Characterization of water-based liquid scintillator for Cherenkov and scintillation separation
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Regular Article - Experimental Physics
Characterization of water-based liquid scintillator for Cherenkov and scintillation separation J. Caravaca1,2,a , B. J. Land1,2 , M. Yeh3 , G. D. Orebi Gann1,2 1
University of California, Berkeley, CA 94720-7300, USA Lawrence Berkeley National Laboratory, Berkeley, CA 94720-8153, USA 3 Brookhaven National Laboratory, Upton, NY 11973-500, USA
2
Received: 1 June 2020 / Accepted: 29 August 2020 © The Author(s) 2020
Abstract This paper presents measurements of the scintillation light yield and time profile for a number of concentrations of water-based liquid scintillator, formulated from linear alkylbenzene (LAB) and 2,5-diphenyloxazole (PPO). We find that the scintillation light yield is linear with the concentration of liquid scintillator in water between 1 and 10% with a slope of 127.9 ± 17.0 ph/MeV/concentration and an intercept value of 108.3 ± 51.0 ph/MeV, the latter being illustrative of non-linearities with concentration at values less than 1%. This is larger than expected from a simple extrapolation of the pure liquid scintillator light yield. The measured time profiles are consistently faster than that of pure liquid scintillator, with rise times less than 250 ps and prompt decay constants in the range of 2.1–2.85 ns. Additionally, the separation between Cherenkov and scintillation light is quantified using cosmic muons in the CHESS experiment for each formulation, demonstrating an improvement in separation at the centimeter scale. Finally, we briefly discuss the prospects for large-scale detectors.
1 Introduction Liquid-based optical detectors have been used to great success in particle physics, in particular for neutrino physics and rare event searches (see Sec. 35.3.1 of [1] for a complete overview). A broad community is pursuing the idea of a hybrid optical detector, that can leverage both Cherenkov and scintillation signals simultaneously [2–4]. Such a detector could achieve good energy resolution while also having sensitivity to particle direction. The ratio of Cherenkov to scintillation light would also offer a powerful handle for particle and event classification, while a clean identification of the Cherenkov cone would be ideal for long-baseline neua e-mail:
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trino physics. A detector with these capabilities would have favorable signal to background ratio across a broad spectrum of physics topics [5–8]. Given the much higher light yield for scintillation over Cherenkov, the detection of a clean Cherenkov signal from pure scintillator is very challenging. Nevertheless, it has been successfully demonstrated in the CHESS experiment [9] and other cases [10] using a technique that exploits the differences in emission time profiles and topology. The pursuit of water-based liquid scintillator (WbLS) [11], a mixture of liquid scintillator (LS) in water, is one possible avenue to allow optical detectors to reach these requirements. First, it provides a scintillator with an absorption length close
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