Decay Form Factors Research Articles

Heavy-light semileptonic decays in staggered chiral perturbation theory

We calculate the form factors for the semileptonic decays of heavy-light pseudoscalar mesons in partially quenched staggered chiral perturbation theory ($\mathrm{S}\ensuremath{\chi}\mathrm{PT}$), working to leading order in $1/{m}_{Q}$, where ${m}_{Q}$ is the heavy-quark mass. We take the light meson in the final state to be a pseudoscalar corresponding to the exact chiral symmetry of staggered quarks. The treatment assumes the validity of the standard prescription for representing the staggered ``fourth-root trick'' within $\mathrm{S}\ensuremath{\chi}\mathrm{PT}$ by insertions of factors of $1/4$ for each sea-quark loop. Our calculation is based on an existing partially quenched continuum chiral perturbation theory calculation with degenerate sea quarks by Be\ifmmode \acute{c}\else \'{c}\fi{}irevi\ifmmode \acute{c}\else \'{c}\fi{}, Prelovsek, and Zupan, which we generalize to the staggered (and nondegenerate) case. As a byproduct, we obtain the continuum partially quenched results with nondegenerate sea quarks. We analyze the effects of nonleading chiral terms, and find a relation among the coefficients governing the analytic valence mass dependence at this order. Our results are useful in analyzing lattice computations of form factors $B\ensuremath{\rightarrow}\ensuremath{\pi}$ and $D\ensuremath{\rightarrow}K$, when the light quarks are simulated with the staggered action.

Bto light meson form factors with end-point cutoff

Decay form factors of B to light pseudoscalar (P) and vector (V) mesons are analyzed with the momentum cutoff near the end point. The cutoff is caused by possible Cherenkov gluon radiation when an energetic light parton from the weak vertex travels through the 'brown muck' of light degrees of freedom. The end-point singularities and the double countings are naturally absent. The soft-overlap contributions where the partonic momenta configuration is highly asymmetric are very suppressed in this framework. A simple calculation gives a plausible results for B{yields}P, V form factors.

Dilepton production in pp and CC collisions with HADES

e + e - production was studied using the High Acceptance DiElectron Spectrometer (HADES). In pp collisions at 2.2GeV kinetic beam energy, the exclusive η production and the Dalitz decay η→γe + e - have been reconstructed. The electromagnetic form factor of the latter decay was found to be in good agreement with the existing theoretical predictions. In addition, an inclusive e + e - invariant-mass spectrum from the 12C + 12C reaction at 2AGeV is presented and compared with a simplified thermal model.

Production ofP-wave charmed mesons in hadronicBdecays

Production of even-parity charmed mesons in hadronic $B$ decays is studied. Specifically, we focus on the Cabibbo-allowed decays $\overline{B}\ensuremath{\rightarrow}{D}^{**}\ensuremath{\pi}$ and ${\overline{D}}_{s}^{**}{D}^{(*)}$, where ${D}^{**}$ denotes generically a $P$-wave charmed meson. While the measured color-allowed decays ${\overline{B}}^{0}\ensuremath{\rightarrow}{D}^{**+}{\ensuremath{\pi}}^{\ensuremath{-}}$ are consistent with the theoretical expectation, the experimental observation of ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{D}^{**0}{\ensuremath{\pi}}^{\ensuremath{-}}$ for the broad ${D}^{**}$ states is astonishing as it requires that the color-suppressed contribution dominates over the color-allowed one, even though the former is $1/{m}_{b}$ suppressed in the heavy quark limit. In order to accommodate the data of $\overline{B}\ensuremath{\rightarrow}{D}^{**}{\ensuremath{\pi}}^{\ensuremath{-}}$, it is found that the real part of ${a}_{2}/{a}_{1}$ has a sign opposite to that in $\overline{B}\ensuremath{\rightarrow}D\ensuremath{\pi}$ decays, where ${a}_{1}$ and ${a}_{2}$ are the effective parameters for color-allowed and color-suppressed decay amplitudes, respectively. The decay constants and form factors for ${D}^{**}$ and the Isgur-Wise functions ${\ensuremath{\tau}}_{1/2}(\ensuremath{\omega})$ and ${\ensuremath{\tau}}_{3/2}(\ensuremath{\omega})$ are extracted from the data of $B\ensuremath{\rightarrow}{D}^{**}\ensuremath{\pi}$ decays. The Isgur-Wise functions calculated in the covariant light-front quark model are in good agreement with experiment. The neutral modes ${\overline{B}}^{0}\ensuremath{\rightarrow}{D}^{**0}{\ensuremath{\pi}}^{0}$ for ${D}^{**}={D}_{0}^{*}(2400)$, ${D}_{1}^{\ensuremath{'}}(2430)$, and ${\overline{B}}^{0}\ensuremath{\rightarrow}{D}_{1}^{\ensuremath{'}0}(2430)\ensuremath{\omega}$ are predicted to have branching ratios of order ${10}^{\ensuremath{-}4}$ which are also supported by the isospin argument. The decay constants of ${D}_{s0}^{*}(2317)$ and ${D}_{s1}^{\ensuremath{'}}(2460)$ are inferred from the measurements of $\overline{B}\ensuremath{\rightarrow}{D}_{s}^{**\ensuremath{-}}D$ to be 58\char21{}86 MeV and 130\char21{}200 MeV, respectively. Contrary to the decay constants ${f}_{{D}_{0}^{*}}$ and ${f}_{{D}_{1}^{\ensuremath{'}}}$ which are similar in size, the large disparity between ${f}_{{D}_{s0}^{*}}$ and ${f}_{{D}_{s1}^{\ensuremath{'}}}$ is surprising and unexpected.

