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1.
A new type of nuclear spectroscopy to study hadron-nucleus bound states is described. The first successful experiment was to search for deeply bound π − states in heavy nuclei using the 208Pb(d, 3He) reaction at GSI, in which a narrow peak arising from the 2p π − orbital coupled with the neutron-hole states was observed at 135 MeV excitation energy. An improved experiment has just been carried out to separately identify the 1s and 2p π − states. These experiments provide important information on the local potential strength, from which the effective mass of π − is deduced to be 20 MeV. This method will be extended to search for η and ω bound states as well as for K − bound states. The advantage of the bound-state spectroscopy versus invariant mass spectroscopy is emphasized. 相似文献
2.
Data were taken at the energy 2 E = 990 MeV to search for multibody events, with the same large solid angle detector which has been used for the measurement of the , ω andφ production by e +e − annilations. Assuming a π +π −π 0π 0 production by the quasi two-body process e +e − → → ωπ 0 we give the correspondi ng cross section σ(e +e − → π +π −π 0π 0) = (1.1 ± 0.5) 10 −32 cm 2. Since no events with 3 and 4 charged pions have been observed σ(e +e − → π +π −π 0π −) 1.5 × 10 −33 cm 2. 相似文献
3.
The charged current nuclear transition 12C(v e, e −) 12N g.s. has been observed in the KARMEN experiment. The flux average cross section for ve from μ + decay at rest is determined to be σ = [8.1±0.9(stat.)±0.75 (syst.)]×10 −42cm 2. For the first time also the energy dependence of the cross section has been measured for neutrino energies up to 50 MeV. 相似文献
4.
Inelastic scattering of π + and π − exhibits strongly excited giant resonance structures. Besides the giant quadrupole resonance centered around 14 MeV, structures are observed at 16.8 MeV which can be fitted with a mixing of L=0 and L=1, and around 25 MeV ( Ex = 110 A−1/3). 相似文献
5.
Narrow structures in the range of a few MeV have been searched for in ppπ + and ppπ − invariant mass spectra ( Mppπ+ and Mppπ−) obtained from exclusive measurements of the pp→ ppπ +π − reaction at Tp=725,750 and 775 MeV using the PROMICE/WASA detector at CELSIUS. The selected reaction is particularly well suited for the search for dibaryon resonances decoupled from NN and/or NΔ. In the mass range 2020 MeV/ c2< mdibaryon<2085 MeV/ c2 no narrow structures could be identified on the 3σ level of statistical significance neither in Mppπ− nor in Mppπ+ giving an upper limit (95% C.L.) for dibaryon production in this reaction of σ<20 nb. 相似文献
6.
Differential cross sections for the reactions 16O(γ, π−π+−) 16F16F to the sum of the four lowest lying states in 16F and 16N have been measured as a function of angle for pions with a kinetic energy of 30 MeV. The extracted ratios R = σ(γ, π −)/σ(γ, π +), the first ones to discrete final states as a function of angle, are in fair agreement with results obtained for the nucleon. For positive pions the energy dependence of the cross section has been measured at the angles of 45° and 90°. Distorted wave impulse approximation calculations fail to describe the energy dependence. 相似文献
7.
Angular distribution of the reaction 12C( d,τ) 11B leading to the 3/2 − ground state and the 4.44 MeV excited (5/2 − state 11B have measured at Ed = 80 MeV up to about 70° and 40°, respectively. The inclusion of second-order processes in the framework of CCBA calculations gives a good reproduction of the 3/2 − as well as of the DWBA forbidden 3/2 − angular distribution. The strong dependence of the cross section on the sign of the deformation supports a positive β 2 value for 11B. 相似文献
8.
A spherical harmonic moment analysis of the reactions K −p → K −π +n and K +p → K +π −Δ ++ at 13 GeV/ c demonstrates the existence of a broad K * state with mass in the vicinity of 1800 MeV and spin parity 3 −. 相似文献
9.
