共查询到20条相似文献,搜索用时 15 毫秒
1.
《The European Physical Journal C - Particles and Fields》2007,49(2):545-558
Ratios of the ψ′ over the J/ψ production cross sections in the dilepton channel for C, Ti and W targets have been measured in 920 GeV proton-nucleus
interactions with the HERA-B detector at the HERA storage ring. The ψ′ and J/ψ states were reconstructed in both the μ+μ- and the e+e- decay modes. The measurements covered the kinematic range -0.35≤xF≤0.1 with transverse momentum pT≤4.5 GeV/c. The angular dependence of the ratio has been used to measure the difference of the ψ′ and J/ψ polarization. All results for the muon and electron decay channels are in good agreement: their ratio, averaged over
all events, is Rψ′(μ)/Rψ′(e)=1.00±0.08±0.04. This result constitutes a new, direct experimental constraint on the double ratio of branching fractions,
(B′(μ)B(e))/(B(μ)B′(e)), of ψ′ and J/ψ in the two channels. The ψ′ to J/ψ production ratio is almost constant in the covered xF range and shows a slow increase with pT. 相似文献
2.
Summary Positron decay in liquid naphthalene and benzene was investigated through measurements of lifetimes and magnetic quenching.
The obtained results when compared with those already known in solid phase suggest that positrons become bound in two different
systems. The first has a lifetime τ3≈1 ns which is unaffected by the melting, while the second (τ4≈3 ns) arises above melting and behaves as a relaxed positronium.
This work was supported by CISM (Centro Interuniversitario di Struttura della Materia) del Ministero della Pubblica Istruzione,
and by GNSM (Gruppo Nazionale di Struttura della Materia) del CNR. 相似文献
3.
Ying-Jia Gao Ce Meng Kuang-Ta Chao 《The European Physical Journal A - Hadrons and Nuclei》2006,28(3):361-367
Belle has observed surprisingly copious production of ψ(3770) in the B meson decay B → ψ(3770)K, whose rate is comparable to that of B → ψ(3686)K. We study this puzzling process in the QCD factorization approach with the effect of the S-D mixing considered. We find that the soft scattering effects in the spectator interactions play an essential role. With a
proper parametrization for the higher-twist soft end-point singularities associated with kaon, and with the S-D mixing angle θ = - 12°, the calculated decay rates can be close to the data. Implications of these soft spectator effects to other charmonium production
in B exclusive decays are also emphasized. 相似文献
4.
A. V. Ivanov 《Optics and Spectroscopy》2011,111(5):786-797
For a semi-infinite wide-gap crystal, expressions for the rates of one- and two-photon transitions caused by the action of
linearly polarized light are obtained in the basis set of model surface and bulk functions. The transition probability is
shown to significantly depend on the angle between the light polarization vector and the normal to the surface Ψ. At a light
intensity of 10 MW/cm2, the probability of one-photon transitions between surface states is in the range 1024−1026 s−1 cm−2 (ψ = π/2 and ψ = 0, respectively). It is shown that, in the case wherein the light polarization vector is perpendicular to the surface,
the rates of allowed n-photon transitions (n = 1, 2) decrease more slowly with increasing n than in the case in which the polarization vector lies in the plane of the surface. 相似文献
5.
Yu. P. Piryatinski A. Yu. Vakhnin A. B. Verbitskii A. K. Kadashchuk 《Physics of the Solid State》2011,53(11):2333-2338
The steady-state and time-resolved fluorescence spectra of n-pentyl-n′-cyanobiphenyl and a related composite material with gold nanoparticles in the liquid crystalline and solid states have been
investigated. The introduction of gold nanoparticles into the liquid crystal leads to a noticeable quenching of fluorescence
in the emission region of the predimer and excimer states of cyanobiphenyl. In the solid phase, a quenching of free excitons
and a short-wavelength shift of fluorescence bands have been observed. 相似文献
6.
K. A. Bronnikov E. N. Chudaeva G. N. Shikin 《International Journal of Theoretical Physics》2009,48(8):2214-2221
We consider Bianchi type I cosmologies with unidirectional magnetic and electric fields, assuming as well the existence of
a global spinor field ψ(t) as one more possible source of gravity able to suppress the inevitable anisotropy accompanying a nonzero vector field. The
field ψ(t) is assumed to contain a nonlinearity in the form s
n
, where
and n=const (the special case n=1 corresponds to a Dirac massive field). The structure of the stress-energy tensor of the spinor field is shown to be the
same as that of a perfect fluid with the equation of state p=w
ρ where w=n−1. The Dirac massive spinor field and nonlinear fields with n<4/3 are shown to be able to provide isotropization. A numerical estimate shows that this isotropization could occur early
enough to be compatible with observations. 相似文献
7.
