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1.
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
2.
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
3.
Granular films of Co-cluster/C60 mixtures have been prepared by the co-deposition of well defined Co clusters (mean diameter
4.5 nm) and C60 fullerenes onto a cold (
35 K) substrate. Films having a Co cluster volume fraction
show a resistivity
, typical for tunneling with a Coulomb barrier. The tunneling magnetoresistance (TMR) has a value of TMR (
% for
and is decreasing by almost one order of magnitude going to
. We explain this unusual decrease of the TMR with increasing
as caused by electron-doping of the C60 fullerenes due to the known charge transfer process occurring between transition metal surface and C60. Increasing electron doping may lead to an increasing probability for spin-flip processes within the tunneling barrier, resulting in a decrease of the TMR.Received: 17 March 2004, Published online: 3 August 2004PACS:
75.47.-m Magnetotransport phenomena; materials for magnetotransport - 73.40.Gk Tunneling - 73.40.Rw Metal-insulator-metal structures 相似文献
4.
Upper limits on the cross-section of the pair-production process
, assuming 100
branching fraction to hadrons, are derived from a new search for the
hadrons final state, independently of the hadronic flavour of the decay products. This study, combined with previously published searches for the neutral Higgs bosons h0 and A0, is used to constrain the Type II Two Higgs Doublet Model (2HDM(II)) with no CP violation in the Higgs sector and no additional non-Standard Model particles besides the five Higgs bosons. The analysis combines LEP1 and LEP2 data collected with the OPAL detector up to the highest available centre-of-mass energies. The searches are sensitive to the
and
decay modes of the Higgs bosons. A benchmark scan of the 2HDM(II) parameter space is performed. Large regions of the 2HDM(II) parameter space explored are excluded at the 95% CL in the (
and
planes, using both direct neutral Higgs boson searches and indirect limits derived from Standard Model high precision measurements. The region
GeV and
GeV is excluded at 95 % CL, independently of
and for selected values of
which are representative of a complete
-scan.Received: 28 July 2004, Revised: 4 January 2005, Published online: 3 March 2005 相似文献
5.
It is shown that the fluctuations of the jamming coverage upon Random Sequential Adsorption (RSA) (
), decay with the lattice size according to the power-law
, with
,where D is the dimension of the substrate and
is the fractal dimension of the set of sites belonging to the substrate where the RSA process actually takes place. This result is in excellent agreement with the figure recently reported by Vandewalle et al. [Eur. Phys. J. B 14, 407 (2000)], namely
for the RSA of needles with D = 2 and
, that gives
. Furthermore, our prediction is in excellent agreement with different previous numerical results. The derived relationships are also confirmed by means of extensive numerical simulations applied to the RSA of dimers on both stochastic and deterministic fractal substrates.Received: 17 October 2003, Published online: 8 December 2003PACS:
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion - 02.50.-r Probability theory, stochastic processes, and statistics 相似文献
6.
The results of first-principles theoretical study of the structural, electronic and optical properties of beryllium monochalcogenides BeTe, BeSe and BeS, performed using the full potential linearized augmented plane wave (FP-LAPW) method are presented. The calculated structural parameters and band gaps compare very well with previous theoretical results. The trends of the band gap pressure coefficients and volume deformation potentials for these II-VI compounds are investigated. The linear pressure coefficients for the
X and
band gaps increase with decrease in anion atomic weight. The dependence of the direct and indirect band gaps on the relative change of lattice constant are found to follow almost the same type of trends in each of these compounds. The volume deformation potential (
) for the direct (
) and indirect (
) gaps are positive, but negative for the indirect (
) gap. Furthermore,
, for
transitions decreases with increase in anion atomic number whereas
, increases. The optical properties have also been calculated. From the reflectivity spectra, the compounds will be useful for optical applications. The variation of the band gaps with respect to the application of pressure and the origin of some of the peaks in the optical spectra are discussed in terms the calculated electronic structure.Received: 26 September 2003, Published online: 18 June 2004PACS:
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.) - 71.15.Mb Density functional theory, local density approximation, gradient and other corrections - 71.20.Nr Semiconductor compounds 相似文献
7.
