Measurement of CP-violating asymmetries in B0 decays to CP eigenstates

Test of CP Symmetry in Hyperon to Neutron Decays

The quantum entangled J/ψ→Σ^{+}Σ[over ¯]^{-} pairs from (1.0087±0.0044)×10^{10}  J/ψ events taken by the BESIII detector are used to study the nonleptonic two-body weak decays Σ^{+}→nπ^{+} and Σ[over ¯]^{-}→n[over ¯]π^{-}. The CP-odd weak decay parameters of the decays Σ^{+}→nπ^{+} (α_{+}) and Σ[over ¯]^{-}→n[over ¯]π^{-} (α[over ¯]_{-}) are determined to be 0.0481±0.0031_{stat}±0.0019_{syst} and -0.0565±0.0047_{stat}±0.0022_{syst}, respectively. The decay parameter α[over ¯]_{-} is measured for the first time, and the accuracy of α_{+} is improved by a factor of 4 compared to the previous results. The simultaneously determined decay parameters allow the first precision CP symmetry test for any hyperon decay with a neutron in the final state with the measurement of A_{CP}=(α_{+}+α[over ¯]_{-})/(α_{+}-α[over ¯]_{-})=-0.080±0.052_{stat}±0.028_{syst}. Assuming CP conservation, the average decay parameter is determined as ⟨α_{+}⟩=(α_{+}-α[over ¯]_{-})/2=-0.0506±0.0026_{stat}±0.0019_{syst}, while the ratios α_{+}/α_{0} and α[over ¯]_{-}/α[over ¯]_{0} are -0.0490±0.0032_{stat}±0.0021_{syst} and -0.0571±0.0053_{stat}±0.0032_{syst}, where α_{0} and α[over ¯]_{0} are the decay parameters of the decays Σ^{+}→pπ^{0} and Σ[over ¯]^{-}→p[over ¯]π^{0}, respectively.

Symmetry in Σ Hyperon Decay

CP symmetry violation is one of the fundamental requirements for having more matter than antimatter in our universe. However, the observed CP violation is not enough to explain the matter dominance. Searching for the new CP violation in the hyperon sector is therefore attracting people’s interests. In this article, we review the theoretical description of the spin one-half hyperon nonleptonic decay. In order to test the CP conservation, the asymmetry decay parameters might be compared between hyperon and antihyperon. The fixed-target experiments achieved the relevant measurements of the hyperon parameters but in the absence of the antihyperon results. The BESIII experiment with e+e− collision provided an entanglement environment to measure Σ+ and Σ¯− simultaneously. The important role of experimental inputs in CP violation evaluation is discussed in this paper, underlying the great potential of the future collider, which may allow us to reach the precision of the Standard Model predictions.

Branching Ratio and CP Violation in B s 0 ¯ → ϕϕ Decay in the Framework of QCD Factorization

We present an analytic calculation of Branching Ratio (BR) and Charge-Parity (CP) violating asymmetries of the B s 0 ¯ meson decay into the two light vectors ϕ ϕ . In doing this we calculate the helicity amplitude of the present decay in the framework of QCD factorization approach. We find the BR of B s 0 ¯ → ϕ ϕ = ( 1.56 ± 0.23 ) × 10 − 5 . We also calculate the direct CP violation, CP violation in mixing and CP violation due to interference which are A C P dir = 0.00355 ± 0.00152 , A C P mix = − 0.00629 ± 0.03119 and A C P Δ Γ = 0.99997 ± 0.00019 , respectively. Our results are in agreement with the recent theoretical predictions and experimental measurements.

Computing and Software at Belle II

In 2019 the Belle II detector began collecting data from e+e− collisions at the SuperKEKB electron-positron collider. Belle II aims to collect a data sample of 50 ab−1, 50 times larger than the previous generation of B-Factories. In order to process this data and release it to physics analysts there are many interconnected pieces of software and computing resources that must be utilised effectively. In this paper, the current Belle II computing systems, software, and data production activities are summarised.

Search for CP violation in positronium decay

CP violation in the quark sector has been well established over the last decade, but has not been observed in the lepton sector. We search for CP violating decay processes in positronium, using the angular correlation of (S x k{1})(S x k{1}x k{2}), where S is the positronium spin and k{1}, k{2} are the directions of the positronium decay photons. To a sensitivity of 2.2x10{-3}, no CP violation has been found, which is at the level of the CP violation amplitude in the K meson. A 90% confidence interval of the CP violation parameter (C{CP}) was determined to be -0.0023<C{CP}<0.0049. This result is a factor 7 more strict than that of the previous experiment.

