Scintillation Pulse Shape Discrimination Research Articles

Novel event classification based on spectral analysis of scintillation waveforms in Double Chooz

Liquid scintillators are a common choice for neutrino physics experiments, but their capabilities to perform background rejection by scintillation pulse shape discrimination is generally limited in large detectors. This paper describes a novel approach for a pulse shape based event classification developed in the context of the Double Chooz reactor antineutrino experiment. Unlike previous implementations, this method uses the Fourier power spectra of the scintillation pulse shapes to obtain event-wise information. A classification variable built from spectral information was able to achieve an unprecedented performance, despite the lack of optimization at the detector design level. Several examples of event classification are provided, ranging from differentiation between the detector volumes and an efficient rejection of instrumental light noise, to some sensitivity to the particle type, such as stopping muons, ortho-positronium formation, alpha particles as well as electrons and positrons. In combination with other techniques the method is expected to allow for a versatile and more efficient background rejection in the future, especially if detector optimization is taken into account at the design level.

Scintillation pulse shape discrimination in a two-phase xenon time projection chamber

The energy and electric field dependence of pulse shape discrimination in liquid xenon have been measured in a 10 g two-phase xenon time projection chamber. We have demonstrated the use of the pulse shape and charge-to-light ratio simultaneously to obtain a leakage below that achievable by either discriminant alone. A Monte Carlo is used to show that the dominant fluctuation in the pulse shape quantity is statistical in nature, and project the performance of these techniques in larger detectors. Although the performance is generally weak at low energies relevant to elastic WIMP recoil searches, the pulse shape can be used in probing for higher energy inelastic WIMP recoils.

Directional anisotropy in organic scintillation crystals

The scintillation pulse height responses and scintillation pulse shape discrimination (PSD) properties of anthracene crystals have been investigated for protons at six different energies in the range 1–22 MeV. Similar investigations were made for stilbene, terphenyl and quaterphenyl crystals at 8 MeV and for stilbene and naphthalene crystals at 22 MeV. The pulse height and PSD responses were investigated as a function of proton direction using recoil protons released within the crystals by monoenergetic incident neutrons. The pulse height anisotropy of anthracene crystals varies from 33% at 1 MeV to 8% at 22 MeV. The pulse height anisotropies of the other crystals are similar to that of anthracene at the same energy. The PSD anisotropy of anthracene expressed as a percentage of the PSD dispersion between Compton electrons and recoil protons varies from 3% at 1 MeV to 92% at 22 MeV. The PSD anisotropy of naphthalene is about half that of anthracene at 22 MeV and the PSD anisotropies of the other crystals are 3–7 times smaller than that of anthracene at 8 MeV. The pulse height and PSD anisotropies of anthracene are consistent with a model which assumes that the transfer of excitation energy during the scintillation process occurs preferentially in directions lying within the ab-planes of the crystal lattice.