CKM Matrix Element Research Articles

Purely leptonic decays of the ground charged vector mesons

The study of the purely leptonic decays of the ground charged vector mesons is very interesting and significant in determining the CKM matrix elements, obtaining the decay constant of vector mesons, examining the lepton flavor universality, and searching for new physics beyond the standard model. These purely leptonic decays of the ground charged vector mesons are induced by the weak interactions within the standard model, and usually have very small branching ratios, mathcal{B}({rho }^{-}{rightarrow }{ell }^{-}{nu }_{ell }){sim }mathcal{O}(10^{-13}), {{{mathcal {B}}}}(K^{{*}-}{rightarrow }{ell }^{-}{nu }_{ell }){sim }{{{mathcal {O}}}}(10^{-13}), mathcal{B}(D_{d}^{{*}-}{rightarrow }{ell }^{-}{nu }_{ell }){sim }mathcal{O}(10^{-10}), mathcal{B}(B_{u}^{{*}-}{rightarrow }{ell }^{-}{nu }_{ell }){sim }mathcal{O}(10^{-10}), mathcal{B}(D_{s}^{{*}-}{rightarrow }{ell }^{-}{nu }_{ell }){sim }mathcal{O}(10^{-6}) and mathcal{B}(B_{c}^{{*}-}{rightarrow }{ell }^{-}{nu }_{ell }){sim }mathcal{O}(10^{-6}). Inspired by the potential prospects of LHCb, Belle-II, STCF, CEPC and FCC-ee experiments, we discussed the probabilities of experimental investigation on these purely leptonic decays. It is found that the measurements of these decays might be possible and feasible with the improvement of data statistics, analytical technique, and measurement precision in the future. (1) With the hadron-hadron collisions, the purely leptonic decays of {rho }^{-}, K^{{*}-}, D_{d,s}^{{*}-} and B_{u,c}^{{*}-} mesons might be accessible at LHC experiments. (2) With the e^{+}e^{-} collisions, the purely leptonic decays of D_{d,s}^{{*}-} and B_{u,c}^{{*}-} mesons might be measurable with over 10^{12}Z^{0} bosons available at CEPC and FCC-ee experiments. In addition, the D_{d,s}^{{*}-}{rightarrow }{ell }^{-}{nu }_{ell } decays could also be studied at Belle-II and SCTF experiments.

Electroweak axial structure functions and improved extraction of the Vud CKM matrix element

We present a comprehensive analysis of the $\gamma W$ interference radiative correction to the neutron $\beta$-decay matrix element. Within a dispersion relations approach, we compute the axial-vector part of the $\gamma W$ box amplitude $\Box^{\gamma W}_{A}$ in terms of the isoscalar part of the $F_3^{\gamma W}$ interference structure function. Using the latest available phenomenology for $F_3^{\gamma W}$ from the nucleon elastic, resonance, deep-inelastic, and Regge regions, we find the real part of the box correction to be $\Box^{\gamma W}_A = 3.90(9) \times 10^{-3}$. This improved correction gives a theoretical estimate of the CKM matrix element $|V_{ud}|^2=0.94805(26)$, which represents a 4$\sigma$ violation of unitarity.

CP violation and measurement of the CKM parameters in B decays

The LHCb collaboration aims at precise measurements of the parameters of the CKM matrix elements. To increase the precision, new measurements of the CKM angle γ make use of the entire dataset collected by the LHCb experiment from 2011 to 2018, which leads to a combination of γ = (67 ± 4)∘. Analyses of semileptonic B decays also allow the determination of |Vcb|, |Vub|/|Vcb| and provide experimental inputs for QCD predictions.

