Semileptonic Decays Research Articles

Search for the semi-leptonic decays [formula omitted] and [formula omitted

We search for the semi-leptonic decays Λc+→Λπ+π−e+νe and Λc+→pKS0π−e+νe in a sample of 4.5fb−1 of e+e− annihilation data collected in the center-of-mass energy region between 4.600GeV and 4.699GeV by the BESIII detector at the BEPCII. No significant signals are observed, and the upper limits on the decay branching fractions are set to be B(Λc+→Λπ+π−e+νe)<3.9×10−4 and B(Λc+→pKS0π−e+νe)<3.3×10−4 at the 90% confidence level, respectively.

Measurement of the top-quark mass using a leptonic invariant mass in pp collisions at sqrt{s} = 13 TeV with the ATLAS detector

A measurement of the top-quark mass (mt) in the toverline{t} → lepton + jets channel is presented, with an experimental technique which exploits semileptonic decays of b-hadrons produced in the top-quark decay chain. The distribution of the invariant mass mℓμ of the lepton, ℓ (with ℓ = e, μ), from the W-boson decay and the muon, μ, originating from the b-hadron decay is reconstructed, and a binned-template profile likelihood fit is performed to extract mt. The measurement is based on data corresponding to an integrated luminosity of 36.1 fb−1 of sqrt{s} = 13 TeV pp collisions provided by the Large Hadron Collider and recorded by the ATLAS detector. The measured value of the top-quark mass is mt = 174.41 ± 0.39 (stat.) ± 0.66 (syst.) ± 0.25 (recoil) GeV, where the third uncertainty arises from changing the Pythia8 parton shower gluon-recoil scheme, used in top-quark decays, to a recently developed setup.

D -meson semileptonic decays to pseudoscalars from four-flavor lattice QCD

We present lattice-QCD calculations of the hadronic form factors for the semileptonic decays $D\to\pi\ell\nu$, $D\to K\ell\nu$, and $D_s\to K\ell\nu$. Our calculation uses the highly improved staggered quark (HISQ) action for all valence and sea quarks and includes $N_f=2+1+1$ MILC ensembles with lattice spacings ranging from $a\approx0.12$ fm down to $0.042$ fm. At most lattice spacings, an ensemble with physical-mass light quarks is included. The HISQ action allows all the quarks to be treated with the same relativistic light-quark action, allowing for nonperturbative renormalization using partial conservation of the vector current. We combine our results with experimental measurements of the differential decay rates to determine $|V_{cd}|^{D\to\pi}=0.2238(11)^{\rm Expt}(15)^{\rm QCD}(04)^{\rm EW}(02)^{\rm SIB}[22]^{\rm QED}$ and $|V_{cs}|^{D\to K}=0.9589(23)^{\rm Expt}(40)^{\rm QCD}(15)^{\rm EW}(05)^{\rm SIB}[95]^{\rm QED}$ This result for $|V_{cd}|$ is the most precise to date, with a lattice-QCD error that is, for the first time for the semileptonic extraction, at the same level as the experimental error. Using recent measurements from BES III, we also give the first-ever determination of $|V_{cd}|^{D_s\to K}=0.258(15)^{\rm Expt}(01)^{\rm QCD}[03]^{\rm QED}$ from $D_s\to K \ell\nu$. Our results also furnish new Standard Model calculations of the lepton flavor universality ratios $R^{D\to\pi}=0.98671(17)^{\rm QCD}[500]^{\rm QED}$, $R^{D\to K}=0.97606(16)^{\rm QCD}[500]^{\rm QED}$, and $R^{D_s\to K}=0.98099(10)^{\rm QCD}[500]^{\rm QED}$, which are consistent within $2\sigma$ with experimental measurements. Our extractions of $|V_{cd}|$ and $|V_{cs}|$, when combined with a value for $|V_{cb}|$, provide the most precise test of second-row CKM unitarity, finding agreement with unitarity at the level of one standard deviation.

