Investigation of the structure of a muon disk for <Emphasis Type="Italic">E</Emphasis><Subscript>0</Subscript> ≥ 5 × 10<Superscript>16</Superscript> eV according to data of the Yakutsk array for studying extensive air showers

The results are presented that were obtained at the Yakutsk array by investigating the time structure of a muon disk in extensive air showers of primary energy in the region E ₀ ≥ 5 × 10¹⁶ eV at distances of 250 to 1500 m from the shower core. The measurements were performed with a large muon detector that has an area of 184 m² and a detection threshold of E _μ≈0.5secθ GeV and which began operating in November 1995. Two components having different muon-disk thicknesses were discovered, and this requires strong modifications in the currently prevalent idea of the development of extensive air showers. The problem of the existence of E ₀ ≥ 10²⁰ eV events is considered. __________ Translated from Yadernaya Fizika, Vol. 68, No. 1, 2005, pp. 74–88. Original Russian Text Copyright ? 2005 by Glushkov, Dedenko, Sleptsov.     

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     

a 0 + (980)-resonance production in the reaction pp → dπ + η close to the K\bar K threshold

The reaction pp → dπ ⁺ η has been measured at a beam energy of T _p = 2.65 GeV (p _p = 3.46 GeV/c) using the ANKE spectrometer at COSY-Julich. The missing-mass distribution of the detected dπ ⁺ pairs exhibits a peak around the η mass on top of a strong background of multipion pp → dπ ⁺(nπ) events. The differential cross section d ⁴ σ/dΩ_d dΩ _π ⁺ dp _d dp _π ⁺ for the reaction pp → dπ ⁺ η has been determined model independently for two regions of phase space. Employing a dynamical model for the a ₀ ⁺ production allows one then to deduce a total cross section of σ(pp → da ₀ ⁺ → dπ ⁺ η) = 1.1 ± 0.3_stat ± 0.7_syst μb for the production of π ⁺ η via the scalar a ₀ ⁺ (980) resonance and σ(pp → dπ ⁺ η) = 3.5 ± 0.3_stat ± 1.0_syst μb for the nonresonant production. Using the same model as for the interpretation of recent results from ANKE for the reaction , the ratio of the total cross sections is , which is in agreement with branching ratios in the literature. The text was submitted by the authors in English.     

Exotic states X ±(1600, I G (J PC)=2+ (2++)) in photoproduction reactions

It is shown that the list of unusual mesons that are planned to be studied in photoproduction reactions can be supplemented with I ^G (J ^PC)=2⁺ (2⁺⁺) exotic states X ^±(1600), which are natural to seek as manifestations of the ρ^±ρ⁰ decay channels in the reactions γN → ρ^±ρ⁰ N and γN → ρ^±ρ⁰Δ. A classification of the ρ^±ρ⁰ states according to their quantum numbers is presented. A model for the spin structure of the amplitudes for the reactions γp → f ₂(1270)p, γp → a ₂ ⁰ (1320)p, and γN → X ^±(N, Δ) is proposed, and estimates are obtained for the corresponding cross sections. At E _γ≈6 GeV, it is found that σ(γP → f ₂(1270)p)≈0.12 μb, σ(γp → a ₂ ⁰ (1320)p)≈0.25 μb, σ(γN → X ^± N → ρ^±ρ⁰ N) ≈ 0.018 μb, and σ(γp → X ⁻Δ⁺⁺ → ρ⁻ρ⁰Δ⁺⁺≈0.031 μb. The problem of isolating signals from X ^± states against the natural background that is associated with other channels of π^±π⁰π⁺π⁻ production is discussed. It is deduced that searches for exotic states X ^±(2⁺ (2⁺⁺)) in experiments at JLAB will be quite efficient—for example, the yield of about 2.8×10⁶ events per month is expected to correspond to the estimated cross sections for the reactions γN → X ^± N → ρ^±ρ⁰ N. __________ Translated from Yadernaya Fizika, Vol. 63, No. 10, 2000, pp. 1904–1912. Original Russian Text Copyright ? 2000 by Achasov, Shestakov.     

