Search

We present a comprehensive treatment of the precise determinations of the parameters Re({var_epsilon}{sup {prime}}/{var_epsilon}), {tau}{sub S}, {Delta}m, {phi}{sub +{minus}}, and {Delta}{phi} in the neutral kaon system with the Fermilab E731 detector. Together, these determinations allow accurate studies of both CP and CPT symmetry. Details of the detector and its performance and the data analysis are given. The extensive Monte Carlo simulation of the detector and comparison with data are also presented. {copyright} {ital 1997} {ital The American Physical Society}

With the E731 apparatus at Fermilab, we have simultaneously collected 6859 ${\mathit{K}}_{\mathit{L}}$ and ${\mathit{K}}_{\mathit{S}}$ decays into ${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\gamma}. Using our sample of over 370 000 ${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$ decays for normalization we have determined that the ratio \ensuremath{\Gamma}(${\mathit{K}}^{0}$\ensuremath{\rightarrow}${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\gamma})/\ensuremath{\Gamma}(${\mathit{K}}^{0}$\ensuremath{\rightarrow}${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$) is (23.0\ifmmode\pm\else\textpm\fi{}0.7)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ for ${\mathit{K}}_{\mathit{L}}$ and (7.10\ifmmode\pm\else\textpm\fi{}0.22)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ for ${\mathit{K}}_{\mathit{S}}$, for photon energies greater than 20 MeV in the kaon center of mass. After removing the inner-bremsstrahlung contribution, we find that the photon energy spectrum of the direct emission decay of the ${\mathit{K}}_{\mathit{L}}$ is consistent with the presence of a vector meson propagator in the form factor.

Interference between ${\mathrm{K}}_{\mathrm{S}}$ and ${\mathrm{K}}_{\mathrm{L}}$ decays into the final state ${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\gamma} has been observed in experiment 731 at Fermilab. By fitting the distribution of decays downstream of a regenerator, a new CP-violation parameter${\mathrm{\ensuremath{\eta}}}_{+\mathrm{\ensuremath{-}}\ensuremath{\gamma}}$, analogous to ${\mathrm{\ensuremath{\eta}}}_{+\mathrm{\ensuremath{-}}}$, has been measured, with its magnitude equal to(2.15\ifmmode\pm\else\textpm\fi{}0.26\ifmmode\pm\else\textpm\fi{}0.20)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$, and ${\mathrm{\ensuremath{\varphi}}}_{+\mathrm{\ensuremath{-}}\ensuremath{\gamma}}$, the associated phase angle, equal to(72\ifmmode\pm\else\textpm\fi{}23\ifmmode\pm\else\textpm\fi{}17)\ifmmode^\circ\else\textdegree\fi{}. Assuming that any difference between this fit value for ${\mathrm{\ensuremath{\eta}}}_{+\mathrm{\ensuremath{-}}\ensuremath{\gamma}}$ and the previously measured value for${\mathrm{\ensuremath{\eta}}}_{+\mathrm{\ensuremath{-}}}$ can be attributed to direct CP violation in this decay, a limit of|${\mathrm{\ensuremath{\epsilon}}}_{+\mathrm{\ensuremath{-}}\ensuremath{\gamma}}^{\ensuremath{'}}$|/\ensuremath{\epsilon}0.3 at the 90% confidence level has been made. \textcopyright{} 1993 The American Physical Society

We have observed 729[plus minus]15 [ital K][sub [ital L]][r arrow][pi][sup [plus minus]][pi][sup 0][ital e[minus plus]][bar [nu]]([nu]) decays in the data set collected in the 1987--1988 run of Fermilab experiment E731. We found the [ital K][sub [ital e]4] branching ratio to be [5.16[plus minus]0.20(stat)[plus minus]0.22(sys)][times]10[sup [minus]5]. We also performed the first measurement of the form factors parametrizing the decay. Our branching ratio result agrees with a prediction using a vector-meson-exchange model. An interpretation of the data in terms of chiral perturbation theory implies a value [ital L][sub 3]=(3.4[plus minus]0.4)[times]10[sup [minus]3] in the O([ital p][sup 4]) chiral Lagrangian.