Highlights on top quark measurements from CMS

Recent results from the CMS Collaboration using top quarks are presented. These results are based on partial datasets collected by the CMS Collaboration during the LHC Run 2, at a center-of-mass energy of 13 TeV. This document includes the first measurement of tt‾ production in association with charm quarks, the first direct measurement of the third generation of the CKM matrix elements, the investigation of the running of the top quark mass, search for CP violation in top quark production, measurement of the forward-backward asymmetry in tt‾ production at the LHC, and the first global approach in constraining EFT operator coefficients using top quarks.

K \u2192 \u03bc+\u03bc\u2212 as a clean probe of short-distance physics

The K → μ+μ− decay is often considered to be uninformative of fundamental theory parameters since the decay is polluted by long-distance hadronic effects. We demonstrate that, using very mild assumptions and utilizing time-dependent interference effects, ℬ(KS → μ+μ−)ℓ=0 can be experimentally determined without the need to separate the ℓ = 0 and ℓ = 1 final states. This quantity is very clean theoretically and can be used to test the Standard Model. In particular, it can be used to extract the CKM matrix element combination mid {V}_{ts}{V}_{td}sin left(beta +{beta}_sright)mid approx mid {A}^2{lambda}^5overline{eta}mid with hadronic uncertainties below 1%.

Measurement of the CKM matrix element $$|V_{cb}|$$ from top quark pair events at the LHC

Measurement of the CKM matrix element $$|V_{cb}|$$ from top quark pair events at the LHC

Erratum: Measurement of the CKM matrix element |Vcb| from B0→D*−ℓ+νℓ at Belle [Phys. Rev. D 100 , 052007 (2019)

Erratum: Measurement of the CKM matrix element <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mo stretchy="false">|</mml:mo><mml:msub><mml:mi>V</mml:mi><mml:mrow><mml:mi>c</mml:mi><mml:mi>b</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">|</mml:mo></mml:math> from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>B</mml:mi><mml:mn>0</mml:mn></mml:msup><mml:mo stretchy="false">→</mml:mo><mml:msup><mml:mi>D</mml:mi><mml:mrow><mml:mo>*</mml:mo><mml:mo>−</mml:mo></mml:mrow></mml:msup><mml:msup><mml:mo>ℓ</mml:mo><mml:mo>+</mml:mo></mml:msup><mml:msub><mml:mi>ν</mml:mi><mml:mo>ℓ</mml:mo></mml:msub></mml:math> at Belle [Phys. Rev. D <b>100</b> , 052007 (2019)

Anomalous constants of three-boson vertices in the process of pair production of W±-bosons in proton collisions at CMS LHC

In this paper, we obtained the expected constraints on the anomalous CP-even constants of three-boson interactions on the basis of cross-section for the pair production of W+-bosons in proton-proton collisions. The constraints were obtained for luminosity and the kinematic constraints on the final states typical for the CMS experiment at the Large Hadron Collider at =13 s TeV. One-dimensional and two-dimensional regions of constraints for the anomalous parameters of three-boson interactions were calculated. When calculating the cross-section, the usual approximations of small quark masses and values of the CKM matrix elements were not used. The expected values of the anomalous constants are almost an order of magnitude less than the constraints found at the LEP collider at = 200 s GeV in the reaction e–e+ → W–W+.

Flavor mixing of quarks and a new texture

The flavor mixing of the quarks is described by the CKM matrix, which is parametrized by three mixing angles and one phase parameter. We discuss a new texture for the two mass matrices of the six quarks. The three flavor mixing angles can be calculated — they are functions of the ratios of the quark masses. The third mixing angle is given by the CKM matrix element [Formula: see text]. We find: [Formula: see text]. The calculated mixing angles agree with the mixing angles, measured in many experiments.