The hypernuclei Σ6H and Σ16C were observed by the (K −, π +) reaction on targets of 6Li and liquid O, respectively, at 713 MeV/ c incident K − momentum. Structure is seen in Σ6H which may be interpreted in terms of particle-hole excitations similar to the previously observed states in Λ6Li. The inablitity to resolve individual Σ hypernuclear levels in Σ16C, due in part to the excitation of non-coherent states as a result of the large momentum transfer of about 130 MeV/ c, precludes the extraction of the Σ-nucleus spin-orbit potential strength. The Σ-nucleus well depth appears to be 7 to 10 MeV less than that for the Λ. 相似文献
10.
A search is made for a short lived neutral particle, ø, in the decay of the 3.68 MeV (3/2 -) state in 13C. No evidence for such a particle with a rest mass in the region of 1.7–2.0 MeV/ c2 is found with a limit on the branching ratio Γ ø/Γ γ7×10 −5. An upper limit of 10 −6 is placed for the coupling of such a particle to proton/neutron. 相似文献
11.
High-spin states have been populated in 54119Xe via the 96Mo( 27Al,p3n) reaction at 133 MeV, using the
γ-ray spectrometer to record triple γ-ray coincidences. The known level scheme has been significantly extended and several band crossings identified. In particular, the ν h11/2 yrast band has been extended to Iπ = (83/2 −) and shows features which are consistent with those of smooth band termination at high spin. Theoretical results for 119Xe at high spin are discussed within the framework of cranked Nilsson-Strutinsky calculations, together with results for 117Xe. 相似文献
12.
β-γ(CP) correlation measurements have been carried out on the
sequence in the decay of the ground state of 49Ca to the (presumed) anti-analogue state at 3.105 MeV excitation in 49Sc. An asymmetry parameter of A = −0.132 ± 0.017 was obtained, making any spin-parity assignment other than
very unlikely for the 3.105 MeV state. The deduced Fermi matrix element for the decay is | Mv| = |1.4 ± 9.7| × 10−3, which leads to an isospin impurity (
) corresponding to the mixing of the analogue state (at 11.6 MeV) and the 3.105 MeV state of || 2 1.6 × 10 −5. This leads in turn to an effective Coulomb matrix element of | Hc| = |3.9 ± 27.4| keV, a low value compared to the value of 100 keV obtained from a theoretical estimate based on simple shell-model wave functions for the
single-particle states involved. 相似文献
13.
The spectra of electrons scattered inelastically from 4He have been measured at incident energies from 150 MeV to 400 MeV for scattering angles from 38° to 90°. Through the use of a liquid 4He target, a high momentum resolution (≈0.25%) was obtained, and the 20 MeV 0 + state of the -particle was observed for the first time in electron scattering. The excitation energy and the total width of this state were determined and are in good agreement with the results from other experimental methods. It was found that the total disintegration cross section appears be smaller than 2(σ p+σ n) by more than an order of magnitude at the lowest q2(≈ 0.33 fm −2). In earlier work the assumption of a total cross section of 2(σ p+σ n) was found to be quite accurate for higher q2. As a new result, the partial radiative width for the 0 + state is determined to be Γ rad = 1.1±0.3 meV. 相似文献
14.
The emission of two photons above 25 MeV energy was observed in the capture of stopped pions by beryllium and carbon with a rate of (1.0 ± 0.1) × 10 −5, respectively (1.4 ± 0.2) × 10 −5 per capture. These rates are about two to four times greater than various free-nucleon estimates based on the π −+π +→γγ annihilation mechanism alone. 相似文献
15.
Measurements have been made of the β-γ circular-polarization correlation paramter A for the 273 keV β-branch in the decay of 59Fe. It has recently been established that each of the principal β-branches of 59Fe involves Δ J=0 and thus has a possible non-zero Fermi matrix element MF which can be determined from the ƒ t value and A. Previous β-γ (_CP) measurements on this nucleide have all employed the usual γ-ray scattering technique. This method is suitable for the 475 keV β-branch but does not produce an accurate measurement of the lower energy branch because of energy discrimination difficulties. A transmission polarimeter with γ-discrimination has been used in the present work to obtain clean data on the 273 keV β-1.29 MeV γ-cascade. Calibration with 60Co (1.33 MeV) and 28Al (1.79 MeV) yielded A = −0.154±0.023. This gives for the isospin impurity coefficient and the effective Coulomb matrix element of the 1.29 MeV state (1.1±1.4) × 10 −3 and 9±11 keV, respectively. 相似文献
16.
