Semileptonic Processes Research Articles

Inclusive B¯→Xsℓ+ℓ−\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\overline{B}\ o {X}_s{\\ell}^{+}{\\ell}^{-} $$\\end{document} with a hadronic mass cut

The hadronic mass spectrum of inclusive B¯→Xsℓ+ℓ−\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\overline{B}\ o {X}_s{\\ell}^{+}{\\ell}^{-} $$\\end{document} is investigated at next to leading order in the heavy quark expansion. For mild cuts on the hadronic mass, the expansion, which applies when the cut is released, remains convergent. However, the cuts used at BaBar and Belle to reduce backgrounds from charged current semileptonic processes are too severe for a description in terms of matrix elements of local operators to apply. Strategies for interpolating between the two regions are discussed.

Significance of the negative binomial distribution in multiplicity phenomena

The negative binomial distribution (NBD) has been theorized to express a scale-invariant property of many-body systems and has been consistently shown to outperform other statistical models in both describing the multiplicity of quantum-scale events in particle collision experiments and predicting the prevalence of cosmological observables, such as the number of galaxies in a region of space. Despite its widespread applicability and empirical success in these contexts, a theoretical justification for the NBD from first principles has remained elusive for fifty years. The accuracy of the NBD in modeling hadronic, leptonic, and semileptonic processes is suggestive of a highly general principle, which is yet to be understood. This study demonstrates that a statistical event of the NBD can in fact be derived in a general context via the dynamical equations of a canonical ensemble of particles in Minkowski space. These results describe a fundamental feature of many-body systems that is consistent with data from the ALICE and ATLAS experiments and provides an explanation for the emergence of the NBD in these multiplicity observations. Two methods are used to derive this correspondence: the Feynman path integral and a hypersurface parametrization of a propagating ensemble.

Lepton Flavour Universality tests in b → clν decays at LHCb

The Standard Model predicts that the electroweak couplings to the three charged leptons are identical. However, in the last decade, experimental measurements have suggested that semileptonic processes involving taus could have a slightly enhanced decay rate compared to their muonic counterparts. If confirmed, this would be an unambiguous sign of New Physics, with various scenarios introducing additional interactions that couple preferentially to the third generation. Two recent lepton universality tests performed at LHCb are presented in these proceedings of the first edition of the New Frontiers in Lepton Flavour workshop.

HighPT: A tool for high-pT Drell-Yan tails beyond the standard model

HighPT is a Mathematica package for the analysis of high-energy data of semileptonic transitions at hadron colliders. It allows to compute high-pT tail observables for semileptonic processes, i.e. Drell-Yan cross sections, for dilepton and monolepton final states at the LHC. These observables can be calculated at tree level within the Standard Model Effective Field Theory, including the relevant operators up to dimension eight to ensure a consistent description of the cross section including terms of O(Λ−4) in the cutoff scale Λ. For New Physics models with new mediators that can be resolved at LHC energies, HighPT can also account for the full propagation effects of these new bosonic states at tree level. Using the available data from the high-pT tails in the relevant LHC run-II searches by the ATLAS and CMS collaborations, HighPT can also construct the corresponding likelihoods for all possible flavors of the leptonic final states. As an illustration, we derive and compare constraints on Wilson coefficients at different orders in the Effective Field Theory expansion, and we investigate lepton flavor violation for the S3 leptoquark model. The HighPT code is publicly available at ▪. Program summaryProgram title:HighPTCPC Library link to program files:https://doi.org/10.17632/zh5yx6j4xj.1Developer's repository link:https://github.com/HighPT/HighPTLicensing provisions: MIT licenseProgramming language: MathematicaNature of problem: Constraining New Physics scenarios with high-pT Drell-Yan data.Solution method: We present the first tool allowing to extract bounds, computed at leading order, on semileptonic transitions in the Standard Model Effective Field Theory, including operators up to dimension eight, and in explicit New Physics models.

