Semileptonic Decay Form Factors Research Articles

Radiative semileptonic overline{B} decays

We consider the form factors for the radiative semileptonic decays overline{B} (v) → D(*)(v′)ℓ overline{nu} ℓγ in the kinematic region where the photon momentum, k, is small enough that heavy quark symmetry (HQS) can be applied without the radiated photon changing the heavy quark velocity (i.e., v(′) ∙ k < m(b,c)). We find that HQS is remarkably powerful, leaving only four new undetermined form factors at leading order in 1/m(b,c). In addition, one of them is fixed in terms of the leading order Isgur-Wise function in the kinematic region, v(′) ∙ k < ΛQCD.

Towards a heavy diquark effective theory for weak decays of doubly heavy baryons

We construct a leading-order effective field theory for both scalar and axial-vector heavy diquarks, and consider its power expansion in the heavy diquark limit. By assuming the transition from QCD to diquark effective theory, we derive the most general form for the effective diquark transition currents based on the heavy diquark symmetry. The short-distance coefficients between QCD and heavy diquark effective field theory are also obtained by a tree level matching. With the effective currents in the heavy diquark limit, we perform a reduction of the form factors for semi-leptonic decays of doubly heavy baryons, and find that only one nonperturbative function is remaining. It is shown that this soft function can be related to the Isgur–Wise function in heavy meson transitions. As a phenomenological application, we take a single pole structure for the reduced form factor, and use it to calculate the semi-leptonic decay widths of doubly heavy baryons. The obtained results are consistent with others given in the literature, and can be tested in the future.

K+→π+νν¯ decay amplitude from lattice QCD

In Ref. [1] we have presented the results of an exploratory lattice QCD computation of the long-distance contribution to the ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ decay amplitude. In the present paper we describe the details of this calculation, which includes the implementation of a number of novel techniques. The ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ decay amplitude is dominated by short-distance contributions which can be computed in perturbation theory with the only required nonperturbative input being the relatively well-known form factors of semileptonic kaon decays. The long-distance contributions, which are the target of this work, are expected to be of $O(5%)$ in the branching ratio. Our study demonstrates the feasibility of lattice QCD computations of the ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ decay amplitude, and in particular of the long-distance component. Though this calculation is performed on a small lattice ($1{6}^{3}\ifmmode\times\else\texttimes\fi{}32$) and at unphysical pion, kaon and charm quark masses, ${m}_{\ensuremath{\pi}}=420\text{ }\text{ }\mathrm{MeV}$, ${m}_{K}=563\text{ }\text{ }\mathrm{MeV}$ and ${m}_{c}^{\overline{\mathrm{MS}}}(2\text{ }\text{ }\mathrm{GeV})=863\text{ }\text{ }\mathrm{MeV}$, the techniques presented in this work can readily be applied to a future realistic calculation.

Measurement of the form factors of charged kaon semileptonic decays

A measurement of the form factors of charged kaon semileptonic decays is presented, based on 4.4 × 106K± → π0e±νe (Ke3±) and 2.3 × 106K± → π0μ±νμ (Kμ3±) decays collected in 2004 by the NA48/2 experiment. The results are obtained with improved precision as compared to earlier measurements. The combination of measurements in the Ke3± and Kμ3± modes is also presented.

Charm physics at BESIII

By analyzing data samples taken at the center-of-mass energies GeV and GeV with the Beijing Spectrometer (BESIII) detector at the Beijing Electron Positron Collider (BEPCII), we determined the decay constants, the form factors of semileptonic decays of D meson, the CKM matrix elements , the hadronic decays, and we search for charm rare decays. In this article we briefly report the results.

Semileptonic B-meson decays to light pseudoscalar mesons on the HISQ ensembles

We report the status of an ongoing lattice-QCD calculation of form factors for exclusive semileptonic decays of B mesons with both charged currents (B → πlv, Bs → Klv) and neutral currents (B → πl+l-, B → Kl+l-). The results are important for constraining or revealing physics beyond the Standard Model. This work uses MILC’s (2+1 + 1)-flavor ensembles with the HISQ action for the sea and light valence quarks and the clover action in the Fermilab interpretation for the b quark. Simulations are carried out at three lattice spacings down to 0.088 fm, with both physical and unphysical sea-quark masses. We present preliminary results for correlation-function fits.