V. V. Anisovich L. G. Dakhno M. A. Matveev V. A. Nikonov A. V. Sarantsev 《Physics of Atomic Nuclei》2007,70(2):364-381
Earlier by the authors (Yad. Fiz. 70, 68 (2007)), the bƃ states were treated in the framework of the spectral integral equation, together with simultaneous calculations of radiative
decays of the considered bottomonia. In the present paper, such a study is carried out for the charmonium
states. We reconstruct the interaction in the c-c sector on the basis of the data for the charmonium levels with J
PC = 0−+, 1−−, 0++, 1++, 2++, 1+− and radiative transitions ψ(2S) → γχ
c0(1P), γχ
c1(1P), γχ
c2(1P), γχ
c(1S) and χ
c0(1P), χ
c1(1P), χ
c2(1P) → γJ/ψ. The c-c levels and their wave functions are calculated for the radial excitations with n ≤ 6. Also, we determine the c-c component of the photon wave function using the e
+
e
−-annihilation data: e
+
e
− → J/ψ(3097), ψ(3686), ψ(3770), ψ(4040), ψ(4160), ψ(4415) and perform the calculations of the partial widths of the two-photon decays for the n = 1 states η
c0(1S), χ
c0(1P), χ
c2(1P) → γγ and n = 2 states η
c0(2S) → γγ, χ
c0(2P) → γγ. We discuss the status of the recently observed c-c states X(3872) and Y(3941): according to our results, the X(3872) can be either χ
c1(2P) or η
c2(1D), while Y(3941) is χ
c2(2P).
The text was submitted by the authors in English. 相似文献
8.
WeiGuo Li 《中国科学G辑(英文版)》2008,51(6):567-576
Recent experimental results from Beijing Spectroscopy (BES) are reviewed, including the hadron spectroscopy from J/ψ decays, and a number of new states are found or confirmed, including σ, κ, X(1835), ωφ threshold enhancement in J/ψ→γωφ, a broad resonance in J/ψ→K
+
K
−
π
0, decay studies of ψ(2S) and χ
CJ
, as well as the results of ψ(3770) non-D
decays. The current status of BEPCII/BESIII, the major upgrade of BEPC/BESII, is also reported.
Supported by the National Natural Science Foundation of China (Grant No. 10491300) 相似文献
9.
G. M. Gurevich A. L. Erzinkyan V. P. Parfenova 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(4):520-525
Low-temperature spin orientation of radioactive nuclei is a nuclear spectroscopic method that allows us to obtain experimental
data on nuclei and extranuclear fields. We present the results from measuring the angular anisotropy of α radiation emitted
by transuranium nuclei of 253,254Es, 255Fm, 241,243Am, along with that of γ radiation from 250Bk nuclei oriented in an iron matrix at temperatures of 10–300 mK. The data allow us to establish the relation between the
mechanism of α decay and nuclear deformation and to compare them to the theoretical data. We also measure the energy of magnetic
hyperfine splitting for the investigated nuclei, and find the magnetic hyperfine field value for Es in Fe to be |B
hf
| = 396(32) T. The nuclear magnetic moment for 254Es was determined, and its value was |μ(254Es)| = 4.35(41)μ
N
. 相似文献
10.
We obtain bounds for the spectrum and for the total width of the spectral gaps for Jacobi matrices on ℓ2(ℤ) of the form (Hψ)
n
=a
n−1
ψ
n−1
+b
nψ
n
+a
nψ
n+1
, where a
n=a
n+q
and b
n=b
n+q
are periodic sequences of real numbers. The results are based on a study of the quasimomentum k(z) corresponding to H. We consider k(z) as a conformal mapping in the complex plane. We obtain the trace identities which connect integrals of the Lyapunov exponent
over the gaps with the normalised traces of powers of H.
Received: 17 April 2002 / Accepted: 1 October 2002 Published online: 13 January 2003
Communicated by B. Simon 相似文献
11.
Solid-state nuclear magnetic resonance (NMR) spectroscopy is utilized to study the molecular behavior of 1,10-dibromodecane
and 1,11-dibromoundecane in their urea inclusion compounds. The guest dynamics and conformational order are explored by 13C cross polarization magic-angle spinning (CP/MAS) and 1H MAS NMR spectroscopy which confirm an all-trans conformation of the guest chains. Dynamic 2H NMR experiments are carried out on two guest molecules selectively deuterated at both end groups. A quantitative analysis
of the experimental data, obtained from variable-temperature line shape, spin–spin and spin–lattice relaxation measurements,
shows that both guest molecules undergo similar motions within the investigated temperature range between 100 and 298 K. The
combination of nondegenerate 6-site (or 3-site) rotational jumps and small-angle overall chain wobbling provides an appropriate
motional model for the guest motions in these compounds. It is found that the populations of the jump sites exhibit a characteristic
temperature dependence, although a discontinuity is missing at the solid–solid phase transition. The same holds for the guest
motions which also remain unaffected by the change of the urea lattice structure. Rather, a discontinuity of the guest dynamics
at about 30 and 10 degrees above the corresponding solid–solid phase transition is observed for 1,10-dibromodecane and 1,11-dibromoundecane
in urea, respectively. Likewise, there is no clear evidence for an odd–even effect due to the change of the guest chain length
on the molecular properties of the present inclusion compounds. As a general result, it is concluded that the intermolecular
interactions in the present materials are stronger than in n-alkane/urea inclusion compounds.
