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1.
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
2.
E. Boos H.-U. Martyn G. Moortgat-Pick M. Sachwitz A. Sherstnev P. M. Zerwas 《The European Physical Journal C - Particles and Fields》2003,30(3):395-407
The basic parameters of supersymmetric theories can be determined at future e
+
e
- linear colliders with high precision. We investigate in this report how polarisation measurements in
and
or
decays to
leptons and t quarks plus neutralinos or charginos can be used to measure
(in particular for large values) and to determine the trilinear couplings
, A
t
and A
b
in sfermion pair production.Received: 17 April 2003, Revised: 3 July 2003, Published online: 29 August 2003 相似文献
3.
Cirigliano V. Ecker G. Neufeld H. Pich A. 《The European Physical Journal C - Particles and Fields》2004,33(3):369-396
We perform a complete analysis of isospin breaking in
amplitudes in chiral perturbation theory, including both strong isospin violation (
) and electromagnetic corrections to next-to-leading order in the low-energy expansion. The unknown chiral couplings are estimated at leading order in the 1/Nc expansion. We study the impact of isospin breaking on CP conserving amplitudes and rescattering phases. In particular, we extract the effective couplings g8 and g27 from a fit to
branching ratios, finding small deviations from the isospin-limit case. The ratio
measuring the
enhancement is found to decrease from
in the isospin limit to
in the presence of isospin breaking. We also analyze the effect of isospin violation on the CP violation parameter
, finding a destructive interference between three different sources of isospin violation. Within the uncertainties of large-Nc estimates for the low-energy constants, the isospin violating correction for
is below 15%.Received: 21 November 2003, Published online: 4 February 2004Work supported in part by IHP-RTN, Contract No. HPRN-CT2002-00311 (EURIDICE) and by Acciones Integradas, Project No. 19/2003 (Austria), HU2002-0044 (MCYT, Spain) 相似文献
4.
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
5.
M. Boglione M. R. Pennington 《The European Physical Journal C - Particles and Fields》2003,30(4):503-512
A guide to the composition of the enigmatic f
0(980) and a
0(980) states is their formation in
-radiative decays. Precision data are becoming available from the KLOE experiment at the DA
NE machine at Frascati, as well as results from SND and CMD-2 at VEPP-2M at Novosibirsk. We show how the coupling of the f
0(980) to this channel can be extracted from these, independently of the background provided by
production. To do this we use the fact that the behaviour of both the f
0(980) and
cannot be determined by these data alone, but is strongly constrained by experimental results from other hadronic processes as required by unitarity. We find that the resulting coupling for the
is
GeV with a background that is quite unlike that assumed if unitarity is neglected. This provides an object lesson in how unitarity teaches us to add resonances. Not surprisingly the result is crucially dependent on the pole position of the f
0(980), for which there are still sizeable uncertainties. At present this leads to an uncertainty in the
branching ratio which can only be fixed by further precision data on the f
0(980). Nevertheless, the
is now the same order of magnitude as the experimental
.Received: 25 March 2003, Published online: 5 September 2003 相似文献
6.
The hadronic photon structure function
is measured from data taken with the ALEPH detector at LEP. At centre-of-mass energies between
and
an integrated luminosity of
is analyzed in two ranges of Q2 with
GeV2 and 67.2 GeV2. Detector effects and acceptance are corrected for with a Tikhonov unfolding procedure. The results are compared to theoretical predictions and measurements from other experiments.Received: 12 June 2003, Published online: 11 August 2003 相似文献
7.
M. Dubinin H. J. Schreiber A. Vologdin 《The European Physical Journal C - Particles and Fields》2003,30(3):337-344
We examine the prospects for measuring the
coupling of a standard model-like Higgs boson with a mass between 120 and 160 GeV at the future TESLA linear e
+
e
- collider, assuming an integrated luminosity of 1 ab-1 and a center-of-mass energy of 500 GeV. We consider the Higgs boson produced in association with
via the W W fusion reaction
, followed by the rare decay into a Z boson and a photon,
. Accounting for all main background contributions, a precision of 27% can be achieved in unpolarized e
+
e
- collisions for M
H
= 140 GeV. With appropriate initial state polarisations
BF(
)/BF(
), or the precisions on the
partial width, can be improved to 17% and provide valuable information on the
coupling. For M
H
= 120 and 160 GeV, the small significance of the signals in unpolarized collisions sets upper limits of 79% respectively 72% at 90% confidence level on the
branching fraction.Received: 5 March 2003, Revised: 14 July 2003, Published online: 5 September 2003 相似文献
8.
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
9.
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
10.
