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1.
In composite models of quarks, leptons and weak bosons whereW-constituents are colored objects, color octet partners ofW ± andZ 0 are predicted. We study in detail the phenomenology of these particles. Independent of the specific model one expects a color octet isotriplet of vector bosons (W 8 ± ,Z 8 0 ) with mass in the range of 100–200 GeV, and a color octet isosinglet vector bosonV 8 0 with substantially larger mass, due to mixing with the gluon. Moreover, relatively light color octet excitations of the leptons appear, while the existence of “color exotic” partners of the quarks is model dependent. These particles decay mainly into a lepton (quark) and a gluon. We construct the couplings ofW 8 ± ,Z 8 0 andV 8 0 to ordinary and “color exotic” fermions. The signals of color octet weak bosons in low energy weak reactions are explored in detail. The production cross section ofW 8 ± (Z 8 0 ) in hadron-hadron collisions is calculated for \(0.54TeV \leqq \sqrt s \leqq 20TeV\) . Various decay modes of colored weak bosons are studied. The most prominent decay signatures ofW 8 ± andZ 8 0 are events of the type (l +-: charged lepton;j: hadronic jet; : missing transverse momentum). The present CERN \(p\bar p\) collider data on such events are discussed in the light ofW 8 ± andZ 8 0 decays. If colored weak bosons are not found with a mass less than ~250 GeV composite model building will be strongly restricted.  相似文献   

2.
The secondary acceptor A1 of the electron transport chain(s) of photosystem (PS) I is a phylloquinone (vitamin K1, VK1). Pulse electron paramagnetic resonance and electron nuclear double resonance (ENDOR) experiments at X-band frequencies were performed on the photoaccumulated acceptor radical A 1 ·? and the radical pair state P 700 ·+ A 1 ·? in PS I ofThermosynechococcus elongatus. The data obtained were compared with data from the respective radical anion of VK1 in organic solvents. The unusualg tensor magnitude of A 1 ·? is explained by the hydrophobic binding pocket of this radical. The hyperfine couplings and the spin (and charge) density distribution is very different for A 1 .? in PS I and VK 1 ·? in frozen alcoholic solution. This is attributed to a rather strong one-sided hydrogen bond to A 1 ·? . The presence of a hydrogen bond to A 1 ·? has only a minor effect ong. The hyperfine coupling constants of A 1 ·? determined from the radical pair spectra deviate only slightly from those derived from photoaccumulated A 1 ·? in PS I treated with dithionite at high pH. ENDOR resonances of the proton in a H bond were detected and an estimate of the strength and geometry of this bond to A 1 ·? was obtained. The significance of the hydrogen bond and other (hydrophobic) interactions of A1 with the surrounding are briefly discussed.  相似文献   

3.
The followingg-factors have been derived from time integral measurements of γ-γ angular correlations in the static magnetic hyperfine field of magnetized gadolinium metal probes:156Gd:g(4 1 + )=+0.310(19)g(6 1 + )=+0.25(21)g(4 3 + , 1511 keV)=+0.809(27)158Gd:g(4 1 + )=+0.409(15). The 5.35d 156Tb sources were produced by the reaction156Gd(d, 2n)156Tb in our cyclotron. A carrier-free 150y 158Tb source was obtained from ISOLDE/CERN. In comparison with the precisely knowng-factors of the 2 1 + states,g(2 1 su+ ,156Gd) =+0.386(4) andg(2 1 + ,158Gd)=0.381(4), we observe a large reduction for the156Gd 4 1 + state whereasg increases slightly for158Gd. The half-life of the 4 1 + state of158Gd was remeasured as158Gd:T 1/2(4 1 + )=148(2) ps. A measurement of the rotation in the 4 3 + state of156Gd in external magnetic fields of various strengths up toB ext=9.5 T did not confirm the anomalous dependence of the magnetic hyperfine field in gadolinium metal on the external field, which has been reported by Persson et al. [29].  相似文献   

4.
Electron paramagnetic resonance (EPR) spectroscopy at W-band (94 GHz) is used to resolve theg-tensors of the radical ions of the primary chlorophyll donor P 700 +? and the quinone acceptor A 1 ?? in photosystem I. The obtainedg-tensor principal values are compared with those of the isolated pigment radicals in organic solvents and the shifts are related to an impact of the protein environment. P 700 +? has been investigated in photosystem I single crystals at 94 GHz. W-band EPR applied to the photoinduced radical pair P 700 +? A 1 ?? is used to correctly assign theg-tensor axes of P 700 +? to the molecular structure of the primary donor. Density functional theory calculations on a model of A 1 ?? in its binding pocket derived from the recent crystal structure of photosystem I were utilized to correlate experimental magnetic resonance parameters with structural elements of the protein.  相似文献   

5.
The transient field technique has been used to determine theg-factor of the 4 2 + state at 6.010MeV excitation in24Mg. The deduced value ofg=+0.5(4) is consistent with collective model expectations. Further, the equality within experimental accuracies, of the g-factors of the 2 1 + , 2 2 + , 4 1 + and 4 2 + states agrees with theoretical predictions for thisT=0 self-conjugate nucleus, in contrast to the results for20Ne.  相似文献   

