Direct CP Violation Parameter Research Articles

New graph-neural-network flavor tagger for Belle II and measurement of sin 2ϕ1 in B0→J/ψKS0 decays

We present GFlaT, a new algorithm that uses a graph-neural-network to determine the flavor of neutral B mesons produced in ϒ(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 ϒ(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 B0→J/ψKS0 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). Published by the American Physical Society 2024

Kaon processes in general 2HDM

We discuss new physics (NP) contributions to kaon mixing parameter εK , direct CP violation parameter ε′/ε of K → ππ, and rare decays , and KL,S → μ+μ− in the context of general two Higgs doublet model. We focus on contributions of top quark related exotic couplings, and show that simultaneous presence of flavor conserving and flavor violating interactions can lead to large NP effects in kaon sector, while being consistent with the stringent constraints from B physics observables such as mixing, Bs → μ+μ−, and b → sγ. We stress on the importance of correlations between εK , and Bs → μ + μ − that can be exploited to distinguish the parameter space corresponding to a light (sub-TeV) or heavy (TeV) scale charged Higgs boson.

Strange processes in general two Higgs doublet model

In the general two Higgs doublet model (g2HDM) that has extra Yukawa couplings, we analyze their New Physics (NP) contributions to kaon mixing parameter εK, direct CP violation parameter ε′/ε, and rare {K}^{+}to {pi}^{+}nu overline{nu} , {K}_Lto {pi}^0nu overline{nu} , and KL,S→ μ+μ− decays. We study correlations between these observables, and call special attention to a unique complementarity of kaon mixing and rare Kto pi nu overline{nu} decays in probing the exotic Higgs mass spectrum of g2HDM. The importance of kaon physics in probing NP vis-à-vis B physics is stressed. One unexpected feature we uncover is the special sensitivity of {K}^{+}to {pi}^{+}nu overline{nu} to TeV scale charged Higgs boson.

K → ππ decay, ε ′ and the RBC-UKQCD kaon physics program

An overview of the kaon physics program of the RBC and UKQCD collaborations will be presented with a focus on the lattice calculation of K → ππ decay and the direct CP violation parameter ε ′. We will describe substantial improvements to our earlier 2015 K → ππ calculation, including the use of three independent ππ interpolating operators and the results we obtain for I = 0 ππ scattering for energies at and below the kaon mass. While the new result for ϵ ′ is not yet complete, the enhanced statistics and improved analysis that underlies our expanded calculation will be presented.

Measurement of CP violation in the {B}_s^0to phi phi decay and search for the B0\u2192 \u03d5\u03d5 decay

A measurement of the time-dependent CP-violating asymmetry in {B}_s^0to phi phi decays is presented. Using a sample of proton-proton collision data corresponding to an integrated luminosity of 5.0 fb−1 collected by the LHCb experiment at centre-of-mass energies sqrt{s} = 7 TeV in 2011, 8 TeV in 2012 and 13 TeV in 2015 and 2016, a signal yield of around 9000 {B}_s^0to phi phi decays is obtained. The CP-violating phase {phi}_s^{soverline{s}s} is measured to be −0.073 ± 0.115(stat) ± 0.027(syst) rad, under the assumption it is independent of the helicity of the ϕϕ decay. In addition, the CP-violating phases of the transverse polarisations under the assumption of CP conservation of the longitudinal phase are measured. The helicity-independent direct CP-violation parameter is also measured, and is found to be |λ| = 0.99 ± 0.05(stat) ± 0.01(syst). In addition, T-odd triple-product asymmetries are measured. The results obtained are consistent with the hypothesis of CP conservation in overline{b}to overline{s}soverline{s}s transitions. Finally, a limit on the branching fraction of the B0 → ϕϕ decay is determined to be mathcal{B}left({B}^0to phi phi right)<2.7times {10}^{-8} at 90 % confidence level.