Isospin Breaking in Lattice QCD Computations of Decay Amplitudes

The remarkable recent progress in the precision of Lattice QCD computations for a number of physical quantities relevant for flavour physics has motivated the introduction of isospin-breaking effects, including in particular electromagnetic corrections, to the computations. The isospin breaking corrections are necessary to fully exploit this improved precision for the determination of the fundamental parameters of the Standard Model, including the CKM matrix elements, and to look for deviations from experimental measurements which might signal the presence of new physics. Together with colleagues from Rome, we have developed and implemented a framework for including isospin-breaking corrections in leptonic decays $P\to\ell\bar\nu_\ell(\gamma)$, where $P$ is a pseudoscalar meson and $\ell$ a charged lepton, and the theoretical framework and numerical results are reviewed below. The status of our studies to extend this framework to semileptonic decays $P_1\to P_2\ell\bar\nu_\ell(\gamma)$, where $P_{1,2}$ are pseudoscalar mesons, is also presented.

Analysis of Bc → τντ at CEPC * *This study was supported by the National Key Programme for S&T Research and Development (2016YFA0400400), the Beijing Municipal Science Technology Commission (Z181100004218003, Z191100007219010), the Natural Science Foundation of China (11735010, 11911530088, 11775110, 11690034), the Natural Science Foundation of Shanghai (15DZ2272100), the DFG Emmy-Noether (BE 6075/1-1)

Precise determination of the branching ratio provides an advantageous opportunity for understanding the electroweak structure of the Standard Model, measuring the CKM matrix element , and probing new physics models. In this paper, we discuss the potential of measuring the process with decaying leptonically at the proposed Circular Electron Positron Collider (CEPC). We conclude that during the Z pole operation, the channel signal can achieve five- significance with Z decays, and the signal strength accuracies for can reach around 1% level at the nominal CEPC Z pole statistics of one trillion Z decays, assuming the total yield is . Our theoretical analysis indicates the accuracy could provide a strong constraint on the general effective Hamiltonian for the transition. If the total yield can be determined to (1%) level of accuracy in the future, these results also imply could be measured up to (1%) level of accuracy.

Charm Physics at BESIII

Recently, BESIII has performed many analyses with the largest e+ e- annihilation data set taken on the mass-thresholds. Those works focus on the measurements of the CKM matrix elements |Vcd(s)|, the transition form factors , tests of lepton flavor universality, precise measurements of branching fraction, studies of interesting intermediate states in the multiple-body decays, and searchs for the new physics. Among those, we present the results with three categorities, the (semi-) leptonic decays, hadronic decays, and the rare decays.

On the Progenitor Quark Mass Matrix

We determined the quark mass matrix in terms of a small expansion parameter $\sqrt{\varepsilon}$, which gives correctly all the quark masses and the CKM matrix elements at the electroweak (EW) scale, and obtain a progenitor form at the GUT scale by running the EW scale mass matrix. Finally, a possible texture form for the progenitor quark mass matrix is suggested.

Probing New Physics in b \u2192 d transitions

Recent experimental data on several observables in semileptonic B-meson decays are found to be in tension with the corresponding Standard Model predictions. Most of these deviations are related to b → c and b → s flavour changing transitions. In this work, we estimate possible New Physics effects in b → dμ+μ− flavour changing neutral currents. We parametrize NP contributions in a model-independent way and determine the allowed ranges of corresponding Wilson coefficients from the data on the exclusive B±→ π±μ+μ− decays measured recently by the LHCb collaboration. Afterwards, we investigate the impact of these results on other b → d processes such as the leptonic B0→ μ+μ− decays and B0− {overline{B}}^0 mixing. As an example, we consider a simplified Z′ model that is found to be consistent with current b → d data in the certain regions of the NP parameter space. In addition, we estimate the correlations between the partial decay widths of B → πμ+μ− and B → K μ+μ− processes to be used for an independent determination of CKM matrix elements as well as for a combined New Physics analysis of both b → d and b → s transitions.

