Search

Abstract The NA48/2 experiment at CERN reports the first observation of the K ± → π ± π 0 e + e − decay from an exposure of 1.7 × 10 11 charged kaon decays recorded in 2003–2004. A sample of 4919 candidates with 4.9% background contamination allows the determination of the branching ratio in the full kinematic region, B R (K ± → π ± π 0 e + e −) = (4.24 ± 0.14) × 10 − 6. The study of the kinematic space shows evidence for a structure dependent contribution in agreement with predictions based on chiral perturbation theory. Several P- and CP-violating asymmetries are also evaluated. [ABSTRACT FROM AUTHOR]

We show how an accidental U ( 1 ) Peccei–Quinn (PQ) symmetry can arise from a discrete A 4 family symmetry combined with a discrete flavour symmetry Z 3 × Z 5 2 , in a realistic Pati–Salam unified theory of flavour. Imposing only these discrete flavour symmetries, the axion solution to the strong CP problem is protected from PQ-breaking operators to the required degree. A QCD axion arises from a linear combination of A 4 triplet flavons, which are also responsible for fermion flavour structures due to their vacuum alignments. We find that the requirement of an accidental PQ symmetry arising from a discrete flavour symmetry constrains the form of the Yukawa matrices, providing a link between flavour and the strong CP problem. Our model predicts specific flavour-violating couplings of the flavourful axion and thus puts a strong limit on the axion scale from kaon decays. [ABSTRACT FROM AUTHOR]

The NA62 experiment recorded a large sample of K + → μ + ν μ decays in 2007. A peak search has been performed in the reconstructed missing mass spectrum. In the absence of a signal, limits in the range 2 × 10 − 6 to 10 − 5 have been set on the squared mixing matrix element | U μ 4 | 2 between muon and heavy neutrino states, for heavy neutrino masses in the range 300–375 MeV/ c 2 . The result extends the range of masses for which upper limits have been set on the value of | U μ 4 | 2 in previous production search experiments. [ABSTRACT FROM AUTHOR]

The mass and decay width of the ϕ meson in cold nuclear matter are computed in an effective Lagrangian approach. The medium dependence of these properties are obtained by evaluating kaon–antikaon loop contributions to the ϕ self-energy, employing the medium-modified kaon masses, calculated using the quark-meson coupling model. The loop integral is regularized with a dipole form factor, and the sensitivity of the results to the choice of cutoff mass in the form factor is investigated. At normal nuclear matter density we find a downward shift of the ϕ mass by a few percent, while the decay width is enhanced by an order of magnitude. For a large variation of the cutoff mass parameter, the results for the ϕ mass and the decay width turn out to vary very little. Our results support results in the literature which suggest that one should observe a small downward mass shift and a large broadening of the decay width. In order to explore the possibility of studying the binding and absorption of ϕ mesons in nuclei, we also present the single-particle binding energies and half-widths of ϕ -nucleus bound states for some selected nuclei. [ABSTRACT FROM AUTHOR]

Precise measurements of charged-kaon multiplicities in deep inelastic scattering were performed. The results are presented in three-dimensional bins of the Bjorken scaling variable x , the relative virtual-photon energy y , and the fraction z of the virtual-photon energy carried by the produced hadron. The data were obtained by the COMPASS Collaboration by scattering 160 GeV muons off an isoscalar 6 LiD target. They cover the kinematic domain 1 ( GeV / c ) 2 < Q 2 < 60 ( GeV / c ) 2 in the photon virtuality, 0.004 < x < 0.4 , 0.1 < y < 0.7 , 0.20 < z < 0.85 , and W > 5 GeV / c 2 in the invariant mass of the hadronic system. The results from the sum of the z -integrated K + and K − multiplicities at high x point to a value of the non-strange quark fragmentation function larger than obtained by the earlier DSS fit. [ABSTRACT FROM AUTHOR]

We propose that three recent anomalies in B meson decays, R D ( ⁎ ) , R K , and P 5 ′ , might be explained by only one vector leptoquark weak triplet state. The constraints on the parameter space are obtained by considering t → b τ + ν data, lepton flavor universality tests in the kaon sector, bounds on the lepton flavor violating decay B → K μ τ , and b → c μ − ν ¯ decays. The presence of such vector leptoquark could be exposed in precise measurements of top semitauonic decays to b quark. The model predicts enhanced decay rate of B → K ν ¯ ν , approximate equality of lepton flavor universality ratios R K ⁎ , R K , and suppressed branching fraction of B s → μ + μ − . [ABSTRACT FROM AUTHOR]

Abstract: The KLOE Collaboration recently reported bounds on the directional dependence of the lifetime of the short-lived neutral kaon with respect to the dipole anisotropy of the cosmic microwave background. We interpret their results in an effective field theory framework developed to probe the violation of Lorentz invariance in the weak interaction and previously applied to semileptonic processes, in particular β decay. In this approach a general Lorentz-violating tensor is added to the standard propagator of the W boson. We perform an exploratory study of the prospects to search for Lorentz violation in nonleptonic decays. For the kaon, we find that the sensitivity to Lorentz violation is limited by the velocity of the kaons and by the extent to which hadronic effects can be calculated. In a simple model we derive the decay rate and calculate the asymmetry for the lifetime. Using the KLOE data, limits on the values of are determined. [Copyright &y& Elsevier]