Scalar leptoquarks and the rareBmeson decays

We study some rare decays of $B$ meson involving the quark level transition $b \to q l^+l^- (q=d,s)$ in the scalar leptoquark model. We constrain the leptoquark parameter space using the recently measured branching ratios of $B_{s,d} \to \mu^+ \mu^-$ processes. Using such parameters, we obtain the branching ratios, direct CP violation parameters and isospin asymmetries in $B \to K \mu^+ \mu^-$ and $B \to \pi \mu^+ \mu^-$ processes. We also obtain the branching ratios for some lepton flavour violating decays $B \to l_i^+ l_j^-$. We find that the various anomalies associated with the isospin asymmetries of $B \to K \mu^+ \mu^-$ process can be explained in the scalar leptoquark model.

CP violation measurements in B mesons at Belle

We present recent measurements of time-dependent CP asymmetries in two neutral B decay modes: B0 → η'K0 and B0 → ωK°S. The measured values of mixing-induced (sin 2ϕ1eff) and direct CP violation parameters are: Sη'Ko = +0.68 ± 0.07stat ± 0.03syst, Aη'K0 = +0.03 ± 0.05stat ± 0.04syst and SωK0S = +0.91 ± 0.32stat ± 0.05syst, AωK0S = -0.36 ± 0.19stat ± 0.05syst, respectively. These results are fully consistent with the current world average of sin 2ϕ1 measured in b → cc̄s transitions, and represent the most accurate measurements in these modes up-to- date. In addition, we present a new preliminary update on branching ratio measurement in B0 → π0π0 decay mode, the result of which: ℬ(B0 → π0π0) = (0.90 ± 0.12stat ± 0.10syst) × 10−6 represents an important ingredient in a ππSU(2) isospin analysis, used to experimentally extract ϕ2 angle from B → ππ measurements. To obtain CP violation parameters (ℬ(B0 → π0π0)) the final data set of 772 × 106 (751.5 × 106) BB̄ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric e+e− collider in Japan (3.5 × 8.0GeV) is used.

Precise Measurement of theCPViolation Parametersin2ϕ1inB0→(cc¯)K0Decays

We present a precise measurement of the CP violation parameter sin2φ1 and the direct CP violation parameter A(f) using the final data sample of 772×10(6) BB[over ¯] pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. One neutral B meson is reconstructed in a J/ψK(S)(0), ψ(2S)K(S)(0), χ(c1)K(S)(0), or J/ψK(L)(0) CP eigenstate and its flavor is identified from the decay products of the accompanying B meson. From the distribution of proper-time intervals between the two B decays, we obtain the following CP violation parameters: sin2φ1=0.667±0.023(stat)±0.012(syst) and A(f)=0.006±0.016(stat)±0.012(syst).

Revisiting the B→πρ, πω decays in the perturbative QCD approach beyond the leading order

We calculate the branching ratios and CP asymmetries of the $B \to \pi \rho$, $\pi\omega $ decays in the perturbative QCD factorization approach up to the next-to-leading-order contributions. We find that the next-to-leading-order contributions can interfere with the leading-order part constructively or destructively for different decay modes. Our numerical results have a much better agreement with current available data than previous leading-order calculations, e.g., the next-to-leading-order corrections enhance the $B^0\rightarrow \pi^0\rho^0$ branching ratios by a factor 2.5, which is helpful to narrow the gaps between theoretic predictions and experimental data. We also update the direct CP-violation parameters, the mixing-induced CP-violation parameters of these modes, which show a better agreement with experimental data than many of the other approaches.

CP Violation results from the NA48 experiments

The main goal of the NA48 experiments at the CERN SPS has been the search for direct CP violation (CPV) in neutral and charged kaon decays. In this paper selected results on CPV from the NA48 and NA48/2 experiments are presented. The direct CPV parameter Re(ε′/ε) has been measured by NA48 from the decay rates of neutral kaons into two pions. In the charged kaon sector, NA48/2 has measured the asymmetry Ag of the linear slope parameter g in the Dalitz plot of K± → 3π decays. Thanks to the high statistics collected in 2003 and 2004, further CPV studies were performed in several kaon decays. Results on CPV studies in K± → π±π0γ K± → π±e+e− and K± → π±μ+μ− decays will be presented, as well as in the KS → π+π−e+e− decay.

