共查询到20条相似文献,搜索用时 31 毫秒
1.
2.
The nuclear system at the limit of excitation energy and angular momentum is here studied in the case of the superdeformed nucleus 143Eu using
-spectroscopy techniques. The data are based on a EUROBALL experiment using the reaction 37Cl + 110Pd
Eu + 4n. The influence of thermal energy on superdeformed configurations is investigated through the analysis of the quasi-continuum spectra formed by E2 transitions among states of excited rotational bands with energy extending up to 4-5 MeV above the yrast line. In particular, the effective lifetimes of the discrete rotational bands forming ridge structures in
-
coincidence matrices is measured by a Doppler Shift Attenuation Method. The deduced quadrupole deformation of
10 eb indicates that the nucleus maintains its collectivity with increasing excitation energy, supporting the superdeformed character of the excited nuclear rotation. The obtained number of superdeformed discrete bands forming the ridge structures is found in good agreement with microscopic cranked shell model calculations including the decay-out process into the lower deformation minimum. In addition, the nuclear properties at higher excitation energies are investigated through the E1
-decay of the giant dipole resonance (GDR). It is found that the intensity of the superdeformed yrast and excited bands increases by a factor of approximately 1.6 when a coincidence with a high-energy
-ray is required, showing the importance of the E1 cooling in the feeding mechanism of the superdeformed states.Received: 2 December 2002, Published online: 2 March 2004PACS:
21.10.Tg Lifetimes - 21.10.Re Collective levels - 23.20.Lv
transitions and level energies - 27.60. + j
相似文献
3.
Variation-after-projection (VAP) calculations in conjunction with the Hartree- Bogoliubov (HB) ansatz have been carried out for A = 68-88, N = Z nuclei. In this framework, the yrast spectra with
, B(E2) transition probabilities and deformation parameter (
) have been obtained. A pairing interaction for like particles as well as protons and neutrons has been included in the model for a two-body interaction.Received: 28 April 2003, Revised: 20 March 2004, Published online: 14 September 2004PACS:
21.10.-k Properties of nuclei; nuclear energy levels - 21.60.-n Nuclear structure models and methods - 27.50. + e
相似文献
4.
The production rates and substructure of jets have been studied in charged current deep inelastic e
+
p scattering for Q
2 > 200 GeV2 with the ZEUS detector at HERA using an integrated luminosity of 110.5 pb-1. Inclusive jet cross sections are presented for jets with transverse energies
GeV and pseudorapidities in the range
. Dijet cross sections are presented for events with a jet having
GeV and a second jet having
GeV. Measurements of the mean subjet multiplicity,
, of the inclusive jet sample are presented. Predictions based on parton-shower Monte Carlo models and next-to-leading-order QCD calculations are compared to the measurements. The value of
, determined from
at
for jets with
GeV, is
. The mean subjet multiplicity as a function of Q
2 is found to be consistent with that measured in NC DIS.Received: 5 June 2003, Published online: 10 October 2003 相似文献
5.
We extend a recent chiral approach to nuclear matter by including the most general (momentum-independent) NN-contact interaction. Iterating this two-parameter contact vertex with itself and with one-pion exchange the emerging energy per particle exhausts all terms possible up to and including fourth order in the small momentum expansion. Two (isospin-dependent) cut-offs
are introduced to regularize the (linear) divergences of some three-loop in-medium diagrams. The equation of state of pure neutron matter,
, can be reproduced very well up to quite high neutron densities of
by adjusting the strength of a repulsive nn-contact interaction. Binding and saturation of isospin-symmetric nuclear matter is a generic feature of our perturbative calculation. Fixing the maximum binding energy per particle to
MeV we find that any possible equilibrium density
lies below
. The additional constraint from the neutron matter equation of state leads however to a somewhat too low saturation density of
. We also investigate the effects of the NN-contact interaction on the complex single-particle potential U(p,k
f
) + i W(p,k
f
). We find that the effective nucleon mass at the Fermi surface is bounded from below by
. This property keeps the critical temperature of the liquid-gas phase transition at somewhat too high values
MeV. The downward bending of the asymmetry energy A(k
f
) above nuclear-matter saturation density is a generic feature of theapproximation to fourth order. We furthermore investigate the effects of the NN-contact interaction on the
-term in the nuclear energy density functional
. Altogether, there is within this complete fourth-order calculation no magic set of adjustable short-range parameters with which one could reproduce simultaneously and accurately all semi-empirical properties of nuclear matter. In particular, the conditions for a good neutron matter equation of state and for good single-particle properties are mutually exclusive.Received: 28 October 2003, Revised: 9 December 2003, Published online: 23 July 2004PACS:
12.38.Bx Perturbative calculations - 21.65. + f Nuclear matter - 24.10.Cn Many-body theory - 31.15.Ew Density-functional theory 相似文献
6.
