Recent NA48 results on rare kaon decays

Recent NA48 results from detailed studies of $K_{L,S}\to \pi^+ \pi^- e^+ e^-$ and $K_S\to\pi^0 \gamma\gamma$ decay modes are presented. The results are based on the data collected with the NA48 detector at the CERN SPS during the 1998-199 9 and 2000 data taking periods, respectively. Prospects for future results on charged kaon decays are briefly described.Comment: 4 pages, 4 figures, Moriond QCD 2003 Conferenc

Overview of detector descriptions

The present overview describes the detector description frameworks implemented by the four LHC experiments. The main reviewed items include the detector geometry implementation, the usage of alignment constants in the simulation and the reconstruction, and the storage and retrieval of the alignment constants. The review concludes with a brief comparison of the experiment frameworks.

Interactions of a j=1j=1 boson in the 2(2j+1)2(2j+1) component theory

The amplitudes for boson-boson and fermion-boson interactions are calculated in the second order of perturbation theory in the Lobachevsky space. An essential ingredient of the used model is the Weinberg's $2(2j+1)$ component formalism for describing a particle of spin $j$, recently developed substantially. The boson-boson amplitude is then compared with the two-fermion amplitude obtained long ago by Skachkov on the ground of the hamiltonian formulation of quantum field theory on the mass hyperboloid, $p_0^2 -{\bf p}^2=M^2$, proposed by Kadyshevsky. The parametrization of the amplitudes by means of the momentum transfer in the Lobachevsky space leads to same spin structures in the expressions of $T$ matrices for the fermion and the boson cases. However, certain differences are found. Possible physical applications are discussed.Comment: REVTeX 3.0 file. 12pp. Substantially revised version of IFUNAM preprints FT-93-24, FT-93-3

Form Factors of Composite Systems by Generalized Wigner-Eckart Theorem for Poincar\'e group

The relativistic approach to electroweak properties of two-particle composite systems developed previously is generalized here to the case of nonzero spin. This approach is based on the instant form of relativistic Hamiltonian dynamics. A special mathematical technique is used for the parametrization of matrix elements of electroweak current operators in terms of form factors. The parametrization is a realization of the generalized Wigner--Eckart theorem on the Poincar\'e group, form factors are corresponding reduced matrix elements and they have the sense of distributions (generalized functions). The electroweak current matrix element satisfies the relativistic covariance conditions and in the case of electromagnetic current it also automatically satisfies the conservation law.Comment: Submitted to Theor. Math. Phy

Spin alignment of K∗(892)±K^*(892)^\pm mesons produced in neutron-carbon interactions

A new precise measurements of spin density matrix element $\rho_{00}$ of $K^*(892)^{\pm}$ mesons produced inclusively in neutron-carbon interactions at \~60 GeV have been carried out in the EXCHARM experiment at the Serpukhov accelerator. The values of $\rho_{00}$ obtained in the transversity frame are $0.424\pm0.011(stat)\pm0.018(sys)$ for $K^*(892)^+$ and $0.393\pm0.025(stat)\pm0.018(sys)$ for $K^*(892)^-$. Significant $P_T$ dependence of $\rho_{00}$ has been observed in $K^*(892)^+$ production.Comment: 8 pages, LaTeX, 3 eps figure

Relativistic instant-form approach to the structure of two-body composite systems

A new approach to the electroweak properties of two-particle composite systems is developed. The approach is based on the use of the instant form of relativistic Hamiltonian dynamics. The main novel feature of this approach is the new method of construction of the matrix element of the electroweak current operator. The electroweak current matrix element satisfies the relativistic covariance conditions and in the case of the electromagnetic current also the conservation law automatically. The properties of the system as well as the approximations are formulated in terms of form factors. The approach makes it possible to formulate relativistic impulse approximation in such a way that the Lorentz-covariance of the current is ensured. In the electromagnetic case the current conservation law is ensured, too. The results of the calculations are unambiguous: they do not depend on the choice of the coordinate frame and on the choice of "good" components of the current as it takes place in the standard form of light--front dynamics. Our approach gives good results for the pion electromagnetic form factor in the whole range of momentum transfers available for experiments at present time, as well as for lepton decay constant of pion.Comment: 26 pages, Revtex, 5 figure

Measurement of the branching ratio of the decay Ξ0→Σ+μ−νˉμ\Xi^{0}\rightarrow \Sigma^{+} \mu^{-} \bar{\nu}_{\mu}

From the 2002 data taking with a neutral kaon beam extracted from the CERN-SPS, the NA48/1 experiment observed 97 $\Xi^{0}\rightarrow \Sigma^{+} \mu^{-} \bar{\nu}_{\mu}$ candidates with a background contamination of $30.8 \pm 4.2$ events. From this sample, the BR($\Xi^{0}\rightarrow \Sigma^{+} \mu^{-} \bar{\nu}_{\mu}$) is measured to be $(2.17 \pm 0.32_{\mathrm{stat}}\pm 0.17_{\mathrm{syst}})\times10^{-6}$

Recent NA48/2 and NA62 results

The NA48/2 Collaboration at CERN has accumulated and analysed unprecedented statistics of rare kaon decays in the $K_{e4}$ modes: $K_{e4}(+-)$ ($K^\pm \to \pi^+ \pi^- e^\pm \nu$) and $K_{e4}(00)$ ($K^\pm \to \pi^0 \pi^0 e^\pm \nu$) with nearly one percent background contamination. It leads to the improved measurement of branching fractions and detailed form factor studies. New final results from the analysis of 381 $K^\pm \to \pi^\pm \gamma \gamma$ rare decay candidates collected by the NA48/2 and NA62 experiments at CERN are presented. The results include a decay rate measurement and fits to Chiral Perturbation Theory (ChPT) description.Comment: Prepared for the Proceedings of "Moriond QCD and High Energy Interactions. March 22-29 2014." conferenc

Measurement of K^0_e3 form factors

The semileptonic decay of the neutral K meson, KL -> pi e nu (Ke3), was used to study the strangeness-changing weak interaction of hadrons. A sample of 5.6 million reconstructed events recorded by the NA48 experiment was used to measure the Dalitz plot density. Admitting all possible Lorentz-covariant couplings, the form factors for vector (f_+(q^2)), scalar (f_S) and tensor (f_T) interactions were measured. The linear slope of the vector form factor lambda_+ = 0.0284+-0.0007+-0.0013 and values for the ratios |f_S/f_+(0)| = 0.015^{+0.007}_{-0.010}+-0.012 and |f_T/f_+(0)| = 0.05^{+0.03}_{-0.04}+-0.03 were obtained. The values for f_S and f_T are consistent with zero. Assuming only Vector-Axial vector couplings, lambda_+ = 0.0288+-0.0004+-0.0011 and a good fit consistent with pure V-A couplings were obtained. Alternatively, a fit to a dipole form factor yields a pole mass of M = 859+-18 MeV, consistent with the K^*(892) mass.Comment: 16 pages, 7 figures. submitted to Phys. Lett.