Two-loop current-current operator contribution to the non-leptonic QCD penguin amplitude

The computation of direct CP asymmetries in charmless B decays at next-to-next-to-leading order (NNLO) in QCD is of interest to ascertain the short-distance contribution. Here we compute the two-loop penguin contractions of the current-current operators Q_{1,2} and provide a first estimate of NNLO CP asymmetries in penguin-dominated b -> s transitions.Comment: 14 pages, 4 figures, 1 tabl

Stopping and Isospin Equilibration in Heavy Ion Collisions

We investigate the density behaviour of the symmetry energy with respect to isospin equilibration in the combined systems $Ru(Zr)+Zr(Ru)$ at relativistic energies of 0.4 and $1.528 AGeV$. The study is performed within a relativistic framework and the contribution of the iso-vector, scalar $\delta$ field to the symmetry energy and the isospin dynamics is particularly explored. We find that the isospin mixing depends on the symmetry energy and a stiff behaviour leads to more transparency. The results are also nicely sensitive to the "fine structure" of the symmetry energy, i.e. to the covariant properties of the isovector meson fields. The isospin tracing appears much less dependent on the in-medium neutron-proton cross-sections ($\sigma_{np}$) and this makes such observable very peculiar for the study of the isovector part of the nuclear equation of state. Within such a framework, comparisons with experiments support the introduction of the $\delta$ meson in the description of the iso-vector equation of state.Comment: 11 pages, 5 figures. Accepted for publication in Phys.Lett.

Probing Mechanical and Chemical Instabilities in Neutron-Rich Matter

The isospin-dependence of mechanical and chemical instabilities is investigated within a thermal and nuclear transport model using a Skyrme-type phenomenological equation of state for neutron-rich matter. Respective roles of the nuclear mean field and the 2-body stochastic scattering on the evolution of density and isospin fluctuations in either mechanically or chemically unstable regions of neutron-rich matter are investigated. It is found that the mean field dominates overwhelmingly the fast growth of both fluctuations, while the 2-body scattering influences significantly the later growth of the isospin fluctuation only. The magnitude of both fluctuations decreases with the increasing isospin asymmetry because of the larger reduction of the attractive isoscalar mean field by the stronger repuslive neutron symmetry potential in the more neutron-rich matter. Moreover, it is shown that the isospin fractionation happens later, but grows faster in the more neutron-rich matter. Implications of these results to current experiments exploring properties of neutron-rich matter are discussed.Comment: 18 pages & 15 figures, Nuclear Physics A (2001) in pres

A national registry for juvenile dermatomyositis and other paediatric idiopathic inflammatory myopathies: 10 years' experience; the Juvenile Dermatomyositis National (UK and Ireland) Cohort Biomarker Study and Repository for Idiopathic Inflammatory Myopathies

Objectives: The paediatric idiopathic inflammatory myopathies (IIMs) are a group of rare chronic inflammatory disorders of childhood, affecting muscle, skin and other organs. There is a severe lack of evidence base for current treatment protocols in juvenile myositis. The rarity of these conditions means that multicentre collaboration is vital to facilitate studies of pathogenesis, treatment and disease outcomes. We have established a national registry and repository for childhood IIM, which aims to improve knowledge, facilitate research and clinical trials, and ultimately to improve outcomes for these patients. Methods: A UK-wide network of centres and research group was established to contribute to the study. Standardized patient assessment, data collection forms and sample protocols were agreed. The Biobank includes collection of peripheral blood mononuclear cells, serum, genomic DNA and biopsy material. An independent steering committee was established to oversee the use of data/samples. Centre training was provided for patient assessment, data collection and entry. Results: Ten years after inception, the study has recruited 285 children, of which 258 have JDM or juvenile PM; 86% of the cases have contributed the biological samples. Serial sampling linked directly to the clinical database makes this a highly valuable resource. The study has been a platform for 20 sub-studies and attracted considerable funding support. Assessment of children with myositis in contributing centres has changed through participation in this study. Conclusions: This establishment of a multicentre registry and Biobank has facilitated research and contributed to progress in the management of a complex group of rare muscloskeletal conditions

On the improvement of the low energy neutrino factory

The low energy neutrino factory has been proposed as a very sensitive setup for future searches for CP violation and matter effects. Here we study how its performance is affected when the experimental specifications of the setup are varied. Most notably, we have considered the addition of the 'platinum' nu_{mu} -> nu_{e} channel. We find that, whilst theoretically the extra channel provides very useful complementary information and helps to lift degeneracies, its practical usefulness is lost when considering realistic background levels. Conversely, an increase in statistics in the 'golden' nu_{e} -> nu_{mu} channel and, to some extent, an improvement in the energy resolution, lead to an important increase in the performance of the facility, given the rich energy dependence of the 'golden' channel at these energies. We show that a low energy neutrino factory with a baseline of 1300 km, muon energy of 4.5 GeV, and either a 20 kton totally active scintillating detector or 100 kton liquid argon detector, can have outstanding sensitivity to the neutrino oscillation parameters theta13, delta and the mass hierarchy. For our estimated exposure of 2.8 x 10^{23} kton x decays per muon polarity, the low energy neutrino factory has sensitivity to theta13 and delta for sin^{2}(2theta13) > 10^{-4} and to the mass hierarchy for sin^{2}(2theta13) > 10^{-3}.Comment: 13 pages, 8 eps figures. Version published in PRD - experimental section with preliminary results removed, abstract and conclusions re-written accordingly, title changed, author list amended

On the flow of kaons produced in relativistic heavy ion collisions

We investigate the different contributions to the in-plane flow of K+ mesons observed recently by the FOPI collaboration in the reaction Ni(1.93 AGeV)+Ni. Due to the kinematics of the three body phase space decay the flow of kaons produced in baryon-baryon interactions is smaller than that of the baryons in the entrance channel. On the contrary, in pi N interactions the flow of the sources and of the kaons are identical. Therefore the total kaon flow depends on the relative number of Delta N -> K+ and pi N -> K+ reactions and hence on the lifetime of the Delta, in addition to the already known dependence on the potential interaction interaction of the kaons with the nuclear environment.Comment: 11 pages, 10 figures, submitted to NP

Two-loop QCD correction to differential semi-leptonic b --> u decays in the shape-function region

We calculate the two-loop QCD correction to the form factors of on-shell b-quark decay to an energetic massless quark, which constitutes the last missing piece required for an O(alpha_s^2) determination of |V_ub| from inclusive semi-leptonic \bar B --> X_u l nu decays in the shape-function region.Comment: 24 pages, 4 figures. Properly MSbar-renormalized coefficient functions introduced. Matches published versio