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1.
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
2.
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
3.
Measurements of on-shell ZZ production are described, using data from the DELPHI experiment at LEP in e
+
e
- collisions at centre-of-mass energies between 183 and 209 GeV, corresponding to an integrated luminosity of about 665 pb-1. Results obtained in each of the final states
,
,
,
,
, l
+
l
-
l
+
l
-, and
(with
) are presented. The measured production cross-sections are consistent with the Standard Model expectations. These results update and supersede those already published at 183 and 189 GeV.Received: 3 March 2002, Revised: 28 May 2003, Published online: 19 September 2003 相似文献
4.
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
5.
We discuss the angular distribution of the lepton pair in the Drell-Yan process,
. This process gives information on the spin-density matrix
of the annihilating quark-antiquark pair in
. There is strong experimental evidence that even for unpolarised initial hadrons
is non-trivial, and therefore the quark-antiquark system is polarised. We discuss the possibilities of a general
- which could be entangled - and a factorising
. We argue that instantons may lead to a non-trivial
of the type indicated by experiments.Received: 6 December 2004, Published online: 9 February 2005 相似文献
6.
A study of Z-boson pair production in e + e- annihilation at center-of-mass energies between 190 GeV and 209 GeV is reported. Final states containing only leptons, (
and
), quark and lepton pairs, (
,
) and only hadrons (
) are considered. In all states with at least one Z boson decaying hadronically, lifetime, lepton and event-shape tags are used to separate
pairs from
final states. Limits on anomalous ZZ
and ZZZ couplings are derived from the measured cross sections and from event kinematics using an optimal observable method. Limits on low scale gravity with large extra dimensions are derived from the cross sections and their dependence on polar angle.Received: 14 July 2003, Published online: 18 December 2003 相似文献
7.
Diffractive W + 2 jet production: a backgroundto exclusive $H\to W W$ production at hadron colliders
Central exclusive double-diffractive Higgs-boson production,
, is now recognised as an important search scenario for the LHC. We consider the case when the Higgs boson decays to two W bosons, one of which may be off-mass-shell, that subsequently decay to the
final state. An important background to this is from the QCD process
, where the two gluons are required to be in a Jz = 0, colour-singlet state. We perform an explicit calculation and investigate the salient properties of this potentially
important background process.
Received: 21 April 2005, Revised: 4 July 2005, Published online: 30 August 2005 相似文献
8.
The L Collaboration 《The European Physical Journal C - Particles and Fields》2005,40(3):333-341
Data collected at LEP at centre-of-mass energies
GeV are used to study correlations of the spin of W bosons using
events. Spin correlations are favoured by data, and found to agree with the Standard Model predictions. In addition, correlations between the W-boson decay planes are studied in
and
events. Decay-plane correlations are measured to be consistent with the Standard Model predictions.Received: 26 October 2004, Revised: 15 January 2005, Published online: 3 March 2005 相似文献
9.
Using e+e-→μ+μ-(γ) and
events radiative to the Z pole, DELPHI has determined the centre-of-mass energy,
, using energy and momentum constraint methods. The results are expressed as deviations from the nominal LEP centre-of-mass
energy, measured using other techniques. The results are found to be compatible with the LEP Energy Working Group estimates
for a combination of the 1997 to 2000 data sets. 相似文献
10.
We present a superfield Lax formalism of the superspace sigma model based on the target space
and show that a one-parameter family of flat superfield connections exists if the target space
is a symmetric space. The formalism has been related to the existence of an infinite family of local and non-local superfield
conserved quantities. A few examples have been given to illustrate the results. 相似文献
11.
A search for pair-produced charged Higgs bosons was performed in the data collected by the DELPHI detector at LEP II at centre-of-mass energies from 189 GeV to 209 GeV. Five different final states,
,
,
,
and
were considered, accounting for the major expected decays in type I and type II Two Higgs Doublet Models. No significant excess of data compared to the expected Standard Model processes was observed. The existence of a charged Higgs boson with mass lower than 76.7 GeV/c2 (type I) or 74.4 GeV/c2 (type II) is excluded at the 95% confidence level, for a wide range of the model parameters. Model independent cross-section limits have also been calculated.Received: 30 September 2003, Revised: 12 February 2004, Published online: 8 April 2004 相似文献
12.
