Neutral Kaon Decays Research Articles

Quantum correlations and three body decays at a ϕ factory

The decays of neutral kaons produced in ϕ decay, ϕ→K L K S , exhibit interesting quantum mechanical interference. The effects of this phenomenon on searches for CP violation have been previously been worked out for two body decays where the decay amplitude is a simple constant. For three body modes where the matrix element varies across the kinematically allowed region, the quantum correlations with enhance or cancel certain terms in the decay distribution. We work out the results for two interesting modes ϕ→(ππ)(ππγ) and ϕ→(3π)(3π). In the former case, the quantum correlation allows the isolation of the direct emission component of the ππγ decay, while in the latter case the intensity asymmetry can uniquely pick out the direct CP violating amplitude.

A study of T violation via the semileptonic decays of neutral kaons in CPLEAR

The method for studying semileptonic neutral kaon decays at CPLEAR is presented together with a preliminary data analysis. For the first time a direct determination of T violation is shown to be possible and low statistics results are given. From the same data the K L - K S mass difference, Δm, the CP violation parameter of K S , ϵ s , and the parameter x testing the ΔS = ΔQ rule are also obtained.

A multi correlated sampler of the high resolution acquisition system for high rate fixed target KTeV experiments at Fermilab

A new facility is being planned at Fermilab for fixed target experiments dealing with CP violation in rate neutral kaon decays; and precision measurements on the “direct” CP-violation parameters e′/ e in the 2 pi decay mode of the neutral kaon system. This new Kaons at the TeVatron(KTeV) beam line is expected to be in operation in 1994. The most important new detector component in the KTeV spectrometer is the precision electromagnetic calorimeter, consisting of bars of Cesium Iodide crystals. The choice has been motivated by its radiation hardness, speed and light output. The size of this detector is 2 meters square and includes over 3200 blocks which are coupled to photomultipliers. We expect a peak anode current pulse of 100 ma from an80 Gev deposit. The pulse shape approximates a signal with a FWHM of 25 nanoseconds, but contains some energy in a long tail that exists for more than 500 nanoseconds. The design for the data acquisition electronics will measure deposited charge in every channel in two 12 bit linear ranges: a low range of 2 MEV per count up to a maximum signal of 82 GEV and a range that will handle signals ten times larger with the same proportion in energy resolution. Since the total required dynamic range of this design is between 15 and 16 bit resolution, the problem of pedestal and pile up is seriously engaged with the configuration of this design.

ANOTHER LOOK AT THE CP VIOLATION PROBLEM

We show that the interpretation of neutral kaon decay (and [Formula: see text] and other decay) experiments is based on a not-too-correct theoretical description of such decays. This description does not take into account the specific early time properties of temporal evolution in the two-component subspace of a state space. The particle interpretation of vectors in such a subspace is shown to be proper for other states in an early time period and other states in a long time period.

First determination of CP violation parameters from K 0− [formula omitted]0 decay asymmetry

We report the first determination of CP violation parameters from parameter from particle—antiparticle asymmetry in the decay of neutral kaons into two charged pions. Observation of such an asymmetry is direct proof of CP violation. A fit to the asymmetry enabled a determination of the parameter η +− to be made, yielding the result | η +−|=[2.32±0.14 (stat.)±0.03 (syst.)]×10 −3 and σ +−=42.3°±4.4° (stat.)±0.4° (syst.), with an additional uncertainty of ±1.0° due to the error on the present published value of Δm, the K L 0-K S 0 mass difference. The magnitudes of both statistical and systematic errors will be significantly reduced in the future.

CP violating asymmetries in the neutral kaon decays

We study the time dependence of the integrated asymmetries in strangeness of kaons in the decays in two and three pions and in two photons with the purpose of disentangling theCP violating effects in the decay amplitudes from the ones related to the\(K^0 - \bar K^0 \) mass matrix. We find two cases where they are not reduced by the ΔI=1/2 rule or hidden byCP violation in the mass matrix, namely the strangeness-energy correlation of the charged pions in the prompt decay (τ<τ S ) in π+π-π0, and the decays in two photons. The semileptonic decays are also briefly studied.

