共查询到20条相似文献,搜索用时 31 毫秒
1.
M.R. Pennington T. Mori S. Uehara Y. Watanabe 《The European Physical Journal C - Particles and Fields》2008,56(1):1-16
We perform an amplitude analysis of the world published data on γγ→π+π- and π0π0. These are dominated in statistics by the recently published results from Belle on the charged pion channel. Nevertheless,
having only limited angular information, a range of solutions remain possible. We present two solutions with Γ(f0(980)→γγ)=0.42 and 0.10 keV, and Γ(f2(1270)→γγ)=3.14±0.20 and 3.82 ± 0.30 keV, respectively: the former being the solution favoured by χ2, the latter at the edge of acceptability. Models of the structure of the f0(980) predict two photon widths to be between 0.2 and 0.6 keV, depending on its composition as mainly K̄K, s̄s or qq̄qq. Presently
available data cannot yet distinguish unambiguously between these predictions. However, we show how forthcoming results on
γγ→π0π0 can not only discriminate between, but also refine, these classes of partial wave solutions. 相似文献
2.
《The European Physical Journal C - Particles and Fields》2007,51(3):525-542
Neutral triple-gauge-boson couplings ZZZ, ZZγ and Zγγ have been studied with the DELPHI detector using data at energies between
183 and 208 GeV. Limits are derived on these couplings from an analysis of the reactions e+e-→Zγ, using data from the final states γff̄, with f=q or ν, from e+e-→ZZ, using data from the four-fermion final states qq̄qq̄, qq̄μ+μ-, qq̄e+e-, qq̄νν̄, μ+μ-νν̄ and e+e-νν̄, and from e+e-→Zγ*, in which the final state γ is off mass-shell, using data from the four-fermion final states qq̄e+e- and qq̄μ+μ-. No evidence for the presence of such couplings is observed, in agreement with the predictions of the Standard Model. 相似文献
3.
Xiao-Gang He Xue-Qian Li Xiang Liu Jian-Ping Ma 《The European Physical Journal C - Particles and Fields》2007,49(3):731-736
Recently the BES collaboration has announced the observation of a resonant state in the π+π-η’ spectrum in J/ψ→γπ+π-η’ decay. Fitting the data with a 0-+ state, the mass is determined to be 1833.7 MeV with 7.7σ statistic significance. This state is consistent with the one extracted
from previously reported pp̄ threshold enhancement data in J/ψ→γpp̄. We study the properties of this state using QCD anomaly
and QCD sum rules, assuming X(1835) to be a pseudoscalar, and we show that it is consistent with the data. We find that this
state has a sizeable matrix element , leading to branching ratios of (2.61–7.37)×10-3 and (2.21–10.61)×10-2 for J/ψ→γGp and for Gp→π+π-η′, respectively. Combining the calculated branching ratio of J/ψ→γGp and data on threshold enhancement in J/ψ→γpp̄, we determine the coupling for the Gp–p–p̄ interaction. We finally study the branching ratios of the other J/ψ→γ+three mesons decay modes. We find that J/ψ→γGp→γ(π+π-η,KKπ0) can provide useful tests for the mechanism proposed.
PACS 11.55.Hx; 12.39.Fe; 12.39.Mk; 13.25.Gv 相似文献
4.
Chiral constituent quark model with configuration mixing (χCQMconfig) is known to provide a satisfactory explanation of the “proton spin problem” and related issues. In order to enlarge the
scope of χCQMconfig, we have attempted to phenomenologically incorporate x-dependence in the quark distribution functions. In particular, apart
from calculating valence and sea quark distributions qval(x) and q̄(x), we have carried out a detailed analysis to estimate the sea quark asymmetries d̄(x)-ū(x), d̄(x)/ū(x) and
as well as spin independent structure functions F2
p(x)-F2
n(x) and F2
n(x)/F2
p(x) as functions of x. We are able to achieve a satisfactory fit for all the above mentioned quantities simultaneously. The
inclusion of effects due to configuration mixing have also been examined in the case F2
p(x)-F2
n(x) and F2
n(x)/F2
p(x) where the valence quark distributions dominate and it is found that it leads to considerable improvement in the results.
Further, the valence quark structure has also be tested by extrapolating the predictions of our model in the limit x→1 where
data is not available. 相似文献
5.
Considering two assumptions on the molecular state, i.e. the S-wave Λ̄–K- and S-wave Σ̄0–K- molecular states, we study the possible decays of N̄X(1625) that include N̄X(1625)→K-Λ̄,π0p̄,ηp̄,π-n̄. Our results indicate that (1) if N̄X(1625) is the Λ̄–K- molecular state, K-Λ̄ is the main decay mode of N̄X(1625), and the branching ratios of the rest decay modes are tiny; (2) if N̄X(1625) is the Σ̄0–K- molecular state, the branching ratio of N̄X(1625)→K-Λ̄ is one or two orders smaller than that of N̄X(1625)→π0p̄,ηp̄,π-n̄. Thus the search for N̄X(1625)→π0p̄,ηp̄,π-n̄ will be helpful to shed light on the nature of N̄X(1625).
