decay, with a statistical significance exceeding six standard deviations, and the best measurement so far of its branching fraction. Furthermore, we obtained evidence for the B 0 ? m 1 m 2 decay with a statistical significance of three standard deviations. Both measurements are statistically compatible with standard model predictions and allow stringent constraints to be placed on theories beyond the standard model. The LHC experiments will resume taking data in 2015, recording proton-proton collisions at a centre-of-mass energy of 13 teraelectronvolts, which will approximately double the production rates of B 0 s and B 0 mesons and lead to further improvements in the precision of these crucial tests of the standard model.Experimental particle physicists have been testing the predictions of the standard model of particle physics (SM) with increasing precision since the 1970s. Theoretical developments have kept pace by improving the accuracy of the SM predictions as the experimental results gained in precision. In the course of the past few decades, the SM has passed critical tests derived from experiment, but it does not address some profound questions about the nature of the Universe. For example, the existence of dark matter, which has been confirmed by cosmological data 3 , is not accommodated by the SM. It also fails to explain the origin of the asymmetry between matter and antimatter, which after the Big Bang led to the survival of the tiny amount of matter currently present in the Universe Fig. 1c, is forbidden at the elementary level because the Z 0 cannot couple directly to quarks of different flavours, that is, there are no direct 'flavour changing neutral currents'. However, it is possible to respect this rule and still have this decay occur through 'higher order' transitions such as those shown in Fig. 1d and e. These are highly suppressed because each additional interaction vertex reduces their probability of occurring significantly. They are also helicity and CKM suppressed. Consequently, the branching fraction for the B 0 s ?m z m { decay is expected to be very small compared to the dominant b antiquark to c antiquark transitions. The corresponding decay of the B 0 meson, where a d quark replaces the s quark, is even more CKM suppressed because it requires a jump across two quark generations rather than just one.The branching fractions, B, of these two decays, accounting for higher-order electromagnetic and strong interaction effects, and using lattice quantum chromodynamics to compute the B 8,9 , such as in the diagrams shown in Fig. 1f and g, that can considerably modify the SM branching fractions. In particular, theories with additional Higgs bosons 10,11 predict possible enhancements to the branching fractions. A significant deviation of either of the two branching fraction measurements from the SM predictions would give insight on how the SM should be extended. Alternatively, a measurement compatible with the SM could provide strong constraints on BSM theories. . Both CMS and LHCb later ...

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The STAR CollaborationNuclear collisions recreate conditions in the universe microseconds after the Big Bang. Only a very small fraction of the emitted fragments are light nuclei, but these states are of fundamental interest. We report the observation of antihypertritons -composed of an antiproton, antineutron, and antilambda hyperon -produced by colliding gold nuclei at high energy. Our analysis yields 70 ± 17 antihypertritons ( Nuclei are abundant in the universe, but antinuclei that are heavier than the antiproton have been observed only as products of interactions at particle accelerators (1, 2). Collisions of heavy nuclei at the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) briefly produce hot and dense matter that has been interpreted as a quark gluon plasma (QGP) (3, 4) with an energy density similar to that of the universe a few microseconds after the Big Bang. This plasma contains roughly equal numbers of quarks and antiquarks. As a result of the high energy density of the QGP phase, many strange-antistrange (ss) quark pairs 1 are liberated from the quantum vacuum. The plasma cools and transitions into a hadron gas, producing nucleons, hyperons, mesons, and their antiparticles.Nucleons (protons and neutrons) contain only up and down valence quarks, while hyperons (Λ, Σ, Ξ, Ω) contain at least one strange quark in its 3-quark valence set. A hypernucleus is a nucleus that contains at least one hyperon in addition to nucleons. All hyperons are unstable, even when bound in nuclei. The lightest bound hypernucleus is the hypertriton ( 3 Λ H), which consists of a Λ hyperon, a proton, and a neutron. The first observation of any hypernucleus was made in 1952 using a nuclear emulsion cosmic ray detector (5). Here, we present the observation of an antimatter hypernucleus. Production of antinuclei:Models of heavy-ion collisions have had good success in explaining the production of nuclei by assuming that a statistical coalescence mechanism is in effect during the late stage of the collision evolution (4, 6). Antinuclei can be produced through the same coalescence mechanism, and are predicted to be present in cosmic rays. An observed high yield could be interpreted as an indirect signature of new physics, such as Dark Matter (7, 8). Heavy-ion collisions at RHIC provide an opportunity for the discovery and study of many antinuclei and antihypernuclei.The ability to produce antihypernuclei allows the study of all populated regions in the 3-dimensional chart of the nuclides. The conventional 2-dimensional chart of the nuclides organizes nuclear isotopes in the (N, Z) plane, where N is the number of neutrons and the Z is the number of protons in the nucleus. This chart can be extended to the negative sector in the (N, Z) plane by including antimatter nuclei. Hypernuclei bring a third dimension into play, based on the strangeness quantum number of the nucleus. The present study probes the territory of antinuclei with non-zero strangeness ( Fig. 1), where proposed ideas (9-12) related to t...

High-energy nuclear collisions create an energy density similar to that of the Universe microseconds after the Big Bang; in both cases, matter and antimatter are formed with comparable abundance. However, the relatively short-lived expansion in nuclear collisions allows antimatter to decouple quickly from matter, and avoid annihilation. Thus, a high-energy accelerator of heavy nuclei provides an efficient means of producing and studying antimatter. The antimatter helium-4 nucleus (4He), also known as the anti-α (α), consists of two antiprotons and two antineutrons (baryon number B = -4). It has not been observed previously, although the α-particle was identified a century ago by Rutherford and is present in cosmic radiation at the ten per cent level. Antimatter nuclei with B < -1 have been observed only as rare products of interactions at particle accelerators, where the rate of antinucleus production in high-energy collisions decreases by a factor of about 1,000 with each additional antinucleon. Here we report the observation of 4He, the heaviest observed antinucleus to date. In total, 18 4He counts were detected at the STAR experiment at the Relativistic Heavy Ion Collider (RHIC; ref. 6) in 10(9) recorded gold-on-gold (Au+Au) collisions at centre-of-mass energies of 200 GeV and 62 GeV per nucleon-nucleon pair. The yield is consistent with expectations from thermodynamic and coalescent nucleosynthesis models, providing an indication of the production rate of even heavier antimatter nuclei and a benchmark for possible future observations of 4He in cosmic radiation.

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