Tests of T and CPT in neutral-kaon decays.

Recent proposals by Lavoura, to extract possible $T$- and $\mathrm{CPT}$-violating parameters from measurements on neutral-kaon decays, are related to earlier suggestions. One apparently new test for $\mathrm{CPT}$ is shown, after correction of a conceptual oversight, to be subject to the same difficulties that Lavoura has emphasized for the test of $T$ proposed earlier.

Reply to "Tests of T and CPT in neutral-kaon decays"

I comment on who discovered first the main result in my paper. I also correct a miswriting of mine in the paper.Received 19 April 1991DOI:https://doi.org/10.1103/PhysRevD.44.2937©1991 American Physical Society

CP violation in the decays of neutral kaons into two photons

We compute the amplitudes for the decay into two photons of neutral kaons in the framework of the chiral effective Lagrangians. In particular we relate the ratios\(\eta _{||} = A(K_L \to 2\gamma _{||} )/A(K_S \to 2\gamma _{||} )\) and\(\eta _ \bot = A(K_S \to 2\gamma _ \bot )/A(K_L \to 2\gamma _ \bot ),\) which would vanish according toCP symmetry, to the prameters ɛ and ɛ′, appearing in the 2π decays ofKL. We find for\(\eta _{||} \) the value ɛ+i|ɛ′|. For the amplitudes into\(2\gamma _ \bot ,\), theCP-conserving amplitude\(A(K_2 \to 2\gamma _ \bot )\) depends very strongly on the parameterf, which gives the percentage of the amplitude\(A(K_2 \to 2\pi ^0 )\) arising from the «penguin» contributions. We predict two possible values for\(\eta _ \bot \): one is ≃ɛ. For the other =ɛ+i70|ɛ′|, which appears to us as more likely, the difference with respect to the superweak theory is larger than in the 2π decays. A distinction between the two theories requires a more precise measurement of γ(KS»γγ).

Rare decays

Rare decay experiments have made significant advances in the last several years. Limits on lepton number violating decays of kaons have been tightened. Large samples of strangeness changing neutral current kaon decays have been collected. For several suppressed processes, discovery windows for new physics have been substantially narrowed. Opportunities for detecting direct CP-violation have been changed by the observation of a new background to one decay mode and the prospects of high statistics studies of another process.

Almost forbidden ΔQ = − ΔS processes

The ΔQ=− ΔS transitions in semileptonic decays of neutral kaons are estimated. We find a suppression of 10 −7 with respect to the allowed ΔQ= ΔS transition, within the standard model. Asymmetries in semileptonic decays of K L and K s as well as time- dependent semileptonic decays of a coherent K SK L state are studied.

Results of the NA31 Experiment on K0 Decays

Decays of neutral kaons are of high interest in high energy physics. The discovery of CP violation1 opened up a field of new physics. Today, interest is concentrated on precision measurements of CP‐violating parameters as well as on searches for rare decays that are suppressed or forbidden in the standard model.

The beam and detector for a high-precision measurement of CP violation in neutral-kaon decays

The K 0 beam and detector used for a high-precision measurement of the CP-violation parameter ϵ′ at the CERN Super Proton Synchrotron (SPS) are described. The beam provides K L and K S alternately through a common decay region. The detection of the decays is based on wire chambers and calorimeters without employing a magnet. The trigger and readout system achieve a high selectively for the suppressed, CP-violating, two-pion decays of the K L by incorporation of hard-wired processors. The readout is based on Fastbus for maximum data rates.