Measurement of the nuclear modification factor of b-jets in 5.02 TeV Pb+Pb collisions with the ATLAS detector

This paper presents a measurement of b-jet production in Pb+Pb and pp collisions at sqrt{s_{_text {NN}}}=5.02 TeV with the ATLAS detector at the LHC. The measurement uses 260 text {pb}^{-1} of pp collisions collected in 2017 and 1.4 text {nb}^{-1} of Pb+Pb collisions collected in 2018. In both collision systems, jets are reconstructed via the anti-k_{t} algorithm. The b-jets are identified from a sample of jets containing muons from the semileptonic decay of b-quarks using template fits of the muon momentum relative to the jet axis. In pp collisions, b-jets are reconstructed for radius parameters R= 0.2 and R= 0.4, and only R= 0.2 jets are used in Pb+Pb collisions. For comparison, inclusive R= 0.2 jets are also measured using 1.7 text {nb}^{-1} of Pb+Pb collisions collected in 2018 and the same pp collision data as the b-jet measurement. The nuclear modification factor, R_text {AA}, is calculated for both b-jets and inclusive jets with R= 0.2 over the transverse momentum range of 80–290 GeV. The nuclear modification factor for b-jets decreases from peripheral to central collisions. The ratio of the b-jet R_text {AA} to inclusive jet R_text {AA} is also presented and suggests that the R_text {AA} for b-jets is larger than that for inclusive jets in central Pb+Pb collisions. The measurements are compared with theoretical calculations and suggest a role for mass and colour-charge effects in partonic energy loss in heavy-ion collisions.

Branching fraction of the decay B+ → π+τ+τ− and lepton flavor universality test via the ratio Rπ(τ/μ)

Among (semi)leptonic rare B-decays induced by the b→d flavor changing neutral current, the decay B+→π+μ+μ− is the only one observed so far experimentally. Related decays involving the e+e− and τ+τ− pairs are the targets for the ongoing experiments at the LHC, in particular LHCb, and Belle II. The muonic and electronic semileptonic decays have almost identical branching fractions in the Standard Model (SM). However, the tauonic decay B+→π+τ+τ− differs from the other two due to the higher reaction threshold which lies slightly below the ψ(2S)-resonance. We present calculations of the ditauon (τ+τ−) invariant-mass distribution and the branching fraction Br(B+→π+τ+τ−) in the SM based on the Effective Electroweak Hamiltonian approach, taking into account also the so-called long-distance contributions. The largest theoretical uncertainty in the short-distance part of the decay rates is due to the B→π form factors, which we quantify using three popular parametrizations. The long-distance contribution can be minimized by a cut on the ditauon mass mτ+τ−>Mψ(2S). Once available, the branching fractions in the tauonic and muonic (and electronic) modes provide stringent test of the lepton flavor universality in the b→d transitions. We illustrate this by calculating the ratio Rπ(τ/μ)≡Br(B+→π+τ+τ−)/Br(B+→π+μ+μ−) in the SM for the total and binned ratios of the branching fractions.

Dispersive constraints on fermion masses

We demonstrate that fermion masses in the Standard Model (SM) can be constrained by the dispersion relations obeyed by hadronic and semileptonic decay widths of a fictitious heavy quark $Q$ with an arbitrary mass. These relations, imposing stringent connections between the high-mass and low-mass behaviors of decay widths, correlate a heavy quark mass and the chiral symmetry breaking scale. Given the known input from leading-order heavy quark expansion and a hadronic threshold for decay products, we solve for a physical heavy quark decay width. It is shown that the charm (bottom) quark mass $m_c= 1.35$ GeV ($m_b= 4.0$ GeV) can be determined by the dispersion relation for the $Q\to du\bar d$ ($Q\to c\bar ud$) decay with the threshold $2m_\pi$ ($m_\pi+m_D$), where $m_\pi$ ($m_D$) denotes the pion ($D$ meson) mass. Requiring that the dispersion relation for the $Q\to su\bar d$ ($Q\to d\mu^+\nu_\mu$, $Q\to u\tau^-\bar\nu_\tau$) decay with the threshold $m_\pi+m_K$ ($m_\pi+m_\mu$, $m_\pi+m_\tau$) yields the same heavy quark mass, $m_K$ being the kaon mass, we constrain the strange quark (muon, $\tau$ lepton) mass to be $m_s= 0.12$ GeV ($m_\mu=0.11$ GeV, $m_\tau= 2.0$ GeV). Moreover, all the predicted decay widths corresponding to the above masses agree with the data. It is pointed out that our formalism is similar to QCD sum rules for probing resonance properties, and that the Pauli interference (weak annihilation) provides the higher-power effect necessary for establishing the solutions of the hadronic (semilaptonic) decay widths. This work suggests that the parameters in the SM may not be free, but arranged properly to achieve internal dynamical consistency.

