We measure the time-integrated CP asymmetry in D-0 -> (KSKS0)-K-0 decays reconstructed in e(+)e(-) -> c (c) over bar events collected by the Belle and Belle II experiments. The corresponding data samples have integrated luminosities of 980 and 428 fb(-1), respectively. The D-0 decays are required to originate from the D*(+) -> D-0 pi(+) decay, which determines the charm flavor at production time. A control sample of D-0 -> K+K- decays is used to correct for production and detection asymmetries. The result, (-1.4 +/- 1.3(stat) +/- 0.1(syst))%, is consistent with previous determinations and with CP symmetry.

The PROSPECT-I detector has several features that enable measurement of the direction of a compact neutrino source. In this paper, a detailed report on the directional measurements made on electron antineutrinos emitted from the High Flux Isotope Reactor is presented. With an estimated true neutrino (reactor to detector) direction of % = 40.8 degrees + 0.7 degrees and theta = 98.6 degrees + 0.4 degrees, the PROSPECT-I detector is able to reconstruct an average neutrino direction of % = 39.4 degrees + 2.9 degrees and theta = 97.6 degrees + 1.6 degrees. This measurement is made with approximately 48 000 inverse beta decay signal events and is the most precise directional reconstruction of reactor antineutrinos to date.

A series of data samples was collected with the Belle II detector at the SuperKEKB collider from March 2019 to June 2022. We determine the integrated luminosities of these data samples using three distinct methodologies involving Bhabha (e(+) e(-) -> e(+) e(-)(n gamma)), digamma (e(+) e(-) -> gamma gamma(n gamma)), and dimuon (e(+) e(-) -> mu(+) mu(-)(n gamma)) events. The total integrated luminosity obtained with Bhabha, digamma, and dimuon events is (426.88 +/- 0.03 +/- 2.61) fb(-1), (429.28 +/- 0.03 +/- 2.62) fb(-1), and (423.99 +/- 0.04 +/- 3.83) fb(-1), where the first uncertainties are statistical and the second are systematic. The resulting total integrated luminosity obtained from the combination of the three methods is (427.87 +/- 2.01) fb(-1).

The PROSPECT experiment is designed to perform precise searches for antineutrino disappearance at short distances (7-9 m) from compact nuclear reactor cores. This Letter reports results from a new neutrino oscillation analysis performed using the complete data sample from the PROSPECT-I detector operated at the High Flux Isotope Reactor in 2018. The analysis uses a multiperiod selection of inverse beta decay neutrino interactions with reduced backgrounds and enhanced statistical power to set limits on electron neutrino disappearance caused by mixing with sterile neutrinos with 0.2-20  eV^{2} mass splittings. Inverse beta decay positron energy spectra from six different reactor-detector distance ranges are found to be statistically consistent with one another, as would be expected in the absence of sterile neutrino oscillations. The data excludes at 95% confidence level the existence of sterile neutrinos in regions above 3  eV^{2} previously unexplored by terrestrial experiments, including all space below 10  eV^{2} suggested by the recently strengthened Gallium Anomaly. The best-fit point of the Neutrino-4 reactor experiment's claimed observation of short-baseline oscillation is ruled out at more than 5 standard deviations.

We report measurements of time-dependent CP asymmetries in B^{0}→K_{S}^{0}π^{0}γ decays based on a data sample of (388±6)×10^{6}  BB[over ¯] events collected at the ϒ(4S) resonance with the Belle II detector. The Belle II experiment operates at the SuperKEKB asymmetric-energy e^{+}e^{-} collider. We measure decay-time distributions to determine CP -violating parameters S and C. We determine these parameters for two ranges of K_{S}^{0}π^{0} invariant mass: m(K_{S}^{0}π^{0})∈(0.8,1.0)  GeV/c^{2}, which is dominated by B^{0}→K^{*0}(→K_{S}^{0}π^{0})γ decays, and a complementary region m(K_{S}^{0}π^{0})∈(0.6,0.8)∪(1.0,1.8)  GeV/c^{2}. Our results have improved precision as compared to previous measurements and are consistent with theory predictions.

