CP-violating Asymmetries Research Articles

Measurement of the branching fraction, and bounds on the CP-violating asymmetries, of neutral B decays to D*+/- D-/+.

We present measurements of the branching fraction and CP-violating asymmetries for neutral B decays to D(*+/-)D-/+. The measurement uses a data sample of approximately 88x10(6) Upsilon(4S)-->BBmacr; decays collected with the BABAR detector at the SLAC PEP-II asymmetric-energy e(+)-e(-) collider. By fully reconstructing the D(*+/-)D-/+ decay products, we measure the branching fraction to be (8.8+/-1.0+/-1.3)x10(-4) and the time-integrated CP-violating asymmetry between the rates to D(*-)D+ and D(*+)D- to be A=-0.03+/-0.11+/-0.05. We also measure the time-dependent CP-violating asymmetry parameters to be S(-+)=-0.24+/-0.69+/-0.12, C(-+)=-0.22+/-0.37+/-0.10 for B-->D(*-)D+ and S(+-)=-0.82+/-0.75+/-0.14, C(+-)=-0.47+/-0.40+/-0.12 for B-->D(*+)D-. In each case, the first error is statistical and the second error is systematic.

Selected physics results from Belle

We present an updated measurement of sin 2 φ 1 in B 0 → c cW decays and first evidence for CP-violating asymmetries in B → π + π − decays. We also report the first observation of the ν c (2 S) meson. The results are based on analyses of a sample of 41.8 million B B meson pairs from the decays of the υ(4 S) resonance, collected with the Belle detector at the KEKB asymmetric-energy e + e − collider. For the B → π + π − CP-violating asymmetry measurement, we fully reconstruct one neutral B meson as a B → π + π − CP eigenstate and identify the flavor of the accompanying B meson from its decay products. From the dependence of the asymmetry on the time intervals between the two B meson decay points, we obtain the CP-violating asymmetry parameters S ππ = −1.21 −0.27 +0.38( stat) −0.13 +0.16( syst) and A gpπ = +0.94 −0.31 +0.25( stat) ± 0.09( syst). In the η c (2 S) meson search, we examined the K s K − π + invariant mass distribution in a sample of exclusive B → KK S K − π + decays. We find a narrow peak mass M = 3654 ± 6( stat) ± 8( syst) MeV/ c 2 and width Γ < 55 MeV/ c 2. The properties agree with heavy-quark potential model expectations for the η c (2 S) meson, the n = 2 singlet S-wave charmonium state.

CP-violating asymmetries in B0 → π+π− decays

We present a measurement of CP-violating asymmetries in B 0 → π + π − decays based on a data sampleof 44.8 million B B pairs collected at the ϒ(4 S) resonance with the Belle detector. We fully reconstruct one neutral B meson as a B 0 → π + π − CP eigenstate and identify the flavor of the accompanying B meson from its decay products. From the distribution of time intervals between the two B meson decay points, we obtain the CP-violating asymmetry parameters S ππ = −1.21 −0.27 +0.38( stat) −0.13 +0.16( syst) and C ππ = +0.94 0.31 +0.25( stat) ± 0.09( syst).

Measurement of sin(2α) at B aB ar

We present updated measurements of branching fractions and CP-violating asymmetries for neutral B meson decays to two-body final states of charged pions and kaons. The results are obtained from a data sample of about 60 million ϒ(4S) → B B decays collected between 1999 and 2001 by the B aB ar detector at the PEP-II asymmetric-energy B Factory at SLAG. The sample contains 124 −02 +16 ππ, 403 ± 24 Kπ, and 0.6 −7.4 +8.0 KK candidates, from which we measure the following quantities: B( B 0 → π + π −) = (5.4 ± 0.7 ± 0.4) × 10 −6, B( B ) → K + π −) = (17.8 ± 1.1 ± 0.8) × 10 −6, B( B 0 → K + K −) < 1.1 × 10 −6 (90% C.L.), A Kπ = −0.05 ± 0.06 ± 0.01 [−0.14, +0.05], S ππ = −0.01 ± 0.37 ± 0.07 [−0.66, +0.62], C ππ = -0.02 ± 0.29 ± 0.07 [−0.54, +0.48], where the errors are statistical and systematic, respectively, and the asymmetry limits correspond to the 90% confidence level. These results are preliminary.

