<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Sure.<br><div><div>On Oct 11, 2010, at 3:41 PM, Johann Goetz wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">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:<br>
<br><a href="http://clasweb.jlab.org/rungroups/g12/wiki/index.php/Image:G12_omega_gflux_tid30.png">http://clasweb.jlab.org/rungroups/g12/wiki/index.php/Image:G12_omega_gflux_tid30.png</a><br><br>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.<br>
<br><span><xi1320_xfncomp.png></span><br><br><div class="gmail_quote">On Mon, Oct 11, 2010 at 11:16 AM, Craig Bookwalter <<a href="mailto:craigb@jlab.org">craigb@jlab.org</a>> wrote:<br>
<blockquote class="gmail_quote">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...<br>
<br>
Lei Guo wrote:<br>
<blockquote class="gmail_quote"><div class="im">
Hi, Johann,<br>
<br>
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.<br>
<br>
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. <br>
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. <br>
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.<br>
<br>
Good luck!<br>
Lei<br>
On Oct 9, 2010, at 8:55 PM, Johann Goetz wrote:<br>
<br>
</div><blockquote class="gmail_quote"><div class="im">
Hi Craig,<br>
did you have total cross section info as a function of beam energy? And if so, did you go below 3.6 GeV?<br>
<br></div><div class="im">
On Fri, Oct 8, 2010 at 9:51 PM, Lei Guo <<a href="mailto:lguo@jlab.org">lguo@jlab.org</a> <mailto:<a href="mailto:lguo@jlab.org">lguo@jlab.org</a>>> wrote:<br>
<br>
Hi, Johann,<br>
<br>
YOu intuition seems correct. However, this is not something that<br>
I believe you could sort out in a couple of days. To get the<br>
cross section right and elimiate the trigger efficiency effect,<br>
you really HAVE to look at a benchmark channel (such as Omega) in<br>
detail, this would normally takes months of work. If I were you,<br>
I would grap whatever craig has for the omega, and try to get the<br>
scaling factor from the expected discontinuity, and compare that<br>
with existing data.<br>
<br>
<br>
Lei<br>
<br>
<br>
-- <br>
Johann Goetz<br>
</div><a href="mailto:jgoetz@ucla.edu">jgoetz@ucla.edu</a> <mailto:<a href="mailto:jgoetz@ucla.edu">jgoetz@ucla.edu</a>><div class="im"><br>
UCLA Dept. Physics & Astronomy<br>
Nefkens Group<br>
</div></blockquote><div class="im">
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Craig Bookwalter FSU Office: (850) 644 3808<br>
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</blockquote></div><br><br clear="all"><br>-- <br>Johann Goetz<br><a href="mailto:jgoetz@ucla.edu">jgoetz@ucla.edu</a><br>UCLA Dept. Physics & Astronomy<br>Nefkens Group<br>
</blockquote></div><br><div>
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