Precise measurements of directCPviolation,CPTsymmetry, and other parameters in the neutral kaon system

We present precise tests of CP and CPT symmetry based on the full dataset of K to pipi decays collected by the KTeV experiment at Fermi National Accelerator Laboratory during 1996, 1997, and 1999. This dataset contains 16 million K to 2pi0 and 69 million K to pi+pi- decays. We measure the direct CP violation parameter Re(epsilon'/epsilon) = (19.2 pm 2.1)x10-4. We find the KL-KS mass difference Deltam = (5270 pm 12)x10^6 hbar/s and the KS lifetime tauS = (89.62 pm 0.05)x10-12 s. We also measure several parameters that test CPT invariance. We find the difference between the phase of the indirect CP violation parameter, epsilon, and the superweak phase, phi_epsilon - phi_SW = (0.40 pm 0.56) degrees. We measure the difference of the relative phases between the CP violating and CP conserving decay amplitudes for K to pi+pi- (phi+-) and for K to 2pi0 (phi00), Delta phi = (0.30 pm 0.35) degrees. From these phase measurements, we place a limit on the mass difference between K0 and K0bar, DeltaM < 4.8 x 10-19 GeV/c^2 at 95% C.L. These results are consistent with those of other experiments, our own earlier measurements, and CPT symmetry.

Measurement ofCPviolating asymmetries inB0→K+K−KS0decays with a time-dependent Dalitz approach

We report a measurement of CP violating asymmetries in B0(B¯0)→K+K−KS0 decays with a time-dependent Dalitz approach. This analysis is based on a data sample of 657×106 BB¯ pairs accumulated at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. As the result of an unbinned maximum likelihood fit to the selected candidates, the mixing-induced and direct CP violation parameters ϕ1eff and ACP are obtained for B0→ϕ(1020)KS0, B0→f0(980)KS0, and other B0→K+K−KS0 decays. We find four solutions that describe the data. There are ϕ1eff(B0→ϕ(1020)KS0)=(32.2±9.0±2.6±1.4)°;ϕ1eff(B0→ϕ(1020)KS0)=(26.2±8.8±2.7±1.2)°;ϕ1eff(B0→ϕ(1020)KS0)=(27.3±8.6±2.8±1.3)°;andϕ1eff(B0→ϕ(1020)KS0)=(24.3±8.0±2.9±5.2)°. The values for the CP violating phase in B0→ϕ(1020)KS0 are similar, but other properties of the Dalitz plot are quite different for the four solutions. These four solutions have consistent ϕ1eff values for all three B-meson decay channels and none of them deviates significantly from the values measured in B→(cc¯)K0 decays with the currently available statistics. In addition, we find no significant direct CP violation.Received 22 July 2010DOI:https://doi.org/10.1103/PhysRevD.82.073011© 2010 The American Physical Society

Chiral logarithms inΔS=1kaon decay amplitudes in general effective flavor theories

We study the chiral logarithms in $\Delta S=1$ kaon decay amplitudes from new flavor physics in beyond-standard-model theories. We systematically classify the chiral structures of dimension-5, 6 and 7 effective QCD operators constructed out of light-quark (up, down and strange) and gluon fields. Using the standard chiral perturbation theory, we calculate the leading chiral-logarithms associated with these operators. The result is useful for lattice calculations of the QCD matrix elements in $K\to \pi\pi$ decay necessary, for example, to understand the physical origin of the direct CP violation parameter $\epsilon'$. As a concrete example, we consider the new operators present in minimal left-right symmetric models.

Direct CP violation in K-decay and minimal left–right symmetry scale

We calculate the new contribution to the direct CP-violation parameter ϵ′ in K→ππ decay in the minimal left–right symmetric model with the recently-obtained right-handed quark Cabibbo–Kobayashi–Maskawa mixing. We pay particular attention to the uncertainty in the hadronic matrix element of a leading four-quark operator O−LR. We find that it can be related to the standard model electromagnetic penguin operator O8 through SU(3)L×SU(3)R chiral symmetry. Using the lattice and large Nc calculations, we obtain a robust constraint on the minimal left–right symmetric scale MWR>5 TeV from the experimental data on ϵ′.