HQET form factors for Bs → Klv decays beyond leading order

We compute semi-leptonic Bs decay form factors using Heavy Quark Effective Theory on the lattice. To obtain good control of the 1 /mb expansion, one has to take into account not only the leading static order but also the terms arising at O (1/mb): kinetic, spin and current insertions. We show results for these terms calculated through the ratio method, using our prior results for the static order. After combining them with non-perturbative HQET parameters they can be continuum-extrapolated to give the QCD form factor correct up to O (1/[see formula in PDF]) corrections and without O (αs(mb)n) corrections.

Isgur–Wise function and a new approach to potential model

Considering the Cornell potential [Formula: see text], we have revisited the Dalgarno’s method of perturbation by incorporating two scales [Formula: see text] and [Formula: see text] as integration limit so that the perturbative procedure can be improved in a potential model. With the improved version of the wave function the ground state masses of the heavy–light mesons [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] are computed. The slopes and curvatures of the form factors of semileptonic decays of heavy–light mesons in both HQET limit and finite mass limit are calculated and compared with the available data.

Continuum limit of the leading-order HQET form factor in Bs→ Kℓν decays

We discuss the computation of form factors for semi-leptonic decays of $\rm B$-, $\rm B_s$- mesons in lattice QCD. Considering in particular the example of the static $\rm B_s$ form factors we demonstrate that after non-perturbative renormalization the continuum limit can be taken with confidence. The resulting precision is of interest for extractions of $V_{\rm ub}$. The size of the corrections of order $1/m_{\rm b}$ is just estimated at present but it is expected that their inclusion does not pose significant difficulties.

B→Dlνform factors at nonzero recoil and extraction of|Vcb|

We present a lattice QCD calculation of the $B \rightarrow D l \nu$ semileptonic decay form factors $f_+(q^2)$ and $f_0(q^2)$ for the entire physical $q^2$ range. Non-relativistic QCD (NRQCD) bottom quarks and Highly Improved Staggered Quark (HISQ) charm and light quarks are employed together with $N_f = 2+1$ MILC gauge configurations. A joint fit to our lattice and BaBar experimental data allows an extraction of the CKM matrix element $|V_{cb}|$. We also determine the phenomenologically interesting ratio $R(D) = {\cal B}(B \rightarrow D \tau \nu_\tau) / {\cal B}(B \rightarrow D l \nu_l)$ ($l = e, \mu$). We find $|V_{cb}|_{excl.}^{B \rightarrow D} = 0.0402(17)(13)$, where the first error consists of the lattice simulation errors and the experimental statistical error and the second error is the experimental systematic error. For the branching fraction ratio we find $R(D) = 0.300(8)$.

Matching of heavy-light flavour currents between HQET at order 1/m and QCD: I. Strategy and tree-level study

We present a strategy how to match the full set of components of the heavy-light axial and vector currents in Heavy Quark Effective Theory (HQET), up to and including 1/m h -corrections, to QCD. While the ultimate goal is to apply these matching conditions non-perturbatively, in this study we first have implemented them at tree-level, in order to find good choices of the matching observables with small $ \mathcal{O}\left( {{1 \left/ {{m_{\mathrm{h}}^2}} \right.}} \right) $ contributions. They can later be employed in the non-perturbative matching procedure which is a crucial part of precision HQET computations of semileptonic decay form factors in lattice QCD.

Form factors for semileptonicDdecays

We study the form factors for semileptonic decays of $D$-mesons. That is, we consider the matrix element of the weak left-handed quark current for the transitions $D \rightarrow P$ and $D \rightarrow V$, where $P$ and $V$ are light pseudoscalar or vector mesons, respectively. Our motivation to perform the present study of these form factors are future calculations of non-leptonic decay amplitudes. We consider the form factors within a class of chiral quark models. Especially, we study how the Large Energy Effective Theory (LEET) limit works for $D$-meson decays. Compared to previous work we also introduce light vector mesons $V = \rho, K^*,...$ within chiral quark models. In order to determine some of the parameters in our model, we use existing data and results based on some other methods like lattice calculations, light-cone sum rules, and heavy-light chiral perturbation theory. We also obtain some predictions within our framework.

