共查询到20条相似文献,搜索用时 31 毫秒
1.
Yu-Ming Wang M. Jamil Aslam Cai-Dian Lü 《The European Physical Journal C - Particles and Fields》2009,59(4):847-860
The exclusive weak decay of Λ
b
→Λ
γ and Λ
b
→Λ
l
+
l
− are investigated in the Appelquist–Cheng–Dobrescu model, which is an extension of the standard model in the presence of universal
extra dimensions. Employing the transition form factors obtained in the light-cone sum rules, we analyze how the invariant-mass
distribution, the forward–backward asymmetry and the polarization asymmetry of the Λ baryon of these decay modes can be used to constrain the only additional free parameter with respect to the standard model,
namely, the radius, R, of the extra dimension. Our results indicate that the Kaluza–Klein modes can lead to approximately 25% suppression of the
branching ratio of Λ
b
→Λ
γ; however, their contributions can bring about 10% enhancement to the decay rate of Λ
b
→Λ
l
+
l
−. It is shown that in the present scenario the zero position of the forward–backward asymmetry of Λ
b
→Λ
μ
+
μ
− is sensitive to the compactification parameter R, while the measurement of polarizations of Λ baryon in the Λ
b
decays are not a useful tool to provide any valuable information for the universal extra-dimension model. 相似文献
2.
Junfeng Sun Dongsheng Du Yueling Yang 《The European Physical Journal C - Particles and Fields》2009,60(1):107-117
The B
c
→J/ψ
π, η
c
π decays are studied with the perturbative QCD approach. It is found that the form factors
and
for the B
c
→J/ψ, η
c
transitions and the branching ratios are sensitive to the parameters ω, v, f
J/ψ
and
, where ω and v are the parameters of the charmonium wave functions for a Coulomb potential and the harmonic-oscillator potential, respectively,
and f
J/ψ
and
are the decay constants of the J/ψ and η
c
mesons, respectively. The large branching ratios and the clear signals of the final states make the B
c
→J/ψ
π, η
c
π decays the prospective channels for measurements at the hadron colliders. 相似文献
3.
Zhi-Gang Luo Xiao-Lin Chen Xiang Liu Shi-Lin Zhu 《The European Physical Journal C - Particles and Fields》2009,60(3):403-411
Stimulated by recent observations of the excited bottom–strange mesons B
s1 and B
s2*, we calculate the semileptonic decays
, which is relevant for the exploration of the potential of searching these semileptonic decays in experiment. 相似文献
4.
5.
The e
+
e
− → π
+
π
−
π
+
π
− cross section is calculated for energies of 0.65 ≤ √s ≤ 1 GeV in the framework of the generalized hidden local symmetry model. The calculations are compared with the data of CMD-2
and BaBaR. It is shown that the inclusion of heavy isovector resonances ρ(1450) and ρ(1700) is necessary for reconciling calculations
with the data. It is found that, at √s ≈ 1 GeV, the contributions of the above resonances are much larger, by a factor of 30, than the ρ(770) one, and amount to
a considerable fraction ∼0.3–0.6 of the latter at √s ∼ m
ρ.
The text was submitted by the authors in English. 相似文献
6.
I. O. Troyanchuk D. V. Karpinsky M. V. Bushinskii O. Prokhnenko M. Kopcevicz R. Szymczak J. Pietosa 《Journal of Experimental and Theoretical Physics》2008,107(1):83-89
Systems of solid solutions Bi1 − x
Ca
x
FeO3 (I) and Bi1 − x
CaxFeO1 − x
Ti
x
O3 (II) have been obtained and their properties have been studied using neutronography and M?ssbauer spectroscopy; magnetization
and permittivity have been measured. It is shown that an increase in the concentration of calcium ions in system I for x > 0.2 changes rhombohedral distortions of a unit cell (space group R3c) to tetragonal distortions (space group I4/mcm), while rhombohedral distortions in system II for x > 0.2 are replaced by orthorhombic distortions (space group Pnma). Analysis of the crystal structure has revealed strong anisotropy in vibrations of Bi and O ions in system I compounds.
Systems I and II are characterized by G-type antiferromagnetic ordering of magnetic moments. In system II, spontaneous magnetization
associated with the Dzyaloshinskii-Moriya interaction has been detected. According to M?ssbauer spectroscopy data, iron ions
in compounds I and II are in the trivalent state and charge compensation occurs due to the formation of oxygen vacancies.