A0(980)-meson twist-2 distribution amplitude within the QCD sum rules and investigation of D → a0(980)(→ηπ)e+νe

In this paper, moments of a0(980)-meson twist-2 light-cone distribution amplitudes were deeply researched by using QCD sum rules approach within background field theory. Up to 9th-order accuracy, we present 〈ξ2;a0n〉|μ0 at the initial scale μ0=1GeV, i.e. 〈ξ2;a01〉|μ0=−0.307(43), 〈ξ2;a03〉|μ0=−0.181(34), 〈ξ2;a05〉|μ0=−0.078(28), 〈ξ2;a07〉|μ0=−0.049(26), 〈ξ2;a09〉|μ0=−0.036(24), respectively. An improved light-cone harmonic oscillator model for a0(980)-meson twist-2 light-cone distribution amplitudes is adopted, where its parameters are fixed by using the least squares method based on the 〈ξ2;a0n〉|μ0, and their goodness of fit reach to 95.4%. Then, we calculate the D→a0(980) transition form factors within the light-cone sum rules approach, and at largest recoil point, we obtain f+D→a0(0)=1.058−0.035+0.068 and f−D→a0(0)=0.764−0.036+0.044. As a further application, the branching fractions of the D→a0(980)ℓν¯ℓ semileptonic decays are given. Taking the decay a0(980)→ηπ into consideration, we obtain B(D0→a0(980)−(→ηπ−)e+νe)=(1.330−0.134+0.216)×10−4, B(D+→a0(980)0(→ηπ0)e+νe)=(1.675−0.169+0.272)×10−4, which are consistent with the BESIII collaboration and PDG data within errors. Finally, we present the angle observables of forward-backward asymmetries, q2-differential flat terms and lepton polarization asymmetry of the semileptonic decay D→a0(980)ℓν¯ℓ.

NLO QCD corrections to off-shell top–antitop production with semi-leptonic decays at lepton colliders

The study of top-quark properties will be a central aspect of the physics programme of any future lepton collider. In this article, we investigate the production of top-quark pairs in the semi-leptonic decay channel in {textrm{e}}^{+}textrm{e}^{-} collisions, whose experimental signature is one charged lepton, jets, and missing energy. We present for the first time fiducial cross sections and differential distributions at next-to-leading-order accuracy in QCD for the full off-shell process. We find that the QCD corrections for the considered process are strongly dependent on the beam energies and range from few per cent up to more than 100% (near threshold and above 1,text {TeV} ). We focus, in particular, on two scenarios: one close to threshold (365,text {GeV} ), dominated by top-pair production, and one at the TeV scale (1.5,text {TeV} ), for which irreducible-background contributions become relevant. An assessment of polarised-beam effects is also provided.

