[G12] urgent help needed please

[Johann Goetz]

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.

[image: 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
>>>
>>
>> **************************************
>>       @
>>      /    *
>>     /   ___  ___  Lei Guo _______________________
>>    L_O_/ ____ Florida International University____/_/
>>        \   |             Physics Dept., CP 212                       /  /
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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
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