共查询到20条相似文献,搜索用时 31 毫秒
1.
《Physics letters. [Part B]》2004,590(3-4):161-169
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
2.
Elastic and inelastic η-photoproduction from complex nuclei is studied in a distorted-wave impulse approximation (DWIA) framework. The elementary operator is obtained by using a dynamical model which employs the reactions πN→πN, πN→ππN and π−p→ηn to fix the hadronic vertex as well as the isobar propagators and the process γN→πN to constrain the electromagnetic vertex. The nuclear structure input for the inelastic transitions has been extracted from electron-scattering form factors. The η final-state interaction has been included via a simple optical potential using the ηN t-matrix as an input. We find that coherent η-production is dominated by the D13(1520) isobar while spin-flip transitions to excited nuclear states are sensitive to the S11(1535) resonance. Predictions are given for coherent production on 4He, 12C and 40Ca, as well as incoherent production on 6Li, 10B and 12C. 相似文献
3.
H. Tamura K. Tanida D. Abe H. Akikawa K. Araki H. Bhang T. Endo Y. Fujii T. Fukuda O. Hashimoto K. Imai H. Hotchi Y. Kakiguchi J. H. Kim Y. D. Kim T. Miyoshi T. Murakami T. Nagae J. Nishida H. Noumi H. Outa K. Ozawa T. Saito J. Sasao Y. Sato S. Satoh R. Sawafta M. Sekimoto T. Takahashi L. Tang H. H. Xia S. H. Zhou L. H. Zhu 《Nuclear Physics A》2000,670(1-4):249-256
We report on the first observation of hypernuclear γ transitions using germanium detectors. Using a large-acceptance Ge detector system, we observed two γ transitions in Λ7Li, the spin-flip
transition at 689±4keV and the
transition at 2050±2 keV (preliminary). The strength of the ΛN spin-spin interaction is derived from the energy of the former transition. As for the latter transition, B(E2) was measured to be 3.9±0.6±0.4 e2fm4 (preliminary), which indicates a shrinkage of the nuclear size of Λ7Li from 6Li and confirms “glue-like role” of Λ. 相似文献
4.
We discuss the possibility of discriminating between different supersymmetric see-saw models by improving the experimental sensitivity to charged lepton flavour violating processes. Assuming a hierarchical neutrino mass spectrum, we classify see-saw models according to how the hierarchy Δm2Δm2atm is generated, and study the predictions of each class for the branching ratios of τ→μγ and μ→eγ. The process τ→μγ is found to be a particularly promising tool to probe the fundamental see-saw parameters, and especially to identify the origin of the large atmospheric mixing angle. Predictions for μ→eγ are more model-dependent. We point out that, even with an improvement of the experimental sensitivities by three orders of magnitude, both τ→μγ and μ→eγ could escape detection in models where Δm2atm is determined by one of the lightest right-handed neutrinos. 相似文献
5.
The theoretical mechanisms for the decays ψ′ → ψπ0 and ψ′ → ψη, which violate SU2 and SU3, respectively discussed. It is argued that symmetry breaking in the decay amplitudes may be as important as π0 −η −η′ mixing. The π0 −η mechanism ψ′ → ψν → ψπ0 leads to Γ(ψ′ → ψπ0) = (3.3±1.0) × 10−3 Γ(ψ′ → ψν), but this number may be enhanced by a factor as large as 12 by π0−η′ mixing and isospin violation in the decay amplitude. The related decays ψ → ηγ and ψ → η′γ are also discussed. 相似文献
6.
John Ellis Toby Falk Gerardo Ganis Keith A. Olive Mark Srednicki 《Physics letters. [Part B]》2001,510(1-4):236-246
We extend previous combinations of LEP and cosmological relic density constraints on the parameter space of the constrained MSSM, with universal input supersymmetry-breaking parameters, to large tanβ. We take account of the possibility that the lightest Higgs boson might weigh about 115 GeV, but also retain the possibility that it might be heavier. We include the most recent implementation of the b→sγ constraint at large tanβ. We refine previous relic density calculations at large tanβ by combining a careful treatment of the direct-channel Higgs poles in annihilation of pairs of neutralinos χ with a complete treatment of χ–
coannihilation, and discuss carefully uncertainties associated with the mass of the b quark. We find that coannihilation and pole annihilations allow the CMSSM to yield an acceptable relic density at large tanβ, but it is consistent with all the constraints only if mχ>140 (180) GeV for μ>0 (μ<0) for our default choices
GeV, mt=175 GeV, and A0=0. 相似文献
7.
We analyze the supersymmetric contributions to direct–CP–violating observables in K→ππγ decays induced by gluino–mediated magnetic–penguin operators. We find that ε′+−γ and the differential width asymmetry of K±→π±π0γ decays could be substantially enhanced with respect to their Standard Model values, especially in the scenario where ε′/ε is dominated by supersymmetric contributions. These observables could therefore provide a useful tool to search for New Physics effects in |ΔS|=1 transitions, complementary to ε′/ε and rare decays. 相似文献
8.
D. H. Wilkinson 《Nuclear Physics A》1970,150(3):478-480
The screening correction to allowed β-decay is given to order 3 and is compared with the “exact” value for light elements. 相似文献
9.
