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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.
The production of
and
charmonium states in proton-nucleus interactions has been investigated by the NA50 experiment, at the CERN SPS. High statistics data sets were collected with collisions induced by 450 GeV protons incident on Be, Al, Cu, Ag and W targets. The
and
production cross-sections have been determined for each p-A system and their dependences on the nucleus size have been studied, leading to the so-called normal nuclear absorption. Comparing the two patterns we see that the nuclear absorption is stronger for the
than for the
. Given the high statistics of the data samples, the
(or rapidity) differential cross-sections of the
and
states have also been studied, for each of the target nuclei.Received: 23 September 2003, Revised: 29 November 2003, Published online: 29 January 2004 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.
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.
A. Capella C.A. Salgado D. Sousa 《The European Physical Journal C - Particles and Fields》2003,30(1):111-116
We compute the mid-rapidity densities of pions, kaons, baryons and antibaryons in Au-Au collisions at
GeV in the dual parton model supplemented with final state interaction (comovers interaction). The ratios
(
) increase between peripheral (
) and central (
collisions by a factor 2.4 (2.0) for the
, 4.8 (4.1) for the
and 16.5 (13.5) for the
. The ratio
increases by a factor 1.3 in the same centrality range. A comparison with the available data is presented.Received: 28 April 2003, Published online: 11 July 2003 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.
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
8.
M. Benayoun P. David L. DelBuono Ph Leruste H. B. O'Connell 《The European Physical Journal C - Particles and Fields》2003,29(3):397-411
We analyze a pion form factor formulation which fulfills the Analyticity requirement within the Hidden Local Symmetry (HLS)
Model. This implies an s-dependent dressing of the
VMD coupling and an account of several coupled channels. The corresponding function
provides nice fits of the pion form factor data from s=-0.25 to s=1 GeV2. It is shown that the coupling to
has little effect, while
improves significantly the fit probability below the
mass. No need for additional states like
shows up in this invariant-mass range. All parameters, except for the subtraction polynomial coefficients, are fixed from
the rest of the HLS phenomenology. The fits show consistency with the expected behaviour of
at s=0 up to
and with the phase shift data on
from threshold to somewhat above the
mass. The
sector is also examined in relation with recent data from CMD-2.
Received: 13 January 2003, Revised: 12 March 2003, Published online: 2 June 2003 相似文献
9.
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
10.
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
11.
Twist-3 distribution amplitudes of the pion and kaon are studied in this paper. We calculate the first several moments for the twist-3 distribution amplitudes (
and
) of the pion and kaon by applying the QCD sum rules. Our results show that (i) the first three moments of
and the first two moments of
and
of the pion and kaon can be obtained with 30
uncertainty; (ii) the fourth moment of the
and the second moment of the
can be obtained when the uncertainty are relaxed to 35
; (iii) the fourth moment of the
can be obtained only when the uncertainty are relaxed to 40
; (iv) we have
and
after including the
-corrections to the perturbative part. These moments will be helpful for constructing the twist-3 wave functions of the pion and kaon.Received: 6 January 2005, Revised: 29 March 2005, Published online: 22 June 2005PACS:
13.20.He, 11.55.Hx 相似文献
12.
Hadronic events from the data collected with the DELPHI detector at LEP within the energy range from 89 Gev to 209 Gev are selected, their jet rates are determined and compared to predictions of four different event generators. One of them is the recently developed APACIC + + generator which performs a massive matrix element calculation matched to a parton shower followed by string fragmentation. The four-jet rate is used to measure
in the next-to-leading-order approximation yielding
The running of
determined by using four-jet events has been tested. The logarithmic energy slope is measured to be
Since the analysis is based on four-jet final states it represents an alternative approach to previous DELPHI
measurements using event shape distributions.Received: 4 August 2004, Revised: 1 October 2004, Published online: 7 December 2004 相似文献
13.
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
14.
A search for lepton-flavor-violating interactions
and
has been performed with the ZEUS detector using the entire HERA I data sample, corresponding to an integrated luminosity
of
. The data were taken at center-of-mass energies,
, of 300 and
. No evidence of lepton-flavor violation was found, and constraints were derived on leptoquarks (LQs) that could mediate such
interactions. For LQ masses below
, limits were set on
, where
is the coupling of the LQ to an electron and a first-generation quark q1, and
is the branching ratio of the LQ to the final-state lepton
(μ or
) and a quark q. For LQ masses much larger than
, limits were set on the four-fermion interaction term
for LQs that couple to an electron and a quark
and to a lepton
and a quark
, where
and
are quark generation indices. Some of the limits are also applicable to lepton-flavor-violating processes mediated by squarks
in R-Parity-violating supersymmetric models. In some cases, especially when a higher-generation quark is involved and for the
process
, the ZEUS limits are the most stringent to date.
Received: 1 April 2005, Revised: 13 July 2005, Published online: 18 October 2005 相似文献
15.
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
16.
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
17.
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
18.
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
19.
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
20.
S. S. Agaev N. G. Stefanis 《The European Physical Journal C - Particles and Fields》2004,32(4):507-528
Employing the standard hard-scattering approach (HSA) in conjunction with the running coupling (RC) method, the latter joined with the infrared renormalon calculus, we compute power-suppressed corrections
to the massless
-meson-virtual-gluon transition form factor (FF)
. Contributions to the form factor from the quark and gluon components of the
meson are taken into account. Analytic expressions for the FFs
and
are also presented, as well as Borel transforms
and resummed expressions. It is shown that except for
, the Borel transform contains an infinite number of infrared renormalon poles. It is demonstrated that in the explored range of the total gluon virtuality
, power corrections found with the RC method considerably enhance the FF
relative to results obtained only in the context of the standard HSA with a frozen coupling.Received: 19 May 2003, Revised: 24 October 2003, Published online: 8 December 2003Permanent address: S.S. Agaev: High Energy Physics Lab., Baku State University, Z. Khalilov St. 23, 370148 Baku, Azerbaijan 相似文献