Multijet production rates in neutral current deep inelastic scattering have been measured in the range of exchanged boson
virtualities
. The data were taken at the ep collider HERA with centre-of-mass energy
using the ZEUS detector and correspond to an integrated luminosity of
. Jets were identified in the Breit frame using the kT cluster algorithm in the longitudinally invariant inclusive mode. Measurements of differential dijet and trijet cross sections
are presented as functions of jet transverse energy (
), pseudorapidity (
) and Q2 with
and
. Next-to-leading-order QCD calculations describe the data well. The value of the strong coupling constant
, determined from the ratio of the trijet to dijet cross sections, is
.
Received: 1 April 2005, Revised: 28 June 2005, Published online: 30 August 2005 相似文献
8.
The production of
, D0, D + , Ds + and
charm hadrons and their antiparticles in e p scattering at HERA was measured with the ZEUS detector using an integrated luminosity of
. The measurement has been performed in the photoproduction regime with the exchanged-photon virtuality
and for photon-proton centre-of-mass energies in the range
. The charm hadrons were reconstructed in the range of transverse momentum
and pseudorapidity
. The production cross sections were used to determine the ratio of neutral and charged D-meson production rates,
, the strangeness-suppression factor,
, and the fraction of charged D mesons produced in a vector state,
. The measured
and
values agree with those obtained in deep inelastic scattering and in e + e- annihilations. The measured
value is smaller than, but consistent with, the previous measurements. The fractions of c quarks hadronising as a particular charm hadron,
, were derived in the given kinematic range. The measured open-charm fragmentation fractions are consistent with previous
results, although the measured
is smaller and
is larger than those obtained in e + e- annihilations. These results generally support the hypothesis that fragmentation proceeds independently of the hard sub-process.
Received: 12 August 2005, Revised: 8 September 2005, Published online: 6 October 2005 相似文献
9.
We present the combined results on electron-pair production in 158 GeV/n Pb-Au (
= 17.2 GeV) collisions taken at the CERN SPS in 1995 and 1996, and give a detailed account of the data analysis. The enhancement over the reference of neutral meson decays amounts to a factor of 2.31
for semi-central collisions (28
) when yields are integrated over m > 200 MeV/c2 in invariant mass. The measured yield, its stronger-than-linear scaling with
, and the dominance of low pair pt strongly suggest an interpretation as thermal radiation from pion annihilation in the hadronic fireball. The shape of the excess centring at
500 MeV/c2, however, cannot be described without strong medium modifications of the
meson. The results are put into perspective by comparison to predictions from Brown-Rho scaling governed by chiral symmetry restoration, and from the spectral-function many-body treatment in which the approach to the phase boundary is less explicit.Received: 2 March 2005, Published online: 8 June 2005 相似文献
10.
The anomalous weak dipole moments of the
lepton are measured in a data sample collected by ALEPH from 1990 to 1995 corresponding to an integrated luminosity of 155 pb-1. Tau leptons produced in the reaction
at energies close to the
mass are studied using their semileptonic decays to
,
,
or
. The real and imaginary components of both the anomalous weak magnetic dipole moment and the CP-violating anomalous weak electric dipole moment,
,
,
and
, are measured simultaneously by means of a likelihood fit built from the full differential cross section. No evidence of new physics is found. The following bounds are obtained (95% CL):
,
,
, and
.Received: 25 September 2002, Published online: 29 August 2003 相似文献
11.
J. P. Marques F. Parente P. Indelicato 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(3):457-465
In this paper, we used the multiconfiguration Dirac-Fock method to compute with high precision the influence of the hyperfine
interaction on the [Ar]
P0 level lifetime in Zn-like ions for stable and some quasi-stable isotopes of nonzero nuclear spin between Z=30 and Z=92. The
influence of this interaction on the
[Ar]
P
P0 separation energy is also calculated for the same ions. 相似文献
12.
