Time of flight detector for charged particle identification based on circular electron-positron collider

Abstract

The circular electron-positron collider (CEPC) requires a 3% precision in the measurement of d<i>E</i>/d<i>x</i> to identify long-lived charged particles. However, the measurement of d<i>E</i>/d<i>x</i> has a blind area for each of charged particles of <inline-formula><tex-math id="M8">\begin{document}$\pi / \rm{K}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M8.png"/></alternatives></inline-formula>, <inline-formula><tex-math id="M9">\begin{document}$\pi / \rm{P}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M9.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M9.png"/></alternatives></inline-formula>, and <inline-formula><tex-math id="M10">\begin{document}$\rm{K} / \rm{P}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M10.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M10.png"/></alternatives></inline-formula>, having transverse momenta of 1 GeV/<i>c</i>, 1.6 GeV/<i>c</i>, and 2 GeV/<i>c</i> respectively. One potential solution is to use a high-precision time-of-flight (TOF) detector with a time resolution of less than 50 ps to fill in the blind area. To address this, we propose a small particle TOF detector that uses small plastic scintillators (<inline-formula><tex-math id="M11">\begin{document}$1 \;\; \mathrm{cm} \times 1 \;\; \mathrm{cm} \times 0.3 \;\; \mathrm{cm}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M11.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M11.png"/></alternatives></inline-formula>) silicon photomultipliers for readout. In this work, we introduce the construction of the detector and calibrate its performance by using <inline-formula><tex-math id="M12">\begin{document}${ }^{90} \mathrm{Sr} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M12.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="12-20222271_M12.png"/></alternatives></inline-formula> electron collimators and high-speed waveform acquisition electronics. Using a constant fraction timing method, we find that the time resolution of the detector is about 48 ps, satisfying the CEPC’s requirements for TOF detection.