Semileptonic decays of doubly charmed baryons in the bag model

We study the semileptonic decays of $B_{cc}$ ${\rightarrow}$ $B_c\ell^+\nu_\ell$ with the bag model, where $\ell$ = $(e, \mu)$, $B_{cc}$ = $(\Xi_{cc}^{++}$, $\Xi_{cc}^+$, $\Omega_{cc}^+$), and $ B_c$ are the singly charmed baryons with $J^P= 1/2^+$. We obtain the decay widths of $\Gamma(\Xi_{cc}^{++}{\rightarrow}\Xi_c^+e^+\nu_e, \Xi_c^{\prime+}e^+\nu_e, \Lambda_c^+e^+\nu_e, \Omega_c^+ e^+\nu_e) =(5.1\pm 0.1 , 11\pm 1, 0.34\pm 0.06, 0.76\pm 0.06)\times 10^{-14}$~GeV, $\Gamma(\Xi_{cc}^+\rightarrow \Xi_c^0e^+\nu_e, \Xi_c^{\prime0}e^+\nu_e , \Sigma_c^0e^+\nu_e) = (5.1\pm 0.6, 11\pm 1, 1.5\pm 0.1) \times 10^{-14}$~GeV, and $\Gamma(\Omega_{cc}^+\rightarrow \Omega_c^0 e^+\nu_e, \Xi_c^0e^+\nu_e , \Xi_c^{\prime0} e^+\nu_e) = (22\pm 2, 0.32 \pm 0.04, 0.77\pm 0.06)\times 10^{-14}$~GeV. We also get that $\Gamma$($B_{cc}$ ${\rightarrow}$ $B_c\mu^+\nu_\mu$)/$\Gamma$($B_{cc}$ ${\rightarrow}$ $B_ce^+\nu_e$) = $0.97\sim 1.00$. In addition, we discuss the $SU(3)$ flavor breaking effects, classified into three aspects: phase space differences, spectator quarks, and overlappings of the transited quarks. In particular, we show that the breaking effects are dominated by the phase space differences, which can be as large as 25\%. Explicitly, we find that $\Gamma(\Xi_{cc}^{++} \to \Lambda_c ^+ e^+ \nu _e) V_{cs}^2/\Gamma(\Xi_{cc}^{++} \to \Xi_c ^+ e^+ \nu_e )V_{cd}^2 = 1.24$, which is expected as $1$ under the exact $SU(3)$ flavor symmetry.

Improvement of q 2 Resolution in Semileptonic Decays Based on Machine Learning

The neutrino closure method is often used to obtain kinematics of semileptonic decays with one unreconstructed particle in hadron collider experiments. The kinematics of decays can be deducted by a twofold ambiguity with a quadratic equation. To resolve the twofold ambiguity, a novel method based on machine learning (ML) is proposed. We study the effect of different sets of features and regressors on the improvement of reconstructed invariant mass squared of ℓ ν system ( q 2 ). The result shows that the best performance is obtained by using the flight vector as the features and the multilayer perceptron (MLP) model as the regressor. Compared with the random choice, the MLP model improves the resolution of reconstructed q 2 by ~40%. Furthermore, the possibility of using this method on various semileptonic decays is shown.

Prospects for Higgs boson and new scalar resonant production searches in ttbb final state at the LHC

In this article we probe resonant associated production of a Standard Model Higgs boson with new heavy scalar resonance in proton-proton collisions at a center-of-mass energy s=13 TeV. The Higgs boson and new scalar resonant are required to decay into a pair of bottom quarks and a pair of top quarks, respectively. Semileptonic decay of top quarks is considered. The searches are projected into operation conditions of the Large Hadron Collider during Run II data taking period at a center-of-mass energy of 13 TeV using Monte Carlo generated events, realistic detector response simulation and available Open Data samples. Analysis strategies are presented and machine learning approach using Deep Neural Network is proposed to resolve ambiguous in jets assignment and improve kinematic reconstruction of signal events. Sensitivity of the CMS detector is estimated as 95% expected upper limits on the product of the production cross section and the branching fractions of the searched particles.