Electron Capture on Nuclei in Stellar Environment

The stellar electron capture on nuclei is an essential, semi-leptonic process that is especially significant in the central environment of core-collapse supernovae and in the explosive stellar nucleosynthesis. In this article, on the basis of the original (absolute) electron-capture cross-sections under laboratory conditions that we computed in our previous work for a set of medium-weight nuclear isotopes, we extend this study and evaluate folded e−-capture rates in the stellar environment. With this aim, we assume that the parent nuclei and the projectile electrons interact when they are in the deep stellar interior during the late stages of the evolution of massive stars. Under these conditions (high matter densities and high temperatures of the pre-supernova and core-collapse supernova phases), we choose two categories of nuclei; the first includes the 48Ti and 56Fe isotopes that have A<65 and belong to the iron group of nuclei, and the second includes the heavier and more neutron-rich isotopes 66Zn and 90Zr (with A>65). In the former, the electron capture takes place mostly during the pre-supernova stage, while the latter occurs during the core-collapse supernova phase. A comparison with previous calculations, which were obtained by using various microscopic nuclear models employed for single-charge exchange nuclear reactions, is also included.

Leptonic and semi-leptonic neutrino interactions with muons in proto-neutron star cooling

Abstract It is known that muons are scarce just after the birth of a proto-neutron star via a supernova explosion, but get more abundant as the proto-neutron star cools via neutrino emissions on the Kelvin–Helmholtz timescale. We evaluate all the relevant rates of the neutrino interactions with muons at different times in the proto-neutron star cooling. We are particularly interested in the late phase ($t \gtrsim 10 \operatorname{s}$), which will be accessible in the next Galactic supernova but has not been studied well so far. We calculate both leptonic and semi-leptonic processes, for the latter of which we also pay attention to the form factors with their dependence on the transferred momentum as well as to the modification of the dispersion relations for nucleons on the mean field level. We find that the flavor-exchange reactions νe + μ− → νμ + e− and $\bar{\nu }_{\mu } + \mu ^- \rightarrow \bar{\nu }_e + e^-$ can be dominant, particularly at low energies, over the capture of νe on neutron and the scatterings of $\bar{\nu }_{\mu }$ on nucleons as the opacity sources for these species, and that the inverse muon decay $\bar{\nu }_e + \nu _{\mu } + e^- \leftrightarrows \mu ^-$ can overwhelm the scatterings of $\bar{\nu }_e$ and νμ on nucleons again at low energies. At high energies, on the other hand, the corrections in the semi-leptonic processes mentioned above are more important. We also show the non-trivial energy and angular dependencies of the flavor-exchange reactions and the inverse muon decay. In the study of the diffusion coefficients from these reactions, we find that $\bar{\nu }_{\mu }$ is most affected. These pieces of information are indispensable for numerical computations and the interpretation of their results for proto-neutron star cooling, particularly at the very late phase.

Charged-current muonic reactions in core-collapse supernovae

The steady advance in core-collapse supernova simulations requires a more precise description of neutrino processes in hot and dense matter. In this work, we study the rates of charged-current (CC) weak processes with (anti)muons in supernova matter. At the relativistic mean field level, we derive results for the rates of CC neutrino-nucleon reactions, taking into account full kinematics, weak magnetism and pseudoscalar terms, and $q^2$-dependent nucleon form factors in the hadronic current. In addition to muonic semileptonic processes we also consider purely leptonic processes. In particular, we show that inverse muon decay can dominate the opacities for low energy $\nu_\mu$ and $\bar\nu_e$ at densities $\gtrsim 10^{13}~\rm{g~ cm^{-3}}$.