6.
Theg-factors of the four lowest states of the ground state rotational band of158Dy have been determined asg(2 1 + )=+0.362(23),g(4 1 su+ )=+0.340(20),g(6 1 su+ )=+0.207(36) andg(8 1 su+ )=+0.21(11). Theg-factors of the 2+ and 4+ states were measured by the IPAC method with radioactive samples of 2.4 h158Er in external magnetic fields. To investigate the higher states, for the first time an on-line γ—γ IPAC experiment was performed with the reaction156Gd(α, 2n)158Dy by use of the static hyperfine field of DyGd.  相似文献   

7.
The relationship between the \(\overline {MS} \) and on-shell renormalization schemes is discussed and the correction, for finite top quark mass, to the formula connecting sin2 θ W =1?M W 2 /M Z 2 and sin2 \(\widehat\theta _W (M_W )\) is given. A table is presented to allow easy conversion. The relative sensitivity, to the top quark and Higgs masses, of the two definitions, when extracted from semi-leptonic neutrino scattering experiments is considered.  相似文献   

8.
The gyromagnetic ratios of the 4 1 + , 6 1 + , and 2 2 + states in186W were measured relative to that of the 2 1 + level by means of the transient field implantation perturbedγ-ray angular distribution technique. The nuclei in the states of interest were Coulomb excited using a beam of 220-MeV63Cu projectiles and recoiled swiftly through a thin, polarized Fe foil. The present measurements yielded ratiosg(4 1 + )/g(2 1 + )=1.04±0.07,g(6 1 + )/g(2 1 + )=1.03 ±0.20 andg(2 2 + )/g(2 1 + )=0.63±0.13. The sizable disparity between the measuredg-factors of the ground- and excited-band is examined within the context of the interacting boson approximation model.  相似文献   

9.
10.
Theg factors of the first excited 2+ levels in the neutron-rich nuclei102Mo and104Mo have been studied through the measurement of the perturbed angular correlations for theγ-γ cascades between the 0 2 + -2 1 + -0 1 + level sequences. The results of g=0.42±0.07 for102Mo and ofg= ?0.11 +0.12 for104Mo agree with the prediction of the vibrational-rotational model. In terms of IBA, with the assumption ofN π=3 for the Mo isotopes which takes into consideration a two particle, two-hole excitation across the Z=40 subshell, the proton-bosong factor is deduced to beg π=1.00±0.23. It is shown that this value provides evidence for subshell effects in100Zr.  相似文献   

11.
We present a careful analysis of the polarized photon-gluon fusion process. Discussing various regularization schemes it is demonstrated that one can safely extract a hard gluonic contribution to the proton's spin dependent structure functiong 1 P . The value of the first moment of the gluonic Wilson coefficient is shown to be in agreement with the anomaly result. Furthermore, we examine the question whether the gluonic contribution alone can account for existing experimental data forg 1 P (x,Q 2) (x≧0.01, <Q 2>?Q 0 2 =10 GeV2) and find a positive answer.  相似文献   

12.
The problem of determining theP-waveπ-π phase-shifts given the modulus of the electromagnetic form-factor in the time-like momentum transfer region has been discussed. The problem ofK 1 0 ?K 2 0 mass difference has been discussed with emphasis on the scalar form-factor rather than models ofπ -π scattering.  相似文献   

13.
The electron capture decays of133Ba (10.4 y) and139Ce (140 d) were investigated with high resolution Ge(Li) detectors. By x-ray — γ-ray coincidences values of the quantityP k ω k ? k for various transitions in the decay of133Ba and139Ce are obtained. The factor ω k ? k was measured independently by means ofK-conversion electron-K x-ray coincidences and was then used to determineP k , theK-capture probability. The independent measurement of the product ω k ? k , together with recent accurate values of ω k , provides a new method for the accurate calibration of semiconductor x-ray detectors. In the decay of139Ce, a value ofP k =0.78±0.03 is found (where the error represents twice the standard deviation) from whichQ ec =326 ?30 +70 keV to the139La ground-state is found by use of theory. In133Ba decay, values are found ofP k 1=0.72±0.04 for theEC transition to the 437 keV level in133Cs,P k 2=0.80±0.07 to the 384 keV level, and from an independent measurement, the ratioP k 1/P k 2=0.87±0.07. From these results the ground-state value ofQ ec =522 ?10 +20 keV is derived from theory for133Ba decay. The gamma spectrum of133Ba also was remeasured. From the present gamma intensities and previous conversion electron intensities, new values forK-shell conversion coefficients are obtained. Previously reported γ-rays at 35 and 391 keV are not confirmed.  相似文献   