Averages of b -hadron, c -hadron, and τ -lepton properties as of 2021

This paper reports world averages of measurements of b-hadron, c-hadron, and τ-lepton properties obtained by the Heavy Flavor Averaging Group using results available before April 2021. In rare cases, significant results obtained several months later are also used. 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, CP violation parameters, parameters of semileptonic decays, and Cabibbo-Kobayashi-Maskawa matrix elements.97 MoreReceived 25 June 2022Accepted 20 September 2022DOI:https://doi.org/10.1103/PhysRevD.107.052008Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBound statesChiral perturbation theoryElectroweak interactionFlavor changing neutral currentsForm factorsHadron mixingLattice QCDParticle decaysParticle interactionsParticle mixing & oscillationsQuark mixingParticles & Fields

Lepton mass correction in partial wave analyses of charmed meson semi-leptonic decays* *HZ and BCK were supported in part by the Joint Large-Scale Scientific Facility Fund of the National Natural Science Foundation of China (NSFC) (11875054, 12192263) and the Chinese Academy of Sciences (U2032104); YY was supported in part by the NSFC (11905023, 12047564, 12147102), the Natural Science Foundation of

We derive a parameterization formula for the partial wave analyses of charmed meson semi-leptonic decays while considering the effects of lepton mass. Because the proposed super-tau-charm factory will reach a significantly enhanced luminosity and BESIII is collecting new data, our results will help improve the measurement precision of future partial wave analyses of charmed meson semi-muonic decays.

Semileptonic Bc decays to P-wave charmonia in the light-cone QCDSR

Bc mesons are laboratories for probing heavy quark physics. Furthermore, they decay into charmonia and hence their decays can be used to analyze possible exotic charmonium. In this work, the semileptonic decays of Bc mesons into P wave charmonia are analysed using light cone QCD sum rules (LCSR). The distributions amplitudes for the charmonia are taken from a quark model computation. The obtained decay rates for the ground state and excited charmonia are compared with the results found in the literature.

Prediction for the Anomalous ZZZ and ZZγ Couplings via two Z-boson Production at the CLIC

The non-Abelian nature of the Standard Model (SM) entails the existence of the gauge bosons' self-interactions. The gauge bosons' self-interactions are important to test the SM and see the new physics effects. These effects can be analyzed in the effective theory approach which is the main aim of this study. We examine the ZZZ and ZZγ anomalous neutral triple gauge couplings (aNTGC) via the process e^- e^+→ZZ with both unpolarized and polarized electron beam with the √s=3 TeV at CLIC. In the final state, semi-leptonic decay of Z-bosons (Z→jj , Z→ν_l (ν_l ) ̅ ) are considered. We focused on CP-violating C_BB/Λ^4 , C_BW/Λ^4 , C_WW/Λ^4 and CP-conserving C_(B ̅W)/Λ^4 couplings. The sensitivities are obtained at 95% Confidence Level with luminosities of L_int=5 ab-1, L_int=1 ab-1 and L_int=4 ab-1 for unpolarized, 80% and -80% polarized electron beams, respectively. Obtained sensitivities on anomalous couplings are 3-20 times stringent than the current experimental limits and comparable with the related phenomenological studies in the literature.

NLO QCD corrections to polarized diboson production in semileptonic final states

Understanding the polarization structure and providing precise predictions for multiboson processes at the LHC is becoming urgent in the light of the upcoming run-3 and high-luminosity data. The CMS and ATLAS collaborations have already started using polarized predictions to perform template fits of the data, getting access to the polarization of W and Z bosons. So far, only fully leptonic decay channels have been considered in this perspective. The natural step forward is the investigation of hadronic decays of electroweak bosons. In this work, we compute NLO QCD corrections to the production and decay of WZ pairs at the LHC in final states with two charged leptons and jets. The calculation relies on the double-pole approximation and the separation of polarized states at the level of Standard Model amplitudes. The presented NLO-accurate results are necessary building blocks for a broad understanding and precise modeling of polarized diboson production in semileptonic decay channels.

