Belle II is an experiment operating at the intensity frontier. Over the next decades, it will record the decay of billions of bottom mesons, charm hadrons, and tau leptons produced in 10 GeV electron-positron collisions at the SuperKEKB high-luminosity collider at KEK. These data, collected in low-background and kinematically known conditions, will allow us to measure hundreds of parameters that test the standard model (SM) and probe for the existence of new particles, at mass scales orders of magnitudes higher than those studied at the energy frontier. We project our sensitivities for measurements that are of primary relevance and where Belle II will be unique or world leading for data corresponding to 1 to 50 ab$^{-1}$. Belle II will uniquely probe non-SM contributions in sensitive $b \to q\bar q s$ decays and charmless $b \to q\bar q d(u)$ decays, semileptonic $b \to s \nu \bar\nu$ and $s \tau^+ \tau^-$ decays, fully leptonic $b \to \ell \nu$ decays, and select $c \to u$ processes. Belle II will lead exploration of non-SM physics in $b \to c \tau \nu$ and $b \to s \gamma$ decays and will most precisely determine the quark-mixing parameters $|V_{ub}|$ and $|V_{cb}|$. Belle II will measure many parameters in $\tau$ physics to precisions that will be world leading for the foreseeable future, including the electric and magnetic dipole moments, branching fractions for charged-lepton-flavor-violating decays, and quantities that test lepton-flavor universality. Belle II will perform unique searches for dark-sector particles with masses in the MeV-GeV range. We will also pursue a broad spectroscopy program for conventional and multiquark $c \bar c$ and $b \bar b$ states and provide essential inputs to sharpen the interpretation of muon magnetic-anomaly results. Our exploration of uncharted regions of non-SM parameter space with high precision will reveal non-SM particles or set stringent constraints on their existence, guiding future endeavors.

The first observation of the Ω−b→Ξ+cK−π− decay is reported using p p collision data at center of mass energies of 7, 8, and 13 TeV collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1. Four excited Ω0c baryons are observed in the Ξ+c K− mass projection of the Ω−b→Ξ+cK−π− decays with the significance of each exceeding five standard deviations. They coincide with the states previously observed in prompt pp and e+e− production. Relative production rates, masses, and natural widths of the states are measured, and a test of spin hypotheses is performed. Moreover, the branching ratio of Ω−b→Ξ+cK−π− is measured relative to the Ω−b→Ω0cπ− decay mode and a precise measurement of the Ω−b mass of 6044.3±1.2±1.1+0.19−0.22 MeV is obtained.Received 8 July 2021Accepted 14 September 2021DOI:https://doi.org/10.1103/PhysRevD.104.L091102Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.© 2021 CERN, for the LHCb CollaborationPhysics Subject Headings (PhySH)Hadron collidersTechniquesExperimental TechniquesParticle acceleratorsHadron collidersResearch AreasBranching fractionHadronic decaysPhysical SystemsBottom baryonsCharmed baryonsPropertiesMassParitySpinTechniquesHadron collidersParticles & Fields

The first untagged decay-time-integrated amplitude analysis of $B^{0}_{s} rightarrow K^{0}_{textrm{S}} K^{pm}pi^{mp}$ decays is performed using a sample corresponding to $3.0,$fb$^{-1}$ of $pp$ collision data recorded with the LHCb detector during 2011 and 2012. The data are described with an amplitude model that contains contributions from the intermediate resonances $K^{*}(892)^{0,+}$, $K^*_2(1430)^{0,+}$ and $K^*_0(1430)^{0,+}$, and their charge conjugates. Measurements of the branching fractions of the decay modes $B^{0}_{s} rightarrow K^{*}(892)^{pm}K^{mp}$ and $B^{0}_{s} rightarrow K^{*}(892)^{0}kern 0.2emoverline{kern -0.2em K}{}^{0}, kern 0.2emoverline{kern -0.2em K}{}^{*}(892)^{0}K^{0}$ are in agreement with, and more precise than, previous results. The decays $B^{0}_{s} rightarrow K^*_0(1430)^{pm} K^{mp}$ and $B^{0}_{s} rightarrow K^{*}_{0}(1430)^{0}kern 0.2emoverline{kern -0.2em K}{}^{0}, kern 0.2emoverline{kern -0.2em K}{}^{*}_{0}(1430)^{0}K^{0}$ are observed for the first time, each with significance over 10 standard deviations.

