0000000000140227
AUTHOR
Z. Liptak
Search for an Invisibly Decaying Z′ Boson at Belle II in e+e−→μ+μ−(e±μ∓) Plus Missing Energy Final States
Theories beyond the standard model often predict the existence of an additional neutral boson, the Z′. Using data collected by the Belle II experiment during 2018 at the SuperKEKB collider, we perform the first searches for the invisible decay of a Z′ in the process e+e-→μ+μ-Z′ and of a lepton-flavor-violating Z′ in e+e-→e±μZ′. We do not find any excess of events and set 90% credibility level upper limits on the cross sections of these processes. We translate the former, in the framework of an Lμ-Lτ theory, into upper limits on the Z′ coupling constant at the level of 5×10-2-1 for MZ′≤6 GeV/c2.
Final results on $${}^\mathbf{82 }{\hbox {Se}}$$ 82Se double beta decay to the ground state of $${}^\mathbf{82 }{\hbox {Kr}}$$ 82Kr from the NEMO-3 experiment
Using data from the NEMO-3 experiment, we have measured the two-neutrino double beta decay ($$2\nu \beta \beta $$ 2νββ ) half-life of $$^{82}$$ 82 Se as $$T_{\smash {1/2}}^{2\nu } \!=\! \left[ 9.39 \pm 0.17\left( \text{ stat }\right) \pm 0.58\left( \text{ syst }\right) \right] \times 10^{19}$$ T1/22ν=9.39±0.17stat±0.58syst×1019 y under the single-state dominance hypothesis for this nuclear transition. The corresponding nuclear matrix element is $$\left| M^{2\nu }\right| = 0.0498 \pm 0.0016$$ M2ν=0.0498±0.0016 . In addition, a search for neutrinoless double beta decay ($$0\nu \beta \beta $$ 0νββ ) using 0.93 kg of $$^{82}$$ 82 Se observed for a total of 5.25 y has been conducted and no evide…
Precise Measurement of the D0 and D+ Lifetimes at Belle II
We report a measurement of the D^{0} and D^{+} lifetimes using D^{0}→K^{-}π^{+} and D^{+}→K^{-}π^{+}π^{+} decays reconstructed in e^{+}e^{-}→cc[over ¯] data recorded by the Belle II experiment at the SuperKEKB asymmetric-energy e^{+}e^{-} collider. The data, collected at center-of-mass energies at or near the ϒ(4S) resonance, correspond to an integrated luminosity of 72 fb^{-1}. The results, τ(D^{0})=410.5±1.1(stat)±0.8(syst) fs and τ(D^{+})=1030.4±4.7(stat)±3.1(syst) fs, are the most precise to date and are consistent with previous determinations.
Detailed studies of $$^{100}$$ 100 Mo two-neutrino double beta decay in NEMO-3
The full data set of the NEMO-3 experiment has been used to measure the half-life of the two-neutrino double beta decay of $$^{100}$$ 100 Mo to the ground state of $$^{100}$$ 100 Ru, $$T_{1/2} = \left[ 6.81 \pm 0.01\,\left( \text{ stat }\right) ^{+0.38}_{-0.40}\,\left( \text{ syst }\right) \right] \times 10^{18}$$ T1/2=6.81±0.01stat-0.40+0.38syst×1018 year. The two-electron energy sum, single electron energy spectra and distribution of the angle between the electrons are presented with an unprecedented statistics of $$5\times 10^5$$ 5×105 events and a signal-to-background ratio of $$\sim $$ ∼ 80. Clear evidence for the Single State Dominance model is found for this nuclear transition. Limit…
Search for B+→K+νν¯ Decays Using an Inclusive Tagging Method at Belle II
A search for the flavor-changing neutral-current decay B^{+}→K^{+}νν[over ¯] is performed at the Belle II experiment at the SuperKEKB asymmetric energy electron-positron collider. The data sample corresponds to an integrated luminosity of 63 fb^{-1} collected at the ϒ(4S) resonance and a sample of 9 fb^{-1} collected at an energy 60 MeV below the resonance. Because the measurable decay signature involves only a single charged kaon, a novel measurement approach is used that exploits not only the properties of the B^{+}→K^{+}νν[over ¯] decay, but also the inclusive properties of the other B meson in the ϒ(4S)→BB[over ¯] event, to suppress the background from other B meson decays and light-qua…