Showing papers on "Meson published in 1997"
TL;DR: In this article, a QCD factorization theorem for hard exclusive electroproduction of mesons in QCD was proved for the leading power in Q and all logarithms.
Abstract: We formulate and prove a QCD factorization theorem for hard exclusive electroproduction of mesons in QCD. The proof is valid for the leading power in Q and all logarithms. This generalizes previous work on vector meson production in the diffractive region of small x. The amplitude is expressed in terms of off-diagonal generalizations of the usual parton densities. The full theorem applies to all kinds of meson and not just to vector mesons. The parton densities used include not only the ordinary parton density, but also ! ,
575 citations
TL;DR: In this article, the meson-meson potentials provided by the lowest order chiral Lagrangian were used to obtain singularities in the S-wave amplitudes corresponding to the σ, f0 and a0 resonances.
552 citations
TL;DR: In this article, an effective chiral lagrangian for heavy and light mesons describing strong interactions among effective meson fields as well as their couplings to electromagnetic and weak currents, including the relevant symmetry-breaking terms is presented.
517 citations
01 Jun 1997
250 citations
TL;DR: In this article, the forward vector meson-nucleon scattering amplitudes were derived based on an effective Lagrangian which combines chiral SU(3) dynamics with vector mesons dominance, and their spectrum entered directly in the left-hand side of QCD sum rules.
250 citations
TL;DR: In this paper, the s-wave amplitudes of the SU(3) chiral meson-baryon Lagrangian with a coupled channel potential were identified in a Lippmann-Schwinger equation, and the strangeness S = −1 resonance Λ(1405) and the S 11(1535) nucleon resonance emerged as quasi-bound states of anti-kaon/nucleon and kaon/Σ-hyperon.
247 citations
TL;DR: In this paper, a set of nine observables, which to one-loop order only depend on the remaining four dimension-two couplings, were determined from a best fit.
188 citations
TL;DR: In this article, a measurement of low-mass electron pairs observed in 158 GeV/nucleon Pb-Au collisions is reported, showing that the pair yield integrated over the range of invariant masses 0.2 < m < 2.0 GeV is enhanced by a factor of 3.5 +/- 0.4 (stat) +/- 1.9 (syst) over the expectation from neutral meson decays.
Abstract: We report a measurement of low-mass electron pairs observed in 158 GeV/nucleon Pb-Au collisions. The pair yield integrated over the range of invariant masses 0.2 < m < 2.0 GeV is enhanced by a factor of 3.5 +/- 0.4 (stat) +/- 0.9 (syst) over the expectation from neutral meson decays. As observed previously in S-Au collisions, the enhancement is most pronounced in the invariant-mass region 300-700 MeV. For Pb-Au we find evidence for a strong increase of the enhancement with centrality. In addition, we show that the enhancement covers a wide range in transverse momentum, but is largest at the lowest observed pt.
170 citations
TL;DR: In this article, a consistent scheme to estimate low-energy constants related to scalar-isoscalar operators in the framework of resonance exchange involving one-loop graphs was developed.
167 citations
TL;DR: In this paper, a theoretical framework is introduced that describes possible CPT-violating effects in the context of quantum electrodynamics, and an alternative figure of merit, comparable to one commonly used in CPT tests with neutral mesons, is proposed.
Abstract: A theoretical framework is introduced that describes possible CPT-violating effects in the context of quantum electrodynamics. Experiments comparing the anomalous magnetic moments of the electron and the positron can place tight limits on CPT violation. The conventional figure of merit adopted in these experiments, involving the difference between the corresponding g factors, is shown to provide a misleading measure of the precision of CPT limits. We introduce an alternative figure of merit, comparable to one commonly used in CPT tests with neutral mesons. To measure it, a straightforward extension of current experimental procedures is proposed. With current technology, a CPT bound better than about 1 part in 1${0}^{20}$ is attainable.
