We revisited the extracting $\left|V_{ub}/V_{cb}\right|$ and $|V_{ub}|$ through calculating the ratios ${\cal B}(B^0\to D_s^{(*)+}(π^-,ρ^-)/ {\cal B}(B^0\to D_s^{(*)+} D^{(*)-})$ in the perturbative QCD approach, which is regarded as an effective theory in dealing with non-leptonic charmed $B$ decays. Utilizing this approach, we could calculate the form factors effectively as well as non-factorizable and annihilation contributions. Within the updated distribution amplitudes and the latest experimental data, we get $\left|{V_{ub}}/{V_{cb}}\right|=0.083\pm0.007$, which favors a bit smaller $|V_{ub}|$ compared with the averaged PDG value, but agrees well the exclusively measured values. Furthermore, we predict the branching ratio of $\bar B^0 \to D_s^-ρ^+$ $\sim$ $(2.7\pm 1.2)\times 10^{-5}$, which could be measured in $B$ factories near future. In our calculation, the major uncertainty is due to our poor knowledge of heavy meson wave functions. We also comment that it is not trivial to generalize this approach to $B_s$ system, primarily because both $\bar B_s^0 $ and $B_s^0$ can decay into the same final states $D_s^+K^-$ and $D_s^+D_s^-$.
In the preprint arXiv:2110.08210, some comments on our paper recently published in JHEP \textbf{09} (2021) 053 have been made. Since some of the comments are completely wrong and others are quite misleading, we decide to clarify the relevant issues in a formal reply. First of all, nothing is wrong about our calculations and physical results in the original paper. Second, there is no logical gap to fill at all. The fact that the $N$-dimensional unitary group over the field of complex numbers ${\rm U}(N,\mathbb{C})$ is not a linear algebraic group is actually irrelevant for the validity of the M…
We discuss the impact of the soft degrees of freedom inside the B_c meson on its rate in the semi-leptonic decay B_c -> X l nu_l where X denotes light hadrons below the D^0 threshold. In particular we identify contributions involving soft hadrons which are non-vanishing in the limit of massless leptons. These contributions become relevant for a measurement of the purely leptonic B_c decay rate, which due to helicity suppression involves a factor m_l^2 and thus is much smaller than the contributions involving soft hadrons.
We present a new determination of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{\rm cb}|$ by using the three-loop perturbative QCD corrections for the $B\to D^{\ast}$ semi-leptonic decay. The decay width of $B\to D^{\ast}$ semi-leptonic decay can be factorized as perturbatively calculable short-distance part and the non-perturbative but universal long-distance part. We adopt the principle of maximum conformality (PMC) single-scale setting approach to deal with the perturbative series so as to achieve a precise fixed-order prediction for the short-distance parameter $η_{A}$. By applying the…
We review a lattice strategy how to non-perturbatively determine the coefficients in the HQET expansion of all components of the heavy-light axial and vector currents, including 1/m_h-corrections. We also discuss recent preliminary results on the form factors parameterizing semi-leptonic B-decays at the leading order in 1/m_h.
We respectfully reply to Wang et al.'s reply to our comment to their [JHEP $\textbf{09}$ (2021) 053]. Some more subtleties and details are discussed for hopefully better clarification and understanding, especially about the conditions in Hilbert's finiteness theorem. We also disprove Wang et al.'s incorrect assertion in their reply [arXiv:2110.13865 [hep-ph]] that there is an isomorphism between ${\rm U}(n,\mathbb{C})$ and ${\rm GL}(n,\mathbb{C})$. We give two proofs for our argument. One proof is in the context of Lie group for arbitrary positive integer $n$, and the other proof is in the con…
With the recent completion of NNNLO results, the perturbative description of the $Υ$ system has reached a very high level of sophistication. We consider the non-perturbative corrections as an expansion in terms of local condensates, following the approach pioneered by Voloshin and Leutwyler. The leading order corrections up to dimension eight and the potential NLO corrections at dimension four are computed and given in analytical form. We then study the convergence of the expansion for the masses, the leptonic decay rates and the non-relativistic moments of the $Υ$ system. We demonstrate that …
We examine the applicability of perturbative QCD to $B$ meson decays into $D$ mesons. We find that the perturbative QCD formalism, which includes Sudakov effects at intermediate energy scales, is applicable to the semi-leptonic decay $B\to D lν$, when the $D$ meson recoils fast. Following this conclusion, we analyze the two-body non-leptonic decays $B\to Dπ$ and $B\to DD_s$. By comparing our predictions with experimental data, we extract the matrix element $|V_{cb}|=0.044$.