We search for the rare decay B+ -> K+ v (v) over bar in a 362 fb(-1) sample of electron-positron collisions at the Upsilon(4S) resonance collected with the Belle II detector at the SuperKEKB collider. We use the inclusive properties of the accompanying B meson in Upsilon(4S) -> B (B) over bar events to suppress background from other decays of the signal B candidate and light-quark pair production. We validate the measurement with an auxiliary analysis based on a conventional hadronic reconstruction of the accompanying B meson. For background suppression, we exploit distinct signal features using machine learning methods tuned with simulated data. The signal-reconstruction efficiency and background suppression are validated through various control channels. The branching fraction is extracted in a maximum likelihood fit. Our inclusive and hadronic analyses yield consistent results for the B+ -> K+ v (v) over bar branching fraction of [2.7 +/- 0.5(stat) +/- 0.5(syst)] x 10(-5) and [1.1(-0.8)(+0.9)(stat)(-0.5)(+0.8)(syst)] x 10(-5), respectively. Combining the results, we determine the branching fraction of the decay B+ -> K+ v (v) over bar to be [2.3 +/- 0.5_stat)(-0.4)(+0.5)(syst)] x 10(-5), providing the first evidence for this decay at 3.5 standard deviations. The combined result is 2.7 standard deviations above the standard model expectation.

We present measurements of the branching fractions of eight B^0→ D^(*)+ K^- K^(*)0_(S), B^-→ D^(*)0 K^- K^(*)0_(S) decay channels. The results are based on data from SuperKEKB electron-positron collisions at the Υ(4S) resonance collected with the Belle II detector, corresponding to an integrated luminosity of 362 fb^-1. The event yields are extracted from fits to the distributions of the difference between expected and observed B meson energy, and are efficiency-corrected as a function of m(K^-K^(*)0_(S)) and m(D^(*)K^(*)0_(S)) in order to avoid dependence on the decay model. These results include the first observation of B^0→ D^+K^-K_S^0, B^-→ D^*0K^-K_S^0, and B^0→ D^*+K^-K_S^0 decays and a significant improvement in the precision of the other channels compared to previous measurements. The helicity-angle distributions and the invariant mass distributions of the K^- K^(*)0_(S) systems are compatible with quasi-two-body decays via a resonant transition with spin-parity J^P=1^- for the K^-K_S^0 systems and J^P= 1^+ for the K^-K^*0 systems. We also present measurements of the branching fractions of four B^0→ D^(*)+ D_s^-, B^-→ D^(*)0 D_s^- decay channels with a precision compatible to the current world averages.

The full data set of the Daya Bay reactor neutrino experiment is used to probe the effect of the charged current non-standard interactions (CC-NSI) on neutrino oscillation experiments. Two different approaches are applied and constraints on the corresponding CC-NSI parameters are obtained with the neutrino flux taken from the Huber-Mueller model with a $5\%$ uncertainty. For the quantum mechanics-based approach (QM-NSI), the constraints on the CC-NSI parameters $\epsilon_{e\alpha}$ and $\epsilon_{e\alpha}^{s}$ are extracted with and without the assumption that the effects of the new physics are the same in the production and detection processes, respectively. The approach based on the weak effective field theory (WEFT-NSI) deals with four types of CC-NSI represented by the parameters $[\varepsilon_{X}]_{e\alpha}$. For both approaches, the results for the CC-NSI parameters are shown for cases with various fixed values of the CC-NSI and the Dirac CP-violating phases, and when they are allowed to vary freely. We find that constraints on the QM-NSI parameters $\epsilon_{e\alpha}$ and $\epsilon_{e\alpha}^{s}$ from the Daya Bay experiment alone can reach the order $\mathcal{O}(0.01)$ for the former and $\mathcal{O}(0.1)$ for the latter, while for WEFT-NSI parameters $[\varepsilon_{X}]_{e\alpha}$, we obtain $\mathcal{O}(0.1)$ for both cases.