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
13.
It has recently been pointed out that a new class of subleading shape functions involving B-meson matrix elements of non-local four-quark operators contributes at order
to
decay distributions in the endpoint region. The corresponding functions
and
are estimated using the vacuum-insertion approximation. A numerical analysis of various
decay spectra suggests that these power corrections are very small, below present theoretical uncertainties due to other
subleading shape-function contributions.
Received: 29 June 2005, Published online: 13 September 2005 相似文献
14.
15.
In the context of the littlest Higgs (LH) model, we study the process
. We find that the new gauge bosons Z
H
and B
H
can produce significant correction effects on this process, which can be further enhanced by suitably polarized beams. In most of the parameter space preferred by the electroweak precision data, the absolute value of the relative correction parameter
is larger than 5 %. As long as
and
the absolute value of the relative correction parameter
is larger than
. With reasonable values of the parameters of the LH model, the possible signals of the new gauge bosons B
H
and Z
H
can be detected via the process
in the future LC experiments with the CM energy
. B
H
exchange and Z
H
exchange can generate significantly corrections to the forward-backward asymmetry
only in a small part of the parameter space.Received: 29 October 2004, Revised: 29 November 2004, Published online: 15 February 2005 相似文献
16.
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
17.
Chong-Xing Yue Wei Wang Zheng-Jun Zong Feng Zhang 《The European Physical Journal C - Particles and Fields》2005,42(3):331-339
In the framework of the littlest Higgs (LH) model, we consider the processes
and
, and we calculate the contributions of new particles to the cross sections of these processes in the future high energy e + e- collider (ILC) with
TeV. We find that, with reasonable values of the free parameters, the deviations of the cross sections for the processes
from their SM values might be comparable to the future ILC measurement precision. The contributions of the light Higgs boson H0 to the process
are significantly large in all of the parameter space preferred by the electroweak precision data, which might be detected in the future ILC experiments. However, the contributions of the new gauge bosons BH and ZH to this process are very small.Received: 22 February 2005, Revised: 27 April 2005, Published online: 6 July 2005PACS:
12.60.Cn, 14.70.Pw, 14.80.Cp 相似文献
18.
We compute the cross section for exclusive double-diffractive
production at the Tevatron,
, and the LHC. We evaluate both the gg and
-channel exchange contributions to the process. The observation of exclusive
production at the Tevatron will provide a check on the model predictions and offer an opportunity to confirm the expectations for exclusive double-diffractive Higgs production at the LHC.Received: 10 September 2004, Revised: 8 October 2004, Published online: 1 December 2004 相似文献
19.
At the Large Hadron Collider at CERN the proton bunches cross at a rate of 40 MHz. At the Compact Muon Solenoid experiment
the original collision rate is reduced by a factor of
(1000) using a Level-1 hardware trigger. A subsequent factor of
(1000) data reduction is obtained by a software-implemented high level trigger (HLT) selection that is executed on a multi-processor
farm. In this review we present in detail prototype CMS HLT physics selection algorithms, expected trigger rates and trigger
performance in terms of both physics efficiency and timing.
PACS 13.85.-t; 07.05.Kf; 07.05.Tp; 02.07.Uu 相似文献
20.
A model describing the leptoproduction of
mesons is considered. For the amplitude of the photon dissociation into a
pair, the light-cone wave function is used. Scattering of the colorless
pair off the nucleon is computed within reggeon exchange phenomenology. The transition of the scattered quark and antiquark into the final
meson is treated with the aid of the parton-hadron duality concept. Numerical calculations of
and r0400 describe the world data at Q2 < 4 GeV2 rather reasonably. The calculations of the
meson spin density matrix show that the computed matrix elements except r0400 are in good agreement with the available experimental data at Q2 up to 8 GeV2 and the total mass of the
system greater than 4 GeV. The Regge phenomenology predictions at the highest experimentally available energies agree with both the HERA data and calculations performed within the perturbative QCD approach even for very high Q2 (
-20 GeV2). The predicted scale of the S-channel helicity non-conservation is in reasonable agreement with the experimental data.Received: 18 September 2003, Revised: 17 December 2003, Published online: 13 February 2004 相似文献