共查询到20条相似文献,搜索用时 46 毫秒
1.
The weak radiative decay Λ
b
→Λγ is studied in the heavy quark effective theory treatings-quark as heavy. This rare decay is induced by the short distance electromagnetic penguins. Including corrections of the order
of (1/m
Q), we obtain the transition matrix element and the corresponding decay width. The Isgur-Wise function is evaluated in the
largeN
c limit and the branching ratio obtained is 1.48×10−5. 相似文献
2.
K. Tsushima K. Saito A. W. Thomas A. Valcarce 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):626-629
We study the bound-nucleon sigma term and the quark condensate in nuclear matter. In the quark-meson coupling (QMC) model
the nuclear correction to the sigma term is small and negative, i.e., it decelerates the decrease of the quark condensate in nuclear matter. However, the quark condensate in nuclear matter is
controlled primarily by the scalar-isoscalar σ field. Compared to the leading term, it moderates the decrease more than that of the nuclear sigma term alone at densities
around and larger than the normal nuclear-matter density. 相似文献
3.
Lepton-pair production from deep inelastic scatteringin peripheral relativistic heavy ion collisions
U. Dreyer T. Baier K. Hencken D. Trautmann 《The European Physical Journal C - Particles and Fields》2006,45(3):783-795
We calculate the inelastic electron- and muon-pair production in peripheral relativistic heavy ion collisions in the region
of large Q2 of one of the photons. This offers a possibility to study the quark distribution functions in ions in "ultraperipheral heavy
ion collisions". The calculations are compared with those making use of the equivalent photon and the equivalent lepton approximation.
We compare the results for Pb-Pb and Pb-p collisions at RHIC (γ ≈ 100) and LHC (γ ≈ 3000) energies. Furthermore we include nuclear modifications to the parton distribution
functions in our calculations to study their effect on the cross sections. 相似文献
4.
D. Fong J. H. Hamilton A. V. Ramayya J. K. Hwang C. Goodin K. Li J. Kormicki J. O. Rasmussen Y. X. Luo S. C. Wu I. Y. Lee A. V. Daniel G. M. Ter-Akopian G. S. Popeko A. S. Fomichev A. M. Rodin Yu. Ts. Oganessian M. Jandel J. Kliman L. Krupa J. D. Cole M. A. Stoyer R. Donangelo W. C. Ma 《Physics of Atomic Nuclei》2006,69(7):1161-1167
The hot bimodal fission of 252Cf is reexamined with new high-statistics data. We constructed a γ-γ-γ coincidence cube for binary fission and LCP-gated γ-γ matrix for ternary fission. By identifying the secondary fission fragments from their γ-ray transitions, we measured the yields for various fission splits. The normal neutron yield distribution is found to be
Gaussian for Xe-Ru. However, the binary fission split of Ba-Mo is found to exhibit a bimodal neutron distribution with the
“hot mode” corresponding to ≈3.1% of the total yield. In α ternary fission, the first measurements of yields for specific fission splits are presented. The Te-α-Ru and Xe-α-Mo neutron yields fit well with a single mode, but the Ba-α-Zr split shows evidence for an enhanced hot mode with an intensity of ≈13.8% of the normal mode.
The text was submitted by the authors in English. 相似文献
5.
P. Kroll 《The European Physical Journal C - Particles and Fields》2011,71(4):1623
The form factors for the transitions πγ, ηγ, η′γ and η
c
γ are analyzed within the modified perturbative approach in which quark transverse degrees of freedom are retained. The results
for the form factors are compared to experiment in detail. As compared to previous calculations within the same approach only
little modifications of the meson distribution amplitudes are required in general in order to achieve reasonable agreement
with experiment. Only for the πγ form factor a strong contribution from the second Gegenbauer term is found. It also commented on the case of two virtual
photons and on the transition form factors in the time-like region. 相似文献
6.
