共查询到20条相似文献,搜索用时 93 毫秒
1.
Huiying Song Xinyu Zhang Bo-Qiang Ma 《The European Physical Journal C - Particles and Fields》2011,71(2):1542
The light flavor antiquark distributions of the nucleon sea are calculated in the effective chiral quark model and compared
with experimental results. The contributions of the flavor-symmetric sea-quark distributions and the nuclear EMC effect are
taken into account to obtain the ratio of Drell–Yan cross sections σ
pD/2σ
pp, which can match well with the results measured in the FermiLab E866/NuSea experiment. The calculated results also match
the [`(d)](x)-[`(u)](x)\bar{d}(x)-\bar{u}(x) measured in different experiments, but unmatch the behavior of [`(d)](x)/[`(u)](x)\bar{d}(x)/\bar{u}(x) derived indirectly from the measurable quantity σ
pD/2σ
pp by the FermiLab E866/NuSea Collaboration at large x. We suggest to measure again [`(d)](x)/[`(u)](x)\bar{d}(x)/\bar{u}(x) at large x from precision experiments with careful treatment of the experimental data. We also propose an alternative procedure for
experimental data treatment. 相似文献
2.
In this article, we study the mass spectrum of the baryon-antibaryon bound states p
[`(p)] \bar{{p}} , S \Sigma
[`(S)] \bar{{\Sigma}} , X \Xi
[`(X)] \bar{{\Xi}} , L \Lambda
[`(L)] \bar{{\Lambda}} , p
[`(N)] \bar{{N}}(1440) , S \Sigma
[`(S)] \bar{{\Sigma}}(1660) , X \Xi
[`(X)]¢ \bar{{\Xi}}^{{\prime}}_{} and L \Lambda
[`(L)] \bar{{\Lambda}}(1600) with the Bethe-Salpeter equation. The numerical results indicate that the p
[`(p)] \bar{{p}} , S \Sigma
[`(S)] \bar{{\Sigma}} , X \Xi
[`(X)] \bar{{\Xi}} , p
[`(N)] \bar{{N}}(1440) , S \Sigma
[`(S)] \bar{{\Sigma}}(1660) , X \Xi
[`(X)]¢ \bar{{\Xi}}^{{\prime}}_{} bound states maybe exist, and the new resonances X(1835) and X(2370) can be tentatively identified as the p
[`(p)] \bar{{p}} and p
[`(N)] \bar{{N}}(1440) (or N(1400)[`(p)] \bar{{p}} bound states, respectively, with some gluon constituents, and the new resonance X(2120) may be a pseudoscalar glueball. On the other hand, the Regge trajectory favors identifying the X(1835) , X(2120) and X(2370) as the excited h¢ \eta^{{\prime}}_{}(958) mesons with the radial quantum numbers n = 3 , 4 and 5, respectively. 相似文献
3.
An intense circularly polarised g \gamma -beam interacts with a cooled antiproton beam in a storage ring. Due to spin-dependent absorption cross-sections for the
reaction g+[`(p)]?p-+[`(n)]\ensuremath \gamma+\overline{p}\rightarrow\pi^{-}+\overline{n} a built-up of polarisation of the stored antiprotons takes place. Figures of merit around 0.1 can be reached in principle
over a wide range of antiproton energies. In this process polarised antineutrons with polarisation
P[`(n)] \succ 70%\ensuremath P_{\overline{n}} \succ 70\% emerge. The method is presented for the case of a 300MeV/c cooled antiproton beam. 相似文献
4.
5.
S. G. Yuan K. W. Wei J. He H. S. Xu B. S. Zou 《The European Physical Journal A - Hadrons and Nuclei》2012,48(5):61
The low-lying energy spectra of five quark systems uudc[`(c)]uudc\bar c (I = 1/2, S = 0) and udsc[`(c)]udsc\bar c (I = 0, S = 1) are investigated with three kinds of schematic interaction: the chromomagnetic interaction, the flavor-spin-dependent
interaction and the instanton-induced interaction. In all the three models, the lowest five-quark state (uudc[`(c)]uudc\bar c or udsc[`(c)]udsc\bar c) has an orbital angular momentum L = 0 and the spin-parity J
P
= 1/2−; the mass of the lowest udsc[`(c)]udsc\bar c state is heavier than the lowest uudc[`(c)]uudc\bar c state. 相似文献
6.
