Two-meson Distribution Amplitudes Research Articles

Branching ratios and CP asymmetries of the quasi-two-body decays Bc→K0∗(1430,1950)D(s)→KπD(s)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c \\rightarrow \\ K^{*}_0(1430,1950) D_{(s)} \\rightarrow K \\pi D_{(s)} $$\\end{document} in the PQCD approach

In this paper, we investigate the quasi-two-body decays Bc→K0∗(1430,1950)D(s)→KπD(s)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c \\rightarrow K_0^{*}(1430,1950) D_{(s)} \\rightarrow K \\pi D_{(s)}$$\\end{document} within the perturbative QCD (PQCD) framework. The S-wave two-meson distribution amplitudes (DAs) are introduced to describe the final state interactions of the Kπ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K\\pi $$\\end{document} pair, which involve the time-like form factors and the Gegenbauer polynomials. In the calculations, we adopt two kinds of parameterization schemes to describe the time-like form factors: one is the relativistic Breit–Wigner (RBW) formula, which is usually more suitable for the narrow resonances, and the other is the LASS line shape proposed by the LASS Collaboration, which includes both the resonant and nonresonant components. We find that the branching ratios and the direct CP violations for the decays Bc→K0∗(1430)D(s)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c \\rightarrow K_0^{*}(1430) D_{(s)}$$\\end{document} obtained from those of the quasi-two-body decays Bc→K0∗(1430)D(s)→KπD(s)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c \\rightarrow K_0^{*}(1430) D_{(s)} \\rightarrow K \\pi D_{(s)}$$\\end{document} under the narrow width approximation (NWA) can be consistent well with the previous PQCD results calculated in the two-body framework by assuming that K0∗(1430)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K^*_0(1430)$$\\end{document} is the lowest lying q¯s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\bar{q} s$$\\end{document} state, which is the so-called scenario II (SII). We conclude that the LASS parameterization is more suitable to describe the K0∗(1430)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K_0^{*}(1430)$$\\end{document} than the RBW formula, and the nonresonant components play an important role in the branching ratios of the decays Bc→K0∗(1430)D(s)→KπD(s)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c \\rightarrow K_0^{*}(1430) D_{(s)} \\rightarrow K \\pi D_{(s)}$$\\end{document}. In view of the large difference between the decay width measurements for the K0∗(1950)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K_0^{*}(1950)$$\\end{document} given by BaBar and LASS collaborations, we calculate the branching ratios and the CP violations for the quasi-two-body decays Bc→K0∗(1950)D(s)→KπD(s)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c \\rightarrow K_0^{*}(1950) D_{(s)} \\rightarrow K \\pi D_{(s)}$$\\end{document} by using two values, ΓK0∗(1950)=0.100±0.04\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Gamma _{K^*_0(1950)}=0.100\\pm 0.04$$\\end{document} GeV and ΓK0∗(1950)=0.201±0.034\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Gamma _{K^*_0(1950)}=0.201\\pm 0.034$$\\end{document} GeV, besides the two kinds of parameterizations for the resonance K0∗(1950)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K^*_0(1950)$$\\end{document}. We find that the branching ratios and the direct CP violations for the decays Bc→K0∗(1950)D(s)→KπD(s)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c \\rightarrow K_0^{*}(1950) D_{(s)} \\rightarrow K \\pi D_{(s)}$$\\end{document} have not as large difference between the two parameterizations as the case of decays involving the K0∗(1430)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K^*_0(1430)$$\\end{document}, especially for the results with ΓK0∗(1950)=0.201±0.034\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Gamma _{K^*_0(1950)}=0.201\\pm 0.034$$\\end{document} GeV. The effect of the nonresonant component in the K0∗(1950)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K^*_0(1950)$$\\end{document} may be not so serious as that in the K0∗(1430)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K^*_0(1430)$$\\end{document}. The quasi-two-body decays Bc+→K0∗+(1430)D0→K0π+D0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B^+_c \\rightarrow K^{*+}_0(1430) D^{0} \\rightarrow K^0 \\pi ^+ D^{0}$$\\end{document} and Bc+→K0∗0(1430)D+→K+π-D+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B^+_c \\rightarrow K^{*0}_0(1430) D^{+} \\rightarrow K^+ \\pi ^- D^{+}$$\\end{document} have large branching ratios, which can reach to the order of 10-4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^{-4}$$\\end{document} and are most likely to be observed in the future LHCb experiments. Furthermore, the branching ratios of the quasi-two-body decays Bc→K0∗(1950)D(s)→KπD(s)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c \\rightarrow K_0^{*}(1950) D_{(s)} \\rightarrow K \\pi D_{(s)}$$\\end{document} are about one order smaller than those of the corresponding decays Bc→K0∗(1430)D(s)→KπD(s)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_c \\rightarrow K_0^{*}(1430) D_{(s)} \\rightarrow K \\pi D_{(s)}$$\\end{document}.

