Abstract
We performed a detailed study of the timing performance of the LHCb VELO Timepix3 Telescope with a 180 GeV/c mixed hadron beam at the CERN SPS. A twofold method was developed to improve the resolution of single-plane time measurements, resulting in a more precise overall track time measurement. The first step uses spatial information of reconstructed tracks in combination with the measured signal charge in the sensor to correct for a mixture of different effects: variations in charge carrier drift time; variations in signal induction, which are the result of a non-uniform weighting field in the pixels; and lastly, timewalk in the analog front-end. The second step corrects for systematic timing offsets in Timepix3 that vary from −2 to 2 ns. By applying this method, we improved the track time resolution from 438(16) ps to 276(4) ps.
Highlights
The first step uses spatial information of reconstructed tracks in combination with the measured signal charge in the sensor to correct for a mixture of different effects: variations in charge carrier drift time; variations in signal induction, which are the result of a non-uniform weighting field in the pixels; and lastly, timewalk in the analog front-end
Not all clock cycles have the same duration. This can be seen by looking at the number of counts from the fast oscillator (640 MHz), which we refer to as the fine time of arrival
We performed a detailed study of the timing performance of the LHCb VELO Timepix3 Telescope, which resulted in a thorough understanding of time measurements with Timepix3
Summary
2.3 Scintillator time measurement using the SPIDR TDC We used fast scintillators with an active area of 1.5 × 1.5 cm to provide two independent time references They are located up- and downstream of the telescope (as was shown in figure 1), and are equipped with constant fraction discriminators (CFD). To correct for this effect, we assume that the particles are uncorrelated to the clock, and measure the occupancy of each bin to determine its actual size. It can be seen that there is a clear spatial dependence: at low y-positions the upstream scintillator is too early with respect to the downstream scintillator, and it is too late at high y-positions This can be explained by considering the two particles in the diagram of figure 4. This eliminates the spatial dependence of the time difference between the scintillators
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