1,344 research outputs found

    New Physics Effects and Hadronic Form Factor Uncertainties in B -> K^* l^+ l^-

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    It is well known that New Physics can contribute to weak decays of heavy mesons via virtual processes during its decays. The discovery of New Physics, using such decays is made difficult due to intractable strong interaction effects needed to describe it. Modes such as B -> K^* l^+ l^- offer an advantage as they provide a multitude of observables via angular analysis. We show how the multitude of "related observables" obtained from B -> K^* l^+ l^-, can provide many new "clean tests" of the Standard Model. The hallmark of these tests is that several of them are independent of the unknown universal form factors in heavy quark effective theory. We derive a relation between observables that is free of form factors and Wilson coefficients, the violation of which will be an unambiguous signal of New Physics. We also derive relations between observables and form factors that are independent of Wilson coefficients and enable verification of hadronic estimates. We show how form factor ratios can be measured directly from helicity fraction with out any assumptions what so ever. We find that the allowed parameter space for observables is very tightly constrained in Standard Model, thereby providing clean signals of New Physics. We examine both the large-recoil and low-recoil regions of the K^* meson and point out special features and derive relations between observables valid in the two limits. In the large-recoil regions several of the relations are unaffected by corrections to all orders in \alpha_s. We present yet another new relation involving only observables that would verify the validity of the relations between form-factors assumed in the low-recoil region. The several relations and constraints derived will provide unambiguous signals of New Physics if it contributes to these decays.Comment: 26 pages, 9 figures (20 pdf figure files). Several typos correcte

    Double charmonium production in exclusive bottomonia decays

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    This paper is devoted to the leading twist exclusive bottomonia decays with double charmonium in the final state. Using models of the twist-2 charmonia distribution amplitudes the widths of these decays are calculated within light cone formalism. In addition, the processes under consideration are studied within nonrelativistic QCD. In our analysis we have found that the production of some of the PP-wave charmonia mesons with Lz0L_z \neq 0 is allowed already at the leading twist approximation. This means that the selection rules which predict the suppression of such decays are violated. The mechanism which lies behind this violation is discussed.Comment: Minor changes, some references adde

    Study of exclusive processes e^+ e^- \to VP

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    This paper is devoted to consideration of the hard exclusive processes e+eVPe^+e^- \to VP, where V=ρ,ϕ;P=η,ηV=\rho,\phi; P=\eta,\eta'. Experimental measurement of the cross section of the process e+eϕηe^+ e^- \to \phi\eta at BaBar collaboration at large center mass energy s=10.6\sqrt s=10.6 GeV and some low energy experimental data s24\sqrt s \sim 2-4 GeV give us the possibility to study the cross section in the broad energy region. As the result, we have determined the asymptotic behavior of the cross section of e+eϕηe^+ e^- \to \phi\eta in the limit ss \to \infty, which is in agreement with perturbative QCD prediction. Assuming that the same asymptotic behavior is valid for the other processes under consideration and using low energy experimental data we have predicted the cross sections of these processes at energies s=3.67, 10.6\sqrt s=3.67,~10.6 GeV. In addition, we have calculated the cross sections of these processes at the same energies within perturbative QCD. Our results are in agreement with available experimental data.Comment: 10 pages, 2 tables, 6 figures; minor changes; article accepted to publication is Phys. Rev.

    Probing Quark Distribution Amplitudes Through Generalized Parton Distributions at Large Momentum Transfer

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    In the large momentum transfer limit, generalized parton distributions can be calculated through a QCD factorization theorem which involves perturbatively-calculable hard kernels and light-cone parton distribution amplitudes of hadrons. We illustrate this through the Hq(x,ξ,t)H_q(x,\xi,t) distribution for the pion and proton, presenting the hard kernels at leading order. As a result, experimental data on the generalized parton distributions in this regime can be used to determine the functional form of the parton distribution amplitudes which has thus far been quite challenging to obtain. Our result can also be used as a constraint in phenomenological GPD parametrizations.Comment: 7 pages, 4 figures; new references and figure added, errors correcte

