共查询到20条相似文献,搜索用时 31 毫秒
1.
E. Accomando A. Denner C. Meier 《The European Physical Journal C - Particles and Fields》2006,47(1):125-146
We have calculated the electroweak
corrections to the processes
,
, and
at the LHC, with l=e,μ and
. The virtual corrections are evaluated in leading-pole approximation, whereas the real corrections are taken into account
exactly. These corrections are implemented into a Monte Carlo generator which includes both phase-space slicing and subtraction
to deal with soft and collinear singularities. We present numerical results for total cross sections as well as for experimentally
interesting distributions. Applying typical LHC cuts, the electroweak corrections are of the order of -5% for the total cross
sections and exceed -20% for observables dominated by high center-of-mass energies of the partonic processes. 相似文献
2.
First measurements of
mesons production properties and their spin alignment in
charged current (CC) and neutral current (NC) interactions are presented. The analysis of the full data sample of the NOMAD
experiment is performed in different kinematic regions. For
and
mesons produced in
CC interactions and decaying into
we have found the following yields per event:
and
respectively, while for the
and
mesons produced in
interactions the corresponding yields per event are:
and
. The results obtained for the
parameter,
and
for
and
produced in
CC interactions, are compared to theoretical predictions tuned on LEP measurements in
annihilation at the
pole. For
mesons produced in
interactions the measured
parameter is
.
PACS 13.15.+g, 13.60.Le, 13.87.Fh, 13.88.+e, 14.40.Ev 相似文献
3.
R.A. Diaz R. Martinez C.E. Sandoval 《The European Physical Journal C - Particles and Fields》2006,46(2):403-405
We find some constraints on the flavor changing vertices of the two Higgs doublet model, from the
measurement. Although bounds from this observable have already been considered, this paper takes into account the role of
a new operator not included previously, as well as the vertices
,
and
. Using the Cheng–Sher parametrization, we find that for a relatively light charged Higgs boson (200–300 GeV), we obtain
, while the parameter
could have values up to about 50. In addition, we use bounds for
and
obtained from
at next to leading order, and study the case where the only vanishing vertex factors are the ones involving quarks from the
first family. We obtain that
is not sensitive to the change of the parameter
, while
. 相似文献
4.
Tau lepton decays with open strangeness in the final state are measured with the OPAL detector at LEP to determine the strange hadronic spectral function of the
lepton. The decays
,
and
with final states consisting of neutral and charged kaons and pions have been studied. The invariant mass distributions of
of these final states have been experimentally determined. Monte Carlo simulations have been used for the remaining
and for the strange final states including
mesons. The reconstructed strange final states, corrected for resolution effects and detection efficiencies, yield the strange spectral function of the
lepton. The moments of the spectral function and the ratio of strange to non-strange moments, which are important input parameters for theoretical analyses, are determined. Furthermore, the branching fractions
and
have been measured.Received: 18 February 2004, Revised: 30 April 2004, Published online: 15 June 2004 相似文献
5.
Measurements of the time-dependent CP-asymmetry in the decay
and its charge conjugate by the BELLE and BABAR collaborations currently yield
and
, characterizing the direct and mixing-induced CP-asymmetries, respectively. We study the implication of these measurements on the CKM phenomenology taking into account the available information in the quark mixing sector. Our analysis leads to the results that the ratio |P
c
/T
c
| involving the QCD-penguin and tree amplitudes and the related strong phase difference
in the
decays are quite substantial. Using the isospin symmetry to constrain |P
c
/T
c
| and
, where
parameterizes the penguin-induced contribution, we present a fit of the current data including the measurements of
and
. Our best-fits yield
,
,
,
, and
. At 68% C.L., the ranges are
,
,
,
and
. Currently en vogue dynamical approaches to estimate the hadronic matrix elements in
decays do not provide a good fit of the current data.Received: 5 April 2004, Published online: 14 July 2004A.Ya. Parkhomenko: On leave of absence from Department of Theoretical Physics, Yaroslavl State University, Sovietskaya 14, 150000 Yaroslavl, Russia. 相似文献
6.
