Useful Things To Know about The Data

After integration with the space craft:
- Starting from December 8, 2006 (EM p29em1) there is a problem with the time tones. They do not seem to be properly stored. This affects the event time stamps. More details in JIRA ROOT-26. This seems to only have affected this specific release.
- Starting from when we integrated the LAT with the space craft there is a large increase in the number of events with a TKR trigger and <6 TKR hits. This behavior is seen when we are not staying powered on for a long time (< 1 shift at a time). After integration we have only been on for one shift per day. When running continously for longer times the efficiency goes back to normal.
- More continuous running started with the CPT on March 24 (around run number 077014293).
- There are still problems with rollovers in the time tones. One consequence is that time sometimes goes backwards. This is supposed to be fixed in FSW B0-10-0 which as of June 12, 2007 still hasn't been used on the LAT.
- During EMI there are numerous GPS dropout ('lock loss'). Note that the meaning of the GPS lock loss bit in the data is currently flipped.
Spectrum Astro (SASS):
- Gamma filter CAL pedestals and gains: Before run 077010608 it used ideal calibration constants. Starting from this run it uses realistic ones. The consequence is that the rate drops from 49 Hz to 25 Hz. Most of the removed events seem to have been low energy events (see for example CalRecon energy distribution in the SVAC Recon reports).
- The MIP filter runs are currently configured to preferentially select off-axis events (see track direction distribution in the SVAC Recon reports).
- TKR FIFO full: Starting from around run 077011026 we changed the TKR FIFO settings to allow for a maximum of 14 hits per layer side. We also reserve space for 126 hits in the GTCC buffer so that we will now never see any TKR FIFO full errors. One consequence of this is that we now have a handfull of phasing errors per 30 minute run.
- TKR Bay 10, layer 0, left side problem: Runs between 07011690 and 077012433 suffer from errors and stale data from the left side of layer 0 in TKR bay 10. Then, by mistake, we reverted back to the original split starting with run 077012749. As of 11.21.2006 we are still using this split and get stale data. One exception: as of 11.17.2006 the following run types have the correct (all right) split: 22x and 71x muon runs and the 20x MIP passthru filter runs. Gammafilter runs (both passthru and not passthru) and the MIP filter runs still have the original split.

LAT LICOS/FSW 70x and 71x Muon runs NRL/TVAC:
- Bug! All runs except the 71x runs have a wrong high energy diode CAL calibration. This means they have no xtals with energy >1 GeV (the exact threshold varies somewhat). This is fixed starting with run 077008316.
LAT LICOS/FSW 70x and 71x Muon runs April 2006:
- Bug! All runs except the 71x runs have a wrong high energy diode CAL calibration. This mans they have no xtals with energy >1 GeV (the exact threshold varies somewhat). All LAT 70x runs in the April runs list have been reprocessed with correct calibrations. Unfortunately these new calibrations had two problems. Seven offline(!) LAC thresholds were put to zero. I have verified that the effect of this is negligeable. The offline CAL LO and CAL HI thresholds used by TriggerAlg (we run TriggerAlg as a monitoring tool for real data) were too low. This means that the two Cal entries in the GltWord are wrong for data. In any case, you should use the GEM information for real data.
- Periodic trigger: No periodic trigger before run 77003051, 10 Hz for runs 77003051-77003064, 2 Hz for runs 77003165-77003571, 10 Hz again for runs 77003573-present.
- ACD Veto threshold: 0.1 MIPs before run 77003572, 0.3 MIPs after that. At the same time we also changed from GSFC pedestals to pedestals found with the ACD on the LAT.
- Both ACD VETO LVDS drivers enabled until April 20.
- CNO threshold: 20 MIPs
- LAT 71x and 4-range readout: Because of a configuration bug, the runs 77002457-77002465 and 77002497-77002502 do not have 4-range readout of the TKR&&ROI trigger engine. The bug was fixed for runs after 77003572.
- LAT 71x runs: After run 77003572 there is a factor three more CAL HI triggers in bay 2 than in the other bays. Known effect.
- Lights on/off: ON in runs 77003656 and 77003657. OFF in runs 77003658-77003665. The runs are normal LAT 70x runs.