    Two-photon exchange in elastic electron-proton scattering : QCD factorization approach

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    We estimate the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer Q2Q^2. It is shown that the leading two-photon exchange amplitude behaves as 1/Q41/Q^4 relative to the one-photon amplitude, and can be expressed in a model independent way in terms of the leading twist nucleon distribution amplitudes. Using several models for the nucleon distribution amplitudes, we provide estimates for existing data and for ongoing experiments.Comment: 4 pages, 4 figure

    Higher twist distribution amplitudes of the pion and electromagnetic form factor Fπ(Q2)F_{\pi}(Q^2)

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    The pion electromagnetic form factor is calculated within the QCD light-cone sum rule method and using a renormalon model for the higher twist distribution amplitudes (DAs). The theoretical predictions are compared with the experimental data and constraints on the pion leading and twist-4 DAs are extracted. An upper bound on the twist-4 contribution to the form factor and estimates of effects due to higher conformal spins in the pion twist-4 DAs are obtained.Comment: 13 pages, 7 figures; the version to appear in Phys.Rev.

    The pion diffractive dissociation into two jets

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    The method used and results obtained are described for calculation of the cross section for the pion diffractive dissociation into two jets. The main new qualitative result is that the distribution of longitudinal momenta for jets is not simply proportional to the profile of the pion wave function ϕπ(x)\phi_{\pi}(x), but depends on it in a complicated way. In particular, it is shown that under conditions of the E791 experiment, the momentum distribution of jets is similar in its shape for the asymptotic and CZ wave functions. It is concluded therefore that, unfortunately, the process considered is really weakly sensitive to the profile of the pion wave function, and the accuracy of data is insufficient to distinguish clearly between different models of ϕπ(x)\phi_{\pi}(x). Comparison with the results of other papers on this subject is given.Comment: Latex, 11 pages, 3 figures. Talk given at the International Workshop: "Exclusive Processes at High Momentum Transfer", Jefferson Lab, Newport News, VA, USA, May 15-18, 200

    Mass Spectrum in SQCD and Problems with the Seiberg Duality. Another Scenario

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    N=1 SQCD with SU(N_c) colors and N_F flavors of light quarks is considered within the dynamical scenario which assumes that quarks can be in two different phases only. These are: a) either the HQ (heavy quark) phase where they are confined, b) or they are higgsed, at the appropriate values of parameters of the Lagrangian. The mass spectra of this (direct) theory and its Seiberg's dual are obtained and compared, for quarks of equal or unequal masses. It is shown that in all cases when there is the additional small parameter at hand (it is 0<(3N_c-N_F)/N_F << 1 for the direct theory, or its analog 0<(2N_F-3N_c)/N_F << 1 for the dual one), the mass spectra of the direct and dual theories are parametrically different. A number of other regimes are also considered.Comment: 30 pages, purely technical improvements for readers convenienc

    The leading-twist pion and kaon distribution amplitudes from the QCD instanton vacuum

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    We investigate the leading-twist light-cone distribution amplitudes for the pion and kaon, based on the nonlocal chiral quark model from the instanton vacuum. Effects of explicit flavor SU(3)-symmetry breaking are taken into account. The Gegenbauer moments are computed, analyzed and compared with those of other models. The one-loop QCD evolution of the moments is briefly discussed. The transverse momentum distributions are also discussed for the pion and kaon light-cone wave functions.Comment: 17 pages, 12 figures. Accepted for publication in Physical Review

    Heat and mass transfer in gases due to pressure and temperature gradients in a laser radiation field

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    Heat and mass transfer in a one-component gas through a capillary in the field of resonant laser radiation in the presence of pressure and temperature gradients are considered. On the basis of the Boltzmann type kinetic equations in the linear approximation the expression for entropy production is obtained. Kinetic coefficients satisfy the Onsager reciprocity relations at all Knudsen numbers and for any nature of the interaction of gas atoms with the surface of the capillary. The pressure and temperature gradients established in the insulated system in a laser field are defined in a nearly free molecular regime. © 2012 American Institute of Physics
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