R. Bijker 《The European Physical Journal A - Hadrons and Nuclei》2007,32(4):403-407
The strange form factors of the nucleon are studied in a two-component model consisting of a three-quark intrinsic structure
surrounded by a meson cloud. A comparison with the available experimental world data from the SAMPLE, PVA4, HAPPEX and G0
Collaborations shows a good overall agreement. It is shown that the strangeness contribution to the electric and magnetic
form factors is of the order of a few percent. In particular, the strange quark contribution to the charge radius is small
〈r
2
s〉E = 0.005 fm^2 and to the magnetic moment it is positive μs = 0.315 μN . 相似文献
7.
We extend our previous investigation about the flavor mixing or the OZI violating process in the light quark systems with the use of the generalized Nambu-Jona-Lasinio model incorporating theU
A
(1) anomaly. The OZI breaking effects newly studied in the meson sector include the and meson decay constants, their couplings with nucleon as well as the masses and the mixing property of the scalar mesons. As for the baryon sector, we reexamine the strangeness content of the proton and the -N sigma term
N
by taking into account the interactions between the constituent quarks. It is found that the short-range spin-spin interaction between the quarks gives anO(10 MeV)-enhancement for the theoretical value of the sigma term. Anomalous quark contents of other octet and decuplet baryons (hyperons) are also examined. It is shown that the axial anomaly induces the anomalous quark contents which are not expected in the naive quark model, while the short-range interaction between the quarks acts to suppress (enhance) the quark contents of the decuplet (octet) baryons. All the results indicate that the following picture holds systematically:m
s
is so large that (i) the strangeness mixing induced by the anomaly is considerably suppressed and that (ii) the naive chiral perturbation does not work in the strange sector even in the tree level of the meson fields (largeN
c
limit). The spin problem of nucleon, which is another subject related to the flavor mixing, is also examined with the use of our effective model.This paper is a modified version of the paper SUNY-NTG-89-49, RYU-THP-89-2 (August 1989) 相似文献
8.
J. F. Gu H. Guo X. G. Li Y. X. Liu F. R. Xu 《The European Physical Journal A - Hadrons and Nuclei》2006,30(2):455-460
Deconfinement phase transition and condensation of Goldstone bosons in neutron star matter are investigated in a chiral hadronic
model (also referred as to the FST model) for the hadronic phase (HP) and in the color-flavor-locked (CFL) quark model for
the deconfined quark phase. It is shown that the hadronic-CFL mixed phase (MP) exists in the center of neutron stars with
a small bag constant, while the CFL quark matter cannot appear in neutron stars when a large bag constant is taken. Color
superconductivity softens the equation of state (EOS) and decreases the maximum mass of neutron stars compared with the unpaired
quark matter. The K0 condensation in the CFL phase has no remarkable contribution to the EOS and properties of neutron star matter. The EOS and
the properties of neutron star matter are sensitive to the bag constant B, the strange quark mass ms and the color superconducting gap Δ. Increasing B and ms or decreasing Δ can stiffen the EOS which results in the larger maximum masses of neutron stars. 相似文献
9.
D. S. Armstrong 《The European Physical Journal A - Hadrons and Nuclei》2007,32(4):451-455
The nucleon's strange electric and magnetic form factors G
E
s and G
M
s can be probed via parity-violating electron scattering. The HAPPEX Collaboration has made new measurements of the parity-violating
asymmetry A
PV in elastic scattering of 3GeV electrons off hydrogen and 4He targets with 〈θlab〉 ≈ 6.0° . For 4He the preliminary result is A
PV = (+ 6.43±0.23(stat)±0.22(syst))×10-6 . For hydrogen the preliminary result is A
PV = (- 1.60±0.12(stat)±0.05(syst))×10-6 . From these values we extract G
s
E = 0.004±0.014±0.013 at 〈Q
2〉 = 0.077 GeV/c^2 , and G
s
E +0.09G
s
M = 0.004±0.011±0.005 at 〈Q
2〉 = 0.109 GeV/c^2 , both consistent with zero, providing stringent new limits on the role of strange quarks in the vector
structure of the nucleon. 相似文献
10.
Ugoccioni R. Giovannini A. Lupia S. 《Zeitschrift fur Physik C Particles and Fields》1994,61(3):453-463
We discuss the relationship of the forward matrix element of the operator $\bar \psi \psi $ , related to the so-called sigma term, to the quark number. We show that in the naive quark model in the canonical formalism these quantities coincide in the limit of small average quarkmomenta. In the QCD parton model defined through light-front quantization this result is preserved at leading perturbative order but it receives radiative corrections. We analyze the theoretical and phenomenological consequences of this result, which provides a bridge between a current algebra quantity, the sigma term, and a deepinelastic quantity, the parton number. 相似文献
11.