The inclusive spectra of radiative and semi-leptonic B-meson decays near the endpoint is computed taking into account renormalons in the Sudakov exponent (Dressed Gluon Exponentiation). In this framework we demonstrate the factorization of decay spectra into hard, jet and soft functions and discuss the universality of the latter two. Going beyond perturbation theory the soft function, which we identify as the longitudinal momentum distribution in an on-shell b quark, is replaced by the b-quark distribution in the B meson. The two differ by power corrections. We show how the resummation of runn…
The QCD radiative corrections to the leptonic decay rate of the $B_c$ meson are calculated using the formalism of nonrelativistic QCD (NRQCD) to separate short-distance and long-distance effects. The $B_c$ decay constant is factored into a sum of NRQCD matrix elements each multiplied by a short-distance coefficient. The short-distance coefficient for the leading matrix element is calculated to order $α_s$ by matching a perturbative calculation in full QCD with the corresponding perturbative calculation in NRQCD. This short-distance correction decreases the leptonic decay rate by approximately …
We present results for two-loop QCD corrections to the short distance coefficient that governs leptonic decay of Bc-meson. After brief discussion of the technics of asymptotic threshold expansion used to perform this calculation, we give comments on the numerical value of two-loop corrections and its impact on NRQCD description of Bc-meson bound state dynamics.
This work is devoted to the study of the non-perturbative contributions in non-leptonic hyperon decays. We show that the instanton-induced 't Hooft interaction can naturally explain the Delta I=1/2 rule, by generating quark-diquark clustering inside octet baryons. We compute P-wave and S-wave amplitudes in the Instanton Liquid Model (ILM), and find good agreement with experiment. We propose a model-independent procedure to test on the lattice if the leading quark-quark attraction in the 0^+ anti-triplet channel responsible for diquark structures in hadrons is originated by the interaction gene…
We point out some serious problems in the investigation of Kundu et al. which claims agreement with the existing data of the proton form factor, calculated without taking into account the intrinsic k_{perp}-dependence of the proton wave function.
We study the semi-leptonic and non-leptonic $B$ weak decays which are governed by the $B\rightarrow D^{(*)}$ transitions. The branching ratios, CP asymmetries (CPA) and polarization fractions (FA) of non-leptonic decays are investigated in the factorization approximation. The $B\rightarrow D^{(*)}$ form factors are estimated in the Salpeter method. Our estimation on branching ratios generally agree with the existent experimental data. For CPA and polarizations, comparisons among the FA results, the perturbative QCD predictions and experimental data are made.
I briefly review the status and recent progress in the theoretical understanding of non-leptonic decays of beauty and charm hadrons. Focusing on a personal selection of topics, this covers perturbative calculations in quantum chromodynamics, analyses using flavour symmetries of strong interactions, and the modelling of the relevant hadronic input functions.
$B$-physics is one of the most promising windows to find new physics in the flavor sector. One key ingredient to these searches are precise theoretical predictions derived from the Standard Model. Focusing at the nonperturbative QCD contributions, we carry out lattice QCD simulations in order to calculate $B$-meson decay constants and semi-leptonic form factors. Combined with experimental measurements our results enable us to determine CKM matrix elements. Here we present $B$ and $B_s$ meson decay constants as well as semi-leptonic form factors including rare decays, CKM or GIM suppressed in t…
Recently in [JHEP 09 (2021) 053], Wang et al. discussed the polynomial ring formed by flavor invariants in the leptonic sector with massive Majorana neutrinos. They have explicitly constructed the finite generating sets of the polynomial rings for both two-generation scenario and three-generation scenario. However, Wang et al.'s claim of the finiteness of the generating sets of the polynomial rings and their calculation by the approach of Hilbert series with generalized Molien-Weyl formula are both based on their assertion that the unitary group ${\rm U}(n,\mathbb{C})$ is reductive, which is u…
We propose a QCD-based model for calculation of the non-perturbative corrections to the factorization approximation in the decays of heavy mesons. In the framework of the model, factorization in pseudoscalar transitions holds exactly at the leading order leaving the opportunity to calculate non-leading corrections consistently.
We give a systematic way to compute higher orders in the 1/m_b expansion in inclusive semi-leptonic decays at tree level. We reproduce the known 1/m_b^3 terms and compute the 1/m_b^4 terms at tree level. The appearing non-perturbative parameters and the impact on the determination of V_{cb} are discussed.
