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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.
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
3.
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
4.
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
5.
We have calculated the next-to-leading order cross sections for the inclusive production of D
* mesons in
collisions at HERA in two approaches using massive or massless charm quarks. The usual massive theory for the direct cross section with charm quarks only in the final state was transformed into a massive theory with
subtraction by subtracting the mass divergent and additional finite terms calculated earlier in connection with the process
. This theory approaches the massless theory with increasing transverse momentum. The difference between the massive and the massless approach with
subtraction is studied in detail in those kinematic regions relevant for comparison with experimental data. With these results and including the resolved cross section which is dominated by the part originating from the charm in the photon, we compute the fully inclusive
cross section and compare it with preliminary data from the ZEUS collaboration at HERA. We find on average good agreement.Received: 5 October 2004, Published online: 26 November 2004 相似文献
6.
7.
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
8.
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
9.
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
10.
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
11.
Inclusive cross-sections for gluon jet production are studied numerically in the perturbative QCD pomeron model for pA and central AA collisions at high energies. Two forms for the inclusive cross-sections, with and without emission from the triple pomeron vertex, are compared. The difference was found to reduce to a numerical factor
for momenta below the saturation momentum Q
s. Above Q
s no difference was found at all. For pA collisions the gluon spectrum was found to be
at momenta k below Q
s and
above it. For central AA collisions it was found to be
at momenta k below Q
s and
above it. At large k the spectrum goes like
, flattening with energy. The multiplicities turned out to be proportional to A
0.7 for pA collisions and A for central AA collisions with a good precision. In the latter case they are becoming more peaked at the center with the growth of energy. Their absolute values are high and grow rapidly with energy in accordance with the high value of the BFKL intercept.Received: 12 October 2004, Revised: 22 November 2004, Published online: 21 January 2005 相似文献
12.
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
13.
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
14.
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
15.
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
16.
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
17.
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
18.
V. A. Khoze A. D. Martin M. G. Ryskin 《The European Physical Journal C - Particles and Fields》2004,34(3):327-334
We study the central diffractive production of the (three neutral) Higgs bosons, with a rapidity gap on either side, in an MSSM scenario with CP-violation. We consider the
and
decay for the light H1 boson and the four b-jet final state for the heavy H2 and H3 bosons, and discuss the corresponding backgrounds. A direct indication of the existence of CP-violation can come from the observation of either an azimuthal asymmetry in the angular distribution of the tagged forward protons (for the exclusive
process) or of a
contribution in the azimuthal correlation between the transverse energy flows in the proton fragmentation regions for the process with the diffractive dissociation of both incoming protons (
). We emphasise the advantage of reactions with the rapidity gaps (that is, production by pomeron-pomeron fusion) to probe CP-parity and to determine the quantum numbers of the produced central object.Received: 16 January 2004, Published online: 31 March 2004 相似文献
19.
Di-jet production is studied in collisions of quasi-real photons at e + e- centre-of-mass energies
from 189 to 209 GeV at LEP. The data were collected with the OPAL detector. Jets are reconstructed using an inclusive
-clustering algorithm for all cross-section measurements presented. A cone jet algorithm is used in addition to study the different structure of the jets resulting from either of the algorithms. The inclusive di-jet cross-section is measured as a function of the mean transverse energy
of the two leading jets, and as a function of the estimated fraction of the photon momentum carried by the parton entering the hard sub-process,
, for different regions of
. Angular distributions in di-jet events are measured and used to demonstrate the dominance of quark and gluon initiated processes in different regions of phase space. Furthermore the inclusive di-jet cross-section as a function of
and
is presented, where
is the jet pseudo-rapidity. Different regions of the
-
-space are explored to study and control the influence of an underlying event. The results are compared to next-to-leading order perturbative QCD calculations and to the predictions of the leading order Monte Carlo generator PYTHIA.Received: 20 December 2002, Published online: 17 October 2003 相似文献
20.
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