The permittivity increases with the calcium concentration.
Original Russian Text ? I.O. Troyanchuk, D.V. Karpinsky, M.V. Bushinskii, O. Prokhnenko, M. Kopcevicz, R. Szymczak, J. Pietosa,
2008, published in Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2008, Vol. 134, No. 1, pp. 105–112. 相似文献
7.
Jeong Ho Ryu Hyong Sik Won Youn-Gon Park Sang Hyun Kim Won Young Song Hideo Suzuki Chulsoo Yoon 《Applied Physics A: Materials Science & Processing》2009,95(3):747-752
Rare-earth-doped oxynitride or nitride compounds have been reported to be photoluminescent and may then serve as new phosphors
because of their good thermal and chemical stabilities. In this work, Eu2+-doped β-SiAlON phosphor with a composition of Eu
x
Si6−z
Al
z
O
z
N8−z
(x=0.018, z=0.23) was prepared by gas-pressured solid state reaction. The crystallinity and particle morphology of the prepared phosphor
were characterized. The Stokes shift and zero-phonon line were calculated mathematically and estimated from the spectral data.
The temperature dependence of photoluminescence was measured from 25 to 250°C. The prepared Eu2+-doped β-SiAlON green phosphor showed superior thermal quenching property compared to silicate (SrBaSiO4:Eu2+) green phosphor. The white light-emitting diode (LED) back-lighting unit (BLU) using the prepared β-SiAlON:Eu2+ green phosphor exhibited higher color gamut than a commercial silicate phosphor. 相似文献
8.
S. Rai Choudhury A. S. Cornell Naveen Gaur 《The European Physical Journal C - Particles and Fields》2008,58(2):251-259
Flavor changing neutral current (FCNC) decays of the B-meson are a very useful tool for studying possible physics scenarios beyond the standard model (SM), where of the many FCNC
modes radiative, purely leptonic and semi-leptonic decays of the B-meson are relatively clean tests. Within this context, the BELLE collaboration has measured the process B→K
*
γ and also searched for the B→K
1(1270)γ process. Theoretical analyses of these processes are yielding similar values of the relevant form factors. In this work we
have used this upper bound in studying the angular correlations for the related semi-leptonic decay mode B
−→K
1−(1270)(→ρ
0
K
−)ℓ
+
ℓ
−, where we have used the form factors that have already been estimated for the B→K
1(1270)γ mode. Note that the additional form factors that are required were calculated using large energy effective theory (LEET). 相似文献
9.
Zhi-Gang Wang 《The European Physical Journal C - Particles and Fields》2008,58(2):245-250
We study the final-state rescattering effects in the decay B
0→η
c
K
*. The numerical results indicate that the corrections are comparable with the contribution from the naive factorizable amplitude,
and the total amplitudes can accommodate the experimental data. 相似文献
10.
The branching ratios and photon spectra of the rare processes ρ(ω) → π
0
π
0
γ, ρ(ω) → ηπ
0
γ are calculated in the framework of the standard local quark Nambu-Jona-Lasinio model. Three types of diagrams are considered:
the quark box and the pole diagrams with scalar (σ, α
0(980)) and vector (ρ, ω) mesons. The obtained estimates for the widths of the processes ρ(ω) → π
0
π
0
γ are in satisfactory agreement with existing experimental data. Predictions are made for the widths of the processes ρ(ω) → ηπ
0
γ.
The text was submitted by the authors in English. 相似文献
11.
Current and upcoming experiments should improve the sensitivity to e
α
→e
β
γ decays by an order of magnitude. This paper assumes that one of the τ→e
β
γ decays is observed, and explores the structure and consequences of the required new flavoured couplings. In simple models
(a low-scale seesaw, leptoquarks) it is shown that the dipole vertex function is proportional to a product of flavoured matrices
from the Lagrangian (a “Jarlskog-like” invariant), provided that the loop particles are weakly coupled to the Higgs. Secondly,
if the dipole vertex function has a hierarchical structure, this might imply that only some of the τ→e
β
γ modes can be observed, due to the “approximate zero” implied by the bound on μ→eγ. The assumptions underlying this potential test of a hierarchical structure are discussed. 相似文献
12.
