共查询到20条相似文献,搜索用时 31 毫秒
1.
《Physics letters. A》1988,127(3):179-182
The electron thermal conductivity λe of a potassium plasma is found by measuring the electron heat flux in a hot-wire device placed in a magnetic field. In the range 2300–3000 K, λe (W/mK) = 0.906 X 1010 T-2e exp(-3.2 X 104/Te) at a plasma pressure of 800 Pa and a gas temperature Ta = Te/1.3. 相似文献
2.
Using new experimental data, we calculated, with a high precision, a contribution to the muon anomalous magnetic moment from the vacuum-polarization intermediate states π0γ and ηγ taking into account a correction for the trapezoidal rule: aμ(π0γ+aμ(ηγ)=(53.1± 1.5)×10?11. We also determined a small contribution from the e+e?π0, e+e?η, and μ+μ?π0 intermediate states, which was found to be equal to 0.5×10?11. 相似文献
3.
We calculate distributions for τ+τ?γ production at LEP 1 taking into account a potentially existing anomalous magnetic moment a τ of the τ lepton. The existing upper limits for ¦a τ¦ are known from the dependence of the decay Z 0 → τ+τ?γ on a τ 2 and are of the order of (1–5)%. We show that such limits are also sensitive to linear terms in a τ, which are of equal importance at ¦a τ¦ ~ (1–2)% and dominate below this value. Contributions from an electric dipole moment dτ do not interfere with the electromagnetic vertex or with the anomalous magnetic moment. Appropriate formulae are derived. 相似文献
4.
The weak correction, aμw, to the anomalous magnetic moment of the muon is calculated in an SU(2) ? U(1) ? U(1) gauge model of weak and electromagnetic interactions. The Rξ gauge is used and Ward-Takahashi indentities are utilized eliminating all ξ-dependence before the loop integration is performed. aμw,expt places no constraint on the mass of one of the neutral vector mesons, which may be arbitrarily small. 相似文献
5.
B. Lautrup 《Physics letters. [Part B]》1976,62(1):103-104
The effective anomalous magnetic moment of the electron vanishes at short distances because the electrodynamic form factor F2(q2) vanishes for |q2| → ∞. The effective potential due to the interaction between the anomalous magnetic moment and the Coulomb field of a nucleus only diverges logarithmically at short distances, and not, as might naively be expected, quadratically. There are no other bound states of an electron in a Coulomb field than the well-known atomic states. In particular, there is no room for high mass resonances emulating the ψ as suggested by Barut and Kraus. 相似文献
6.
Yu. M. Bystritskiy É. A. Kuraev A. V. Bogdan F. V. Ignatov G. V. Fedotovich 《JETP Letters》2006,83(2):51-53
A new definition is proposed for the hadronic contribution to the muon anomalous magnetic moment that is based on the inclusion of the effects of vacuum polarization by leptons into the cross section for one-photon annihilation of a lepton pair into hadrons. The formula for the hadronic contribution includes the convolution of the measured cross section for annihilation into hadrons with a certain standard function. This remark concerns radiative correction to this function. A particular form has been proposed for this correction. It has been shown that the use of the new function makes it possible to reduce the uncertainty in such contributions due to radiative correctioins to δa h/a h ~ 10?4. 相似文献
7.
A.O. Barut 《Physics letters. [Part B]》1978,73(3):310-312
It is shown that a classical relativistic charged particle has an anomalous magnetic moment g=4α/3. If such a “dressed” particle with its mass m, charge e, and anomalous magnetic moment g is quantized by a generalized Dirac equation, then the wave equation predicts a second mass mμ=me(3/2α+1). It is suggested that a magnetic portion of the self-energy is quantized. 相似文献
8.
《Nuclear Physics B》1995,436(3):474-486
We calculate the prediction for the anomalous weak-magnetic form factor of the tau lepton at q2 = M2 within the Standard Model. With all particles on-shell, this is an electroweak gauge-invariant quantity. Its value is aτw(MZ2)= − (2.10+0.61 i) × 10−6. We show that the transverse and normal components of the single-tau polarization of tau pairs produced at e+e− unpolarized collisions are sensitive to the real and absorptive parts of the anomalous weak-magnetic dipole moment of the tau. The sensitivity one can achieve at LEP in the measurement of this dipole moment is discussed. 相似文献
9.
The effect of point defects on the magnetic properties of La0.67Ca0.33MnO3 polycrystals and single crystals has been studied. The magnetic susceptibility χ dc of the initial samples and samples irradiated by electrons to the maximum dose F = 9 × 1018 cm?2 has been measured in the temperature region 80 K < T < 650 K. Local variations of Mn-O-Mn bond angles and lengths result in a nonmonotonic dose dependence of the Curie temperature T C. At high doses of electron irradiation, F ≥ 5 × 1018 cm?2, the temperature of the transition from the ferromagnetic to polaron state in a single crystal is found to increase. In the paramagnetic region close to T C, ferromagnetically ordered polarons are observed to exist, while at T > 1.2T C, localization of e g electrons initiates formation of paramagnetic polarons with a higher magnetic moment. Electron irradiation stimulates persistence of magnetic polarons up to higher temperatures T > 2T C. 相似文献
10.