Quasi-two-body decays in perturbative QCD* *Supported by the National Natural Science Foundation of China (11347030), the Program of Science and Technology Innovation Talents in Universities of Henan Province, China (14HASTIT037), and the Natural Science Foundation of Henan Province, China (232300420116)

In this work, we investigate the quasi-two-body decays with using the perturbative QCD (PQCD) approach. The description of final state interactions of the pair is achieved through the two-meson distribution amplitudes (DAs), which are normalized to the time-like form factor. The PQCD predictions on the branching ratios of the quasi-two-body decays show an obvious hierarchy: and . From the invariant mass -dependence of the decay spectrum for each channel, one can find that the branching fraction is concentrated in a narrow region around the pole mass. Thus, one can obtain the branching ratios for the corresponding two-body decays under the narrow-width approximation. We find that the branching ratios of the decays are consistent with the previous PQCD calculations within errors. These predictions will be tested in future experiments.

Quasi-two-body decays in the perturbative QCD approach* *Supported in part by the National Natural Science Foundation of China under (11347030), the Program of Science and Technology Innovation Talents in Universities of Henan Province (14HASTIT037)

In this study, we investigate quasi-two-body decays in the perturbative QCD approach. Two-meson distribution amplitudes are introduced to describe the final state interactions of the pair, which involve time-like form factors and Gegenbauer polynomials. We calculate the CP averaged branching ratios of the decays. Our results are in agreement with newly updated data measured by Belle II. This suggests that it is more appropriate to analyze these quasi-two-body B decays in the three-body framework than the two-body framework. We also predict direct CP asymmetries for the considered decay modes and find that is small and less than % in magnitude, whereas is larger and can reach a few percent. Our predictions can be tested in future B meson experiments.

Study of B(s)0→ϕϕ→(K+K−)(K+K−) decays in the perturbative QCD approach

In this work, we make a detailed analysis on the penguin-dominant processes $B_{(s)}^0 \to \phi\phi \to (K^+K^-)(K^+K^-)$ in the perturbative QCD (PQCD) approach. In addition to the dominant $P$-wave resonance, the scalar background $f_0(980) \to K^+K^-$ is also accounted for. We improve the Gegenbauer moments in $KK$ two-meson distribution amplitudes by fitting the PQCD factorization formulas to measured branching ratios of three-body and four-body $B$ decays. We extract the branching ratios of two-body $B_{(s)}^0 \to \phi\phi$ decays from the corresponding four-body decay modes and calculate the relevant polarization fractions together with two relative phases $\phi_{\parallel,\perp}$, which are consistent with the previous theoretical predictions. The PQCD predictions for the "true" triple product asymmetries (TPAs) are zero which are expected in the standard model due to the vanishing weak phase difference, and support the current data reported by the CDF and LHCb Collaborations. A large "fake" TPA $\mathcal{A}_\text{T-fake}^1=30.4\%$ of the decay $B^0_s \to \phi\phi \to (K^+K^-)(K^+K^-)$ is predicted for the first time, which indicates the presence of the significant final-state interactions. The TPAs of the rare decay channel $B^0 \to \phi\phi\to (K^+K^-)(K^+K^-)$ are also predicted and can be tested in the near future.

Global determination of two-meson distribution amplitudes from three-body B decays in the perturbative QCD approach

We perform a global analysis of three-body charmless hadronic decays $B\to VP_3\to P_1P_2P_3$ in the perturbative QCD (PQCD) approach, where $V$ denotes an intermediate vector resonance, and $P_i$, $i=1,2,3$, denote final-state pseudoscalar mesons. Fitting the PQCD factorization formulas at leading order in the strong coupling $\alpha_s$ to measured branching ratios and direct $CP$ asymmetries, we determine the Gegenbauer moments in the two-meson distribution amplitudes (DAs) for the meson pairs $P_1P_2=\pi\pi, K\pi, KK$. The fitted Gegenbauer moments are then employed to make predictions for those observables, whose data are excluded in the fit due to larger experimental uncertainties. A general consistency between our predictions and data is achieved, which hints the validity of the PQCD formalism for the above three-body $B$ meson decays and the universality of the nonperturbative two-meson DAs. The obtained two-meson DAs can be applied to PQCD studies of other multi-body $B$ meson decays involving the same meson pairs. We also attempt to determine the dependence of the Gegenbauer moments on the meson-pair invariant mass, and demonstrate that this determination is promising, when data become more precise.

