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-- PeterKammel - 14 Feb 2007
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As explained in Tom's Muon Detector Inefficiency report, there exist time independent ( TIIE) and time dependent ( TDIE) inefficiencies of the entrance muon detectors. Both potentially lead to distortions of the observed time spectrum.

  • by histogramming the electron time from a mu' against the time of the primary muon mu, which is detected by the entrance muon counters ( wrong electron)

  • by accepting a mu stopping in the walls, while the mu' delivers the required stop track in the TPC ( wall stop).
where mu is defined as the muon detected by the entrance counters and mu' as the muon missed by them.

TIIE distortions caused by wrong electron effect

TIIE is determined from the muon drift distribution.

Tom analysis rep
Tom corrected ? 8.
Steve new analysis rep 3.2

One issue with this determination is the possibility of fake stop signatures in the TPC uncorrelated to the TIIE.

The wrong electron effect on the lifetime was estimated by Tom with his fast MC, giving -0.2 +- 1.1 Hz for TTIE=34 ppm. It is hard to confirm that from Tom's report. It would be interesting to see if Tom can roughly reproduce Steve's MuSC only PU spectrum.

Steve estimate the effect with a zero extrapolation for different entrance counter combinations and got 2.7 Hz. As discussed a larger range of efficiencies provided by different run groups would be helpful. Tom claims significant statistical uncertainty in this value.

Alternatively, Steve determines TIIE of the mPC as a ratio of (muSC+muPCX+muPCY)/muSC with a TPC stop signal. This method might not scale proportional to the total TIIE if the counts are not independent. The resulting extrapolated correction is 0.9 Hz.

Tom's fast MC indicates a significant start time dependence of the fitted lifetime, which is not observed in the data? Tom pointed out that we don't have enough statistics to see this.

TDIE distortions caused by wrong electron effect

Tom estimates the TDIE from the MuSC deadtime as 126 ppm. As a deadtime of 12 ns is assumed, that should not change the fitted lifetime.

TIIE distortions caused by wall stop effect

Let us pessimistically assume TIIE= 8 ppm. The probability that a mu' fakes a good TPC stop after mu is TIIE * 0.63 * 21 kHz 0.024 ms = 2.5 ppm

Thus a contribution P(te-tmuSC)* 2.5 ppm is added to the undisturbed time distribution. According Tom's report, the most dangerous components are P(te-mu)= ... + 0.03 exp(-t/854ns) + 0.08 exp (-t/151ns). The total distorting amplitudes are thus are 0.08 ppm for Al and 0.2 ppm for Fe, which should be ok.

TDIE distortions caused by wall stop effect

According to Tom's estimate TDIE=126 ppm. I.e. the wall stop effect is 15x larger than for the TIIE case. Such a contribution would lead to 10 Hz start time sensitivity of the fitted lifetime.

Steve studies the change of the lifetime both for muPC and muSC deadtime variations and sees only small effects. A start time fit of mSC standard and 100 ns would be informative. But as it stands now, the data does not support Tom's TDIE estimate.

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Topic revision: r2 - 2007-02-14 - PeterKammel
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