Abstract: CP asymmetries have been measured recently by the LHCb collaboration in three-body decays to final states involving charged pions and kaons. Large asymmetries with opposite signs at a level of about have been observed in and for restricted regions in the Dalitz plots involving and with low invariant mass. U-spin is shown to predict corresponding and asymmetries with opposite signs and inversely proportional to their branching ratios, in analogy with a successful relation predicted thirteen years ago between asymmetries in and . We compare these predictions with the measured integrated asymmetries. Effects of specific resonant or non-resonant partial waves on enhanced asymmetries for low-pair-mass regions of the Dalitz plot are studied in . The closure of low-mass and channels involving only rescattering may explain by CPT approximately equal magnitudes and opposite signs measured in and . [Copyright &y& Elsevier]

Abstract: The neutral Kaon system has both CP violation in the mass matrix and a non-vanishing lifetime difference in the width matrix. This leads to an effective Hamiltonian which is not a normal operator, with incompatible (non-commuting) masses and widths. In the Weisskopf–Wigner Approach (WWA), by diagonalizing the entire Hamiltonian, the unphysical non-orthogonal “stationary” states are obtained. These states have complex eigenvalues whose real (imaginary) part does not coincide with the eigenvalues of the mass (width) matrix. In this work we describe the system as an open Lindblad-type quantum mechanical system due to Kaon decays. This approach, in terms of density matrices for initial and final states, provides a consistent probabilistic description, avoiding the standard problems because the width matrix becomes a composite operator not included in the Hamiltonian. We consider the dominant decay channel to two pions, so that one of the Kaon states with definite lifetime becomes stable. This new approach provides results for the time dependent decay rates in agreement with those of the WWA. [Copyright &y& Elsevier]

Abstract: A precision measurement of the ratio of the rates of kaon leptonic decays and with the full data sample collected by the NA62 experiment at CERN in 2007–2008 is reported. The result, obtained by analysing reconstructed candidates with 11% background contamination, is , in agreement with the Standard Model expectation. [Copyright &y& Elsevier]

Abstract: The decay of the hadronic atom kaonium is investigated non-perturbatively using meson–meson interaction amplitudes taken from leading order chiral perturbation theory in an approach adapted from that proposed by Oller and Oset (1997) . The Kudryavtsev–Popov eigenvalue equation is solved numerically for the energy shift and decay width due to strong interactions in the 1s state. These calculations introduce a cutoff ∼1.4 GeV in momentum space that is necessary to regulate divergent loop contributions to the meson–meson scattering amplitudes in the strong-interaction sector. One finds lifetimes of for the ground state of kaonium. [Copyright &y& Elsevier]

Abstract: Charged B decays to three charged kaons are analysed in the framework of the QCD factorization approach. The strong final state interactions are described using the kaon scalar and vector form factors. The scalar non-strange and strange form factors at low effective masses are constrained by chiral perturbation theory and satisfy the two-body unitarity conditions. The latter stem from the properties of the meson–meson amplitudes which describe all possible S-wave transitions between three coupled channels consisting of two kaons, two pions and four pions. The vector form factors are fitted to the data on the electromagnetic kaon interactions. The model results are compared with the Belle and BaBar data. Away from resonance, in the S-wave dominated mass spectra, a possibility for a large CP asymmetry is identified. [Copyright &y& Elsevier]

Abstract: A precision test of lepton flavour universality has been performed by measuring the ratio of kaon leptonic decay rates and in a sample of 59 813 reconstructed candidates with background contamination. The result is in agreement with the Standard Model expectation. [Copyright &y& Elsevier]

Abstract: A sample of 3120 decay candidates with background contamination has been collected by the NA48/2 experiment at the CERN SPS, allowing a detailed study of the decay properties. The branching ratio was measured to be . The form factor , where , was parameterized according to several models. In particular, the slope of the linear form factor was measured to be . Upper limits of and on possible charge asymmetry and forward–backward asymmetry were established at 90% CL. An upper limit was established at 90% CL for the rate of the lepton number violating decay. [Copyright &y& Elsevier]

Abstract: A sample of 7253 decay candidates with 1.0% background contamination has been collected by the NA48/2 experiment at the CERN SPS, which allowed a precise measurement of the decay properties. The branching ratio in the full kinematic range was measured to be , where the uncertainty includes also the model dependence. The shape of the form factor , where , was parameterized according to several models, and, in particular, the slope δ of the linear form factor was determined to be . A possible CP violating asymmetry of and decay widths was investigated, and a conservative upper limit of at 90% CL was established. [Copyright &y& Elsevier]

We present the result of the first measurement of the T-violating transverse muon polarization PT in the decay K+→μ+νγ. This polarization is sensitive to new sources of CP-violation in the Higgs sector. Using data accumulated in the period 1996–1998 we have obtained PT=(−0.64±1.85(stat)±0.10(syst))×10−2 which is consistent with no T-violation in this decay. [Copyright &y& Elsevier]