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1.
An experimental search for the Θ(1540)- and Λ(1520)-resonance was performed in quasi-real photoproduction on deuterium at the HERMES experiment. While evidence for Θ(1540) was found in the decay channel pK 0 S + π -, no evidence for the corresponding anti-particle was found. In some models it is expected that the Θ(1540) and the Λ(1520) have similar production mechanisms. The photoproduction cross-sections for the Λ(1520) in the decay channel Λ(1520)→pK - and the corresponding anti-particle are determined. The partial photoproduction cross-sections for Λ(1520) and ˉ(1520) are obtained as σ Λ(1520) = 65.3±8.8(stat)±6.9(syst)nb and σ ˉ(1520) = 9.8±2.6(stat)±0.9(syst)nb, corresponding to a ratio R Λ(1520) = σ ˉ(1520)/σ Λ(1520) = 0.15±0.05(stat)±0.02(syst).  相似文献   

2.
The reaction pp + 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 + pairs exhibits a peak around the η mass on top of a strong background of multipion pp +() events. The differential cross section d 4 σ/dΩd dΩ π + dp d dp π + for the reaction pp + 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(ppda 0 + + η) = 1.1 ± 0.3stat ± 0.7syst μb for the production of π + η via the scalar a 0 + (980) resonance and σ(pp + η) = 3.5 ± 0.3stat ± 1.0syst 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.  相似文献   

3.
We calculate target fragmentation in ppnX and γpnX reactions in the meson cloud picture of the nucleon. The ppnX 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/dEn distribution to higher neutron energies for photofragmentation. Received: 12 June 1999 / Revised version: 12 October 1999  相似文献   

4.
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 pppK+K-p and pppK+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.  相似文献   

5.
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 ππKˉ. 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.  相似文献   

6.
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 M0 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  相似文献   

7.
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 γpf 2(1270)p, γpa 2 0 (1320)p, and γNX ±(N, Δ) is proposed, and estimates are obtained for the corresponding cross sections. At E γ≈6 GeV, it is found that σ(γPf 2(1270)p)≈0.12 μb, σ(γpa 2 0 (1320)p)≈0.25 μb, σ(γNX ± N → ρ±ρ0 N) ≈ 0.018 μb, and σ(γpX Δ++ → ρρ0Δ++≈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 γNX ± N → ρ±ρ0 N. __________ Translated from Yadernaya Fizika, Vol. 63, No. 10, 2000, pp. 1904–1912. Original Russian Text Copyright ? 2000 by Achasov, Shestakov.  相似文献   

8.
Vector meson degrees of freedom are incorporated into the Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian by using a scheme which relies on spin-flavor SU(6) symmetry. The corresponding Bethe-Salpeter approximation successfully reproduces previous SU(3)-flavor WT results for the lowest-lying s-wave negative-parity baryon resonances, and it also provides some information on the dynamics of the heavier ones. Moreover, it also predicts the existence of an isoscalar spin-parity - K*N bound state (strangeness +1) with a mass around 1.7-1.8GeV, unstable through K* decay. Neglecting d-wave KN decays, this state turns out to be quite narrow ( Γ≤15MeV) and it might provide clear signals in reactions like γp→ˉ0 pK + π - by looking at the three-body pK + π - invariant mass.  相似文献   

9.
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 epep 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.  相似文献   

10.
In a combined analysis of the experimental data on the coupled processes ππ↦ππ, KˉK in the channel with I G J PC = 0+0+ +, the various scenarios of these reactions (with different numbers of resonances) are considered. In a model-independent approach, based only on analyticity and unitarity, a resonance is represented by a pole cluster (poles on the Riemann surface) of the definite type that is defined by the state nature. The best scenario contains the resonances f 0(665) (with properties of the σ-meson), f 0(980) (with a dominant sˉs component), f 0(1500) (with a dominant flavour-singlet, e.g., glueball component) and the f 0(1710) (with a considerable sˉs component). If the f 0(1370) exists, it has a dominant sˉs component. The coupling constants of the observed states with the considered channels and the ππ and KˉK scattering lengths are obtained. The conclusion on the linear realization of chiral symmetry is drawn. Received: 25 April 2002 / Accepted: 4 June 2002 / Published online: 26 November 2002 RID="a" ID="a"e-mail: surovcev@thsun1.jinr.ru RID="b" ID="b"e-mail: krupa@savba.sk RID="c" ID="c"e-mail: fyzinami@nic.savba.sk Communicated by V.V. Anisovich  相似文献   

