Search for a Stable Six-Quark State at BABAR

Searching for a dark matter particle with anti-protonic atoms

A wide range of dark matter candidates have been proposed and are actively being searched for in a large number of experiments, both at high (TeV) and low (sub meV) energies. One dark matter candidate, a deeply bound uuddss sexaquark, S , with mass ∼ 2 GeV (having the same quark content as the hypothesized H-dibaryon, but long lived) is particularly difficult to explore experimentally. In this paper, we propose a scheme in which such a state could be produced at rest through the formation of p ¯ -3 He antiprotonic atoms and their annihilation into S + K + K + π - , identified both through the unique tag of a S = + 2 , Q = + 1 final state, as well as through full kinematic reconstruction of the final state recoiling against it.

Weakly Bound H Dibaryon from SU(3)-Flavor-Symmetric QCD

We present the first study of baryon-baryon interactions in the continuum limit of lattice QCD, finding unexpectedly large lattice artifacts. Specifically, we determine the binding energy of the H dibaryon at a single quark-mass point. The calculation is performed at six values of the lattice spacing a, using O(a)-improved Wilson fermions at the SU(3)-symmetric point with m_{π}=m_{K}≈420  MeV. Energy levels are extracted by applying a variational method to correlation matrices of bilocal two-baryon interpolating operators computed using the distillation technique. Our analysis employs Lüscher's finite-volume quantization condition to determine the scattering phase shifts from the spectrum and vice versa, both above and below the two-baryon threshold. We perform global fits to the lattice spectra using parametrizations of the phase shift, supplemented by terms describing discretization effects, then extrapolate the lattice spacing to zero. The phase shift and the binding energy determined from it are found to be strongly affected by lattice artifacts. Our estimate of the binding energy in the continuum limit of three-flavor QCD is B_{H}^{SU(3)_{f}}=4.56±1.13_{stat}±0.63_{syst}  MeV.

Deuteronlike Heavy Dibaryons from Lattice Quantum Chromodynamics

We report the first lattice quantum chromodynamics (QCD) study of deuteronlike (np-like) dibaryons with heavy quark flavors. These include particles with the following dibaryon structures and valence quark contents: Σ_{c}Ξ_{cc}(uucucc), Ω_{c}Ω_{cc}(sscscc), Σ_{b}Ξ_{bb}(uububb), Ω_{b}Ω_{bb}(ssbsbb), and Ω_{ccb}Ω_{cbb}(ccbcbb), and with spin (J) parity (P), J^{P}≡1^{+}. Using a state-of-the art lattice QCD calculation, after controlling relevant systematic errors, we unambiguously find that the ground state masses of dibaryons Ω_{c}Ω_{cc}(sscscc), Ω_{b}Ω_{bb}(ssbsbb), and Ω_{ccb}Ω_{cbb}(ccbcbb) are below their respective two-baryon thresholds, suggesting the presence of bound states that are stable under strong and electromagnetic interactions. We also predict their masses precisely. For dibaryons Σ_{c}Ξ_{cc}(uucucc), and Σ_{b}Ξ_{bb}(uububb), we could not reach to a definitive conclusion about the presence of any bound state due to large systematics associated with these states. We also find that the binding of these dibaryons becomes stronger as they become heavier in mass. This study also opens up the possibility of the existence of many other exotic nuclei, which can be formed through the fusion of heavy baryons, similar to the formation of nuclei of elements in the periodic table.