@article{4d4ce562f72f4949a1eec3a4cddcdbff,
title = "Precision Analysis of the Xe 136 Two-Neutrino ββ Spectrum in KamLAND-Zen and Its Impact on the Quenching of Nuclear Matrix Elements",
abstract = "We present a precision analysis of the Xe136 two-neutrino ββ electron spectrum above 0.8 MeV, based on high-statistics data obtained with the KamLAND-Zen experiment. An improved formalism for the two-neutrino ββ rate allows us to measure the ratio of the leading and subleading 2νββ nuclear matrix elements (NMEs), ζ312ν=-0.26-0.25+0.31. Theoretical predictions from the nuclear shell model and the majority of the quasiparticle random-phase approximation (QRPA) calculations are consistent with the experimental limit. However, part of the ζ312ν range allowed by the QRPA is excluded by the present measurement at the 90% confidence level. Our analysis reveals that predicted ζ312ν values are sensitive to the quenching of NMEs and the competing contributions from low- and high-energy states in the intermediate nucleus. Because these aspects are also at play in neutrinoless ββ decay, ζ312ν provides new insights toward reliable neutrinoless ββ NMEs.",
author = "{(KamLAND-Zen Collaboration)} and A. Gando and Y. Gando and T. Hachiya and {Ha Minh}, M. and S. Hayashida and Y. Honda and K. Hosokawa and H. Ikeda and K. Inoue and K. Ishidoshiro and Y. Kamei and K. Kamizawa and T. Kinoshita and M. Koga and S. Matsuda and T. Mitsui and K. Nakamura and A. Ono and N. Ota and S. Otsuka and H. Ozaki and Y. Shibukawa and I. Shimizu and Y. Shirahata and J. Shirai and T. Sato and K. Soma and A. Suzuki and A. Takeuchi and K. Tamae and K. Ueshima and H. Watanabe and D. Chernyak and A. Kozlov and S. Obara and S. Yoshida and Y. Takemoto and S. Umehara and K. Fushimi and S. Hirata and Berger, {B. E.} and Fujikawa, {B. K.} and Learned, {J. G.} and J. Maricic and Winslow, {L. A.} and Y. Efremenko and Karwowski, {H. J.} and Markoff, {D. M.} and W. Tornow and T. O'Donnell",
note = "Funding Information: We thank P. Vogel for useful discussions. The KamLAND-Zen experiment is supported by JSPS KAKENHI Grants No. 21000001 and No. 26104002; the World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan; Netherlands Organisation for Scientific Research; and under the U.S. Department of Energy (DOE) Award No. DE-AC02-05CH11231, as well as other DOE and NSF grants to individual institutions. The Kamioka Mining and Smelting Company has provided service for activities in the mine. We acknowledge the support of NII for SINET4. J. M. is supported by the JSPS KAKENHI Grant No. 18K03639, MEXT as “Priority issue on post-K computer” (Elucidation of the fundamental laws and evolution of the universe), JICFuS, the CNS-RIKEN joint project for large-scale nuclear structure calculations, and the U.S. DOE (Award No. DE-FG02-00ER41132). J. M. thanks the Institute for Nuclear Theory at the University of Washington for its hospitality. F. S. is supported by the Slovak Research and Development Agency under Contract No. APVV-14-0524 and European Regional Development Fund-Project “Engineering applications of microworld physics” (CZ.02.1.01/0.0/0.0/16_019/0000766).",
year = "2019",
month = may,
day = "13",
doi = "10.1103/PhysRevLett.122.192501",
language = "English",
volume = "122",
journal = "Physical Review Letters",
issn = "0031-9007",
publisher = "American Physical Society",
number = "19",
}