The Drightarrow rho semileptonic and radiative decays within the light-cone sum rules

The measured branching ratio of the D meson semileptonic decay D rightarrow rho e^+ nu _e, which is based on the 0.82~{mathrm{fb}^{-1}} CLEO data taken at the peak of psi (3770) resonance, disagrees with the traditional SVZ sum rules analysis by about three times. In the paper, we show that this discrepancy can be eliminated by applying the QCD light-cone sum rules (LCSR) approach to calculate the Drightarrow rho transition form factors A_{1,2}(q^2) and V(q^2). After extrapolating the LCSR predictions of these TFFs to whole q^2-region, we obtain 1/|V_{mathrm{cd}}|^2 times Gamma (D rightarrow rho e nu _e) =(55.45^{+13.34}_{-9.41})times 10^{-15}~mathrm{GeV}. Using the CKM matrix element and the D^0(D^+) lifetime from the Particle Data Group, we obtain mathcal{B} (D^0rightarrow rho ^- e^+ nu _e) = (1.749^{+0.421}_{-0.297}pm 0.006)times 10^{-3} and mathcal{B} (D^+ rightarrow rho ^0 e^+ nu _e) = (2.217^{+0.534}_{-0.376}pm 0.015)times 10^{-3}, which agree with the CLEO measurements within errors. We also calculate the branching ratios of the two D meson radiative processes and obtain mathcal{B}(D^0rightarrow rho ^0 gamma )= (1.744^{+0.598}_{-0.704})times 10^{-5} and mathcal{B}(D^+ rightarrow rho ^+ gamma ) = (5.034^{+0.939}_{-0.958})times 10^{-5}, which also agree with the Belle measurements within errors. Thus we think the LCSR approach is applicable for dealing with the D meson decays.

|Vub| determination and testing of lepton flavour universality in semileptonic Bc\u2009\u2192\u2009D(\u2217) decays

In light of prospects for measurements of Bc → D(∗)lv decays in the upcoming Upgrade II of the LHC, we show that by using calculated Bc → D(∗) form factors a competitive extraction of the |Vub| CKM matrix element from the {B}_cto Dmu {overline{v}}_{mu } decay might be possible. To minimize experimental and theoretical uncertainties we provide the ratio |Vub|/|Vcb| by normalizing the {B}_cto {D}^{left(ast right)}mu {overline{v}}_{mu } to {B}_cto J/psi mu {overline{v}}_{mu } decay. We also briefly examine the suggestion to extract |Vub|/|Vcs| from the theoretically interesting ratio of {B}_cto {D}^0e{overline{v}}_e and {B}_cto {B}_se{overline{v}}_e decay rates in the zero-recoil limit. With the present average value of |Vub|, the predicted branching ratios are estimated to be BRleft({B}_cto {D}^0mu {overline{nu}}_{mu}right)=left(2.4pm 0.4right)cdotp {10}^{-5} and BRleft({B}_cto {D}^{ast}mu {overline{nu}}_{mu}right)=left(7pm 3right)cdotp {10}^{-5}, and the semileptonic ratios for testing the lepton flavour universality in these Bc decays are Rc(D0) = 0.64 ± 0.05 and Rc(D∗) = 0.55 ± 0.05. We also provide q2 distributions and various angular observables of Bc→ D(∗)lν decays.

Finite family groups for fermionic and leptoquark mixing patterns

We employ a bottom-up and model-independent technique to search for non-Abelian discrete flavour symmetries capable of predicting viable CKM and PMNS matrices alongside of special patterns of leptoquark couplings. In particular, we analyze patterns de- rived when an ultra-violet flavour theory is assumed to break to global Abelian symmetries in Standard Model fermion masses and new Yukawa-like terms sourced by the leptoquark representation. The phenomenology of different classes of these ‘simplified models’ can be explored without reference to explicit model-building assumptions, e.g. the nature of flavour symmetry breaking or any additional field content associated to it, and are also capable of explaining hints of lepton non-universality in {mathcal{R}}_{K^{left(ast right)}} . Assuming experimentally interesting CKM and PMNS matrix elements, our algorithm finds an abundance of predictive non-Abelian flavour groups and therefore provides promising directions for future model building in the flavoured leptoquark space, regardless of whether the anomalous {mathcal{R}}_{K^{left(ast right)}} measurements withstand further experimental scrutiny.