Extracting the charm cross-section from its semileptonic decay at RHIC

Abstract We propose a sensitive measurement of the charm total cross-section at RHIC through muon identification from charm semileptonic decay at low transverse momentum ( p T ). This can test the binary-collision scaling ( N bin ) properties of the charm total cross-section and be used to study whether heavy-flavor quarks, which are used as a probe, are produced exclusively at the initial impact in hadron–hadron collisions. The effect of the charm semileptonic decay form factor on extracting the total charm cross section and on the shape of the lepton spectra are also discussed in detail. We conclude that lepton spectra from charmed hadron decays at transverse momentum p T ≃ 1.0 GeV / c are sensitive to the charmed hadron spectrum shape. Therefore, the interactions of heavy quarks with the medium created in relativistic heavy-ion collisions, especially the flow effects, can be extracted from the lepton spectra from charmed hadron decays at low p T .

Analysis of exclusiveBs→Ds0(2317)ℓν¯ℓdecay with QCD sum rules

The transition form factors of the semileptonic decay B{sub s} into scalar D{sub s{sub 0}}(2317) meson is calculated in the framework of 3-point QCD sum rule. The branching ratio is found to be {approx}10{sup -3} for the B{sub s}{yields}D{sub s{sub 0}}(2317)l{nu}{sub l}(l=e,{mu}) decay, and {approx}10{sup -4} for the B{sub s}{yields}D{sub s{sub 0}}(2317){tau}{nu}{sub {tau}} decay, respectively.

PARITY-EVEN AND PARITY-ODD MESONS IN COVARIANT LIGHT-FRONT APPROACH

Decay constants and form factors for parity-even (s-wave) and parity-odd (p-wave) mesons are studied within a covariant light-front approach. The three universal Isgur-Wise functions for heavy-to-heavy meson transitions are obtained.

Study of the B → Xcℓν Decays and Determination of |Vcb|

We report studies of semileptonic decays, B → Xcℓν, based on a sample of 88 million [Formula: see text] events recorded with the BABAR detector. We have measured four moments of the electron energy and hadronic mass distributions and determined the inclusive branching fraction, the CKM matrix element |Vcb|, and other heavy quark parameters, using Heavy Quark Expansions in the kinetic mass scheme. In addition, we have studied a large sample of B0 → D*-ℓ+ν decays and extracted the decay form factors and |Vcb|.

B→f0(980)Kdecays and subleading corrections

The decay $B\to f_0(980)K is studied within the framework of QCD factorization and the two-quark scenario for $f_0(980)$. There are two distinct penguin contributions and their interference depends on the unknown mixing angle $\theta$ of strange and nonstrange quark contents of $f_0(980)$: destructive for $0<\theta<\pi/2$ and constructive for $\pi/2<\theta<\pi$. The QCD sum rule method is applied to evaluate the leading-twist light-cone distribution amplitudes and the scalar decay constant of $f_0$. We conclude that the short-distance approach is not adequate to explain the observed large rates of $f_0K^-$ and $f_0\ov K^0$. Among many possible subleading corrections, we study and estimate the contributions from the three-parton Fock states of the $f_0$ and from the intrinsic gluon inside the $B$ meson. It is found that the spectator gluon of the $B$ meson may play an eminent role for the enhancement of $f_0(980)K$. We point out that if $f_0(980)$ is a four-quark state as widely perceived, there will exist extra diagrams contributing to $B\to f_0(980)K$. However, in practice it is difficult to make quantitative predictions based on the four-quark picture for $f_0(980)$ as it involves additional nonfactorizable contributions that are difficult to estimate and the calculations of the decay constant and form factors of $f_0(980)$ are beyond the conventional quark model.