We present the complete next-to-next-to-next-to-leading order short-distance and bound-state QCD correction to the leptonic decay rate Gamma(Upsilon(1S)->l+l-) of the lowest-lying spin-1 bottomonium state. The perturbative QCD prediction is compared to the measurement Gamma(Upsilon(1S)->e+e-)=1.340(18) keV.
With a consistent definition of transverse-momentum-dependent(TMD) light-cone wave function of $B$-meson, we show that the amplitude of the radiative leptonic B-decay can be factorized at one-loop level as a convolution with the wave function and a perturbative coefficient function, combined with a soft factor. In this TMD factorization, the transverse momenta of partons in the $B$-meson are taken into account and all soft divergences are contained in the wave function and the soft factor. The coefficient function is infrared-safe. The factorization works on a diagram-by-diagram basis and is p…
We review the current status of theoretical study of non-leptonic two body B decays. There are two independent directions for this purpose. One is the so called QCD factorization approach (or BBNS approach), which is based on naive factorization approach. The other one is named perturbative QCD approach. We list the different ideas and applications of the two method, and make a comparison between the two.
In the cross section for single-inclusive jet production in electron-nucleon collisions, the distribution of a quark in an electron appears at next-to-next-to-leading order. The numerical calculations in Ref. [1] were carried out using a perturbative approximation for the distribution of a quark in an electron. We point out that that distribution receives nonperturbative QCD contributions that invalidate the perturbative approximation. Those nonperturbative effects enter into cross sections for hard-scattering processes through resolved-electron contributions and can be taken into account by d…
Hyperon non-leptonic weak decay amplitudes are studied in the chiral perturbation theory. We employ the low energy effective weak Hamiltonian which contains the perturbative QCD correction. To include the non-perturbative QCD effect, quark currents of the effective Hamiltonian are substituted with hadronic currents which are color singlet and are derived by the chiral perturbation theory. We find that the amplitudes caused by the product of hadronic currents are small. It reproduce the small amplitudes of $ΔI=3/2$, which are derived by the strong interaction correction.
We present a QCD-based calculation of the exclusive semileptonic decay Lambda_b -> p l nu-bar. Using the ideas of Heavy Quark Effective Theory, we discuss the factorization of the amplitude. Further, resummed Sudakov effects are put in to ensure a consistent perturbative expansion.
We discuss the role of so-called "intrinsic-charm" operators in semi-leptonic B-meson decays, which appear first at order 1/m_b^3 in the heavy quark expansion. We show by explicit calculation that -- at scales mu <= m_c -- the contributions from "intrinsic-charm" effects can be absorbed into short-distance coefficient functions multiplying, for instance, the Darwin term. Then, the only remnant of "intrinsic charm" are logarithms of the form ln(m_c^2/m_b^2), which can be resummed by using renormalization-group techniques. As long as the dynamics at the charm-quark scale is perturbative, alpha_s…
The two-loop QCD radiative corrections to the $B_c$ meson leptonic decay rate are calculated in the framework of NRQCD factorization formalism. Two types of master integrals appearing in the calculation are obtained analytically for the first time. We get the short-distance coefficient of the leading matrix element to order $α_s^2$ by matching the full perturbative QCD calculation results to the corresponding NRQCD ones. The result in this work helps the evaluation of the $B_c$ leptonic decay constant, as well as the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$, to the full next-to-next…
Non-leptonic Decays of Hyperons can provide a detailed determination of the a priori mixing angles that appear in physical hadrons in the approach in which non-perturbative flavor and parity violations are present in tiny pieces of the hadron mass operator. The determination of such angles in these decays will provide a bench mark to test their necessary universality-like property in other types of decays. Our main result is that the magnitudes of the a priori mixing angles can be determined quite accurately.
We discuss local duality for weak non leptonic B and Lambda_b decays in the m_b -> infinity limit under the hypothesis of factorization and in the Shifman-Voloshin limit. We show that, under these hypotheses, local duality holds for the first two terms in the 1/m_b expansion and at the order alpha_s in the perturbative expansion. The possible relevance of these results for the operator product expansion evaluation of the b-hadron lifetimes is discussed.
Within the Standard Model, we investigate the semi-leptonic weak decays of $J/ψ$. The various form factors of $J/ψ$ transiting to a single charmed meson ($D^{(*)}_{(d,s)}$) are studied in the framework of the QCD sum rules. These form factors fully determine the rates of the weak semi-leptonic decays of $J/ψ$ and provide valuable information about the non-perturbative QCD effects. Our results indicate that the decay rate of the semi-leptonic weak decay mode $J/ψ\to D^{(*)-}_{s}+e^{+}+ν_{e}$ is at order of $10^{-10}$.
