CP Violation Parameter Research Articles

Measurement ofCP-violating asymmetries inB0→(ρπ)0decays using a time-dependent Dalitz plot analysis

We present results for a time-dependent Dalitz plot measurement of CP-violating asymmetries in the mode B^0 -> pi^+ pi^- pi^0. The dataset is derived from the complete sample of 471 x 10^6 BBbar meson pairs collected with the BABAR detector at the PEP-II asymmetric-energy e^+e^- collider at the SLAC National Accelerator Laboratory operating on the Upsilon(4S) resonance. We extract parameters describing the time-dependent B^0 -> rho pi decay probabilities and CP asymmetries, including C = 0.016\pm0.059\pm0.036, DeltaC = 0.234\pm0.061\pm0.048, S = 0.053\pm0.081\pm0.034, and DeltaS = 0.054\pm0.082\pm0.039, where the uncertainties are statistical and systematic, respectively. We perform a two-dimensional likelihood scan of the direct CP-violation asymmetry parameters for B^0 -> rho^\pm pi^\mp decays, finding the change in chi^2 between the minimum and the origin (corresponding to no direct CP violation) to be Delta(chi^2)=6.42. We present information on the CP-violating parameter alpha in a likelihood scan that incorporates B^\pm -> rho pi measurements.

Minimal neutrino texture with neutrino mass ratio and Cabibbo angle

We present neutrino mass matrix textures in a minimal framework of the type-I seesaw mechanism, where two right-handed Majorana neutrinos are introduced in order to reproduce experimental results of neutrino oscillations. The textures can lead to experimentally favored leptonic mixing angles described by tri-bimaximal mixing with one additional rotation. We present minimal and next to minimal textures for the normal mass hierarchy case in the context of the texture zero. A minimal texture in the inverted hierarchy case is also constructed, which does not have any vanishing entries in a Dirac neutrino mass matrix. We also discuss some cases in which the model parameters in the textures are supposed to be a neutrino mass ratio and/or the Cabibbo angle. Predicted regions of mixing angles, a leptonic CP-violation parameter, and an effective mass for the neutrinoless double beta decay are presented in all textures.

BrokenS3neutrinos

Motivated by recent measurements which strongly support a nonzero reactor mixing angle $\theta_{13}$, we study a deviation from $S_3$ neutrino discrete symmetry by explicitly breaking the neutrino mass matrix with a general retrocirculant matrix. We show that nonzero $\theta_{13}$ and nonzero CP violation parameter $J_{CP}$ arise due to the difference between $y_2$ and $y_3$. We demonstrate that it is possible to obtain the experimentally favored results for neutrino masses and mixing angles from this mass matrix. Furthermore, we estimate the effective masses $m_{\beta}$ and $m_{\beta \beta}$ and total neutrino mass $\sum |m_i|$ predicted by this mass matrix.

Flavor constraints on scenarios with two or three heavy squark generations

We re-assess constraints from flavor-changing neutral currents in the kaon system on supersymmetric scenarios with a light gluino, two heavy generations of squarks and a lighter third generation. We compute for the first time limits in scenarios with three heavy squark families, taking into account QCD corrections at the next-to-leading order. We compare our limits with those in the case of two heavy families. We use the mass insertion approximation and consider contributions from gluino exchange to constrain the mixing between the first and second squark generation. While it is not possible to perform a general analysis, we assess the relevance of each kind of flavor- and CP-violating parameters. We also provide ready to use magic numbers for the computation of the Wilson coefficients at 2 GeV for these scenarios.

Measurement ofCPasymmetries and branching fractions in charmless two-bodyB-meson decays to pions and kaons

We present improved measurements of CP-violation parameters in the decays $B^0 \to \pi^+ \pi^-$, $B^0 \to K^+ \pi^-$, and $B^0 \to \pi^0 \pi^0$, and of the branching fractions for $B^0 \to \pi^0 \pi^0$ and $B^0 \to K^0 \pi^0$. The results are obtained with the full data set collected at the $\Upsilon(4S)$ resonance by the BABAR experiment at the PEP-II asymmetric-energy $B$ factory at the SLAC National Accelerator Laboratory, corresponding to $467 \pm 5$ million $B\bar B$ pairs. We find the CP-violation parameter values and branching fractions $ S_{\pi^+\pi^-} = -0.68 \pm 0.10 \pm 0.03, C_{\pi^+\pi^-} = -0.25 \pm 0.08 \pm 0.02, A_{K^-\pi^+} = -0.107 \pm 0.016 ^{+0.006}_{-0.004}, C_{\pi^0\pi^0} = -0.43 \pm 0.26 \pm 0.05, Br(B^0 \to \pi^0 \pi^0) = (1.83 \pm 0.21 \pm 0.13) \times 10^{-6}, Br(B^0 \to K^0 \pi^0) = (10.1 \pm 0.6 \pm 0.4) \times 10^{-6},$ where in each case, the first uncertainties are statistical and the second are systematic. We observe CP violation with a significance of 6.7 standard deviations for $B^0 \to\pi^+\pi^-$ and 6.1 standard deviations for $B^0 \to K^+ \pi^-$, including systematic uncertainties. Constraints on the Unitarity Triangle angle $\alpha$ are determined from the isospin relations among the $B \to \pi\pi$ rates and asymmetries. Considering only the solution preferred by the Standard Model, we find $\alpha$ to be in the range $[71^\circ,109^\circ]$ at the 68% confidence level.