A search for charge-parity (CP) violation in Cabibbo-suppressed Ds+→KS0π+, D+→KS0K+, and D+→ϕπ+ decays is reported using proton-proton collision data, corresponding to an integrated luminosity of 3.8  fb-1, collected at a center-of-mass energy of 13 TeV with the LHCb detector. High-yield samples of kinematically and topologically similar Cabibbo-favored D(s)+ decays are analyzed to subtract nuisance asymmetries due to production and detection effects, including those induced by CP violation in the neutral kaon system. The results areACP(Ds+→KS0π+)=(1.3±1.9±0.5)×10-3,ACP(D+→KS0K+)=(-0.09±0.65±0.48)×10-3,ACP(D+→ϕπ+)=(0.05±0.42±0.29)×10-3,where the first uncertainties are statistical and the second systematic. They are the most precise measurements of these quantities to date, and are consistent with CP symmetry. A combination with previous LHCb measurements, based on data collected at 7 and 8 TeV, is also reported.

The decay of the narrow resonance ${\overline{B}}_{s2}^{*0}\ensuremath{\rightarrow}{B}^{\ensuremath{-}}{K}^{+}$ can be used to determine the ${B}^{\ensuremath{-}}$ momentum in partially reconstructed decays without any assumptions on the decay products of the ${B}^{\ensuremath{-}}$ meson. This technique is employed for the first time to distinguish contributions from ${D}^{0}$, ${D}^{*0}$, and higher-mass charmed states (${D}^{**0}$) in semileptonic ${B}^{\ensuremath{-}}$ decays by using the missing-mass distribution. The measurement is performed using a data sample corresponding to an integrated luminosity of $3.0\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ collected with the LHCb detector in $pp$ collisions at center-of-mass energies of 7 and 8 TeV. The resulting branching fractions relative to the inclusive ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{D}^{0}X{\ensuremath{\mu}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}$ are ${f}_{{D}^{0}}=\mathcal{B}({B}^{\ensuremath{-}}\ensuremath{\rightarrow}{D}^{0}{\ensuremath{\mu}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}})/\mathcal{B}({B}^{\ensuremath{-}}\ensuremath{\rightarrow}{D}^{0}X{\ensuremath{\mu}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}})=\phantom{\rule{0ex}{0ex}}0.25\ifmmode\pm\else\textpm\fi{}0.06,{f}_{{D}^{**0}}=\mathcal{B}({B}^{\ensuremath{-}}\ensuremath{\rightarrow}({D}^{**0}\ensuremath{\rightarrow}{D}^{0}X){\ensuremath{\mu}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}})/\mathcal{B}({B}^{\ensuremath{-}}\ensuremath{\rightarrow}{D}^{0}X{\ensuremath{\mu}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}})=0.21\ifmmode\pm\else\textpm\fi{}0.07,$ with ${f}_{{D}^{*0}}=1\ensuremath{-}{f}_{{D}^{0}}\ensuremath{-}{f}_{{D}^{**0}}$ making up the remainder.

The LHCb collaboration reports measurements of three charmed baryon lifetimes using 7 and 8 TeV data. These results significantly improve on the precision of existing world averages. The new ${\mathrm{\ensuremath{\Xi}}}_{c}^{0}$ lifetime is found to be somewhat higher than previous estimates.