The full E731 data set is used to provide precise determinations of several parameters of the neutral kaon. We find the [ital K][sub [ital S]] lifetime [tau][sub [ital S]]=(0.8929[plus minus]0.0016)[times]10[sup [minus]10] s, the [ital K][sub [ital L]-][ital K[ital S]] mass difference [Delta][ital m]=(0.5286[plus minus]0.0028)[times]10[sup 10][h bar] s[sup [minus]1] the phase of [eta][sub +[minus]], [Phi][sub +[minus]]=42.4[degree][plus minus]1.4[degree], and the phase difference between [Phi][sub 00] and [Phi][sub +[minus]], [Delta][Phi]=[minus]1.6[degree][plus minus]1.2[degree]. Comparisons with previous experiments and with [ital CPT] symmetry are given.

A measurement of the [ital CP]-violation parameter Re([var epsilon][prime]/[var epsilon]) has been made using the full E731 data set. We find Re([var epsilon][prime]/[var epsilon])=(7.4[plus minus]5.2[plus minus]2.9)[times]10[sup [minus]4] where the first error is statistical and the second systematic.

We report a value of -[3.3±1.1 (stat)±0.7(syst)]×10 -3 for the quadratic slope parameter h in the Dalitz plot of the K L →3π 0 decay. This result is obtained from a sample of 5.1×10 6 decays. The validity of the ΔI=1/2 rule in the quadratic term is investigated using this result. This is the first measurement of the 3 0 slope parameter, and also the most sensitive measurement of any of the quadratic slope parameters for the charged or neutral kaons

Using the complete Fermilab E371 data set, we find {Gamma}({ital K}{sub {ital L}}{r arrow}{pi}{sup 0}{gamma}{gamma},+{ital m}{sub {gamma}{gamma}}{ge}0.280 GeV)/{Gamma}({ital K}{sub {ital L}}{r arrow}all) =(1.86{plus minus}0.60{plus minus}0.60){times}10{sup {minus}6}, in good agreement with a recent report of the first observation of this decay. For the low {gamma}{gamma} mass region we find {Gamma}({ital K}{sub {ital L}}{r arrow}{pi}{sup 0}{gamma}{gamma},{ital m}{sub {gamma}{gamma}}{lt}0.264 GeV)/{Gamma}({ital K}{sub {ital L}}{r arrow}all){lt} 5.1{times}10{sup {minus}6} (90% confidence).

Data collected by the E731 experiment at Fermilab were used to search for {ital CPT} violation in {ital K}{sup 0}{r arrow}{pi}{pi} decays by measuring the difference {Delta}{phi} between the phases of the {ital CP}-violating parameters {eta}{sub 00} and {eta}{sub +{minus}}. Our result, {Delta}{phi}={minus}0.3{degree}{plus minus}2.4{degree}{plus minus}1.2{degree}, where the first error is statistical and the second systematic, is consistent with {ital CPT} symmetry.

A new beam line and detector were constructed to increase statistical precision and greatly reduce systematic uncertainty on the ratio of the CP-nonconserving parameters epsilon'/epsilon. Major improve- ments are discussed together with a result from a first run: epsilon'/epsilon = 0.0032 +- 0.0028 (statistical) +- 0.0012 (systematic). The precision is better than earlier measurements yet the result is still consistent with the superweak mechanism (which predicts zero) and that due to Kobayashi and Maskawa. Significantly more data are being collected.

Results of an experiment to measure the cross section for production of the D*/sup +/(D*/sup -/) in 200-GeV/c r/sup -/N interactions are reported. 78 +- 26 events are observed, corresponding to a D* production cross section ds/dy = 1.6 +- 0.5 mb at y = 0.