Search for new physics in heavy quark decays at LHCb

Heavy quark decays are an excellent laboratory to search for physics beyond the Standard Model. The LHCb detector is specially design to measure CP violation parameters and rare decays processes involving decays containing b– or c– quarks. In this paper, recent LHCb measurements concerning CP violation parameters in the BS0 and charm sector, as well as measurements of rare b→sl+l− transitions, are presented.

Measurement of branching fraction and first evidence ofCPviolation inB0→a1±(1260)π∓decays

We present a measurement of the branching fraction and time-dependent CP violation parameters in B0 --> a_1^+-(1260) pi^-+ decays. The results are obtained from the final data sample containing 772x10^6 BBbar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. We also measure an upper limit on the product branching fraction for a possible decay with the same final state B0 --> a_2^+-(1320) pi^-+. In a time-dependent measurement to extract CP asymmetries, we find evidence of mixing-induced CP violation in B0 --> a_1^+-(1260) pi^-+ decays with a 3.1 sigma significance and the rate where the a_1^+-(1260) does not contain the spectator quark is found to dominate the rate where it does at the 4.1 sigma level. However, there is no evidence for either time and flavor integrated direct CP violation or flavor-dependent direct CP violation.

First observation ofCPviolation and improved measurement of the branching fraction and polarization ofB0→D*+D*−decays

We report the measurement of the branching fraction, the polarization, and the parameters of the time-dependent CP violation in B0 -> D*+ D*- decays using a data sample of 772 million BB pairs, collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We obtain a branching fraction of B = (7.82 +- 0.38 +- 0.63) x10^{-4}, a CP-odd fraction of R_\perp = 0.138 +- 0.024 +- 0.006 and, additionally, a fraction of the longitudinal component in the transversity base of R_0 = 0.624 +- 0.029 +- 0.011. The measured values of the parameters of the CP violation are S_{D*+ D*-} = -0.79 +- 0.13 +- 0.03 and A_{D*+ D*-} = 0.15 +- 0.08 +- 0.04.

Model-independent $ {D^0}-{{\overline{D}}^0} $ mixing and CP violation studies with $ {D^0}\to K_{\mathrm{S}}^0{\pi^{+}}{\pi^{-}} $ and $ {D^0}\to K_{\mathrm{S}}^0{K^{+}}{K^{-}} $

Simulation studies are performed to assess the sensitivity of a model-independent analysis of the flavour-tagged decays $D^0 \to K^0_{\rm S}\pi^+\pi^-$ and $D^0 \to K^0_{\rm S}K^+K^-$ to mixing and CP violation. The analysis takes as input measurements of the $D$ decay strong-phase parameters that are accessible in quantum-correlated $D-\bar{D}$ pairs produced at the $\psi(3770)$ resonance. It is shown that the model-independent approach is well suited to the very large data sets expected at an upgraded LHCb experiment, or future high luminosity $e^+e^-$ facility, and that with 100M $K^0_{\rm S}\pi^+\pi^-$ decays a statistical precision of around 0.01 and $0.7^\circ$ is achievable on the CP violation parameters $r_{CP}$ and $a_{CP}$, respectively. Even with this very large sample the systematic uncertainties associated with the strong-phase parameters will not be limiting, assuming that full use is made of the available $\psi(3770)$ data sets of CLEO-c and BES-III. Furthermore, it is demonstrated that large flavour-tagged samples can themselves be exploited to provide information on the strong-phase parameters, a feature that will be beneficial in the measurement of the CKM angle $\gamma/\phi_3$ with $B^- \to DK^-$ decays.