New parametrization of the form factors in B¯→Dℓν¯ℓ decays

A new model-independent parametrization is proposed for the hadronic form factors in the semileptonic $\bar{B}\to D\ell\bar{\nu}_\ell$ decay. By a combined consideration of the recent experimental and lattice QCD data, we determine precisely the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|=41.01(75)\times 10^{-3}$ and the ratio $\mathcal{R}_D=\frac{\mathcal{BR}(\bar{B}\to D \tau \bar{\nu}_\tau)}{\mathcal{BR}(\bar{B}\to D \ell \bar{\nu}_\ell)}=0.301(5)$. The coefficients in this parametrization, related to phase shifts by sumrulelike dispersion relations and hence called phase moments, encode important scattering information of the $\bar{B}\bar{D}$ interactions which are poorly known so far. Thus, we give strong hints about the existence of at least one bound and one virtual $\bar B \bar D$ $S$-wave $0^+$ states, subject to uncertainties produced by potentially sizable inelastic effects. This formalism is also applicable for any other semileptonic processes induced by the weak $b\to c$ transition.

Light-cone sum rules analysis of Xi _{QQ^{prime }}rightarrow Sigma _{Q^{prime }} weak decays

As a continuation of our previous work, we investigate the weak decays of doubly-heavy baryons Xi _{QQ^{prime }} into sextet Sigma _{Q^{prime }} with light-cone sum rules. We calculate the form factors for these decays with the parallel light-cone distribution amplitudes of Sigma _{Q^{prime }}. Numerical results of these form factors are used to predict the decay widths and branching ratios of the corresponding semi-leptonic processes. Parametric uncertainties and theoretical analyses are also given in detail. We find that the decay widths of Xi _{cc} and Xi _{bc} decays are several orders of magnitude larger than those of Xi _{bb} decays.

Deformed Hartree-Fock calculations for semileptonic processes in nuclei

In nuclear structure calculations, the Deformed Hartree-Fock (DHF) provides generally a good description for the low-lying spectroscopic properties of odd-even, odd-odd and even-even nuclear systems of which the consideration of the deformation is motivated by many reasons. The common random phase approximations (RPA, QRPA, etc.) mostly used to accurately evaluate the transition matrix elements in many nuclear processes [1,2], are appropriate for only spherical even-even nuclear systems even though, sometimes, isotopes considered as rather deformed are studied. In the present work, we discuss the treatment within the DHF method of nuclei in the region A = 70 — 80. This region includes isotopes (like 72Ge, 76Ge, 72Se, etc) interesting for studying many nuclear processes as the ,0/3-decay, scattering of dark matter candidates off nuclei, μ~ —> e± conversions in nuclei. In our calculations the model space comprises 1P3/2, 0f5/2, 1pi/2 and 0p9/2 single particle Orbitals assuming 56Ni to be the inert core. The effective interaction employed, has been quite successfully used previously to describe many important features of the nuclei in this region. The lowest prolate Hartree-Fock single particle spectrum of some isotopes (72Ge, 76Ge) has been used to test the good angular momentum states which in this method are projected out from the intrinsic HF states. As an application, we examine the predictions of DHF for the exotic (μ~,ε~) conversion process. The contributions of all basic μ~ —> e~ operators originating from a general effective Lagrangian [2] are compared with those of normal QRPA methods obtained previously.