STUDY OF THE RARE DECAY K± → π±γγ AND HIGH PRECISION MEASUREMENT OF THE FORM FACTORS OF THE SEMILEPTONIC DECAYS K± → π0ℓ±ν

The NA48/2 experiment presents preliminary measurements of the form factors of the charged kaon semileptonic decays. The Ke3 and Kμ3 results are in good agreement allowing for a combined result which matches the precision of the current world average on the vector and scalar form factors. Recent study of the rare decay K± → π±γγ from the NA48/2 and NA62 data samples is also reported.

PION AND KAON STRUCTURES FROM THE INSTANTON VACUUM

In this presentation, we briefly review recent investigations on pion and kaon structures from the instanton vacuum. Starting from the low-energy QCD partition function, we have computed the Gasser-Leutwyler low-energy constants, electromagnetic form factors of the pion and kaon, and semileptonic decay form factors of the kaon. The results are in good agreement with the experimental and empirical data.

B and D mesons on the lattice

I review the status of lattice calculations of D and B mesons decay constants and semileptonic decay form factors, as well as B 0 – B ¯ 0 mixing parameters. I will mainly discuss those calculations that fully incorporate vacuum polarization effects by considering three flavours of sea quarks.

Semileptonic decays of the lightJP=1/2+ground state baryon octet

We calculate the semileptonic baryon octet-octet transition form factors using a manifestly Lorentz covariant quark model approach based on the factorization of the contribution of valence quarks and chiral effects. We perform a detailed analysis of SU(3)-breaking corrections to the hyperon semileptonic decay form factors. We present complete results on decay rates and asymmetry parameters including lepton mass effects for the rates.

The transition form factors for semi-leptonic weak decays of J/ψ in QCD sum rules

Within the standard model, we investigate the semi-leptonic weak decays of J/psi. The various form factors of J/psi making the transition to a single charmed meson (D-(d,D-s)(*)) are studied in the framework of QCD sum rules. These form factors fully determine the rates of the weak semi-leptonic decays of J/psi and provide valuable information on non-perturbative QCD effects. Our results indicate that the decay rate of the semi-leptonic weak decay mode J/psi -> D-s(*)(-) + e(+) + nu(e) is at the order of 10(-10).

Semileptonic [formula omitted] and [formula omitted] decays in [formula omitted] flavor lattice QCD

We present results for form factors of semileptonic decays of D and B mesons in 2+1 flavor lattice QCD using the MILC gauge configurations. With an improved staggered action for light quarks, we successfully reduce the systematic error from the chiral extrapolation. The results for D decays are in agreement with experimental ones. The results for B decays are preliminary. Combining our results with experimental branching ratios, we then obtain the CKM matrix elements |Vcd|, |Vcs|, |Vcb| and |vub|. We also check CKM unitarity, for the first time, using only lattice QCD as the theoretical input.

Exclusive semileptonic decays of D mesons produced at threshold

Initial running of the CLEO-c detector has provided the world's largest sample of ψ(3770) decays. Using this data sample, we have reconstructed D mesons decaying to hadronic final states and have used them to tag events with a charm-anti-charm pair. In this contribution, we present preliminary results from this data sample, which constitute a first step towards measurements of semileptonic decay form factors and the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements Vcs and Vcd with the full CLEO-c data set to be collected in the near future.

HEAVY QUARKS ON THE LATTICE

▪ Abstract Lattice quantum chromodynamics provides first-principles calculations for hadrons containing heavy quarks—charm and bottom quarks. Their mass spectra, decay rates, and some hadronic matrix elements can be calculated on the lattice in a model-independent manner. In this review, we introduce the effective theories that treat heavy quarks on the lattice. We summarize results on the heavy quarkonium spectrum, which verify the validity of the effective theory approach. We then discuss applications to B physics, which is the main target of the lattice theory of heavy quarks. We review progress in lattice calculations of the B meson decay constant, the B parameter, semileptonic decay form factors, and other important quantities.