Topological aggregation, the twin paradox and the No Show paradox

International audienceConsider the framework of topological aggregation introduced by Chichilnisky (1980). We prove that in this framework the Twin Paradox and the No Show Paradox cannot be avoided. Anonymity and unanimity are not needed to obtain these results

ChPT tests at the NA48 and NA62 experiments at CERN

The NA48/2 Collaboration at CERN has accumulated unprecedented statistics of rare kaon decays in the Ke4 modes: Ke4(+-) ($K^\pm \to \pi^+ \pi^- e^\pm \nu$) and Ke4(00) ($K^\pm \to \pi^0 \pi^0 e^\pm \nu$) with nearly one percent background contamination. The detailed study of form factors and branching rates, based on these data, has been completed recently. The results brings new inputs to low energy strong interactions description and tests of Chiral Perturbation Theory (ChPT) and lattice QCD calculations. In particular, new data support the ChPT prediction for a cusp in the $\pi^0\pi^0$ invariant mass spectrum at the two charged pions threshold for Ke4(00) decay. New final results from an analysis of about 400 $K^\pm \to \pi^\pm \gamma \gamma$ rare decay candidates collected by the NA48/2 and NA62 experiments at CERN during low intensity runs with minimum bias trigger configurations are presented. The results include a model-independent decay rate measurement and fits to ChPT description.Comment: XIIth International Conference on Heavy Quarks and Leptons 2014, Mainz, German

First Observation and Measurement of the Decay K+- -> pi+- e+ e- gamma

Using the full data set of the NA48/2 experiment, the decay K+- -> pi+- e+ e- gamma is observed for the first time, selecting 120 candidates with 7.3 +- 1.7 estimated background events. With K+- -> pi+- pi0D as normalisation channel, the branching ratio is determined in a model-independent way to be Br(K+- -> pi+- e+ e- gamma, m_eegamma > 260 MeV/c^2) = (1.19 +- 0.12_stat +- 0.04_syst) x 10^-8. This measured value and the spectrum of the e+ e- gamma invariant mass allow a comparison with predictions of Chiral Perturbation Theory.Comment: 13 pages, 3 figures. Accepted for publication in Phys.Lett.

Empirical parameterization of the K+- -> pi+- pi0 pi0 decay Dalitz plot

As first observed by the NA48/2 experiment at the CERN SPS, the \p0p0 invariant mass (M00) distribution from \kcnn decay shows a cusp-like anomaly at M00=2m+, where m+ is the charged pion mass. An analysis to extract the pi pi scattering lengths in the isospin I=0 and I=2 states, a0 and a2, respectively, has been recently reported. In the present work the Dalitz plot of this decay is fitted to a new empirical parameterization suitable for practical purposes, such as Monte Carlo simulations of K+- -> pi+- pi0 pi0 decays.Comment: 9 pages, 3 figures

Search for direct CP-violation in K+- --> pi+-pi0pi0 decays

A search for direct CP-violation in K+- --> pi+-pi0pi0 decays based on 47.14 million events has been performed by the NA48/2 experiment at the CERN SPS. The asymmetry in the Dalitz plot linear slopes A_g=(g^+ - g^-)/(g^+ + g^-) is measured to be A_g=(1.8 +- 2.6).10^{-4}. The design of the experiment and the method of analysis provide good control of instrumental charge asymmetries in this measurement. The precision of the result is limited by statistics and is almost one order of magnitude better than that of previous measurements by other experiments.Comment: 14 page

Direct search for light gluinos

We present the results for a direct search for light gluinos through the appearance of $\eta\rightarrow 3\pi^{0}$ with high transverse momentum in the vacuum tank of the NA48 experiment at CERN. We find one event within a lifetime range of $10^{-9}-10^{-3}$s and another one between $10^{-10}-10^{-9}$s. Both events are consistent with the expected background from neutrons in the beam, produced by 450 GeV protons impinging on the Be targets, which interact with the residual air in the tank. From these data we give limits on the production of the hypothetical $g\widetilde{g}$ bound state, the $R^0$ hadron, and its $R^0\rightarrow\eta\widetilde{\gamma}$ decay in the $R^0$ mass range between 1 and 5~GeV

New high statistics measurement of Ke4K_{e4} decay form factors and ππ\pi\pi scattering phase shifts

We report results from a new measurement of the $K_{e4}$ decay $K^{\pm} \rightarrow \pi^{+}\pi^{-}e^{\pm}\nu$ by the NA48/2 collaboration at the CERN SPS, based on a partial sample of more than 670000 $K_{e4}$ decays in both charged modes collected in 2003. The form factors of the hadronic current (F, G, H) and $\pi\pi$ phase difference ($\delta=\delta_{s}-\delta_{p}$) have been measured in ten independent bins of the $\pi\pi$ mass spectrum to investigate the variation. A sizeable acceptance at large $\pi\pi$ mass, a low background and a very good resolution contribute to an improved experimental accuracy, a factor two better than in the previous measurement, when extracting the $\pi\pi$ scattering lengths $a^{0}_{0}$ and $a^{2}_{0}$. Under the assumption of isospin symmetry and using numerical solutions of the Roy equations, the following values are obtained in the plane ($a^{0}_{0}, a^{2}_{0}): a^{0}_{0}=0.233 \pm 0.016_{stat} \pm 0.007_{syst}, a^{2}_{0}=-0.0471 \pm 0.011_{stat} \pm 0.004_{syst}$. The presence of potentially large isospin effects is also considered and will allow comparison with precise predictions from Chiral Perturbation Theory