April 6, 2016 Calibration
GlueX Calibration Meeting
Wednesday, April 6, 2016
11:00 am, EST
JLab: CEBAF Center, F326
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- Subdetector Reports
- Calibration Tasks
Attending: Sean (NU); Simon, Eugene, Curtis, Paul M., Adesh, Alex B., George, Luke, Beni, Nathan, Lubomir, Mark D., Elton (JLab); Mahmoud (FIU); Mike S., Naomi (CMU); Matt S. (IU)
- Paul has been looking into the cause of the poor thread scaling behavior he reported at last week's Offline meeting. The global ROOT lock used for histogram filling is the problem. Tried disabling the locks for part of the running, but this ran into crashes. Has devised a scheme to improve the situation with David L., requires a new version of JANA and changes to sim-recon wherever histograms are filled.
- Paul plans to launch another round of monitoring on Friday, if the above changes are finished. The other big slowdown was kinematic fitting in the exclusive reaction plugins; this will be disabled. A higher TAGM threshold will be used, since the current REST files are swamped with background in this range; ~30% of hits have two microscope hits.
- The first set of calibration jobs has finished, including calorimeter and TOF skims; Sean has started a new set of jobs over the 3.4 mm collimator data.
- Sean has been keeping up with timing calibration corrections over the past few weeks. Generally these have been stable, with small changes due to calorimeter trigger studies. Lubomir changed the FDC hold off time by 80 ns, which led to forward going tracks being reconstructed with bad chi^2. Sean fixed this using the eyeball technique, having a better defined procedure for FDC times would be more helpful.
- Mark Ito set up a GlueX software help email list. Paul stated that he won't answer any more direct email questions, and will forward them to the list.
- Subdetector Reports
- FCAL - Mike's recent changes to the DAQ library corrected the number of pedestal samples that were being used, so Adesh is in the process of updating the gain calibrations (it was previously noted that the pi0 peak had shifted to lower mass). He is running over the official pi0 skims, using 3 M pi0s to get an initial calibration before the monitoring launch. It takes him ~8 hours to do an iteration, which is a ~3x speed increase.
- BCAL - Substantial changes to the clustering algorithm are being finalized. Will is working on updating gain calibrations, and George's quadratically fitted effective velocities have been added to the CCDB. After discussion, we agreed that these improvements should be checked in after the monitoring launch.
- CDC - Mike showed some slides comparing wire efficiencies and resolutions. Simulation (sigma ~ 150 um) and cosmics (sigma ~ 120um) agree reasonably well, but beam data looks worse (sigma ~ 210um). Probably the t0 calculation (SC?) is off? Mike is looking at the causes. The long tails are due to multiple scattering. Simon's alignment studies indicate that the CDC needs to be shifted by ~1 cm.
- FDC - Lubomir has been looking at straight track data, and sees the best resolutions yet (< 150um), but lower efficiency (~90% for 3D points). This could be a t0 problem as well, also gain calibrations are being revisited, they look a little lower than before.
- TOF - Beni is updating his code and running calibration jobs over the new skims. Simon saw some potential 6-fold ambiguity problems in run 11059. Sean has seen this to be pretty stable, but will take a look at it.
- SC - Sean has been looking into problems with the time resolution in simulation with Mahmoud (sigma = 300 ps in, ~370 os out). They've tracked down an inconsistency with how propagation times are corrected for in simulation and how the resolutions are calculated. Sean is working on fixing this.
- TAGH - No news, Nathan noted that the pedestal seems to decrease with higher rates, looking into this.
- TPOL - Nathan showed some slides on the current state of the polarimeter analysis. See his slides for details. Major results: analyzing power of 75 um radiator is twice that of 750 um radiator. Sees little difference in polarization when changing diamonds or going to the smaller hole, consistently ~36-40%.
- TAGM - Alex has been busy resolving discrepancies between mode 7 and 8 data.
- PS - Alex showed some slides updating his work on calibrating the energies reported by the PS. Things are looking better, but the resolution is still much larger than expected.
- Calibration Tasks
- Performance - Matt mentioned some updated plots he'd like to have for his APS talk: Plots of pi0's in the same energy range in the BCAL and FCAL, updated PID plots would be good, Mahmoud said that he'd send a plot of start counter resolutions.
- Simulations - Sean showed a plot with a rough estimate of the TOF time resolution, which corresponds to a hit resolution of ~180 ps, compared to the input of ~155 ps. In any case, this is much larger than the ~70 ps resolution seen by Beni in data. Also, after finishing a pass through the mcsmear parameters, it would be worth thinking of generating another set of simulations.