Challenges in semileptonic B decays Gambino, P.; Kronfeld, A. S.; Rotondo, M. ...
The European physical journal. C, Particles and fields,
10/2020, Letnik:
80, Številka:
10
Journal Article
Recenzirano
Odprti dostop
Two of the elements of the Cabibbo–Kobayashi–Maskawa quark mixing matrix,
|
V
ub
|
and
|
V
cb
|
, are extracted from semileptonic
B
decays. The results of the
B
factories, analysed in the light of ...the most recent theoretical calculations, remain puzzling, because for both
|
V
ub
|
and
|
V
cb
|
the exclusive and inclusive determinations are in clear tension. Further, measurements in the
τ
channels at Belle, Babar, and LHCb show discrepancies with the Standard Model predictions, pointing to a possible violation of lepton flavor universality. LHCb and Belle II have the potential to resolve these issues in the next few years. This article summarizes the discussions and results obtained at the MITP workshop held on April 9–13, 2018, in Mainz, Germany, with the goal to develop a medium-term strategy of analyses and calculations aimed at solving the puzzles. Lattice and continuum theorists working together with experimentalists have discussed how to reshape the semileptonic analyses in view of the much higher luminosity expected at Belle II, searching for ways to systematically validate the theoretical predictions in both exclusive and inclusive
B
decays, and to exploit the rich possibilities at LHCb.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We calculate the bag parameters for neutral B-meson mixing in and beyond the Standard Model, in full four-flavor lattice QCD for the first time. We work on gluon field configurations that include the ...effect of u, d, s, and c sea quarks with the highly improved staggered quark (HISQ) action at three values of the lattice spacing and with three u/d quark masses going down to the physical value. The valence b quarks use the improved nonrelativistic QCD action and the valence light quarks, the HISQ action. Our analysis was blinded. Our results for the bag parameters for all five operators are the most accurate to date. For the Standard Model operator between Bs and Bd mesons we find BBs = 1.232(53) and BBd = 1.222(61). Combining our results with lattice QCD calculations of the decay constants using HISQ quarks from the Fermilab/MILC Collaboration and with experimental values for Bs and Bd oscillation frequencies allows determination of the Cabibbo-Kobayashi-Maskawa (CKM) elements Vts and Vtd. We find |Vts| = 0.04189(93), |Vtd| = 0.00867(23), and |Vts|/|Vtd| = 0.2071(27). Our results agree well (within 2σ) with values determined from CKM unitarity constraints based on tree-level processes (only). Using a ratio to ΔMs,d in which CKM elements cancel in the Standard Model, we determine the branching fractions Br(Bs→μ+μ−) = 3.81(18)×10−9 and Br(Bd →μ+μ−)=1.031(54)×10−10. We also give results for matrix elements of the operators R0, R1, and R1 that contribute to neutral B-meson width differences.
We determine the normalization of scalar and pseudoscalar current operators made from nonrelativistic b quarks and highly improved staggered light quarks in lattice quantum chromodynamics (QCD) ...through O(αs) and ΛQCD/mb. We use matrix elements of these operators to extract B meson decay constants and form factors, and then compare to those obtained using the standard vector and axial-vector operators. This provides a test of systematic errors in the lattice QCD determination of the B meson decay constants and form factors. We provide a new value for the B and Bs meson decay constants from lattice QCD calculations on ensembles that include u, d, s, and c quarks in the sea and those that have the u/d quark mass going down to its physical value. Our results are fB=0.196(6) GeV, fBs=0.236(7) GeV, and fBs/fB=1.207(7), agreeing well with earlier results using the temporal axial current. By combining with these previous results, we provide updated values of fB=0.190(4) GeV, fBs=0.229(5) GeV, and fBs/fB=1.206(5).
We determine the contribution to the anomalous magnetic moment of the muon from the αQED2 hadronic vacuum polarization diagram using full lattice QCD and including u/d quarks with physical masses for ...the first time. We use gluon field configurations that include u, d, s and c quarks in the sea at multiple values of the lattice spacing, multiple u/d masses and multiple volumes that allow us to include an analysis of finite-volume effects. We obtain a result for aμHVP,LO of 667(6)(12)×10−10, where the first error is from the lattice calculation and the second includes systematic errors from missing QED and isospin-breaking effects and from quark-line disconnected diagrams. Our result implies a discrepancy between the experimental determination of aμ and the Standard Model of 3σ.
All lattice-QCD calculations of the hadronic-vacuum-polarization contribution to the muon's anomalous magnetic moment to date have been performed with degenerate up- and down-quark masses. Here we ...calculate directly the strong-isospin-breaking correction to a_{μ}^{HVP} for the first time with physical values of m_{u} and m_{d} and dynamical u, d, s, and c quarks, thereby removing this important source of systematic uncertainty. We obtain a relative shift to be applied to lattice-QCD results obtained with degenerate light-quark masses of δa_{μ}^{HVP,m_{u}≠m_{d}}=+1.5(7)%, in agreement with estimates from phenomenology.
In a 2019 AMR threat assessment, the US Centers for Disease Control and Prevention reported 18% fewer deaths due to AMR since 2013, but increases in several severe multidrug-resistant bacterial ...infections, including a 315% increase in erythromycin-resistant group A Streptococcus, a 124% increase in drug-resistant Neisseria gonorrhoeae, and a 50% increase in extended-spectrum β-lactamase-producing Enterobacteriaceae.3 A 2019 report from the US Presidential Advisory Council on Combating Antibiotic-Resistant Bacteria endorsed most priorities from the 2015 national action plan and proposed new targets for 2020–25.10 The US approach to AMR has been mixed and, looking ahead, needs to move beyond priority setting to concrete action. The recommendations of the UN Interagency Coordination Group on AMR provide a roadmap by taking a One Health approach to intervene on AMR at the interface between humans, animals, and the environment.5 The US Federal Government could accelerate progress on its AMR national action plan in several ways: first, by permanently ceasing use of medically important antibiotics in agribusiness; second, by supporting antibiotic stewardship programmes; third, by encouraging the development of new antibiotics through bipartisan initiatives such as the Developing an Innovative Strategy for Antimicrobial Resistant Microorganisms (DISARM) Act,10,13 which some legislators have proposed as part of a COVID-19 relief bill, as well as the Pioneering Antimicrobial Subscriptions to End Up Surging Resistance (PASTEUR) Act, which incorporates an antibiotic subscription programme similar to that in the UK; and, finally, by simultaneously investing in innovation to identify and evaluate other anti-infectives. ...to accelerate and sustain progress against AMR, the USA should support the multilateral global architecture needed to confront AMR, including WHO, the UN Food and Agriculture Organization, and the World Organisation for Animal Health.
Based on analysis of texture and in-grain misorientation axes (IGMA) distribution, we investigate the effects of initial orientation and deformation temperature on the rollability of magnesium alloy ...AZ31 and the associated deformation mechanisms. Plate samples oriented favorably for basal 〈
a
〉 slip exhibited the best rollability at room temperature, whereas under the warm-rolling condition, surprisingly, the plate oriented for prism 〈
a
〉 slip exhibited the best rollability. The enhanced rollability of the latter plate is attributed to increased activity of prism 〈
a
〉 slip, which exhibits a lower texture hardening rate than basal 〈
a
〉 slip. The increased activity of prism 〈
a
〉 slip is shown experimentally by the development of the
//RD texture and 〈0001〉-type IGMA distribution. Asymmetric texture is also suggested to impair the rollability of plate oriented for basal 〈
a
〉 slip.
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