Marisílvia Donadelli 《Indian Journal of Physics》2011,85(1):27-32
The ratio of the ψ′ over the J
ψ production cross section in the dielectron channel has been measured in $
\sqrt s
$
\sqrt s
= 200 GeV p + p collisions with the PHENIX detector at RHIC. The analysis is based on fitting of the dielectron invariant mass spectra in
the area around the J
ψ and ψ′ signals in order to extract a ratio ψ′ over J
ψ of 0.019 ± 0.005 (stat) ± 0.002 (sys) and a fractional feed-down contribution to J
ψ from ψ′ of 8.6 ± 2.5%. 相似文献
13.
Dian-Yong Chen Xiang Liu Xue-Qian Li 《The European Physical Journal C - Particles and Fields》2011,71(11):1808
To solve the discrepancy between the experimental data on the partial widths and lineshapes of the dipion emission of ϒ(4S) and the theoretical predictions, we suggest that there is an additional contribution, which had not been taken into account
in previous calculations. Noticing that the mass of ϒ(4S) is above the production threshold of B[`(B)]B\bar{B}, the contribution of the sequential process
\varUpsilon(4S)? B[`(B)]? \varUpsilon(nS)+S?\varUpsilon(nS)+p+p-\varUpsilon(4S)\to B\bar{B}\to \varUpsilon(nS)+S\to\varUpsilon(nS)+\pi^{+}\pi^{-} (n=1,2) may be sizable, and its interference with that from the direct production would be important. The goal of this work
is to investigate if a sum of the two contributions with a relative phase indeed reproduces the data. Our numerical results
on the partial widths and the lineshapes
d\varGamma(\varUpsilon(4S)?\varUpsilon(2S,1S)p+p-)/d(mp+p-)d\varGamma(\varUpsilon(4S)\to\varUpsilon(2S,1S)\pi^{+}\pi^{-})/d(m_{\pi ^{+}\pi^{-}}) are satisfactorily consistent with the measurements; thus the role of this mechanism is confirmed. Moreover, with the parameters
obtained by fitting the data of the Belle and BaBar collaborations, we predict the distributions dΓ(ϒ(4S)→ϒ(2S,1S)π
+
π
−)/dcosθ, which have not been measured yet. 相似文献
14.
Susana Coito George Rupp Eef van Beveren 《The European Physical Journal C - Particles and Fields》2011,71(10):1762
The nature of the X(3872) enhancement is analyzed in the framework of the Resonance-Spectrum Expansion, by studying it as a regular J
PC
=1++ charmonium state, though strongly influenced and shifted by open-charm decay channels. The observed but Okubo–Zweig–Iizuka-forbidden
ρ
0
J/ψ and ωJ/ψ channels are coupled as well, but effectively smeared out by using complex ρ
0 and ω masses, in order to account for their physical widths, followed by a rigorous algebraic procedure to restore unitarity. A
very delicate interplay between the D
0
D
∗0, ρ
0
J/ψ, and ωJ/ψ channels is observed. The data clearly suggest that the X(3872) is a very narrow axial-vector c[`(c)]c\bar{c} resonance, with a pole at or slightly below the D
0
D
∗0 threshold. 相似文献
15.
P. Thiyagarajan Brajesh Tiwari M. Kottaisamy N. Rama M. S. Ramachandra?Rao 《Applied Physics A: Materials Science & Processing》2009,94(3):607-612
Cool white light was realized in Y2−x−y
Gd
x
SiO5: Ce
y
phosphor under near UV excitation, due to the occupation Ce3+ in Y3+ 1st and 2nd site, synthesized using solid state carbothermal reduction route. SEM with elemental analysis show the existence
of Gd in Y2SiO5:Ce enhances the particles size in comparison to Y2SiO5:Ce phosphors alone. Gd3+ (0.00≤x≤0.75) and Ce3+ (0.02≤y≤0.10) concentration was optimized to 0.50 and 0.08 in Y2SiO5, respectively. The CIE chromaticity color coordinates (0.24, 0.20) are close to cool white light value which could be useful
for the fabrication of cool white LED. 相似文献
16.
The widths with respect to the radiative decays f
0(980) → ργ and a
0(980) → ωγ were calculated within the local Nambu-Jona-Lasinio model. The contributions of both quark and meson loops were taken into
account. The latter and the former play a dominant role for the radiative decays of, respectively, the f
0(980) and the a
0(980) meson. 相似文献
17.