We show that the modification of the photon propagator in the presence of the conducting walls of an apparatus leads to a new contribution Δge to the magnetic moment ge of the electron. This change is of order Δge ~ αlog(2Λa)/ma, where a is the characteristic size of the apparatus, and Λ is the frequency above which the apparatus becomes transparent to photons. Numerically Δge is comparable to other contributions which arise in order (α/π)4, which is the current level of sensitivity of theory and experiment. 相似文献
11.
The elastic scattering amplitude, taking into account the mass correction to the propagation function, is found for electrons interacting with an intense electromagnetic field characteristic of non-linear quantum electrodynamics. The probability for two-photon emission e → e2γ, the mass correction to the probability for one-photon emission and the mass correction to the anomalous field-dependent magnetic moment of the electron are found with the aid of the amplitude. 相似文献
12.
T. N. Mamedov D. G. Andrianov D. Herlach V. N. Gorelkin K. I. Gritsai V. N. Duginov O. Kormann J. Major A. V. Stoikov U. Zimmermann 《JETP Letters》2001,73(12):674-677
Results of studying the temperature dependence of the residual polarization of negative muons in crystalline silicon with germanium (9×10 19 cm ?3 ) and boron (4.1×10 18 , 1.34×10 19 , and 4.9×10 19 cm ?3 ) impurities are presented. It is found that, similarly to n-and p-type silicon samples with impurity concentrations up to ~10 17 cm ?3 , the relaxation rate ν of the magnetic moment of a μ Al acceptor in silicon with a high impurity concentration of germanium (9×10 19 cm ?3 ) depends on temperature as ν~T q , q≈3 at T=(5–30) K. An increase in the absolute value of the relaxation rate and a weakening of its temperature dependence are observed in samples of degenerate silicon in the given temperature range. Based on the experimental data obtained, the conclusion is made that the spin-exchange scattering of free charge carriers makes a significant contribution to the magnetic moment relaxation of a shallow acceptor center in degenerate silicon at T?30 K. Estimates are obtained for the effective cross section of the spin-exchange scattering of holes (σ h ) and electrons (σ e ) from an Al acceptor center in Si: σ h ~10?13 cm2 and σ e ~8×10?15 cm2 at the acceptor (donor) impurity concentration n a (n d )~4×1018 cm?3. 相似文献
13.
The effect of Higgs bosons on the anomalous magnetic moment of the muon is considered within the model that is based on the SU(2)L×SU(2)R×U(1)B–L gauge group and which involves a bidoublet and two triplets of Higgs fields (left-right model). For the Yukawa coupling constants and the masses of Higgs bosons, the regions are found where the model leads to agreement with experimental results obtained at the Brookhaven National Laboratory (BNL) for the anomalous magnetic moment of the muon. In order to explore corollaries from the constraints obtained for the parameters of the Higgs sector, the processes e+e? → μ+μ?, τ+τ? and μ+μ? → μ+μ?, τ+τ? are considered both within the left-right model and within the model involving two Higgs doublets (two-Higgs-doublet model). It is shown that, if the mass of the lightest neutral Higgs boson does indeed lie in the range 3.1–10 GeV, as is inferred from the condition requiring the consistency of the two-Higgs-doublet model with the data of the BNL experiment, this Higgs boson may be observed as a resonance peak at currently operating e+e? colliders (VEPP-4M, CESR, KEKB, PEP-II, and SLC). In order to implement this program, however, it is necessary to reduce considerably the scatter of energy in the e+ and e? beams used, since the decay width of the lightest neutral Higgs boson is extremely small at such mass values. It is demonstrated that, in the case of the left-right model, for which the mass of the lightest neutral Higgs boson is not less than 115 GeV, the resonance peak associated with it may be detected at a muon collider. 相似文献
14.
The 59Co nuclear magnetic resonance spectra of powdered metal have been investigated in the temperature range from 3 K – 295 K. Both HCP resonance lines, coming from nuclei at the center and the edge of the domain walls (v1 = 221 MHzv2 = 214 MHz at 295 K, respectively) have been observed as in bulk material. The quadrupole splitting, directly measured only by Kawakami et al., was verified. The line spacing vq = 3e2Qq/2I(2I - 1)h is vq = (178 ± 5) kHz at 295 K. A new line with v = 221.7 MHz at 295 K was found, which is probably due to a stacking fault.The temperature behaviour of the FCC-linewidth is anomalous. Between 3 and 10 K a line splitting due to frequency pulling, already predicted by De Gennes et al. in 1962, was discovered. The frequency shift derived from the splitting of the FCC line at 3 K is δω0 ≈ 2.51 MHz. The corresponding anisotropy field and zero field ferromagnetic resonance frequency of FCC cobalt are HA ≈ 1.25 × 102 Oe and ωe ≈ 2.27 × 109 Hz, respectively. 相似文献
15.
