1,720,986 research outputs found
Hadronic corrections to μ-e scattering at NNLO with space-like data
No full textAbstract The Standard Model prediction for μ-e scattering at Next-to-Next-to-Leading Order (NNLO) contains non-perturbative QCD contributions given by diagrams with a hadronic vacuum polarization insertion in the photon propagator. By taking advantage of the hyperspherical integration method, we show that the subset of hadronic NNLO corrections where the vacuum polarization appears inside a loop, the irreducible diagrams, can be calculated employing the hadronic vacuum polarization in the space-like region, without making use of the R ratio and time-like data. We present the analytic expressions of the kernels necessary to evaluate numerically the two types of irreducible diagrams: the two-loop vertex and box corrections. As a cross check, we evaluate these corrections numerically and we compare them with the results given by the traditional dispersive approach and with analytic two-loop vertex results in QED
Muon-Electron Scattering at Next-To-Next-To-Leading Order: The Hadronic Corrections
No full textThe standard model prediction for muon-electron scattering beyond leading order requires the inclusion of QCD contributions which cannot be computed perturbatively. At next-to- and next-to-next-to-leading order, they arise from one- and two-loop diagrams with hadronic vacuum polarization insertions in the photon propagator. We present their evaluation using the dispersive approach with hadronic e(+) e(-) annihilation data and estimate their uncertainty. We find that these corrections are crucial for the analysis of future high-precision muon-electron scattering data, like those of the recently proposed MUonE experiment at CERN
Next-to-leading order prediction for the decay mu -> e (e(+)e(-))nu(nu)over-bar
No full textWe present the di ff erential decay rates and the branching ratios of the muon decay with internal conversion, mu -> e (e(+)e(-)) nu(nu) over bar, in the Standard Model at next-to-leading order (NLO) in the on-shell scheme. This rare decay mode of the muon is among the main sources of background to the search for mu -> eee decay. We found that in the phase space region where the neutrino energies are small, and the three-electron momenta have a similar signature as in the mu -> eee decay, the NLO corrections decrease the leading-order prediction by about 10 - 20% depending on the applied cut
Third order corrections to the semileptonic b -> c and the muon decays
Full text linkWe compute corrections of order alpha(3)(s) to the decay b -> b -> cl ( nu) over bar taking into account massive charm quarks. In the on-shell scheme large three-loop corrections are found. However, in the kinetic scheme the three-loop corrections are below 1% and thus perturbation theory is well under control. We furthermore provide results for the order alpha(3)(s) corrections to b -> cl (nu ) over bar and the third-order QED corrections to the muon decay which will be important input for reducing the uncertainty of the Fermi coupling constant G(F)
On the decays B → K(⁎)+ leptonium
Full text linkWe determine the rates of the B meson decays into a K(⁎) and an ℓ+ℓ− bound state, the leptonium, where ℓ=e,μ,τ. The two spin states of the leptonium, the spin singlet and the spin triplet, couple to the axial current and to the vector current, respectively, thus probing different helicity structures of the underlying b→sℓ+ℓ− effective Hamiltonian. Since ortho- and para-leptonia have different decay modes, a distinction between the two is relatively easy and these decays may become a cross check for the results of lepton-flavor-violation searches obtained with free leptons. We find that some of the decays involving muon and tau have a branching ratio of the order of 10−13 and they may become accessible at the LHCb with 50 fb−1 of integrated luminosity. In addition, since the tau-pair threshold lies right between the J/ψ and the ψ(2S) resonances, we estimate the charm-loop contribution to the decays B→K(⁎)+tauonium
Exact results for ZmOS and Z2OS with two mass scales and up to three loops
Full text linkWe consider the on-shell mass and wave function renormalization constants ZmOS and Z2OS up to three-loop order allowing for a second non-zero quark mass. We obtain analytic results in terms of harmonic polylogarithms and iterated integrals with the additional letters 1-tau 2 and 1-tau 2/tau which extends the findings from ref. [1] where only numerical expressions are presented. Furthermore, we provide terms of order O(E-2) and O(E) at two- and three-loop order which are crucial ingredients for a future four-loop calculation. Compact results for the expansions around the zero-mass, equal-mass and large-mass cases allow for a fast high-precision numerical evaluation
The heavy quark expansion for inclusive semileptonic charm decays revisited
Full text linkThe Heavy Quark Expansion (HQE) has become an extremely powerful tool in flavor physics. For charm decays, where the expansion parameters alpha (s)(m(c)) and Lambda (QCD)/m(c) are bigger than for bottom decays, it remains to be seen if the HQE can be applied with similar success. Nevertheless, to make optimal use of the plethora of data already available and coming in the near future, a better understanding of HQE for charm decays is crucial. This paper discusses in detail how the HQE for charm decays is set up, what is the role of four-quark (weak annihilation) operators and how this compares to the well understood bottom decays. Subtleties concerning radiative corrections and the charm mass scheme are briefly discussed. An experimental study of the relevant HQE hadronic matrix elements will then show if the HQE expansion for charm converges well enough. Besides serving as an important cross check for inclusive B decays, in the end, this study might open the road for inclusive |V-cs| and |V-cd| extractions
Kinetic Heavy Quark Mass to Three Loops
Full text linkWe compute three-loop corrections to the relation between the heavy quark masses defined in the pole and kinetic schemes. Using known relations between the pole and (MS) over bar quark masses, we can establish precise relations between the kinetic and (MS) over bar charm and bottom masses. As compared to two loops, the precision is improved by a factor of 2 to 3. Our results constitute important ingredients for the precise determination of the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cb vertical bar at Belle II
V-cb determination from inclusive b c decays: an alternative method
No full textThe determination of V-cb relies on the Heavy-Quark Expansion and the extraction of the non-perturbative matrix elements from inclusive b c decays. The proliferation of these matrix elements complicates their extraction at 1/mb4 and higher, thereby limiting the V-cb extraction. Reparametrization invariance links different operators in the Heavy-Quark expansion thus reducing the number of independent operators at 1/mb4 to eight for the total rate. We show that this reduction also holds for spectral moments as long as they are defined by reparametrization invariant weight-functions. This is valid in particular for the leptonic invariant mass spectrum (q(2)), i.e. the differential rate and its moments. Currently, V-cb is determined by fitting the energy and hadronic mass moments, which do not manifest this parameter reduction and depend on the full set of 13 matrix elements up to 1/mb4. In light of this, we propose an experimental analysis of the q(2) moments to open the possibility of a model-independent V-cb extraction from semileptonic decays including the 1/mb4 terms in a fully data-driven way
Relation between the (MS)over-bar and the kinetic mass of heavy quarks
No full textWe compute the relation between the pole mass and the kinetic mass of a heavy quark to three loops. Using the known relation between the pole and the (MS) over bar mass we obtain precise conversion relations between the (MS) over bar and kinetic masses. The kinetic mass is defined via the moments of the spectral function for the scattering involving a heavy quark close to threshold. This requires the computation of the imaginary part of a forward-scattering amplitude up to three-loop order. We discuss in detail the expansion procedure and the reduction to master integrals. For the latter analytic results are provided. We apply our result both to charm and bottom quark masses. In the latter case we compute and include finite charm quark mass effects. Furthermore, we determine the large-beta(0) result for the conversion formula at four-loop order. For the bottom quark we estimate the uncertainty in the conversion between the (MS) over bar and kinetic masses to about 15 MeV which is an improvement by a factor of 2-3 as compared to the two-loop formula. The improved precision is crucial for the extraction of the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cb vertical bar at Belle II
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