Neutral Kaon Decays Research Articles

Impact of indirect CP violation on Br(KS→ μ+μ−)ℓ=0

The decay KS → (μ+μ−)ℓ=0, with the final muon pair in an angular-momentum zero state, is a sensitive probe of short-distance physics. It has recently been shown how to extract this branching ratio from neutral kaon decay data. We point out that the impact of indirect CP violation on the standard-model prediction of this mode, while nominally of order |ϵK| ∼ 10−3, is enhanced by a large amplitude ratio and leads to a shift of the branching ratio Br(KS → μ+μ−)ℓ=0 by a few percent, depending on the size of a relative phase that can be extracted from data. We also update the standard-model prediction of the short-distance contribution.

Geometric phases in kaon decays and baryogenesis

We studied the formalism for construction of Bargmann invariants (BIs) as quantum mechanical geometric phases and identified the CP invariance with the rephasing invariant phases in neutral kaon system, kaon decays, baryogenesis and leptogenesis. We develop this formalism to express the CP violation in terms of the Bargmann invariants, which allow us to interpret them as geometric phases. We then comment on the application of such generalized treatment of CP phases.

About the decay of the neutral Kaon into three Pions in the book: The Feynman Lectures on Physics

In this article we present a mathematical solution that extends and explores the solution found in chapter 11 of the book “Quantum Mechanics”, from “The Feynman Lectures on Physics”, about the neutral Kaon. The extension is built within the context of the CP symmetry for the two neutral Kaon decays considered in this chapter: (i) In two Pions, starting in the |K1⟩ state; (ii) In three Pions, from the |K2⟩ state. We found two mathematical expressions that allow to accommodate, separately, each one of the mean lifetime for these decays, unlike the solution given by Feynman that allows to accommodate only one of these mean lifetime. The extended solution is approximate because a small break in CPT symmetry is assumed in these decays; however, it has the advantage of avoiding the colloquially commented situation by Feynman of remaining “forever” from the neutral Kaon in the |K2⟩ state in the situation in which the only possible decay channel was in two Pions.

The Data Acquisition System of the KOTO Experiment and the RCE Platform Technology Upgrade

The KOTO experiment at J-PARC, Japan, aims to observe the rare neutral kaon decay mode $K_{L}\rightarrow \pi ^{0}\nu \bar {\nu }$ . After the first experimental run in May 2013 at a 24-kW beam power, the KOTO data acquisition (DAQ) system was upgraded in 2015 to provide efficient and reliable data collection at higher beam intensities. Lossless data compression in the analog-to-digital converter modules was implemented to reduce the size of data packets, resulting in a threefold increase in data collection rate. A new software trigger on a 47-node cluster was designed to use Infiniband hardware with message passing interface protocol to establish a mesh network inside the computer clusters for parallel data processing. The upgrade to the KOTO DAQ system was commissioned in 2015 and successfully collected data with a beam intensity of up to 42 kW. In preparation for increasing beam intensities in future runs, the hardware trigger upgrades using the reconfigurable clustering element platform technology are under development.

Calculation of atmospheric high-energy neutrino spectra and the measurement data of IceCube and ANTARES experiments

Presented are results of calculation of the atmospheric neutrino spectra in the energy range from 100 GeV to 10 PeV using the QGSJET-II and SIBYLL 2.1 models of hadron–nuclear interactions and two experimentally based Zatsepin–Sokol’skaya and Hillas–Gaisser models of the cosmic ray spectrum. It is shown that rare decays of short-lived neutral kaons produce about one third of the flux of electron neutrinos and up to 10% of muon neutrinos at energies above 100 TeV. The calculated spectra agree satisfactorily with the IceCube and ANTARES measurement data. The measurement errors leave open the possibility of a contribution from decays of charmed particles to fluxes of muon neutrinos with energies above 500 TeV and electron neutrinos with energies above 30 TeV.

