共查询到20条相似文献,搜索用时 609 毫秒
1.
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
2.
We present the results of a study of the exclusive reactions π + 4He → π − 4p (double charge exchange, DCE) and π + 4He → π + π − 3pn (one-pion production). The experiment was performed with the Oxford/RHEL helium bubble chamber irradiated with a 1.7 GeV/ c π + beam. A general review of DCE models is presented and experimental results at other energies are discussed in the light of these models. None of the existing theoretical models is compatible with out data at 1.7 GeV/ c. We propose a new mechanism for DCE, involving three nucleons, which reproduces the integrated as well as the differential cross sections. Some consequences for other models are also discussed. 相似文献
3.
Oxygen tracer diffusion ( D*) and surface exchange rate constant ( k*) have been measured, using isotopic exchange and depth profiling by secondary ion mass spectrometry (SIMS), in La 1−xSr xFe 0.8Cr 0.2O 3−δ ( x=0.2, 0.4 and 0.6). Measurements were made as a function of temperature (700–1000 °C) and oxygen partial pressure (0.21–10 −21 atm) in dry oxygen, water vapour and water vapour/hydrogen/nitrogen mixtures. At high oxygen activity, D* was found to increase with increasing temperature and Sr content. The activation energies for D* in air are 2.13 eV ( x=0.2), 1.53 eV ( x=0.4) and 1.21 eV ( x=0.6). As the oxygen activity decreases, D* increases as expected qualitatively from the increase in oxygen vacancy concentration. Under strongly reducing conditions, the measured values of D* at 1000 °C range from 10 −8 cm 2 s −1 for x=0.2 to 10 −7 cm 2 s −1 for x=0.4 and 0.6. The activation energies determined at constant H 2O/H 2 ratio are 1.21 eV ( x=0.2), 1.59 eV ( x=0.4) and 0.82 eV ( x=0.6). The surface exchange rate constant of oxygen for the H2O molecule is similar in magnitude to that for the O2 molecule and both increase with increasing Sr concentration. 相似文献
4.
In our work single crystals of Mg 4.5Na 7(P 2O 7) 4 were prepared, pulverized, pressed into pellets and sintered in order to measure the electrical conductivity of polycrystalline specimens. The conductivity was also measured on glassy specimens obtained by the melting of previously prepared crystals. The electrical conductivities at 25°C with values of the order of 10 −16 Ω −1 cm −1 for polycrystalline samples and a value of the order of 10 −14 Ω −1 cm −1 for glass, show that the glassy phase of Mg 4.5Na 7(P 2 because of its greater molar volume and loosely packed structure, is a better matrix for ionic motion. 相似文献
5.
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
6.
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
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.
Cross sections for the production of hypernuclei were measured in the reaction A(K −, π −) ΛA. on light and heavy nuclear targets, using a separated K − beam at the CERN Proton Synchrotron. The pions were detected in the forward direction. The results are compared with cross sections calculated under the assumption that the reaction took place on a single neutron. The good agreement between the measured and the calculated cross sections justifies the use of the (K −, π −) reaction in order to obtain spectroscopic information on hypernuclei. 相似文献
9.
A C.W. multi-mode dye laser is used to obtain by optical pumping an orientation of the 2p 5 3s 3P 0 ( F = 3/2) state of 21Ne. A magnetic resonance experiment leads to the measurement of the g factor g ( 3P 0) = 3.027 (8) × 10 −4 to be compared with the theoretical prediction (3.025(6) × 10 −4). One obtains also the metastability exchange cross section σ( 3P 0) = 18.4 ± 4 Å 2 for collisions between metastable ( 3P 0) Ne atoms and ground state Ne atoms. This result is compared with other measurements and theoretical evaluation. 相似文献
10.