$ B \to D^{(*)}$ transitions in a quark model

We propose a constituent quark model to evaluate heavy decay constants and form factors relevant for B=>D(*) semileptonic transitions. We show that the model reproduces the scaling laws dictated by the spin-flavour symmetry in the heavy quark limit and describes quite well the experimental data.

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.

High statistic measurement of the K$minus;$rarr;$pi;0e$minus;$nu; decay form-factors

High statistic measurement of the K$minus;$rarr;$pi;0e$minus;$nu; decay form-factors

Covariant light-front approach fors-wave andp-wave mesons: Its application to decay constants and form factors

We study the decay constants and form factors of the ground-state s-wave and low-lying p-wave mesons within a covariant light-front approach. Numerical results of the form factors for transitions between a heavy pseudoscalar meson and an s-wave or p-wave meson and their momentum dependence are presented in detail. In particular, form factors for heavy-to-light and B to D** transitions, where D** denotes generically a p-wave charmed meson, are compared with other model calculations. The experimental measurements of the decays B^- to D** pi^- and B to D D**_s are employed to test the decay constants of D**_s and the B to D** transition form factors. The heavy quark limit behavior of the decay constants and form factors is examined and it is found that the requirement of heavy quark symmetry is satisfied. The universal Isgur-Wise (IW) functions, one for s-wave to s-wave and two for s-wave to p-wave transitions, are obtained. The values of IW functions at zero recoil and their slope parameters can be used to test the Bjorken and Uraltsev sum rules.

High statistic measurement of the K−→π0e−ν decay form-factors

The decay K−→π0e−ν is studied using in-flight decays detected with the “ISTRA+” spectrometer. About 920K events are collected for the analysis. The λ+ slope parameter of the decay form-factor f+(t) in the linear approximation (average slope) is measured: λ+lin=0.02774±0.00047(stat)±0.00032(syst). The quadratic contribution to the form-factor was estimated to be λ′+=0.00084±0.00027(stat)±0.00031(syst). The linear slope, which has a meaning of df+(t)/dt|t=0 for this fit, is λ+=0.02324±0.00152(stat)±0.00032(syst). The limits on possible tensor and scalar couplings are derived: fT/f+(0)=−0.012±0.021(stat)±0.011(syst), fS/f+(0)=−0.0037+0.0066−0.0056(stat)±0.0041(syst).

Measurement of the Λb0 decay form factor

The form factor of Λb0 baryons is estimated using 3.46×106 hadronic Z decays collected by the DELPHI experiment between 1992 and 1995. Charmed Λc+ baryons fully reconstructed in the pK−π+, pK0S, and Λπ+π+π− modes, are associated to a lepton with opposite charge in order to select Λb0→Λc+l−ν̄l decays. From a combined likelihood and event rate fit to the distribution of the Isgur–Wise variable w, and using the Heavy Quark Effective Theory (HQET), the slope of the b-baryon form factor is measured to be ρ̂2=2.03±0.46(stat)+0.72−1.00(syst). The exclusive semileptonic branching fraction Br(Λb0→Λc+l−ν̄l) can be derived from ρ̂2 and is found to be (5.0+1.1−0.8(stat)+1.6−1.2(syst))%. Limits on other branching fractions are also obtained.

High statistics study of the K−→π0μ−ν decay

The decay K−→π0μ−ν has been studied using in-flight decays detected with the “STRA+” spectrometer. About 540K events were collected for the analysis. The λ+ and λ0 slope parameters of the decay form-factors f+(t), f0(t) have been measured: λ+=0.0277±0.0013(stat)±0.0009(syst), λ0=0.0183±0.0011(stat)±0.0006(syst), and dλ0/dλ+=−0.348. The limits on the possible tensor and scalar couplings have been derived: fT/f+(0)=−0.0007±0.0071, fS/f+(0)=0.0017±0.0014. No visible non-linearity in the form-factors have been observed.

Weak decays of the B c meson to B s and B mesonsin the relativistic quark model

Semileptonic and nonleptonic decays of the B_c meson to B_s and B mesons, caused by the c\to s,d quark transitions, are studied in the framework of the relativistic quark model. The heavy quark expansion in inverse powers of the active c and spectator \bar b quark is used to simplify calculations while the final s and d quarks in the B_s and B mesons are treated relativistically. The decay form factors are explicitly expressed through the overlap integrals of the meson wave functions in the whole accessible kinematical range. The obtained results are compared with the predictions of other approaches.

Weak decays of theBcmeson to charmonium andDmesons in the relativistic quark model

Semileptonic and nonleptonic decays of the ${B}_{c}$ meson to charmonium and D mesons are studied in the framework of the relativistic quark model. The decay form factors are explicitly expressed through the overlap integrals of the meson wave functions in the whole accessible kinematical range. The relativistic meson wave functions are used for the calculation of the decay rates. The obtained results are compared with the predictions of other approaches.