158 citations
TL;DR: In this paper, a lattice calculation of the masses of mesons with exotic quantum numbers is presented, where the quenched approximation partially suppresses this mixing, and the hybrid meson masses are large {emdash} over 4 GeV for charmonium and more than twice the vector meson mass at our smallest quark mass.
Abstract: Since gluons in QCD are interacting fundamental constituents just as quarks are, we expect that in addition to mesons made from a quark and an antiquark, there should also be glueballs and hybrids (bound states of quarks, antiquarks, and gluons). In general, these states would mix strongly with the conventional {bar q}q mesons. However, they can also have exotic quantum numbers inaccessible to {bar q}q mesons. Confirmation of such states would give information on the role of {open_quotes}dynamical{close_quotes} color in low energy QCD. In the quenched approximation we present a lattice calculation of the masses of mesons with exotic quantum numbers. These hybrid mesons can mix with four quark ({bar q}{bar q}qq) states. The quenched approximation partially suppresses this mixing. Nonetheless, our hybrid interpolating fields also couple to four quark states. Using a four-quark source operator, we demonstrate this mixing for the 1{sup {minus}+} meson. Using the conventional Wilson quark action, we calculate both at reasonably light quark masses, intending to extrapolate to small quark mass, and near the charmed quark mass, where we calculate the masses of some {bar c}cg hybrid mesons. The hybrid meson masses are large {emdash} over 4 GeV for charmonium and more than twice themore » vector meson mass at our smallest quark mass, which is near the strange quark mass. {copyright} {ital 1997} {ital The American Physical Society}« less
TL;DR: In this paper, the color dipole phenomenology of diffractive photo-and electroproduction was developed for light vector mesons and their radial excitations, and a direct evaluation of the dipole cross section from these data was presented.
Abstract: We develop the color dipole phenomenology of diffractive photo- and electroproduction γ* N → V(V′)N of light vector mesons (V(1S) = ϕ0, ω0, ρ0) and their radial excitations (V′(2S) ϕ′, ω′, ρ′). The node of the radial wave function of the 2S states in conjunction with the energy dependence of the color dipole cross section is shown to lead to a strikingly different Q
2 and ν dependence of diffractive production of the V(1S) and V′(2S) vector mesons. We discuss the restoration of flavor symmetry and universality properties of production of different vector mesons as a function of Q
2 + m
V
2
. The color dipole model predictions for the ρ
0 and ϕ
0 production are in good agreement with the experimental data from the EMC, NMC, ZEUS and H1 collaborations. We present the first direct evaluation of the dipole cross section from these data.
TL;DR: In this paper, the spectral functions of the dominant two-and four-pion tau decay channels are compared to published results of ece-annihilation experiments via isospin rotation.
Abstract: A measurement of the spectral functions of non-strange tau vector current final states is presented, using 124 358 tau pairs recorded by the ALEPH detector at LEP during the years 1991 to 1994. The spectral functions of the dominant two-and four-pion tau decay channels are compared to published results of ece-annihilation experiments via isospin rotation. A combined fit of the pion form factor from tau decays and e(+)e(-)data is performed using different parameaizations. The mass and the width of the rho(+/-)(770) and the p(0)(770) are separately determined in order to extract possible isospin violating effects. The mass and width differences are measured to be M
TL;DR: A confining, Goldstone theorem preserving, separable ansatz for the ladder kernel of the two-body Bethe-Salpeter equation is constructed from phenomenologically efficacious $u$, $d, and $s$ dressed-quark propagators as mentioned in this paper.
Abstract: A confining, Goldstone theorem preserving, separable ansatz for the ladder kernel of the two-body Bethe-Salpeter equation is constructed from phenomenologically efficacious $u$, $d$, and $s$ dressed-quark propagators. The simplicity of the approach is its merit. It provides a good description of the ground-state flavor-octet pseudoscalar, vector, and axial-vector meson spectrum facilitates an exploration of the relative importance of various components of the two-body Bethe-Salpeter amplitudes, showing that subleading Dirac components are quantitatively important in the flavor-octet pseudoscalar meson channels, and allows a scrutiny of the domain of applicability of ladder truncation studies. A color-antitriplet diquark spectrum is obtained. The shortcomings of separable Ans\"atze and the ladder kernel are highlighted.
