Search for the Lepton-Number-Violating Decay Ξ-→pμ-μ-

A sensitive search for the lepton-number-violating decay Ξ-→pμ-μ- has been performed using a sample of ∼109  Ξ- hyperons produced in 800  GeV/c p-Cu collisions. We obtain B(Ξ-→pμ-μ-)\u3c4.0×10-8 at 90% confidence, improving on the best previous limit by 4 orders of magnitude

Evidence for the Decay Σ+→pμ+μ-

We report the first evidence for the decay Σ+→pμ+μ- from data taken by the HyperCP (E871) experiment at Fermilab. Based on three observed events, the branching ratio is B(Σ+→pμ+μ-)=[8.6-5.4+6.6(stat)±5.5(syst)]×10-8. The narrow range of dimuon masses may indicate that the decay proceeds via a neutral intermediate state, Σ+→pP0,P0→μ+μ- with a P0 mass of 214.3±0.5  MeV/c2 and branching ratio B(Σ+→pP0,P0→μ+μ-)=[3.1-1.9+2.4(stat)±1.5(syst)]×10-8

High Statistics Search for the θ+ (1.54) Pentaquark State

We have searched for θ+(1.54)→K0p decays using data from the 1999 run of the HyperCP experiment at Fermilab. We see no evidence for a narrow peak in the KS0p mass distribution near 1.54  GeV/c among 106 000 KS0p candidates, and obtain an upper limit for the fraction of θ+(1.54) to KS0p candidates o

Measurement of the α Asymmetry Parameter for the Ω-→ΛK- Decay

We have measured the α parameter of the Ω-→ΛK- decay using data collected with the HyperCP spectrometer during the 1997 fixed-target run at Fermilab. Analyzing a sample of 0.96×106 Ω-→ΛK-, Λ→pπ- decays, we obtain αΩαΛ=[1.33±0.33(stat)±0.52(syst)]×10-2. With the accepted value ofαΛ, αΩ is found to be [2.07±0.51(stat)±0.81(syst)]×10-2

Rare Decays with a Light CP-Odd Higgs Boson in the NMSSM

We have previously proposed a light pseudoscalar Higgs boson in the next-to-minimal supersymmetric standard model (NMSSM), the A_1^0, as a candidate to explain the HyperCP observations in Sigma^+ -> p mu^+ mu^-. In this paper we calculate the rates for several other rare decay modes that can help confirm or refute this hypothesis. The first modes we evaluate are K_L -> pi pi A_1^0, which are interesting because they are under study by the KTeV Collaboration. We next turn to eta -> pi pi A_1^0, which are interesting because they are independent of the details of the flavor-changing sector of the NMSSM and may be accessible at DAPhNE. For completeness, we also evaluate Omega^- -> Xi^- A_1^0.Comment: 17 pages, 11 figure

Light-Front Approach for Pentaquark Strong Decays

Assuming the two diquark structure for the pentaquark state as advocated in the Jaffe-Wilczek model, we study the strong decays of light and heavy parity-even pentaquark states using the light-front quark model in conjunction with the spectator approximation. The narrowness of the Theta width is ascribed to the p-wave configuration of the diquark pair. Taking the Theta width as a benchmark, we estimate the rates of the strong decays Xi_{3/2}-- to Xi- pi-, Sigma- K-, Sigma_{5c}0 to D_s- p, D_{s0}*- p and Xi_{5c}0 to D_s- Sigma+, D_{s0}^{*-} Sigma+ with Sigma_{5c} Xi_{5c} being antisextet charmed pentaquarks and D_{s0}* a scalar strange charmed meson. The ratio of Gamma(P_c to Baryon D_{s0}*)/Gamma(P_c to Baryon D_s) is very useful for verifying the parity of the antisextet charmed pentaquark P_c. It is expected to be of order unity for an even parity P_c and much less than one for an odd parity pentaquark.Comment: 24 pages, 2 figure

Search for CP Violation in Charged-Xi and Lambda Hyperon Decays

We have compared the proton and antiproton angular distributions in 117 million Xi-minus -> Lambda + pi-minus -> proton + pi-minus + pi-minus and 41 million anti-Xi-minus -> anti-Lamba + pi-plus -> antiproton + pi-plus + pi-plus decays using a subset of the data from the HyperCP experiment (E871) at Fermilab. We find no evidence of CP violation, with the direct-CP-violating parameter $A_{\Xi\Lambda} = \frac{\alpha_{\Xi}\alpha_{\Lambda} - \bar{\alpha}_{\Xi}\bar{\alpha}_{\Lambda}}{\alpha_{\Xi}\alpha_{\Lambda} + \bar{\alpha}_{\Xi}\bar{\alpha}_{\Lambda}} = [0.0+/-5.1(stat)+/-4.4(syst)]{\times}10^{-4}$.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Let

A measurement of the branching ratio of K+-- ->pi+--mu+mu- decays in the Hyper CP experiment

Large samples of hyperon and kaon decays were collected with the Hyper CP spectrometer during two fixed-target runs at Fermilab. Based on an analysis of 110 million K pm decays from the 1997 data sample we present a branching ratio for K pm right arrow pi pm mu+ mu-. This is the first observation of K- right arrow pi- mu+ mu- decay

A measurement of the branching ratio of K+-- ->pi+--mu+mu- decays in the Hyper CP experiment

Large samples of hyperon and kaon decays were collected with the Hyper CP spectrometer during two fixed-target runs at Fermilab. Based on an analysis of 110 million K pm decays from the 1997 data sample we present a branching ratio for K pm right arrow pi pm mu+ mu-. This is the first observation of K- right arrow pi- mu+ mu- decay

Examining CP symmetry in strange baryon decay

Non-conservation of CP symmetry can manifest itself in non-lepton ichyperon decays as a difference in the decay parameter between the strange-baryon decay and its charge conjugate. By comparing the decay distribution in the $\Lambda$ helicity frame for the decay sequence $\Xi- \to \Lambda \pi-$,$\Lambda \to p \pi-$with that of $\overline Xi+$ decay, E756 at Fermilab did not observe any CP-odd effect at the $10-2$ level. The status of a follow-up experiment, HyperCP (FNAL E871), to search for CP violation in charged $\Xi-\Lambda$ decay with a sensitivity of $10-4$is also presented