. THis
> obviously means you overestimated your flux (or did not acccount for
> trigger inefficiency, or whatever you want to call it), therefore
> your current Xsection would have been lower THAN what it should be.
> This is in line with what one observe now when you compare your
> results with g11 and g12. There is better agreement above 3.6 GeV,
> but your results are systematically lower below that.
>
> I think in g11, the events below the lowest energy (1.9GeV) in the
> trigger had to be scaled up by a big factor (~50%?) You sould check
> Mike Williams's note on Omega.
> Instead of looking at some benchmark channel's Xsection, which would
> take a lot of time to figure out, and how appropriate the comparison
> will be complicate, you best bet would probably be looking at your
> events above 3.6 GeV, and check how often it also has the 3-prong
> trigger bit. You can also compare that with your simulation and
> check how often you have at least another charged particle detected
> other than the two kaons . THIS FACTOR MIGHT ALSO BE ENERGY
> DEPENDENT. You can then compare these two methods if they are
> consistent.
> On another note, when I did the g11 analysis, total Xsec extracted
> from different ways of summing the differential cross sections has
> typically a spread of two nb. I quoted the half of that spread as a
> systematic error simply on the extraction of total Xsection from
> differentiall Xsection, in addition to the model dependence. I
> belive you would have to quote something similar along that line.
>
> Good luck!
> Lei
> On Oct 9, 2010, at 8:55 PM, Johann Goetz wrote:
>
> Hi Craig,
> did you have total cross section info as a function of beam energy?
> And if so, did you go below 3.6 GeV?
>
> On Fri, Oct 8, 2010 at 9:51 PM, Lei Guo <lguo at jlab.org <mailto:lguo at jlab.org
> >> wrote:
>
> Hi, Johann,
>
> YOu intuition seems correct. However, this is not something that
> I believe you could sort out in a couple of days. To get the
> cross section right and elimiate the trigger efficiency effect,
> you really HAVE to look at a benchmark channel (such as Omega) in
> detail, this would normally takes months of work. If I were you,
> I would grap whatever craig has for the omega, and try to get the
> scaling factor from the expected discontinuity, and compare that
> with existing data.
>
>
> Lei
>
>
> --
> Johann Goetz
> jgoetz at ucla.edu <mailto:jgoetz at ucla.edu>
>
> UCLA Dept. Physics & Astronomy
> Nefkens Group
>
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>
> --
> -------------------------------------------------------------------------
> Craig Bookwalter FSU Office: (850) 644 3808
> Department of Physics JLab Office: (757) 269 5465
> Florida State University craigb at hadron.physics.fsu.edu
> Tallahasse, FL 32306 craigb at jlab.org
>
>
> "One toke? You poor fool. Just wait till you see those (expletive)
> bats."
> -------------------------------------------------------------------------
>
>
>
>
> --
> Johann Goetz
> jgoetz at ucla.edu
> UCLA Dept. Physics & Astronomy
> Nefkens Group
**************************************
@
/ *
/ ___ ___ Lei Guo _______________________
L_O_/ ____ Florida International University____/_/
\ | Physics Dept., CP
212 / /
/ \ | Miami, FL
33199 / / /
/ I_/ \ ____ USA _____ /______/__________/ /
/ /
L
/ / / / /
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/_/__________/______/______/__________/_/
305-348-0234(o)
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