Discrimination of Neutral Kaon Decay, $K_{L}^{0} to pi^{0}pi^{0}gamma$, from Neutral Kaon Decay, $K_{L}^{0} to pi^{0}pi^{0}$

Discrimination of Neutral Kaon Decay, $K_{L}^{0} to pi^{0}pi^{0}gamma$, from Neutral Kaon Decay, $K_{L}^{0} to pi^{0}pi^{0}$

Four-body Dalitz plot contribution to the radiative corrections inKl30decays and its role in the determination of|Vus|

The four-body contribution of the model-independent radiative corrections to the Dalitz plot of the semileptonic decays of neutral kaons are computed to order (\alpha/\pi)(q/M_1), where q is the momentum transfer and M_1 is the kaon mass. The final result is presented in two forms. The first one is given in terms of the triple integration of the bremsstrahlung photon ready to be performed numerically; the second one is a fully analytical expression. This paper is organized to make it accessible and reliable in the analysis of the Dalitz plot of precision experiments involving kaons and is not compromised to fixing the form factors at predetermined values. As a byproduct, gathering together three- and four-body contributions of radiative corrections yields, through a least-squares fit to the measured kaon decay rates, the value f_+^{K^0\pi^-}|V_{us}| = 0.2168(3).

Radiative corrections to the Dalitz plot ofKl30decays

A model-independent expression for the Dalitz plot of semileptonic decays of neutral kaons, ${K}_{l3}^{0}$, including radiative corrections to order $(\ensuremath{\alpha}/\ensuremath{\pi})(q/{M}_{1})$, where $q$ is the momentum transfer and ${M}_{1}$ is the mass of the kaon, is presented. The model dependence of radiative corrections is kept in a general form within this approximation, which is suitable for model-independent experimental analyses. Expressions for bremsstrahlung radiative corrections are presented in two forms: one with the triple integral over the kinematical variables of the photon ready to be performed numerically and the other one in a fully analytical form. The final result is restricted to the so-called three-body region of the Dalitz plot and it is not compromised to fixing the values of the form factors at predetermined values.

Study of KS semileptonic decays and CPT test with the KLOE detector

Study of semileptonic decays of neutral kaons allows to perform a test of discrete symmetries, as well as basic principles of the Standard Model. In this paper a general review on dependency between charge asymmetry constructed for semileptonic decays of short- and long-lived kaons and CPT symmetry is given. The current status of determination of charge asymmetry for short-lived kaon, obtained by reconstruction of about 105 KS → πeν decays collected at DAΦNE with the KLOE detector is also reviewed.

Discrete Symmetries CP, T, CPT

CP-Violation (CPV) was discovered in 1964 in the weak decays of neutral Kaons. This Symmetry Breaking is understood in the Standard Model as a consequence of its Particle Content, codified in the 3×3 Cabibbo-Kobayashi-Maskawa Unitary Mixing Matrix. The measured CPV asymmetries for Kaons and B's are well described by this Mechanism, but the current level of experimental accuracy and theoretical uncertainties leaves room for additional sources of CPV, as demanded by Baryogenesis. A direct Time-Reversal-Violation (TRV) Effect was clearly observed in 2012 in the time evolution of neutral B-mesons. The conceptual basis to bypass the irreversibility of decays, and prepare in the B-Factories both the Reference and the T-reverse transitions, is provided by the quantum properties of Entanglement and the Decay as a Filtering Measurement. Flavour and CP eigenstate decay channels allow a separate independent measurement of CP, T and CPT asymmetries. Prospects for extending such a programmeto any pair of B-decays and for Kaonsin DAPHNE are discussed. The interest in measuring CPTV asymmetries in transitions is emphasized. This includes the search for CPT-breaking as well as the case of not having a well-defined CPT operator.

$K_{\rm S}$ Semileptonic Decays and Test of CPT Symmetry with the KLOE Detector

Study of semileptonic decays of neutral kaons allows to perform a test of discrete symmetries, as well as basic principles of the Standard Model. In this paper a general review on dependency between charge asymmetry constructed for semileptonic decays of short- and long-lived kaons and $\mathcal{CPT}$ symmetry is given.

Status and prospects of J-PARC KOTO experiment

The J-PARC KOTO experiment was designed to observe the rare decay of long lived neutral kaons, KL→π0νν¯. The goal of KOTO is to observe the decay with the sensitivity of the Standard Model prediction, and search for new physics beyond the Standard Model. The KOTO apparatus consists of a high intensity KL beam line, an electromagnetic calorimeter, and veto counters. The beam line and the calorimeter have already been built at J-PARC, and the veto counters are being constructed and tested for upcoming physics runs. In this paper, the KOTO experiment will be briefly introduced and the status and the prospects of the KOTO experiment will be described.