Two measurements of ππ scattering lengths [formula omitted] and [formula omitted] from studies of [formula omitted] decays with the CERN-NA48/2 experiment

The NA48 experiment at the CERN SPS has used K L 0 and K S 0 kaons for the precise measurement of the direct CP violation parameter Re ( ɛ ′ / ɛ ) . In 2002 it was re-designed as NA48/2 to search for CP violation in K ± → 3 π decays. This configuration has also allowed studying several rare decay processes of charged kaons to test chiral perturbation theory. With data samples of ∼ 10 6 K ± → π ± π − e ± ν decays, precise values of a 0 and a 2 , the isospin I=0 and I=2 s -wave ππ scattering lengths, are extracted with an unprecedented experimental precision. The same scattering lengths are also measured using ∼ 60 × 10 6 K ± → π ± π 0 π 0 decays where a cusp structure in the Dalitz plot has been observed for the first time.

Signature of new physics in [formula omitted] decay

We investigate the effect of an extra fourth quark generation and FCNC mediated Z and Z′ bosons on the rare decay mode B−→ϕπ−. In the Standard Model, this mode receives only b→d penguin contributions and therefore, highly suppressed with branching ratio ∼5×10−9. This in turn makes this mode a very sensitive probe for new physics. We find that due to the above mentioned new physics contributions there is a significant enhancement in its branching ratio. Furthermore, the direct CP violation parameter which is identically zero in the SM is found to be quite significant. If this mode will be observed in the upcoming LHCb experiment, it will not only provide a clear signal of new physics but also can be used to constrain the new physics parameter space.

Measurement ofCPasymmetry inB0→Ks0π0π0decays

We present a measurement of the time-dependent CP asymmetry for the neutral B-meson decay into the CP = +1 final state Ks pi0 pi0, with Ks -> pi+ pi-. We use a sample of approximately 227 million B-meson pairs recorded at the Upsilon(4S) resonance with the BABAR detector at the PEP-II B-Factory at SLAC. From an unbinned maximum likelihood fit we extract the mixing-induced CP-violation parameter S = 0.72 +/- 0.71 +/- 0.08 and the direct CP-violation parameter C = 0.23 +/- 0.52 +/- 0.13, where the first uncertainty is statistical and the second systematic.

Charmless nonleptonic B decays into scalar and pseudoscalar mesons

The charmless nonleptonic decay modes B → f0K(π) involving a scalar and a pseudoscalar meson in the final state are studied. The scalar meson f0 is considered as a qq state, as favored by some recent studies. Using the generalized factorization approach, the branching ratios and CP violation parameters are computed for these modes. The form factors are calculated using the results from relativistic light front quark model and the ISGW2 model. It is found that the direct CP violation parameters in these modes are small. However, the obtained branching ratios are not in agreement with the experimental data. Therefore, these modes may be considered as possible probes for new physics.

Application of the Monte Carlo method with overlapping beam-monitor-triggered events in NA-48 experiment

A Monte Carlo method with overlapping beam-monitor-triggered events for the calculation of effects caused by time coincidences of events under study and accidental activity in detectors of the NA-48 setup is developed. Its application in measurement of the direct CP violation parameter Re(∈′/∈) is described.

MEASUREMENT OF CP ASYMMETRY IN $B^0 \to f_0 K^0_S$, B0 → ϕK0 AND $B^0 \to K^+K^-K^0_S$ DECAYS

We present results on time-dependent CP asymmetries in [Formula: see text] and B0 → K+K-K0. The measurements use a data sample consisting of approximately [Formula: see text] and 227(B0 → K+K-K0) million B-meson pairs recorded at the ϒ(4S) resonance with the BABAR detector at the PEP-II B-meson Factory at SLAC. From a time-dependent maximum likelihood fit, we measure for [Formula: see text]: the mixing-induced CP violation parameter [Formula: see text] and the direct CP violation parameter Cf0K = -0.24 ± 0.31 ( stat ) ± 0.15 ( syst ). From a simultaneous fit to [Formula: see text] and [Formula: see text] decays, we find: [Formula: see text] and CϕK = 0.00 ± 0.23 ( stat ) ± 0.05 ( syst ). For [Formula: see text] decays with [Formula: see text] decays excluded, we find: [Formula: see text] and [Formula: see text]. From the [Formula: see text] decays with [Formula: see text] decays excluded, we extract the fraction of CP-even final states from angular moments feven = 0.89 ± 0.08 ± 0.06.