A new evaluation of the hadronic vacuum polarization contribution to the muon magnetic moment is presented. We take into account the reanalysis of the low-energy e
+
e
-annihilation cross section into hadrons by the CMD-2 Collaboration. The agreement between e
+
e
-and
spectral functions in the
channel is found to be much improved. Nevertheless, significant discrepancies remain in the center-of-mass energy range between 0.85 and
, so that we refrain from averaging the two data sets. The values found for the lowest-order hadronic vacuum polarization contributions are
where the errors have been separated according to their sources: experimental, missing radiative corrections in e
+
e
-data, and isospin breaking. The corresponding Standard Model predictions for the muon magnetic anomaly read
where the errors account for the hadronic, light-by-light (LBL) scattering and electroweak contributions. The deviations from the measurement at BNL are found to be
(1.9
) and
(0.7
) for the e
+
e
-- and
-based estimates, respectively, where the second error is from the LBL contribution and the third one from the BNL measurement.Received: 7 September 2003, Published online: 30 October 2003 相似文献
7.
The decays of 152Tb (T
1/2 = 17.5 h) and 152Gd excited states have been investigated by the analysis of
-rays and
-coincidences measured with the use of high-resolution HPGe detectors. The source of 152Tb was prepared by chromatographic isolation followed by electromagnetic separation from a tantalum target irradiated by an internal proton beam of the LNP JINR phasotron. New and more precise data on the
-transitions and excited states of 152Gd are reported. Using previously published data on internal-conversion electrons many transition multipolarities are suggested, some of them with E0 admixture. The
ratio was found for a number of low-lying levels, for most of the levels their spins, parities, and
are given. The excited levels of 152Gd were deduced from the analysis of
-coincidences. The experimental level energies and reduced transition probabilities are compared with the calculations by phenomenological formulae as well as in the frameworks of theoretical models.Received: 21 May 2002, Revised: 26 May 2003, Published online: 18 November 2003PACS:
29.30.Kv X- and gamma-ray spectroscopy - 23.20.-g Electromagnetic transitions - 21.10.-k Properties of nuclei; nuclear energy levels - 21.60.-n Nuclear structure models and methodsJ. Adam: On leave from Nuclear Physics Institute of ASCR, e, Czech Republic.V.S. Pronskikh: On leave from Saint Petersburg State Institute of Technology, Russia 相似文献
8.
We review CP-violating effects in
jet and
4 jet decays, assuming the presence of CP-violating effective
and
couplings. Longitudinal beam polarization is included in the studies. We propose a direct search for such CP-violating couplings by using various CP-odd observables. The data of a future linear collider running at the Z-resonance in the so-called GigaZ option should give significant information on the couplings. Finally we show that stringent bounds on the mass of excited b quarks can be derived if appropriate couplings are of a size characteristic of a strong interaction.Received: 21 August 2003, Published online: 20 November 2003 相似文献
9.
J. Cao Z. Xiong J. M. Yang 《The European Physical Journal C - Particles and Fields》2004,32(2):245-252
In the supersymmetric seesaw model, large flavor mixings of sleptons induce the lepton flavor violating (LFV) interactions
(
), which give rise to various LFV processes. In this work we examine the LFV decays
. Subject to the constraints from the existing neutrino oscillation data and the experimental bounds on the decays
, these LFV Z-decays are found to be sizable, and among them the largest-rate channel
can occur with a branching ratio of 10-8 and may be accessible at the LHC or GigaZ experiment.Received: 1 September 2003, Published online: 20 November 2003 相似文献
10.
We explore CP violation in
decay processes in the presence of the anomalous right-handed
and
couplings. The complex anomalous top coupling can be a source of new CP violation and may lead to a deviation of the observed weak phase in
decays, which accounts for the present disagreement of the observed
between
and
decays. Direct CP violation is also predicted.
Received: 27 November 2002, Revised: 28 March 2003, Published online: 2 June 2003 相似文献
11.
