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We report on a search for heavy neutrinos in B-meson decays. The results are obtained using a data sample that contains 772 × 10 6 B B pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e − collider. No signal is observed and upper limits are set on mixing of heavy neutrinos with left-handed neutrinos of the Standard Model in the mass range 0.5 GeV/c 2 − 5.0 GeV/c 2 .

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We report on a new constraint on gravitylike short-range forces, in which the interaction charge is mass, obtained by measuring the angular distribution of 5Å neutrons scattering off atomic xenon gas. Around 10 7 scattering events were collected at the 40 m small angle neutron scattering beam line located at the HANARO research reactor of the Korean Atomic Energy Research Institute. The extracted coupling strengths of new forces in the Yukawa-type parametrization areĝ 2 = (0.2 ± 6.8 ± 2.0)×10 −15 GeV −2 andĝ 2 = (−5.3±9.0GeV −2 for interaction ranges of 0.1 and 1.0 nm, respectively. These strengths correspond to 95% confidence level limits of g 2 < (1.4 ± 0.2) × 10GeV −2 and g 2 < (1.3 ± 0.2) × 10 −16 GeV −2 , improving the current limits for interaction ranges between 4 and 0.04 nm by a factor of up to 10.Extensions of the standard model of particle physics have long been discussed. Some of these theories, based on supersymmetry or extra space dimensions, naturally involve gravity or gravitylike interactions even at low energies. Several models predict new bosons mediating gravitylike forces that couple to mass, baryon number, or, in the case of grand unification models, to the difference of baryon and lepton numbers [1][2][3][4][5][6]. This class of models induces modifications to the Newtonian inversesquare law of gravitational interactions, and may also cause violation of the weak equivalence principle. These proposals motivate us to search for new gravitylike forces. Comprehensive reviews of such theories, and the forces they predict, can be found in Refs. [7][8][9].The forces due to such new bosons can be simply modeled by a Yukawa-type scattering potential written in natural units aswhere g 2 is a coupling strength, Q i are coupling charges, and µ is the mass of the boson mediating the force. Such models can be considered in the g 2 − µ or g 2 − λ parameter space, where λ ≡ 1/µ is the interaction range. Current experimental limits at 95% confidence level (C.L.) for interactions that couple to mass are shown in Fig. 1. Constraints A and B were obtained by microscopic experiments that precisely measured interactions between neutrons and atoms [10,11]. The experimental method used to achieve the results reported in this Letter follows a similar approach. Constraints C to I were obtained by macroscopic tests, searching for non-Newtonian forces between test masses using techniques such as torsion balances and microcantilevers [12][13][14][15][16][17][18].This experiment was performed at the 40 m small angle neutron scattering (SANS) beam line located at the HA-NARO research reactor of the Korean Atomic Energy Research Institute [19]. [10,11], while constraints C to I were obtained using macroscopic methods [12][13][14][15][16][17][18]. Theoretical expectations from an extra U (1) gauge boson at different symmetry breaking scales Λ U (1) (∼ 246 GeV and 10 TeV) [1,2], and from a baryon number gauge field in the bulk of extra space dimensions [3,4] are shown as dashed lines and the hatched area, respectively.of ...