We measure the tau-to-light-lepton ratio of inclusive B-meson branching fractions R ( X tau= l ) equivalent to B ( B-* X tau nu ) = B ( B-* X l nu ) , where l indicates an electron or muon, and thereby test the universality of charged-current weak interactions. We select events that have one fully reconstructed B meson and a charged lepton candidate from 189 fb-1 - 1 of electron-positron collision data collected with the Belle II detector. We find R ( X tau= l ) = 0.228 + 0.016(stat) ( stat ) + 0.036(syst), ( syst ) , in agreement with standard-model expectations. This is the first direct measurement of R ( X tau= l ) .

We present GFlaT, a new algorithm that uses a graph-neural-network to determine the flavor of neutral $B$ mesons produced in $\Upsilon(4S)$ decays. It improves previous algorithms by using the information from all charged final-state particles and the relations between them. We evaluate its performance using $B$ decays to flavor-specific hadronic final states reconstructed in a 362 $\text{fb}^{-1}$ sample of electron-positron collisions collected at the $\Upsilon(4S)$ resonance with the Belle II detector at the SuperKEKB collider. We achieve an effective tagging efficiency of $(37.40 \pm 0.43 \pm 0.36) \%$, where the first uncertainty is statistical and the second systematic, which is $18\%$ better than the previous Belle II algorithm. Demonstrating the algorithm, we use $B^{0}\to J/\psi K^0_\text{S}$ decays to measure the mixing-induced and direct $CP$ violation parameters, $S = (0.724 \pm 0.035 \pm 0.009)$ and $C = (-0.035 \pm 0.026 \pm 0.029)$.

We report a measurement of decay-time-dependent charge-parity (CP) asymmetries in B0→KS0KS0KS0 decays. We use 387×106 BB¯ pairs collected at the ϒ(4S) resonance with the Belle II detector at the SuperKEKB asymmetric-energy electron-positron collider. We reconstruct 220 signal events and extract the CP-violating parameters S and C from a fit to the distribution of the decay-time difference between the two B mesons. The resulting confidence region is consistent with previous measurements in B0→KS0KS0KS0 and B0→(cc¯)K0 decays and with predictions based on the standard model. Published by the American Physical Society 2024

We present GFlaT, a new algorithm that uses a graph-neural-network to determine the flavor of neutral B mesons produced in Upsilon(4S) decays. It improves previous algorithms by using the information from all charged final-state particles and the relations between them. We evaluate its performance using B decays to flavor-specific hadronic final states reconstructed in a 362 fb(-1) sample of electron-positron collisions collected at the Upsilon(4S) resonance with the Belle II detector at the SuperKEKB collider. We achieve an effective tagging efficiency of (37.40 +/- 0.43 +/- 0.36%), where the first uncertainty is statistical and the second systematic, which is 18% better than the previous Belle II algorithm. Demonstrating the algorithm, we use B-0 -> J/psi K-S(0) decays to measure the mixing-induced and direct CP violation parameters, S = (0.724 +/- 0.035 +/- 0.009) and C = (-0.035 +/- 0.026 +/- 0.029).

