Probing the interactions of charmed mesons with nuclei in ¯p-induced reactions

We study the perspectives of resonant and nonresonant charmed-meson production in ˉp + A reactions within the Multiple Scattering Monte Carlo (MSMC) approach. We calculate the production of the resonances Ψ(3770),Ψ(4040) and Ψ(4160) on various nuclei, their propagation and decay to D,ˉD, D ^*,ˉD^*, D _s,ˉD_s in the medium and vacuum, respectively. The modifications of the open charm vector mesons in the nuclear medium are found to be rather moderate or even small such that dilepton spectroscopy will require an invariant mass resolution of a few MeV. Furthermore, the elastic and inelastic interactions of the open charm mesons in the medium are taken into account, which can be related to (u, d )-, s- or c-quark exchange with nucleons. It is found that by studying the D/ˉD ratio for low momenta in the laboratory ( ? 2 - 2.2 GeV/c) as a function of the target mass A stringent constraints on the c-quark exchange cross-section can be obtained. On the other hand, the ratios D ^- _s/D ⁺ _s as well as D/D ^- _s and D/D ⁺ _s at low momenta as a function of A will permit to fix independently the strength of the s-quark exchange reaction in D ^- _s N scattering. Received: 1 March 2002 / Accepted: 21 March 2002     

Interactions of charmed mesons with nucleons in the ¯<Emphasis Type="Italic">p</Emphasis><Emphasis Type="Italic">d</Emphasis> reaction

We study the possibility to measure the elastic ΦN (Φ≡J/ψ,ψ(2S), ψ(3770), χ_2c) scattering cross section in the reaction ˉp+d→Φ+n _sp and the elastic D(ˉD)N scattering cross section in the reaction ˉp+d→D ⁻ D ⁰ p _sp. Our studies indicate that the elastic scattering cross sections can be determined for Φ momenta about 4–6 GeV/c and D/ˉD momenta 2–5 GeV/c by selecting events with p _t≥ 0.4 GeV/c for Φ's and p _t(p _sp) ≥ 0.5 GeV/c for D/ˉD-meson production. Received: 8 November 1999     

Dilepton production from ρ-mesons in a quark-gluon plasma

Assuming that ρ-mesons exist in a quark-gluon plasma at temperatures close to the QCD phase transition, we calculate the dilepton production rate from q-ˉq annihilation via a ρ-meson state using Vector Meson Dominance. The result is compared to the rates from direct q-ˉq annihilation and from π⁺-π⁻ annihilation. Furthermore we discuss the suppression of low mass dileptons if the quarks assume an effective mass in the quark-gluon plasma. Received: 8 September 1999 / Revised version: 22 October 1999     

Threshold open charm production in nucleon-nucleon collisions

The associative charm particles production in nucleon-nucleon collisions N + N↦Λ_c(Σ_c) + ˉD + N, is described in a general way and the spin and isospin structure of the corresponding matrix elements are derived. Using an analogy with strange-particle (ΛK) production, the D-meson exchange model is considered in detail. Estimations of the energy behavior of the threshold cross-sections show a large dependence on the form of the phenomenological hadron form factors and indicate that, at threshold, the cross-section is three orders of magnitude smaller than for strange-particle production. Received: 18 October 2002 / Accepted: 5 December 2002 / Published online: 18 March 2003 RID="a" ID="a"Permanent address: National Science Center KFTI, 310108 Kharkov, Ukraine. RID="b" ID="b"e-mail: etomasi@cea.fr Communicated by V.V. Anisovich     

Chiral invariant phase space event generator

The Geant4 CHIPS model simulates both decay and nuclear capture of negative muons. In hadron level models the muon is captured by a proton, p(μ,ν_μ)n , and the neutron transfers to the nucleus only 5MeV, which is not enough to split a nucleon from the nucleus, while the measured spectra of emitted nucleons reach 80MeV. In CHIPS, which considers asymptotically free quark-partons, the muon can be captured by a quark, u(μ,ν_μ)d , and transfers 52MeV to the nucleus. This capture mechanism fits the main part of the nucleon spectra, while the high-energy part of the spectra is not fitted. A precise fit of the high-energy part of the nucleon spectra can be made if the muon decay μ → dˉν_μ is taken into account.     