Four-body decays B(s) \u2192 (K\u03c0)S/P(K\u03c0)S/P in the perturbative QCD approach

We investigate the four-body decays B(s) → (Kπ)S/P(Kπ)S/P in the Kπ-pair invariant mass region around the K*(892) resonance in the perturbative QCD (PQCD) approach, where (Kπ)S/P denotes a S- or P-wave Kπ configuration. The contributions from the P-wave resonance K*(892) and from possible S-wave components are included into the parametrization of the Kπ two-meson distribution amplitudes, which are the non-perturbative inputs in this formalism. We calculate the branching ratio for each resonance and observe sizable S-wave contributions to the Bs modes, well consistent with recently available LHCb data. We also deduce the polarization fractions for the {K}^{ast }{overline{K}}^{ast } final states, and compare our predictions to those in previous PQCD analyses of the corresponding two-body B → {K}^{ast }{overline{K}}^{ast } decays. The polarization puzzle associated with the two U-spin related channels B0 → {K}^{ast 0}{overline{K}}^{ast 0} and {B}_s^0to {K}^{ast 0}{overline{K}}^{ast 0} still exists. In addition to direct CP asymmetries, triple-product asymmetries and S-wave induced direct CP asymmetries originating from the interference among various helicity amplitudes, are presented. It is shown that true triple-product asymmetries are rather small, while direct CP asymmetries and S-wave-induced direct CP asymmetries are significant in some decays. Our results will be subject to stringent tests with precise data from B factories in the near future.

Quasi-two-body decays Bc → ηc(1S,2S)D0∗+(2400) → ηc(1S,2S)D0π+ in the perturbative QCD approach

We extend our recent works on the resonant state [Formula: see text] in the quasi-two-body [Formula: see text] meson decays to the [Formula: see text] cases within the perturbative QCD approach. With the help of the two-meson distribution amplitudes, we calculate the [Formula: see text]-averaged branching fractions and direct [Formula: see text] violations of the quasi-two-body decays [Formula: see text] in this work. We also present the [Formula: see text] invariant mass dependence of the differential branching fraction for the considered decay modes. Our results could be tested by further experiments in the LHCb.

Quasi-two-body decays B rightarrow D K^*(892) rightarrow D K pi in the perturbative QCD approach

We study the quasi-two-body decays Brightarrow D K^*(892) rightarrow D Kpi by employing the perturbative QCD approach. The two-meson distribution amplitudes Phi _{Kpi }^{Ptext {-wave}} are adopted to describe the final state interactions of the kaon–pion pair in the resonance region. The resonance line shape for the P-wave Kpi component K^*(892) in the time-like form factor F_{Kpi }(s) is parameterized by the relativistic Breit-Wigner function. For most considered decay modes, the theoretical predictions for their branching ratios are consistent with currently available experimental measurements within errors. We also disscuss some ratios of the branching fractions of the concerned decay processes. More precise data from LHCb and Belle-II are expected to test our predictions.

Resonant and non-resonant contributions of B → K∗(p1,𝜖1){Kπ,ππ,KK} decay modes

In this paper, the non-leptonic three-body decays [Formula: see text], [Formula: see text], [Formula: see text] are studied by introducing two-meson distribution amplitude for the [Formula: see text], [Formula: see text] and [Formula: see text] pairs in naive and QCD factorization (QCDF) approaches, such that the analysis is simplified into quasi-two body decays. By considering that the vector meson is being ejected in factorization, the resonant and non-resonant contributions are analyzed by using intermediate mesons in Breit–Wigner resonance formalism and the heavy meson chiral perturbation theory (HMChPT), respectively. The calculated values of the resonant and non-resonant branching ratio of [Formula: see text], [Formula: see text] and [Formula: see text] decay modes are compared with the experimental data. For [Formula: see text] and [Formula: see text], the non-resonant contributions are about 70–80% of experimental data, for which the total results by considering resonant contributions are in good agreement with the experiment.

Three-body radiative decay B_srightarrow phi bar{K}^0 gamma in the PQCD approach

We study the three-body radiative decay B_srightarrow phi bar{K}^0 gamma by introducing the phi K pair distribution amplitudes (DAs) in the perturbative QCD approach. This nonperturbative input, the two-meson DAs, is very important to simplify the calculations. Besides the dominant electromagnetic penguin operator O_{7gamma }, the subleading contributions from the chromomagnetic penguin operator O_{8g}, quark-loop corrections and annihilation type amplitudes are also considered. We find that the branching ratio for the decay B_srightarrow phi bar{K}^0 gamma is about (9.26^{+1.79+3.12+0.64}_{-1.61-3.86-0.49})times 10^{-8}, which is much smaller than that for the decay B^0rightarrow phi K^0gamma . It is mainly because the former decay induced by brightarrow dgamma with small CKM matrix element is proportional to lambda ^3. The prediction for the direct CP asymmetry is A^{dir}_{CP}(B_srightarrow phi bar{K}^0 gamma )=(-4.1^{+0.4+1.7+0.2}_{-0.6-1.2-0.1})%, which is well consistent with the result from the U-spin symmetry approach. We also predict the B_s rightarrow phi bar{K}^0gamma decay spectrum, which exhibits a maximum at the phi K invariant masss around 1.95 GeV.