Abstract We present a measurement of the ratio $$ {R}_{\mu }=\mathcal{B}\left({\tau}^{-}\to {\mu}^{-}{\overline{\nu}}_{\mu }{\nu}_{\tau}\right)/\mathcal{B}\left({\tau}^{-}\to {e}^{-}{\overline{\nu}}_e{\nu}_{\tau}\right) $$ R μ = B τ − → μ − ν ¯ μ ν τ / B τ − → e − ν ¯ e ν τ of branching fractions $$ \mathcal{B} $$ B of the τ lepton decaying to muons or electrons using data collected with the Belle II detector at the SuperKEKB e+e− collider. The sample has an integrated luminosity of 362 ± 2 fb−1 at a centre-of-mass energy of 10.58 GeV. Using an optimised event selection, a binned maximum likelihood fit is performed using the momentum spectra of the electron and muon candidates. The result, Rμ = 0.9675 ± 0.0007 ± 0.0036, where the first uncertainty is statistical and the second is systematic, is the most precise to date. It provides a stringent test of the light-lepton universality, translating to a ratio of the couplings of the muon and electron to the W boson in τ decays of 0.9974 ± 0.0019, in agreement with the standard model expectation of unity.

AbstractWe present measurements of the branching fractions of eight $$ {\overline{B}}^0 $$ B ¯ 0 → D(*)+K−$$ {K}_{(S)}^{\left(\ast \right)0} $$ K S ∗ 0 , B− → D(*)0K−$$ {K}_{(S)}^{\left(\ast \right)0} $$ K S ∗ 0 decay channels. The results are based on data from SuperKEKB electron-positron collisions at the Υ(4S) resonance collected with the Belle II detector, corresponding to an integrated luminosity of 362 fb−1. The event yields are extracted from fits to the distributions of the difference between expected and observed B meson energy, and are efficiency-corrected as a function of m(K−$$ {K}_{(S)}^{\left(\ast \right)0} $$ K S ∗ 0 ) and m(D(*)$$ {K}_{(S)}^{\left(\ast \right)0} $$ K S ∗ 0 ) in order to avoid dependence on the decay model. These results include the first observation of $$ {\overline{B}}^0 $$ B ¯ 0 → D+K−$$ {K}_S^0 $$ K S 0 , B− → D*0K−$$ {K}_S^0 $$ K S 0 , and $$ {\overline{B}}^0 $$ B ¯ 0 → D*+K−$$ {K}_S^0 $$ K S 0 decays and a significant improvement in the precision of the other channels compared to previous measurements. The helicity-angle distributions and the invariant mass distributions of the K−$$ {K}_{(S)}^{\left(\ast \right)0} $$ K S ∗ 0 systems are compatible with quasi-two-body decays via a resonant transition with spin-parity JP = 1− for the K−$$ {K}_S^0 $$ K S 0 systems and JP = 1+ for the K−K*0 systems. We also present measurements of the branching fractions of four $$ {\overline{B}}^0 $$ B ¯ 0 → D(*)+$$ {D}_s^{-} $$ D s − , B− → D(*)0$$ {D}_s^{-} $$ D s − decay channels with a precision compatible to the current world averages.

We report a measurement of decay-time dependent charge-parity (CP) asymmetries in B^0 → K^0_S K^0_S K^0_S decays. We use 387 × 10^6 BB̅ pairs collected at the Υ(4S) resonance with the Belle II detector at the SuperKEKB asymmetric-energy electron-positron collider. We reconstruct 220 signal events and extract the CP-violating parameters S and C from a fit to the distribution of the decay-time difference between the two B mesons. The resulting confidence region is consistent with previous measurements in B^0 → K^0_S K^0_S K^0_S and B^0 → (cc̅)K^0 decays, and with predictions based on the standard model.

The ratio of branching fractions R(D*) = B((B) over bar -> D* tau(-) (nu) over bar (tau))/B((B) over bar -> D* l(-)(nu) over bar (l)), where l is an electron or muon, is measured using a Belle II data sample with an integrated luminosity of 189 fb(-1) at the SuperKEKB asymmetric-energy e(+)e(-) collider. Data is collected at the Upsilon(4S) resonance, and one B meson in the Upsilon(4S) -> B (B) over bar decay is fully reconstructed in hadronic decay modes. The accompanying signal B meson is reconstructed as (B) over bar -> D* tau(-) (nu) over bar (tau)using leptonic t decays. The normalization decay, (B) over bar -> D* l(-)(nu) over bar (l,) produces the same observable final-state particles. The ratio of branching fractions is extracted in a simultaneous fit to two signal-discriminating variables in both channels and yields R(D*) = 0.262(-0.039)(+0.041) (stat)(-0.032)(+0.035) (syst). This result is consistent with the current world average and with Standard Model predictions.