P. Krolak R. A. Briere E. Cheu D. A. Harris K. S. McFarland A. Roodman B. Schwingenheuer S. V. Somalwar Y. W. Wah B. Winstein R. WinstonK. Arisaka D. Roberts W. Slater M. WeaverA. R. BarkerE. C. Swallow G. J. Bock R. Coleman M. Crisler J. Enagonio R. Ford Y. B. Hsiung D. A. Jensen E. Ramberg R. TschirhartE. M. Collins G. D. GollinT. Nakaya T. YamanakaP. Gu P. Haas W. P. Hogan S. K. Kim J. N. Matthews S. S. Myung S. Schnetzer G. B. ThomsonY. Zou 《Physics letters. [Part B]》1994,320(3-4):407-410
A FNAL E799 Collaboration has carried out a search for the lepton-family number violating decay π0 → μ±e using π0's produced from KL → π0π0π0 decays in flight. No events were observed. Assuming that lepton-family number violation is charge independent, the 90% confidence level upper limit on was determined to be 8.6 × 10−9. 相似文献
10.
The decays η,η′→π+π−γ are investigated within an approach that combines one-loop chiral perturbation theory with a coupled channel Bethe–Salpeter equation which satisfies unitarity constraints and generates vector mesons dynamically from composite states of two pseudoscalar mesons. It is furthermore shown that the inclusion of the η′ as a dynamical degree of freedom does not renormalize the Wess–Zumino–Witten term. 相似文献
11.
We propose to test CP symmetry in the decay J/ψ→γφφ, for which large data sample exists at BESII, and a data sample of 1010 J/ψ's will be collected with BESIII and CLEO-C program. We suggest some CP asymmetries in this decay mode for CP test. Assuming that CP violation is introduced by the electric- and chromo-dipole moment of charm quark, these CP asymmetries can be predicted by using valence quark models. Our work shows a possible way to get information about the electric- and chromo-dipole moment of charm quark, which is little known. Our results show that with the current data sample of J/ψ, electric- and chromo-dipole moment can be probed at order of 10−13 e cm. In the near future with a 1010 data sample, these moments can be probed at order of 10−14 e cm. 相似文献
12.
L. Zem
o W. Drenckhahn A. Feigel E. Finckh K. Rüskamp P. Urbainsky M. Wangler 《Nuclear Physics A》1982,380(3):493-501
The yield of the 209Bi(d, γ)211g.s.Po and 211mPo (T1/2 = 25.2s) reaction was measured for deuteron energies Ed = 8–11.5 MeV. The reaction was identified by the -activities of the Po isotope. At Ed = 10.43 MeV, the (d, γ) cross section for the population of the ground state of 211Po is σg.s. = 16 ± 3 μb, the ratio relative to the cross section for the metastable state is σg.s./σm = 25.4 ± 0.9. These values and the yield curves were compared with calculations using a simple model for the population of the two states. In the excitation region E* = 15–19 MeV, the branching ratio of γ- to particle emission is nearly constant and has a value of about 0.4 × 10−4. 相似文献
13.
We calculate the amplitude of the decays η → π0π+π− and η → π0π0π0 to first non-leading order in the low-energy expansion. It is shown that the infrared singularities of chiral perturbation theory strongly enhance the perturbation generated by the quark mass term. The corrections of order ms increase the current algebra prediction for the rate by more than a factor of two and remove the well-known discrepancy between the low-energy theorems of current algebra and experiment. 相似文献
14.
《Nuclear Physics A》2001,690(4):1-493
A stack of annular detectors made of high-purity germanium was used to measure simultaneously pd → 3H π+ and pd → 3He π0 differential cross sections at beam momenta of 750 MeV/c, 800 MeV/c, and 850 MeV/c over a large angular range. The extracted total cross sections for the pd → 3He π0 reactions bridge a gap between near threshold data and those in the resonance region. The ratio of the cross sections for the two reaction channels taken at the same η=pcmπ/mπ yields 2.11±0.08 indicating that a deviation from isospin symmetry is very small. 相似文献
15.
16.
The process η → π0π0γγ is discussed in Chiral Perturbation Theory (ChPT). Special attention is deveted to one-loop corrections, η-η′ mixing effects and vector-meson dominance of ChPT counter-terms. The less interesting η → π+π−γγ transition is briefly discussed too. 相似文献
17.
18.
H. Claus U. Gebhard G. Linker K. R hberg S. Riedling J. Franz T. Ishida A. Erb G. Mü ller-Vogt H. Wü hl 《Physica C: Superconductivity and its Applications》1992,200(3-4):271-276
X-ray diffraction, resistivity, AC and DC magnetization data on high-quality single crystals of YBa2Cu3O7−δ are presented. We demonstrate that for δ<0.08, the (0 0 l) diffraction lines are split into two, indicating that at these high oxygen concentrations the crystals are no longer single phase but actually consist of two (or more) different phases with slightly different c-axis parameters. In the two-phase region, the electrical resistivity and the AC and DC magnetic susceptibilities show a broadening of the superconducting transition. This broadening is thought to be due to the proximity effect or strains in two finely dispersed phases with slightly different transition temperatures. 相似文献
19.
The current experimental determination of the absolute values of the CKM elements indicates that 2|Vub/VcbVus|=(1−z), with z given by z=0.19±0.14. This fact implies that irrespective of the form of the quark Yukawa matrices, the measured value of the SM CP phase β is approximately the maximum allowed by the measured absolute values of the CKM elements. This is for , which implies =π/2. Alternatively, assuming that β is exactly maximal and using the experimental measurement sin(2β)=0.726±0.037, the phase γ is predicted to be γ=(π/2−β)=66.3°±1.7°. The maximality of β, if confirmed by near-future experiments, may give us some clues as to the origin of CP violation. 相似文献
20.
A method of searching for 3ν solutions of the solar neutrino problem in terms of 2ν solutions is proposed. It gives “iso-SNU strips” on the plot of Δm2 versus sin22θ. A combined analusis of Cl---Ar experiment data and results of the 8B neutrino flux measurement by νe scattering (Kamiokande II) is presented. 相似文献