A series of polyacrylonitrile–dimethylsulfoxide–CuX 2 (X=CF 3SO 3−, Cl −, Br −), films (foils) were prepared by means of the solution cast technique. The thickness of the foils was between 0.04 and 0.09 cm and they contained 70–80 wt.% of the solvent. Conductivities of the solid electrolytes were obtained from impedance measurements. The conductivity increases with the increase of the salt content up to 8 wt.%; at higher concentrations (>8 wt.%) the conductivity is more or less stable, and reaches, in the case of Cu(CF 3SO 3) 2 and CuCl 2, the level of ca. 10 −3 Ω −1 cm −1 at room temperature. The foils based on the CuBr 2 show even higher conductivity, close to 10 −2 Ω −1 cm −1 at room temperature, a value comparable to that characteristic for liquid solutions. The temperature variation of the conductivity for all the systems studied is of the Arrhenius type. The activation energy, determined from linear plots ln σ=f( T−1), is of the order ca. 14 kJ mol −1 for the PAN/CuBr 2/DMSO and of ca. 21 kJ mol −1 for the PAN/CuCl 2/DMSO and the PAN/Cu(CF 3SO 3) 2/DMSO systems. 相似文献
11.
Reversible and irreversible domain wall (DW) motions have been investigated in La 0.7Sr 0.3MnO 3 ceramic samples using frequency-response complex permeability with various amplitudes of AC field. We also examine the effects of temperature in the range from 293 to 368 K and transverse DC magnetic field with a maximum of 4.40×10 5 A/m on the real part of permeability (μ′). Two relaxations corresponding to reversible wall motions and domain rotations occur in low and high frequency regions, respectively. The irreversible DW displacements can be activated as the amplitude larger than the pinning field of 3 A/m, leading to an increase in μ′. The μ′ obeys a Rayleigh law at the temperature below 343 K or under DC field of less than 4.22×10 4 A/m. The Rayleigh constant η increases from 5.45×10 −2 to 1.54×10 −1 (A/m) −1 as the temperature rises from 293 to 343 K, and η decreases from 5.58×10 −2 to 3.67×10 −2 (A/m) −1 with increasing DC field from 1.99×10 3 to 4.22×10 4 A/m. 相似文献
12.
The electron impact behavior of CO adsorbed on Pd 1/W(110) was investigated. The desorption products observed were neutral CO, CO +, and O +. After massive electron impact residual carbon, C/ W = 0.15, but not oxygen was also found, suggesting that energetic neutral O, not detected in a mass analyzer must also have been formed. Formation of β-CO, i.e., dissociated CO with C and O on the surface was not seen. The total disappearance cross section varies only slightly with coverage, ranging from 9 × 10 −18 cm 2 at low to 5 × 10 −18 cm 2 at saturation ( CO/ W = 0.75). The cross section for CO + formation varies from 4 × 10 −22 cm 2 at satura to 2 × 10 −21 cm 2 at low coverage. That for O + formation is 1.4 × 10 −22 cm 2 at saturation and 2 × 10 −21 cm 2 Threshold energies are similar to those found previously [J.C. Lin and R. Gomer, Surf. Sci. 218 (1989) 406] for CO/W(110) and CO/Cu 1/W(110) which suggests similar mechanisms for product formation, with the exception of β-CO on clean W(110). It is argued that the absence or presence of β-CO in ESD hinges on its formation or absence in thermal desorption, since electron impact is likely to present the surface with vibrationally and rotationally activated CO in all cases; β-CO formation only occurs on surfaces which can dissociate such CO. It was also found that ESD of CO led to a work function increase of the remaining Pd 1/W(110) surface of 500 meV, which could be annealed out only at 900 K. This is attributed to surface roughness, caused by recoil momentum of energetic desorbing entities. 相似文献
13.
The Θ +(1540), recently observed at LEPS, DIANA and CLAS, is hypothesized to be an isotensor resonance. This implies the existence of a multiplet where the Θ ++, Θ + and Θ 0 have isospin-violating strong decays, and the Θ +++ and Θ − have weak decays and so are long-lived. Production mechanisms for the weakly-decaying states are discussed. The JP assignment of the Θ is most likely 1/2 − or 3/2 −. 相似文献
14.