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     

Magnetic moment of the <Emphasis Type="Italic">ρ</Emphasis> meson in QCD sum rules

The magnetic moment μ of the ρ meson is calculated in the framew ork of QCD sum rules in external fields. Bare-loop calculations (parton model) give μ_part=2.0 (in units e/(2m_ρ)). The contribution of operators of dimension 6 reduces this value: μ = 1.5 ± 0.3. From Yadernaya Fizika, Vol. 68, No. 1, 2005, pp. 116–120. Original English Text Copyright ? 2005 by Samsonov. This article was submitted by the author in English.     

Hadron diffractive processes: the structure of soft pomeron and colour screening

On the basis of the experimental data on diffractive processes in πp, pp and pˉp collisions at intermediate, moderately high and high energies, we restore the scattering amplitude related to the t-channel exchange by vacuum quantum numbers by taking account of the diffractive s-channel rescatterings. At intermediate and moderately high energies, the t-channel exchange amplitude turns, with a good accuracy, into an effective pomeron which renders the results of the additive quark model. At superhigh energies the scattering amplitude provides a Froissart-type behaviour, with an asymptotic universality of cross sections such as σ^tot _πp/σ^tot _pp→ 1 at s→∞. The quark structure of hadrons being taken into account at the level of constituent quarks, the cross sections of pion and proton (antiproton) in the impact parameter space of quarks, σ_π(r _1⊥, r _2⊥; s) and σ_p(r _1⊥, r _2⊥, r _3⊥; s), are found as functions of s. These cross sections implicate the phenomenon of colour screening: they tend to zero at |r _i⊥−r _k⊥|→ 0. The effective colour screening radius for pion (proton) is found for different s. The predictions for the diffractive cross sections at superhigh energies are presented. Received: 15 December 1998     

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.     

Covariant tensor formalism for partial-wave analyses of ψ decays into γB¯, γγV and ψ(2s)↦γχ<Subscript>c0,1,2</Subscript> with χ<Subscript>c0,1,2</Subscript>↦K¯πand 2π<Superscript>+</Superscript>2π<Superscript>-</Superscript>

With accumulation of high statistics data at BES and CLEO-c, many new interesting channels can get enough statistics for partial-wave analysis (PWA). Among them, ψ↦γpˉ,γΛˉ,γΣˉ,γΞˉ channels provide a good place for studying baryon-antibaryon interactions; the double radiative decays ψ↦γγV with V ≡ ρ,ω,φ have a potential to provide information on the flavor content of any meson resonances (R) with positive charge parity (C = +) and mass above 1 GeV through ψ↦γR↦γγV; ψ(2s)↦γχ_c0,1,2 with χ_c0,1,2↦Kˉπ⁺π^- and 2π⁺2π^- decays are good processes to study χ_cJ charmonium decays. Using the covariant tensor formalism, here we provide theoretical PWA formulae for these channels.     

New data on the p + N → [Σ0K+] + N reaction at E p= 70 GeV and the search for exotic baryons

New data for the diffractive reaction p+N→ [Σ⁰ K ⁺] +N at E _p= 70 GeV were obtained with partially upgraded SPHINX setup. The data are in a good agreement with the results of our previous study of this reaction. In the mass spectrum M(Σ⁰ K ⁺) a structure at the threshold region with a mass ∼1810 MeV and a distinct X(2000) peak with M= 1989 ± 6 MeV and γ= 91 ± 20 MeV are observed. Unusual features of the massive X(2000) state (narrow decay width, anomalously large branching ratio for the decay channel with strange particle emission) make it a serious candidate for cryptoexotic pentaquark baryon with hidden strangeness |qqqsˉs>. We also present new results on the narrow threshold structure X(1810) with M= 1807 ± 7 MeV and γ= 62 ± 19 MeV which is produced in the region of very small P ² _T < 0.01 GeV². The possibility of the Coulomb production mechanism for X(1810) is discussed. Received: 28 April 1999     

Scalar-isovector K¯ production close to threshold

The reaction pp → dK ⁺ˉ has been investigated at excess energies Q = 47.4 and 104.7MeV above the K ⁺ˉ threshold at COSY Jülich. Coincident dK⁺ pairs were detected with the ANKE spectrometer, and subsequently ∼ 2000 events with a missing ˉ invariant mass were identified, which fully populate the Dalitz plot. The joint analysis of invariant mass and angular distributions reveals s-wave dominance between the two kaons, in conjunction with a p-wave between the deuteron and the kaon pair, i.e. Kˉ production via the a ₀ ⁺(980) channel. Integration of the differential distributions yields total cross-sections of σ(pp → dK ⁺ˉ) = (38±2_stat±14_syst)nb and (190±4_stat±39_syst)nb for the low and high Q value, respectively.     

