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1.
A. Bartl H. Fraas O. Kittel W. Majerotto 《The European Physical Journal C - Particles and Fields》2004,36(2):233-243
We study CP-sensitive observables in the neutralino production
and the subsequent two-body decays of the neutralino
and of the Z boson
. We identify the CP-odd elements of the Z boson density matrix and propose CP-sensitive triple-product asymmetries. We calculate these observables and the cross sections in the minimal supersymmetric standard model with complex parameters and M
1 for an e
+
e
- linear collider with
GeV and longitudinally polarized beams. We show that the asymmetries can reach
for
and
for
and discuss the feasibility of measuring these asymmetries.Received: 4 February 2004, Revised: 17 May 2004, Published online: 2 July 2004 相似文献
2.
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
3.
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
4.
V. A. Khoze A. D. Martin M. G. Ryskin W. J. Stirling 《The European Physical Journal C - Particles and Fields》2004,35(2):211-220
The double-diffractive production of
and
mesons, with a rapidity gap on either side, is studied, using both the Regge formalism and the perturbative QCD approach. Due to the rather low scale, the exclusive double-diffractive process
is predicted to dominate, whereas the probability that the incoming protons dissociate is expected to be relatively small. We evaluate the corresponding
production cross sections at the Tevatron and LHC energies. For the double-diffractive process with proton dissociation, it is possible to select events with large transverse momenta transferred through the rapidity gaps, by measuring the transverse energy,
, flows in the proton fragmentation regions. Then the large
provides a scale to justify the use of perturbative QCD, and to allow a spin-parity analysis of the centrally produced system to be performed, by studying the azimuthal angular correlations between the directions of the forward and backward
flows. The central production of the new X(3872) charmonium state is considered.Received: 24 March 2004, Published online: 11 May 2004 相似文献
5.
The CP asymmetries of the decay
, which originates from
flavor-changing neutral-current processes, and its CP-averaged branching ratio BR
offer interesting avenues to explore flavor physics. We show that we may characterize this channel, within the standard model, in a theoretically clean manner through a surface in observable space. In order to extract the relevant information from BR
, further information is required, which is provided by the
system and the SU(3) flavor symmetry, where we include the leading factorizable SU(3)-breaking corrections and discuss how experimental insights into non-factorizable effects can be obtained. We point out that the standard model implies a lower bound for BR
, which is very close to its current experimental upper bound, thereby suggesting that this decay should soon be observed. Moreover, we explore the implications for color suppression in the
system, and convert the data for these modes in a peculiar standard-model pattern for the CP-violating
observables.Received: 3 August 2004, Published online: 15 November 2004 相似文献
6.
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
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.
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
9.
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
10.
D. V. Bugg 《The European Physical Journal C - Particles and Fields》2004,36(2):161-168
A partial wave analysis of PS185 data for
is presented. A 3
S
1 cusp is identified in the inverse process
at threshold, using detailed balance to deduce cross sections from
. Partial wave amplitudes for
3
P
0, 3
F
3, 3
D
3 and 3
G
3 exhibit a behaviour very similar to resonances observed in Crystal Barrel data. With this identification, the
data then provide evidence for a new I = 0, J
PC
= 1- resonance with mass
MeV,
MeV, coupling to both 3
S
1 and 3
D
1.Received: 4 June 2004, Published online: 9 July 2004 相似文献
11.
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
12.
Hubaut F. Monnier E. Pralavorio P. Smolek K. Simak V. 《The European Physical Journal C - Particles and Fields》2005,44(1):13-25
The inelastic production of
mesons in ep collisions has been studied with the ZEUS detector at HERA using an integrated luminosity of
. The
mesons were identified using the decay channel
. The measurements were performed in the kinematic range
,
, 0.2 < z < 0.9 and
, where Q2 is the virtuality of the exchanged photon, W is the photon-proton centre-of-mass energy, z is the fraction of the photon energy carried by the
meson in the proton rest frame and
is the rapidity of the
in the laboratory frame. The measured cross sections are compared to theoretical predictions within the non-relativistic QCD framework including colour-singlet and colour-octet contributions, as well as to predictions based on the kT-factorisation approach. Calculations of the colour-singlet process generally agree with the data, whereas inclusion of colour-octet terms spoils this agreement.Received: 18 May 2005, Revised: 24 June 2005, Published online: 27 July 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.
By employing the QCD factorization approach, we calculated the next-to-leading order new physics contributions to the branching ratios, CP asymmetries, isospin and U-spin symmetry breaking of the exclusive decays
(
), induced by the charged Higgs penguins in general two-Higgs-doublet models. Within the considered parameter space, we found that (a) the new physics corrections to the observables are generally small in model I and model III-A, moderate in model II, but large in model III-B; (b) from the well measured branching ratios and upper limits, a lower bound of MH > 200 GeV in model II was obtained, while the allowed range of MH in model III-B is
GeV; these bounds are comparable with those from the inclusive
decay; (c) the NLO Wilson coefficient C7(mb) in model III-B is positive and disfavored by the measured value of isospin symmetry breaking
, but it still cannot be excluded if we take the large errors into account; (d) the CP asymmetry
in model III-B has an opposite sign to the one in the standard model (SM), which may be used as a good observable to distinguish the SM from model III-B; (e) the isospin symmetry breaking
is less than
in the region of
preferred by the global fit result, but it can be as large as 20 to
in the regions of
and
. The SM and model III-B predictions for
are opposite in sign for small or large values of the CKM angles; (f) the U-spin symmetry breaking
in the SM and the general two-Higgs-doublet models is generally small in size:
.Received: 9 October 2003, Revised: 11 November 2003, Published online: 18 February 2004 相似文献
15.
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
16.
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
17.
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
18.
The H Collaboration 《The European Physical Journal C - Particles and Fields》2004,36(4):441-452
Deep-inelastic positron-proton interactions at low values of Bjorken-x down to
which give rise to high transverse momentum
-mesons are studied with the H1 experiment at HERA. The inclusive cross section for
-mesons produced at small angles with respect to the proton remnant (the forward region) is presented as a function of the transverse momentum and energy of the
and of the four-momentum transfer Q
2 and Bjorken-x. Measurements are also presented of the transverse energy flow in events containing a forward
-meson. Hadronic final state calculations based on QCD models implementing different parton evolution schemes are confronted with the data.Received: 8 April 2004, Revised: 7 July 2004, Published online: 30 July 2004Dedicated to the memory of Krzysztof Rybicki 相似文献
19.
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
20.
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