By undertaking AC electrochemical impedance experiments on yttria stabilised zirconia electrolytes with polished Y 1Ba 2Cu 3O 7−x electrodes, the activation energy for oxygen ion transport within the bulk of Y 1Ba 2Cu 3O 7−x, in air, over the temperature range 823 K–1043 K, was determined to be 1.50 ± 0.05 eV. At 1000 K the oxygen ionic conductivity was calculated to be around one order of magnitude lower than that in yttria stabilised zirconia. Typical calculated values were σ=5×10 −5 (ω cm) −1 and 6×10 −3 (ω cm) −1 at the respective temperatures 823 K and 1043 K. By employing a similar cell but with Y 1Ba 2Cu 3O 7−x paste electrodes, oxygen transfer between the Y 1Ba 2Cu 3O 7−x and the electrolyte was found to occur via a surface diffusional processes. Over the temperature range 873 K–1098 K, in air, the activation energy for in-diffusion at the surface was found to be 1.4±0.1 eV and that for out-diffusion at the surface to be 1.76±0.05 eV. 相似文献
15.
Six rotational bands in the odd-odd nucleus 174Ta have been populated with the 160Gd( 19F,5n) reaction. High-spin states were identified using the NORDBALL array. Both signatures of the doubly decoupled π1/2 − [541] ν1/2 − [521] band and semi-decoupled π1/2 − [541] ν7/2 − [633] band are observed, in addition to the high-K couplings of the π9/2 − [514] ν7/2 + [633], π9/2 − [514] ν5/2 − [512], π7/2 + [404] ν7/2 + [633], and π5/2 + [402] ν5/2 − [512] configurations. The signature splitting of the π1/2 − [541] ν7/2 + [633] band is inverted from the expected splitting, and this is interpreted as being due to a residual proton-neutron interaction. It is shown empirically that this interaction, together with deformation changes, can account for the increased crossing frequency associated with the alignment of i13/2 neutrons in the π1/2 − [541] bands of odd-Z nuclei. 相似文献
16.
The similarity between the weak interactions of electron and muon is extended to the principle that all e and μ interactions in gauge models are invariant under e ↔ μ exchange. This necessitates the existence of two Higgs doublets φ e and φ μ, and an extended e ↔ μ permutation invariance. After symmetry-breaking, a multiplicatively conserved “permutation parity” π = ± 1 for all particles naturally emerges, with π μ = −π e = 1. The model forbids μ → eγ but predicts e −e − → μ −μ − mediated by π = −1 Higgs bosons at 10 −11 times the rate of typical weak cross sections. 相似文献
17.
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
18.
The production rate for η′ in pp → ppη′ at rest is calculated in a covariant one boson exchange model, previously applied to study π 0 and η production in NN collisions. The transition amplitudes for the elementary BN → η′ N processes with B being the meson exchanged ( B = π, σ, η, , ω and a0) are taken to be the sum of s- and u-channels with a nucleon in the intermediate states, and an a0 meson pole in a t-channel. The couplings of the η′ to hadrons are a factor 0.4 weaker than the respective η-hadron couplings, as suggested by a quark model and a singlet-octet mixing angle θ = −23°. The model reproduces near threshold cross sections for the quasielastic processes π −p → nη(η′) and pp → ppη(η′) reactions. 相似文献
19.
The K+−nucleus cross sections have been calculated in relativistic non-linear models taking into account the in-medium modifications of nucleons and mesons properties. More precisely, we have taken into account both the dressing of the nucleon effective mass by the scalar nuclear field in the target and the coupling of the mesons exchanged between the K+ and the nucleons to the polarization of the medium. First, using the most recent relativistic non-linear models, the in-medium σ, ω and ρ meson masses have been obtained in the nuclear matter rest frame. The influence of the non-linear contributions on the K+−nucleus cross sections has then been studied. Finally, we have compared our results with the experimental data. 相似文献
20.
37 years after the discovery of CP violation in π +π − decays of neutral K mesons, the experiments BABAR and BELLE have found a second system which violates CP symmetry. J K SO decays of neutral B mesons show very large symmetry breaking. The effect has now, with the most recent data, a significance of about 13 standard deviations. The presentation describes the B-meson factories, the experiments, and their analyses. The results are in agreement with the Standard Model explanation of CP violation, i. e. with different couplings of the Higgs boson to quarks and antiquarks. 相似文献
|