共查询到20条相似文献,搜索用时 187 毫秒
1.
The time-dependence of the decay rate of initially pure K 0 into the final state (π +π −π 0) has been studied in search for the decay k S0→π +π −π 0. No evidence is found in a sample of 384 observed events. The ratio of the CP -violating K S0 amplitude and the K L0 amplitude is η +−0 = (0.13 −0.20+0.17) + i(0.17 −0.26+0.27); the ratio of the CP-conserving K S0 amplitude and the K L0 amplitude is < 0.4. The energy dependence of the K 0→π +π −π 0 matrix element is found to be a+−0 = −0.31 ± 0.03. 相似文献
2.
We compute non-perturbative contributions to B → Xsl+l− that are not explicitly suppressed by powers of the b-quark mass. They are proportional to
and arise from an interference between the free-quark amplitude and high order terms in the matrix element of the four-quark operator s−γ μ(1 − γ 5) cc−βγ μ(1 − γ 5) bβ. This correction is found to be small over most of the dalitz plot except near the charm threshold. Unfortunately, the perturbative computation we have performed is invalid near charm threshold and we do not except to see the structure found at lowest order reproduced in the data. We conclude that these non-perturbative contributions do not significantly modify the previous analysis of B → Xsl+l−. 相似文献
3.
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
4.
Limits on neutrino electromagnetic properties from laboratory experiments and astrophysical arguments are reviewed with an emphasis on the currently favored range of small neutrino masses. We derive a helioseismological limit on the charge and dipole moment for all flavors of eν6×10 −14e and μ ν4×10 −10μ B (Bohr magneton). The most restrictive limits remain those from the plasmon decay in globular-cluster stars of eν2×10 −14e and μ ν3×10 −12μ B. 相似文献
5.
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
6.
Coherent Λπ − production on Pb of 600 GeV Σ − hyperons has been studied with the SELEX facility at Fermilab. Using the Primakoff formalism, we set a 90% CL upper limit on the radiative decay width Γ[Σ(1385) −→Σ −γ]<9.5 keV, and estimate the cross section for γΣ −→Λπ − at
GeV to be 56±16 μb. 相似文献
7.
The properties of the charge fluctuation are investigated in the d---p model with the repulsion Upd between holes on the nearest-neighbor Cu and O sites and the infinite on-site repulsion Ud at the Cu site. We calculate the charge susceptibility χ c( q, iω n) and the charge correlation function Sc( q) = TΣ ωn χ c( q, iω n). It is found that Sc( q) has a peak at the Γ point and a maximum in a ring around the Γ point. The former is due to Tχ c( q, 0). Its intensity is proportional to temperature T and strongly enhanced by Upd. The latter is due to TΣ ωn ≠ 0 χ c( q, iω n) and shows a weak T and Upd dependence. The intensity of the diffuse X-ray scattering on taking the charge fluctuation into account is also calculated. The result is consistent with the experiments in La 2−δSr δCuO 4. 相似文献
8.
We argue that the presence of second-class neutral currents can be tested from the observations of
and electron polarisation in η→π 0e+e-. Consequences of this model in η→π ±eν e,τ ±→ηπ ±ν τ and τ ±→ωπ ±ν τ decays which would establish second-class charged currents are also discussed. 相似文献
9.
A calculation of the neutron electric dipole moment, assuming a threshold dominated, unsubtracted sideways dispersion relation, yields the result 4×10 −23 sinθ Δ cm, with θ Δ the T non-invariant phase at the vertex Δ(1236)pγ. Other calculations are reported giving contributions an order of magnitude smaller and an estimate is made of the effect of direct-channel resonance enhancement. 相似文献
10.
I investigate the evolution of finite temperature, classical Yang-Mills field equations under the influence of a chemical potential for Chern-Simons number Ncs. The rate of Ncs diffusion,, Γ d, and the linear response of Ncs to a chemical potential, Γ μ, are both computed; the relation Γ d = 2Γ μ is satisfied numerically and the results agree with the recent measurement of Γ d by Ambjørn and Krasnitz. The response of Ncs under chemical potential remains linear at least to μ = 6 T, which is impossible if there is a free energy barrier to the motion of Ncs. The possibility that the result depends on lattice artefacts via hard thermal loops is investigated by changing the lattice action and by examining elongated rectangular lattices; provided that the lattice is fine enough, the result is weakly if at all dependent on the specifics of the cutoff. I also compare SU(2) with SU(3) and find Γ SU(3) 7( s/w)4ΓSU(2). 相似文献
11.
The critical exponents ζ( X) and amplitudes κ( X) of superfluid fraction s/ λ in 3He--- 4He mixtures were determined by oscillating disk method approaching 10 −4 K to lambda temperatures determined from velocity minima of first sound. 相似文献
12.
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
13.
We study the ρ 0 and φ decays into π +π −γ, π 0π 0γ and φ into π 0ηγ using a chiral unitary approach to deal with the final state interaction of the MM system. The final state interaction modifies only moderately the large momenta tail of the photon spectrum of the ρ 0→π +π −γ decay. In the case of φ decay the contribution to π +π −γ and π 0π 0γ decay proceeds via kaonic loops and gives a distribution of ππ invariant masses in which the f0(980) resonance shows up with a very distinct peak. The spectrum found for φ→π 0π 0γ decay agrees with the recent experimental results obtained at Novosibirsk. The branching ratio for φ→π 0ηγ, dominated by the a0(980), is also in agreement with recent Novosibirsk results. 相似文献
14.
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
15.
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
16.
Two-loop radiative mechanism, when combined with an U(1) L′ symmetry generated by Le − Lμ − Lτ (= L′), is shown to provide an estimate of Δ m2/Δ m2atm ε me/ mτ, where ε measures the U(1) L′-breaking. Since Δ m2atm 3.5×10 −3 eV 2, we find that Δ m2 ε10 −6 eV 2, which will fall into the allowed region of the LOW solution to the solar neutrino problem for ε 0.1. 相似文献
18.
Results are reported on the precise measurement of the lifetime and the weak-decay branching ratios with charged particle(π − and proton) emission from Λ12C formed via 12C(π +, K+) reaction. The π − mesonic decay width is consistent with the calculations including the pion wave function distortion effect. We observed large contribution of the neutron-stimulated decay widths, Γ(Λ + n → n + n), in the non-mesonic weak decay, which cannot be explained by the current theoretical calculations. 相似文献
19.
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
20.
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
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