Summary of E835 meeting, Thursday 4/13/2000 Present: Rusack, Graham, Gollwitzer, Kasper, Seo, Obertino, Pastrone, Calabrese, Bettoni, Baldini, Negrini, Stancari (M), Stancari (G), Pordes The stack seems to have gone really quite well. With hand-tuning of the jet-target temperature, densities up to 4*10^14 were achieved allowing us to keep high luminosity down to 10 mA or so. The beam was quite stable, the P77 baby sitter bahaved well and the live-time was typically 95% (or more). As reported by Matteo we took 2.41 pb-1 from 26 mA net and have a chi0 -> psi gamma observed cross-section of 37 pb. He will publish the plot of the electron pair mass. Stephen commented that he was (as always) impressed by the experiment's ability to get these results so quickly and impressed by the dedication of the people (currently Matteo and Margherita) who produce them. He would like to encourage that the mechanics of the process be written down and that one or two more people be inducted into the group that does this analysis. It was agreed that Matt would learn the process. Keith and Michelle remarked that they are writing some procedures to automate things - there is an issue with stacks where we run at more than one energy. Michelle gave a preliminary gamma-gamma analysis for the week's three stacks energy luminosity events observed cross section 3470 2.52 pb-1 33 13.1 +/- 2.3 pb (background) 3417 1.47 pb-1 30 20.4 +/- 3.7 pb (peak) 3415 2.41 pb-1 53 22.0 +/- 3.0 pb (peak) (note that the week gave us 6.4 pb-1 - which I believe is a record for the experiment since the beginning of time). Michelle's numbers are reasonably consistent with 835 phase 1. Work is still being done to identify hot blocks (wide pedestals) in the analysis. Giulio showed some data on the "vertical bump" implemented to raise the beam at AP-50. A plot of the average event vertex position provided by Michelle did not show any obvious change but this may not be a sensitive measure. Data from the Beam Position Monitors suggests that the beam is within 0.2 mm to 0.3 mm of its desired height at the chi0 energy. One can define a quantity DZ, the effective target length seen by the average pbar beam particle as in the equation Luminosity = rho * I * DZ where rho is the gas-jet density and I is the pbar beam current. Comparing the luminosity for a run in January with given rho and I and a run now for a given rho and I, Giulio infers that the present DZ is about 30% larger (longer) than in January - suggesting that we have improved the matching of the vertical height of the beam with the gas-jet significantly. Michelle explained the process used to derive the new set of CCaL calibration constants. The previous calibration constants used for this data were derived from January running and extrapolated to the present using the laser monitor. The calibration data (pi0-pi0) files from (some of) the present data have now been processed and they have better statistics than the january data. A plot of the statistical uncertainty in the calibration shows that most of the channels have a less than 2% uncertainty now. A comparison of the constants derived by extrapolation from January and the measured new values had an rms difference of about 4% - consistent with the statistical precision of the various data sets (january, laser and present). Michelle commented that the logistics of the process now (data sets on disk, richer in relevant events) made the process of deriving the constants less work and much faster than before. Nadia reviewed Giovanni Borreani's mail on the prospects for the 1p1 search with the stated aim of getting everyone to read it. (It has worked with me). In summary, (I think this is right) Giovanni suggests that the likelihood that what we saw in 760 was a fluctuation of the background is less probable than we estimated in the published paper (1/400). He also analyses a set of MC experiments done with 51 pb-1 (17 points * 3pb-1/point) and concludes that we have a very good chance to find it again even if the cross section is only half of what we measured. Go read... he 1p1 search with the stated aim of getting everyone to read it. (It has worked with me). In summary, (I think this is right) Giovanni suggests that the likelihood that what we saw in 760 was a fluctuation of the background is less probable than we estimated in the published paper (1/400). He also analyses a set of MC experiments done with 51 pb-1 (17 points * 3pb-1/point) and concludes that we have a very good chance to find it again even if the cross section is only half of what we measured. Go read... Wander said that he would like to implement a pbar-p trigger using the fibers at the beginning of the next stack. Keith had some specific technical questions and suggestions. Stephen asked Wander to send around an e-mail on what he was proposing to do - just to get things written down. Margherita said she is working on understanding how a CCal multiplicity cut could be used for the pbar-p trigger. buona notte.. Stephen