Procedures for SOS drift chamber calibration and checkout.
Minimum calibration to get tracking
Open up tracking cuts (step 8).
Analyze ~2k events. Set hardware windows (steps 1 and 2 below) .
Reanalyze ~5k events. Determine drift chamber time offsets (step 3).
Reanalyze >20k events. Generate time to distance map (step 4).
Reanalyze ~10k events. Check detector positions (step 5)
To check that everything is working
Make sure drift time spectrum is nearly flat
Make sure that the drift chamber residuals are good.
Before executing paw
kumacs remember to first execute the kumac
paw/paw[runnumber].kumac to define the aliases.
The paw kumacs are available in the directory /group/hallc/mkj/replay/akumacs
For improved timing/tracking:
Reanalyze with MANY events (>20k, 100k for full fitting (including pulse height corrections).
Fit hodoscope timing parameters and/or set tracking cuts (steps 7/8).
step 1> Set scintillator
TDC window: (requires ~2k events -)
Parameters sstart_time_center and sstart_time_slop (in PARAM/shodo.param file) define a window for "real" scintillator hits. Set the slop to a very large number (~50) and look at the sscintimes histogram with paw kumac stime.kumac to decide on a good central value. The cut should be loose to avoid throwing out good events (it only needs to be tightened for detailed tracking studies).
step 2> Set drift
chamber TDC window: (requires ~2k events )
Parameters sdc_tdc_min_win and sdc_tdc_max_win (in PARAM/sdc.param file) define the window for good drift chamber TDC values. Look at the 'sdc raw tdcs' histogram using thepaw kumac stime.kumac to determine the TDC window. This should be large enough to include ALL events that are near the main peak, to avoid throwing out good events. The cut usually only needs to be tightened for detailed efficiency tests.
step 3> Determine
drift chamber time offsets: (~5k events )
The parameters sdc_plane_time_zero (1 per plane) is used to determine the 'zero' for the drift time. Look at the dtime histograms with paw kumac sdtime.kumac The drift time spectra already have the 'zero' for the drift time subtracted and if the sdc_plane_time_zero is correct then the drift time spectrum should start somewhere around t=0. The sdtime.kumac calculates how much the sdc_plane_time_zero for each plane needs to be changed. If the drift spectra need to be shifted the change sdc_plane_time_zero array values (in file PARAM/sdc.param) . The order of the array is for c1u1, c1u2, c1x1,c1x2, c1v1,c1v2,c2u1, c2u2, c2x1,c2x2, c2v1,c2v2 . The shift calculated by sdtime.kumac should be subtracted from the present value in the sdc.param. You should be able to get them all fairly close with the same value of sdc_plane_time_zero for each plane.
step 4> Generate
time-to-distance maps for the drift chamber: (>20k events)
First look at the plots of the drift distances by executing the paw kumac sdist.kumac . A typical output might look like this. A good drift distance spectra are like the ones for hdc2 which are flat while a bad spectra might look like the spectra for hdc1 which droop down. Execute paw kumac sdrift.kumac after replaying a high statistics run. This will create the file sos.driftmap. The values from this must be pasted into PARAM/sdriftmap.param. Now replay the run again and excute the paw kumac sdist.kumac and the drift distance spectra all should be flat as shown here. The driftmap values always go from 0.000 to 1.000, but you should make sure that the values are not changing significantly at the beginning or end of the tabulated values. If they are, you may need to readjust sdc_plane_time_zero (step 3) in order to better center the distribution within the drift map time window.
step 5> Determine
detector positions: (~10k events - spos.kumac)
The 'dpos' histograms show the difference between the track position and the center of the detector elements for each plane (summed over all counters in the plane). An example of the histograms is here. The first two scintillator planes should have fairly clear edges. The later detector elements have longer tails because of the multiple scattering in previous detectors. The signs are such that increasing the position in the parameter files will move the dpos to a higher value. The calorimeter xpositions have to be changed for each block individually. Each scintillator plane has an offset value, that is added to the nominal positions for each element.
step 6> Check wire
chamber residuals: (>20k events)
Execute the paw kumac hres.kumac . An example of the histograms is here.
step 7> Fit time
of flight parameters: (>20k events)
Requires external code (TOF calibration).
NOTE: any change in the timing will have some effect on the drift chamber drift distances. If you change the timing in any way, you should check that the drift distance histograms look good. If not, you need to adjust the sdc_time_zero parameters and/or the driftmap (steps 3 and 4 above). Most timing changes only affect the offset, so it usually not necessary to redo the drift map once you adjust the time zero properly.
step 8> Set cleantrack
There are several cuts for defining good tracks. The parameters are in PARAM/stracking.param. There is a chisquared cut, a beta cut, a calorimeter cut, and a dedxcut (scintillator ADC's). Initially, these should be WIDE OPEN (e.g. -100000 to 100000). If you want to require that the particle hit the scintillators (calorimeter), you should modify the cut to exclude zero (e.g. .001 to 100000). This ensures that the track points at the scintillators (or Pb glass blocks) that fired, but does not rely on good particle ID.
File initially written by I. Niculescu. Presently maintained by M Jones (x7733 , firstname.lastname@example.org). Last updated Feb. 10, 2003.