Decay modes of the scalar exotic meson Tbs;u¯d¯−

We investigate the semileptonic decay of the scalar tetraquark $T_{bs; \overline{u}\overline{d}}^{-}$ to final state $T_{cs;\overline{u}\overline{d} }^{0} l \overline{\nu}_l$, which proceeds due to the weak transition $b \to c l \overline{\nu}_l$. For these purposes, we calculate the spectroscopic parameters of the final-state scalar tetraquark $T_{cs;\overline{u}\overline{ d}}^{0}$. In calculations we use the QCD sum rule method by taking into account the quark, gluon, and mixed condensates up to dimension 10. The mass of the $T_{cs;\overline{u}\overline{d}}^{0}$ obtained in the present work $( 2878 \pm 128 )~\mathrm{MeV}$ indicates that it is unstable against the strong interactions, and can decay to the mesons $D^{0}\overline{K}^{0}$ and $D^{+}K^{-}$. Partial widths of these $S$-wave modes as well as the full width of the tetraquark $T_{cs;\overline{u}\overline{d}}^{0}$ are found by means of the QCD light-cone sum rule method and technical tools of the soft-meson approximation. The partial widths of the main semileptonic processes $T_{bs;\overline{u}\overline{d}}^{-} \to T_{cs;\overline{u} \overline{d}}^{0}l\overline{\nu}_l$, $l=e, \mu$, and $\tau$ are computed by employing the weak form factors $G_{1}(q^2)$ and $G_{2}(q^2)$, which are extracted from the QCD three-point sum rules. We also trace back the weak transformations of the stable tetraquark $T_{bb;\overline{u}\overline{d} }^{-} $ to conventional mesons. The obtained results for the full width $ \Gamma_{\mathrm{full}}=(3.28\pm 0.60) \times 10^{-10}~\mathrm{MeV} $ and mean lifetime $\tau=2.01_{-0.31}^{+0.44}~\mathrm{ps}$ of $T_{bs;\overline{u} \overline{d}}^{-}$, as well as predictions for decay channels of the tetraquark $T_{bb;\overline{u}\overline{d}}^{-}$ can be used in experimental studies of these exotic states. \end{abstract}

Thermal quasiparticle random-phase approximation calculations of stellar electron capture rates with the Skyrme effective interaction

A microscopic thermodynamically consistent approach is applied to compute electron capture (EC) rates and cross sections on nuclei in hot stellar environments. The cross section calculations are based on the Donnelly-Walecka multipole expansion method for treatment of semi-leptonic processes in nuclei. To take into account thermal effects, we express the electron capture cross section in terms of temperature- and momentum-dependent spectral functions for respective multipole charge-changing operators. The spectral functions are computed by employing the self-consistent thermal quasiparticle RPA (TQRPA) with the Skyrme effective interaction. Three different Skyrme parametrizations (SkM$^*$, SGII and SLy4) are used to investigate thermal effects on EC for $^{56}$Fe and $^{78}$Ni. For $^{56}$Fe, the impact of thermally unblocked GT$_+$ transitions on EC is discussed and the results are compared with those from shell-model calculations. In particular, it is shown that for some temperature and density regimes the TQRPA rates exceed the shell-model rates due to violation of the Brink-Axel hypothesis within the TQRPA. For neutron-rich $^{78}$Ni the full momentum-dependence of multipole transition operators is considered and it is found that not only thermally unblocked allowed $1^+$ transitions but also thermally unblocked first-forbidden $1^-$ and $2^-$ transitions favour EC.

Semileptonic and nonleptonic weak decays of Λb0

The recent experimental developments require a more precise theoretical study of weak decays of heavy baryon $\Lambda_b^0$. In this work, we provide an updated and systematic analysis of both the semi-leptonic and nonleptonic decays of $\Lambda^0_b$ into baryons $\Lambda^+_c$, $\Lambda$, $p$, and $n$. The diquark approximation is adopted so that the methods developed in the $B$ meson system can be extended into the baryon system. The baryon-to-baryon transition form factors are calculated in the framework of a covariant light-front quark model. The form factors $f_3, ~g_3$ can be extracted and are found to be non-negligible. The semi-leptonic processes of $\Lambda^0_b\to \Lambda^+_c(p)l^-\bar\nu_l$ are calculated and the results are consistent with the experiment. We study the non-leptonic processes within the QCD factorization approach. The decay amplitudes are calculated at the next-to-leading order in strong coupling constant $\alpha_s$. We calculate the non-leptonic decays of $\Lambda^0_b$ into a baryon and a s-wave meson (pseudoscalar or vector) including 44 processes in total. The branching ratios and direct CP asymmetries are predicted. The numerical results are compared to the experimental data and those in the other theoretical approaches. Our results show validity of the diquark approximation and application of QCD factorization approach into the heavy baryon system.