New approach to semileptonic tags in B -meson semi-invisible decays

Kinematic variables designed for pairwise decays to partly undetected final states -- a prominent example being $M_{T2}$ and its Lorentz-invariant version $M_2$ -- have been extensively deployed in high-$p_T$ collider searches. A new range of potential applications at flavour facilities -- where $B$ mesons or $\tau$ leptons are also pairwise produced -- was recently proposed. One general challenge in these decays arises if both the signal parent and the 'other' parent, often used as a tag, decay semi-invisibly. In such cases, which notably include semi-leptonic tags, signal identification is generally hindered by the ensuing lack of knowledge of the signal-parent boost. $M_2$ helps precisely to overcome this challenge, and allows to leverage the otherwise superior efficiency of semi-leptonic decays. Our strategy rests on two novel constraints that can be imposed on $M_2$. The first is that of the known mass of the decaying-parent mass squared which, in connection with other constraints, gives rise to $M_{2sB}$. The second is on the flight direction of the signal parent, often well reconstructed at facilities with high vertexing capabilities such as Belle II and LHCb. This constraint gives rise to the $M_{2V}$ variable, that can be used even at facilities where the collision energy is not known. We test these ideas in a decay of great current interest in the context of the persistent discrepancies in $B$ decays, namely $B \to K \tau \mu$. We find that a bare-bones application of $M_{2sB}$ leads, alone, to an improvement that is already halfway between the current approach and the "truth-level" semi-leptonic case. Ceteris paribus -- in particular statistics -- our approach thus makes semi-leptonic tags competitive with fully reconstructed hadronic tags.

Semileptonic decays of doubly charmed baryons with [formula omitted] mixing

We study the Ξc−Ξc′ mixing effects in the semileptonic decays the doubly charm baryons of Ξcc. We focus on the ratio of R(θc)≡B(Ξcc→Ξc′e+νe)/B(Ξcc→Ξce+νe) and find that (R(θ0),R(−θ0))=(0.46±0.01,7.33±0.23) with θ0=0.137π, which are in sharp contrast to R(0)=2.15±0.11 without the mixing. The ratio is enhanced (suppressed) by a factor of four for a negative (positive) θc. In addition, the polarization asymmetries of Ξc(′) are found to be α(−θ0)=0.32(−0.76) and α(θ0)=−0.82(−0.38). As R and α are highly sensitive to θc and unaffected by the W-exchange contributions, they provide excellent opportunities to determine θc in the ongoing experiments.

Revisiting D-meson twist-2, 3 distribution amplitudes* *Supported in part by the National Natural Science Foundation of China (12265009, 12265010), the Project of Guizhou Provincial Department of Science and Technology (ZK[2021]024, ZK[2023]142), the Project of Guizhou Provincial Department of Education (KY[2021]030) and the Chongqing Graduate Research and Innovation Foundation (ydstd1912)

Owing to the significant difference between the experimental measurements and the theoretical predictions of the standard model (SM) for the value of of the semileptonic decay , researchers speculate that this decay may be evidence of new physics beyond the SM. Usually, the D-meson twist-2, 3 distribution amplitudes (DAs) , , and are the main error sources when perturbative QCD factorization and light-cone QCD sum rules are used to study . Therefore, it is important to obtain more reasonable and accurate behaviors for these DAs. Motivated by our previous work [Phys. Rev. D 104, no.1, 016021 (2021)] on pionic leading-twist DA, we revisit D-meson twist-2, 3 DAs , , and . New sum rule formulae for the -moments of these three DAs are suggested for obtaining more accurate values. The light-cone harmonic oscillator models for the DAs are improved, and their parameters are determined by fitting the values of ξ -moments via the least squares method.

A Light Shed on Lepton Flavor Universality in B Decays

Behind succeeding measurements of anomalies in semileptonic decays at LHCb and several collider experiments hinting at the possible violation of lepton flavor universality, we undertake a concise review of theoretical foundations of the tree- and loop-level b-hadron decays, b→clνl and b→sl+l− along with experimental environments. We revisit the world averages for RD(D*), RK(K*), RJ/ψ, and Rηc, for the semileptonic transitions and provide results within the framework of the relativistic independent quark model in addition to the results from model-independent studies. If the ongoing evaluation of the data of LHC Run 2 confirms the measurements of Run 1, then the statistical significance of the effect in each decay channel is likely to reach 5 σ. A confirmation of these measurements would soon turn out to be the first remarkable observation of physics beyond the Standard Model, providing a wider outlook on the understanding of new physics.