Resonant active-to-active (
), as well as active-to-sterile (
) neutrino (
) oscillations can take place during the core bounce of a supernova collapse. Besides, over this phase, weak magnetism increases the antineutrino (
) mean free path, and thus its luminosity. Because the oscillation feeds mass-energy into the target
species, the large mass-squared difference between the species (
) implies a huge amount of energy to be given off as gravitational waves (
erg s-1), due to anisotropic but coherent
flow over the oscillation length. This asymmetric
-flux is driven by both the spin-magnetic and the universal spin-rotation coupling. The novel contribution of this paper stems from (1) the new computation of the anisotropy parameter
-0.01, and (2) the use of the tight constraints from neutrino experiments as SNO and KamLAND, and the cosmic probe WMAP, to compute the gravitational-wave emission during neutrino oscillations in supernovae core collapse and bounce. We show that the mass of the sterile neutrino
that can be resonantly produced during the flavor conversions makes it a good candidate for dark matter as suggested by Fuller et al. , Phys. Rev. D 68, 103002 (2003). The new spacetime strain thus estimated is still several orders of magnitude larger than those from
diffusion (convection and cooling) or quadrupole moments of neutron star matter. This new feature turns these bursts into the more promising supernova gravitational-wave signals that may be detected by observatories as LIGO, VIRGO, etc., for distances far out to the VIRGO cluster of galaxies.Received: 26 November 2003, Revised: 26 February 2004, Published online: 3 June 2004 相似文献
7.
We analyze the pion electromagnetic, charged-current, and
transition form factors at timelike momentum transfers q,
GeV2, using a dispersion approach. We discuss in detail the propagator matrix of the photon-vector meson system and define certain reduced amplitudes, or vertex functions, describing the coupling of this system to final states. We then apply the derived analytic expressions to the analysis of the recent
,
, and
data. We find the reduced amplitudes for the coupling of the photon and vector mesons to two pseudoscalars to be constant, independent of s, in the range considered, indicating a freezing of the amplitudes for
GeV. The fit to the form factor data leads to the following values of the Breit-Wigner resonance masses
MeV,
MeV and
MeV, where the errors are only statistical.Received: 8 December 2003, Published online: 23 March 2004T. Paulus: Now at Philips 相似文献
8.
The one-loop contributions to the branching ratios for leptonic
decays are calculated in the CP-conserving 2HDM(II). The analysis is focused on large
enhanced contributions. We found that these contributions, involving loops with both neutral and charged Higgs bosons, dominate
over the tree-level
exchange, the latter one being totally negligible for the decay into e. We derive a simple analytical expression for the one-loop contribution which holds in the large
case. We show that the leptonic branching ratios of
are complementary to the Higgsstrahlung processes for h(H) and have a large potential in constraining the parameters of the model. In this work we provide upper limits on the Yukawa
couplings for both light h and light A scenarios, and we derive a new lower limit on the mass of
as a function of
which differs significantly from what was considered as a standard constraint based on the tree-level
exchange only. Interestingly we also obtain an upper limit on
.
Received: 22 February 2005, Revised: 12 July 2005, Published online: 6 October 2005
D. Temes: * UMR 5108 du CNRS, associée á l'Université de Savoie. 相似文献
9.
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
10.
A resonance search has been made in the
invariant-mass spectrum with the ZEUS detector at HERA using an integrated luminosity of
. The decay channels
and
(and the corresponding antiparticle decays) were used to identify
mesons. No resonance structure was observed in the
mass spectrum from more than 60 000 reconstructed
mesons. The results are not compatible with a report of the H1 Collaboration of a charmed pentaquark,
.Received: 14 September 2004, Revised: 29 September 2004, Published online: 9 November 2004 相似文献
11.
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
12.
Jian-Feng Cheng Dong-Sheng Du Cai-Dian Lü 《The European Physical Journal C - Particles and Fields》2006,45(3):711-720
We investigate the branching ratios and direct CP-asymmetries of the
and
decays in the PQCD approach. All the diagrams with emission topology or annihilation topology are calculated strictly. A
branching ratio of 10-6 and 10-7 for
and
decay is predicted, respectively. Because of the different weak phase and strong phase from penguin operator and two kinds
of tree operator contributions, we predict a possible large direct CP-violation:
and
when γ = 55°, which can be tested in the coming LHC.
PACS:
13.25.Hw, 12.38.Bx 相似文献
13.