Direct CP violation in $ {B\rightarrow \pi^{+}\pi^{-} V}$ with $\rho^{0}$ - $\omega$ mixing effects: phenomenological approach

We present a detailed study of direct CP violation and branching ratios in the channels $B^{0,\pm} \to \pi^{+}\pi^{-} V^{0,\pm}$, where $V$ is a vector meson ($K^{* 0,\pm}$ or $\rho^{\pm}$). Emphasis is placed upon the important role played by ${{\rho}^{0}}-{\omega}$ mixing effects in the estimation of the CP-violating asymmetry parameter, $a_{cp}$, associated with the difference of $B$ and $\bar B$ decay amplitudes. A thorough study of the helicity amplitudes is presented as a function of the pion-pion invariant mass. All of the calculations and simulations considered correspond to channels which will be analyzed at the LHCb facility.

The analysis of $B_{d}\rightarrow (\eta, \eta^{{'}})\ell^+\ell^-$ decays in the standard model

We study the differential branching ratio, branching ratio and the CP-violating asymmetry for the exclusive $B_{d}->(\eta, \eta^{\prime}) \ell^+ \ell^-$ decays in the standard model. We deduce the $B_{d}->(\eta, \eta^{\prime})$ form factors from the form factors of $B -> \pi$ available in the literature, by using the $SU(3)_F$ symmetry. We observe that these decay modes, which are within the reach of forthcoming B-factories, are very promising to observe CP-violation.

Charge asymmetry inK±→π±γγinduced by the electromagnetic penguin operators

The $\mathrm{CP}$-violating charge asymmetry in the decays ${K}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\gamma}\ensuremath{\gamma},$ which is induced by the electromagnetic penguin operators, has been studied both in the standard model and in its extensions. Because of a large enhancement of the Wilson coefficients of the electromagnetic penguin operators in the supersymmetric extensions of the standard model, a significant upper bound on this charge asymmetry could be expected, and thus high-precision measurements of this interesting $\mathrm{CP}$-violating quantity might explore new physics effects beyond the standard model.

Measurement of sin2β with BABAR

We present updated results on time-dependent CP-violating asymmetries in neutral B decays to several CP eigenstates containing charmonium. In the Standard Model, the amplitude of these asymmetries is proportional to sin2β. We measure sin2β = 0.741 ± 0.067 (stat) ± 0.034 (syst) from a data sample of about 88 million γ(4 S) → B B decays collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We have also measured CP-violating asymmetries in open charm, and penguin modes sensitive to sin2β, which provide important consistency tests of the Standard Model.

BABAR explores CP violation

The most recent results obtained by the BABAR experiment at the PEP-II asymmetric-energy B Factory at SLAC on CP-violating asymmetries and branching fractions for neutral and charged B decays are presented here. The analysis was performed on a data sample of ∼ 88 million γ (4 S) → B B decays collected between 1999 and 2002. Using b → c cs decays, we measure sin2 β = 0.741 ± 0.067 (stat) ± 0.034 (syst). We also present sin2β measurements from, b → s ss and b → c cd processes . From neutral B meson decays to two-body final states of charged pions and kaons, we derive for the CP violating parameters, S ππ = 0.02 ± 0.34 ± 0.05 [− 0.54, +0.58] and C ππ = − 0.30 ± 0.25 ± 0.04 [− 0.72, +0.12]. First results for B → π + π − π 0 and K ± π ∓ π 0 final states dominated by the ϱ ± resonance, are also presented.

CPviolation in hyperon nonleptonic decays within the standard model

We calculate the CP-violating asymmetries A(Lambda_-^0) and A(Xi_-^-) in nonleptonic hyperon decay within the Standard Model using the framework of heavy-baryon chiral perturbation theory (chiPT). We identify those terms that correspond to previous calculations and discover several errors in the existing literature. We present a new result for the lowest-order (in chiPT) contribution of the penguin operator to these asymmetries, as well as an estimate for the uncertainty of our result that is based on the calculation of the leading nonanalytic corrections.

