131 research outputs found

    A novel way to probe distribution amplitudes of neutral mesons in e^+e^- annihilation

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    We derive the amplitude for the process e+eπ0π0e^+e^-\to \pi^0\pi^0 at large invariant energy. The process goes through the two-photon exchange and its amplitude is expressed in terms of the convolution integral which depends on the shape of the pion distribution amplitude (DA) and the centre of mass scattering angle. Remarkable feature of the integral is that it is very sensitive to the end-point behaviour of the pion DA -- it starts to diverge if pion DA nullifies at the end-point as x\sqrt x or slower. That makes the e+eπ0π0e^+e^-\to \pi^0\pi^0 process unique probe of the shape of the meson DAs. The estimated cross section is rather small, for s=3\sqrt s = 3 GeV it ranges from a fraction of femtobarn (for the asymptotic DA) to couple of femtobarn (for the Chernyak-Zhitnitsky DA). The observation of the process e+eπ0π0e^+e^-\to\pi^0\pi^0 with the cross section higher as estimated here would imply very unusual form of the pion DA, e.g. the flat one. The derived amplitude can be easily generalized to other processes like e+eσσ,KSKS,ηη,ηη,π0f2e^+e^-\to \sigma\sigma, K_SK_S, \eta\eta, \eta^\prime\eta, \pi^0 f_2, etc.Comment: 5 pages, 3 figure

    Coulomb dissociation of a fast pion into two jets

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    We calculate the electromagnetic contribution to the scattering amplitude of pion diffractive dissociation into di-jets which is described by one photon exchange. The result shows that the factorization procedure known for the description of exclusive reactions holds also for this quasi-exclusive process. We find that the longitudinal momentum distribution of di-jets does not depend on the form of the pion distribution amplitude. We discuss the magnitude of the cross section.Comment: 7 pages, 3 .eps figures, Late

    Operator Relations for SU(3) Breaking Contributions to K and K* Distribution Amplitudes

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    We derive constraints on the asymmetry a1 of the momentum fractions carried by quark and antiquark in K and K* mesons in leading twist. These constraints follow from exact operator identities and relate a1 to SU(3) breaking quark-antiquark-gluon matrix elements which we determine from QCD sum rules. Comparing our results to determinations of a1 from QCD sum rules based on correlation functions of quark currents, we find that, for a1^\parallel(K*) the central values agree well and come with moderate errors, whereas for a1(K) and a1^\perp(K*) the results from operator relations are consistent with those from quark current sum rules, but come with larger uncertainties. The consistency of results confirms that the QCD sum rule method is indeed suitable for the calculation of a1. We conclude that the presently most accurate predictions for a1 come from the direct determination from QCD sum rules based on correlation functions of quark currents and are given by: a1(K) = 0.06\pm 0.03, a1^\parallel(K*) = 0.03\pm 0.02, a1^\perp(K*) = 0.04\pm 0.03.Comment: 21 page

    On mixed phases in gauge theories

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    In many gauge theories at different values of parameters entering Lagrangian, the vacuum is dominated by coherent condensates of different mutually non-local fields (for instance, by condensates of electric or magnetic charges, or by various dyons). It is argued that the transition between these "dual to each other" phases proceeds through the intermediate "mixed phase", having qualitatively different features. The examples considered include: ordinary YM, N=1 SYM, N=1 SQCD, and broken N=2 SYM and SQCD.Comment: Latex, 19 pages; Talk given at "Continuous Advances in QCD-2002/Arkadyfest", honoring the 60-th birthday of Arkady Vainshtein; 17-23 May 2002, University of Minneapolis, Minnesota, USA; v.3: the extended and improved versio

    Mass corrections in J/ψBBˉJ/\psi \to B\bar B decay and the role of distribution amplitudes

