One of the most promising approaches for the next generation of neutrino experiments is the realization of large hybrid Cherenkov/scintillation (C/S) detectors. The potential arising from time separation of the components of the light signal is foreseen to be realized with innovations in photon detection technology and liquid scintillator chemistry (see [1–5]). In such a hybrid detector it will be possible to exploit the Cherenkov signal for the reconstruction of directional and topological information while the high light yield of an organic scintillator would ensure the excellent energy resolution and low thresholds necessary for several applications. However, a crucial technique in all large-scale liquid scintillator (LS) detectors is background discrimination by particle identification (PID). The PID arises from the fact that the time profile of scintillation light emitted in response to a recoiling proton may differ from electron-like events due to quenching effects. This can be exploited in a pulse-shape discrimination (PSD) analysis leading to background reduction typically by several orders of magnitude. Beyond that, in a hybrid detector the ratio of Cherenkov to scintillation signal strength enhances PID further and background suppression potential exceeds by far the one provided only by pulse-shape discrimination [1, 6]. Moreover, with such a novel liquid scintillator doped successfully with a large quantity of a double-beta emitting isotope (e.g. ¹³⁰Te, ¹⁰⁰Mo or ¹³⁶Xe), the way towards a multi-ton experiment (namely JUNO Phase II or Theia) for the search of the 0νββ decay is paved.

Over the last three years, a slow scintillator suitable for the second phase of the JUNO experiment and the neutrino detectors EoS and Theia, which also allows loading with isotopes to search for neutrino-less double beta decay was developed at TUM. Therefore, the approach of blended solvent scintillation cocktails to reach a slowed scintillation light emission with conventional fluors PPO (2,5-Diphenyloxazole, CAS 92-71-7) and BPO (2-(4-Biphenyl)-5-phenyloxazole, CAS 852-37-9) was used. Here, a scintillation cocktail based on the combination of the intrinsically slow but highly transparent solvents linear alkylbenzene (LAB, CAS 67774-74-7) and Diisopropylnaphthalene (DIN, CAS 38640-62-9) was synthesized and extensively investigated with respect to its light yield, transparency, spectral light emission and characteristic pulse-shape for e- /𝛾-interactions and neutron induced proton recoils [7]. Last year, loading techniques for tellurium (via tellur-diols), molybdenum via molybdenum hexacarbonyls, and xenon were successfully developed [8]. 

References and Publications

[1] S. Biller, Phys. Rev. D 87, 071301(R) (2013) 349.
[2] C. Aberle et al, JINST 9, P06012 (2014) 350.
[3] M. Li et al., Nuc. Instrum. and Meth. A, Volume 830 (2016) 351.
[4] H. Wei et al., Phys. Lett. B 769 (2017) 352.
[5] Z. Guo et al., Astropart. Phys., 109 (2019) 353.
[6] S. Biller et al., Nuc. Instrum. and Meth. A, Volume 972 (2020).
[7] H. Steiger et al., JINST 19, P09015, (2024).
[8] H. Steiger et al., arXiv: 2510.06665, (2025). 

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