Weakly-induced strong CP violation

Weak interaction contributions to the strong θ parameter are revisited in the frame of a large-Nc Chiral Perturbation Theory. Focusing on the hadronic η(′)→ππ amplitudes, we express these second-order corrections in terms of the CP-violating parameter in K→ππ decays to obtain Δwθ≈10−17 at O(GF2ε′).

Study ofCPviolation in Dalitz-plot analyses ofB0→K+K−KS0,B+→K+K−K+, andB+→KS0KS0K+

We perform amplitude analyses of the decays B0→K+K−KS0, B+→K+K−K+, and B+→KS0KS0K+, and measure CP-violating parameters and partial branching fractions. The results are based on a data sample of approximately 470×106 BB¯ decays, collected with the BABAR detector at the PEP-II asymmetric-energy B factory at the SLAC National Accelerator Laboratory. For B+→K+K−K+, we find a direct CP asymmetry in B+→ϕ(1020)K+ of ACP=(12.8±4.4±1.3)%, which differs from zero by 2.8σ. For B0→K+K−KS0, we measure the CP-violating phase βeff(ϕ(1020)KS0)=(21±6±2)°. For B+→KS0KS0K+, we measure an overall direct CP asymmetry of ACP=(4−5+4±2)%. We also perform an angular-moment analysis of the three channels and determine that the fX(1500) state can be described well by the sum of the resonances f0(1500), f2′(1525), and f0(1710).15 MoreReceived 31 January 2012DOI:https://doi.org/10.1103/PhysRevD.85.112010© 2012 American Physical Society

Amplitude analysis ofD0→K+K−π+π−

The first flavor-tagged amplitude analysis of the decay D0 to the self-conjugate final state K+K−π+π− is presented. Approximately 3000 signal decays are selected from data acquired by the CLEO II.V, CLEO III, and CLEO-c detectors. The three most significant amplitudes, which contribute to the model that best fits the data, are ϕρ0, K1(1270)±K∓, and nonresonant K+K−π+π−. Separate amplitude analyses of D0 and D¯0 candidates indicate no CP violation among the amplitudes at the level of 5% to 30% depending on the mode. In addition, the sensitivity to the CP-violating parameter γ/ϕ3 from a sample of 2000 B+→D˜0(K+K−π+π−)K+ decays, where D˜ is a D0 or D¯0, collected at LHCb or a future flavor facility, is estimated to be (11.3±0.3)° using the favored model.Received 27 January 2012DOI:https://doi.org/10.1103/PhysRevD.85.122002© 2012 American Physical Society

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).

Measurement of theCP-violating phaseβsJ/ψϕinBs0→J/ψϕdecays with the CDF II detector

We present a measurement of the \CP-violating parameter \betas using approximately 6500 $\BsJpsiPhi$ decays reconstructed with the CDF\,II detector in a sample of $p\bar p$ collisions at $\sqrt{s}=1.96$ TeV corresponding to 5.2 fb$^{-1}$ integrated luminosity produced by the Tevatron Collider at Fermilab. We find the \CP-violating phase to be within the range $\betas \in [0.02, 0.52] \cup [1.08, 1.55]$ at 68% confidence level where the coverage property of the quoted interval is guaranteed using a frequentist statistical analysis. This result is in agreement with the standard model expectation at the level of about one Gaussian standard deviation. We consider the inclusion of a potential $S$-wave contribution to the $\Bs\to J/\psi K^+K^-$ final state which is found to be negligible over the mass interval $1.009 < m(K^+K^-)<1.028 \gevcc$. Assuming the standard model prediction for the \CP-violating phase \betas, we find the \Bs decay width difference to be $\deltaG = 0.075 \pm 0.035\,\textrm{(stat)} \pm 0.006\,\textrm{(syst)} \ps$. We also present the most precise measurements of the \Bs mean lifetime $\tau(\Bs) = 1.529 \pm 0.025\,\textrm{(stat)} \pm 0.012\,\textrm{(syst)}$ ps, the polarization fractions $|A_0(0)|^2 = 0.524 \pm 0.013\,\textrm{(stat)} \pm 0.015\,\textrm{(syst)}$ and $|A_{\parallel}(0)|^2 = 0.231 \pm 0.014\,\textrm{(stat)} \pm 0.015\,\textrm{(syst)}$, as well as the strong phase $\delta_{\perp}= 2.95 \pm 0.64\,\textrm{(stat)} \pm 0.07\,\textrm{(syst)} \textrm{rad}$. In addition, we report an alternative Bayesian analysis that gives results consistent with the frequentist approach.