S.M. Wasim L. Essaleh G. Marín J. Leotin 《Journal of Physics and Chemistry of Solids》2005,66(11):1887-1890
The Hall coefficient RH of n-type CuInSe2 single crystals is measured between 10 and 300 K in pulsed magnetic field up to 35 T. The threshold field Bth, above which the magnetic freezeout starts to occur, varies linearly with temperature. From the analysis of the temperature dependence of electron concentration in the activation regime above 100 K at different field values, it is established that the density of states effective mass is independent of the magnetic field B and the activation energy ED, above around 6 T, varies as B1/3. Similar B1/3 dependence of the magnetoresistance in the high magnetic field regime, reported earlier in the same material, suggests that theoretical work that could explain this coincidence is needed. 相似文献
16.
T. Goverdhan Reddy P. Yadagiri Reddy V. Raghavendra Reddy Ajay Gupta K. Rama Reddy 《Hyperfine Interactions》2005,160(1-4):253-260
Electrical conductivity with and without magnetic field, d.c. magnetization and 151Eu Mössbauer studies were carried out in La0.38Eu0.29Ca0.33MnO3 perovskite manganite system. An insulating ground state is found throughout the temperature range with charge ordered (CO) state emerging at T CO ~ 140 K, where as an external magnetic field of 6 T induces metal-insulator transition at ~120 K. D.C. magnetization measurements show the antiferromagnetic (AFM) transition occurring at T N ≈ 48 K. The temperature dependent 151Eu Mössbauer measurements showed that the substituted Eu replaces La3+ in the 3+ charge state and a small magnetic moment gets induced at the Eu nucleus at low temperatures. The anomalous variation of the f- factor with temperature occurring around T N and T CO corroborates the occurrence of antiferromagnetic (AFM) and charge ordering (CO) transition, respectively. 相似文献
17.
The new experiment planned at Brookhaven to measure the anomalous magnetic moment of the muona μ≡(g μ?2)/2 will improve the present accuracy of 7 ppm by about a factor of 20. This requires a careful reconsideration of the theoretical uncertainties of theg?2 predictions, which are dominated by the error of the contribution from the light quarks to the photon vacuum polarization. This issue is cruicial also for the precise determination of the running fine structure constant at theZ-peak as LEP/SLC experiments continue to increase their precision. In this paper we present an updated analysis of the hadronic vacuum polarization using all presently availablee +e? data. This seems to be justified because previous work on the subject was based to some extent on preliminary or incomplete experimental data. Contributions from different energy ranges are presented separately forg?2 of the muon and the τ-lepton and for α(M Z 2 ). We obtain the resultsa μ had* =(725±16)×10?10 anda τ had* =(351±10)×10?8, where the asterisk indicates the dressed (renormalization group improved) value. For the effective fine structure constant atM Z=91.1888 GeV we obtainΔα had (5) =0.0280±0.0007 and α(M Z 2 )?1=128.896±0.090. Further improvement in the accuracy of theoretical predictions which depend on the hadronic vacuum polarization requires more precise measurements ofe +e? cross-sections at energies below about 12 GeV in future experiments. 相似文献
18.
《Zeitschrift fur Physik C Particles and Fields》1997,74(4):577-586
Data are presented on the reaction e+e? → γ + no other detected particle at centre-of-mass energies of 89.48, 91.26 and 93.08 GeV. The cross-section for this reaction is related directly to the number of light neutrino generations which couple to the Z° boson, and to several other possible phenomena such as the production of excited neutrinos, the production of any invisible ‘X’ particle, and the magnetic moment of the tau neutrino. Based on the observed number of single photon events, the number of light neutrinos that couple to the Z° is measured to be Nv = 2.89 ± 0.38. No evidence is found for anomalous production of energetic single photons, and upper limits at 95% confidence level are determined for excited neutrino production (BR < 4 ? 8 × 10?6 depending on its mass), production of an invisible ‘X’ particle (σ, < 0.1 pb for masses below 60 GeV), and the magnetic moment of the tau neutrino (< 5.1 × 10-6 μB). 相似文献
19.
A procedure is developed to derive an optimal lower bounds for the pionic contribution to the muon magnetic moment from analyticity of the pion form factor F(t), its normalization F(0)=1 and from experimental information from both the processes e?p → e?π+n and e+e? → π+π?. It represents essentially the solution of a certain kind of optimization problem in Hilbert space. Numerical results are presented and compared to the recent data for the muon magnetic moment; we find aμ(π+π?) ? 42 × 10?9. 相似文献
20.
M. P. Rekalo 《Russian Physics Journal》1983,26(12):1135-1138
A general analysis is made of the polarization properties of γ-quanta in the e+ + e? → Z + γ reaction. Besides the standard mechanism of this reaction; which is determined by the eeZ interaction (neutral weak currents), the possible anomalous magnetic moment χ of the Z boson is also taken into account. A linear contribution in χ. to the differential cross section of the e+ + e? → Z + γ process (with unpolarized particles in the initial and final states) leads to CP-odd asymmetry of the angular distribution of γ-quanta relative to the substitution cos Θ→?cos Θ, where Θ is the angle of emission of the γ-quantum relative to the electron. Measurement of this asymmetry with an accuracy of the order of 1% makes it possible to get a “sense” of the contribution of the magnetic moment of a Z boson of the order of 10?3 GeV?1. 相似文献