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1.
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
2.
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
3.
A. Mischke 《The European Physical Journal C - Particles and Fields》2005,43(1-4):311-316
In this paper, preliminary results are presented on high
inclusive neutral pion measurements in d-Au collisions at
GeV in the pseudo-rapidity range
. Photons from the decay
are detected in the Barrel Electromagnetic Calorimeter of the STAR experiment at RHIC. The analysis of this first BEMC hadron
measurement is described in detail. The results are compared to earlier RHIC findings. Furthermore, the obtained
invariant differential cross sections show good agreement with next-to-leading order (NLO) perturbative QCD calculations.
Arrival of the final proofs: 4 July 2005
PACS:
25.75.-q 相似文献
4.
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
5.
6.
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
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.
The one-loop contributions to the branching ratios for leptonic
decays are calculated in the CP-conserving 2HDM(II). The analysis is focused on large
enhanced contributions. We found that these contributions, involving loops with both neutral and charged Higgs bosons, dominate
over the tree-level
exchange, the latter one being totally negligible for the decay into e. We derive a simple analytical expression for the one-loop contribution which holds in the large
case. We show that the leptonic branching ratios of
are complementary to the Higgsstrahlung processes for h(H) and have a large potential in constraining the parameters of the model. In this work we provide upper limits on the Yukawa
couplings for both light h and light A scenarios, and we derive a new lower limit on the mass of
as a function of
which differs significantly from what was considered as a standard constraint based on the tree-level
exchange only. Interestingly we also obtain an upper limit on
.
Received: 22 February 2005, Revised: 12 July 2005, Published online: 6 October 2005
D. Temes: * UMR 5108 du CNRS, associée á l'Université de Savoie. 相似文献
9.
The two-scale model and its improved version were used to perform a fit to the HERMES data for the
(the virtual photon energy) and z (the fraction of
carried by hadron) dependences of the nuclear multiplicity ratios for
and
mesons electro-produced on two nuclear targets (14N and 84Kr). The quantitative criterion
was used for the first time to analyze the results of the model fit to the nuclear multiplicity ratios data. The two-parameter's
fit gave satisfactory agreement with the HERMES data. Best values of the parameters were then used to calculate the
and z dependences of the nuclear attenuation for
, K + , K-, and
produced on the 84Kr target, and also make predictions for
, z, and the Q2 (the photon virtuality) dependences of the nuclear attenuation data for those identified hadrons and nuclei that will be
published by HERMES.
Received: 10 February 2005, Revised: 7 July 2005, Published online: 13 September 2005
L. Grigoryan Supported by DESY, Deutsches Elektronen-Synchrotron. 相似文献
10.
The W + W- production cross section is measured from a data sample corresponding to a total integrated luminosity of 683 pb-1, collected by the ALEPH experiment at LEP at centre-of-mass energies from 183 to 209 GeV. Individual cross sections for the different topologies arising from W decays into leptons or hadrons, as well as the total W-pair cross section are given at eight centre-of-mass energies. The results are found to be in agreement with recently developed Standard Model calculations at the one percent level. The hadronic branching fraction of the W boson is measured to be
= 67.13
0.37(stat.)
0.15(syst.)%, from which the CKM matrix element
is determined to be 0.958
0.017(stat.)
0.008(syst.)Received: 1 October 2004, Published online: 15 November 2004 相似文献
11.
The production of
, D0, D + , Ds + and
charm hadrons and their antiparticles in e p scattering at HERA was measured with the ZEUS detector using an integrated luminosity of
. The measurement has been performed in the photoproduction regime with the exchanged-photon virtuality
and for photon-proton centre-of-mass energies in the range
. The charm hadrons were reconstructed in the range of transverse momentum
and pseudorapidity
. The production cross sections were used to determine the ratio of neutral and charged D-meson production rates,
, the strangeness-suppression factor,
, and the fraction of charged D mesons produced in a vector state,
. The measured
and
values agree with those obtained in deep inelastic scattering and in e + e- annihilations. The measured
value is smaller than, but consistent with, the previous measurements. The fractions of c quarks hadronising as a particular charm hadron,
, were derived in the given kinematic range. The measured open-charm fragmentation fractions are consistent with previous
results, although the measured
is smaller and
is larger than those obtained in e + e- annihilations. These results generally support the hypothesis that fragmentation proceeds independently of the hard sub-process.