J. Bielcikova 《The European Physical Journal C - Particles and Fields》2005,43(1-4):323-327
A study of elliptic flow and two-particle azimuthal correlations of charged particles (
GeV/c) and high-
pions (
GeV/c) in Pb + Au collisions at 158A GeV/c, close to midrapidity, is presented. Elliptic flow (v
2) rises linearly with
to a value of about 10
at 2 GeV/c. Beyond
1.5 GeV/c, the slope decreases and possibly indicates a v
2 saturation at high
. Two-pion azimuthal anisotropies for
1.2 GeV/c exceed the v
2 values by about 60
in semicentral collisions. This non-flow component is attributed to near-side and away-side jetlike correlations. While the
near-side peak remains constant with centrality 0.23
0.03 rad, as expected for fragmentation, the away-side peak experiences broadening and disappears in central collisions.
Arrival of the final proofs: 30 June 2005
PACS:
25.75.Ld, 25.75.Gz 相似文献
11.
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
12.
M. Benayoun P. David L. DelBuono Ph Leruste H. B. O’Connell 《The European Physical Journal C - Particles and Fields》2003,31(4):525-547
We examine the decay modes
within the context of the hidden local symmetry (HLS) model. Using numerical information derived in previous fits to the
and Ve
+
e
- decay modes in isolation and the
lineshape determined in a previous fit to the pion form factor, we show that all aspects of these decays can be predicted with fair accuracy. Freeing some parameters does not improve the picture. This is interpreted as strong evidence in favor of the box anomaly in the
decays, which occurs at precisely the level expected. We also construct the set of equations defining the amplitudes for
and
at the chiral limit, as predicted from the anomalous HLS Lagrangian appropriately broken. This provides a set of four equations depending on only one parameter, instead of three for the traditional set. This is also shown to match the (two-angle, two-decay-constant)
-
mixing scheme recently proposed and is also fairly well fulfilled by the data. The information returned from the fits also matches expectations from previously published fits to the
decay modes in isolation.Received: 29 June 2003, Revised: 17 September 2003, Published online: 4 November 2003 相似文献
13.
The H Collaboration 《The European Physical Journal C - Particles and Fields》2003,29(4):497-513
Inclusive jet cross sections are measured in photoproduction at HERA using the H1 detector. The data sample of
events in the kinematic range of photon virtualities
and photon-proton centre-of-mass energies
represents an integrated luminosity of
. Jets are defined using the inclusive
algorithm. Single- and multi-differential cross sections are measured as functions of jet transverse energy ET jet and pseudorapidity
in the domain
and
. The cross sections are found to be in good agreement with next-to-leading order perturbative QCD calculations corrected for fragmentation and underlying event effects. The cross section differential in ET jet, which varies by six orders of magnitude over the measured range, is compared with similar distributions from
colliders at equal and higher energies.Received: 24 February 2003, Revised: 26 May 2003, Published online: 11 July 2003 相似文献
14.
A. J. Buras R. Fleischer S. Recksiegel F. Schwab 《The European Physical Journal C - Particles and Fields》2003,32(1):45-54
The standard-model interpretation of the ratios of charged and neutral
rates, R
c and R
n, respectively, points towards a puzzling picture. Since these observables are affected significantly by colour-allowed electroweak (EW) penguins, this
puzzle could be a manifestation of new physics in the EW penguin sector. Performing the analysis in the R
n- R
c plane, which is very suitable for monitoring various effects, we demonstrate that we may, in fact, move straightforwardly to the experimental region in this plane through an enhancement of the relevant EW penguin parameter q. We derive analytical bounds for q in terms of a quantity L, which measures the violation of the Lipkin sum rule, and point out that strong phases around
are favoured by the data, in contrast to QCD factorisation. The
modes imply a correlation between q and the angle
that, in the limit of negligible rescattering effects and colour-suppressed EW penguins, depends only on the value of L. Concentrating on a minimal flavour-violating new-physics scenario with enhanced Z
0 penguins, we find that the current experimental values on
require roughly
. As the
data give
, L has either to move to smaller values once the
data improve or new sources of flavour and CP violation are needed. In turn, the enhanced values of L seen in the
data could be accompanied by enhanced branching ratios for the rare decays
,
,
and
. Most interesting turns out to be the correlation between the
modes and
, with the latter depending approximately on a single scaling variable
.Received: 8 September 2003, Published online: 12 November 2003 相似文献
15.
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
16.
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
17.
M. M. Block 《The European Physical Journal C - Particles and Fields》2003,30(4):497-501
The robustness of the factorization theorem for total cross sections,
for nn (the even portion of pp and
scattering),
and
scattering, originally proved by Block and Kaidalov using an eikonal formalism, is demonstrated. Factorization theorems for the nuclear slope parameter B and
, the ratio of the real to the imaginary portion of the forward scattering amplitude, are derived under very general conditions, using analyticity and the optical theorem.Received: 19 February 2003, Revised: 10 July 2003, Published online: 19 September 2003Work partially supported by Department of Energy contract DA-AC02-76-Er02289 Task D. 相似文献
18.
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
19.
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
20.
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