V. A. Kovalchuk 《Physics of Atomic Nuclei》2007,70(4):722-731
A method for determining the angle γ and the ratio of the amplitudes A
λ(B
− →
K
*−) and A
λ)B
− → D
*0
K
*−), r
Bλ, for all three vector-meson polarization states by using the decays B
∓ → D
*
K
*∓ is proposed. This method relies on the interference between the decays B
− → D
*0
K
*− and B
− →
K
*−, which arises if D
*0 and
decay to D
0/
π
0 and D
0/
γ, whereupon D
0 and
mesons decay to common final hadron states. The doubly Cabibbo-suppressed modes of D
0-meson decay are chosen here to specify such final states.
Original Russian Text ? V.A. Kovalchuk, 2007, published in Yadernaya Fizika, 2007, Vol. 70, No. 4, pp. 754–763. 相似文献
18.
V. V. Atuchin V. N. Kruchinin A. V. Kalinkin V. Sh. Aliev S. V. Rykhlitski? V. A. Shvets E. V. Spesivtsev 《Optics and Spectroscopy》2009,106(1):72-77
Optical characteristics of the HfO2 − x
N
x
and TiO2 − x
N
x
films obtained by reactive ion beam sputtering have been investigated by spectral ellipsometry. The chemical composition
of the films was determined using X-ray photoelectron spectroscopy. The nitrogen content in the oxynitride films (determined
by the N2/O2 ratio in the gas mixture during synthesis) reached ≈9 at % for TiO2 − x
N
x
and ≈ 6 at % for HfO2 − x
N
x
. It is found that the dispersion relations n(λ) and k(λ) for the TiO2 − x
N
x
films change from those characteristic of titanium dioxide to those typical of titanium nitride with an increase in the nitrogen
content from 0 to ≈9 at %. The optical parameters of the HfO2 − x
N
x
films depend weakly on the nitrogen content in the range 0–6 at %.
Original Russian Text ? V.V. Atuchin, V.N. Kruchinin, A.V. Kalinkin, V.Sh. Aliev, S.V. Rykhlitskiĭ, V.A. Shvets, E.V. Spesivtsev,
2009, published in Optika i Spektroskopiya, 2009, Vol. 106, No. 1, pp. 77–82. 相似文献
19.
J. Ryckebusch W. Van Nespen 《The European Physical Journal A - Hadrons and Nuclei》2004,20(3):435-441
Differential cross-sections for exclusive 16O(e,epp)14C processes are computed within a distorted-wave framework which includes central short-range correlations and intermediate
excitations. The cross-sections are compared to high-resolution data from the MAMI facility at Mainz for a central energy and momentum transfer of
MeV and
MeV, respectively. A fair agreement between the numerical calculations and data is reached when using spectroscopic information extracted from a 15N
C experiment. The comparison between the calculations and the data provides additional evidence that short-range correlations exclusively affect nucleon pairs with a small center-of-mass momentum residing in a relative S state.Received: 3 September 2003, Revised: 2 December 2003, Published online: 18 June 2004PACS:
24.10.-i Nuclear-reaction models and methods - 21.60.-n Nuclear-structure models and methods - 25.30.Fj Inelastic electron scattering to continuum 相似文献
20.
N. I. Kourov V. V. Marchenkov V. G. Pushin A. V. Korolev E. B. Marchenkova H. W. Weber 《Physics of the Solid State》2008,50(11):2127-2132
The effect of atomic disordering and deviation from the Ni2MnGa stoichiometric composition on the low-temperature properties of alloys with magnetically controlled shape memory effect
is studied. The specific features of the magnetic, galvanomagnetic, and electrical properties of alloys with magnetically
controlled shape memory effect are discussed. The specific features of the magnetic, galvanomagnetic, and electrical properties
of alloys Ni50Mn25Ga25, Ni54Mn21Ga25, and Ni50Mn28.5Ga21.5 in the temperature range 2 ≤ T ≤ 80 K under magnetic fields H ≤ 12 MA/m are studied.
Original Russian Text ? N.I. Kourov, V.V. Marchenkov, V.G. Pushin, A.V. Korolev, E.B. Marchenkova, H.W. Weber, 2008, published
in Fizika Tverdogo Tela, 2008, Vol. 50, No. 11, pp. 2037–2042. 相似文献