We report on the design, production, and performance of compact 40-cm3 Time Projection Chambers (TPCs) that detect fast neutrons by measuring the three-dimensional (3D) ionization distribution of nuclear recoils in 4He:CO2 gas at atmospheric pressure. We use these detectors to characterize the fast-neutron flux inside the Belle II detector at the SuperKEKB electron–positron collider in Tsukuba, Japan, where the primary design constraint is a small form factor. We find that the TPCs meet or exceed all design specifications, and are capable of measuring the 3D surface shape and charge density profile of ionization clouds from nuclear recoils and charged tracks in exquisite detail. Scaled-up detectors based on the detection principle demonstrated here may be suitable for directional dark matter searches, measurements of coherent neutrino–nucleus scattering, and other experiments requiring precise detection of neutrons or nuclear recoils.

We present a summary of future prospects for direct detection of dark matter within the GeV/c2 to TeV/c2 mass range. This is paired with a new definition of the neutrino fog in order to better quantify the rate of diminishing returns on sensitivity due to irreducible neutrino backgrounds. A survey of dark matter candidates predicted to fall within this mass range demonstrates that fully testing multiple well-motivated theo-ries will require expanding the currently-funded generation of experiments down to and past the neutrino fog. We end with the status and plans for next-generation exper-iments and novel R&D concepts which will get us there.

We present measurements of the branching fraction and time-dependent CP asymmetries in B0→J/ψπ0 decays based on (231.8±2.6) ×106Υ(4S)→BB̄ decays collected with the BABAR detector at the SLAC PEP-II asymmetric-energy B factory. We obtain a branching fraction B(B0→J/ψπ0)=(1.94±0.22(stat)±0.17(syst))×10-5. We also measure the CP asymmetry parameters C=-0.21±0.26(stat)±0. 06(syst) and S=-0.68±0.30(stat)±0.04(syst). © 2006 The American Physical Society.

We present first evidence that the cosine of the CP-violating weak phase 2β is positive, and hence exclude trigonometric multifold solutions of the Cabibbo-Kobayashi-Maskawa (CKM) Unitarity Triangle using a time-dependent Dalitz plot analysis of B^{0}→D^{(*)}h^{0} with D→K_{S}^{0}π^{+}π^{-} decays, where h^{0}∈{π^{0},η,ω} denotes a light unflavored and neutral hadron. The measurement is performed combining the final data sets of the BABAR and Belle experiments collected at the ϒ(4S) resonance at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain (471±3)×10^{6}BB[over ¯] pairs recorded by the BABAR detector and (772±11)×10^{6}BB[over ¯] pairs recorded by the Belle detector. The results of the measurement are sin2β=0.80±0.14(stat)±0.06(syst)±0.03(model) and cos2β=0.91±0.22(stat)±0.09(syst)±0.07(model). The result for the direct measurement of the angle β of the CKM Unitarity Triangle is β=[22.5±4.4(stat)±1.2(syst)±0.6(model)]°. The measurement assumes no direct CP violation in B^{0}→D^{(*)}h^{0} decays. The quoted model uncertainties are due to the composition of the D^{0}→K_{S}^{0}π^{+}π^{-} decay amplitude model, which is newly established by performing a Dalitz plot amplitude analysis using a high-statistics e^{+}e^{-}→cc[over ¯] data sample. CP violation is observed in B^{0}→D^{(*)}h^{0} decays at the level of 5.1 standard deviations. The significance for cos2β>0 is 3.7 standard deviations. The trigonometric multifold solution π/2-β=(68.1±0.7)° is excluded at the level of 7.3 standard deviations. The measurement resolves an ambiguity in the determination of the apex of the CKM Unitarity Triangle.

We report a measurement of the time-dependent CP asymmetry of B[over ¯]^{0}→D_{CP}^{(*)}h^{0} decays, where the light neutral hadron h^{0} is a π^{0}, η, or ω meson, and the neutral D meson is reconstructed in the CP eigenstates K^{+}K^{-}, K_{S}^{0}π^{0}, or K_{S}^{0}ω. The measurement is performed combining the final data samples collected at the ϒ(4S) resonance by the BABAR and Belle experiments at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain (471±3)×10^{6} BB[over ¯] pairs recorded by the BABAR detector and (772±11)×10^{6} BB[over ¯] pairs recorded by the Belle detector. We measure the CP asymmetry parameters -η_{f}S=+0.66±0.10(stat)±0.06(syst) and C=-0.02±0.07(stat)±0.03(syst). These results correspond to the first observation of CP violation in B[over ¯]^{0}→D_{CP}^{(*)}h^{0} decays. The hypothesis of no mixing-induced CP violation is excluded in these decays at the level of 5.4 standard deviations.

We report measurements of sin2β and cos2β using a time-dependent Dalitz plot analysis of B0→D(∗)h0 with D→KS0π+π- decays, where the light unflavored and neutral hadron h0 is a π0, η, or ω meson. The analysis uses a combination of the final data sets of the BaBar and Belle experiments containing 471×106 and 772×106 BB pairs collected at the (4S) resonance at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. We measure sin2β=0.80±0.14(stat)±0.06(syst)±0.03(model) and cos2β=0.91±0.22(stat)±0.09(syst)±0.07(model). The result for the direct measurement of the angle is β=(22.5±4.4(stat)±1.2(syst)±0.6(model))°. The last quoted uncertainties are due to the composition of the D0→KS0π+π- decay amplitude model, which is newly established by a Dalitz plot amplitude analysis of a high-statistics e+e-→cc data sample as part of this analysis. We find the first evidence for cos2β>0 at the level of 3.7 standard deviations. The measurement excludes the trigonometric multifold solution π/2-β=(68.1±0.7)° at the level of 7.3 standard deviations and therefore resolves an ambiguity in the determination of the apex of the CKM Unitarity Triangle. The hypothesis of β=0° is ruled out at the level of 5.1 standard deviations, and thus CP violation is observed in B0→D(∗)h0 decays. The measurement assumes no direct CP violation in B0→D(∗)h0 decays.

The Belle II detector will provide a major step forward in precision heavy flavor physics, quarkonium and exotic states, searches for dark sectors, and many other areas. The sensitivity to a large number of key observables can be improved by about an order of magnitude compared to the current measurements, and up to two orders in very clean search measurements. This increase in statistical precision arises not only due to the increased luminosity, but also from improved detector efficiency and precision for many channels. Many of the most interesting observables tend to have very small theoretical uncertainties that will therefore not limit the physics reach. This book has presented many new ideas for measurements, both to elucidate the nature of current anomalies seen in flavor, and to search for new phenomena in a plethora of observables that will become accessible with the Belle II dataset. The simulation used for the studiesinthis book was state ofthe artat the time, though weare learning a lot more about the experiment during the commissioning period. The detector is in operation, and working spectacularly well.