The doubly Cabibbo-suppressed decay Ξ$_{c}^{+}$  → pϕ with ϕ → K$^{+}$K$^{−}$ is observed for the first time, with a statistical significance of more than fifteen standard deviations. The data sample used in this analysis corresponds to an integrated luminosity of 2 fb$^{−1}$ recorded with the LHCb detector in pp collisions at a centre-of-mass energy of 8 TeV. The ratio of branching fractions between the decay Ξ$_{c}^{+}$  → pϕ and the singly Cabibbo-suppressed decay Ξ$_{c}^{+}$  → pK$^{−}$π$^{+}$ is measured to be $ frac{mathrm{mathcal{B}}left({varXi}_c^{+}to pphi right)}{mathrm{mathcal{B}}left({varXi}_c^{+}to p{K}^{-}{pi}^{+}right)}=left(19.8pm 0.7pm 0.9pm 0.2right)times {10}^{-3}, $

Decays of $B_{s}^{0}$ and $overline{B}{}_{s}^{0}$ mesons into $J/psipi^+pi^-$ final states are studied in a data sample corresponding to 1.9 fb$^{-1}$ of integrated luminosity collected with the LHCb detector in 13 TeV $pp$ collisions. A time-dependent amplitude analysis is used to determine the final-state resonance contributions, the $CP$-violating phase $phi_s=-0.057pm 0.060pm 0.011$ rad, the decay-width difference between the heavier mass $B_{s}^{0}$ eigenstate and the $B^{0}$ meson of $-0.050pm 0.004pm 0.004$ ps$^{-1}$, and the $CP$-violating parameter $|lambda|=1.01_{-0.06}^{+0.08}pm0.03$, where the first uncertainty is statistical and the second systematic. These results are combined with previous LHCb measurements in the same decay channel using 7 TeV and 8 TeV $pp$ collisions obtaining $phi_s =0.002pm0.044pm0.012$ rad, and $|lambda| =0.949pm0.036pm0.019$.

A search for the rare leptonic decay $B^{+} rightarrow {mu}^{+}{mu}^{-}{mu}^{+}{nu}_{{mu}}$ is performed using proton-proton collision data corresponding to an integrated luminosity of $4.7$ fb$^{-1}$ collected by the LHCb experiment. The search is carried out in the region where the lowest of the two ${mu}^{+}{mu}^{-}$ mass combinations is below $980$MeV/c$^{2}$. The data are consistent with the background-only hypothesis and an upper limit of $1.6 times 10^{-8}$ at 95% confidence level is set on the branching fraction in the stated kinematic region.

The first observation of the Bs0→D¯*0ϕ decay is reported, with a significance of more than seven standard deviations, from an analysis of pp collision data corresponding to an integrated luminosity of 3  fb-1, collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV. The branching fraction is measured relative to that of the topologically similar decay B0→D¯0π+π- and is found to be B(Bs0→D¯*0ϕ)=(3.7±0.5±0.3±0.2)×10-5, where the first uncertainty is statistical, the second systematic, and the third from the branching fraction of the B0→D¯0π+π- decay. The fraction of longitudinal polarization in this decay is measured to be fL=(73±15±4)%. The most precise determination of the branching fraction for the Bs0→D¯0ϕ decay is also obtained, B(Bs0→D¯0ϕ)=(3.0±0.3±0.2±0.2)×10-5. An upper limit, B(B0→D¯0ϕ)u003c2.0 (2.3)×10-6 at 90% (95%) confidence level is set. A constraint on the ω-ϕ mixing angle δ is set at |δ|u003c5.2° (5.5°) at 90% (95%) confidence level.

The doubly charmed baryon decay Ξcc++→Ξc+π+ is observed for the first time, with a statistical significance of 5.9σ, confirming a recent observation of the baryon in the Λc+K-π+π+ final state. The data sample used corresponds to an integrated luminosity of 1.7  fb-1, collected by the LHCb experiment in pp collisions at a center-of-mass energy of 13 TeV. The Ξcc++ mass is measured to be 3620.6±1.5(stat)±0.4(syst)±0.3(Ξc+)  MeV/c2 and is consistent with the previous result. The ratio of branching fractions between the decay modes is measured to be [B(Ξcc++→Ξc+π+)×B(Ξc+→pK-π+)]/[B(Ξcc++→Λc+K-π+π+)×B(Λc+→pK-π+)]=0.035±0.009(stat)±0.003(syst).