We examine the electronic width ratios of Upsilon resonances below the BBbar threshold by means of an effective (Cornell-type) QCD potential incorporating 1/m_b corrections obtained from a prior fit to the bottomonium spectrum. From our analysis we conclude that the Upsilon(2S) and Upsilon(3S) states should belong to the strong-coupling (nonperturbative) regime while the Upsilon(1S) state should belong to the weak-coupling (perturbative) regime, in agreement with a previous study based on radiative decays.
We calculate the dynamical relativistic corrections, originating from radiative one-gluon-exchange, to the leptonic decay width of heavy quarkonia in the framework of a covariant formulation of Light-Front Dynamics. Comparison with the non-relativistic calculations of the leptonic decay width of J=1 charmonium and bottomonium S-ground states shows that relativistic corrections are large. Most importantly, the calculation of these dynamical relativistic corrections legitimate a perturbative expansion in $α_s$, even in the charmonium sector. This is in contrast with the ongoing belief based on c…
In the present work, we assume D_{s0}(2317) meson as the c\bar{s} state and study its parameters at finite temperature using QCD sum rules. It is calculated the annihilation and scattering parts of spectral function in the lowest order of perturbation theory. Taking into account perturbative two-loop order α_{s} corrections and nonperturbative corrections up to the dimension six condensates it is investigated the temperature dependences of mass and leptonic decay constant of D_{s0}(2317) meson.
We discuss the decay of Bc mesons into two light mesons (pi, K^(*), eta', rho, omega, phi). All these decay channels come from a single type of diagram, namely tree annihilation. This allows us to derive extremely simple SU(3) relations among these processes. The size of annihilation contributions is an important issue in B physics, and we provide two different estimates in the case of non-leptonic charmless Bc decays, either a comparison with annihilation decays of heavy-light mesons or a perturbative model inspired by QCD factorisation. We finally discuss a possible search for these channels…
Within the nonrelativistic QCD (NRQCD) factorization framework, we compute the order-$α_s^3$ perturbative corrections to the leptonic decay of the $Υ$ and $J/ψ$ with high numerical accuracy, at the lowest order in velocity expansion. We confirm the existing three-loop results in literature. Furthermore, we explicitly consider the complex-valued light-by-light (singlet) contributions. We for the first time also consider the finite charm quark mass effect for $Υ$ leptonic decay, and obtain a new piece of 3-loop contribution to the anomalous dimension related to the composite NRQCD bilinear of ve…
We present a non-perturbative lattice calculation of the form factors which contribute to the amplitudes for the radiative decays $P\to \ell \bar ν_\ell γ$, where $P$ is a pseudoscalar meson and $\ell$ is a charged lepton. Together with the non-perturbative determination of the corrections to the processes $P\to \ell \bar ν_\ell$ due to the exchange of a virtual photon, this allows accurate predictions at $O(α_{em})$ to be made for leptonic decay rates for pseudoscalar mesons ranging from the pion to the $D_s$ meson. We are able to separate unambiguously and non-pertubatively the point-like co…
We present a non-perturbative calculation of the form factors which contribute to the amplitudes for the radiative decays $P\to \ell \bar ν_\ell γ$, where $P$ is a pseudoscalar meson and $\ell$ is a charged lepton. Together with the non-perturbative determination of the virtual photon corrections to the processes $P\to \ell \bar ν_\ell$, this will allow accurate predictions to be made at $O(α_{em})$ for leptonic decay rates for pseudoscalar mesons ranging from the pion to the $B$ meson. We are able to separate unambiguously the point-like contribution, the square of which leads to the infrared…
We use the operator product expansion (OPE) to show that non-perturbative QCD corrections to $Δρ$ can be calculated using unsubtracted dispersion relations for either the transverse or the longitudinal vacuum polarization functions. Recent calculations of the non-perturbative contribution to $Δρ$ based on a non-relativistic calculation of corrections to the $\ttbar$ threshold are inconsistent with this result.
At LEP II it is hoped to measure the W mass to an accuracy of around 40 MeV. This will require direct reconstruction of the mass of the W from its decay products in both the semi-leptonic and hadronic decay channels. Final state perturbative reconnection effects in hadronic decays are considered and their effect on 6-jet distributions and the reconstructed mass. The perturbative mass shift is found to be ~ 50 keV in the negative direction.
