[G12] Minutes from 4/28/2010 meeting

[Craig Bookwalter]

Hi folks,
  Minutes from today's meeting can be found at the following link:

http://clasweb.jlab.org/rungroups/g12/wiki/index.php/28Apr10#Minutes

and pasted below:

* Attending: Craig, Dennis, Will, Carlos, Valery, Diane, Ben, Sasha S., 
John Price, Mike P., Gagik, Moskov, Chandra, Paul, Mukesh, Johann
* Paul raises the issue of prepping the kinematic fitter for analyses. 
Dennis is unclear on what channels would benefit from kinematic fitting. 
It seems only the K-short to pi pi is the only viable need--the 
pentaquark search could benefit in this regard. Diane's analysis could 
benefit by constraining the two photons to the eta, but the EC was not 
implemented in the CMU fitter at least.
* On the <tt>gpp</tt> issue, we tentatively decided on this as the 
proper command for g12:
<pre>
]$ gpp -P7f -s -R10 <input_file> 
</pre>
Valery is going to find out what g11 used for this. Also, Mukesh is 
going to confirm the omission of the `-Y' option for the efficiency map. 
Also we should confirm whether we should use run 10 or run 1.
* Diane looked at various sources to determine the torus current used by 
g12. There are different answers depending on where you look. It is 
unclear whether if the prlink file used in pass1 cooking used 1930A or 
1920A. Johann continues to work on a function to get the magnetic field 
at a point in space, but he's having trouble with the C/Fortran 
interface. Gagik will assist him.
* Craig reports that he did a study to look for missing tracks, 
motivated by Gagik's claims that g12 lost tracks from pass0_v3 to pass1. 
He found no evidence to support the claim that g12 has lost tracks 
relative to pass0_v3.
* Craig reports that he has found his missing tracks in the charged 3pi 
channel -- they were being lost to poorly-constructed selections on the 
ST vertex time and the 4-momentum beta.
* Craig provides an update on the omega MC and shows that the g12 data 
have a t-slope of 2.1 while the generated MC provided by CMU has a slope 
of 1.1. Discussions ensue about selecting the right region of beam 
energy to overlap with g11 and yet still be dominated by t-channel 
processes which we can accurately model with event generators. Craig 
will ask around to see if he can figure out what event generator Mike 
Williams used.
* Carlos shows some results from his pKK analysis. His phi looks 
suspicious given that above 2 GeV it's a tossup identifying pions and 
kaons.  Dennis claims he might find the 1680 if he can remove his Y* 
background. In his phi-eta analysis he is experimenting with a single 
photon in the EC and trying to find the missing photon. He can see the 
eta in the missing mass but when he selects those events and then looks 
for gammas in the EC his eta disappears.
* Moskov shows some analysis of theta-phi interference in gamma p -> pi+ 
K+ K- n, an analysis he performed during g11. A peak shows up at 1.5 GeV 
in the missing mass off the pi+K-. It may be an artifact of sideband 
subtraction to select the phi. Valery suggests he fit the phi meson to 
avoid the snafus possible with this sideband subtraction.
* Diane shows a fit to the t-slope in the region of the a2 with the 
sidebands around the a2 removed. The value for the slope is now 2.83.
* Valery shows some results from g11 comparing the 
reconstructed-generated momenta of tracks passed through gsim. These 
differences are all less than 1 MeV. In g12 these differences are 8-10 
MeV, but this may be attributed to energy loss corrections not being 
applied. More to come.
* Johann shows some plots from K+K+K- data, he sees the lambda and the 
sigma. The mean of the sigma is 1193 MeV. But these numbers are not 
corrected for energy loss in the target and start counter. Dennis wants 
some opinions on the production mechanisms for the high-mass cascades in 
photoproduction.