7.
Zhi-Gang Wang Zhi-Cheng Liu Xiao-Hong Zhang 《The European Physical Journal C - Particles and Fields》2009,64(3):373-386
In this article, we assume that there exist scalar D*[`(D)]*{D}^{\ast}{\bar {D}}^{\ast}, Ds*[`(D)]s*{D}_{s}^{\ast}{\bar{D}}_{s}^{\ast}, B*[`(B)]*{B}^{\ast}{\bar {B}}^{\ast} and Bs*[`(B)]s*{B}_{s}^{\ast}{\bar{B}}_{s}^{\ast} molecular states, and study their masses using the QCD sum rules. The numerical results indicate that the masses are about
(250–500) MeV above the corresponding D
*–[`(D)]*{\bar{D}}^{\ast}, D
s
*–[`(D)]s*{\bar {D}}_{s}^{\ast}, B
*–[`(B)]*{\bar{B}}^{\ast} and B
s
*–[`(B)]s*{\bar {B}}_{s}^{\ast} thresholds, the Y(4140) is unlikely a scalar Ds*[`(D)]s*{D}_{s}^{\ast}{\bar{D}}_{s}^{\ast} molecular state. The scalar D*[`(D)]*D^{\ast}{\bar{D}}^{\ast}, Ds*[`(D)]s*D_{s}^{\ast}{\bar{D}}_{s}^{\ast}, B*[`(B)]*B^{\ast}{\bar{B}}^{\ast} and Bs*[`(B)]s*B_{s}^{\ast}{\bar{B}}_{s}^{\ast} molecular states maybe not exist, while the scalar D¢*[`(D)]¢*{D'}^{\ast}{\bar{D}}^{\prime\ast}, Ds¢*[`(D)]s¢*{D}_{s}^{\prime\ast}{\bar{D}}_{s}^{\prime\ast}, B¢*[`(B)]¢*{B}^{\prime\ast}{\bar{B}}^{\prime\ast} and Bs¢*[`(B)]s¢*{B}_{s}^{\prime\ast}{\bar{B}}_{s}^{\prime\ast} molecular states maybe exist. 相似文献
8.
Su Houng Lee Shigehiro Yasui 《The European Physical Journal C - Particles and Fields》2009,64(2):283-295
Based on the color–spin interaction in diquarks, we argue why some multiquark configurations could be stable against strong
decay when heavy quarks are included. After showing the stability of previously discussed states we identify new possible
stable states. These are the T0cb(ud[`(c)][`(b)])T^{0}_{cb}(ud\bar{c}\bar{b}) tetraquark, the
\varTheta bs(udus[`(b)])\varTheta _{bs}(udus\bar{b}) pentaquark and the H
c
(udusuc) dibaryon, and so forth. 相似文献
9.
The polarizations of Λ and
[`\varLambda]{\bar{\varLambda}} are thought to retain memories of the spins of their parent s quarks and [`(s)]{\bar{s}} antiquarks, and are readily measurable via the angular distributions of their daughter protons and antiprotons. Correlations between the spins of Λ and
[`\varLambda]{\bar{\varLambda}} produced at low relative momenta may therefore be used to probe the spin states of s [`(s)]s {\bar{s}} pairs produced during hadronization. We consider the possibilities that they are produced in a 3P0 state, as might result from fluctuations in the magnitude of á[`(s)] s ?\langle {\bar{s}} s \rangle, a 1S0 state, as might result from chiral fluctuations, or a 3S1 or other spin state, as might result from production by a quark–antiquark or gluon pair. We provide templates for the p [`(p)]p {\bar{p}} angular correlations that would be expected in each of these cases, and discuss how they might be used to distinguish s [`(s)]s {\bar{s}} production mechanisms in pp and heavy-ion collisions. 相似文献
10.