PACS 13.30.Eg, 13.75.Jz 相似文献
6.
L.A. Trevisan C. Mirez T. Frederico L. Tomio 《The European Physical Journal C - Particles and Fields》2008,56(2):221-229
Within a statistical model of linear confined quarks we obtain the flavor asymmetry and corresponding structure function of
the nucleon. The model parameters are fixed by the experimental available data. The temperature parameter is adjusted by the
Gottfried sum rule violation and the chemical potentials by the corresponding up (u) and down (d) quark normalizations in
the nucleon. The light antiquark and quark distributions in the proton, given by d̄/ū, d/u and d̄-ū, as well as the neutron
to proton ratio of the structure functions, extracted from the experimental data, are well fitted by the model. As the quark-confining
strengths should be flavor dependent, a mechanism is introduced in the model to adjust the corresponding distribution, in
order to improve the comparison obtained for the sea-quark asymmetries in the nucleon with the available experimental analysis.
PACS 11.30.Hv; 14.20.Dh; 12.39.Ki; 12.40.Ee; 11.55.Hx 相似文献
7.
We study different types of radiative decays involving f0(980) and a0(980) mesons within a unified ChPT-based approach at one-loop level. Light scalar resonances, which are seen in the ππ, πη
and KK̄ channels of the φ(1020) radiative decays and in the J/ψ decays are responsible for key questions of low-energy dynamics
in the strong interaction sector, and the decays φ(1020)→γa0(980), φ(1020)→γf0(980), a0(980)→γγ and f0(980)→γγ are of interest for current experimental programs in Jülich, Frascati and Novosibirsk. From the theoretical point
of view it is important to verify whether light scalar mesons are members of some flavor octet or nonet. We find a value for
the mixing angle dictated by consistency with experiment and the coupling structures of the ChPT Lagrangian. The decay widths
f0(980)/a0(980)→γρ(770)/ω(782), which have not been experimentally studied yet, are predicted. We also obtain several relations between
the widths, which hold independently of the coupling constants and which represent a fingerprint of the model.
PACS 11.30.Hv; 12.39.Fe; 13.30.Eg; 14.40.-n 相似文献
8.
Xiang Liu 《The European Physical Journal C - Particles and Fields》2008,54(3):471-474
Very recently a new enhancement around 4.05 GeV was observed by the Belle experiment. We discuss some possible assignments
for this enhancement, i.e. the ψ(3S) and D*D̄* molecular states. In these two assignments, Y(4008) can decay into J/ψπ0π0 with a branching ratio comparable with that of Y(4008)→J/ψπ+π-. Thus, one suggests high energy experimentalists to look for Y(4008) in J/ψπ0π0 channel. Furthermore one proposes further experiments to search for the missing channels DD̄, DD̄*+h.c. and especially χcJπ+π-π0 and ηcπ+π-π0, which will be helpful to distinguish the ψ(3S) and D*D̄* molecular state assignments for this new enhancement.
PACS 13.30.Eg 13.75.Lb 相似文献
9.
The problem of determining the field enhancement factor in field-emission cathodes based on carbon nanotubes (CNTs) is considered.
The electrostatic problem of finding the field enhancement factor for nanotubes with different shapes of the tip as a function
of the angle the nanotube makes with the cathode surface and of the interelectrode spacing is solved. The dependence of the
electric field enhancement factor on the spacing between vertically oriented nanotubes constituting an array is derived. Making
allowance for this dependence gives an optimal value of the surface density of nanotubes in the array at which the emission
current density is maximal. The I—V characteristic of CNT-based cathodes is studied with regard to the statistical straggling of their orientation angles. This
I—V characteristic is compared with the characteristic obtained with regard to the statistical straggling of the CNT geometrical
parameters. 相似文献
10.
《The European Physical Journal C - Particles and Fields》2008,53(1):15-20
The decay J/ψ→ωpp̄ is studied using a 5.8×107 J/ψ event sample accumulated with the BES II detector at the Beijing Electron–Positron Collider. The decay branching fraction
is measured to be B(J/ψ→ωpp̄)=(9.8±0.3±1.4)×10-4. No significant enhancement near the pp̄ mass threshold is observed, and an upper limit of B(J/ψ→ωX(1860))B(X(1860)→pp̄)<1.5×10-5 is determined at the 95% confidence level, where X(1860) designates the near-threshold enhancement seen in the pp̄ mass spectrum
in J/ψ→γpp̄ decays. 相似文献
11.