Forward dispersion relations and Roy equations in <Emphasis Type="Italic">ππ</Emphasis> scattering

We first review the results of an analysis of ππ interactions in S, P and D waves for the two-pion effective mass from threshold to about 1.4GeV. In particular, we show a recent improvement of this analysis above the Kˉ threshold using more data for phase shifts and including the S0-wave inelasticity from ππ→Kˉ. In addition, we have improved the fit to the f ₂(1270)-resonance and used a more flexible P-wave parametrization above the Kˉ threshold and included an estimation of the D2-wave inelasticity. The better accuracy thus achieved also required a refinement of the Regge analysis above 1.42GeV. Finally, in this work we check that the ππ scattering amplitudes obtained in this approach satisfy remarkably well forward dispersion relations and Roy's equations.     

ππ scattering and the meson resonance spectrum

A ππ, ˉKK, and ρρ(ωω) fully coupled channel model is used to predict the lowest isospin S, P, D, F-wave phase shifts and inelasticities for elastic ππ scattering from threshold to 2.0 GeV. As input the S-matrix is required to exhibit poles corresponding to the meson resonance table of the Particle Data Group. As expected, the ππ inelasticity is very strongly related to the opening of the ˉK channel near 1 GeV, and the opening of ρρ(4π) and ωω(6π) channels in the 1.5 GeV region. The predictions of this model are compared to the various elastic ππ→ππ amplitudes, that were obtained from analyses of π⁻ p →π⁻π⁺n data. The role of the various resonances, in particular the glueball candidate f ₀(1500) and the f _J(1710) is investigated. Received: 19 November 1997     

On the Absorption of antibaryons in nuclei

Antiproton (ˉp) and antilambda (ˉΛ) production has been measured for minimum bias in p+A collisions and central A₁+ A₂ collisions at the CERN-SPS by the collaborations NA35/49 and NA44. The measurements are extrapolated from rapidity distributions to absolute minimum bias cross sections. It is shown that the ˉp cross sections divided by A₁· A₂ follow an exponential trend as a function of a characteristic length obtained from a Glauber type absorption model, while the ˉΛ cross sections divided by A₁· A₂ are constant. The exponential trend also holds for ˉp production at the lower energies of the Brookhaven AGS. A discussion of the physics interpretation of the established trends in terms of an effective absorption cross section is presented. Received: 15 July 1999 / Revised version: 10 November 1999     

A remark on transition probability

Uhlmann's transition probability P(ψ, φ) of two normal states of a von Neumann algebra M, which is the supremum of |(Ψ, Φ)|² for all possible choices of representative vectors Ψ and Φ of ψ and φ, is shown to be the infimum of (∫d(μ_{ψ, e})^1/2)² for the induced measures μ_{ω, e}(B)=ω(e(B)) (B: Borel set in ℝ, ω=ψ, φ) for all possible projection-valued measures e belonging to M.     

Partial widths for the decays η:(1295) →γγ and η:(1440) →γγ

We discuss γγ partial widths of pseudoscalar/isoscalar mesons η:(M) in the mass region M∼ 1000–1500 MeV. The transition amplitudes η:(1295) →γγ and η:(1440) →γγ are studied within an assumption that the decaying mesons are the members of the first radial excitation nonet 2¹ S ₀qˉq. The calculations show that partial widths being of the order of 0.1 keV are dominantly due to the nˉn meson component while the contribution of the sˉs component is small. Received: 24 September 1999     

Registration of hydrogen-like leptonic bound states ( e-μ+) and ( e+μ-) in reactions of high-energy scattering of polarized electrons and positrons by nuclei with Z ～ 100 and analysis of CPT invariance

The cross-sections for the reactions of muonium (anti-muonium) production in the high-energy electron (positron) scattering by nuclei e ^-(e ⁺) + Z↦Z + M ⁰(ˉM) + μ^-(μ⁺) are calculated in dependence on energy and polarization of the initial electron (positron) and polarization of the final μ^-(μ⁺)-meson. Since this is a coherent phenomenon the cross-sections are proportional to Z². For Z ∼ 100, due to the factor Z², the cross-sections are large enough to be measured at the energies available for the HERA Collider at DESY. The results are discussed in connection with a test of CPT invariance. Received: 24 September 2002 / Accepted: 12 March 2003 / Published online: 27 May 2003     

