Semileptonic and nonleptonic decays of Bc

Using our relativistic constituent quark model we present results on the exclusive nonleptonic and semileptonic decays of the Bc-meson. The nonleptonic decays are studied in the framework of the factorization approximation. We calculate the branching ratios for a large set of exclusive nonleptonic and semileptonic decays of the Bc-meson and compare our results with the results of other models.Comment: 4 pages, proceeding of the talk given by Pietro Santorelli at IFAE 2006, Pavia, 19-21 Aprile 200

J/\psi dissociation cross sections in a relativistic quark model

We calculate the amplitudes and the cross sections of the charm dissociation processes J/\psi \pi => D \bar D, D* \bar D, D \bar D*, D* \bar D* within a relativistic constituent quark model. We consistently account for the contributions coming from both the box and triangle diagrams that contribute to the dissociation processes. The cross section is dominated by the D* \bar D and D* \bar D* channels. When summing up the four channels we find a maximum total cross section of about 2.3 mb at sqrt(s) \approx 4.1 GeV. We compare our results to the results of other model calculations.Comment: 22 pages, 9 figures, typos corrected, this version will appear on Phys. Rev.

Semileptonic decays of Bc mesons into charmonium states in a relativistic quark model

We use the framework of a relativistic constituent quark model to study the semileptonic transitions of the Bc meson into CCbar charmonium states where CCbar = etaC (1S0), J/psi (3S1), chiC0 (3P0), chiC1 (3P1), hc (1P1), chiC2 (3P2), psi (3D2). We compute the q^2-dependence of all relevant form factors and give predictions for their semileptonic Bc decay modes including also their tau-modes. We derive a formula for the polar angle distribution of the charged lepton in the (l nu) c.m. frame and compute the partial helicity rates that multiply the angular factors in the decay distribution. For the discovery channel [B_c => J/psi (=> mu+ mu-) l nu] we compute the transverse/longitudinal composition of the J/psi which can be determined by an angular analysis of the decay J/psi => mu+ mu-. We compare our results with the results of other calculations.Comment: 16 pages RevTex, this version will appear in Physical Review

Integrating the evidence for a terrestrial carbon sink caused by increasing atmospheric CO2

Atmospheric carbon dioxide concentration ([CO2]) is increasing, which increases leaf‐scale photosynthesis and intrinsic water‐use efficiency. These direct responses have the potential to increase plant growth, vegetation biomass, and soil organic matter; transferring carbon from the atmosphere into terrestrial ecosystems (a carbon sink). A substantial global terrestrial carbon sink would slow the rate of [CO2] increase and thus climate change. However, ecosystem CO2‐responses are complex or confounded by concurrent changes in multiple agents of global change and evidence for a [CO2]‐driven terrestrial carbon sink can appear contradictory. Here we synthesise theory and broad, multi‐disciplinary evidence for the effects of increasing [CO2] (iCO2) on the global terrestrial carbon sink. Evidence suggests a substantial increase in global photosynthesis since pre‐industry. Established theory, supported by experiments, indicates that iCO2 is likely responsible for about half of the increase. Global carbon budgeting, atmospheric data, and forest inventories indicate a historical carbon sink, and these apparent iCO2‐responses are high in comparison with experiments and theory. Plant mortality and soil carbon iCO2‐responses are highly uncertain. In conclusion, a range of evidence supports a positive terrestrial carbon sink in response to iCO2, albeit with uncertain magnitude and strong suggestion of a role for additional agents of global change