Performance of a liquid scintillator containing a zirconium β-keto ester complex developed for the ZICOS experiment

A liquid scintillator containing a zirconium β-keto ester complex has been developed for the ZIrconium Complex in Organic Scintillator (ZICOS) neutrinoless double beta decay experiment. We are aiming to develop a detector which has a good energy resolution (4% at 2.5 MeV), a large light yield (60% that of BC505) and a low background rate (0.1 counts/tonne・year) with several tonnes of 96Zr isotope, so we have investigated the zirconium β-keto ester complexes tetrakis (isopropyl acetoacetato) zirconium and tetrakis (ethyl acetoacetato) zirconium, which have high solubility (over 10 wt.%) in anisole. We measured the performance of liquid scintillators containing these zirconium β-keto ester complexes and obtained 40% of the light yield of BC505 and energy resolution of 4.1% at 2.5 MeV assuming 40% photo coverage of the photomultiplier in the ZICOS detector. Thus we almost achieved our initial goal. Preliminary investigations indicate that tetrakis (diethyl malonato) zirconium will give us no quenching of the light yield and an energy resolution of 2.9% at 2.5 MeV. This will be a suitable complex for the ZICOS experiment, if it has a large solubility

Direct measurement of spectral shape of Cherenkov light using cosmic muons

The spectral pulse shape of Cherenkov lights was directly measured by using cosmic muons. The observed decay times for early and late timing were 5.0 and 5.2ns, respectively. They were actually shorter than the time of scintillation lights which were also measured as 9.3ns and 9.2ns, respectively. However we could not see the difference of the rise time between scintillation and Cherenkov lights. This was due to the slow response of our DAQ equipment, photomultiplier and FADC digitize

Precise pulse shape measurement of Cherenkov light using sub-MeV electrons from Sr-90/Y-90 beta source

The precise spectral pulse shape from Cherenkov lights was directly measured by using sub-MeV electrons from 90Sr/90Y beta source. The observed shape was clearly different from the shape of scintillation light. The pulse rise and fall （decay） time for Cherenkov light were 0.8 ns and 2.5 ns, respectively. They were actually shorter than those times of scintillation light which were also measured by 1.6 ns and 6.5 ns, respectively. This clear Thisclearclear difference of rise time will be used for the pulse shape discrimination in order to select PMTs which receive Cherenkov lights, and the topological information due to Cherenkov light will be used for the reduction of backgrounds from 208Tl beta decay which should be major backgrounds observed around Q-value （3.35MeV）of 96Zr neutrinoless double beta decay

ZICOS : New project for neutrinoless double beta decay experiment using zirconium complex in liquid scintillator

　A liquid scintillator containing a zirconium β-keto ester complex has been developed for the Zirconium COmplex in liquid Scintillator (ZICOS) experiment which is new project of neutrinoless double beta decay search. We are aiming to develop a detector which has a good energy resolution (3.5% at 3.35 MeV), a large light yield (60% that of BC505) and a low background rate (0.1 counts/tonne・year) with several hundred kg of 96Zr isotope, so we have investigated the zirconium β-keto ester complexes such as tetrakis (isopropyl acetoacetato) zirconium and tetrakis (ethyl acetoacetato) zirconium, which have high solubility (over 30 wt.%)in anisole. We measured the performance of liquid scintillator containing these zirconium β-keto ester complexes, and obtained 48.7+-7.1% of the light yield of BC505 and the energy resolution of 4.1+-0.6% at 3.35 MeV assuming 40% photo coverage of the photomultiplier in the detector. This results reached our initial goal, so we estimated that ZICOS experiment should be sensitive to < 0.2 - 0.3 eV assuming gA = 1.25, gPP = 1.11 and QRPA model, if a radius of the balloon is 1.5 m and the balloon is filled with a liquidscintillator containing 10 wt.% concentration of a zirconium β-keto ester complex with an enriched 96Zr

Augmented TLR9-induced Btk activation in PIR-B–deficient B-1 cells provokes excessive autoantibody production and autoimmunity

Pathogens are sensed by Toll-like receptors (TLRs) expressed in leukocytes in the innate immune system. However, excess stimulation of TLR pathways is supposed to be connected with provocation of autoimmunity. We show that paired immunoglobulin (Ig)-like receptor B (PIR-B), an immunoreceptor tyrosine-based inhibitory motif–harboring receptor for major histocompatibility class I molecules, on relatively primitive B cells, B-1 cells, suppresses TLR9 signaling via Bruton's tyrosine kinase (Btk) dephosphorylation, which leads to attenuated activation of nuclear factor κB p65RelA but not p38 or Erk, and blocks the production of natural IgM antibodies, including anti-IgG Fc autoantibodies, particularly rheumatoid factor. The autoantibody production in PIR-B–deficient (Pirb−/−) mice was further augmented in combination with the Faslpr mutation, which might be linked to the development of autoimmune glomerulonephritis. These results show the critical link between TLR9-mediated sensing and a simultaneously evoked, PIR-B–mediated inhibitory circuit with a Btk intersection in B-1 cells, and suggest a novel way toward preventing pathogenic natural autoantibody production