Model independent bound on the unitarity triangle from CP violation in B-->pi(+)pi(-) and B-->psiK(S)

We derive model-independent lower bounds on the CKM parameters (1-rho) and eta as functions of the mixing-induced CP asymmetry S in B-->pi(+)pi(-) and sin(2 beta from B-->psiK(S). The bounds do not depend on specific results of theoretical calculations for the penguin contribution to B-->pi(+)pi(-). They require only the very conservative condition that a hadronic phase, which vanishes in the heavy-quark limit, does not exceed 90 degrees in magnitude. The bounds are effective if -sin(2 beta</=S</=1. Dynamical calculations indicate that the limits on rho and eta are close to their actual values.

Rare B decays into states containing a J/psi meson and a meson with s(-)s quark content

We report a study of the B meson decays, B+ --> J/psiphiK+, B0 --> J/psiphiK(0)(S), B0 --> J/psiphi, B0 --> J/psieta, and B0 --> J/psieta' using 56 x 10(6) B(-)B events collected at the Upsilon(4S) resonance with the BABAR detector at the PEP-II e(+)e(-) asymmetric-energy storage ring. We measure the branching fractions B(B+ --> J/psiphiK+)=(4.4+/-1.4(stat)+/-0.5(syst))x 10(-5) and B(B0 --> J/psiphiK(0)(S))=(5.1+/-1.9(stat)+/-0.5(syst))x 10(-5), and set upper limits at 90% confidence level for the branching fractions B(B0 --> J/psiphi)<9.2 x 10(-6), B(B0 --> J/psieta)<2.7 x 10(-5), and B(B0 --> J/psieta')<6.3 x 10(-5).

Measurement of decay parameters for Xi- --> Lambda pi- decay

Based on 1.35 x 10(6) polarized Xi(-) events, we measure the parameter phi(Xi) to be -1.61 degrees +/-2.66 degrees +/-0.37 degrees for the Xi(-)-->Lambda pi(-) decay. New results for the parameters beta(Xi) and gamma(Xi) are also presented. Assuming that the CP-violating phase difference is negligible, we deduce the strong phase difference between the P-wave and S-wave amplitudes of the Lambda pi final state to be 3.17 degrees +/-5.28 degrees +/-0.73 degrees, reducing the uncertainty in estimating the level of CP violation in Xi-hyperon decay.

Observation of large CP violation in the neutral B meson system

We present a measurement of the standard model CP violation parameter sin2 phi(1) based on a 29.1 fb(-1) data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. One neutral B meson is fully reconstructed as a J/psi K(S), psi(2S)K(S), chi(c1)K(S), eta(c)K(S), J/psi K(L), or J/psi K(*0) decay and the flavor of the accompanying B meson is identified from its decay products. From the asymmetry in the distribution of the time intervals between the two B meson decay points, we determine sin2 phi(1) = 0.99+/-0.14(stat)+/-0.06(syst). We conclude that we have observed CP violation in the neutral B meson system.

Observation of CP violation in the B(0) meson system

We present an updated measurement of time-dependent CP-violating asymmetries in neutral B decays with the BABAR detector at the PEP-II asymmetric B Factory at SLAC. This result uses an additional sample of Upsilon(4S) decays collected in 2001, bringing the data available to 32 x 10(6) BB macro pairs. We select events in which one neutral B meson is fully reconstructed in a final state containing charmonium and the flavor of the other neutral B meson is determined from its decay products. The amplitude of the CP-violating asymmetry, which in the standard model is proportional to sin2 beta, is derived from the decay time distributions in such events. The result sin2 beta = 0.59+/-0.14(stat)+/-0.05(syst) establishes CP violation in the B(0) meson system. We also determine absolute value of lambda = 0.93+/-0.09(stat)+/-0.03(syst), consistent with no direct CP violation.

Model of soft CP violation using scalars with quark number two

We propose a model of soft CP violation that evades the strong CP problem and can describe observed CP violation in the neutral kaon sector, both direct and indirect. Our model requires two "duark" mesons carrying quark number two that have complex (CP-violating) bare masses and are coupled to quark pairs. Aside from the existence of these potentially observable new particles with masses of several hundred GeV, we predict a flat unitarity triangle (i.e., no observable direct CP violation in the B-meson sector) and a possibly anomalous branching ratio for the decay mode K+-->pi(+)+nu(nu).