Received: 12 August 2005, Revised: 8 September 2005, Published online: 6 October 2005 相似文献
12.
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
13.
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
14.
H. Buesching 《The European Physical Journal C - Particles and Fields》2005,43(1-4):303-310
Transverse momentum (
) spectra measured by the PHENIX experiment at RHIC in Au + Au, d + Au and pp collisions at
and in Au + Au collisions at
are presented. A suppression of the yield of high
hadrons in central Au + Au collisions by a factor 4-5 at
is found relative to the pp reference scaled by the nuclear overlap function
. In contrast, direct photons are not suppressed in central Au + Au collisions and no suppression of high
particles can be seen in d + Au collisions. This leads to the conclusion that the dense medium formed in central Au + Au
collisions is responsible for the suppression.
Arrival of the final proofs: 30 June 2005
PACS:
25.75.Dw 相似文献
15.
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
16.
In the SUSY SO(10) GUT context, we study the exclusive processes
. Using the Wilson coefficients of the relevant operators including the new operators
which are induced by neutral Higgs boson (NHB) penguins, we evaluate some possible observables associated with these processes like the invariant mass spectrum (IMS), lepton pair forward-backward asymmetry (FBA), lepton polarization asymmetries etc. In this model the contributions from Wilson coefficients
, among new contributions, are dominant. Our results show that the NHB effects are sensitive to the FBA,
, and
of
decay, which are expected to be measured in B factories, the deviation of
in
can reach 0.1 from SM, which could be seen in B factories, and the average of the normal polarization
can reach several percent for
and it is 0.05 or so for
, which could be measured in the future super B factories and provide useful information to probe new physics and discriminate different models.Received: 30 October 2004, Published online: 9 March 2005 相似文献
17.
M. Beneke Th Feldmann D. Seidel 《The European Physical Journal C - Particles and Fields》2005,41(2):173-188
We provide standard model expectations for the rare radiative decays
,
and
, and the electroweak penguin decays
and
at the next-to-leading order (NLO), extending our previous results to
transitions. We consider branching fractions, isospin asymmetries and direct CP asymmetries. For the electroweak penguin decays, the lepton-invariant mass spectrum and forward-backward asymmetry is also included. Radiative and electroweak penguin transitions in
are mainly interesting in the search for new flavor-changing neutral current interactions, but in addition the
decays provide constraints on the CKM parameters
. The potential impact of these constraints is discussed.Received: 16 January 2005, Published online: 16 March 2005
Corresponding author: Th. Feldmann 相似文献
18.
H. K. Wöhri 《The European Physical Journal C - Particles and Fields》2005,43(1-4):407-413
During the June 2002 run NA60 collected around 600 000 dimuon triggers in proton-nucleus collisions at 400 GeV. We show that
the collected dimuon mass spectra can be understood in terms of known sources. The specific target setup, consisting of Beryllium,
Indium and Lead targets, simultaneously exposed to the beam, allowed us to study the nuclear dependence of the production
cross-section of the
and
resonances. The elementary nucleon-nucleon production cross-sections at 400 GeV for the
,
and
mesons are also presented. By using the
-Dalitz decay, dominating the mass range below 450 MeV, we, furthermore, extracted the
production cross-section and its nuclear dependence. The results are discussed in the framework of previous measurements,
mostly obtained in different decay channels, performed by NA27, HELIOS-1 and CERES-TAPS.
Arrival of the final proofs: 1 July 2005
PACS:
25.75.Dw, 25.75.Nq 相似文献
19.
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
20.
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