14.
Using the Mössbauer technique electric hyperfine interactions of the first excited non-rotational states at 64 keV in157Gd and at 86.5 keV in155Gd have been determined in GdF3 and GdCl3· 6H2O. For the ratio of quadrupolmoments the ratiosQ 64 157 /Q g 157 =1.74±0.04,Q 86.5 155 /Q g 157 =?0.07 ± 0.21 andQ g 155 /Q g 157 =0.78 ± 0.06 were found. In addition isomer shifts were observed from which a ratio δ〈r2 64 157 /δ〈r2 86.5 155 =?2.6±0.15 can be inferred.  相似文献   

15.
We study the effect of vector and axial isovector mesons in the soliton of the SU(2) NJL-model for static hedgehog configurations and on the chiral circle. The Lagrangian reproduces Sakurai's Universality and implements vector dominance through current-field identities. The parameters of the Lagrangian are fixed by means of a heat-kernel expansion up to second order taking theA-π mixing into account. For the corresponding set of parameters we find solitons for constituent quark masses betweenM~265–345 MeV which are much lower than those found without vector mesons. For the valueM=315 MeV which corresponds both to the KSFR relation 2g ρ 2 f π 2 =m ρ 2 and the Weinberg sum rule m A 2 =m ρ 2 the soliton has a clearly negative quark eigenvalue. The soliton mass is about 1100 MeV. For this choise of parameters the radius and axial coupling constant turn out to be too small.  相似文献   

16.
The relativistic3 P 0 model is applied to the \(p\bar p\) annihilation into twoS-wave mesons. We calculate the branching ratios of the \(p\bar p\) annihilation at rest into two mesons in the quark rearrangement model and in the quark annihilation model. In the annihilation model, we project the intermediate \(cq\bar q\) state to eigenstates ofSU (4) with the relative angular momentum of \(cq\bar q\) equals orp. In the rearrangement model, no annihilation occurs from theS-wave \(p\bar p\) and certain branching ratios conflict with the experimental data. Detailed comparison with the experiment needs inclusion ofP-wave mesons in the final state, nevertheless we find that the annihilation model gives qualitatively better results than the rearrangement model. The effect of initial state interaction through \(N\bar \Delta \pm \Delta \bar {\rm N}\) or \(\Delta \bar \Delta \) channels is discussed.  相似文献   

17.
The two-spin asymmetries \(A_{LL}^{\pi ^0 } (\mathop p\limits^{( - )} p)\) and \(A_{LL}^\gamma (\mathop p\limits^{( - )} p)\) are calculated in a new model incorporating the nonrelativistic quark model and the parton model which interprets well EMCg 1 p (x) data. The model can reproduce the experimental data for inclusive π0 rather well.  相似文献   

18.
The electron capture decay energy of183Re has been determined from the fraction ofK-capture in the transition to the 453.08 keV level in183W by delayed coincidences. From this value the total decay energy from183Re→183W is obtained to beQ=555 ?7 +9 keV according to the theory ofBrysk andRose with corrections ofBahcall. The resulting logft values and consequences for the decay scheme are discussed.  相似文献   

19.
The isomer shift in the optical transition Eu II 4f7(8S 7 2/o )6p3/2 (7/2,3/2)4?4f7 (8S 7 2/o )5d9D 4 o , λ=6O4.95 nm, has been measured between the isotope152gEu(3?) and its isomer152mEu(0?). From the valuev(152gEu)–v(152mEu)=736(10) MHz the deformation parameter of152mEu has been estimated to be152mβ?+0.25. This value is smaller than152gβ as obtained from isotope shift measurements and the spectroscopic quadrupole moment. The influence of the shape difference on the decay of152mEu is discussed.  相似文献   

20.
In the rare-earth SmCoO3 perovskite, Co3+ ions at low temperatures appear to be in the low-spin state with S = 0, t 2g 2 e g 0 . If Ca2+ ions partially substitute Sm3+ ions, oxygen deficient Sm1 ? x Ca x CoO3 ? δ solid solutions with δ = x/2 appear. The oxygen deficiency leads to the formation of pyramidally coordinated cobalt ions Co pyr 3+ in addition to the existing cobalt ions Co oct 3+ within the oxygen octahedra. Even at low temperatures, these ions have a magnetic state, either S = 1, t 2g 5 e g 1 or S = 2, t 2g 4 e g 2 . At low temperatures, the magnetization of Sm1 ? x Ca x CoO3 ? δ is mainly determined by the response of Co pyr 3+ ions. Owing to the characteristic features of the crystal structure of the oxygen deficient perovskite, these ions form a set of nearly isolated dimers. At high temperatures, the magnetization of Sm1 ? x Ca x CoO3 ? δ is mainly determined by the response of Co oct 3+ ions, which exhibit a tendency to undergo the transition from the S = 0, t 2g 6 e g 0 state to the S = 1, t 2g 5 e g 1 or S = 2, tt 2g 4 e g 2 state. In addition, the magnetization and specific heat of the solid solutions under study include the contribution from the rare-earth subsystem, which undergoes a magnetic ordering at low temperatures.  相似文献   

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