Possible features in the calibration plots

The different cases considered below are:

• Muted LED
• Magnetic field inside the DIRC shield
• HV not nominal
• DFB changed
• DCC changed
• Summary

• Muted LED: BAD calibration
The sector 10 LED didn't emit any light during this calibration, preventing the PMTs from this region to be properly calibrated. Therefore, this calibration is bad although it was loaded in the DB as the online validation process is turned off or is accepting everything.The LED can emit no light for two main reasons: either it is broken or it doesn't receive triggers from the DCC (bad board or bad connection). In this case, the cable connecting the DCC to the light generator crate was not plugged conveniently.
• Magnetic field inside the DIRC shield: BAD calibration In that case, the DIRC was calibrated by mistake by the pilot while the solenoid was OFF but the bucking coil ON. As the bucking coil is here to compensate the magnetic field from the solenoid, it was generating some B-field inside the DIRC magnetic shield which was affecting the PMTs. Hence, T0 was significantly modified for several PMTs which made this calibration bad. The DIRC can be calibrated properly when both fields are nominal or at zero. The two other states (one field ON and the other OFF) would lead to bad results.
• HV not nominal: potentially BAD calibration Some PMTs show reduced efficiencies in the outermost part of sector 4. Even more PMTs show a large shift in the T0 calibration.

  Such pattern was due to two HV spare boards which were put in HV crate 3 to replaced two broken boards. After being put in, the nominal HV values were not reloaded and so the default values were not appropriate for the powered channels. Yet, as these boards had been in some HV crates in the past, the nominal V0 voltages were not that far from the expected values (in average, 50% above and 50% below!). So in fact this was not a real problem (fixed after a few hours): calibrations didn't diverge and the runs taken in the meantime were flagged 'OK' , both by the DIRC and by the PID group. Always reset the nominal HV after having changed some boards!

• DFB changed: a priori GOOD calibration
  The T0s include electronics-related effects. Hence, after changing a front-end boards, fluctuations in the T0 plots are expected. That's what we can (hardly next time a DFB gets changed, replace the current plots by nicer ones!!!) see on the upper border of sector 5 ('blue' radius). The DFB 'radial structure' should be visible on the plot: affected PMTs should form a blue or black 'line'. After a second calibration, the troubled area becomes invisible. The last two calibrations have been taken with the same electronics and are hence in agreement! So, after having changed an electronics board, take two calibrations in a row and make sure they agree.
• DCC changed: a priori GOOD calibration For the same reason as explained above, changing a DCC modifies the T0 correction in a whole sector. Again, take two calibrations in a row and make sure they agree.