Productions of X(1835) as baryonium with sizable gluon content

X(1835) has been treated as a baryonium with sizable gluon content, and to be almost flavor singlet. This picture allows us to rationally understand X(1835) production in J/ψ radiative decays, and its large couplings with pˉ, η^′ππ. The processes ϒ(1S) → γX(1835) and J/ψ → ωX(1835) have been examined. It has been found that Br(ϒ(1S) → γX(1835))Br(X(1835) → pˉ) < 6.45×10^-7, which is compatible with CLEO's recent experimental result (Phys. Rev. D 73, 032001 (2006) hep-ex/0510015). The branching fractions Br(J/ψ → ωX(1835)), Br(J/ψ → ρX(1835)) with X(1835) → pˉ and X(1835) → η^′π⁺π^- have been estimated by the quark-pair creation model. We show that they are heavily suppressed, so the signal of X(1835) is very difficult, if not impossible, to be observed in these processes. The experimental checks for these estimations are expected. The existence of the baryonium nonet is conjectured, and a model-independent derivation of their production branching fractions is presented.     

¯N interaction from meson-exchange and quark-gluon dynamics

We investigate the ˉN interaction at low energies using a meson exchange model supplemented with a short-distance contribution from one-gluon exchange. The model is developed in close analogy to the meson-exchange KN interaction of the Jülich group utilizing SU(4) symmetry constraints. The main ingredients of the interaction are provided by vector meson (ρ , ω exchange and higher-order box diagrams involving ˉ^* N , ˉΔ , and ˉ^*Δ intermediate states. The short-range part is assumed to receive additional contributions from genuine quark-gluon processes. The predicted cross-sections for ˉN for excess energies up to 150MeV are of the same order of magnitude as those for KN but with average values of around 20mb, roughly a factor two larger than for the latter system. It is found that the ω -exchange plays a very important role. Its interference pattern with the ρ -exchange, which is basically fixed by the assumed SU(4) symmetry, clearly determines the qualitative features of the ˉN interaction --very similiar to what happens also for the KN system.     

Scales in nuclear matter: Chiral dynamics with pion nucleon form factors<Superscript>⋆</Superscript>

A systematic calculation of nuclear matter is performed which includes the long-range correlations between nucleons arising from one- and two-pion exchange. Three-body effects from 2π exchange with excitations of virtual Δ(1232)-isobars are also taken into account in our diagrammatic calculation of the energy per particle ˉ(k _f). In order to eliminate possible high-momentum components from the interactions we introduce at each pion-baryon vertex a form factor of monopole type. The empirical nuclear matter saturation point, ρ₀ ≃ 0.16fm^-3, ˉ₀ ≃ - 16MeV, is well reproduced with a monopole mass of Λ ≃ 4πf _π ≃ 1.16GeV. As in the recent approach based on the universal low-momentum NN potential V _low-k, the inclusion of three-body effects is crucial in order to achieve saturation of nuclear matter. We demonstrate that the dependence of the pion exchange contributions to ˉ(k _f) on the “resolution” scale Λ can be compensated over a wide range of Λ by counterterms with two “running” contact couplings. As a further application we study the in-medium chiral condensate 〈ˉq〉(ρ) beyond the linear density approximation. For ρ ⩽ 1.5ρ₀ we find small corrections from the derivative dˉ(k _f)/dm _π, which are stable against variations of the monopole regulator mass Λ.     

Optical properties of thin films of closely packed SiO2 spheres

Ordered, closely packed, defect-free one-, two-, and three-layer thick films of SiO₂ spheres of diameter D varying from 0.6 to 1.4 μm were obtained. Their optical transmittance and reflectance spectra were measured in the range 0.3–2.5 eV. The one-layer structures reveal a transmittance minimum whose spectral position is described by the Bragg law with the plane separation equal to the sphere radius D/2. As the number of the layers increases, a spectral feature appears which signals the formation of a photonic gap in the 〈111〉 direction of the fcc crystal lattice and is determined by the distance between the {111} planes equal to 0.816D. The spectra of two-and three-layer structures measured with a diverging light beam contain additional lines originating from the formation of photonic gaps by the {111} and {221} planes. __________ Translated from Fizika Tverdogo Tela, Vol. 44, No. 6, 2002, pp. 1026–1031. Original Russian Text Copyright ? 2002 by Bazhenov, Gorbunov, Aldushin, Masalov, Emel’chenko.     

