Abstract: Symmetry transformations have been proven a bedrock tool for understanding the nature of particle interactions, formulating, and testing fundamental theories. Based on the up to now unbroken CPT symmetry, the violation of the CP symmetry between matter and antimatter by weak interactions, discovered in the decay of kaons in 1964 and observed more recently in 2001 in B mesons, strongly suggests that the behavior of these particles under weak interactions must also be asymmetric under time reversal T. However, until recent years there has not been a direct detection of the expected time-reversal violation in the time evolution of any system. This Colloquium examines the field of time-reversal symmetry breaking in the fundamental laws of physics. For transitions, its observation requires an asymmetry with exchange of initial and final states. A discussion is given of the conceptual basis for such an exchange with unstable particles, using the quantum properties of Einstein-Podolsky-Rosen entanglement available at B meson factories combined with the decay as a filtering measurement. The method allows a clear-cut separation of different transitions between flavor and CP eigenstates in the decay of neutral B mesons. These ideas have been implemented for the experiment by the BABAR Collaboration at SLAC's B factory. The results, presented in 2012, prove beyond any doubt the violation of time-reversal invariance in the time evolution between these two states of the neutral B meson.

Abstract: We use the local hidden gauge approach in order to study the B (B) over bar* and B*(B) over bar* interactions for isospin I = 1. We show that both interactions via one light meson exchange are not allowed by the Okubo-ZweigIizuka rule and, for that reason, we calculate the contributions due to the exchange of two pions, interacting and noninteracting among themselves, and also due to the heavy vector mesons. Then, to compare all these contributions, we use the potential related to the heavy vector exchange as an effective potential corrected by a factor which takes into account the contribution of the other light meson exchanges. In order to look for poles, this effective potential is used as the kernel of the Bethe-Salpeter equation. As a result, for the B (B) over bar* interaction we find a loosely bound state with mass in the range 10587-10601 MeV, very close to the experimental value of the Z(b)(10610) reported by the Belle Collaboration. For the B*(B) over bar* case, we find a cusp at 10650 MeV for all spin J = 0, 1, 2 cases.

Abstract: A search is presented for the decay Upsilon(1S) -> gamma A(0), A(0) -> c (c) over barc, where A(0) is a candidate for the CP-odd Higgs boson of the next-to-minimal supersymmetric standard model. The search is based on data collected with the BABAR detector at the Upsilon(2S) resonance. A sample of Upsilon(1S) mesons is selected via the decay Upsilon(2S) -> pi(+)pi(-)Upsilon(1S) . The A(0) -> c (c) over bar decay is identified through the reconstruction of hadronic D-0, D+,and D-0 (2010)(+) meson decays. No significant signal is observed. The measured 90% confidence-level upper limits on the product branching fraction beta(Upsilon(1S) -> gamma A(0)) x beta(A(0) -> (c) over barc range from 7.4 x 10(-5) to 2.4 x 10(-3) for A(0) masses from 4.00 to 8.95 GeV/c(2) and 9.10 to 9.25 GeV/c(2), where the region between 8.95 and 9.10 GeV/c(2) is excluded because of background from Upsilon(2S) -> gamma chi(bJ)(1P), chi(bJ)(1P) -> gamma Upsilon(1S) decays.