QCD corrections to inclusive heavy hadron weak decays at ΛQCD3/mQ3

We present an analytical calculation of the $\alpha_s$ corrections for the coefficient of $\rho_D/m_Q^3$ term in the heavy quark expansion for the inclusive semileptonic decays of heavy hadrons, such as $B \to X_c \ell \bar{\nu}$. The full dependence of the coefficient on the final-state quark mass is taken into account. Our result leads to further improvement of the theoretical predictions for the precision determination of CKM matrix element $|V_{cb}|$.

Erratum: Scalar and vector form factors of D→π(K)ℓν decays with Nf=2+1+1 twisted fermions [Phys. Rev. D 96 , 054514 (2017)

We present a lattice determination of the vector and scalar form factors of the $D \to \pi(K) \ell \nu$ semileptonic decays, which are relevant for the extraction of the CKM matrix elements $|V_{cd}|$ and $|V_{cs}|$ from experimental data. Our analysis is based on the gauge configurations produced by the European Twisted Mass Collaboration with $N_f = 2+1+1$ flavors of dynamical quarks, at three different values of the lattice spacing and with pion masses as small as 210 MeV. The matrix elements of both vector and scalar currents are determined for a plenty of kinematical conditions in which parent and child mesons are either moving or at rest. Lorentz symmetry breaking due to hypercubic effects is clearly observed in the data and included in the decomposition of the current matrix elements in terms of additional form factors. After the extrapolations to the physical pion mass and to the continuum limit we determine the vector and scalar form factors in the whole kinematical region from $q^2 = 0$ up to $q^2_{max} = (M_D - M_{\pi(K)})^2$ accessible in the experiments, obtaining a good overall agreement with experiments, except in the region at high values of $q^2$ where some deviations are visible. A set of synthetic data points, representing our results for $f_+^{D \pi(K)}(q^2)$ and $f_0^{D \pi(K)}(q^2)$ for several selected values of $q^2$, is provided and also the corresponding covariance matrix is available. At zero 4-momentum transfer we get: $f_+^{D \to \pi}(0) = 0.612 ~ (35)$ and $f_+^{D \to K}(0) = 0.765 ~ (31)$. Using the experimental averages for $|V_{cd}| f_+^{D \to \pi}(0)$ and $|V_{cs}| f_+^{D \to K}(0)$, we extract $|V_{cd}| = 0.2330 ~ (137)$ and $|V_{cs}| = 0.945 ~ (38)$, respectively. The second-row of the CKM matrix is found to be in agreement with unitarity within the current uncertainties: $|V_{cd}|^2 + |V_{cs}|^2 + |V_{cb}|^2 = 0.949 ~ (78)$.

Complete vectorlike fourth family and new U(1)′ for muon anomalies

We consider the Standard Model (SM) with the addition of a $\mathrm{U(1)^\prime}$ gauge symmetry and a complete fourth family of quarks and leptons which are vector-like with respect to the full $\mathrm{SU(3)_C}\times \mathrm{SU(2)_L} \times \mathrm{U(1)_Y}\times \mathrm{U(1)^\prime}$ gauge symmetry. The model provides a unified explanation of experimental anomalies in $(g - 2)_\mu$ as well as $b \rightarrow s \ell^+ \ell^-$ decays. We find good fits to the deviations from the SM, while at the same time fitting all other SM observables. The model includes a new $Z^\prime$ gauge boson, a $\mathrm{U(1)^\prime}$-breaking scalar, and vector-like leptons all with mass of order a few $100$ GeV. It is consistent with all currently released high energy experimental data, however, it appears imminently testable with well designed future searches. Also precision flavor experiments, especially more accurate direct determinations of CKM matrix elements, would allow to probe the best fit points.