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    We consider mass correction effects on the polar angular distribution of a baryon--antibaryon pair created in the chain decay process ee+J/ψBBˉe^-e^+ \to J/\psi \to B\bar B, generalizing a previous analysis of Carimalo. We show the relevance of the features of the baryon distribution amplitudes and estimate the electromagnetic corrections to the QCD results.Comment: 26 pages + 3 figures, REVTEX 3.0, figures appended as uuencoded, tar-compressed postscript fil

    QCD Calculation of the Bπ,KB \rightarrow \pi,K Form Factors

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    We calculate the form factors for the heavy-to-light transitions Bπ,KB\rightarrow \pi,K by means of QCD sum rules using π\pi and KK light-cone wave functions. Higher twist contributions as well as gluonic corrections are taken into account. The sensitivity to the shape of the leading-twist wave functions and effects of SU(3)-breaking are discussed. The results are compared with quark model predictions and with the results from QCD sum rules for three-point correlators.Comment: 13 pages +5 figures available upon request , LaTeX , CERN-TH.6880/93, MPI-Ph/93-32, LMU-07/9

    Models for Light-Cone Meson Distribution Amplitudes

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    Leading-twist distribution amplitudes (DAs) of light mesons like pi,rho etc. describe the leading nonperturbative hadronic contributions to exclusive QCD reactions at large energy transfer, for instance electromagnetic form factors. They also enter B decay amplitudes described in QCD factorisation, in particular nonleptonic two-body decays. Being nonperturbative quantities, DAs cannot be calculated from first principles, but have to be described by models. Most models for DAs rely on a fixed order conformal expansion, which is strictly valid for large factorisation scales, but not always sufficient in phenomenological applications. We derive models for DAs that are valid to all orders in the conformal expansion and characterised by a small number of parameters which are related to experimental observables.Comment: 19 pages, 10 figure

    Symmetries and Asymmetries of B -> K* mu+ mu- Decays in the Standard Model and Beyond

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    The rare decay B -> K* (-> K pi) mu+ mu- is regarded as one of the crucial channels for B physics as the polarization of the K* allows a precise angular reconstruction resulting in many observables that offer new important tests of the Standard Model and its extensions. These angular observables can be expressed in terms of CP-conserving and CP-violating quantities which we study in terms of the full form factors calculated from QCD sum rules on the light-cone, including QCD factorization corrections. We investigate all observables in the context of the Standard Model and various New Physics models, in particular the Littlest Higgs model with T-parity and various MSSM scenarios, identifying those observables with small to moderate dependence on hadronic quantities and large impact of New Physics. One important result of our studies is that new CP-violating phases will produce clean signals in CP-violating asymmetries. We also identify a number of correlations between various observables which will allow a clear distinction between different New Physics scenarios.Comment: 56 pages, 18 figures, 14 tables. v5: Missing factor in eqs. (3.31-32) and fig. 6 corrected. Minor misprints in eq. (2.10) and table A corrected. Conclusions unchange

    DDπD^*D\pi and BBπB^*B\pi couplings in QCD

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    We calculate the DDπD^*D\pi and BBπB^*B\pi couplings using QCD sum rules on the light-cone. In this approach, the large-distance dynamics is incorporated in a set of pion wave functions. We take into account two-particle and three-particle wave functions of twist 2, 3 and 4. The resulting values of the coupling constants are gDDπ=12.5±1g_{D^*D\pi}= 12.5\pm 1 and gBBπ=29±3g_{B^*B\pi}= 29\pm 3 . From this we predict the partial width \Gamma (D^{*+} \ra D^0 \pi^+ )=32 \pm 5~ keV . We also discuss the soft-pion limit of the sum rules which is equivalent to the external axial field approach employed in earlier calculations. Furthermore, using gBBπg_{B^*B\pi} and gDDπg_{D^*D\pi} the pole dominance model for the B \ra \pi and D\ra \pi semileptonic form factors is compared with the direct calculation of these form factors in the same framework of light-cone sum rules.Comment: 27 pages (LATEX) +3 figures enclosed as .uu file MPI-PhT/94-62 , CEBAF-TH-94-22, LMU 15/9
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