J. Haidenbauer G. Krein U. -G. Meißner L. Tolos 《The European Physical Journal A - Hadrons and Nuclei》2011,47(2):18
A model of the DN interaction is presented which is developed in close analogy to the meson-exchange [`(K)] \bar{{K}}
N potential of the Jülich group utilizing SU(4) symmetry constraints. The main ingredients of the interaction are provided by vector meson (r \rho , w \omega exchange and higher-order box diagrams involving D
*
N , D
D \Delta , and D
*
D \Delta intermediate states. The coupling of DN to the p \pi
Lc \Lambda_{c}^{} and p \pi
Sc \Sigma_{c}^{} channels is taken into account. The interaction model generates the Lc \Lambda_{c}^{}(2595) -resonance dynamically as a DN quasi-bound state. Results for DN total and differential cross sections are presented and compared with predictions of two interaction models that are based
on the leading-order Weinberg-Tomozawa term. Some features of the Lc \Lambda_{c}^{}(2595) -resonance are discussed and the role of the near-by p \pi
Sc \Sigma_{c}^{} threshold is emphasized. Selected predictions of the orginal [`(K)] \bar{{K}}
N model are reported too. Specifically, it is pointed out that the model generates two poles in the partial wave corresponding
to the L \Lambda(1405) -resonance. 相似文献
11.
12.
13.
C. S. Fischer T. Goecke R. Williams 《The European Physical Journal A - Hadrons and Nuclei》2011,47(2):28
Using the Dyson-Schwinger and Bethe-Salpeter equations, we calculate the hadronic light-by-light scattering contribution to
the anomalous magnetic moment of the muon am\ensuremath a_\mu , using a phenomenological model for the gluon and quark-gluon interaction. We find am=(84 ±13)×10-11\ensuremath a_\mu=(84 \pm 13)\times 10^{-11} for meson exchange, and am = (107 ±2 ±46)×10-11\ensuremath a_\mu = (107 \pm 2 \pm 46)\times 10^{-11} for the quark loop. The former is commensurate with past calculations; the latter much larger due to dressing effects. This
leads to a revised estimate of am=116 591 865.0(96.6)×10-11\ensuremath a_\mu=116 591 865.0(96.6)\times 10^{-11} , reducing the difference between theory and experiment to ≃ 1.9s \sigma . 相似文献
14.
R. N. Kyutt 《Technical Physics》2011,56(5):668-675
Three-wave diffraction of X-rays is measured using the Renninger scheme for a series of GaN epitaxial layers of various thicknesses
and degrees of structural perfection. In each 30°-angular interval of azimuthal rotation, all ten three-wave peaks determined
by the geometry of diffraction with the 0001 first forbidden reflection and CuK
α radiation are observed. The φ- and θ-scanned diffraction curves are measured for each three-wave combination. The angular
FWHM of the diffraction peaks formed in experiments and its relation with the parameters of the two-wave diffraction pattern
and the dislocation structure of the layers are analyzed. It is shown that the φ-scan peaks are less sensitive to the degree
of structural perfection than the γ-mode peaks. The strongest dependence on the dislocation density for the latter peaks is
observed for the (1[`1]00)/([`1]101)(1\bar 100)/(\bar 1101) and (3[`2][`1]0)/([`3]211)(3\bar 2\bar 10)/(\bar 3211) three-wave combinations with a pure Laue component of secondary radiation, while the (01[`1]3)/(0[`1]1[`2])(01\bar 13)/(0\bar 11\bar 2) combination with a large Bragg component exhibits the weakest dependence. Splitting of three-wave Renninger peaks associated
with the coarse-block structure of some of the layers with rotations of the blocks about the normal to the surface is detected.
The total integrated intensity of all three-wave combinations is determined and their ratios are in qualitative agreement
with the theory. 相似文献
15.
