Hadronic vs. electromagnetic pulse shape discrimination in CsI(Tl) for high energy physics experiments

Abstract

A: Pulse shape discrimination using CsI(Tl) scintillators to perform neutral hadron particle identification is explored with emphasis towards application at high energy electronpositron collider experiments. Through the analysis of the pulse shape differences between scintillation pulses from photon and hadronic energy deposits using neutron and proton data collected at TRIUMF, it is shown that the pulse shape variations observed for hadrons can be modelled using a third scintillation component for CsI(Tl), in addition to the standard fast and slow components. Techniques for computing the hadronic pulse amplitudes and shape variations are developed and it is shown that the intensity of the additional scintillation component can be computed from the ionization energy loss of the interacting particles. These pulse modelling and simulation methods are integrated with GEANT4 simulation libraries and the predicted pulse shape for CsI(Tl) crystals in a 5 × 5 array of 5×5×30 cm 3 crystals is studied for hadronic showers from 0.5 and 1 GeV/c K 0 L and neutron particles. Using a crystal level and cluster level approach for photon vs hadron cluster separation we demonstrate proof-of-concept for neutral hadron detection using CsI(Tl) pulse shape discrimination in high energy electron-positron collider experiments.

CsI(Tl) pulse shape discrimination with the Belle II electromagnetic calorimeter as a novel method to improve particle identification at electron–positron colliders

“…Following the initial pre-amplification stage, the two signals are summed then processed by a CR-(RC) 4 shaping amplifier with shaping time of 0.5 µs [14]. The signal is then digitized into 31 samples with 18-bit precision and at a sample frequency of 1.7669 MHz (sample time of 0.56594 µs).…”

“…To characterize the waveform pulse shape the techniques developed in reference [4] are applied. The study in reference [4] demonstrated that energy deposits by highly ionizing particles produce a CsI(Tl) scintillation component measured to have a decay time of 630 ± 10 ns.…”

“…To characterize the waveform pulse shape the techniques developed in reference [4] are applied. The study in reference [4] demonstrated that energy deposits by highly ionizing particles produce a CsI(Tl) scintillation component measured to have a decay time of 630 ± 10 ns. This scintillation component is referred to as the hadron component as it is only produced by highly ionizing energy deposits and thus not present in scintillation emission from electromagnetic showers or energy deposits from low dE/dx particles, such as minimum ionizing particles [4].…”

“…The scintillation response of CsI(Tl) is empirically well known to depend on the ionization dE/dx of the particle that is depositing energy in the crystal [3]. Highly ionizing particles, such as stopping protons or alpha particles, are observed to produce CsI(Tl) scintillation emission with a faster decay time relative to the CsI(Tl) scintillation emission produced from energy deposits by photons or low dE/dx particles [3,4]. This phenomenon has been widely exploited in the energy regime of < 10 MeV to discriminate between interactions caused by electrons, protons and alpha particles [3,5], as well as in nuclear physics for low energy nuclei identification [6,7].…”

“…This phenomenon has been widely exploited in the energy regime of < 10 MeV to discriminate between interactions caused by electrons, protons and alpha particles [3,5], as well as in nuclear physics for low energy nuclei identification [6,7]. Recent studies have demonstrated the significant potential for PSD to improve hadronic shower identification at electron-position collider experiments [4]. Although several past and present detectors operating at high energy e + e − colliders have employed CsI(Tl) calorimeters, such as Belle [8], BaBar [9,10] and BE-SIII [11], applying CsI(Tl) PSD to improve particle identification has yet to be attempted at a high energy e + e − collider experiment.…”