Measurements of branching fractions and CP-violating asymmetries in B0-->pi+pi-, K+pi-, K+K- decays.

We present measurements of branching fractions and CP-violating asymmetries for two-body neutral B meson decays to charged pions and kaons based on a sample of about 88x10(6) Upsilon(4S)-->BB decays. From a time-independent fit we measure the charge-averaged branching fractions B(B0-->pi+pi-)=(4.7+/-0.6+/-0.2)x10(-6), B(B0-->K+pi-)=(17.9+/-0.9+/-0.7)x10(-6), and the direct CP-violating charge asymmetry A(Kpi)=-0.102+/-0.050+/-0.016 [-0.188,-0.016], where the ranges in square brackets indicate the 90% confidence intervals. From a time-dependent fit we measure the B0-->pi+pi- CP-violating parameters S(pipi)=0.02+/-0.34+/-0.05 [-0.54,+0.58] and C(pipi)=-0.30+/-0.25+/-0.04 [-0.72,+0.12].

CP violation in charged Higgs boson decays into tau and neutrino

We calculate the CP-violating rate asymmetry of H^\pm decays into tau and neutrino at one loop in the MSSM with complex parameters. We find that the asymmetry is typically of the order of 10^-3, depending mainly on the phases of the trilinear coupling A_\tau and of the gaugino mass M_1.

B → Kτ+τ− decay in the general two Higgs doublet model

We study the branching ratio, CP-violating asymmetry, forward-backward asymmetry and the CP-violating asymmetry in the forward-backward asymmetry for the exclusive decay B → Kτ+τ− in the two Higgs doublet model with tree level flavor changing neutral currents (model III). We analyse the dependencies of these quantities on the neutral Higgs boson contributions and the CP parameter sinθ in the model III. We observe that to determine the neutral Higgs boson effects, the measurements of the forward-backward asymmetry and the CP-violating asymmetry in the forward-backward asymmetry for the decay B → Kτ+τ− are promising.

Implications of $B \to \rho \gamma$ measurements in the standard model and supersymmetric theories

We study the implications of the recently improved upper limits on the branching ratios for the decays B -> rho gamma, expressed as R(rho gamma/K^* gamma) = BR(B -> rho gamma)/BR(B -> K^* gamma) <0.047. We work out the constraints that the current bound on R(rho gamma/K^* gamma) implies on the parameters of the quark mixing matrix in the standard model (SM). Using the present profile of the unitarity triangle, we predict this ratio to be R(rho gamma/K^* gamma) = 0.023 +/- 0.012. We also work out the correlations involving R(rho gamma/K^* gamma), the isospin-violating ratio Delta (rho gamma), and the direct CP-violating asymmetry A_CP (rho gamma) in B -> rho gamma decays in the SM, in the minimal supersymmetric extension of the SM (MSSM), and in an extension of the MSSM involving an additional flavor-changing structure in b -> d transitions.

Measurement of CP-violating parameters in B→η′K decays

We present measurements of CP-violating parameters in B0(B0)→η′KS0 and B±→η′K± decays based on a 41.8 fb−1 data sample collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. We fully reconstruct one neutral B meson as a B0(B0)→η′KS0CP eigenstate and identify the flavor of the accompanying B from its decay products. From the distribution of proper time intervals between pairs of B meson decay points, we obtain the CP-violating asymmetry parameters Sη′KS0=0.28±0.55(stat)+0.07−0.08(syst), and Aη′KS0=0.13±0.32(stat)+0.09−0.06(syst). We also reconstruct charged B±→η′K± decays and determine a direct-CP-violating asymmetry value of Aη′K±=(−1.5±7.0(stat)±0.9(syst))%.

Convention-independent study ofCP-violating asymmetries inB→ππ

CP-violating asymmetries in the decay $B^0(t)\to \pi^+ \pi^-$ are a potentially rich source of information about both strong and weak phases. In a previous treatment by the present authors use was made of an assumption about the relative magnitude of tree and penguin amplitudes contributing to this process. This assumption involved an ambiguity in relating the tree amplitude to the amplitude for $B \to \pi \ell \nu$. It is shown here that one can avoid this assumption, which adopted a particular convention for tree and penguin amplitudes, and that the results are convention-independent.