M. S. Veshchunov 《Journal of Engineering Thermophysics》2011,20(3):260-271
A new approach to the diffusion-limited reaction rate theory is developed on the base of a similar approach to consideration
of Brownian coagulation, recently proposed by the author. The traditional diffusion approach to calculation of the reaction
rate is critically analyzed. In particular, it is shown that the traditional approach is applicable only to the special case
of reactions with a large reaction radius, [`(r)]A << RAB << [`(r)]B\bar r_A \ll R_{AB} \ll \bar r_B (where [`(r)]A\bar r_A, [`(r)]B\bar r_B are the mean interparticle distances), and becomes inappropriate to calculation of the reaction rate in the case of a relatively
small reaction radius, RAB << [`(r)]AR_{AB} \ll \bar r_A, [`(r)]B\bar r_B. In the latter, most general case particles collisions occurmainly in the kinetic regime (rather than in the diffusion one)
characterized by a homogeneous (at random) spatial distribution of particles. Homogenization of particles distribution occurs
owing to particles diffusion mixing on the length scale of the mean interparticle distance with the characteristic diffusion
time being small in comparison with the characteristic reaction time. The calculated reaction rate for a small reaction radius
in 3D formally (and casually) coincides with the expression derived in the traditional approach for reactions with a large
reaction radius, however, notably deviates at large times from the traditional result in the plane (2D) geometry. 相似文献
16.
E.?Ruchowska W.?A.?P?óciennik H.?Mach K.?Gulda B.?Fogelberg H.?Gausemel L.?M.?Fraile W.?Kurcewicz K.?Mezilev M.?Sanchez-Vega 《The European Physical Journal A - Hadrons and Nuclei》2010,45(1):1-10
Lifetime measurements of excited states in 149Nd have been performed using the advanced time-delayed b \beta
g \gamma
g \gamma(t) method. Half-lives of 14 excited states in 149Nd have been determined for the first time or measured with higher precision. Twelve new g \gamma -lines and 5 new levels have been introduced into the decay scheme of 149Pr based on results of the g \gamma
g \gamma coincidence measurements. Reduced transition probabilities have been determined for 40 g \gamma -transitions in 149Nd . Configuration assignments for 6 rotational bands in 149Nd are proposed. Enhanced E1 transitions indicate that the ground-state band and the band built on the 332.9keV level constitute a pair of the Kp = 5/2±\ensuremath K^{\pi} = 5/2^{\pm} parity doublet bands. Potential energy surfaces on the (b2,b3)\ensuremath (\beta_{2},\beta_{3}) -plane have been calculated for the lowest single quasi-particle configurations in 149Nd using the Strutinski method and the axially deformed Woods-Saxon potential. The predicted occurrence of the octupole-deformed
K = 5/2 configuration is in agreement with experiment. Unexpectedly low |D0|\ensuremath \vert D_0\vert values obtained for the Kp = 5/2±\ensuremath K^{\pi} = 5/2^{\pm} parity doublet bands may result from cancellation between the proton and neutron shell correction contributions to |D0|\ensuremath \vert D_0\vert . 相似文献
17.
Percolation theory is extensively studied in statistical physics and mathematics with applications in diverse fields. However,
the research is focused on systems with only one type of links, connectivity links. We review a recently developed mathematical
framework for analyzing percolation properties of realistic scenarios of networks having links of two types, connectivity
and dependency links. This formalism was applied to study Erdős-Rényi (ER) networks that include also dependency links. For
an ER network with average degree [`(k)]\bar{k} that is composed of dependency clusters of size s, the fraction of nodes that belong to the giant component, P
∞, is given by P¥=ps-1[1-exp(-[`(k)]pP¥) ]sP_{\infty}=p^{s-1}[1-\exp{(-\bar{k}pP_{\infty})} ]^{s} where 1−p is the initial fraction of randomly removed nodes. Here, we apply the formalism to the study of random-regular (RR) networks
and find a formula for the size of the giant component in the percolation process: P
∞=p
s−1(1−r
k
)
s
where r is the solution of r=p
s
(r
k−1−1)(1−r
k
)+1, and k is the degree of the nodes. These general results coincide, for s=1, with the known equations for percolation in ER and RR networks respectively without dependency links. In contrast to s=1, where the percolation transition is second order, for s>1 it is of first order. Comparing the percolation behavior of ER and RR networks we find a remarkable difference regarding
their resilience. We show, analytically and numerically, that in ER networks with low connectivity degree or large dependency
clusters, removal of even a finite number (zero fraction) of the infinite network nodes will trigger a cascade of failures
that fragments the whole network. Specifically, for any given s there exists a critical degree value, [`(k)]min\bar{k}_{\min}, such that an ER network with [`(k)] £ [`(k)]min\bar{k}\leq \bar{k}_{\min} is unstable and collapse when removing even a single node. This result is in contrast to RR networks where such cascades
and full fragmentation can be triggered only by removal of a finite fraction of nodes in the network. 相似文献
18.