The three body decaysB+→π+π−π+in perturbative QCD approach

Abstract In this work, we study three body decays B + → π + π − π + in the perturbative QCD (pQCD) approach. The analysis is simplified into the one for two-body decays by introducing two-meson distribution amplitudes. We calculate both nonresonant and resonant contributions, and show the contribution to the B + → π + π − π + decays spectrum with respect to the dipion invariant mass M ( π + π − ) . Besides the usual factorizable diagrams, the non-factorizable and annihilation diagrams are also calculated analytically. The pQCD predictions for the branching ratios of B + → π + π − π + (nonresonant) are Br = 5.7 × 10 − 6 , the results of the resonant contributions are Br ( B + → π + ρ ( 770 ) ) = 8.9 × 10 − 6 . The above pQCD predictions agree well with current available data. We also predict another resonant contribution Br ( B + → π + f 0 ( 980 ) ) = 7.3 × 10 − 6 , but with large error. We still do not have a clear understanding about the inner structure of the scalar mesons f 0 . Further improvement in theory and experiments are expected.

Final state interaction in B0 → J/ψπ+π− decay

In this research, we study three body non-leptonic decay B0 → J/ψπ+π− by introducing a two-meson distribution amplitude for the π+π− pair, such that the analysis is simplified into the one for two body decay. By applying the final state interaction, the branching ratio of resonance decay is calculated by generalized factorization and improved quantum chromodynamics factorization (QCDF). Our results are (2.96 ± 0.06) × 10−5 and (4.30 ± 0.02) × 10−5 in these approximations, respectively. In QCDF at an energy scale μ = 2mb, the obtained branching ratio is in agreement with available experimental data: (4.6 ± 0.9) × 10−5.

Vector-pseudoscalar two-meson distribution amplitudes in three-bodyBmeson decays

We study three-body nonleptonic decays $B\to VVP$ by introducing two-meson distribution amplitudes for the vector-pseudoscalar pair, such that the analysis is simplified into the one for two-body decays. The twist-2 and twist-3 $\phi K$ two-meson distribution amplitudes, associated with longitudinally and transversely polarized $\phi$ mesons, are constrained by the experimental data of the $\tau\to\phi K\nu$ and $B\to\phi K\gamma$ branching ratios. We then predict the $B\to\phi K\gamma$ and $B\to\phi\phi K$ decay spectra in the $\phi K$ invariant mass. Since the resonant contribution in the $\phi K$ channel is negligible, the above decay spectra provide a clean test for the application of two-meson distribution amplitudes to three-body $B$ meson decays.

Three-body nonleptonic B decays in perturbative QCD

We develop perturbative QCD formalism for three-body nonleptonic B meson decays. Leading contributions are identified by defining power counting rules for various topologies of amplitudes. The analysis is simplified into the one for two-body decays by introducing two-meson distribution amplitudes. This formalism predicts both nonresonant and resonant contributions, and can be generalized to baryonic decays.

Exclusive production of pion pairs in γ*γ collisions at large Q2

We perform a QCD analysis of the exclusive production of two mesons in gamma^* gamma collisions in the kinematical domain of large photon virtuality Q and small hadronic invariant mass W. This reaction is dominated by a scale invariant mechanism which factorizes into a perturbative subprocess, gamma^* gamma --> q qbar or gamma^* gamma --> g g, and a generalized two-meson distribution amplitude. We develop in detail the phenomenology of this process at e^+ e^- colliders. Using a simple model for the two-pion distribution amplitude, based on its general properties, we estimate the cross section for the kinematics accessible at BABAR, BELLE, CLEO and LEP.

Exclusive hadronization in [formula omitted

We perform a QCD analysis of exclusive two-meson production in γ ∗γ- collisions in the kinematical domain of large photon virtuality Q 2 and small hadronic invariant mass W 2. In these kinematics the amplitude factorizes into a perturbative subprocess γ ∗γ → q q and a two-meson distribution amplitude. This opens the way to study new hadronic matrix elements related with the physics of hadronization and confinement.