Kobayashi-Maskawa Matrix Elements Research Articles

Towards a discovery of BSM physics from the Cabibbo angle anomaly

New developments in both the theories and experiments related to the extraction of the top-row Cabibbo–Kobayashi–Maskawa matrix elements [Formula: see text] and [Formula: see text] led to a series of new anomalies, for instance, the apparent violation of the top-row unitarity relation. It is important to further reduce all the associated Standard Model theory uncertainties in order to better understand whether such observations point towards the possibility of physics beyond the Standard Model, or rather some unexpectedly large Standard Model effects. This requires improved studies of tree-level and higher-order Standard Model corrections that enter the beta decays of pions, neutron, nuclei and kaons. We will briefly review the recent progress along this direction and discuss possible improvements in the future.

Measurement of the branching fraction of the {{B} ^0} {rightarrow }{{D} ^+_{s}} {{pi } ^-} decay

A branching fraction measurement of the {{B} ^0} {rightarrow }{{D} ^+_{s}} {{pi } ^-} decay is presented using proton–proton collision data collected with the LHCb experiment, corresponding to an integrated luminosity of 5.0,text {fb} ^{-1} . The branching fraction is found to be {mathcal {B}} ({{B} ^0} {rightarrow }{{D} ^+_{s}} {{pi } ^-} ) =(19.4 pm 1.8pm 1.3 pm 1.2)times 10^{-6}, where the first uncertainty is statistical, the second systematic and the third is due to the uncertainty on the {{B} ^0} {rightarrow }{{D} ^-} {{pi } ^+} , {{D} ^+_{s}} {rightarrow }{{K} ^+} {{K} ^-} {{pi } ^+} and {{D} ^-} {rightarrow }{{K} ^+} {{pi } ^-} {{pi } ^-} branching fractions. This is the most precise single measurement of this quantity to date. As this decay proceeds through a single amplitude involving a b{rightarrow }u charged-current transition, the result provides information on non-factorisable strong interaction effects and the magnitude of the Cabibbo–Kobayashi–Maskawa matrix element V_{ub}. Additionally, the collision energy dependence of the hadronisation-fraction ratio f_s/f_d is measured through {{overline{B}} {}^0_{s}} {rightarrow }{{D} ^+_{s}} {{pi } ^-} and {{B} ^0} {rightarrow }{{D} ^-} {{pi } ^+} decays.

Averages of b-hadron, c-hadron, and tau -lepton properties as of summer 2016

This article reports world averages of measurements of b-hadron, c-hadron, and tau -lepton properties obtained by the Heavy Flavor Averaging Group using results available through summer 2016. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters, C!P violation parameters, parameters of semileptonic decays, and Cabbibo–Kobayashi–Maskawa matrix elements.

Moments in inclusive semileptonic B meson decays at the Belle experiment

Since my return to Austria in the year 2003, I have measured observables in inclusive B meson decays at the Belle experiment and worked together with theorists on the interpretation of these measurements in terms of the Cabibbo–Kobayashi–Maskawa matrix element |Vcb|. And in fact, only this memorial book project made me fully aware of Kolya Uraltsev's ground breaking theoretical contributions to this field. He was not a theorist who talked a lot to an experimentalist like me, and maybe this is not a bad thing for good science. I certainly remember his enthusiasm from conferences, e.g., when I was powerless to keep his presentation to the scheduled time as a session chair at the CKM2005 workshop in San Diego. Still I feel there is some amount of irony in the fact, that I know so little about a person whose work has been so decisive for my career in high energy physics. To commemorate Kolya Uraltsev's pioneering work on inclusive semileptonic B meson decays B → Xcℓν and on the Heavy Quark Expansion (HQE), which has already been paid tribute to in other articles in this volume, I will review the measurement of the electron energy and the hadronic mass moments in B → Xcℓν decays performed at the Belle experiment. These measurements allow to both test his theoretical calculations and to extract |Vcb| and non-perturbative quantities, such as the b-quark mass, from his formulae.