C. Castagnoli C. Morello G. Navarra L. Periale P. Vallania J. A. Chinellato M. De Castro Souza A. Turtelli P. Miranda A. Velarde 《Il Nuovo Cimento C》1990,13(2):345-352
Summary We present the results of a search for very high energy γ-rays (E
γ≈100 TeV) from SN 1987A between August 1987 and May 1988. No counting rate excess from the source is observed. The larger
enhancement is seen in January 1988, but is statistically not significant (1.4 s.d.). The derived upper limits to the γ-ray
and proton luminosities of the SN areL
γ≤1.9·1040 erg/s andL
p≤1.2·1042 erg/s.
To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee. 相似文献
12.
A. N. Vodin I. V. Ushakov G. E. Tuller 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(7):1005-1008
It is inferred from the analysis of the experimental data that the reduced probabilities of isovector l-forbidden M1 transitions achieve maximum values in nuclei with a magic core. The minimum values are related to γ transitions in nuclei
belonging to the region of stable deformation with A ≈ 25. Isovector l-forbidden M1 transitions in mirror nuclei are explored. The ratio of the reduced probabilities for proton and neutron transitions shows
the maximum deviation from the theoretical evaluations for the pair of nuclei 41Ca-41Sc consisting of the even-even magic core 40Ca and one nucleon outside the closed 1d2s shell. 相似文献
13.
B. Kämpfer O.P. Pavlenko S. Zschocke 《The European Physical Journal A - Hadrons and Nuclei》2003,17(1):83-87
QCD sum rules predict that the change of the strange quark condensate 〈ˉss〉 in hadron matter at finite baryon density causes a shift of the peak position of the di-electron spectra from φ-meson decays.
Due to the expansion of hadron matter in heavy-ion collisions, the φ peak suffers a smearing governed by the interval of density
in the expanding fireball, which appears as an effective broadening of the di-electron spectrum in the φ region. The emerging
broadening is sensitive to the in-medium change of 〈ˉss〉. This allows to probe directly in-medium modifications of 〈ˉss〉 via di-electron spectra in heavy-ion collisions at SIS energies with HADES.
Received: 22 November 2002 / Accepted: 30 January 2003 / Published online: 29 April 2003 相似文献
14.
On the basis of the experimental data on diffractive processes in πp, pp and pˉp collisions at intermediate, moderately high and high energies, we restore the scattering amplitude related to the t-channel exchange by vacuum quantum numbers by taking account of the diffractive s-channel rescatterings. At intermediate and moderately high energies, the t-channel exchange amplitude turns, with a good accuracy, into an effective pomeron which renders the results of the additive
quark model. At superhigh energies the scattering amplitude provides a Froissart-type behaviour, with an asymptotic universality
of cross sections such as σtot
πp/σtot
pp→ 1 at s→∞. The quark structure of hadrons being taken into account at the level of constituent quarks, the cross sections of pion
and proton (antiproton) in the impact parameter space of quarks, σπ(r
1⊥, r
2⊥; s) and σp(r
1⊥, r
2⊥, r
3⊥; s), are found as functions of s. These cross sections implicate the phenomenon of colour screening: they tend to zero at |r
i⊥−r
k⊥|→ 0. The effective colour screening radius for pion (proton) is found for different s. The predictions for the diffractive cross sections at superhigh energies are presented.
Received: 15 December 1998 相似文献
15.
