Interference of Conversion and Bremsstrahlung Amplitudes in the Decay K_L -> mu^+ mu^- gamma

In the region of large mu^+ mu^- invariant mass, the decay spectrum of K_L -> mu^+ mu^- gamma deviates from the Dalitz pair spectrum, as a result of interference between conversion (K_L -> gamma^* gamma -> mu^+ mu^- gamma) and bremsstrahlung amplitudes. The latter is proportional to the K_L -> mu^+ mu^- matrix element, whose 2 gamma-absorptive part appears to dominate the observed K_L -> mu^+ mu^- decay rate. We examine the extent to which a scrutiny of the K_L -> mu^+ mu^- gamma spectrum in the end-point region could provide evidence on the real part of the K_L -> mu^+ mu^- amplitude. As a by-product, we obtain the absorptive part of the K_L -> gamma^* gamma form factor, using data on the K_L -> pi^+ pi^- gamma spectrum.Comment: 7 pages, 4 figure

Latest Results on Weak Semi-Leptonic Hyperon Decays in KTeV

The KTeV experiment at Fermilab has finished its $\Xi^0$ semi-leptonic decay analysis from the 1997 run and presented here are the final numbers for the branching ratio and form factors. A new run with three times the statistics was taken in 1999 and a first look at the data shows the quality and consistency of the results, predicting a similar improvement in these measurements.Comment: 4 pages and 4 figures, presented at IV Int. Conference on Hyperons, Charm and Beauty, Valencia Spain, 26-30 June 200

Time Evolution of Decay Spectrum in K^0, K^0 bar -> pi^+ pi^- e^+ e^-

We consider the decay K^0 (K^0 bar) -> pi^+ pi^- e^+ e^- of a neutral K meson prepared in a state of strangeness +1 (-1). The time evolution of the state produces remarkable time-dependent effects in the angular distribution of the pi^+ pi^- e^+ e^- system. These effects are correlated with the time-dependence of the photon polarization in the radiative decay K^0 (K^0 bar) -> pi^+ pi^- gamma. We study, in particular, the CP-odd, T-odd term in the distribution d Gamma / d phi of the angle between the pi^+ pi^- and the e^+ e^- planes. We also give the spectrum in the case that the decaying meson is an incoherent mixture of K^0 and K^0 bar, and discuss the case of K_S regeneration in a K_L beam.Comment: 16 pages, 8 figures, minor typos corrected, to appear in Phys. Lett.

Beam Halo Monitoring at CDF

Losses from the proton and antiproton beams of the Fermilab Tevatron have been shown to produce a halo which contribute to backgrounds to physics signals in the Collider Detector at Fermilab (CDF). To provide a measure of the beam halo and losses, we have installed arrays of scintillation counters on both sides of the CDF detector. We describe here the physical configuration of these counters, their implementation and performance within the Fermilab Accelerator Control Network (ACNET). We show correlations between these new devices and the accelerator operating conditions. We point out that the use of these monitors is leading to improvement in the accelerator operations and reduced backgrounds in CDF.Comment: 27 pages, 17 figures, submitted to NIM

Ω−\Omega^- Hyperon Decay Modes with the HyperCP Experiment at Fermilab

The HyperCP experiment (Fermilab E871) has the largest recorded sample of $\Omega^-$ hyperon decays, allowing new searches for three rare decay modes, each with five charged tracks in the final state. Results are presented for $\Omega^-\to\Xi^-\pi^+\pi^-$; $\Omega^- \to \Xi^0(1530)\pi^-$; and the flavor-changing neutral-current decay $\Omega^- \to \Xi^-\mu^+\mu^-$. Normalization of these measurements were to the decay $\Omega^- \to \Lambda K^-$ with a five-track topology similar to the signal mode with the subsequent decay of $\Lambda \to p \pi^-$ and $K^- \to \pi^- \pi^+ \pi^-$ in the decay volume.Comment: Presented at the 5th International Conference on Hyperons, Charm and Beauty Hadrons, June 2002., Vancouver, Canada: 4 pages, 5 figures, New Result

Extracting short-distance physics from K_{L,S} -> pi0 e+ e- decays

We present a new analysis of the rare decay K_L -> pi0 e+ e- taking into account important experimental progress that has recently been achieved in measuring K_L -> pi0 gamma gamma and K_S -> pi0 e+ e-. This includes a brief review of the direct CP-violating component, a calculation of the indirect CP-violating contribution, which is now possible after the measurement of K_S -> pi0 e+ e-, and a re-analysis of the CP conserving part. The latter is shown to be negligible, based on experimental input from K_L -> pi0 gamma gamma, a more general treatment of the form factor entering the dispersive contribution, and on a comparison with the CP violating rate, which can now be estimated reliably. We predict B(K_L -> pi0 e+ e-) = (3.2 +1.2 -0.8) 10^{-11} in the Standard Model, dominated by CP violation with a sizable contribution (~40%) from the direct effect, largely through interference with the indirect one. Methods to deal with the severe backgrounds for K_L -> pi0 e+ e- using Dalitz-plot analysis and time-dependent K_L-K_S interference are also briefly discussed.Comment: 24 pages, 6 figures; v2: minor modifications, published versio

Direct CP violation in neutral kaon decays

The final result is presented of the NA48 Experiment performed at CERN SPS neutral kaon beams on the direct CP violation parameter Re(epsilon'/epsilon), as maesured from the decay rates of neutral kaons into two pions. The data collected in years 1997-2001 yield the evidence for direct CP violation with Re(epsilon'/epsilon)=(14.7+-2.2)10^-4. Description of expermental method and systematics, comparison with world data and some discussion of implications for theory are given.Comment: 5 pp., 3 figs, presented on behalf of NA48 Collaboration at PASCOS 2003 Conference, Mumbai, India, 2-8 Jan 2003, to appear in Praman

The final measurement of ϵ′ϵ\epsilon'\epsilon by NA48

The direct CP violation parameter Re($\epsilon'\epsilon$) has been measured from the decay rates of neutral kaons into two pions using the NA48 detector at the CERN SPS. The 2001 running period was devoted to collecting additional data under varied conditions compared to earlier years (1997-99). The 2001 data yield the result: Re($\epsilon\epsilon'$)=$(13.7\pm3.1)\times10^{-4}$. Combining this result with that published from the 1997,98 and 99 data, an overall value of Re($\epsilon'\epsilon$)=$(14.7\pm2.2)\times10^{-4}$ is obtained from the NA48 experiment.Comment: 5 pages, 3 figures. Proceedings for the ICHEP02 conferenc