Minutes of FT Meeting, 16th and 17th December, 1997. ==================================================== Present: Steve Burke, Tim Greenshaw, Rob Henderson, Dave Milstead, John Morris, Dave Sankey, Terry Sloan, Paul Sutton. 1) New L5 hists (Dave Milstead). -------------------------------- Dave showed the plots now created at L5 (filled for every tenth event). The results came from the processing of about 10% of the 1997 DST data (i.e. from about 1% of the 1997 events). The photon conversion vertex position in z showed nicely the CJC end-wall plus electronics and cables and the location of the material in the FT. As yet no MC results are available. Some assymmetries in phi were observable in the CJC end-wall region and also at positions further forward in the FT. These look to be largely due to dead planar cells. Higher statistics and comparison with MC will help in the understanding of these plots. Dave also showed the results of K^0 searches using two CT, one CT and one FT track, and two FT tracks. The mass resolution deteriorated successively. There was some evidence of a Lambda peak in the two CT track sample, perhaps a hint of the same in the one CT one FT track sample. Such events would allow interesting studies using the Lambda decay to identify its polarisation. 2) FT/CT momentum measurement (Dave Milstead). ---------------------------------------------- Dave showed us his +/- asymmetry plots as a function of phi. He showed us the correction procedure he has developed, based on comparison of the momentum measurements in the CT and FT as a function of phi. These corrections to the FT measurements largely remove the +/- asymmetry. They involve shifts in p_T of typically 300 MeV for tracks with a p_T of 3 GeV, the large apparent asymmetry arising because of the steeply falling p_T distribution. Dave's FT tracks use the primary vertex information, but he has also checked that similar results are obtained if the vertex is not included in the fit. Steve Burke showed that similar results are obtained without the vertex constraint. He also showed that, prior to requirements on the number of planar segments etc. made in standard FT track selections, the asymmetry is not there; the asymmetry arises after making requirements like number of planar segments > 0. 3) Muons in FT (Paul Sutton). ----------------------------- Paul showed results on searches for quasi-elastic and inelastic J/psi photoproduction, with the psi decaying to muons seen in the forward detectors. The mass of the psi when the muons are seen in the FT is lower than expected (about 2.7 GeV, expect 3.1 GeV). Efficiency studies have been made using muons detected in the Iron and/or Fmuon systems and the CJC. Such tracks, with CJC momenta above 2 GeV, were interpolated through the FT and associated FT tracks searched for. This led to an efficincy measurement for the FT, with the "Lee" FT track selection (something like at least one planar segment and at least one other segment on the track). The efficiency observed was 70%. Paul also sees a mismatch of the CT and FT theta measurements which changes as a function of phi. 4) Delta ray simulations (Terry Sloan). --------------------------------------- Terry showed results from his simulation of delta production in the FT. He looked at single high momentum pions going through the FT and studied the number and location of the deltas they produce. The number per incident pion changes as a function of the minimum delta kinetic energy considered (T_min). For T_min = 1 Mev, about 10-20% of tracks have an associated delta. This number rises as T_min is reduced. The low energy deltas are produced in the chamber wall just before the pion enters the gas volume. The separation of the deltas and the primary track in an x-y plane just before the pion leaves the planar gas volume is relatively large, only in a few per cent of cases are deltas within 4 mm of the primary. 5) H1sim and delta rays (Tim Greenshaw). ---------------------------------------- Tim showed results similar to Terry's obtained by Girish Patel using GEANT to simulate a much simplified FT. Numbers at T_min = 1 MeV are similar to those extracted by Terry, with the difference that deltas also enter the chamber from the rear (so the "smaller r" signature for deltas is a misconception). Terry realised these were excluded in his MC due to a bug. (This was fixed and results will be shown at the next opportunity!) At the time of the meeting there were problems with lowering the T_min cut in GEANT; these have since been solved and again results will be shown at the next meeting. Some plots are to be found at: http://hep.ph.liv.ac.uk/h1/delta 6) QT and FADC pulses (John