Frank D. Smith Jr. 《International Journal of Theoretical Physics》1985,24(2):155-174
From a number of qualitative conjectures, the constantsm
e
,c, , and a spin(8) gauge field theory, I derive the following particle masses (quark masses are constituent masses) and force constants: up quark mass=312.7542 MeV; down quark mass=312.7542 MeV; proton mass=938.2626 MeV; neutrino masses (all types)=0; muon mass=104.76 MeV; strange quark mass=523 MeV; charmed quark mass=1989 MeV; tauon mass=1877 MeV; bottom quark mass=5631 MeV; top quark mass=129.5 GeV;W
+ mass=80.87 GeV;W
– mass=80.87 GeV;W
0 mass=99.04 GeV; fine structure constant= 1/137.036082; weak constant times the proton mass squared M
p
2
=0.97×10–5; color constant=0.6286. From the pion mass in addition, I derive the Planck mass (1–1.6)×1019 GeV, so that the gravitational constant times the proton mass squared GM
p
2
(3.6–8.8)×10–39. 相似文献
16.
E. Kolbe K. Langanke F.-K. Thielemann 《The European Physical Journal A - Hadrons and Nuclei》1998,3(4):389-396
We study the influence of a strange axial vector form factor Gs of the nucleon on the neutrino-induced proton and neutron knockout of 16O. In particular, we calculate how much Gs≠0 might affect the recently proposed signal for supernova νμ and ντ neutrinos in the Superkamiokande detector. We discuss whether Superkamiokande might be able to determine the value of Gs in a hypothetical neutrino-beam experiment. Finally we comment on the possible effect Gs≠0 might have on neutrino-nucleus cross sections in the neutrino-driven wind model for the nuclear r-process.
Received: 30 April 1998 / Revised version: 10 August 1998 相似文献
17.
In this paper we study the matrix element of the transverse component of the bilocal vector current in the context of deep inelastic scattering. The BJL limit of high energy amplitudes together with light-front current algebra imply the same parton interpretation for its matrix element as that of the plus component. On the other hand, the transverse component depends explicitly on the gluon field operator in QCD, appears as “twist three” and hence its matrix element has no manifest parton interpretation. In this paper we perform calculations in light-front time-ordering perturbative QCD for a dressed quark target to order αs and demonstrate that the matrix element of the transverse component of the bilocal vector current has the same parton interpretation as that of the plus component. 相似文献
18.
G. Oh C. Eom F. Wang W.-S. Jung H. E. Stanley S. Kim 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,79(1):55-60
We investigate the statistical properties of the cross-correlation
matrix between individual stocks traded in the Korean stock market
using the random matrix theory (RMT) and observe how these affect
the portfolio weights in the Markowitz portfolio theory. We find
that the distribution of the cross-correlation matrix is positively
skewed and changes over time. We find that the eigenvalue
distribution of original cross-correlation matrix deviates from the
eigenvalues predicted by the RMT, and the largest eigenvalue is 52 times larger than the maximum value among the eigenvalues
predicted by the RMT. The b473\beta_{473} coefficient, which reflect
the largest eigenvalue property, is 0.8, while one of the
eigenvalues in the RMT is approximately zero. Notably, we show
that the entropy function E(s)E(\sigma) with the portfolio risk
σ for the original and filtered cross-correlation matrices are
consistent with a power-law function, E(σ) ~
s-g\sigma^{-\gamma}, with the exponent γ ~ 2.92 and those for Asian currency crisis decreases significantly. 相似文献
19.
Néstor Armesto Carlos Pajares Paloma Quiroga-Arias 《The European Physical Journal C - Particles and Fields》2009,61(4):779-784
We study the modification of the multiplicity distributions in MLLA due to the presence of a QCD medium. The medium is introduced
through a multiplicative constant (f
med) in the soft infrared parts of the kernels of the QCD evolution equations. Using the asymptotic ansatz for mean multiplicities
of the quark and gluons, 〈n
G〉=e
γ
y
and 〈n
Q〉=r
−1e
γ
y
, respectively, we study two cases: fixed γ as previously considered in the literature, and fixed α
s
. We find opposite behaviors of the dispersion of the multiplicity distributions with increasing f
med in both cases. For fixed γ the dispersion decreases, while for fixed α
s
it increases. 相似文献
20.
The strange meson production on a proton target in theK
0Σ+ channel is sensitive to nucleon resonance contributions. TheK
0 production on a deuteron target can provide information on the hyperon-nucleon final-state interaction. The experiments γp →K
0Σ+ andγd →
K
0Σ+n have been carried out at the ELSA facility at Bonn. In this paper, we report the preliminary results of both experiments 相似文献