Determination of $$f_+^K(0)$$ f + K ( 0 ) and extraction of $$|V_{cs}|$$ | V c s | from semileptonic $$D$$ D decays

By globally analyzing all existing measured branching fractions and partial rates in different four momentum transfer-squared $$q^2$$ bins of $$D\rightarrow Ke^+\nu _e$$ decays, we obtain the product of the form factor and magnitude of Cabibbo–Kobayashi–Maskawa matrix element $$V_{cs}$$ to be $$f_+^K(0)|V_{cs}|=0.717\pm 0.004$$ . With this product, we determine the $$D\rightarrow K$$ semileptonic form factor $$f_+^K(0)=0.737\pm 0.004\pm 0.000$$ in conjunction with the value of $$|V_{cs}|$$ determined from the standard model global fit. Alternately, with the product together with the input of the form factor $$f_+^K(0)$$ calculated in lattice quantum chromodynamics (LQCD) recently, we extract $$|V_{cs}|^{D\rightarrow Ke^+\nu _e}=0.962\pm 0.005\pm 0.014$$ , where the error is still dominated by the uncertainty of the form factor calculated in LQCD. Combining the $$|V_{cs}|^{D_s^+\rightarrow \ell ^+\nu _\ell }=1.012\pm 0.015\pm 0.009$$ extracted from all existing measurements of $$D^+_s\rightarrow \ell ^+\nu _\ell $$ decays and $$|V_{cs}|^{D\rightarrow Ke^+\nu _e}=0.962\pm 0.005\pm 0.014$$ together, we find the most precisely determined $$|V_{cs}|$$ to be $$|V_{cs}|=0.983\pm 0.011$$ , which improves the accuracy of the PDG’2014 value $$|V_{cs}|^\mathrm{PDG'2014}=0.986\pm 0.016$$ by $$45\,\%$$ .

Form factors for B meson weak decays in QCD light cone sum rules with a chiral current correlator

We report some applications of QCD light cone sum rules (LCSR) to \(B\) meson weak decays. Special emphasis is on estimates of the form factors for \(B\) decays into a pseudoscalar (\(P\))/vector (\(V\)) meson, with a certain chiral current correlator. The main new ingredient, as compared with the case of the standard correlators, is that in the operator product expansion calculations, the contributions due to the twist-3 distribution amplitudes of the related light mesons, which are less known and would bring a larger uncertainty to the calculations with the standard correlators, cancel out fully in the \(B\rightarrow P\) case and do out partially in the \(B\rightarrow V\) one. An important observation, which is similar to that in soft collinear effective theory, is made in twist-3 approximation: whereas only one independent form factor is needed for parameterizing the hadronic matrix elements for a \(B\rightarrow P\) transition induced by all the relevant heavy-light quark currents, there exist two independent form factors under the condition of neglecting the terms suppressed by a factor of \(m_V^2\), for the \(B\rightarrow V\) transition. Therefore, the improved LCSR approach could be of stronger predictive power for the weak form factors. Also, this approach is employed to understand the \(B\rightarrow D\) transitions by introducing a leading twist-2 DA for an energetic \(D\) meson, combined with some of other QCD-based approaches. A detailed QCD next-to-leading order calculation of the \(B\rightarrow \pi \) form factors is presented for an illustrative purpose, and the sum rule results are used to extract the Cabibbo–Kobayashi–Maskawa matrix element \(|V_{ub}|\) from the latest BaBar data.

Measurement of the ratio [formula omitted] in pp collisions at [formula omitted

The ratio of the top-quark branching fractions R=B(t→Wb)/B(t→Wq), where the denominator includes the sum over all down-type quarks (q=b,s,d), is measured in the tt¯ dilepton final state with proton–proton collision data at s=8 TeV from an integrated luminosity of 19.7 fb−1, collected with the CMS detector. In order to quantify the purity of the signal sample, the cross section is measured by fitting the observed jet multiplicity, thereby constraining the signal and background contributions. By counting the number of b jets per event, an unconstrained value of R=1.014±0.003(stat.)±0.032(syst.) is measured, in a good agreement with current precision measurements in electroweak and flavour sectors. A lower limit R>0.955 at the 95% confidence level is obtained after requiring R≤1, and a lower limit on the Cabibbo–Kobayashi–Maskawa matrix element |Vtb|>0.975 is set at 95% confidence level. The result is combined with a previous CMS measurement of the t-channel single-top-quark cross section to determine the top-quark total decay width, Γt=1.36±0.02(stat.)−0.11+0.14(syst.) GeV.

ISOSPIN MIXING IN THE VICINITY OF THE N = Z LINE

We present the isospin- and angular-momentum-projected nuclear density functional theory (DFT) and its applications to the isospin-breaking corrections to the superallowed β-decay rates in the vicinity of the N = Z line. A preliminary value obtained for the Cabibbo–Kobayashi–Maskawa matrix element, |Vud| = 0.97463(24), agrees well with the recent estimate by Towner and Hardy [Phys. Rev.C77, 025501 (2008)]. We also discuss new opportunities to study the symmetry energy by using the isospin-projected DFT.