Looking for new physics via semi-leptonic and leptonic rare decays of D and Ds**Supported by National Natural Science Foundation of China (11675082, 11375128, 11405046) and Special Grant of the Xuzhou University of Technology (XKY2016211)

It is well recognized that looking for new physics at lower energy colliders is a path which is complementary to high energy machines such as the LHC. Using the large volume of data collected by BESIII, we may have a unique opportunity to tackle this. In this paper we calculate the branching ratios of the semi-leptonic processes and , and the leptonic processes D0→e−e+ and D0→e−μ+, in the frameworks of the U(1)′ model, 2HDM and unparticle model. It is found that both the U(1)′ model and 2HDM may influence the semi-leptonic decay rates, but only the U(1)′ model offers substantial contributions to the pure leptonic decays, and the resultant branching ratio of D0→e−μ+ can be as large as 10−7∼10−8. This might be observed at the future super τ-charm factory.

Neutrino-nucleus scattering offXe136

Background: Theoretical estimates of the cross sections for the neutrino-nucleus scattering off relevant nuclei for supernova neutrinos are essential for many applications in neutrino physics and astrophysics. The double-$\ensuremath{\beta}$-decaying nucleus $^{136}\mathrm{Xe}$ nucleus is used by the EXO Collaboration in the search for neutrinoless double-$\ensuremath{\beta}$ decay. A ton-scale experiment based on $^{136}\mathrm{Xe}$ could also be used for studies of supernova neutrinos and/or solar neutrinos.Purpose: The purpose of the present work is, thus, to perform a study of the charged-current and neutral-current nuclear responses to supernova neutrinos for $^{136}\mathrm{Xe}$.Method: The cross sections are computed by using the well-established framework for studies of semileptonic processes in nuclei introduced by O'Connell, Donnelly, and Walecka [Phys. Rev. C 6, 719 (1972)]. The nuclear wave functions of the initial and the final nuclear states for the neutral-current neutrino-nucleus scattering in $^{136}\mathrm{Xe}$ are computed by using the quasiparticle random-phase approximation (QRPA). Similarly, the pnQRPA is adopted to construct the initial and final nuclear states which are relevant for the charged-current reactions. The nuclear responses to supernova neutrinos are subsequently computed by folding the cross sections with appropriate energy spectra for the incoming neutrinos.Results: We present results for the cross sections of the charged-current and neutral-current neutrino and antineutrino scatterings off $^{136}\mathrm{Xe}$. Nuclear responses to supernova neutrinos are also given. For the considered scenario for the neutrino mixing we have found that neutrino interactions with matter and so-called collective neutrino oscillations enhance significantly the neutrino and antineutrino flux-averaged cross sections.Conclusions: We have found that for the charged-current and neutral-current neutrino scatterings off $^{136}\mathrm{Xe}$ transitions mediated by the ${1}^{+}$ multipole are the most important ones. However, for the charged-current antineutrino channel ${0}^{+}$ and ${1}^{+}$ transitions are largely suppressed due to the large neutron excess. Transitions to ${1}^{\ensuremath{-}}$ and ${2}^{\ensuremath{-}}$ final nuclear states are thus relatively more important for the charged-current antineutrino scattering.

Exploration of Lorentz violation in neutral-kaon decay

The KLOE Collaboration recently reported bounds on the directional dependence of the lifetime of the short-lived neutral kaon KS0 with respect to the dipole anisotropy of the cosmic microwave background. We interpret their results in an effective field theory framework developed to probe the violation of Lorentz invariance in the weak interaction and previously applied to semileptonic processes, in particular β decay. In this approach a general Lorentz-violating tensor χμν is added to the standard propagator of the W boson. We perform an exploratory study of the prospects to search for Lorentz violation in nonleptonic decays. For the kaon, we find that the sensitivity to Lorentz violation is limited by the velocity of the kaons and by the extent to which hadronic effects can be calculated. In a simple model we derive the KS0 decay rate and calculate the asymmetry for the lifetime. Using the KLOE data, limits on the values of χμν are determined.