TL;DR: In this article, form factors for P{r_arrow}P and P{ r_arrow V transitions due to the valence-quark configuration are calculated directly in the entire physical range of momentum transfer.
Abstract: Within the light-front framework, form factors for P{r_arrow}P and P{r_arrow}V transitions (P denotes a pseudoscalar meson, V a vector meson) due to the valence-quark configuration are calculated directly in the entire physical range of momentum transfer. The behavior of the form factors in the infinite quark mass limit are examined to see if the requirements of heavy-quark symmetry are satisfied. We find that the Bauer-Stech-Wirbel-type light-front wave function fails to give a correct normalization for the Isgur-Wise function at zero recoil in P{r_arrow}V transition. Some of the P{r_arrow}V form factors are found to depend on the recoiling direction of the daughter mesons relative to their parents. Thus the inclusion of the nonvalence contribution arising from quark-pair creation is mandatory in order to ensure that the physical form factors are independent of the recoiling direction. The main feature of the nonvalence contribution is discussed. {copyright} {ital 1997} {ital The American Physical Society}
TL;DR: In this article, the lower moments of the deep-inelastic structure functions of the meson on the lattice were calculated with Wilson fermions and for three values of the quark mass.
Abstract: We calculate the lower moments of the deep-inelastic structure functions of the $\ensuremath{\pi}$ and the $\ensuremath{\rho}$ meson on the lattice. Of particular interest to us are the spin-dependent structure functions of the $\ensuremath{\rho}$. The calculations are done with Wilson fermions and for three values of the quark mass, so that we can perform an extrapolation to the chiral limit.
TL;DR: In this paper, the authors performed a many-body calculation of the inclusive (e, e′) cross section which runs over the three traditional regions at intermediate energies: the quasielastic peak, the dip region and the delta region.
TL;DR: In this article, a nonperturbative QCD calculation of diffractive vector meson production in virtual photon nucleon scattering at high energy is presented, using light cone wave functions of the photon and vector mesons.
Abstract: We present a nonperturbative QCD calculation of diffractive vector meson production in virtual photon nucleon scattering at high energy. We use the nonperturbative model of the stochastic QCD vacuum which yields linear confinement and makes specific predictions for the dependence of high-energy scattering cross sections on the hadron size. Using light cone wave functions of the photon and vector mesons, we calculate electroproduction cross sections for {rho}, {omega}, {phi}, and J/{psi}. We emphasize the behavior of specific observables such as the ratio of longitudinal to transverse production cross section and the t dependence of the differential cross section. {copyright} {ital 1997} {ital The American Physical Society}
TL;DR: In this article, the quark-meson coupling model was extended to investigate the change of hadron properties in finite nuclei, and a simple scaling relation for the changes of the hadron masses was found, which can be described in terms of the number of nonstrange quarks in a hadron and the value of the scalar mean field in a nucleus.
Abstract: The quark-meson coupling model, based on a mean-field description of nonoverlapping nucleon bags bound by the self-consistent exchange of $\ensuremath{\sigma}$, $\ensuremath{\omega}$, and $\ensuremath{\rho}$ mesons, is extended to investigate the change of hadron properties in finite nuclei. Relativistic Hartree equations for spherical nuclei have been derived from a relativistic quark model of the structure of bound nucleons and mesons. Using this unified, self-consistent description of both infinite nuclear matter and finite nuclei, we investigate the properties of some closed-shell nuclei and study the changes in the hadron masses of the nonstrange vector mesons, the hyperons, and the nucleon in those nuclei. We find a new, simple scaling relation for the changes of the hadron masses, which can be described in terms of the number of nonstrange quarks in the hadron and the value of the scalar mean field in a nucleus.