Measurement of theCP-Violation Parametersin2ϕ1with a New Tagging Method at theΥ(5S)Resonance

We report a measurement of the CP-violation parameter sin2φ1 at the Υ(5S) resonance using a new tagging method, called "B-π tagging." In Υ(5S) decays containing a neutral B meson, a charged B, and a charged pion, the neutral B is reconstructed in the J/ψK(S)(0) CP-eigenstate decay channel. The initial flavor of the neutral B meson at the moment of the Υ(5S) decay is opposite to that of the charged B and may thus be inferred from the charge of the pion without reconstructing the charged B. From the asymmetry between B-π(+) and B-π(-) tagged J/ψK(S)(0) yields, we determine sin2φ1=0.57±0.58(stat)±0.06(syst). The results are based on 121 fb(-1) of data recorded by the Belle detector at the KEKB e(+)e(-) collider.

Radiative neutrino mass generation through vectorlike quarks

A new model of radiative neutrino masses generated via two-loop diagrams is proposed involving a charge $2/3$ vectorlike quark and a doublet of leptoquark scalars. This model predicts one of the neutrinos to be massless and admits both the normal and inverted neutrino mass hierarchies with correlated predictions for ${\ensuremath{\ell}}_{i}\ensuremath{\rightarrow}{\ensuremath{\ell}}_{j}+\ensuremath{\gamma}$ branching ratios. New contributions to CP violation in ${B}_{s}^{0}\ensuremath{-}{\overline{B}}_{s}^{0}$ mixing arise in the model through leptoquark box diagrams, which can explain the anomalous di-muon events reported by the D0 collaboration. These leptoquarks, with masses below 500 GeV, also provide a natural resolution to the apparent discrepancy in the measured values of the CP-violation parameters $\mathrm{sin}2\ensuremath{\beta}$ and ${ϵ}_{K}$.

Measurement of mixing and CP violation parameters in two-body charm decays

Abstract A study of mixing and indirect CP violation in D 0 mesons through the determination of the parameters y CP and A Γ is presented. The parameter y CP is the deviation from unity of the ratio of effective lifetimes measured in D 0 decays to the CP eigenstate K + K − with respect to decays to the Cabibbo favoured mode K −π+. The result measured using data collected by LHCb in 2010, corresponding to an integrated luminosity of 29 pb−1, is y CP = (5.5 ± 6.3stat ± 4.1syst) × 10−3. The parameter A Γ is the asymmetry of effective lifetimes measured in decays of D 0 and $ {\overline D^0} $ mesons to K + K −. The result is A Γ = (−5.9 ± 5.9stat ± 2.1syst) × 10−3. A data-driven technique is used to correct for lifetime-biasing effects.

Search for CP violation in decays at Belle

We report on a search for CP violation in τ±→KS0π±ντ decays using a data sample of 699 fb−1 collected in the Belle experiment at the KEKB electron-positron asymmetric-energy collider. The CP asymmetry is measured in four bins of the invariant mass of the KS0π± system and found to be compatible with zero with a precision of O(10−3) in each mass bin. Limits for the CP violation parameter ℑ(ηS) are given at a 90% confidence level. These limits are |ℑ(ηS)|<0.026 or better, depending on the parameterization used to describe the hadronic form factors and improve upon previous limits by one order of magnitude.

Amplitude analysis and measurement of the time-dependentCPasymmetry ofB0→KS0KS0KS0decays

We present the first results on the Dalitz-plot structure and improved measurements of the time-dependent CP-violation parameters of the process B0→KS0KS0KS0 obtained using 468×106 BB¯ decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. The Dalitz-plot structure is probed by a time-integrated amplitude analysis that does not distinguish between B0and B¯0 decays. We measure the total inclusive branching fraction B(B0→KS0KS0KS0)=(6.19±0.48±0.15±0.12)×10−6, where the first uncertainty is statistical, the second is systematic, and the third represents the Dalitz-plot signal model dependence. We also observe evidence for the intermediate resonant states f0(980), f0(1710), and f2(2010). Their respective product branching fractions are measured to be (2.70−1.19+1.25±0.36±1.17)×10−6, (0.50−0.24+0.46±0.04±0.10)×10−6, and (0.54−0.20+0.21±0.03±0.52)×10−6. Additionally, we determine the mixing-induced CP-violation parameters to be S=−0.94−0.21+0.24±0.06 and C=−0.17±0.18±0.04, where the first uncertainty is statistical and the second is systematic. These values are in agreement with the standard model expectation. For the first time, we report evidence of CP violation in B0→KS0KS0KS0 decays; CP conservation is excluded at 3.8 standard deviations including systematic uncertainties.3 MoreReceived 16 November 2011DOI:https://doi.org/10.1103/PhysRevD.85.054023© 2012 American Physical Society

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.