Daya Bay presents the first measurement of cosmogenic He-8 isotope production in liquid scintillator, using an innovative method for identifying cascade decays of He-8 and its child isotope, Li-8. We also measure the production yield of Li-9 isotopes using well-established methodology. The results, in units of 10(-8)mu-1g(-1) cm(2), are 0.307 +/- 0.042, 0.341 +/- 0.040, and 0.546 +/- 0.076 for He-8, and 6.73 +/- 0.73, 6.75 +/- 0.70, and 13.74 +/- 0.82 for 9Li at average muon energies of 63.9 GeV, 64.7 GeV, and 143.0 GeV, respectively. The measured production rate of He-8 isotopes is more than an order of magnitude lower than any other measurement of cosmogenic isotope production. It replaces the results of previous attempts to determine the ratio of He-8 to Li-9 production that yielded a wide range of limits from 0% to 30%. The results provide future liquid-scintillator-based experiments with improved ability to predict cosmogenic backgrounds.

This Letter reports the first measurement of the oscillation amplitude and frequency of reactor antineutrinos at Daya Bay via neutron capture on hydrogen using 1958 days of data. With over 3.6 million signal candidates, an optimized candidate selection, improved treatment of backgrounds and efficiencies, refined energy calibration, and an energy response model for the capture-on-hydrogen sensitive region, the relative ν[over ¯]_{e} rates and energy spectra variation among the near and far detectors gives sin^{2}2θ_{13}=0.0759_{-0.0049}^{+0.0050} and Δm_{32}^{2}=(2.72_{-0.15}^{+0.14})×10^{-3}  eV^{2} assuming the normal neutrino mass ordering, and Δm_{32}^{2}=(-2.83_{-0.14}^{+0.15})×10^{-3}  eV^{2} for the inverted neutrino mass ordering. This estimate of sin^{2}2θ_{13} is consistent with and essentially independent from the one obtained using the capture-on-gadolinium sample at Daya Bay. The combination of these two results yields sin^{2}2θ_{13}=0.0833±0.0022, which represents an 8% relative improvement in precision regarding the Daya Bay full 3158-day capture-on-gadolinium result.

We report a measurement of decay-time-dependent charge-parity (CP) asymmetries in B-0 -> (KSKSKS0)-K-0-K-0 decays. We use 387 x 10(6) B (B) over bar pairs collected at the Upsilon(4S) resonance with the Belle II detector at the SuperKEKB asymmetric-energy electron-positron collider. We reconstruct 220 signal events and extract the CP-violating parameters S and C from a fit to the distribution of the decay-time difference between the two B mesons. The resulting confidence region is consistent with previous measurements in B-0 -> (KSKSKS0)-K-0-K-0 and B-0 -> (c (c) over bar )K-0 decays and with predictions based on the standard model.

We present a search for the baryon number B and lepton number L violating decays tau(-) -> Lambda pi(-) and tau(-) -> (Lambda) over bar pi(-) produced from the e(+) e(-) -> tau(+) tau(-) process, using a 364 fb(-1) data sample collected by the Belle II experiment at the SuperKEKB collider. No evidence of signal is found in either decay mode, which have vertical bar Delta(B - L)vertical bar equal to 2 and 0, respectively. Upper limits at 90% credibility level on the branching fractions of tau(-) -> Lambda pi(-) and tau(-) -> (Lambda) over bar pi(-) are determined to be 4.7 x 10(-8) and 4.3 x 10(-8), respectively.