TL;DR: In this article, a perturbative QCD factorization theorem was developed which is compatible with effective field theory, which involves three scales: an infrared cutoff of order $\Lambda_{\rm QCD}$, a hard scale of order the $B$ meson mass, and an ultraviolet cutoff of course the W$ boson mass.
Abstract: We develop a perturbative QCD factorization theorem which is compatible with effective field theory. The factorization involves three scales: an infrared cutoff of order $\Lambda_{\rm QCD}$, a hard scale of order the $B$ meson mass, and an ultraviolet cutoff of order the $W$ boson mass. Our approach is renormalization group invariant and moderates the scale-dependence problem in effective field theory. Applying this formalism to exclusive nonleptonic $B$ meson decays, we clarify the controversy over the Bauer-Stech-Wirbel parameters $a_2/a_1$ for charm and bottom decays. It is found that the nonfactorizable contribution plays an important role in the explanation of the sign and magnitude of $a_2/a_1$.
TL;DR: In this article, the spectrum of hybrid mesons produced by gluonic excitations in quenched QCD with quark masses near the strange quark mass was evaluated from first principles.
TL;DR: In this article, the p-wave polarization operator of the ϱ-meson due to ϱN interactions via the N∗(1720) and Δ(1905) resonances was studied and the corresponding production rate for e+e− pairs at finite temperature and baryon density.
TL;DR: In this article, the relativistic Hartree Bogoliubov model is applied in the self-consistent mean-field approximation to the description of the neutron halo in the mass region above the s-d shell.
Abstract: The relativistic Hartree Bogoliubov model is applied in the self-consistent mean-field approximation to the description of the neutron halo in the mass region above the s-d shell. Pairing correlations and the coupling to particle continuum states are described by finite range two-body forces. Finite element methods are used in the coordinate space discretization of the coupled system of Dirac-Hartree-Bogoliubov integro-differential eigenvalue equations, and Klein-Gordon equations for the meson fields. Calculations are performed for the isotopic chains of Ne and C nuclei. We find evidence for the occurrence of neutron halo in heavier Ne isotopes. The properties of the 1f-2p orbitals near the Fermi level and the neutron pairing interaction play a crucial role in the formation of the halo. Our calculations display no evidence for the neutron halo phenomenon in C isotopes. {copyright} {ital 1997} {ital The American Physical Society}
TL;DR: In this article, the authors performed a many body calculation of the inclusive (e,e') cross section which runs over the three traditional regions at intermediate energies: the quasielastic peak, the dip region and the delta region.
Abstract: We have performed a many body calculation of the inclusive (e,e') cross section which runs over the three traditional regions at intermediate energies: the quasielastic peak, the dip region and the delta region. The longitudinal and transverse response functions in the quasielastic peak have also been evaluated. Traditional effects like polarization, meson exchange currents, final state interaction and delta renormalization in the nuclear medium have been included.
Meson exchange currents are generated from a model of pion electroproduction on the nucleon which reproduces accurately the experimental data.
The inclusive cross section accounts for 1N,2N,3N mechanisms of virtual photon absorption and one pion production. Meson exchange currents associated to the (\gamma^*,2\pi) reaction are also accounted for.
We obtain good results for the (e,e') cross sections in the whole energy range and for different nuclei. The response functions are also in good agreement with the latest experimental analysis. On the other hand, the method provides the separation of the contribution to the inclusive cross section from different physical channels which is a necessary input to evaluate cross sections like (e,e' N), (e,e' NN), (e,e' \pi) etc.
TL;DR: A Fortran program for the calculation of the ground state properties of axially deformed even-even nuclei in the framework of Relativistic Mean Field Theory (RMF) is presented in this article.
TL;DR: In this article, the authors derive and update light-cone sum rules for all the semileptonic form factors, using recent results on the meson distribution amplitudes, and also derive a set of ''improved'' three-point sum rules, in which some of the problems of the short-distance expansion are avoided.
