Weekly Meeting Minutes - October 28, 2005

Attending: L. Benton, E. Clinton, K. Hardy, M. Ito, M. Khandaker, D. McNulty, V. Mochalov, Y. Prok, A. Teymurazyan By phone: A. Bernstein, D. Dale, L. Gan, A. Gasparian

Summary of Meeting Discussions:

All. Nominate secretary: Dustin McNulty (next secretary: LaRay)

All. Approval of last meeting's minutes (2 weeks ago):

Approved. You can find the previous meeting minutes here. Highlights: Dan talked about flux status. Dave showed nice result of tagger time matching with hycal.

All. New Business: Itemized below

1: Collaboration Meeting Plan:

At first, the meeting was scheduled for Nov 18,19 2005, but Aron and Stanley had some conflicts or problems with this date.

Next date was Dec 3,4, but Liping, Dan, and maybe others cannot attend for this date.

A consensus was reached that perhaps Jan 14,15 2006 is best date (there is PAC, Jan 9-13, and holiday on 16th).

Official date not yet set.

2: Slides for Volker:

To be presented at Nov 3,4 Hall B CLAS collaboration meeting.

The (Power Point) slides package sent to Volker can be found here.

3: Eric's Status of the Tagger -- deferred until next meeting.

4: Vasilly's Topics in HyCal Reconstruction (html Presentation):

Location of new Calibration constants for HyCal -- /w/work2803/mochalov/myprogs/prog2005_10_20/saved_gains -- new constants need to be put in primex_calib database (Vasilly suggested giving them a new ATTRIBUTE in crystal and glass SYSTEM, so we can more easily keep the old constants accessible).

Calibration root files are saved to the Silo -- /mss/hallb/primex/DST/october_2004/calib_root/ -- Note that these were prepared with the old timing scheme (pre Fall 2005 Dave Lawrence modifications).

Vasilly shows histogram of the difference between the iterational and matrix inversion methods. Conclusion is that they agree with each other at the 0.1 % level.

Longterm stability--difference between end and beginning snake calibration constants. Vasily shows that the crystal are very stable between the beginning and end snake scans WITH THE EXCEPTION of the central 14 x 14 channel area around the beam hole. Also, the glass channels are very stable from beginning to end calibration.

Vasilly shows superb plot of HyCal energy resolution for both crystal and glass.

Nice plot of coordinate resolution across the transition region can be found here.

Vasilly found that the best energy resolution achieved by hycal was ~1.3% -- this occurred when the highest energy photons from the snake scan hit very near the center of a crystal channel.

Sparsification-induced energy reconstruction non-linearities: Vasilly introduced a correction for this effect based on analysis of snake scan data; this study can be found here. The correction is of order 3 - 4% for a 0.5 GeV shower (which is quite sizable) -- remember we used a 5 ADC count (above pedestal) sparsification level for all channels and there was about 0.75MeV/ADC count. Further study is needed here.

Crystal Linearity: The ratio of shower energy to tagger energy during snake scan is not flat (or even smooth), it is close to 1.0 as it should be, but it has many well defined bumps indicating some systematic problem which is affecting energy reconstruction at the 0.5% level. Vasilly found that these bumps are perfectly correlated with Tchannels (see this plot). Ashot suggested that Vasilly should look at this sort of plot for a single crystal--using the dedicated long statistics run we took near the end of first snake scan. The worry here is that due to the small time variations in each of the Tcounters' trigger signals being passed to the MOR, part of the HyCal readout signal is being chopped-off by the gate (either at beginning or end). This needs further investigation since it can be as high as 0.5% effect.

Coordinate reconstruction Oddity: During production running, photons which hit hycal do so at a slight angle (upto ~4.8 degrees); this angle causes the reconstructed coordinate to be bigger (further from 0,0) than reality. Employing Ilya's angular correction helps but is not enough--Vasilly says this is due to ASYMMETRIC SHOWER shape where the shower's spread in angle and variation is a function of the coordinate. This needs further investigation. Vasilly mentioned that this effect could be a big reason why glass invariant mass and elasticity ratio are too small.

5: Yelena's Compton, Two-Arm Status and One-Arm Plans -- deferred until next meeting.

6: LaRay's Status of LMS Data Correction -- deferred until next meeting.