A. Bartl H. Fraas T. Kernreiter O. Kittel 《The European Physical Journal C - Particles and Fields》2004,33(3):433-442
We define a CP-sensitive asymmetry in the sfermion decays
, based on triple product correlations between the momenta of the outgoing fermions. We study this asymmetry in the MSSM with complex parameters. We show that the asymmetry is sensitive to the phases of the parameters and M1. The leading contribution stems from the decay chain
, for which we obtain analytic formulae for the amplitude squared. The asymmetry can go up to
for
, and up to
for
. We also estimate the rates necessary to measure the asymmetry.Received: 2 July 2003, Revised: 7 November 2003, Published online: 13 February 2004 相似文献
12.
The T = 1 admixture into the T = 0 member of a recently discovered
isospin-doublet in 54Co is obtained from the measured electromagnetic E2/M1 multipole mixing ratio,
of the
transition. Combining these data with shell model calculations for strong isovector M1 and isoscalar E2 electromagnetic matrix elements one obtains a value for the T = 1 admixture into the T = 0, 4 + state of
. The corresponding mixing matrix element in the 4 + doublet is
keV.Received: 31 October 2002, Published online: 9 March 2004PACS:
21.10.Hw Spin, parity, and isobaric spin - 21.60.Cs Shell model - 23.20.Gq Multipole mixing ratios 相似文献
13.
Cross sections for e
+
p charged current deep inelastic scattering at a centre-of-mass energy of
have been determined with an integrated luminosity of
collected with the ZEUS detector at HERA. The differential cross sections
,
and
for
are presented. In addition,
has been measured in the kinematic range
and . The predictions of the Standard Model agree well with the measured cross sections. The mass of the W boson propagator is determined to be
from a fit to
. The chiral structure of the Standard Model is also investigated in terms of the (1-y)2 dependence of the double-differential cross section. The structure-function
has been extracted by combining the measurements presented here with previous ZEUS results from e
-
p scattering, extending the measurement obtained in a neutrino-nucleus scattering experiment to a significantly higher Q
2 region.Received: 17 July 2003, Published online: 12 November 2003
a supported by the Natural Sciences and Engineering Research Council
of Canada (NSERC)
b supported by the German
Federal Ministry for Education and Research (BMBF), under contract numbers HZ1GUA 2,
HZ1GUB 0, HZ1PDA 5, HZ1VFA 5
c supported by the
MINERVA Gesellschaft für Forschung GmbH, the Israel Science Foundation, the U.S.-Israel
Binational Science Foundation and the Benozyio Center for High Energy Physics
d supported by
the German-Israeli Foundation and the Israel Science Foundation
e supported
by the Italian National Institute for Nuclear Physics (INFN)
f supported
by the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) and its grants
for Scientific Research
g supported by the
Korean Ministry of Education and Korea Science and Engineering Foundation
h supported
by the Netherlands Foundation for Research on Matter (FOM)
i supported by the
Polish State Committee for Scientific Research, grant no. 620/E-77/SPUB-M/DESY/P-03/DZ 247/2000-2002
j partially
supported by the German Federal Ministry for Education and Research (BMBF)
k supported by
the Fund for Fundamental Research of Russian Ministry for Science and Education and by
the German Federal Ministry for Education and Research (BMBF)
l supported by the
Spanish Ministry of Education and Science through funds provided by CICYT
m supported by
the Particle Physics and Astronomy Research Council, UK
n supported by the
US Department of Energy
o supported by the US
National Science Foundation
p supported by the
Polish State Committee for Scientific Research, grant no. 112/E-356/SPUB-M/DESY/P-03/DZ 301/2000-2002, 2 P03B 13922
q supported by the Polish State Committee for Scientific Research, grant no. 115/E-343/SPUB-M/DESY/P-03/DZ 121/2001-2002, 2 P03B 07022 相似文献
14.
A simple coalescence model based on the same diagrammatic approach of antimatter production in hadronic collisions as used previously for antideuterons is used here for the hadroproduction of mass-3 antinuclei. It is shown that the model is able to reproduce the existing experimental data on the
and
production without any additional parameter.Received: 28 January 2003, Revised: 10 July 2003, Published online: 18 November 2003PACS:
24.10.-i Nuclear reaction models and methods 相似文献
15.
