37 research outputs found
QCD-Factorization of inclusive B decays and |Vub|
Recent progress in the theoretical description of inclusive B to X_u l nu
decays in the shape-function region is reported. Finite moments of the shape
function are related to HQET parameters. Event fractions for several
experimental cuts are presented, with a particular emphasis on the hadronic
variable P+. The aim of this talk is to introduce the P+ spectrum, to compare
it to the hadronic invariant mass spectrum and the charged-lepton energy
spectrum, and to study the prospect of evaluating |Vub| in the presence of a
large background from B to X_c decays.Comment: 8 pages, 7 figures, uses espcrc2.sty (included). Talk presented at
the Sixth International Conference on Hyperons, Charm and Beauty Hadrons,
IIT, Chicago, June 27--July 3 200
A two-loop relation between inclusive radiative and semileptonic B-decay spectra
A shape-function independent relation is derived between the partial
B->X_u+l+nu decay rate with a cut on P_+=E_X-P_X<Delta and a weighted integral
over the normalized B->X_s+gamma photon-energy spectrum. The leading-power
contribution to the weight function is calculated at next-to-next-to-leading
order in renormalization-group improved perturbation theory, including exact
two-loop matching corrections at the scale mu_i^2 ~ m_b*Lambda_{QCD}. The
overall normalization of the weight function is obtained up to yet unknown
corrections of order [alpha_s(m_b)]^2. Power corrections from phase-space
factors are included exactly, while the remaining subleading contributions are
included at first order in 1/m_b. At this level unavoidable hadronic
uncertainties enter, which are estimated in a conservative way. The combined
theoretical accuracy in the extraction of |V_{ub}| is at the level of 5% if a
value of Delta near the charm threshold can be achieved experimentally.Comment: 22 pages, 4 figures; few comments and one reference added; version to
appear in JHE
Proposal for a Precision Measurement of |Vub|
A new method for a precision measurement of the CKM matrix element |Vub| is
discussed, which combines good theoretical control with high efficiency and a
powerful discrimination against charm background. The resulting combined
theoretical uncertainty on |Vub| is estimated to be 10%.Comment: 4 pages, 2 figures, RevTe
Factorization and the Soft Overlap Contribution to Heavy-to-Light Form Factors
Using the formalism of soft-collinear effective theory, a complete separation
of short- and long-distance contributions to heavy-to-light transition form
factors at large recoil is performed. The universal functions
parameterizing the ``soft overlap'' contribution to the form factors are
defined in terms of matrix elements in the effective theory. Endpoint
configurations corresponding to kinematic situations where one of the valence
partons in the external mesons carries very small momentum are accounted for in
terms of operators involving soft-collinear messenger fields. They contribute
at leading order in and spoil factorization. An analysis
of operator mixing and renormalization-group evolution in the effective theory
reveals that the intermediate scale is without significance
to the soft functions , and that the soft overlap contribution does
not receive a significant perturbative (Sudakov) suppression.Comment: 30 pages, 6 figures. Erratum adde
Twenty-three unsolved problems in hydrology (UPH) – a community perspective
This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through on-line media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focussed on process-based understanding of hydrological variability and causality at all space and time scales.
Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come