11.
Using a constituent-quark model we study possible bound or resonance Nˉ states. The model fits the pˉ and pˉ cross-sections and explains the large 3 P 0 antiprotonium energy shift. Only a resonance is found in the 3 P 0 I = 0 partial wave. The threshold enhancement in the J/Ψγpˉ decay can be explained with FSI effects in S-waves and no Nˉ bound state is needed.  相似文献   

12.
The scalar contributions to the radiative decay φK 0ˉ0 γ are studied within the framework of the Linear Sigma Model (LσM). Theoretical predictions for the associated subprocesses φf 0 γ and φa 0 γ as well as the ratio φf 0 γ/a 0 γ are also given.  相似文献   

13.
Using data collected with the ISTRA+ spectrometer during the 2001 run of the U-70 proton synchrotron in Protvino, the first observation of the radiative kaon decay K → μπ0γν is reported. The ratio Br(K μ3γ, 5 < E*γ < 30 MeV)/Br(K μ3) is found to be [0.270 ± 0.029(stat.) ± 0.026(syst.)]% and the ratio Br(K μ3γ, 30 < E*γ < 60 MeV)/Br(K μ3) = [0.0448 ± 0.0068(stat.) ± 0.0099(syst.)]%. These ratios are consistent with the theoretical predictions 0.21 and 0.047%, respectively. The measured angular distribution asymmetry for the region 5 < E*γ < 30 MeV, A(cos ϑ*μγ) = 0.093 ± 0.141, is two standard deviations away from the theoretical prediction of 0.354. The measured asymmetry in the T-odd variable ξ = pγ · (pμ × pπ)/m K 3 is −0.03 ± 0.13. The text was submitted by the authors in English.  相似文献   

14.
Using a pulsed capilary discharge through helium as a light source fluorescence within the Lyman bands (transitionX 1 g +B 1 u + of molecular hydrogen and deuterium has been investigated. Selecting a narrow spectral range (width ≈ 8 ?) from the continuum radiation with a spectrometer, lines in the wavelength range from 1060 ? to 1110 ? have been excited having a vibrational quantum number υ″=0 in the lower state, and ≦υ′≦4 in the upper state. The fluorescence intensity has been measured as a function of υ′ and of the hydrogen density. Agreement with calculations has been found to be within ±30%. The method at present allows the determination of densities between 1010 and 1015 molecules per cm3 with a temporal resolution of 1μs and with a spacial resolution of 0.1 cm3  相似文献   

15.
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 →ππ+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  相似文献   

16.
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 σtot πptot 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, σπ(r 1⊥, r 2⊥; s) and σp(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  相似文献   

17.
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 .  相似文献   

18.
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)↦γχc0,1,2 with χc0,1,2Kˉπ+π- and 2π+- decays are good processes to study χcJ charmonium decays. Using the covariant tensor formalism, here we provide theoretical PWA formulae for these channels.  相似文献   

19.
The mechanism of 1:1 dipolar complexation of some long-chain aliphatic alcohols with chlorobenzene and acetic acids in a non-polar medium is studied. The interaction dipole moment △μ, the excess molar polarization ΔP and apparent complex formation constantK app are evaluated following two independent methods. It is observed from the value of △μ that the complex formation is mostly due to polarization interaction and is of the same type as involving lower alcohols. ΔP andK app are, however, of different nature compared to those in lower alcohols suggesting that the unlike molecules form relatively stable linear linkage resulting in antiparallel orientation prior to forming complexes.  相似文献   

20.
We define a general procedure, based on analyticity and dispersion relations, to estimate low-energy amplitudes for processes like: φe + e - M and φγM, 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 φηγ 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.  相似文献   

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