In the CP-violating minimal supersymmetric standard model (MSSM), for certain values of the CP-violating phases associated to the universal trilinear couplings (At, Ab) and the gluino mass
, e.g.,
or
, for
GeV and
-5, the lightest Higgs boson mass (
) is
GeV. This mass interval is still allowed by results of standard LEP Higgs searches because of a strongly suppressed H1ZZ coupling. However, in the same region of parameter space in which these two conditions occur, the
coupling is enhanced because the two mentioned sets of couplings satisfy a sum rule. In this paper we probe such a light Higgs scenario at the Large Hadron Collider (LHC) by studying
associate production, leading to a
signal. We show that the latter is readily accessible at the CERN hadron collider, upon the application of suitable selection cuts against the standard model (SM) backgrounds. Our parton level Monte Carlo (MC) analysis yields
-45 signal events, completely free of SM background, for
- 30 fb-1 of accumulated luminosity, after taking into account the overall efficiency for tagging four b-jets.Received: 21 February 2005, Published online: 6 July 2005 相似文献
13.
Noiret I. Schamps J. Danede F. Odou G. Lamiot J. 《The European Physical Journal B - Condensed Matter and Complex Systems》2004,41(1):23-30
Structural properties of two RbCdCl3 samples grown either from the melt or from aqueous solution are studied via X-ray diffraction over a closed temperature cycle between 20
C and 300
C. During cooling step (300
C), the crystal grown from the melt undergoes a phase transition at 110
C that drives it from the cubic structure into a tetragonal structure that still persists at 20
C. It undergoes exactly the reverse phase transition at the same temperature during the heating (
C) step that immediately follows. The other crystal grows from aqueous solution at 20
C in an orthorhombic structure (i.e. not tetragonal as that of the crystal grown from the melt and cooled down to this temperature). During the heating (
C) step, it undergoes a direct orthorhombic-cubic phase transition at 240
C (without passing through the tetragonal phase) whereas, during subsequent cooling (300
C), it does not exhibit the corresponding reverse phase transition but rather exhibits exactly the same cubic-tetragonal phase transition at 110
C as the crystal grown from the melt. However, for both crystals, this tetragonal phase observed at room temperature is unstable and slowly converts into an orthorhombic phase over the course of time. Complementary Differential Scanning Calorimetry (D.S.C.) and Thermo Gravimetric Analysis (T.G.A.) measurements have been carried out over the range (
)
C in order to interpret diffraction experiments.Received: 19 May 2004, Published online: 30 September 2004PACS:
61.10.Nz X-ray diffraction - 64.70.Kb Solid-solid transitions - 65.40.Ba Heat capacity 相似文献
14.
H. Buesching 《The European Physical Journal C - Particles and Fields》2005,43(1-4):303-310
Transverse momentum (
) spectra measured by the PHENIX experiment at RHIC in Au + Au, d + Au and pp collisions at
and in Au + Au collisions at
are presented. A suppression of the yield of high
hadrons in central Au + Au collisions by a factor 4-5 at
is found relative to the pp reference scaled by the nuclear overlap function
. In contrast, direct photons are not suppressed in central Au + Au collisions and no suppression of high
particles can be seen in d + Au collisions. This leads to the conclusion that the dense medium formed in central Au + Au
collisions is responsible for the suppression.
Arrival of the final proofs: 30 June 2005
PACS:
25.75.Dw 相似文献
15.
J. Voigt E. Kentzinger U. Rücker W. Schweika D. Wermeille W. Schmidt Th. Brückel 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(4):441-451
We have investigated the structural and magnetic properties of
Er|Tb
multilayers by different scattering methods. Diffuse X-ray scattering under
grazing incidence reveals the interface structure in
Er|Tb
bilayers and trilayers, indicating vertically correlated roughness between the Er and Tb interfaces. The magnetic properties
of
ErnEr|TbnTb
superlattices have been studied as a function of the superlattice composition (indices denote the number of atomic layers).
Coupled ferromagnetic structures exist in all investigated samples. The phase transition temperature varies with the Tb layer
thickness.
Modulated magnetic order is short range for all samples beside the
Er20|Tb5
superlattice, the sample with the smallest Tb layer thickness.