Primakoff production of the K/sup 0asterisk/(896) by incident K/sub L/'s was observed in the energy range 100--200 GeV. Production from Cu and Pb targets was measured simultaneously leading to a new value for the K/sup 0asterisk/(896) radiative width GAMMA(K/sup 0asterisk/(896)..-->..K/sup 0/+..gamma..) of 116.5 +- 9.9 keV. The result agrees with a previous determination while being considerably more precise and allows for more stringent tests of quark-model relations among the radiative widths of the low-lying vector mesons.

Data taken in a Fermilab experiment designed to measure to CP-violation parameter epsilon/epsilonfrom a study of K..-->..2..pi.. decays were used to look for the as yet unseen decay modes K/sub L//sub ,//sub S/..--> pi../sup 0/e/sup +/e/sup -/. The detector was optimized for the detection of kaon decays with four electromagnetic showers in the final state. The results (90% confidence) are branching ratios pi../sup 0/e/sup +/e/sup -/ and K/sub S/..--> pi../sup 0/e/sup +/e/sup -/, respectively.

An upper limit GAMMA(K/sup 0//sup */(1430)..-->..K/sup 0/..gamma..)

The ratio R-italic/sub ..nu../ of the neutral- to charged-current cross sections of neutrinos in iron has been measured in an exposure of the CERN-Dortmund-Heidelberg-Saclay neutrino detector to a 160-GeV/c-italic neutrino narrow-band beam at the CERN Super Proton Synchrotron. The result is R-italic/sub ..nu../ = 0.3072 +- 0.0025(stat) +- 0.0020(syst), for hadronic energy greater than 10 GeV. The electroweak mixing parameter is sin/sup 2/theta/sub W/ = 0.225 +- 0.005(expt ) +- 0.003(theor)+0.013(m-italic/sub c-italic/-1. 5 GeV/c-italic/sup 2/), where m-italic/sub c-italic/ is the charm-quark mass.

A measurement of the ratio of the CP-nonconservation parameters, epsilon'/epsilon, in the K/sup 0/K /sup 0/ system was performed through a study of two-pion decays with and without a regenerator. To reduce systematic effects, K/sub L/ and K/sub S/ decays were recorded simultaneously with a double beam. Over 3100 K/sub L/..-->..2..pi../sup 0/ events were reconstructed leading to the result epsilon'/epsilon = -0.0046 +- 0.0053 +- 0.0024 (the first error is statistical, the second systematic). The measurement agrees with previous less precise determinations but, because of theoretical uncertainties, is not able to test decisively the Kobayashi-Maskawa mechanism.

An experiment on the decay K/sup +/ ..-->.. ..pi../sup +/..pi../sup -/e/sup +/..nu.. was performed at the CERN proton synchrotron with spark-chamber and counter techniques. The K/sub e//sub 4/ branching ratio has been measured relative to the tau decay. The ..pi pi.. phase-shift difference delta/sup 0//sub 0/ - delta/sup 1//sub 1/ and the form factors of the hadronic current have been determined as functions of the ..pi pi.. energy. The ..pi pi.. scattering length a/sup 0//sub 0/ has been evaluated from the phase shifts with a phenomenological model. The results are compared with the theoretical predictions of current-algebra and other models.