- Light on/off: ON in runs 77004796-77004798. OFF in runs 77004799-77004801. The runs have a special configuration with a 100 Hz periodic trigger with unsuppressed, 1-range readout. Even though the other triggers are enabled, only the periodic trigger is allowed to open the trigger window.
- Gem sequence counter problem: In several runs there seems to be a block of events where the GEM sequence counter (the 'Event ID') is wrong. Looking at the elapsed time (and also the GEM discarded counter) it looks like the events should have been earlier in the sequence than they actually are. This will affect people doing deadtime studies as it will appear that time goes backwards for some events. More details in JIRA COM-54.
- Other interesting JIRAs under investigation: COM-9, COM-51, COM-56, COM-57 and COM-58
LAT SVAC muon runs January 13-16, 2006:
- B30 runs: Same as B10 except CAL LO and CAL HI are not allowed to open the trigger window.
- B30 runs: Residual retriggering from Bay 2. To remove them, require no CAL HI trigger in Bay 2. Use for example SVAC ntuple variable: GemCalHeVector[2]==0. This removed about 0.08% of the total event sample.
- Six xtals are always read out because of too low LAC (zero-suppression) thresholds. They are (Bay,Layer,Column): (0,1,8), (2,0,3), (3,3,5), (8,0,5), (10,1,5) and (11,5,10). They at least sometimes make it through the energy cut in CalRecon. These xtals do not cause extra triggers!
- CNO is allowed to open the trigger window. The threshold was set to ~~7.8~~ 20 30 MIPs.
- ROI was not allowed to open the trigger window. It had one Region Of Interest which included all the ACD tiles. It worked as a trigger i.e. if any tile had a signal above the Veto threshold the ROI bit in the GEM word was set. The Veto threshold was set to 0.2 MIP, but was actually more like 0.1 MIP.
- There was a 10 Hz periodic trigger that was allowed to open the trigger window.
- The Merit variable 'EvtRun' is not correct for runs in the range we have in the data and should not be used. It is correct for the DC2 runs though.
- The ACD tile in row 3, column 4 (Tile ID 34) has the wrong thickness: 12 mm instead of 10 mm.
Six towers:
- We have now enabled a 10 Hz periodic trigger that is allowed to open the trigger window.
- Bug in a CAL calibration files concerning all 4 and 6 tower data: The high energy range is not correct. Both for runs with flight and the high energy muon gain this corresponds to above 1 GeV in a single xtal.
- TKR TOT was not processed with all the latest fixes (charge scale is a little off).
Four towers:
- Bug in a CAL calibration files concerning all 4 and 6 tower data: Only the lowest energy range is correct.
- We still have the Event ID initialization bug.
- SVAC ntuple 'TkrNumClusters' has a bug and should not be used until further notice!
- The Cal Low trigger thresholds for the CALs in bay positions 1 and 5 were set to one fixed value - a little on the high side.
- The LAC thresholds for the CALs in bay positions 1 and 5 were not correct (too low) so we have lots of noise hits - about 67 and 44 xtals read out per event respectively. Very few of these make it into recon which has an energy cut - only 1 per event for all the towers combined.
- We are now using the 1-shot TKR trigger.
- Most of the TKR trigger primitives are missing - only about 10% are there. This is probably due to timing changes introduced by the 1-shot TKR trigger. Note that the CAL trigger primitives should not be affected by this, but of course: most of the triggers are TKR triggers.
- The TKR Hot strips calibration file had a bug. All trackers except FM A and FM B were marked as dead. This did not affect the data digis. However, any missing hit in TkrRecon was flagged as a hot strip.
- TKR TOT was not processed with all the latest fixes (charge scale is a little off).
Two towers:
- Event ID is now 32 bits i.e. no more roll overs (multiple events with the same Event ID).
- Initialization bug in online means the Event ID sometimes starts at 131073.
- Trigger window is now 12 ticks (1 tick is 50 ns) instead of 5 ticks which we used for the 1 tower runs.
- New SVAC variable available: EvtTick. Can be used to find the time between any two events. Does not saturate like the GemDeltaEventTime.
- SVAC ntuple 'TkrNumClusters' has a bug and should not be used until further notice!
- To find out which tower triggered, use GemTkrVector[iTower], GemCalLeVector[iTower] etc.
- TKR TOT was not processed with all the latest fixes (charge scale is a little off).