共查询到20条相似文献,搜索用时 328 毫秒
1.
P. Abreu W. Adam T. Adye E. Agasi G. D. Alekseev P. Allen S. Almehed S. J. Alvsvaag U. Amaldi E. G. Anassontzis et al. 《Zeitschrift fur Physik C Particles and Fields》1992,55(4):555-567
From the analysis of a data sample corresponding to an integrated luminosity of 4.63 pb–1 taken during the 1990 run of LEP at centre of mass energies between 88.2 GeV an 94.2 GeV, the tau decays
and their charge conjugates have been studied. The following branching ratios have been measured;
,
, Br(– – (K–)v)=11.9±0.7±0.7%, BR (– – v)= 22.4±0.8±1.3%, in good agreement with world averages. The measured electronic and muonic branching ratios lead to a measurement of the strong coupling constant, s (m) = 0.26
–0.12
+0.09
. Extrapolating the s value fromm
tom
Z
yields s (mZ) = 0.109
–0.028
+0.012
.The average polarizationP
of taus produced in Z s s decays has also been measured using the above decay modes. The weighted mean of the polarizations obtained from the four decay modes isP
=–0.24±0.07. This value ofP
gives, in the improved Born approximation, a ratio between the axial and vector coupling constants of the tau of /a = 0.12 ± 0.04, and hence a value of the effective electroweak mixing parameter sin2 W(m
Z
2
). 相似文献
2.
W. Bernreuther G. W. Botz O. Nachtmann P. Overmann 《Zeitschrift fur Physik C Particles and Fields》1991,52(4):567-573
We calculate CP-odd correlations inZ decays to leptons,
. These correlations are sensitive to the weak dipole moment
of the . With 107 producedZ particles and with observation of the decay channels
and v
we estimate that
can be determined with an accuracy of about
(1 s.d.). 相似文献
3.
R. Akers G. Alexander J. Allison K. J. Anderson S. Arcelli S. Asai A. Astbury D. Axen G. Azuelos A. H. Ball et al. 《Zeitschrift fur Physik C Particles and Fields》1995,65(2):183-188
An upper limit for the
mass is determined through the kinematic reconstruction of the decay5
±
in the OPAL detector at LEP. The limit is obtained using a new method based on the comparison of the two-dimensional distribution of energy and invariant mass of the five-pion system with expectations from different neutrino mass hypotheses. From a sample of five events surviving the selection criteria we obtain an upper limit of 74 MeV at 95% confidence level. It is the first measurement at LEP energies, where the larger average multiplicity of
events makes the suppression of this background more robust compared to lower energies. 相似文献
4.
H. Albrecht H. Ehrlichmann T. Hamacher R. P. Hofmann T. Kirchhoff A. Nau S. Nowak H. Schr?der H. D. Schulz M. Walter et al. 《Zeitschrift fur Physik C Particles and Fields》1992,56(3):339-345
An analysis of the decay --0
v
has been performed using the ARGUS detector at the DORIS II storage ring. The branching ratio has been determined to be Br(--0
v
=(22.6±0.4±0.9)%. The shape of the -0 invariant mass spectrum is found to be in good agreement with the predictions obtained using the conserved vector current (CVC) hypothesis, suggesting that the -0 system is produced in aJ
P=1– state. An analysis of the measured decay angular distribution of the pions with respect to the flight direction of the -0 system demonstrates the vector nature of the coupling at the v
vertex. With the assumption of zerov
mass thev
spin has been shown to be
.Supported by the German Bundesministerium für Forschung und Technologie, under contract number 054DO51 P 相似文献
5.
J. Cleymans V. V. Goloviznin K. Redlich 《Zeitschrift fur Physik C Particles and Fields》1993,57(3):495-500
The most general angular decay distribution of the hadronic system in the decay of a polarized into one pseudoscalar plus a vector is calculated. Emphasis is put on decays ine
+
e
– experiments where the neutrino escapes detection and the restframe cannot be reconstructed. We propose a model for the decay intov
involving both a vector- and a second class axial vector-current contribution. Then we present numerical results for this decay channel. 相似文献
6.
We evaluate the multiplicity of hadrons in thee
+
e
–-annihilation at a given thrustT in the modified leading-log approximation, including
corrections. The calculation is done at a large value of =1–T by the use of the factorisation which takes place in the one-particle-inclusive cross section at a given . At a small , a different type of factorisation takes place, which also enable us to evaluate the multiplicity. Two approaches are compared numerically. Measuring this quantity near =1/3, we can determine the multiplicity ratio between a gluon-jet and a quark-jet. 相似文献
7.
8.
New measurements of the reactione
+
e
– confirm previous evidence for the decay1 and provide a strong constraint on the mass of the1. The results from a detailed analysis of these data are compared with those from a corresponding analysis of new data on the reactione
+
e
–. It is shown that
in accord with expectation. This identification of a strong1 decay supports a previous claim that the1 and theC(1480), observed in the channel, cannot be different manifestations of the same particle. 相似文献
9.
D. J. Broadhurst 《Zeitschrift fur Physik C Particles and Fields》1993,58(2):339-345
We calculate analytical contributions to then-loop asymptotic photon propagator from diagrams withn–1 electron loops, i.e. theO(1/N) terms in the largeN limit. The corresponding contributions to the on-shell -function, ()=6 log / logm reduced to rational combinations of
s
=
p
p
–s
. For the -function of the MOM scheme (i.e. the Gell-Man-Low function) we obtain theO(1/N) terms of
相似文献
10.
