Y. B. Hsiung

Observation of Direct CP Violation in KS,L ! ππ Decays

We have compared the decay rates of K_L and K_S to pi^+ pi^- and pi^0 pi^0 final states using a subset of the data from the KTeV experiment (E832) at Fermilab. We find that the direct-CP-violation parameter Re(epsilon/epsilon) is equal to (28.0 pm 3.0 (stat) pm 2.8 (syst)) times 10^{-4}. This result definitively establishes the existence of CP violation in a decay process.

Polarization of Λ and Λ produced by 800-GeV protons☆

Abstract We have measured the polarization of Λ and Λ hyperons produced by 800 GeV protons on a Be target at a fixed targeting angle of 4.8 mrad. Comparison with previous data at 400 GeV production energy and twice the targeting angle shows no significant energy dependence for the Λ polarization. This is in striking contrast to the energy dependence found for σ+ and Ξ− polarizations. We find no evidence for Λ polarization at 800 GeV.

Simultaneous measurement of KS and KL decays into π+π-γ

With the E731 apparatus at Fermilab, we have simultaneously collected 6859 [ital K][sub [ital L]] and [ital K][sub [ital S]] decays into [pi][sup +][pi][sup [minus]][gamma]. Using our sample of over 370 000 [pi][sup +][pi][sup [minus]] decays for normalization we have determined that the ratio [Gamma]([ital K][sup 0][r arrow][pi][sup +][pi][sup [minus]][gamma])/[Gamma]([ital K][sup 0][r arrow][pi][sup +][pi][sup [minus]]) is (23.0[plus minus]0.7)[times]10[sup [minus]3] for [ital K][sub [ital L]] and (7.10[plus minus]0.22)[times]10[sup [minus]3] for [ital K][sub [ital 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 [ital K][sub [ital L]] is consistent with the presence of a vector meson propagator in the form factor.

Energy loss of fast quarks in nuclei

We report an analysis of the nuclear dependence of the yield of Drell-Yan (DY) dimuons from the 800 GeV/c proton bombardment of

New limits on KL,S--> pi 0e+e-

^2H

Limit on the branching ratio of KL → π0e+e-

, C, Ca, Fe, and W targets. A light-cone formulation of the DY process is employed in the rest frame of the nucleus. In this frame, for

Measurements of the rare decay K(L) --> e+ e- e+ e-

x_2ll x_1

Observation of direct CP violation in

, DY production appears as bremsstrahlung of a virtual photon followed by decay into dileptons. We treat the two sources of nuclear suppression, energy loss and shadowing, in a consistent formulation. Shadowing, involving no free parameters, is calculated within the light-cone dipole formalism. Initial-state energy loss, the only unknown in the problem, is determined from a fit to the nuclear-dependence ratio versus

K_{S,L} \to \pi \pi

x_1

decays

. With the assumption of constant energy loss per unit path length, we find