The branching fraction and direct $C!P$ asymmetry of the decay $B^{+}rightarrow J/psi rho^{+}$ are measured using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV, corresponding to a total integrated luminosity of 3$mbox{fb}^{-1}$. The following results are obtained: begin{align} mathcal{B}(B^{+}rightarrow J/psi rho^{+}) u0026= (3.81 ^{+0.25}_{-0.24} pm 0.35) times 10^{-5}, nonumber mathcal{A}^{C!P} (B^{+}rightarrow J/psi rho^{+}) u0026= -0.045^{+0.056}_{-0.057} pm 0.008, nonumber end{align} where the first uncertainties are statistical and the second systematic. Both measurements are the most precise to date.

The first observation of the B-s(0) -> (D) over bar K-0 (+) K- decay is reported, together with the most precise branching fraction measurement of the mode B-0 -> (D) over bar K-0 (+) K- The results are obtained from an analysis of pp collision data corresponding to an integrated luminosity of 3.0 fb(-1). The data were collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, The branching fraction of the B-0 -> (D) over bar K-0 (+) K- decay is measured relative to that of the decay B-0 -> (D) over bar (0)pi (+) pi(-) to be B(B-0 -> (D) over bar K-0 (+) K-)/B(B-0 -> (D) over bar (0)pi (+) pi(-)) =(69 +/- 0.4 +/- 0.3)%, where the first uncertainty is statistical and the second is systematic. The measured branching fraction of the B-s(0) -> (D) over bar K-0 (+) K- decay mode relative to that of the corresponding B-0 decay is B(B-0 -> (D) over bar K-0 (+) K-)/B(B-0 -> (D) over bar K-0 (+) K-) = (93.0 +/- 809 +/- 6.9)%. Using the known branching fraction of B-0 -> (D) over bar (0)pi (+) pi(-), the values of B-0 -> (D) over bar K-0 (+) K- = (6.1 +/- 0.4 +/- 0.3 +/- 0.3) x 10(-5) and B(B-s(0) -> (D) over bar K-0 (+) K- = (5.7 +/- 0.5 +/- 0.4 +/- 0.5) x 10(-5) are obtained, where the third uncertainties arise from the branching fraction of the decay modes B-0 -> (D) over bar (0)pi (+) pi(-) and B-0 -> (D) over bar K-0 (+) K-, respectively.

A measurement of the time-integrated $CP$ asymmetry in $D^0rightarrow K^0_S K^0_S$ decays is reported. The data correspond to an integrated luminosity of about $2$ fb$^{-1}$ collected in 2015-2016 by the LHCb collaboration in $pp$ collisions at a centre-of-mass energy of $13$ TeV. The $D^0$ candidate is required to originate from a $D^{ast +} rightarrow D^0 pi^+$ decay, allowing the determination of the flavour of the $D^0$ meson using the pion charge. The $D^0 rightarrow K^{+}K^{-}$ decay, which has a well measured $CP$ asymmetry, is used as a calibration channel. The $CP$ asymmetry for $D^0rightarrow K^0_S K^0_S$ is measured to be begin{equation*} mathcal{A}^{CP}(D^0rightarrow K^0_S K^0_S) = (4.3pm 3.4pm 1.0)%, end{equation*} where the first uncertainty is statistical and the second is systematic. This result is combined with the previous LHCb measurement at lower centre-of-mass energies to obtain begin{equation*} mathcal{A}^{CP}(D^0rightarrow K^0_S K^0_S) = (2.3pm 2.8pm 0.9)%. end{equation*}

A search for CP violation in Λb0→pK− and Λb0→pπ− decays is presented using a sample of pp collisions collected with the LHCb detector and corresponding to an integrated luminosity of 3.0 fb−1 . The CP -violating asymmetries are measured to be ACPpK−=−0.020±0.013±0.019 and ACPpπ−=−0.035±0.017±0.020 , and their difference ACPpK−−ACPpπ−=0.014±0.022±0.010 , where the first uncertainties are statistical and the second systematic. These are the most precise measurements of such asymmetries to date.