Zhi Yang Xing-Gang Wu Li-Cheng Deng Jia-Wei Zhang Gu Chen 《The European Physical Journal C - Particles and Fields》2011,71(3):1563
In Deng et al. (Eur. Phys. J. C 70:113, 2010), we have dealt with the production of the two color-singlet S-wave (c[`(b)])(c\bar{b})-quarkonium states Bc(|(c[`(b)])1[1S0]?)B_{c}(|(c\bar {b})_{\mathbf{1}}[^{1}S_{0}]\rangle) and B*c(|(c[`(b)])1[3S1]?)B^{*}_{c}(|(c\bar{b})_{\mathbf{1}}[^{3}S_{1}]\rangle) through the Z
0 boson decays. As an important sequential work, we make a further discussion on the production of the more complicated P-wave excited (c[`(b)])(c\bar{b})-quarkonium states, i.e. |(c[`(b)])1[1P1]?|(c\bar{b})_{\mathbf{1}}[^{1}P_{1}]\rangle and |(c[`(b)])1[3PJ]?|(c\bar{b})_{\mathbf{1}}[^{3}P_{J}]\rangle (with J=(1,2,3)). More over, we also calculate the channel with the two color-octet quarkonium states |(c[`(b)])8[1S0]g?|(c\bar{b})_{\mathbf{8}}[^{1}S_{0}]g\rangle and |(c[`(b)])8[3S1]g?|(c\bar{b})_{\mathbf{8}}[^{3}S_{1}]g\rangle, whose contributions to the decay width maybe at the same order of magnitude as that of the color-singlet P-wave states according to the naive nonrelativistic quantum chromodynamics scaling rules. The P-wave states shall provide sizable contributions to the B
c
production, whose decay width is about 20% of the total decay width
\varGamma Z0? Bc\varGamma _{Z^{0}\to B_{c}}. After summing up all the mentioned (c[`(b)])(c\bar {b})-quarkonium states’ contributions, we obtain
\varGamma Z0? Bc=235.9+352.8-122.0\varGamma _{Z^{0}\to B_{c}}=235.9^{+352.8}_{-122.0} KeV, where the errors are caused by the main sources of uncertainty. 相似文献
19.
The structure of the low-temperature triclinic phase of the (NH4)3WO3F3 crystal has been determined and the structure of the cubic phase of this crystal has been refined from data of an X-ray diffraction
experiment performed for a powder sample. The profile and structural parameters have been refined according to the procedure
implemented in the DDM program. The results obtained have been discussed with invoking the group-theoretical analysis of the
complete order parameter condensate, which takes into account the critical and noncritical atomic orderings and allows one
to interpret the obtained experimental data. It has been found that the symmetry transformation in the crystal can be schematically
represented in the following form: Fm[`3]m(Z = 4) ? P[`1](Z = 1) ? P[`1](Z = 6)Fm\bar 3m(Z = 4) \to P\bar 1(Z = 1) \to P\bar 1(Z = 6). This transformation is accompanied by the complete ordering of WO3F3 polyhedra and the displacement of NH4 ions. 相似文献
20.
F.?Huang A.?Sibirtsev J.?Haidenbauer S.?Krewald U.?-G.?Mei?ner 《The European Physical Journal A - Hadrons and Nuclei》2010,44(1):81-92
A global analysis of the world data on differential cross-sections and polarization asymmetries of backward pion-nucleon scattering
for invariant collision energies above 3GeV is performed in a Regge model. Including the Na\ensuremath N_{\alpha} , Ng\ensuremath N_{\gamma} , Dd\ensuremath \Delta_{\delta} and Db\ensuremath \Delta_{\beta} trajectories, we reproduce both angular distributions and polarization data for small values of the Mandelstam variable u , in contrast to previous analyses. The model amplitude is used to obtain evidence for baryon resonances with mass below
3GeV. Our analysis suggests a G39\ensuremath G_{39} -resonance with a mass of 2.83GeV as member of the Db\ensuremath \Delta_{\beta} -trajectory from the corresponding Chew-Frautschi plot. 相似文献