C.A. Nelson J.J. Berger J.R. Wickman 《The European Physical Journal C - Particles and Fields》2006,46(2):385-402
This continuation of the derivation of general beam-referenced stage-two spin-correlation functions is for the analysis of
top–antitop pair-production at the Tevatron and at the Large Hadron Collider. Both the gluon-production and the quark-production
contributions are included for the charged-lepton-plus-jets reaction pp or
. There is a simple 4-angle beam-referenced spin-correlation function for determination of the relative sign of or for measurement
of a possible non-trivial phase between the two dominant
helicity amplitudes for the
decay mode. There is an analogous function and tests for
decay. This signature requires use of the
energy of the hadronically decaying W-boson, or the kinematically equivalent cosine of the polar angle of
emission in the antitop (top) decay frame. Spinors and their outer-products are constructed so that the helicity-amplitude
phase convention of Jacob and Wick can be used throughout for the fixing of the signs associated with this large W-boson longitudinal–transverse
interference effect. 相似文献
14.
The Standard Model constraints on
which can be derived from the
decays are revisited in some depth. As experimental inputs, the
,
decays complemented by the
decays, the CP parameters
and
, and/or the value of
as determined by the global CKM fit are used. The constraints discussed here are model independent in the sense that they rely only on Isospin symmetry, following the Gronau-London proposal. A new bound on
and the function
are introduced. While another bound applied to BABAR results is shown to imply that
is negative. The Grossman-Quinn bound is rediscussed. A close form expression is given for
as a function of the measurements. Various scenarios for the future of the isospin analysis are explored. To probe the Standard Model the
plane is introduced.Received: 17 December 2004, Published online: 25 January 2005 相似文献
15.
16.
production in
interactions has been detected via its decays into
,K
+
K
-
K
+
K
- and
in the data taken with the DELPHI detector at LEP1 and LEP2 energies. The two-photon radiative width averaged over all observed decay channels is
= 13.9
2.0 (stat.)
1.4(syst.)
2.7 (BR) keV. No direct decay channel
has been observed. An upper limit
< 5.5 keV at 95% confidence level has been evaluated for this decay mode.Received: 3 July 2003, Published online: 7 November 2003 相似文献
17.
18.
S. Y. Choi H.-U. Martyn P. M. Zerwas 《The European Physical Journal C - Particles and Fields》2005,44(2):175-182
The measurement of the trilinear couplings A in the part of the Lagrangian which breaks supersymmetry softly will be a difficult experimental task. In this report the
heavy Higgs decays
to stau pairs are investigated for measuring the stau trilinear coupling
. Based on detailed simulations of signal and backgrounds for a specific reference point in future high luminosity e + e- linear collider experiments, it is concluded that the parameter
can be determined with a precision at the 10% level in the region of moderate to large
.
Received: 2 August 2005, Published online: 13 September 2005 相似文献
19.
We consider the flavor symmetry
for the neutrino mass matrix. The most general neutrino mass matrix conserving
predicts quasi-degenerate neutrino masses with one maximal and two zero mixing angles. The presence of
can also be motivated by the near-bimaximal form of the neutrino mixing matrix. Furthermore, it is a special case of
symmetric mass matrices. Breaking the flavor symmetry by adding a small flavor-blind term to the neutrino mass matrix and/or by applying radiative corrections is shown to reproduce the observed neutrino oscillation phenomenology. Both the normal and inverted mass ordering can be accommodated within this scheme. Moderate cancellation for neutrinoless double beta decay is expected. The observables |U
e3|2 and
are proportional to the inverse of the fourth power of the common neutrino mass scale. We comment on whether the atmospheric neutrino mixing is expected to lie above or below
. We finally present a model based on the see-saw mechanism which generates a light neutrino mass matrix with an (approximate)
flavor symmetry. This is a minimal model with just one standard Higgs doublet and three heavy right-handed neutrinos. It needs only small values for the soft
breaking terms to reproduce the phenomenological viable mass textures analyzed.Received: 18 November 2004, Revised: 13 December 2004, Published online: 15 February 2005 相似文献
20.
We describe the spectra and decays of
and
atoms within a non-relativistic effective field theory. The evaluations of the energy shifts and widths are performed at next-to-leading order in isospin symmetry breaking. We provide general formulae for all S-states, and discuss the states with angular momentum one in some detail. The prediction for the lifetime of the
atom in its ground state yields
s.Received: 9 May 2004, Published online: 23 July 2004 相似文献