Study of time-dependentCP-violating asymmetries and flavor oscillations in neutralBdecays at theΥ(4S)

We present a measurement of time-dependent CP-violating asymmetries in neutral B meson decays collected with the BABAR detector at the PEP-II asymmetric-energy e+e− collider at the Stanford Linear Accelerator Center. The data sample consists of 29.7 fb−1 recorded at the Υ(4S) resonance and 3.9 fb−1 off resonance. One of the neutral B mesons, which are produced in pairs at the Υ(4S), is fully reconstructed in the CP decay modes J/ψKS0, ψ(2S)KS0, χc1KS0, J/ψK*0 (K*0→KS0π0) and J/ψKL0, or in flavor-eigenstate modes involving D(*)π/ρ/a1 and J/ψK*0 (K*0→K+π−). The flavor of the other neutral B meson is tagged at the time of its decay, mainly with the charge of identified leptons and kaons. A neural network tagging algorithm is used to recover events without a clear lepton or kaon tag. The proper time elapsed between the decays is determined by measuring the distance between the decay vertices. Wrong-tag probabilities, the time-difference resolution function, and the B0−B0 oscillation frequency Δmd are measured with a sample of about 6350 fully-reconstructed B0 decays in hadronic flavor-eigenstate modes. A maximum-likelihood fit to this flavor eigenstate sample finds Δmd=0.516±0.016(stat)±0.010(syst)ps−1. The value of the asymmetry amplitude sin2β is determined from a simultaneous maximum-likelihood fit to the time-difference distribution of the flavor-eigenstate sample and about 642 tagged B0 decays in the CP-eigenstate modes. We find sin2β=0.59±0.14(stat)±0.05(syst), demonstrating that CP violation exists in the neutral B meson system. We also determine the value of the CP violation parameter |λ|=0.93±0.09(stat)±0.03(syst), which is consistent with the expectation of |λ|=1 for no direct CP violation.Received 10 January 2002DOI:https://doi.org/10.1103/PhysRevD.66.032003©2002 American Physical Society

THE CP-VIOLATING ASYMMETRY IN η → π+ π-e+e-

We study the CP-violating asymmetry [Formula: see text], which arises, in η → π+π-e+e-, from the angular correlation of the e+e- and π+ π- planes due to the interference between the magnetic and electric decay amplitudes. With the phenomenologically determined magnetic amplitude and branching ratio as input, the asymmetry, induced by the electric bremsstrahlung amplitude through the CP-violating decay η → π+π-, and by an unconventional tensor type operator, has been estimated respectively. The upper bound of [Formula: see text] from the former is about 10-3, and the asymmetry from the latter might be up to O(10-2). One can therefore expect that this CP asymmetry would be an interesting CP-violating observable for the future precise measurements in the η factories.

Study of CP-violating asymmetries in B0-->pi(+)pi(-) decays.

We present a measurement of CP-violating asymmetries in B0-->pi(+)pi(-) decays based on a 41.8 fb(-1) data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. We fully reconstruct one neutral B meson as a B0-->pi(+)pi(-) CP eigenstate and identify the flavor of the accompanying B meson from its decay products. From the asymmetry in the distribution of the time intervals between the two B meson decay points, we obtain the CP-violating asymmetry parameters S(pipi)=-1.21(+0.38)(-0.27)(stat)+0.16-0.13(syst) and A(pipi)=+0.94(+0.25)(-0.31)(stat)+/-0.09(syst).

The exclusive [formula omitted] decays in a CP softly broken two Higgs doublet model

We study the differential branching ratio, forward-backward asymmetry, CP-violating asymmetry, CP-violating asymmetry in the forward-backward asymmetry and polarization asymmetries in the B→ Kℓ +ℓ − and B→K ∗ℓ +ℓ − decays in the context of a CP softly broken two Higgs doublet model. We analyze the dependencies of these observables on the model parameters by paying a special attention to the effects of neutral Higgs boson (NHB) exchanges and possible CP-violating effects. We find that NHB effects are quite significant for both decays. A combined analysis of above-mentioned observables seems to be very promising as a testing ground for new physics beyond the SM, especially for the existence of the CP-violating phase in the theory.