The quark mass function
in QCD is revisited, using a gluon propagator in the form 1/(k
2 + m
g
2) plus
, where the second (IR) term gives linear confinement for m
g
= 0 in the instantaneous limit, being another scale. To find
we propose a new (differential) form of the Dyson-Schwinger equation (DSE) for
, based on an infinitesimal subtractive renormalization via a differential operator which lowers the degree of divergence in integration on the RHS, by two units. This warrants
in the integrand since its k-dependence is no longer sensitive to the principal term (p-k)2 in the quark propagator. The simplified DSE (which incorporates the Ward-Takahashi (WT) identity in the Landau gauge) is satisfied for large p
2 by
=
, except for Log factors. The limit p
2 = 0 determines
. A third limit, p
2 = -m
0
2, defines the dynamical mass m
0 via
. After two checks (
MeV and
=
), for
with
MeV, the T-dependent DSE is used in the real time formalism to determine the critical index
analytically, with the IR term partly serving as the H-field. We find
MeV and check the vanishing of
and
at T
c.Received: 31 August 2004, Published online: 11 January 2005PACS:
24.85. + p, 12.38.Lg, 12.38.AwA.N. Mitra: Permanent address: 244 Tagore Park, Delhi-110009, India. 相似文献
16.
We investigate the violation of time reversal invariance in the decay of the free neutron in the framework of the minimal supersymmetric standard model (MSSM). The coefficient of the triple product of the neutron spin and the momenta of electron and neutrino, the so-called D parameter, is computed at one-loop order including all diagrams. We find that D is mainly sensitive to the trilinear A coupling in the squark sector and to the phase of the coefficient
which mixes the two Higgs superfields. The maximal MSSM contribution using parameters still allowed by experiment is however at
, while QED final state interactions give a value of
. Explicit expressions for all relevant diagrams are given in an appendix.Received: 3 March 2003, Revised: 16 May 2003, Published online: 3 July 2003 相似文献
17.
During the last decade, as the experimental and computing means and techniques have rapidly evolved, the experimental investigation of the f7/2-shell nuclei has gained renewed interest. TheN = Z nuclei studied with the GASP array range from 44Ti to 52Fe. The results extended the knowledge of their structure up to high spins and excitation energies, above band terminations, where the competition with the charged-particles emission was initially thought to obscure the possibility of gamma-ray spectroscopy investigation. The paper highlights some of the most outstanding properties of these nuclei such as the nuclear rotation and backbending effects, band termination states, yrast traps, non-natural parity bands, competition between T = 0 and T = 1 pn pairing modes.Received: 30 October 2002, Published online: 16 March 2004PACS:
21.10.-k Properties of nuclei; nuclear energy levels - 21.60.Cs Shell model - 23.20.Lv
transitions and level energies - 27.40. + z
C.A. Ur: On leave from NIPNE Bucharest, Romania 相似文献
18.
F. P. Heßberger S. Hofmann D. Ackermann P. Cagarda R. -D. Herzberg I. Kojouharov P. Kuusiniemi M. Leino R. Mann 《The European Physical Journal A - Hadrons and Nuclei》2004,22(3):417-427
The isotopes 251No and 253No were produced in nuclear reactions 206Pb(48Ca,3n)251No and 207Pb (48Ca,2n)253No. Radioactive decay of these isotopes and their daughter products has been investigated by means of
- and
-
- spectroscopy. An isomeric state 251m
No, having a half-life of
s and decaying by emission of
particles of
keV was identified. The measured decay data allowed for the construction of partial level schemes for 251No, 247,249Fm and 243,245Cf and an extrapolation of energy systematics of single particle levels of N = 145, 147 and 149 isotones with even Z towards higher atomic numbers up to Z = 102.PACS:
23.60. + e
decay - 27.90. + b
- 21.10.-k Properties of nuclei; nuclear energy levels 相似文献
19.
20.
D. Bećirević Ph. Boucaud V. Giménez V. Lubicz M. Papinutto 《The European Physical Journal C - Particles and Fields》2004,37(3):315-321
We report our results for the bag parameter B
K
obtained from the quenched simulations on the lattice with Wilson fermions for three values of the lattice spacing. We implemented the method by which no subtraction of the mixing with other four-fermion
operators is needed. Our final result, in terms of the renormalization group invariant bag parameter, is
.Received: 9 July 2004, Revised: 27 July 2004, Published online: 21 September 2004 相似文献