Time-of-Flight Spectrometer

The final part of the forward spectrometer is the Time-of-Flight Spectrometer used to measure particles β. Together with the momentum measurement provided by the other parts of the forward spectrometer this provides particle identification. The ToF-Spectrometer consists of 3 walls each segmented into individual horizontally oriented

Wall Origin Number of bars Length / cm Height / cm Depth / cm Time res. / ps
1 GrAAL 14 300 11.5 3 350
2 GrAAL 14 300 11.5 3 350
3 SAPHIR 18 340 21.5 5 700

The ToF spectrometer covers a total area of 3 × 3 m². Scintillator bars from the former GrAAL and SAPHIR experiments were used with the specifications shown in the table. To let the photon beam pass through and to avoid signals from e⁺/e⁻ pairs abundantly produced each wall has a 10 to 22 cm large horizontal gap. The readout of the scintillator bars is performed with photomultiplier tubes on both ends of the bars, providing position information along the bars. When combining information from multiple walls a time resolution of 0.34 ns can be achieved.

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