A quantum theory with possible leakage of information

A model of quantum theory is presented where the evolution of pure states into mixed states is possible, so that information on the system states is not conserved. The theory is based upon an evolution equation for the density operator, which is an extension of the Landau-von Neumann equation. The equation contains the system hamiltonian and a single parameter characterizing the deviation from the standard theory. The model does not break usual conservation laws. The general solution is represented as an average over the solutions of conventional theory; this is an effect of the uncertainty in time. Predictions of the model are discussed in brief. Spectrometry and scattering do not experience the modification, it manifests itself only in processes with an observable time dependence. Neutral kaon decays are considered. The model is proposed in view of Hawking's suggestion that quantum gravity may be a reason for an additional unpredictability in elementary particle physics.

CPT symmetry and neutral kaons

We discuss the accuracy of CPT invariance tests in the neutral kaon decays. The possible CPT non-invariance is parametrized by amplitudes of two types: (i) CP violating, but T conserving, and (ii) T violating, but CP conserving. It is shown that the experimental data are consistent with CPT symmetry essentially within two standard deviations. The source of this not quite satisfactory agreement is the experimental value of the phase φ 00 of the ratio A( K L 0→π 0π 0) A( K S 0→π 0π 0) , which differs by two standard deviations from the phase φ +− of the ratio A( K L 0→π +π −) A( K S 0→π +π −) decay amplitude. We argue that to get better agreement with CPT invariance, the value of the phase φ 00 has to be equal to the value of the phase φ +− within the errors of the latter. New, more accurate measurements of the phase φ 00 would be very interesting to rest CPT invariance, especially taking into account that neutral kaons allow the test with much better accuracy than any other particle.

CPsymmetry violation—the search for its origin

The author presents a brief review of the progress which has been made in understanding CP violation since its discovery. Experiments in Kaon systems and the measurement of parameters associated with long-lived neutral kaon decay are described. Theoretical ideas about CP violation are briefly considered. Forty eight references are given.

CP Symmetry Violation: The Search for Its Origin

The author presents a brief review of the progress which has been made in understanding CP violation since its discovery. Experiments in Kaon systems and the measurement of parameters associated with long-lived neutral kaon decay are described. Theoretical ideas about CP violation are briefly considered. Forty eight references are given.

Particle-antiparticle symmetry and irreversibility

A statistical theory of neutral kaon decay is presented, in which the violation of combined CP parity arises through non-equilibrium interaction with a heat bath, and not through a microscopic CP-violating term in the Hamiltonian. The theory is set up in the language of the Takahashi-Umezawa 'thermo-field theory', generalized to admit non-equilibrium processes. The usual 'superweak' theory emerges as a special case, but the theory also permits other solutions, which for a pure K0 meson beam are identical with superweak theory, but which restore K0-K0 symmetry.

On the determination of χl,η+−0 AND η000 from bubble chamber measurements

Formulae for time distribution of neutral kaon decay in material medium are derived and discussed. Essential effects of the medium are emphasized which should be taken into account in the discussion of the bubble chamber experiments in which theΔS=ΔQ rule and CP-violation are studied.

Allomorphic corrections to semileptonic processes

The notion of allomorphic corrections to $S$-matrix elements for semileptonic processes, which by definition are absent in the lowest nontrivial order of perturbation theory, is introduced and analyzed. The complete fourth-order allomorphic corrections to the leptonic weak currents are calculated in an arbitrary gauge model of weak and electromagnetic interactions, treating the strong interactions (assumed mediated purely by gauge vector gluons) to all orders. These results are used to analyze the induced leptonic pseudoscalar current in charged-pion decay, and it is shown that weak restrictions on particle masses suffice to preserve the $V\ensuremath{-}A$ structure at the leptonic vertex to $O(\ensuremath{\alpha}{G}_{F})$. A preliminary discussion of the allomorphic corrections to hadronic weak currents is presented in the context of neutral-kaon decay (${K}^{0}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\mu}}^{+}$). It is shown that in theories in which the kaon field dimensionality is two or less, the usual suppression mechanisms involving charmed quarks probably do not suffice to remove induced neutral, strangeness-changing currents in $O(\ensuremath{\alpha}{G}_{F})$.