Authors' address: Klaus Müller, Institut für Physikalische Chemie, Universit?t Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart,
Germany 相似文献
12.
Summary In previous studies the average number of neighbors (n
avrg) of an atom in the surface phase was found to increase by about (5÷20)% between 0 K and the melting temperature for all solid
chemical elements in the periodic table. This increment makes the solid surface “geometrically impossible” to exist at the
melting temperature. The latter results in the collapse of crystal structure, beginning with the formation of liquid in the
surface layers. Ratio of critical and melting temperature is also discussed. 相似文献
13.
An attempt is made to study the interaction Hamiltonian,H
int =Gψ
2(x)U(φ(x)) in the Bethe-Salpeter framework for the confined states of theψ particles interactingvia the exchange of theU field, whereU(φ) = cos (gφ). An approximate solution of the eigenvalue problem is obtained in the instantaneous approximation by projecting the Wick-rotated
Bethe-Salpeter equation onto the surface of a four-dimensional sphere and employing Hecke’s theorem in the weak-binding limit.
We find that the spectrum of energies for the confined states,E =2m+B (B is the binding energy), is characterized byE ∼n
6, wheren is the principal quantum number. 相似文献
14.
N. Kawamura K. Nagamine T. Matsuzaki K. Ishida S.N. Nakamura S. Sakamoto M. Iwasaki M. Tanase M. Kato K. Kurosawa T. Hashimoto H. Sugai K. Kudo N. Takeda G.H. Eaton 《Hyperfine Interactions》1999,118(1-4):213-215
This article reports the accumulation effect of the 3He originating from tritium β decay; 3He created in solid remains in it, while one in liquid diffuses and goes out to the vapor gas. We observed this effect through
the neutron detection from muon catalyzed fusion phenomenon (μCF), and gave it qualitative understanding, by which the muon
transfer rate from (dμ) and (tμ) to helium was derived.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
16.
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
17.
The kinetics of recombination of electrons and acceptor-bound holes in AlGaAs-GaAs heterostructure obey a single-exponential
decay in the liquid phase of 2D electrons, whereas localization gives rise to a broad spectrum of recombination rates, especially
in the magnetic freeze-out regime. This results in a power-law dependence I(t)∝(τ/t)α in the tail of the recombination kinetics, with the universal exponent α=(1−ν)−1 at ν<1 for all the samples examined experimentally in this work.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 118–122 (25 January 1996)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
18.
Alexander N. Tarasov 《Central European Journal of Physics》2011,9(4):1057-1076
Within a generalized non-relativistic Fermi-liquid approach we have found general analytical formulae for phase-transition
temperatures T
c,1(n, H) and T
c,2(n, H) (which are nonlinear functions of density, n, and linear of magnetic field, H) for phase transitions in spatially uniform, dense, pure neutron matter from normal to superfluid states with spin-triplet
p-wave pairing (similar to anisotropic superfluid phases 3He - A1 and 3He - A2) in steady and homogeneous sufficiently strong magnetic field (but |μ
n
|H ≪ E
c
< ɛ
F
(n), where μ
n
is the magnetic dipole moment of a neutron, E
c
is the cutoff energy and ɛ
F
(n)is the Fermi energy in neutron matter). General formulae for T
c,1,2(n,H) are valid for arbitrary parameterization of the effective Skyrme forces in neutron matter. We have used for definiteness
the so-called SLy2, Gs and RATP parameterizations of the Skyrme forces with different exponents in their power dependence
on density n (at sub- and supranuclear densities) from the interval 0.7 n
0 ≲ n < n
c
(Skyrme)< 2 n
0, where n
0 =0.17 fm−3 is the nuclear density and n
c
(Skyrme)is the the critical density of the ferromagnetic instability in superfluid neutron matter. These phase transitions might
exist in the liquid outer core of magnetized neutron stars. 相似文献
19.
Yu-Ming Wang Hao Zou Zheng-Tao Wei Xue-Qian Li Cai-Dian Lü 《The European Physical Journal C - Particles and Fields》2008,54(1):107-121
Within the standard model, we investigate the semi-leptonic weak decays of J/ψ. The various form factors of J/ψ making the
transition to a single charmed meson (D(*)
(d,s)) are studied in the framework of QCD sum rules. These form factors fully determine the rates of the weak semi-leptonic decays
of J/ψ and provide valuable information on non-perturbative QCD effects. Our results indicate that the decay rate of the semi-leptonic
weak decay mode J/ψ→D(*)-
s+e++νe is at the order of 10-10.
PACS 13.20.Gd; 13.25.Gv; 11.55.Hx 相似文献
20.
In this paper we give a complete characterization of Morita equivalent star products on symplectic manifolds in terms of
their characteristic classes: two star products ⋆ and ⋆' on (M,ω) are Morita equivalent if and only if there exists a symplectomorphism ψ\colon M
M such that the relative class t(⋆, ψ⋆(⋆')) is 2 π i-integral. For star products on cotangent bundles, we show that this integrality condition is related to Dirac's
quantization condition for magnetic charges.
Received: 19 July 2001 / Accepted: 23 January 2002 相似文献