Abstract: The existing calculations of the form factors describing the decay $B\ensuremath{\rightarrow}\ensuremath{\rho}e\ensuremath{
u}$ from QCD sum rules have yielded conflicting results at small values of the invariant mass squared of the lepton pair. We demonstrate that the disagreement originates from the failure of the short-distance expansion to describe the $\ensuremath{\rho}$ meson distribution amplitude in the region where almost the whole momentum is carried by one of the constituents. This limits the applicability of QCD sum rules based on the short-distance expansion of a three-point correlation function to heavy-to-light transitions and calls for an expansion around the light cone, as realized in the light-cone sum rule approach. We derive and update light-cone sum rules for all the semileptonic form factors, using recent results on the $\ensuremath{\rho}$ meson distribution amplitudes. The results are presented in detail together with a careful analysis of the uncertainties, including estimates of higher-twist effects, and compared to lattice calculations and recent CLEO measurements. We also derive a set of ``improved'' three-point sum rules, in which some of the problems of the short-distance expansion are avoided and whose results agree to good accuracy with those from light-cone sum rules.
TL;DR: In this paper, the in-medium properties of K − mesons in nuclear matter were discussed, including the effect of K ± sub-threshold production in heavy-ion collisions.
TL;DR: In this article, the effect of the breakdown of rotational symmetry for the one-body current operator in the null plane is investigated by comparing calculations within light-front and covariant approaches.
Abstract: The $\ensuremath{\rho}$-meson electromagnetic form factors are calculated, both in covariant and light-front frameworks with constituent quarks. The effect of the breakdown of rotational symmetry for the one-body current operator in the null plane is investigated by comparing calculations within light-front and covariant approaches. This allows to choose the appropriate light-front prescription, among the several ones, to best evaluate the $\ensuremath{\rho}$-meson form factors.
TL;DR: In this paper, a chiral Lagrangian was derived in the large-N{sub c} limit from a Nambu{endash}Jona-Lasinio (NJL) quark model with separable nonlocal interactions, with form factors corresponding to three-dimensional ground and excited-state wave functions.
Abstract: We construct a chiral Lagrangian containing, in addition to the usual pion field ({pi}), also its first radial excitation ({pi}{sup {prime}}). The Lagrangian is derived in the large-N{sub c} limit from a Nambu{endash}Jona-Lasinio (NJL) quark model with separable nonlocal interactions, with form factors corresponding to three-dimensional ground- and excited-state wave functions. Chiral symmetry breaking is governed by the NJL gap equation. The effective Lagrangian for {pi} and {pi}{sup {prime}} mesons shows the decoupling of the Goldstone pion and the vanishing of the {pi}{sup {prime}} leptonic decay constant f{sub {pi}{sup {prime}}} in the chiral limit, as required by axial-vector current conservation. We derive the excited-state contribution to the axial-vector current of the model using Noether{close_quote}s theorem. For a finite pion mass and {pi}{sup {prime}} masses in the range of 750{endash}1300 MeV, f{sub {pi}{sup {prime}}}/f{sub {pi}} is found to be of the order of 1{percent}. {copyright} {ital 1997} {ital The American Physical Society}
TL;DR: In this paper, the quark-meson coupling (QMC) model is applied to describe the properties of both infinite nuclear matter and finite nuclei, which automatically leads to a very weak spin-orbit interaction for the $\Lambda$ in a hypernucleus.
Abstract: The quark-meson coupling (QMC) model, which has been successfully used to describe the properties of both infinite nuclear matter and finite nuclei, is applied to a systematic study of $\Lambda, \Sigma$ and $\Xi$ hypernuclei. Assumptions made in the present study are, (i) the (self-consistent) exchanged scalar, and vector, mesons couple only to the u and d quarks, and (ii) an SU(6) valence quark model for the bound nucleons and hyperon. The model automatically leads to a very weak spin-orbit interaction for the $\Lambda$ in a hypernucleus. Effects of the Pauli blocking at the quark level, particularly in the open, coupled, $\Sigma N - \Lambda N$ channel (strong conversion), is also taken into account in a phenomenological way.