The results of the impedance spectroscopy measurements on eutectic samples based on zirconium oxide are presented here. Samples of CaZrO 3---ZrO 2(cubic) and MgO---ZrO 2(cubic) have been grown by a directional solidification procedure such that the different phases appear nearly oriented along the growth direction (lamellae in the system of CaZrO 3-ZrO 2(cubic) and fibers of MgO in a ZrO 2 matrix in the other system). The DC electrical conductivity has been measured by impedance spectroscopy along and across the growth axis. For CaZrO 3---ZrO 2 the coductivity is clearly anisotropic. The following values for σ T have been obtained: the conductivity at 600 °C equals 2.0 × 10 −6 Ω −1 cm −1 perpendicular to the fiber axis and 1.4 × 10 −5 Ω −1 cm −1 parallel to it and with an activation energy of 1.3 eV for σ T. For MgO---ZrO 2(cubic) the isotropic value of the conductivity at 600 °C is 10 −4 Ω −1 cm−1 with activation energy for σ T of 1.5 eV. The anisotropic conductivity in the CaZrO 3---ZrO 2 (cubic) system has been explained by a model of an ordered stacking of oxygen conducting (cubic ZrO 2) and non-conducting (CaZrO 3 or MgO) phases. 相似文献
18.
The reactions π −p → 2π −π +p, π −p → 2π −π +π op and π −p → 2π −2π +n are analysed at 11 and 16 GeV/ c using longitudinal phase space (LPS) plots. The weighted LPS distributions for π −p → 2π −π +p is dominated by two well separated structures corresponding to single diffraction dissociation of the pion, π −p → (2π −π +)p, and of the proton, π −p → π −(π −π +p). The former is more abundant than the latter, and both are approximately constant with energy. In contrast, processes of type π −p → (2π)(πp) decrease with increasing energy. In the five-body reactions the weighted LPS distribution reveals especially at 16 GeV/c a maximum for single dissociation of the proton into 3πp, namely π−p → π−(π−π+πop); this process is likely to be diffractive. The neutron channel has a corresponding maximum displaced toward a multiperipheral configuration π−p → π−(π−2π+)n. Another strong maximum corresponds to the pion dissociation π−p → (2π−π+πo)p. This is interpreted to be an ω-exchange process because no analogous structure occurs in π−p → (2π−2π+)n. Finally, a broad structure reveals double dissociation of both incident particles; it occurs in the two channels π−p → (2π−π+)(πop) and π−p → (2π−π+)(π+n), being stronger in the latter. Further analysis of this process in terms of isospin exchange suggests that it is partially diffractive. Factorization is also discussed. An appendix gives general aspects of the LPS analysis for the asymptotic study of n-body collisions at very high energy. 相似文献
19.
Differential cross sections for Compton scattering by the proton have been measured in the energy interval between 200 and 500 MeV at scattering angles of θ cms = 75° and θ cms = 90° using the CATS, the CATS/TRAJAN, and the COPP setups with the Glasgow Tagger at MAMI (Mainz). The data are compared with predictions from dispersion theory using photo-meson amplitudes from the recent VPI solution SM95. The experiment and the theoretical procedure are described in detail. It is found that the experiment and predictions are in agreement as far as the energy dependence of the differential cross sections in the Δ-range is concerned. However, there is evidence that a scaling down of the resonance part of the M1+3/2 photo-meson amplitude by (2.8 ± 0.9)% is required in comparison with the VPI analysis. The deduced value of the M1+3/2-photoproduction amplitude at the resonance energy of 320 MeV is: | M1+3/2| = (39.6 ± 0.4) × 10 −3 mπ+−1. 相似文献
20.
The reaction γ p → π °γ′ p has been measured with the TAPS BaF 2 calorimeter at the Mainz Microtron accelerator facility MAMI for energies between √2 = 1221–1331 MeV. Cross sections differential in angle and energy have been determined for the photon γ′ in three bins of the excitation energy. This reaction channel provides access to the magnetic dipole moment of the Δ +(1232) resonance and, for the first time, a value of μ Δ+ = (2.7 +1.0−1.3( stat) ± 1.5( syst) ± ( theor)) π N has been extracted. 相似文献
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