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.     

Helicity amplitudes and crossing relations for one-photon exchange antiproton proton reactions

Antiproton proton annihilation reactions allow unique access to the moduli and phases of nucleon electromagnetic form factors in the time-like region. We present the helicity amplitudes for the unequal-mass single-photon reaction pˉ → l ⁺ l ^- in the s channel including the lepton mass. The relative signs of these amplitudes are determined using simple invariance properties. Helicity amplitudes for one-photon exchange annihilation reaction pˉ → Bˉ are also given, where B is any spin-one-half particle with structure. Crossing relations between the ep → ep scattering and the pˉ → l ⁺ l ^- annihilation channels are discussed and the crossing matrix for the helicity amplitudes is given. This matrix may be used to verify known expressions for the space-like helicity amplitudes due to one-photon exchange.     

In-medium spectral functions of charmonia studied by ¯p + A reactions<Superscript>a</Superscript>

We study the perspectives of resonant charmonium production in ˉp + A reactions within the Multiple Scattering Monte Carlo (MSMC) approach. We calculate the production of the resonances Ψ(2S) and Ψ(3770) on various nuclei, their propagation and decay to dileptons and D + ˉD in the medium and vacuum, respectively, employing parametrizations for the D,ˉD self-energies taken from QCD sum rule studies. The elastic and inelastic interactions of the charmonia and open-charm mesons in the medium are taken into account, too. It is found that the D,ˉD invariant-mass spectra from light and heavy nuclei are not sufficiently sensitive to the in-medium properties of the Ψ(2S) and Ψ(3770). However, a “suppression” of low-mass dileptons from the Ψ(3770) might be seen experimentally as well as a small broadening of the Ψ(2S) dilepton spectra. Received: 19 December 2002 / Accepted: 28 February 2003 / Published online: 5 June 2003     

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 .     

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.     

Target fragmentation in pp, ep and γp collisions at high energies

We calculate target fragmentation in pp→nX and γp→nX reactions in the meson cloud picture of the nucleon. The pp→nX reaction is used to fix the pnπ⁺ form factor for three different models. We take into account the possible destruction of the residual neutron by the projectile. Using the form factor from the hadronic reaction we calculate photoproduction and small x _Bj electroproduction of forward neutrons at HERA. Here the qˉq dipoles in the photon can rescatter on the residual neutron. In photoproduction we observe slightly less absorption than in the hadronic reaction. For deep inelastic events (Q ² > 10 GeV²) screening is weaker but still present at large Q ². The signature for this absorptive rescattering is a shift of the dσ/dE_n distribution to higher neutron energies for photofragmentation. Received: 12 June 1999 / Revised version: 12 October 1999     

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.     

Calculation of O(p6) corrections to the muon transverse polarization in Kl2γ decay

The contribution of final-state interactions to the muon transverse polarization in the decay K ⁺ → μ⁺ v γ is calculated within chiral perturbation theory to O(p ⁶) terms. It is shown that the O(p ⁶) corrections to the transverse polarization are much smaller than the O(p ⁴) leading contribution. Original Russian Text ? V.V. Braguta, A.A. Likhoded, A.E. Chalov, 2007, published in Yadernaya Fizika, 2007, Vol. 70, No. 2, pp. 386–391.     

Unraveling the f<Subscript>0</Subscript> nature by connecting KLOE and BABAR data through analyticity

We define a general procedure, based on analyticity and dispersion relations, to estimate low-energy amplitudes for processes like: φ→e ⁺ e ^- M and φ→γM, starting from cross-section data on e ⁺ e ^-→φM, where M is a generic light scalar or pseudoscalar meson. In particular this procedure is constructed to obtain predictions on the radiative decay rate which are crucially linked on the assumed quark structure for the meson M under consideration. Three cases are analyzed: M = η, M = f ₀(qˉ) and M = f ₀(qqˉ). While in the η case the estimate of the branching fraction for the radiative decay φ→ηγ is in agreement with the data, in the case of f ₀, such agreement is obtained only under the hypothesis of a tetraquark scalar meson.