A measurement of the CP-violation parameter Re(e'/e) has been made using the full E731 data set. We find Re(e'/e) -(7.4 ± 5.2 ± 2.9) x 10 ~4 where the first error is statistical and the second systematic.
We present a comprehensive treatment of the precise determinations of the parameters Re(Ј/), S , ⌬m, ϩϪ , and ⌬ 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. ͓S0556-2821͑97͒06311-X͔
Interference between Ks and KL decays into the final state n*'n~ y has been observed in experiment 731 at Fermilab. By fitting the distribution of decays downstream of a regenerator, a new CP-violation parameter n+-y, analogous to //+-, has been measured, with its magnitude equal to (2.15 ±0.26 ±0.20)xl0 -3 , and 0+y , the associated phase angle, equal to (72±23±17)°. Assuming that any difference between this fit value for 77+y and the previously measured value for n+-can be attributed to direct CP violation in this decay, a limit of |6+_ y |/6 < 0.3 at the 90% confidence level has been made.Decays of the neutral kaons, KL and K §, have been studied in great detail because they represent the only known example of a system that exhibits violation of CP symmetry. A demonstration of this symmetry violation is the fact that the KL can decay into both CP-odd and CP-even final states [ll. Because mixing can occur in the neutral kaon system, it is possible to see an interference pattern in the proper time distribution of its decays [2]. We report here the first observation of K L -Ks interference for the decay into the final state K + K~Y, and our measurement of the level of CP violation in this decay. By comparing the magnitude of the observed CP violation to that of the K*n~ decay mode, a limit for the amount of direct CP violation in the decay has been obtained.The two electroweak eigenstates of neutral kaons can be described aswhere e is the complex parameter describing the amount of CP violation.Because the magnitude of e is small (~2.3xlO~~3), KL decays primarily into CP-odd states and K § into CP-dN oc F (E K )e-x [\p\ 2 e-rsr + I 12 ~ r z. T + 2|p| |r7|cos(Amr + 0 p -
With the E731 apparatus at Fermilab, we have simultaneously collected 6859 KL and Ks decays into 7r + 7t~ y. Using our sample of over 370000 K + K~ decays for normalization we have determined that the ratio r(K°-+ 7t+x-y)/r(K°-+ 7z + 7t-) is (23.0±0.7)x 10~3 for K L and (7.10±0.22)x 10~3 for K s , for photon energies greater than 20 MeV in the kaon center of mass. After removing the innerbremsstrahlung contribution, we find that the photon energy spectrum of the direct emission decay of the KL is consistent with the presence of a vector meson propagator in the form factor. PACS numbers: 13.25.+m, 13.40.Hq, 14.40.Aq It has long been recognized [1,2] that the decays KL,S~* 7t + K~ y may hold promise for illuminating the experimentally unresolved mechanisms of CP violation. The KL decay also provides a testing ground for models based on chiral perturbation theory [3][4][5] which are relevant to understanding CP violation in rare decays such as KL~^ 7t°e + e~. A critical issue in these models is whether the direct-emission (DE) photon energy distribution is characterized by a pure magnetic dipole (Ml) transition or manifests some additional energy dependence [5]. In this Letter we report the most precise results to date for the K*K~y branching ratios and demonstrate the presence of a modification to the M1 amplitude in this decay. In the following Letter we demonstrate KL~KS interference in this mode for the first time and extract new CP-violation parameters for the decay [6].The Ks~^ n + K~y decay is dominated [7] by inner bremsstrahlung (IB) in which a pion from the decay into K + 7T-radiates a photon. However, for KL decays, the IB rate is suppressed because the underlying /r + /r~~ decay is CP violating. This permits the more interesting CPconserving DE process, in which the photon originates from the primary decay vertex, to be significant.The IB decay can be described very well with a pure E\ bremsstrahlung spectrum [7]. In contrast, previous experimental results [8] have supported the idea that the DE decay occurs through an Ml amplitude, modified by a form factor F which includes the effects of vector meson intermediaries. One chiral perturbation model of the decay [3] suggests that F is a sum of two terms, one of which contains the p meson propagator:where E* is the energy of the photon in the center-ofmass system. The constants M p and M# are the masses of the neutral rho meson and neutral kaon. The coefficient a\ and #2 depend on the mixing angle 0^-^ for the SU(3) nonet members r\ and r\\ This formulation leads to an energy spectrum for the emitted photon that is shifted lower in energy than the pure Ml spectrum. In other models, however, F consists of a sum of amplitudes which results in no net shift in the DE photon energy spectrum [4,5]. The 7t*K~y decays studies here were collected by the E731 experiment at Fermilab, which measured the direct CP violation parameter e'/e and concentrated on high acceptance and accurate measurement of two pion decays, both neutral and charged [9]. The apparatus, desc...
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