New results for the production of Λ and Σhyperons in antineutrino scattering from protons

We obtain total and differential cross-sections for the strangeness changing charged current reactions ˉ + p → Λ + L ⁺ and ˉ + p → Σ⁰ + L ⁺ , where L is a charged lepton, either an electron, muon or tau. We do this by making use of the standard dipole form factors normally used and of the new form factors recently obtained from recoil proton measurements in electron-proton electromagnetic scattering. We also obtain the contributions of the individual form factors to the total and differential cross-sections for both sets of form factors. We find that the differential and total cross-sections for Λ production change only slightly between the two sets of form factors but that the differential and total cross-sections change substantially for Σ⁰ production. We discuss the possibility of distinguishing between the two cases for the experiments planned by the MINERν A Collaboration.     

OZI rule violation in p¯p annihilation into φππ by two step processes

The φπ⁺π⁻ production in pˉp annihilation at rest is strongly enhanced by a two step mechanism with intermediate KˉKππ states. The relative yield of the φ production due to the resonant final state interaction decreases with increasing total energy of the pˉp system. Received: 4 August 1997     

Electromagnetic polarizabilities of the nucleon and properties of the σ-meson pole contribution

The t-channel contribution to the difference of electromagnetic polarizabilities of the nucleon, (α - β)^t, can be quantitatively understood in terms of a σ-meson pole in the complex t-plane of the invariant scattering amplitude A ₁(s, t) with properties of the σ-meson as given by the quark-level Nambu-Jona-Lasinio model (NJL). Equivalently, this quantity may be understood in terms of a cut in the complex t-plane where the properties of the σ-meson are taken from the ππ → σ → ππ, γγ → σ → ππ and Nˉ → σ → ππ reactions. This equivalence may be understood as a sum rule where the properties of the σ-meson as predicted by the NJL model are related to the f ₀(600) particle observed in the three reactions. In the following, we describe details of the derivation of (α - β)^t making use of predictions of the quark-level NJL model for the σ-meson mass. An erratum to this article is available at .     

Subthreshold ϕ-meson production and medium effects in proton-nucleus reactions

Within the spectral function approach, we study the direct production and decay via the dikaon (dimuon) channel of ϕ mesons in the interactions of 2.4-and 2.7-GeV protons with light and medium target nuclei. It is shown that the K ⁺ K ⁻ (μ⁺ μ⁻) invariant-mass distribution consists of the two components, which correspond to the ϕ decay “outside” and “inside” the target nucleus. The first (narrow) component has the free ϕ width, while the second (broad) component is distorted by the nuclear matter owing to resonance-nucleon scattering and a possible in-medium modification of the kaons and ρ meson at finite baryon density. The relative strength of the “inside” and “outside” components is analyzed in different scenarios for the ϕ width and momentum cut. It is demonstrated that the width of the resulting dimuon invariant-mass distribution on medium nuclei is larger than the free ϕ width by a factor of about 2 if the total ϕ in-medium width is used and the respective cutoff for the ϕ three-momentum is applied, whereas the resulting dikaon invariant-mass distribution has an insignificant sensitivity to the ϕ in-medium properties owing to the strong absorption of the K ⁻ in the surrounding nuclear matter. On the other hand, because of the distortion of the K ⁺ and K ⁻ on their way out of the target nucleus mainly due to the hadronic kaon potentials, the latter distribution is broadened and shifted to higher invariant masses, which means that the measurement of such broadening would give additional evidence for the modification of the kaon and antikaon properties in the nuclear medium. The text was submitted by the author in English.     

Testing the nature of the Λ(1520)-resonance in proton-induced production

The Λ(1520)-resonance has been recently studied in a unitarized coupled-channel formalism with πΣ(1385), KΞ(1530), ˉN and πΣ as constituents blocks. We provide a theoretical study of the predictions of this model in physical observables of the pp → pK⁺K^-p and pp → pK⁺π⁰π⁰Λ reactions. In particular, we show that the ratio between the π⁰π⁰Λ and K^-p mass distributions can provide valuable information on the ratio of the couplings of the Λ(1520)-resonance to πΣ(1385) and ˉN than the theory predicts. Calculations are done for energies which are accessible in an experimental facility like COSY at Jülich or the developing CSR facility at Lanzhou.