Constraining CKM elements with direct top measurements

In this paper the current bounds on the CKM matrix elements |V td|, |Vts| and |Vtb| from direct measurements are discussed and an improved model-independent analysis is proposed. PACS 12.15. -y - Electroweak interactions. PACS 12.15.Ff - Quark and lepton masses and mixing. PACS 12.15 .Hh - Determination of Kobayashi-Maskawa matrix elements.

Fermion masses, leptogenesis, and supersymmetric SO(10) unification

Current neutrino oscillation data indicate the existence of two large lepton mixing angles, while Kobayashi-Maskawa matrix elements are all small. Here we show how supersymmetric SO(10) with extra chiral singlets can easily reconcile large lepton mixing angles with small quark mixing angles within the framework of the successful Fritzsch ansatz. Moreover, we show how this is fully consistent with the thermal leptogenesis scenario, avoiding the so-called gravitino problem. A sizable asymmetry can be generated at scales as low as possible within the leptogenesis mechanism. We present our results in terms of the leptonic $CP$ violation parameter that characterizes neutrino oscillations.

The average kinetic energy of the heavy quark in [formula omitted] in the Bethe–Salpeter equation approach

In the previous paper, based on the SU(2)f×SU(2)s heavy quark symmetries of the QCD Lagrangian in the heavy quark limit, the Bethe–Salpeter equation for the heavy baryon Λb was established with the picture that Λb is composed of a heavy quark and a scalar light diquark. In the present work, we apply this model to calculate μπ2 for Λb, the average kinetic energy of the heavy quark inside Λb. This quantity is particularly interesting since it can be measured in experiments and since it contributes to the inclusive semileptonic decays of Λb when contributions from higher order terms in 1/Mb expansions are taken into account and consequently influences the determination of the Cabibbo–Kobayashi–Maskawa matrix elements Vub and Vcb. We find that μπ2 for Λb is 0.25GeV2∼0.95GeV2, depending on the parameters in the model including the light diquark mass and the interaction strength between the heavy quark and the light diquark in the kernel of the BS equation. We also find that this result is consistent with the value of μπ2 for Λb which is derived from the experimental value of μπ2 for the B meson with the aid of the heavy quark effective theory.

Different kind of textures of Yukawa coupling matrices in the two Higgs doublet model type III

The quark mass matrices ansatze proposed by Fritzsch, Du–Xing and Fukuyama–Nishiura in the framework of the general two Higgs doublet model are studied. The corresponding Yukawa matrices in the flavor basis in the various cases considered are discussed. The corresponding Cabibbo–Kobayashi–Maskawa matrix elements are computed in all cases and compared with their experimental values. The complex phases of the ansatze are taken into account, and the CP violating phase δ is computed. Finally, in order to observe the influence of the various kinds of texture of the Yukawa coupling matrices considered, some issues in the phenomenology of the two body decays of the top quark, the lightest Higgs boson and the charged Higgs boson are discussed.

SEMILEPTONIC B DECAYS AND DETERMINATION OF |Vub|

Semileptonic decays of the B mesons provide an excellent probe for the weak and strong interactions of the bottom quark. The large data samples collected at the B Factories have pushed the experimental studies of the semileptonic B decays to a new height and stimulated significant theoretical developments. We review recent progresses in this fast-evolving field, with an emphasis on the determination of the magnitude of the Cabibbo–Kobayashi–Maskawa matrix element |Vub|.

Time-dependent CP violation in B0→ K0 s φ, $K^0_s\eta'$ and K0 s K+ K– in the Belle and BaBar experiments

Both the Belle and BaBar collaborations have recently measured time-dependent CP violation in B0 decays to $ss\overline{s}$ states and compared the results to those for $sc\overline{c}$ states for which quite precise results were previously available. Within the framework of the standard model the same results should be expected for both cases. The decays to $ss\overline{s}$ states are dominated by penguin diagrams and may be sensitive to physics beyond the standard model. For these states, compared to the results for $sc\overline{c}$ states, a discrepancy in the mixing-induced CP violation of 2.7 standard deviations was found, and may be interpreted as an indication for physics beyond the standard model. PACS: 11.30.Er Charge conjugation, parity, time reversal, andother discrete symmetries – 12.15.Hh Determination of Kobayashi-Maskawa matrix elements – 13.25.Hw Decays of bottom mesons