Balk S. Körner J. G. Pirjol D. Schilcher K. 《Zeitschrift fur Physik C Particles and Fields》1994,64(1):37-44
Starting from an operator product expansion in the heavy quark effective theory up to order 1/m
b
2
we calculate the inclusive semileptonic decays of unpolarized bottom hadrons including lepton mass effects. We calculate the differential decay spectra d/(dE
), and the total decay rate forB meson decays to final states containing a lepton.Supported by the Graduiertenkolleg Teilchenphysik, Universität Mainz 相似文献
11.
G. Amelino-Camelia F. Buccella G. D'Ambrosio A. R. Gallo G. Mangano M. Miragliuolo 《Zeitschrift fur Physik C Particles and Fields》1992,55(1):63-74
We study the time dependence of the integrated asymmetries in strangeness of kaons in the decays in two and three pions and in two photons with the purpose of disentangling theCP violating effects in the decay amplitudes from the ones related to the
mass matrix. We find two cases where they are not reduced by the I=1/2 rule or hidden byCP violation in the mass matrix, namely the strangeness-energy correlation of the charged pions in the prompt decay (
S
) in +-0, and the decays in two photons. The semileptonic decays are also briefly studied. 相似文献
12.
The divergent large-order behaviour of the perturbative series relevant for the determination of
s
from decay is controlled by the leading ultraviolet (UV) renormalon. Even in the absence of the first infrared (IR) renormalon, an ambiguity of order
2/m
2 is introduced. We make a quantitative study of the practical implications of this ambiguity. We discuss the magnitude of UV renormalon corrections obtained in the large-N
f
limit, which, although unrealistic, is nevertheless interesting to some extent. We then study a number of improved approximants for the perturbative series, based on a change of variable in the Borel representation, such as to displace the leading UV renormalon singularity at a larger distance from the origin than the first IR renormalon. The spread of the resulting values of
s
(m
2) obtained by different approximants, at different renormalization scales, is exhibited as a measure of the underlying ambiguities. Finally, on the basis of mathematical models, we discuss the prospects of an actual improvement, given the signs and magnitudes of the computed coefficients, the size of
s
(m
2) and what is known of the asymptotic properties of the series. Our conclusion is that a realistic estimate of the theoretical error cannot go below
s
(m
2)±0.060, or
s
(m
Z
2)±0.006.On leave of absence from INFN, Sezione di Milano, Milan, Italy 相似文献
13.
Nikolai N. Nikolaev Vladimir R. Zoller 《Zeitschrift fur Physik C Particles and Fields》1992,56(4):623-628
One expects a similarity of the energy dependence of the difference
tot(*p)–
tot(*n) for virtual (deep inelastic scatteringQ
2m
2) and real (Q
2=0) photons. Previous analysis of D structure functions with allowence for nuclear shadowing (NS) in the deuteron has led to conclusion that
tot(*p)–
tot(*n)<0>0>x<0.015. the=" early=" evidence=" from=" the=" real=" photoproduction=" data=">0.015.>
tot(p)–
tot(n)<0. we=" critically=" reexamine=" determinations=" of=" the=">0.>
tot(p)–
tot(n), using more accurate calculations of NS correction to
tot(D), and discuss a possibility of
tot(n)
tot(p) at moderately high energies. 相似文献
14.
M. T. Dova L. N. Epele H. Fanchiotti C. A. García Canal P. E. Lacentre 《Zeitschrift fur Physik C Particles and Fields》1995,67(1):115-121
The spin correlated angular distribution for ++ pairs at energies of theZ
0 resonance, both decaying semi-leptonically up to 3 hadrons in each final state, was derived assuming general vector and axial vector couplings. The use of these distributions to test the V-A structure of the -W-v
vertex at LEP energies is analized.Partially supported by CONICET, Argentina 相似文献
15.
D. Decamp B. Deschizeaux C. Goy J. -P. Lees M. -N. Minard R. Alemany J. M. Crespo M. Delfino E. Fernandez V. Gaitan et al. 《Zeitschrift fur Physik C Particles and Fields》1992,54(2):211-228
Using the data accumulated at LEP in 1989 and 1990 with the ALEPH detector, the inclusive and exclusive branching ratios of the lepton have been measured assuming lepton universality inZ
0 decays. The inclusive branching fractions for the decay into one, three, and five charged particles have been determined to be (85.45±0.97)%, (14.35±0.48)%, and (0.10±0.05)%, respectively, in agreement with the world averages. New undetected decay modes are determined to have a branching fraction of less than 2.1% at 95% CL. The measured branching ratios for quasi-exclusive channels are slightly larger than, but consistent with the world averages, except for the modes 3 hadrons+v
andhadron+20
v
, which are significantly larger. These latter branching ratios have been found to be (9.5±0.7)% and (10.2±1.1)%, respectively. The sum of all the measured quasi-exclusive branching ratios is (100.4±1.8)%. A fully exclusive analysis of modes with neutral pions shows no evidence for new photonic decay modes with a branching fraction limit of 3.4% at 95% CL.Supported by CAICYT, Spain 相似文献
16.
R. Akers G. Alexander J. Allison K. Ametewee K. J. Anderson S. Arcelli S. Asai D. Axen G. Azuelos A. H. Ball et al. 《Zeitschrift fur Physik C Particles and Fields》1995,66(4):543-554
The leptonic branching ratios of the tau lepton have been determined from data collected by the OPAL detector in 1991 and 1992. From a sample of 27196 e+e–+– candidates we find 7322
and 7941
candidates. Using efficiency and background estimates determined from a study of Monte Carlo events and control samples of data, the branching ratios
=(18.14±0.20±0.28)% and
=(17.48±0.18±0.23)% have been obtained. These new results have been combined with the published results for the 1990 OPAL data to yield the following branching ratios for data taken between 1990 and 1992:
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