Publications (6)11.61 Total impact
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ABSTRACT: We report a measurement of the neutrinoelectron elastic scattering rate of 862 keV 7Be solar neutrinos based on a 165.4 ktonday exposure of KamLAND. The observed rate is 582 +/ 90 (ktonday)^1, which corresponds to a 862 keV 7Be solar neutrino flux of (3.26 +/ 0.50) x 10^9 cm^2s^1, assuming a pure electron flavor flux. Comparing this flux with the standard solar model prediction and further assuming three flavor mixing, a nu_e survival probability of 0.66 +/ 0.14 is determined from the KamLAND data. Utilizing a global three flavor oscillation analysis, we obtain a total 7Be solar neutrino flux of (5.82 +/ 0.98) x 10^9 cm^2s^1, which is consistent with the standard solar model predictions.  [Show abstract] [Hide abstract]
ABSTRACT: The recent longterm shutdown of Japanese nuclear reactors has resulted in a significantly reduced reactor (nu) over bar (e) flux at KamLAND. This running condition provides a unique opportunity to confirm and constrain backgrounds for the reactor (nu) over bar (e) oscillation analysis. The data set also has improved sensitivity for other (nu) over bar (e) signals, in particular (nu) over bar (e)'s produced in betadecays from U238 and Th232 within the Earth's interior, whose energy spectrum overlaps with that of reactor (nu) over bar (e)'s. Including constraints on theta(13) from accelerator and shortbaseline reactor neutrino experiments, a combined threeflavor analysis of solar and KamLAND data gives fit values for the oscillation parameters of tan (2)theta(12) = 0.436(0.025)(+0.029), Delta m(21)(2) = 7.53(0.18)(+0.18) x 10(5) eV(2), and sin (2)theta(13) = 0.023(0.002)(+0.002). Assuming a chondritic Th/U mass ratio, we obtain 116(27)(+28) (nu) over bar (e) events from U238 and Th232, corresponding to a geo (nu) over bar (e) flux of 3.4(0.8)(+0.8) x 10(6) cm(2) s(1) at the KamLAND location. We evaluate various bulk silicate Earth composition models using the observed geo (nu) over bar (e) rate.Physical Review D 08/2013; 88(3):033001. DOI:10.1103/PhysRevD.88.033001 · 4.86 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present results from the first phase of the KamLANDZen doublebeta decay experiment, corresponding to an exposure of 89.5 kg yr of ^{136}Xe. We obtain a lower limit for the neutrinoless doublebeta decay halflife of T_{1/2}^{0ν}>1.9×10^{25} yr at 90% C.L. The combined results from KamLANDZen and EXO200 give T_{1/2}^{0ν}>3.4×10^{25} yr at 90% C.L., which corresponds to a Majorana neutrino mass limit of ⟨m_{ββ}⟩<(120250) meV based on a representative range of available matrix element calculations. Using those calculations, this result excludes the Majorana neutrino mass range expected from the neutrinoless doublebeta decay detection claim in ^{76}Ge, reported by a part of the HeidelbergMoscow Collaboration, at more than 97.5% C.L.Physical Review Letters 02/2013; 110(6):062502. · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present limits on Majoronemitting neutrinoless doubleβ decay modes based on an exposure of 112.3 days with 125 kg of 136Xe. In particular, a lower limit on the ordinary (spectral index n=1) Majoronemitting decay halflife of 136Xe is obtained as T1/20νχ0>2.6×1024 yr at 90% C.L., a factor of five more stringent than previous limits. The corresponding upper limit on the effective Majoronneutrino coupling, using a range of available nuclear matrix calculations, is 〈gee〉<(0.8–1.6)×10−5. This excludes a previously unconstrained region of parameter space and strongly limits the possible contribution of ordinary Majoron emission modes to 0νββ decay for neutrino masses in the inverted hierarchy scheme.Physical Review C 05/2012; 86(2). DOI:10.1103/PhysRevC.86.021601 · 3.88 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present results from the KamLANDZen doublebeta decay experiment based on an exposure of 77.6 days with 129 kg of 136 Xe. The measured twoneutrino doublebeta decay halflife of 136 Xe is T 2ν 1/2 = 2.38 ± 0.02(stat) ± 0.14(syst) × 10 21 yr, consistent with a recent measurement by EXO200. We also obtain a lower limit for the neutrinoless doublebeta decay halflife, T 0ν 1/2 > 5.7 × 10 24 yr at 90% confidence level (C. L.), which corresponds to almost a fivefold improvement over previous limits.Physical Review C 04/2012; 8560. DOI:10.1103/PhysRevC.85.045504 · 3.88 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present results from the KamLANDZen doublebeta decay experiment based on an exposure of 77.6 days with 129 kg of {sup 136}Xe. The measured twoneutrino doublebeta decay halflife of {sup 136}Xe is T{sup 2{nu}}{sub 1/2} = 2:38 {+}#6; 0:02(stat)#6;{+}0.14(syst)#2;x10{sup 21} yr, consistent with a recent measurement by EXO200. We also obtain a lower limit for the neutrinoless doublebeta decay halflife, T{sup 0{nu}}{sub 1/2} > 5.7 x#2; 10{sup 24} yr at 90% C.L.
Publication Stats
62  Citations  
11.61  Total Impact Points  
Top Journals
Institutions

2012–2013

Tohoku University
 Research Center for Neutrino Science
Sendai, Kagoshimaken, Japan
