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1.
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
2.
We compute the one-loop
-functions describing the renormalisation of the coupling constant
and the frequency parameter
for the real four-dimensional duality-covariant non-commutative
-model, which is renormalisable to all orders. The contribution from the one-loop four-point function is reduced by the one-loop wavefunction renormalisation, but the
-function remains non-negative. Both
and
vanish at the one-loop level for the duality-invariant model characterised by
. Moreover,
also vanishes in the limit
, which defines the standard non-commutative
-quantum field theory. Thus, the limit
exists at least at the one-loop level.Received: 19 March 2004, Published online: 5 May 2004 相似文献
3.
The spin-parity analysis of the data on the
annihilation reaction at rest in liquid and in gaseous hydrogen at 3 bar pressure and in flight at
momentum of
MeV/c, collected by the Obelix spectrometer at the LEAR complex of CERN, is presented. The relative branching ratios
and
are obtained. It is also shown that the inclusion of the exotic meson
, JPC = 1- + , mass and width
,
GeV/c2, in its decay to
, improves the fit and some implications of these results are briefly discussed. The relative S and P-wave annihilation percentages in four charged pions at two target densities are obtained.Received: 2 December 2003, Published online: 23 April 2004 相似文献
4.
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
5.
The tau lepton lifetime has been measured with the
events collected by the DELPHI detector at LEP in the years 1991-1995. Three different methods have been exploited, using both one-prong and three-prong
decay channels. Two measurements have been made using events in which both taus decay to a single charged particle. Combining these measurements gave
. A third measurement using taus which decayed to three charged particles yielded
These were combined with previous DELPHI results to measure the tau lifetime, using the full LEP1 data sample, to be
.Received: 12 November 2003, Revised: 1 June 2004, Published online: 20 July 2004 相似文献
6.
Z. G. Wang S. L. Wan W. M. Yang 《The European Physical Journal C - Particles and Fields》2006,45(1):201-209
In this article, we study the magnetic moment of the pentaquark state Θ+(1540) as a diquark-diquark-antiquark (
) state with the QCD sum rules in an external weak electromagnetic field (EFSR) and the light-cone QCD sum rules (LCSR) respectively.
The numerical results indicate that the magnetic moment is about
for the EFSR and
-
for the LCSR. As the values obtained from the EFSR are more stable than the corresponding ones from the LCSR,
is more reliable.
Received: 29 March 2005, Revised: 28 June 2005, Published online: 21 October 2005
PACS:
12.38.Aw, 12.38.Lg, 12.39.Ba, 12.39.-x 相似文献
7.
D. V. Bugg 《The European Physical Journal C - Particles and Fields》2004,33(4):505-509
The latest
elastic scattering data are re-analysed to determine the coupling constant gc of the charged pion, using the dispersion relation for the invariant amplitude B(+ ). Depending on the choice of data-base, values
to 13.65 are obtained with errors of
. The mass difference between charge states of
is
MeV, close to twice the mass difference between neutron and proton. The difference in widths on resonance is
MeV. One may account for a width difference of 4.5 MeV from phase space for decays and the extra channel
.Received: 21 January 2004, Published online: 3 March 2004 相似文献
8.
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
9.
A. Bartl K. Hohenwarter-Sodek T. Kernreiter H. Rud 《The European Physical Journal C - Particles and Fields》2004,36(4):515-522
We consider the process
at a linear collider with transverse
beam polarization. We investigate the influence of the CP phases on azimuthal asymmetries in
with subsequent two-body decays
and
. We show that triple product correlations involving the transverse
beam polarization vanish if at least one subsequent chargino decay is not observed. We derive this result within the minimal supersymmetric standard model (MSSM) with complex parameters; however, it holds also in the general MSSM with SUSY flavor violation.Received: 29 March 2004, Published online: 30 July 2004 相似文献
10.
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
11.
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
12.
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
13.
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
14.
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
15.
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
16.
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
17.
We discuss the time-dependent CP asymmetry of the decay
in an extension of the standard model with both a two Higgs doublet and additional fourth-generation quarks. We show that, although the standard model with a two Higgs doublet and the standard model with fourth-generation quarks alone are not likely to largely change the effective
from the decay
, the model with both an additional Higgs doublet and fourth-generation quarks can easily account for the possible large negative value of
without conflicting with other experimental constraints. In this model, additional large CP violating effects may arise from the flavor-changing Yukawa interactions between neutral Higgs bosons and the heavy fourth-generation down type quark, which can modify the QCD penguin contributions. With the constraints obtained from
processes such as
and
, this model can lead to an effective
as large as - 0.4 in the CP asymmetry of
.Received: 25 March 2004, Revised: 20 April 2004, Published online: 18 June 2004 相似文献
18.
M. Neubert 《The European Physical Journal C - Particles and Fields》2005,40(2):165-186
Using results on soft-collinear factorization for inclusive B-meson decay distributions, a systematic study of the partial
decay rate with a cut
on photon energy is performed. For values of E
0 below about 1.9 GeV, the rate can be calculated without reference to shape functions using a multi-scale operator product expansion (MSOPE). The transition from the shape-function region to the MSOPE region is studied analytically. The resulting prediction for the
branching ratio depends on three large scales: m
b
,
, and
. Logarithms associated with these scales are resummed at next-to-next-to-leading logarithmic order. While power corrections in
turn out to be small, the sensitivity to the scale
GeV (for
GeV) introduces significant perturbative uncertainties, which so far have been ignored. The new theoretical prediction for the
branching ratio with
GeV is
, where the first error is an estimate of perturbative uncertainties and the second one reflects uncertainties in input parameters. With this cut
of all events are contained. When this fraction is combined with the previously best prediction for the total decay rate, one obtains
, with a somewhat less conservative estimate of parametric uncertainties. The implications of larger theory uncertainties for new physics searches are briefly explored with the example of the type-II two-Higgs-doublet model, for which the lower bound on the charged-Higgs mass is reduced compared with previous estimates to approximately 200 GeV at 95% confidence level.Received: 18 September 2004, Revised: 18 January 2005, Published online: 21 February 2005 相似文献
19.
Approximately 438 pb-1 of e + e- data from the OPAL detector, taken with the LEP collider running at centre-of-mass energies of 192-209 GeV, are analyzed to search for evidence of chargino pair production,
, or neutralino associated production,
. Limits are set at the 95% confidence level on the product of the cross-section for the process
and its branching ratios to topologies containing jets and missing energy, or jets with a lepton and missing energy, and on the product of the cross-section for
and its branching ratio to jets. R-parity conservation is assumed throughout this paper. When these results are interpreted in the context of the Constrained Minimal Supersymmetric Standard Model, limits are also set on the masses of the
and
, and regions of the parameter space of the model are ruled out. Nearly model-independent limits are also set at the 95% confidence level on
with the assumption that each chargino decays via a W boson, and on
with the
assumed to decay via a Z0.Received: 15 December 2003, Revised: 16 February 2004, Published online: 23 April 2004 相似文献
20.
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