The recent discovery of the B_c meson by the CDF collaboration and proposed new experiments at Fermilab and CERN motivate new theoretical studies of the B_c system. Here we investigate the radiative leptonic decay B_c -> gamma l nu. This process is an important background to the annihilation process B_c -> l nu, which will be used to extract the B_c decay constant. We perform a model-independent calculation, based on QCD, of the partial width and various kinematic distributions. We also examine the decay within the framework of NRQCD, an effective field theory of nonrelativistic quarks, genera…
The colour-suppressed tree amplitude in non-leptonic B decays is particularly sensitive to perturbative and non-perturbative corrections. We calculate the two-loop (NNLO) vertex corrections to the colour-suppressed and colour-allowed tree amplitudes in QCD factorization. Our results are given completely analytically, including the full dependence on the charm quark mass. We then update theoretical predictions for a range of interesting observables derived from pi pi, pi rho, and rho rho final states that do not depend (significantly) on penguin contributions, and hence are now available with N…
We present a general scheme and scale independent parameterization of two-body non-leptonic B decay amplitudes which includes perturbative QCD corrections as well as final state interactions in a consistent way. This parameterization is based on the Next-to-Leading effective Hamiltonian for non-leptonic B decays and on Wick contractions in the matrix elements of the local operators. Using this parameterization, and making no dynamical assumption, we present a classification of two-body B decay channels in terms of the parameters entering in the decay amplitudes. This classification can be cons…
In this comment we point out several problems concerning kinematical singularities which are encountered in the calculation of the dilepton rates in {Ruppert:2004yg}. We also comment on the method introduced in {vanHees:2000bp} and further used in refs. {Riek:2004kx,Renk:2006dt,Renk:2006ax,Ruppert:2004yg}
We discuss one-particle inclusive B sub s -> D bar sub s X decays using a QCD based method already applied to B -> D bar X. A link between the right charm non-perturbative form factors of the semi-leptonic decays and those of the non-leptonic decays is established. Our results are compatible with current experimental knowledge.
Theoretical descriptions for the nonleptonic decays of heavy flavour hadrons have emerged that incorporate non-perturbative corrections in a systematic way and are genuinely based on QCD. One can reproduce $τ(D^+)/τ(D^0)$, $BR_{SL}(D^+)$ and $BR_{SL}(D^0)$ as due mainly to destructive interference in $D^+$ decays; one predicts $τ(B^-)$ to exceed $τ(B_d)$ by a few per cent; $BR_{SL}(B)$ is reduced only slightly, raising the prospects of a serious and tantalizing conflict with ARGUS \& CLEO data. It is emphasized that the lifetimes for the two mass eigenstates in the $B_s$-$\bar B_s$ system coul…
`Anyone who keeps the ability to see beauty never grows old' Franz Kafka. In the last few years considerable progress has been achieved in our understanding of the decays of heavy flavour hadrons. One can now calculate inclusive transition rates in QCD proper through an expansion in inverse powers of the heavy flavour quark mass without recourse to phenomenological assumptions. The non-perturbative contributions are treated systematically in this way; they are found to produce corrections of order a few percent in beauty decays, i.e. typically somewhat smaller than the perturbative corrections…
We compute the form factors parametrizing radiative leptonic decays of heavy mesons B^+\toγe^+νfor photon energies much larger than Λ_{QCD}, where perturbative QCD methods for exclusive processes can be combined with the heavy quark effective theory. The form factors can be reliably obtained in this region in an expansion in powers of Λ/E_γ. The leading term in this expansion displays an additional spin symmetry manifested in the equality of form factors of vector and axial currents. The leading twist form factors can be written as the convolution of the B meson light-cone wave function with a…
We study the scaling with the number of colours, $N_c$, of the weak amplitudes mediating kaon mixing and decay. We evaluate the amplitudes of the two relevant current-current operators on the lattice for $N_c=3-7$. We conclude that the subleading $1/N_c$ corrections in $\hat{B}_K$ are small, but those in the $K \rightarrow ππ$ amplitudes are large and fully anti-correlated in the $I=0, 2$ isospin channels. We briefly comment on the implications for the $ΔI=1/2$ rule.
We present a new mechanism for $B^{\pm}\to η' K^{\pm}$, and analyze it strictly within perturbative QCD. We find that such a new mechanism may dominate non-leptonic $B$-decays to light mesons. Within a reasonable parameter space, our prediction is in good agreement with the recent CLEO data on $B^{\pm}\to η' K^{\pm}$. We conclude that there is no room for an abnormally large \bsg vertex from physics beyond the Standard Model.