We observe dipolar antiferromagnetic coupling between single ferromagnetic Tb layers in all samples, with the onset of this
ordering depending on the Tb layer thickness. Due to competing interactions, exchange coupling is limited to the interface
near region. Therefore long range modulated magnetic order is observed in the
Er20|Tb5
superlattice only, where the interface regions overlap.
The distinct differences to the magnetic structure of an Er0.8Tb0.2
alloy film are explained by a highly anisotropic arrangement of neighbouring
atoms due to the correlated roughness. 相似文献
16.
A presence of a Meissner-Ochsenfeld effect in a gas of spin 1/2 fermions with an interaction
, where
is a volume of a region
in real space which is taken by thesystem and
with
,
satisfying Fermi anticommutation relations, is investigated. The effect proves to be weaker than in BCS by a factor 3/4 at T = 0, implying a greater penetration depth
of external magnetic field. V
4 is nonzero only within a thin layer of 1-fermion energies around the chemical potential .Received: 14 June 2004, Published online: 12 October 2004PACS:
74.20.-z Theories and models of superconducting state - 74.20.Fg BCS theory and its development 相似文献
17.
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
18.
A. Mischke 《The European Physical Journal C - Particles and Fields》2005,43(1-4):311-316
In this paper, preliminary results are presented on high
inclusive neutral pion measurements in d-Au collisions at
GeV in the pseudo-rapidity range
. Photons from the decay
are detected in the Barrel Electromagnetic Calorimeter of the STAR experiment at RHIC. The analysis of this first BEMC hadron
measurement is described in detail. The results are compared to earlier RHIC findings. Furthermore, the obtained
invariant differential cross sections show good agreement with next-to-leading order (NLO) perturbative QCD calculations.
Arrival of the final proofs: 4 July 2005
PACS:
25.75.-q 相似文献
19.
Surface structures in the Te/Ni(111) system are revealed by using reflection high-energy electron diffraction combined with X-ray and ultraviolet photoelectron spectroscopies. At a 0.33 mono-layer (ML)-Te/Ni(111) surface, a reversible structural phase transition is observed with a transition temperature Tc of 380
C. The diffraction pattern from the low temperature phase is accompanied by streaks. The high and low temperature phases are characterized by
and
rectangle, respectively. The mechanism of the phase transition is explained by the order-disorder transition with a rumpled chain model. Both 0.51 ML- and 0.44 ML-Te/Ni(111) surfaces exhibit the complex diffraction patterns accompanied by diffuse streaks. These surface structures are characterized by the
rectangle and
, respectively. All diffuse streaks obtained at the above surfaces are consistently interpreted in the view of the ill-ordered arrangements of the well-ordered
linear chains. It is shown that the
linear structure is the key in the Te/Ni(111) system.Received: 1 December 2003, Published online: 20 April 2004PACS:
61.14.Hg Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED) - 68.65.-k Low-dimensional, mesoscopic, and nanoscale systems: structure and nonelectronic properties - 64.60.Cn Order-disorder transformations; statistical mechanics of model systems 相似文献
20.
D. Bensimon R. Zeyher 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(2):141-150
Phase fluctuations of a d-wave superconducting order parameter are
theoretically studied in the context of high-Tc cuprates. We consider
an extended t-J model describing electrons in a layer which also contains
long-range Coulomb interactions. The constraint of having at most singly
occupied sites is enforced by an additional Hubbard term. The Heisenberg interaction is decoupled by a d-wave order parameter
in the particle-particle channel. Assuming first that the equilibrium state has long-range phase order, the effective action
is derived perturbatively for small fluctuations within a path integral formalism, in the presence of the
Coulomb and Hubbard interaction terms. In a second step, a more general
derivation of
is performed in terms of a gradient
expansion which only assumes that the gradients of the order parameter are
small whereas the value of the phase may be large. We show that in the
phase-only approximation the resulting
reduces in
leading order in the field gradients to the perturbative one which thus allows to treat also the case without long-range phase
order or vortices. Our result generalizes previous
expressions for
to the case of interacting electrons,
is explicitly gauge invariant, and avoids problematic singular
gauge transformations. 相似文献