Determination of the pion distribution amplitude

Right now, we have not enough knowledge to determine the hadron distribution amplitudes (DAs) which are universal physical quantities in the high energy processes involving hadron for applying pQCD to exclusive processes. Even for the simplest pion, one can't discriminate from different DA models. Inversely, one expects that processes involving pion can in principle provide strong constraints on the pion DA. For example, the pion-photon transition form factor (TFF) can get accurate information of the pion wave function or DA, due to the single pion in this process. However, the data from Belle and BABAR have a big difference on TFF in high $Q^2$ regions, at present, they are helpless for determining the pion DA. At the present paper, we think it is still possible to determine the pion DA as long as we perform a combined analysis of the most existing data of the processes involving pion such as $\pi \to \mu \bar{\nu}$, $\pi^0 \to \gamma \gamma$, $B\to \pi l \nu$, $D \to \pi l \nu$, and etc. Based on the revised light-cone harmonic oscillator model, a convenient DA model has been suggested, whose parameter $B$ which dominates its longitudinal behavior for $\phi_{\pi}(x,\mu^2)$ can be determined in a definite range by those processes. A light-cone sum rule analysis of the semi-leptonic processes $B \to \pi l \nu$ and $D \to \pi l \nu$ leads to a narrow region $B = [0.01,0.14]$, which indicate a slight deviation from the asymptotic DA. Then, one can predict the behavior of the pion-photon TFF in high $Q^2$ regions which can be tested in the future experiments. Following this way it provides the possibility that the pion DA will be determined by the global fit finally.

Investigation of the semileptonic weak decays of B (s) to S (Scalar Meson) via light-cone QCD sum rules

In this paper, the semileptonic weak decay process of B(s) → S scalar mesons is investigated by using the light-cone QCD sum rules (LCSR) in the nonperturbative part. The corresponding transition matrix elements leading to form factors and the branching ratio of this process are determined.

Charged-current neutrino-nucleus scattering off95,97Mo

Background: Reliable cross sections for the neutrino-nucleus scattering off relevant nuclei for supernova neutrinos are essential for various applications in neutrino physics and astrophysics (e.g., supernova mechanisms). Studies of the nuclear responses for the stable molybdenum isotopes are of great interest for the planned MOON (Mo Observatory of Neutrinos) experiment.Purpose: The purpose of the present work is, thus, to perform a detailed study of the charged-current nuclear responses to supernova neutrinos for the stable odd molybdenum isotopes. A special effort will be devoted to discuss in detail the structures of the most relevant final states in the corresponding proton-odd nucleus.Method: The cross sections are computed by using the well-established framework for studies of semileptonic processes in nuclei developed by Donnelly and Walecka. The nuclear wave functions of the initial and the final nuclear states are computed by using the microscopic quasiparticle-phonon model. The nuclear responses to supernova neutrinos are subsequently estimated by folding the cross sections with realistic energy profiles for the incoming neutrinos.Results: We present results for the cross sections of the charged-current neutrino and antineutrino scatterings off ${}^{95}\text{Mo}$ and ${}^{97}\text{Mo}$. Nuclear responses to supernova neutrinos (both nonoscillating and oscillating ones) are also given. The inclusion of neutrino oscillations enhances significantly the neutrino and antineutrino cross sections.Conclusions: We have found that the most important transitions are the Gamow-Teller--like ones which are mediated by the ${1}^{+}$ multipole. Furthermore, the three-quasiparticle degrees of freedom are essential in order to describe quantitatively the neutrino-nucleus scattering off odd open-shell nuclei.

Bulk viscosity in the nonlinear and anharmonic regimes of strange quark matter

The bulk viscosity of cold, dense three-flavor quark matter is studied as a function of temperature and the amplitude of density oscillations. The study is extended to the case of two different types of anharmonic oscillations of density. We point out several qualitative effects due to the anharmonicity, although quantitatively they appear to be relatively small. We found that, in most regions of the parameter space, except for very large amplitudes of density oscillations (i.e. 10% and above), nonlinear effects and anharmonicity have a small effect on the interplay of the nonleptonic and semileptonic processes in the bulk viscosity.