Webinar: Energy resolution of CANDLES detector for studying neutrino-less double beta decay of 48Ca

Starts: 29 October, 2020

Ends: 29 October, 2020




Neutrino-less double beta decay (0νββ) is useful for determining the neutrino mass and confirming the Majorana nature of neutrino. In a 0νββ experiment, an irremovable two-neutrino double beta decay (2νββ) background surrounds the Q-value of the double-beta-decay isotope. The energy resolution must be improved to differentiate between 0νββ and 2νββ events. CAlcium fluoride for studies of Neutrino and Dark matters by Low Energy Spectrometer (CANDLES) discerns the 0νββ of 48Ca using CaF2(un-doped, non-enriched) scintillator crystals as detectors and sources. Scintillation photons are collected by surrounding photomultiplier tubes (PMTs). Ideally, the energy resolution should equal the statistical fluctuation of the number of photoelectrons. At the Q-value of 48Ca, the current energy resolution (2.6%) exceeds this fluctuation (1.6%). Because of CaF2’s long decay constant of 1000 ns, a signal integration in 4000 ns is used to calculate the energy. The baseline fluctuation (σbaseline) is accumulated in the signal integration, degrading the energy resolution. Therefore, this paper studies the σbaseline in the CANDLES III detector, which has a severe effect (1%) at the Q-value of 48Ca. To avoid σbaseline, photon counting can be used to obtain the number of photoelectrons in each PMT; however, a significant photoelectron signal overlapping probability in each PMT causes missing photoelectrons in counting and reduces the energy resolution. “Partial photon counting” reduces the σbaseline and minimizes photoelectron loss. We thus obtain improved energy resolutions of 4.5–4.0% at 1460.8 keV (γ-ray of 40K), and 3.3–2.9% at 2614.5keV (γ-ray of 208Tl). The energy resolution at the Q-value shows an estimated improvement of 2.2%, with improved detector sensitivity by factor 1.09 for the half-life of 0νββ of 48Ca. In this talk, I also discuss a possibility to improve CANDLES energy resolution with CaF2(un-doped) operated at low temperature and photon counting. It is estimated to achieve the sensitivity close to (or can be better than) the current world best limit of effective neutrino mass.

Date/time: Oct. 29th, 2020, 9:30-11:00 GMT+7 (VN timezone)
Connection: https://us02web.zoom.us/j/88603205534?pwd=Y0lnNXlTU3JSSDU3K2VLTHhZeGVOZz09
Meeting ID: 886 0320 5534 / Passcode: 459942