1,721,043 research outputs found
Nonperturbative calculations of form factors for exclusive semileptonic decays
No full textPrecise theoretical predictions derived from the Standard Model are a key ingredient in searches for new physics in the flavor sector. The large mass and long lifetime of the quark make processes involving quarks of particular interest. We use lattice simulations to perform nonperturbative QCD calculations for semileptonic decays. We present results from our determinations of and semileptonic form factors and provide an outlook for our calculation. In addition we discuss the determination of -ratios testing lepton-flavor universality and suggest use of an improved ratio. Our calculations are based on the set of 2+1 flavor domain wall Iwasaki gauge field configurations generated by the RBC-UKQCD collaboration featuring three lattice spacings of , , and . Heavy -quarks are simulated using the relativistic heavy quark action
Exclusive semileptonic decays on the lattice
Full text linkSemileptonic decays provide an alternative -decay
channel to determine the CKM matrix element , and to obtain a
-ratio to investigate lepton-flavor-universality violations. Results for the
CKM matrix element may also shed light on the discrepancies seen between
analyses of inclusive or exclusive decays. We calculate the decay form factors
using lattice QCD with domain-wall light quarks and a relativistic -quark.
We analyze data at three lattice spacings with unitary pion masses down to
. Our numerical results are interpolated/extrapolated to
physical quark masses and to the continuum to obtain the vector and scalar form
factors and with full error budgets at values
spanning the range accessible in our simulations. We provide a possible
explanation of tensions found between results for the form factor from
different lattice collaborations. Model- and truncation-independent
-parameterization fits following a recently proposed Bayesian-inference
approach extend our results to the entire allowed kinematic range. Our results
can be combined with experimental measurements of and
semileptonic decays to determine . The error is
currently dominated by experiment. We compute differential branching fractions
and two types of ratios, the one commonly used as well as a variant better
suited to test lepton-flavor universality.Comment: Version accepted and published (Phys. Rev. D 107, 114512) 30 pages,
13 Figures, supplementary data fil
Long-distance contribution to from lattice QCD
No full textA lattice QCD approach to the calculation of the long-distance contributions to is presented. This parameter describes indirect CP violation in decay. While the short-distance contribution to can be accurately calculated in terms of standard model parameters and a single hadronic matrix element, , there is a long-distance part which is estimated to be approximately of the total and is more difficult to determine. A method for determining this small but phenomenologically important contribution to using lattice QCD is proposed and a complete exploratory calculation of the contribution is presented. This exploratory calculation uses an unphysical light quark mass corresponding to a 339 MeV pion mass and an unphysical charm quark mass of 968 MeV, expressed in the scheme at 2 GeV. This calculation demonstrates that future work should be able to determine this long-distance contribution from first principles with a controlled error of 10\% or less
Semi-leptonic form factors for Bs→ K\ell ν and Bs → Ds \ell ν
No full textSemi-leptonic and decays provide an alternative -decay channel to determine the CKM matrix elements and or to obtain -ratios to investigate lepton flavor universality violations. In addition, these decays may shed further light on the discrepancies seen in the analysis of inclusive vs. exclusive decays. Using the nonperturbative methods of lattice QCD, theoretical results are obtained with good precision and full control over systematic uncertainties. This talk will highlight ongoing efforts of the -physics program by the RBC-UKQCD collaboration
Form factors for semi-leptonic <i>B</i> decays
No full textSemi-leptonic decays provide promising channels to test the Standard Model, search for signs of new physics, or determine fundamental parameters like CKM matrix elements. We present an update on our calculation of short distance contributions to GIM suppressed rare decays focusing in particular on decays. Furthermore we show first results for our calculation of semi-leptonic decays involving transitions. Our calculations are based on RBC-UKQCD's 2+1 flavor domain-wall fermion and Iwasaki gauge field configurations featuring three lattice spacings in the range GeV GeV and pion masses down to the physical value. We calculate the form factors by simulating -quarks using the relativistic heavy quark action, create light and quarks with standard domain-wall kernel, and use optimised M\"obius domain-wall fermions for charm quarks
Optimised strategy for direct CPV in charm decays: circa 2018
No full textOptimised strategy for direct CPV in charm decays: circa 2018</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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