《The European Physical Journal C - Particles and Fields》2007,51(3):503-523
Measurements of Zγ* production are presented using data collected by the DELPHI detector at centre-of-mass energies ranging from 183 to 209 GeV,
corresponding to an integrated luminosity of about 667 pb-1. The measurements cover a wide range of the possible final state four-fermion configurations: hadronic and leptonic (e+e-qq̄, μ+μ-qq̄, qq̄νν̄), fully leptonic (l+l-l’+l’-) and fully hadronic final states (qq̄qq̄, with a low mass qq̄ pair). Measurements of the Zγ* cross-section for the various final states have been compared with the Standard Model expectations and found to be consistent
within the errors. In addition, a total cross-section measurement of the l+l-l’+l’- cross-section is reported, and found to be in agreement with the prediction of the Standard Model. 相似文献
12.
Analytical expressions are derived for the components of the intrinsic frame inverse mass tensor of the Bohr Hamiltonian.
These expressions contain parameters which are determined by the experimental data on the B(E2)’s and the excitation energies of the low-lying collective states. It is shown that the nondiagonal component of the intrinsic
frame mass tensor has a small effect on the collective motion. It is shown also that the values of the B
ββ
, B
γγ
and the rotational mass coefficientB
1 differ in the well-deformed nuclei by factor 3 or more. 相似文献
13.
V. V. Varlamov B. S. Ishkhanov V. N. Orlin S. Yu. Troshchiev 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(6):842-849
The results from experimental and theoretical studies of the total and partial cross sections of photoneutron reactions on
the 197Au isotope were analyzed. The cross sections for reactions σ(γ, nX) = σ(γ, n) + σ(γ, np) + … + σ(γ, 2nX) = σ(γ, 2n) + σ(γ, 2np) + … were evaluated in the energy range 7 ≤ E
γ ≤ 30 MeV using an approach free of the shortcomings of experimental photoneutron multiplicity sorting methods. The total
photoneutron reaction cross sections σexp(γ, xn) = σexp(γ, nX) + 2σexp(γ, 2nX) + … = σexp(γ, n) + σexp(γ, np) + 2σexp(γ, 2n) + 2σexp(γ, 2np) + … were used as the initial experimental data. The contributions from the cross sections σ(γ, nX) and σ(γ, 2nX) to the cross sections σexp(γ, xn) were separated using the multiplicity transition functions F
1
theor = σtheor(γ, 1nX)/σtheor(γ, xn) and F
2
theor = σtheor(γ, 2nX)/σtheor(γ, xn), calculated within an updated version of the pre-equilibrium model of photonuclear reactions. New evaluated data for both
partial reaction cross sections, i.e., σeval (γ, 1nX) = F
1
theorσexp(γ, xn) and σeval(γ, 2nX) = F
2
theorσexp(γ, xn), were obtained. The cross sections σeval(γ, nX) and σeval.(γ, 2nX) evaluated using the theoretically calculated functions F
1,2theor are consistent with the Livermore data, but substantially contradict the Saclay data. 相似文献
14.
V. V. Varlamov B. S. Ishkhanov V. N. Orlin V. A. Chetvertkova 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(6):833-841
A combined analysis of experimental data on total and partial photoneutron reaction cross sections, obtained using bremsstrahlung
γ-radiation and quasi-monoenergetic annihilation photon beams, was performed for nine Sn isotopes. The partial reactions σeval(γ, nX) and σeval(γ, 2nX) cross sections were evaluated using an approach free of the shortcomings of experimental neutron multiplicity sorting methods.
This approach involves calculations within the photonuclear reaction model, based on Fermi gas densities and considering the
effects of nucleus deformation, the isospin splitting of its giant dipole resonance (GDR), and experimental data on the total
photoneutron cross sections σexp(γ, xn) = σexp(γ, nX) + 2σexp(γ, 2nX) = σexp(γ, n) + σexp(γ, np) + … + 2σexp(γ, 2n) + 2σexp(γ, 2np) + …. The evaluated σeval(γ, nX) and σeval(γ, 2nX) reactions cross sections were obtained using the introduced transition multiplicity functions F
theor = σtheor(γ, 2nX)/σtheor(γ, xn) = σtheor(γ, 2nX)/[σtheor(γ, nX) + 2σtheor(γ, 2nX) + …]; and σeval.(γ, 2nX) = F
theor.σexp.(γ, xn) = σeval(γ, nX) = (1 − 2F
theor)σexp(γ, xn). The evaluated partial reaction cross sections were used to assess the total photoneutron reaction cross sections σeval(γ, sn) = σeval(γ, nX) + σeval(γ, 2nX) + … as functions of the mass number A. The GDR features of 112, 114, 116, 117, 118, 119, 120, 122, 124Sn isotopes were studied and are discussed here. 相似文献
15.