CP violation and flavor [formula omitted] breaking in D-meson decays

We carry out a systematic flavor SU(3) analysis of D-meson decays including the leading order symmetry breaking effects. We find that SU(3) breaking can easily account for the recent LHCb measurement of the difference in CP asymmetries in the decays of D0 into K+K− and π+π− mesons, once an enhancement mechanism, similar to the Δ=1/2 rule in neutral kaon decays is assumed. As a byproduct of the analysis, one can make predictions regarding the individual asymmetries in K+K−, π+π−, as well as the D0→π0π0 decay channels. Moreover, we find that the asymmetry in the decay D+→π+π0 vanishes in the leading approximation.

CP Violation in Kaon Decay in the Scalar Strong Interaction Hadron Theory

CP conservation and violation in neutral kaon decay are considered from a first principles’ theory, recently published as “Scalar Strong Interaction Hadron Theory”. The arbitrary phase angle relating K0 and 0 in current phenomenology is identified to be related to the product of the relative energy to the relative time between the s and d quarks in these kaons. The argument of the CP violating parameter ? is predicted to be 45? without employing measured data. The K0S decay rate is twice the K0L -K0S masss difference, in near agreement with data, and both are proportional to the square of the relative energy 29.44 eV. Any pion from K0L decay will also have a mass shift of ≈1.28 × 10-5 eV. The present first principles’ theory is consistent with CP conservation. To achieve CP violation, the relative time cannot extend to both +∞ and -∞ but is bounded in at least one direction. The values of these bounds lie outside the present theory and it is unknown how they can be brought forth. -B0 mixing is also considered and the relative energy is 663.66 eV.

CP Violation results from the NA48 experiments

The main goal of the NA48 experiments at the CERN SPS has been the search for direct CP violation (CPV) in neutral and charged kaon decays. In this paper selected results on CPV from the NA48 and NA48/2 experiments are presented. The direct CPV parameter Re(ε′/ε) has been measured by NA48 from the decay rates of neutral kaons into two pions. In the charged kaon sector, NA48/2 has measured the asymmetry Ag of the linear slope parameter g in the Dalitz plot of K± → 3π decays. Thanks to the high statistics collected in 2003 and 2004, further CPV studies were performed in several kaon decays. Results on CPV studies in K± → π±π0γ K± → π±e+e− and K± → π±μ+μ− decays will be presented, as well as in the KS → π+π−e+e− decay.

Radiative corrections in K→π ℓ + ℓ − decays

We calculate radiative corrections to the flavor-changing neutral current process K --> pi l+ l-, both for charged and neutral kaon decays. While the soft-photon approximation is shown to work well for the muon channels, we discuss the necessity of further phase space cuts with electrons in the final state. It is also shown how to transfer our results to other decays such as eta --> gamma l+ l- or omega --> pi0 l+ l-.

Experimental study of the decayKL0→π0νν¯

The first dedicated search for the rare neutral-kaon decay $K_L^0\to\pi^0\nu\bar{\nu}$ has been carried out in the E391a experiment at the KEK 12-GeV proton synchrotron. The final upper limit of 2.6 $\times 10^{-8}$ at the 90% confidence level was set on the branching ratio for the decay.

Blind background prediction using a bifurcated analysis scheme

A technique for background prediction using data, but maintaining a closed signal box is described. The result is extended to two background sources. Conditions on the applicability under correlated cuts are described. This technique is applied to both a Toy model and an analysis of data from a rare neutral kaon decay experiment.

Vus and CP violation from kaon decays with the KLOE detector

The KLOE experiment has provided precise measurements of the branching ratio of the main neutral and charged kaon decay modes, of the Kl and the K± lifetimes, and of the Kl vector and scalar form factors. We present a description of the above measurements and an overall fit of all our data, with particular attention to correlations. These data provide the basis for the determination of the value of the CKM matrix element Vus and a test of the unitarity of the quark mixing matrix. In addition our first measurement of the charge asimmetry in KS semileptonic decays, AS, gaves us the possibility to contribute to the knowledge of ℛ(ϵ) and testing the CPT symmetry through the Bell Steinberger relation.

Dirac's causality leads to time asymmetry

On the basis of Dirac's causality, we will show that the time evolution is limited to a semigroup. The abstract vector space for states and (yes-or-no) observables are then not the entire Hilbert space but its particular dense subspaces, called Hardy spaces. The Hardy spaces and their functional spaces together make the Hardy rigged Hilbert spaces, which is also called the time-asymmetric boundary condition (TABC). We will illustrate the usage of the TABC with the neutral kaon decay experiment.