W and Z pair production at LEP2

The measurements of W-pair, WWγ and ZZ cross sections performed by the four experiments at the LEP collider are herein reported. The statistics collected in the period 1996-2000 amounts to about 40000 WW, 400 WWγ and 1000 ZZ events distributed over a large center-of-mass energy range of 161-209 GeV. From the WW cross section measurements, also the W branching fractions in leptons and hadrons are derived with a percent precision: BR(W→ qq) = 67.77 ± 0.18 ± 0.22% and BR(W→ lν)=10.74 ± 0.06 ± 0.07%. PACS: 12.15.Hh Determination of Kobayashi-Maskawa matrix elements – 12.15.Mm Neutral currents – 12.15.Lk Electroweak radiative corrections – 13.38.Be Decays of W bosons – 13.38.Dg Decays of Z bosons – 13.66.Fg Gauge and Higgs boson production in e-e+ interactions – 14.70.Fm W bosons – 14.70.Hp Z bosons

|V cb |, |V ub |, and HQET at CLEO

I report results from the CLEO collaboration on semileptonic B decays, highlighting measurements of the Cabibbo-Kobayashi-Maskawa matrix elements |V cb | and |V ub |. I describe the techniques used to obtain the recent improvements in precision for these measurements, including the use of the b→ sγ photon spectrum to reduce hadronic uncertainties in semileptonic B decays. I also report new measurements of |V cb | using the inclusive semileptonic branching fraction ${\cal B}(B\to X e \nu)$ and of |V ub | through study of the q2 dependence of B→πℓν and B→ρℓν. PACS: 12.15.Hh Determination of Kobayashi-Maskawa matrix elements – 13.20.He Decays of bottom mesons

Determination of the semi-leptonic branching fraction of charm hadrons produced in neutrino charged-current interactions

During the years 1994–1997, the emulsion target of the CHORUS detector was exposed to the CERN-SPS Wide Band Neutrino Beam. The improvements of the past few years in the automatic emulsion scanning systems allowed a sample of events located in emulsion to be used for studies of charm production. Based on a sample of 56172νμ charged-current interactions analysed so far, we find a value of Bμ=0.093±0.009(stat.)±0.009(syst.) for the semi-leptonic branching fraction of charm hadrons. The result for events with visible energy larger than 30 GeV, Bμ=0.102±0.016(stat.)±0.010(syst.), can be combined with the existing measurements of the dimuon rate to yield a value of 0.219±0.022 for the magnitude of the Cabibbo–Kobayashi–Maskawa matrix element |Vcd|.

Measurement of the inclusive semileptonic branching fraction of B mesons and |Vcb|

We present a measurement of the electron spectrum from inclusive semileptonic B decay, using 5.1 fb−1 of ϒ(4S) data collected with the Belle detector. A high-momentum lepton tag was used to separate the semileptonic B decay electrons from secondary decay electrons. We obtained the branching fraction, B(B→Xe+ν)=(10.90±0.12±0.49)%, with minimal model dependence. From this measurement, we derive a value for the Cabibbo–Kobayashi–Maskawa matrix element |Vcb|=0.0408±0.0010(exp)±0.0025(th).

Radiative corrections to $K_{\ell 3}$ decays

We present a complete calculation of the $K_{\ell 3}$ decays $K^+ \to \pi^0 \ell^+ \nu_{\ell}$ and $K^0 \to \pi^- \ell^+ \nu_\ell$ to $\mathcal O(p^4, (m_d-m_u) p^2, e^2 p^2)$ in chiral perturbation theory with virtual photons and leptons. We introduce the concept of generalized form factors and kinematical densities in the presence of electromagnetism, and propose a possible treatment of the real photon emission in $K^+_{\ell 3}$ decays. We illustrate our results by applying them to the extraction of the Kobayashi–Maskawa matrix element $|V_{us}|$ from the experimental $K^+_{e3}$ decay parameters.

Measurement of (→Dℓ) and determination of |V|

We present a measurement of the branching fraction for the semileptonic B decay B ̄ 0 →D + ℓ − ν ̄ , where ℓ − can be either an electron or a muon. We find Γ( B ̄ 0 →D + ℓ − ν ̄ )=(13.79±0.76±2.51) ns −1 , and the resulting branching fraction B ( B ̄ 0 →D + ℓ − ν ̄ )=(2.13±0.12±0.39)% , where the first error is statistical and the second systematic. We also investigate the B ̄ 0 →D + ℓ − ν ̄ form factor and the implications of the result for | V cb |. From a fit to the differential decay distribution we obtain the rate normalization | V cb | F D (1)=(4.11±0.44±0.52)×10 −2 . Using a theoretical calculation of F D (1), the Cabibbo–Kobayashi–Maskawa matrix element | V cb |=(4.19±0.45±0.53±0.30)×10 −2 is obtained, where the last error comes from the theoretical uncertainty of F D (1). The results are based on a data sample of 10.2fb −1 recorded at the ϒ (4 S ) resonance with the Belle detector at the KEKB e + e − collider.