16.
β-γ-γ directional correlation studies for the cascades (i)β-rays ofE
max=0.12 MeV,γ-rays of 557 keV andγ-rays of 53 keV and (ii)β-rays ofE
max=0.21 MeV,γ-rays of 444 keV andγ-rays of 53 keV have been made. The triple correlation functionsW(θ) were obtained to beW(θ)=1+(−0.153±0.031)P
2(cosθ)+(0.004±0.035)P
4(cosθ) forβ-rays ofE
max 0.12 MeV→557→53 keV cascade andW(θ)=1+(0.163±0.042)P
2(cosθ)+(−0.035±0.058)P
4(cosθ) forβ rays ofE
max=0.21 MeV→444 keV→53 keV cascade.
Spins and parities of the 650, 537 and 93 keV levels of103Rh are deduced by triple angular correlation and the internal conversion coefficient studies. Multipolarities of the transitions
are also determined. 相似文献
17.
First calculations of the Sternheimer charge perturbed antishieldingfunction β(r) within the uncoupled Hartree-Fock theory are reported for the He, Ne, Ar, Kr, and Xe isoelectronic series, respectively.
The results should complement the previously reported calculations of the dual moment perturbed antishieldingfunction γ(r) [Hyp. Int. 12(1982)113; 14(1983)243] and would facilitate more complete calculations of the as yet to be fully evaluated
theory of electric field gradients in metals based on the energy of interaction approach. The general trends in β(r) are pointed out and explained. 相似文献
18.
Sergei M. Pimenov Vadim D. Frolov Evgeny V. Zavedeev Nikolay P. Abanshin He-Yun Du Wei-Chao Chen Li-Chyong Chen Jih-Jen Wu Kuei-Hsien Chen 《Applied Physics A: Materials Science & Processing》2011,105(1):11-16
In this paper, we have studied field emission properties of highly dense arrays of multi-walled carbon nanotubes (CNTs) used
as cathodes in diode-type field emission devices with a phosphor screen. For the high-density CNT emitters it is demonstrated
that the emission sites are located on the CNT-cathode edges, which is direct experimental evidence of the ‘edge effect’.
The results of computer simulations (using ‘ANSYS Electromagnetic’ software) are presented to confirm the experimental data
and to analyze the effect of patterning on the electric field distribution for high-density CNT arrays. It is shown that selective-area
removal of nanotubes in the arrays leads to the formation of additional edges characterized by the high field enhancement
factor and enhanced emission from the CNT cathodes. In addition, scanning probe microscopy techniques are employed to examine
surface properties of the high-density CNT arrays. For CNT arrays of ‘short’ nanotubes, the work function distribution over
the sample surface is detected using a scanning Kelvin microscopy method. 相似文献
19.
We have studied multiple regressions between the spectral aerosol extinction coefficient ε, backscatter indicatrix gπ, and light-scattering coefficients βθ at angles of θ = 1–180°, which we used to select the optimal scattering angle for determining the extinction coefficient
at the wavelengths 0.350, 0.532, and 1.060 μm. We have estimated the errors in determination of the values of ε and gπ at the given wavelengths for different atmospheric situations with different meteorological parameters. We have shown that
it is possible to use the spectral βθ values at a 33° angle to determine the reference values for ε(λ) and gπ(λ) at λ = 0.350, 0.532, and 1.060 μm in laser detection and ranging (lidar) measurements, and we give examples of recovering
the vertical profiles of ε in a slightly turbid atmosphere from the results of simultaneous multiwavelength lidar and nephelometric
measurements.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 767–772, November–December, 2007. 相似文献
20.
《The European Physical Journal C - Particles and Fields》2007,50(2):315-328
The inclusive production cross sections of the strange vector mesons K*0, K̄*0, and φ have been measured in interactions of 920 GeV protons with C, Ti, and W targets with the HERA-B detector at the HERA
storage ring. Differential cross sections as a function of rapidity and transverse momentum have been measured in the central
rapidity region and for transverse momenta up to pT = 3.5 GeV/c. The atomic number dependence is parametrised as σpA=σpN*Aα, where σpN is the proton–nucleon cross section. Within the phase space accessible, α(K*0)=0.86±0.03, α(K̄*0)=0.87±0.03, and α(φ)=0.96±0.02. The total proton–nucleon cross sections, determined by extrapolating the differential measurements
to full phase space, are σpN→K*0=(5.06±0.54) mb, σpN→K̄*0=(4.02±0.45) mb, and σpN→φ=(1.17±0.11) mb. For all resonances the Cronin effect is observed; compared to the measurements of Cronin et al. for K± mesons, the measured values of α for φ mesons coincide with those of K+ mesons for all transverse momenta, while the enhancement for K*0/K̄*0 mesons is smaller. 相似文献