We have used precision spark-chamber spectrometers to measure the dipion mass spectrum from the reaction ${\ensuremath{\pi}}^{\ensuremath{-}}+p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}+{\ensuremath{\pi}}^{+}+n$ at an incident momentum of 1.5 BeV/c. The spectrum was observed between 450 and 1000 MeV, with $\ensuremath{\pi}\ensuremath{-}\ensuremath{\pi}$ scattering angles at 90\ifmmode\pm\else\textpm\fi{}30 deg, and with four-momentum transfer to the nucleon between the minimum ${\ensuremath{\Delta}}_{min}$ and ${\ensuremath{\Delta}}_{min}+2\ensuremath{\mu}$. The mass resolution of the apparatus was \ifmmode\pm\else\textpm\fi{}4 MeV. With more than 6000 events we observe a peak in the $\ensuremath{\pi}\ensuremath{-}\ensuremath{\pi}$ mass spectrum at \ensuremath{\sim}750 MeV with a width $\ensuremath{\Gamma}\ensuremath{\cong}130$ MeV. We do not observe any other structure in the mass range explored. With these results we can set an upper limit for the branching ratio ($\ensuremath{\omega}\ensuremath{\rightarrow}\frac{{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}}{\ensuremath{\omega}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$) of \ensuremath{\le}1.0%, based on the assumption that there is no interference between the $\ensuremath{\rho}$ and $\ensuremath{\omega}$ amplitudes. Interpreting the data with the one-pion exchange (OPE) model, we have computed the differential cross section $\frac{d{\ensuremath{\sigma}}_{\ensuremath{\pi}\ensuremath{\pi}}}{dcos{\ensuremath{\theta}}_{\ensuremath{\pi}\ensuremath{\pi}}}$ at 90 deg. This quantity shows a strong peak at the mass of the ${\ensuremath{\rho}}^{0}$ meson, but the peak is much larger than expected from a $J=1$ $\ensuremath{\pi}\ensuremath{-}\ensuremath{\pi}$ resonant state produced by OPE. If this peak is really the ${\ensuremath{\rho}}^{0}$ meson, we must be observing it because of absorption phenomena in the initial $\ensuremath{\pi}\ensuremath{-}N$ and final $\ensuremath{\rho}\ensuremath{-}N$ states which tend to depolarize the $\ensuremath{\rho}$. Expressing the $\ensuremath{\rho}$ decay intensity as $a+b{cos}^{2}{\ensuremath{\theta}}_{\ensuremath{\pi}\ensuremath{\pi}}$, our data require $\frac{a}{b}\ensuremath{\approx}0.06$, while the simple OPE model predicts $\frac{a}{b}=0$. Other features of the data, the momentum-transfer distribution and the Treiman-Yang angular distribution, fit the OPE predictions fairly well. We discuss some evidence that the effect of a 1.4-BeV, $T=\frac{1}{2}$ isobar can be seen in the data.

This Letter reports the results of experimental studies designed to search for the 2m decay of the K, meson. Several previous experiments have served"~ to set an upper limit of 1/300 for the fraction of K2 's which decay into two charged pions. The present experiment, using spark chamber techniques, proposed to extend this limit.

Results are presented of a measurement of the production of ${D}^{\mathrm{*}+}$ (${D}^{\mathrm{*}\mathrm{\ensuremath{-}}}$) in 250-GeV/c ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$N interactions. We observe 2.1\ifmmode\pm\else\textpm\fi{}7.8 events corresponding to a charge-${D}^{\mathrm{*}}$ cross section \ensuremath{\sigma}(${D}^{\mathrm{*}}$) of 0.4\ifmmode\pm\else\textpm\fi{}1.5 \ensuremath{\mu}b/nucleon. When averaged with our previous measurement made at 200 GeV/c, the result is \ensuremath{\sigma}(${D}^{\mathrm{*}}$)=2.3\ifmmode\pm\else\textpm\fi{}1.0 \ensuremath{\mu}b/nucleon with (d\ensuremath{\sigma}/dx)${\ensuremath{\Vert}}_{x=0}$=4.6\ifmmode\pm\else\textpm\fi{}2.0 \ensuremath{\mu}b.

We have measured the ratio GAMMA(K/sub L/..--> pi../sup +/..pi../sup -/)/GAMMA(K/sub L/..--> pi..l..nu.. ) to be (3.13 +- 0.14) x 10/sup -3/ for K/sub L/ with a mean laboratory momentum of 65 GeV/c. This value corresponds to the CP-nonconservation parameter Vertical Bareta/sub +/-Vertical Bar = (2.28 +- 0.06) x 10/sup -/ 3, and is consistent with the world average Vertical Bareta/sub +/-Vertical Bar = (2.274 +- 0.022) x 10 /sup -3/ which is derived from measurements with K/sub L/ laboratory momenta less than 10 GeV/c. In this experiment we find no evidence for an energy dependence of Vertical Bareta/sub +/-Vertical Bar.