Evidence for the Decay Sigma+ -> p mu+ mu-

Abstract

We report the first evidence for the decay Sigma+ -> p mu+ mu- from data taken by the HyperCP experiment(E871) at Fermilab. Based on three observed events, the branching ratio is B(Sigma+ -> p,mu+,mu-) = [8.6 +6.6,-5.4(stat) +/-5.5(syst)] x 10**-8. The narrow range of dimuon masses may indicate that the decay proceeds via a neutral intermediate state, Sigma+ -> p P0, P0 -> mu+ mu-, with a P0 mass of 214.3 +/- 0.5 MeV/c**2 and branching ratio B(Sigma+ -> p P0; P0 -> mu+ mu-) = [3.1 +2.4,-1.(stat) +/-1.5(syst)] x 10**-8.

Figures (5)

• Figure 1: Feynman diagrams for $\Sigma^{+}_{pll}$ decays in the SM (a)--(c) and via new physics (d). The SM processes are referred to as FCNC (a) and internal conversion (b)--(c).
• Figure 2: Plan view of the HyperCP spectrometer.
• Figure 3: $M_{p\mu\mu}$ distribution for the positive-secondary-beam data, (a) after the standard cuts, (b) within $\pm 15$ MeV/$c^2$ of the $\Sigma^+$ mass, and (c) after the additional cuts. The arrow represents the $\Sigma^+$ mass.
• Figure 4: Real (points) and MC (histogram) dimuon mass distributions for (a) $\Sigma^{+}_{p \mu \mu}$ MC events (arbitrary normalization) with a form-factor decay (solid histogram) and uniform phase-space decay (dashed histogram) model, and (b) $\Sigma^{+}_{p P \mu \mu}$ MC events normalized to match the data.
• Figure 5: The reconstructed $p e^+ e^-$ mass distribution for the normalization mode after all cuts. The histogram is the sum of MC samples of $\Sigma^{+}_{p e e \gamma}$, $K^{+}_{\pi e e \gamma}$ decays and a uniform background, where the relative amounts of each were determined by a fit, and the number of MC events was normalized to match the number of data events. The hatched area shows the main background source (uniform background).