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Time alignment studies

Time alignment studies. disclaimer: 1) we’ve not set up an alternative time alignment procedure with respect to what presented by Giacomo/Giovanni/Maddalena 2) we report on a couple of issues (mostly related to hardware) which could be useful to better understand timing.

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Time alignment studies

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  1. Time alignment studies disclaimer: 1) we’ve not set up an alternative time alignment procedure with respect to what presented by Giacomo/Giovanni/Maddalena 2) we report on a couple of issues (mostly related to hardware) which could be useful to better understand timing M. Palutan, A. Sarti, A. Sciubba 10/11/08

  2. Introduction • We use Giacomo/Giovanni software tools to reconstruct cosmic muon tracks • Data sample: 33878-33892 + 34063-34120 (september) + mask 133 noisy channels • (as Firenze analysis) • From a sample of 700k events we selected ~80k FORWARD tracks, with 3 or 4 • associated hits (we reject events with more than one track) • We don’t apply any correction to account for track projectivity; the expected muon time is evaluated as the average of the track hit times • We focus on two aspects of the time alignment procedure • 1) The use of tX and tY instead of their average • 2) The effect of the TDC non-linearities

  3. Time residuals before alignment: ODE 109 (ns) tX-t0 tY-t0 ODE channel M3R4: with IB (ns) <tX-t0> <tY-t0> ODE channel M3R4: 4 chambers let’s define 4 padY tX-t0 = Rx tY-t0 = RY 24 padX

  4. Time residuals before alignment: ODE 60 (ns) Rx RY ODE channel M2R2: no IB (ns) ODE channel M2R2: 1 chamber 4 padY an average alignment could introduce trigger inefficiency 48 padX

  5. Time residuals: M2R2 vs M2R3 M2R2: no IB M2R3: with IB Rx Rx RY RY (ns) (ns) <RX> = -0.66 ns <RX> = -0.67 ns <RY> = 3.85 ns <RY> = -0.47 ns M2R2: 1 chamber M2R3: 2 chambers 4 padY 4 padY 48 padX 24 padX

  6. Time residuals before alignment: ODE 149 (ns) Rx RY ODE channel M5R4: with IB (ns) ODE channel M5R4: 4 chambers M5R4: 4 chambers 4 padY the alignment is correct only on average 6 padX

  7. Time alignment <Rx> • Each ODE channel is shifted by the average time residual • We don’t correct channel with 1 entry • warning: the same data are used both for evaluating the correction and to check the quality of the procedure <RY> ODE channel ODE channel ODE channel

  8. Time residuals before/after alignment <RX> ns <RY>ns M2 M3 M4 M5 M2 M3 M4 M5 before alignment after alignment RMS(RX) ns RMS(R) ns M2 M3 M4 M5 M2 M3 M4 M5 pad time: t=(tX+tY)/2 R = t-t0

  9. PAD time residuals before/after alignment before RMS = 7.7 ns (X+Y)/2 all stations R (ns) after RMS = 6.8 ns R (ns)

  10. PAD time residuals after alignment M3R4 Rx RY (ns) Dt = (tX-tY)/2 (ns)

  11. Time spectra vs TDC range To investigate if tails are due to bad time measurement, a symmetric cut is applied: we eliminate TDC bins 14-15 on one side and bins 0-1 on the other side, to avoid systematic displacement of the time average The aim is to use only the center of the TDC range, where time is better determined Time alignment should be insensitive to this cut, but for some reduction in statistics

  12. Time spectra vs TDC range 1 < binX AND binY < 14 binX OR binY = 1, 14, 15 time of the other tX tY tX tY (ns) (ns) Dt Dt (ns) (ns)

  13. tYvs tX 1 < binX AND binY < 14 binX OR binY = 1, 14, 15 tY tY ns ns tX tX

  14. An example: ODE 106 (M3R4) tX tY RX RY all hits 1 < binX AND binY < 14 RX RY

  15. Time alignment without bin 1, 14, 15 RX RY all hits padX padY M3R4 ns 1 < binX AND binY < 14 RX RY ns

  16. Time alignment without bin 1, 14, 15 all hits before align. RMS = 7.7 ns after align. RMS = 6.8 ns (X+Y)/2 all stations R (ns) = 3.6 ns 1 < binX AND binY < 14 before align. RMS = 6.9 ns after align. RMS = 5.8 ns R (ns) = 3.7 ns

  17. Comparison of alignment constants Let’s compare the alignment constants evaluated without the TDC cut (K0) with the ones evaluated using the TDC cut (K1) K0 – K1 (ns) K1 vs K0 (ns) When applying the TDC cut, the number of empty ODE channels increases -> K1=0

  18. Conclusions • The use of tX and tY in the alignment procedure is more directly related to the hardware misalignments • 2) In some steps of the alignment procedure, it could be useful to use only the central region of the TDC range

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