We reanalyze critically the generalized factorization hypothesis in non-leptonic two-body B-decays discussed recently by several authors. In particular we address the determination of the factorization scale $μ_f$ and of the non-perturbative parameters $ξ^{NF}_1 (m_b)$ and $ξ^{NF}_2 (m_b)$ which are supposed to measure non-factorizable contributions to hadronic matrix elements with $ξ^{NF}_i (μ_f) = 0$. We emphasize that both $μ_f$ and $ξ^{NF}_i (m_b)$ are renormalization scheme dependent and we demonstrate analytically and numerically that for any chosen scale $μ_f=\ord(m_b)$ it is possible t…
To start the $b$-decay session we briefly introduce and comment some important theoretical tools which are currently used in $b$ physics. Heavy Quark Symmetry and its consequences for heavy to heavy and heavy to light semi-leptonic decays, as well as for leptonic decays, are briefly summarised. It is stressed that symmetry must be completed with dynamical calculations. A critical discussion of the nearest pole dominance (VMD) assumption is performed. Parton model and its higher twist corrections are discussed on the example of lifetimes. Finally non-leptonic decays are considered via the examp…
A recently proposed approach to compute the inclusive semi-leptonic decay rate on the lattice allows for the calculation of various quantities (differential distributions and moments) in different subchannels. We systematically compare the lattice QCD results for an unphysically light bottom quark with OPE-based predictions, including leading order perturbative and $\mathcal{O}\left(1/m^3 \right)$ power corrections, and explore possible strategies to decrease the systematic uncertainty.
Resummation of large QCD radiative corrections, including leading and next-to-leading logarithms, in pion electromagnetic form factor is reviewed. Similar formalism is applied to exclusive processes involving heavy mesons, and leads to Sudakov suppression for the semi-leptonic decay $B\toπlν$. It is found that, with the inclusion of Sudakov effects, perturbative QCD analysis of this decay is possible for the energy fraction of the pion above 0.3. By combining predictions from the soft pion theorems, we estimate that the upper limit of the KM matrix element $|V_{ub}|$ is roughly 0.003.
I argue that perturbative scattering of quarks and gluons are incompatible with lattice and heavy ion data on QGP properties. The non-perturbative mechanisms for quasiparticle rescattering and quark production are briefly discussed, as well as experiments needed to measure matter anisotropy and quark density at early stages of the collisions.
Soft-collinear effective theory is used to prove factorization of the B->gamma+l+nu decay amplitude at leading power in Lambda/m_b, including a demonstration of the absence of non-valence Fock states and of the finiteness of the convolution integral in the factorization formula. Large logarithms entering the hard-scattering kernel are resummed by performing a two-step perturbative matching onto the low-energy effective theory, and by solving evolution equations derived from the renormalization properties of the leading-order B-meson light-cone distribution amplitude. As a byproduct, the evolut…
We compute the non-perturbative contribution of semileptonic tensor operators $(\bar q σ^{μν} q)(\bar \ell σ_{μν} \ell)$ to the purely leptonic process $μ\to e γ$ and to the electric and magnetic dipole moments of charged leptons by matching onto chiral perturbation theory at low energies. This matching procedure has been used extensively to study semileptonic and leptonic weak decays of hadrons. In this paper, we apply it to observables that contain no strongly interacting external particles. The non-perturbative contribution to $μ\to e $ processes is used to extract the best current bound on…
We present a new, universally applicable toy model of colour reconnections in hadronic final states. The model is based on hadronising strings and has one free parameter. We next present an implementation of this model in the Pythia event generator and provide several parameter sets ("tunes"), constrained by fits to Tevatron minimum-bias data. Finally, we consider the sensitivity of a simplified top mass analysis to these effects, in exclusive semi-leptonic top events at the Tevatron. A first attempt at isolating the genuine non-perturbative effects gives an estimate of order delta(m_top) ~ 0.…
We investigate the spectroscopy and decays of the charmonium and upsilon systems in a potential model consisting of a relativistic kinetic energy term, a linear confining term including its scalar and vector relativistic corrections and the complete perturbative one-loop quantum chromodynamic short distance potential. The masses and wave functions of the various states are obtained using a variational technique, which allows us to compare the results for both perturbative and nonperturbative treatments of the potential. As well as comparing the mass spectra, radiative widths and leptonic width…