Morris). ------------------------------------ John showed the results available on the web at: http://dice2.desy.de/~jvmorris/fpqt.html He compared the signals seen on the inner and outer wires of the planars. There are no differences between the signals on the outer wires at the front and back of the chamber. The gain on the outer wires is 1.9 times that on the inner wires, but this is compensated for in the charge determinations shown. John also showed some plots showing how the parameters in the QT algorithm for the planars were optimised (see above web site). There is no evidence from these that the parameters should be changed, but John pointed out that this conclusion could change if the optimisation was based on different criteria; some measure of tracking efficiency/track quality, for example. Varying the QT parameters, and changing to using a first electron algorithm will be tried by John and Dave, using track criteria to judge whether the changes result in improvements or not. Useful numbers are: Mean single pulse length about 10 FADC bins (~3 mm in drift). Rise time about 3 FADC bins. The signals expected if a track is accompanied by a 1 MeV delta ray were also discussed (again, see above web site). 7) Track related noise studies (Rob Henderson). ----------------------------------------------- Rob showed some interesting results on track related noise. He defined track related noise to be any hits between 2(?)mm and 5 mm of a segment which were themselves not on a cluster. This probably means many of these hits are not associated with delta rays. Rob showed that the frequency of such hits is higher on the inner (lower gain) wires. He also showed that the charge of these hits is significantly lower than those of hits used on tracks or segments. This suggests that this type of "track related noise" results from the splitting of pulses. It was noted that this will tend to move the reconstructed position of the first hit. 8) Correlated shifts of clusters (Rob Henderson). ------------------------------------------------- Rob studied tracks found in all three planar modules. Interpolating between the outer modules gives him expected positions for the track in the central planar module. He looked at the perpendicular distance, d, between the planes defined by the measured clusters in the central module and the exprapolated track (expect zero), and at the angle between the normal to the planes and the track (expect 90 deg). The distribution of d showed some evidence for a correlated shift of the hits on a cluster. Such a shift has been introduced into the MC. Similar (less accurate) results were obtained using the information from two clusters to define a segment and looking at the position of the third cluster with respect to the segment, all within one planar module. 9) State of FT simulation (Steve Burke). ---------------------------------------- Steve gave a presentation on aspects of the FT data and how they are simulated. Some interesting numbers were: About 70% of planar hits are not used on tracks. About 50% of hits not used on clusters. The MC attempts to model many features of the data including individual hit efficiencies, track related noise, hit resolutions, correlated shifts of clusters... He showed comparisons of data and MC for a large number of quantities, some used in optimising the simulation and some not. The overall level of agreement was impressive. The improvement over earlier FT MC results is also noteworthy. 10) Field off cosmics (Rob Henderson). -------------------------------------- Rob showed the results of a study of field off cosmics. With the B-field off, there is no evidence for an internal misalignment of the FT that could explain the +/- asymmetry as a function of phi seen by Dave M. 11) FT/CT alignment (John Morris). ---------------------------------- John presented the results of a study of the orientation of the FT w.r.t. the CT using tracks passing through both trackers. There is evidence for a shift and a rotation...John will produce a correction function which will allow the +/- asymmetry results etc. to be re-examined. 12) Tasks. ---------- a) Breakdown of causes of loss of clusters/segments. (Rob/Girish?) b) Figures for cluster efficiency, segment efficiency, from poking tracks. Demonstration that effects in planar chambers are independent. (Rob?) c) QT optimisation using tracking criteria, study of changing pulse splitting parameters, use of 1st electron algorithm. (John/Dave S) d) "Fix" for FT/CT position errors. (John) e) Study of momentum measurement shifts, +/- asymmetry etc. (Dave M/John) f) Delta ray simulation work. (Girish/Tim/Terry) g) Evidence for delta rays in pulses. (Dave S) h) More physics for proposal. (Tim)