Weekly Meeting Minutes - July 7, 2006

Attending: P. Ambrozewicz, E. Clinton, J. Feng, L. Gan, A. Gasparian, M. Ito, O. Kosinov, N. Kostecki, I. Larin, C. Mauney, D. McNulty, E. Pasyuk, Y. Prok, A. Teymurazyan, M. Wood By phone: D. Dale, R. Miskimen

Summary of Meeting Discussions:

All. Nominate secretary: Dustin McNulty (next secretary: Liping Gan)

All. Approval of last meeting's minutes:

Approved. You can find the previous meeting minutes here. No comments on last weeks meeting minutes other than it was a very long, grueling meeting that should not be repeated anytime soon.

All. New Business: Itemized below

3: Update on contribution to Science and Technology Review Presentation.

There was a request to label all plots with "Error bars are Statistical Only"; Primex plots were deemed very nice and acceptable...however, final results with total errors are anxiously anticipated.

4: Review of Collaboration Meeting.

5: Pawel presented an Intro to Beam Position Stability.

One of the goals of this work is to determine the precise trajectory of the photon beam on a run-by-run basis.

UNCW summer student Nicolette is studying the PGP (PrimEx Gamma Profiler) data (in book_keeping database); a triple Gaussian fit is being applied to the profile data for an improved mean/sigma determination. This data is available approximately every 10 seconds during production runs. Preliminary analysis is consistent with Mike Grissom's analysis of last summer.

The plan is to correlate the PGP beam position results event-by-event with Hall B BPM and harp scan data. Work in progress.

PGP analysis results (mean only) still need to be transformed to hall B coordinate system using survey data transmittal B945.

It is currently not clear how to obtain precise location of BPMs in hall B coordinate system since there is/was no survey. One suggestion for this is to use the survey location of the tagger radiator and measure the physical distance with a ruler from the radiator to the 2C24A nA BPM module (its approximately 1 - 2 meters).

6: Nicolette presented More on Beam Position Stability.

Near the middle of run 5284, the PGP data shows a significant jump in mean position (~1cm), width (gets wider), and amplitude (gets smaller); it was commented here by Eugene that it appears that the integral counts in profile histograms look the same before and after the jump--indicating the beam intensity probably didn't change. Luckily, this situation does not occur often, but we need to know exactly when it occurs to either correct for it or omit it from analysis.

Immediate question--Is this PGP jump correlated with a BPM jump?

7: Mike presented his Normalized Yields from Single-arm Compton.

For this analysis, Mike extracts the Compton yield per run per incident photon; he performs an in-time analysis with non-Compton kinematic event bkgd subtraction (using a fit -- signal to noise is ~4 or 5 to 1); he also employs a sideband-style accidental timing bkgd subtraction. He has a VETO cut (to identify neutrals) and loops over events with only one cluster.

You can follow his analysis here. The main result and point of Mike's presentation is seen in the middle plot (Normalized yield vs. run number); this plot shows a very strong anti-correlation between his yield results and the beam current.

It is believed that these beam current dependent normalized yields are primarily a result of considering only one cluster events and secondarily a result of using a VETO cut...since as beam current goes up, accidentals and other beam-related junk goes up squared--thus there are less single cluster events at higher beam currents and perhaps more junk around beamline interfering with proper VETO signal...

It was suggested that removing the VETO cut and analyzing events with one or more clusters should help flatten the normalized yield run history.

8: Ilya and UNCW summer student Chris presented Hycal Resolution

Ilya and Chris are working to understand and characterize several data analysis-related quantities using the first snake scan data. These projects are listed below.

Energy Resolution of each of HyCal's channels. These are obtained from the sigma of the fit to E_cluster/E_gamma using events where at least 80% of cluster energy is deposited in central cell.

Trigger Efficiency. Since the event trigger during snake scan1 was a MOR trigger and not a coincidence trigger between MOR and HyCal, a sense of HyCal trigger efficiency can be obtained. More on this in near future. No results yet.

Tdiff Alignment. Examine time difference (tdiff) between hycal event trigger and fully reconstructed tagged photon for each HyCal channel as a function of cluster energy or Tcounter. This will give us a sense of the time-walk correction (channel-by-channel), if one is needed. More on this in near future. No results yet.

Response function of each of HyCal's channels. Ilya plans to characterize the response function of individual hycal channels by examining the size and shape of energy leakage seen in their individual calibration (E_cluster/E_gamma) plots. We will hear more details on this in future.

For crystals, this leakage is typically only seen as a surplus of counts (small bump) to the left of peak that does not fit inside the Gaussian. Ilya believes that there is approximately 2% transverse leakage due to 5x5 cluster shape constraint, and an additional 1% longitudinal loss out the back.

For glass counters, there is an additional loss due to transparency effects combined with the long longitudinal size of the glass counters; this combination results in the increased chance that a partial shower developing near the photo tube end of the counter could give rise to a larger than expected ADC response - thus producing a small bump to the right of the peak that does not fit inside the Gaussian and is thus leakage.

Tagging Ratio. Ilya performed an independent check of the tagging ratios measured by the TAC. He did this by using the HyCal as a TAC and found very good agreement (at the < 0.1% level) with Aram's TAC analysis.

9: Other new business.

Ilya suggests some analysis software default changes:

1. Remove Fastbus Error event skipping -- he says that these are in fact good events and that we are throwing away 0.5% of our data (and thus our cross section measurements should be adjusted up by 0.5%).

2. Max_hit cut should be changed from 250 to 400. Ilya says that 250 is not enough because ROC4 noise problem causes some events to be analyzed that are not reconstructible.

3. cluster_Min_hits should be changed from 2 to 3. I cannot remember why?

Ashot reminds us that we need to make a decision about when to have our next collaboration meeting.