共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
3.
H. Albrecht T. Hamacher R. P. Hofmann T. Kirchhoff R. Mankel A. Nau S. Nowak H. Schr?der H. D. Schulz M. Walter et al. 《Zeitschrift fur Physik C Particles and Fields》1995,68(2):215-220
Using the ARGUS detector at the storage ring DORIS II we have measured decays into three charged mesons containingK
* mesons. Exploiting the good particle identification capabilities of the detector we have determined the following branching ratios:
,B
r
(–K
*0
K
–
v
)= (0.20±0.05±0.04)%, andB
r
(–K
*–
X
0
v
) =(1.15±0.15–0.18
+0.13)%.Supported by the German Bundesministerium für Forschung und Technologie, under contract number 054DO51P. 相似文献
4.
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
5.
H. Albrecht T. Hamacher R. P. Hofmann T. Kirchhoff R. Mankel A. Nau S. Nowak D. Re?ing H. Schr?der H. D. Schulz et al. 《Zeitschrift fur Physik C Particles and Fields》1995,68(1):25-28
Lepton spectra in decays have been studied with the ARGUS detector at thee
+
e
– storage ring DORIS II at DESY using the pseudo-rest-frame technique. We have improved upper limits for two-body -decays into a lepton and an unobservable particle.Supported by the German Bundesministerium für Forschung und Technologie, under contract number 054DO51P 相似文献
6.
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
7.
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
8.
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
9.
W. Adam T. Adye E. Agasi I. Ajinenko R. Aleksan G. D. Alekseev P. P. Allport S. Almehed S. J. Alvsvaag U. Amaldi et al. 《Zeitschrift fur Physik C Particles and Fields》1995,68(3):363-374
The lifetimes of charged and neutral B hadrons have been measured using data collected by the DELPHI experiment at LEP between 1991 and 1993. B hadrons are tagged as jets with a secondary vertex and the charge of the B candidate is taken to be the sum of the charges of the particles in the secondary vertex. Approximately 1,434,000 multihadronic Z0 decays yielded 1817 B hadron candidates. The B purity was estimated to be around 99.1±0.3%, and 83% (70%) of the events measured as neutral (charged) came from neutral (charged) B's. The mean lifetimes of charged and neutral B hadrons were found to be 1.72±0.08 (stat.) ±0.06 (syst.) ps and 1.58±0.11 (stat.)±0.09 (syst.) ps respectively. The ratio of their lifertimes, charged/neutral, was 1.09
–0.10
+0.11
(stat.)±0.08 (syst.). By making assumptions about the B
s
0
and
b
0
states, the B+ and B0 meson lifetimes were determined to be B+ = 1.72 ± 0.08 (stat.) ±0.06 (syst.) ps and B+ = 1.63 ± 0.14 (stat.)±0.13 (syst.) ps and the ratio of their lifetimes was:B+/B0 = 1.06
–0.11
+0.13
±0.10. The mean B lifetime was also deduced to be <> > = 1.64 ±0.06 (stat.)±0.04 (syst.) ps. 相似文献
10.
D. Buskulic D. Decamp C. Goy J. -P. Lees M. -N. Minard B. Mours B. Pietrzyk R. Alemany F. Ariztizabal P. Comas et al. 《Zeitschrift fur Physik C Particles and Fields》1993,59(2):215-229
Contact interactions are searched for using the differential cross sections for the reactionse
+
e
–e
+
e
–,e
+
e
–µ
+
µ
–,e
+
e
–
+
– ande
+
e
– measured at 12 energies around theZ peak and corresponding to about 20 pb–1 of cumulated luminosity. Four-fermion contact term models assuming various chiralities of lepton currents are fitted to the lepton data and lower limits on the energy scale of such terms are set at 95% c.l. The limits vary in the range 0.9–4.7 TeV, depending on the model and on the lepton flavour. Theee contact terms are searched for assuming various chiralities. Limits on the energy scale between 79 and 130 GeV are extracted from the data. The results are compared and combined with those reported at lower energies.Deceased 相似文献
11.
H. Hinkelmann 《Zeitschrift für Physik B Condensed Matter》1976,111(1):147-153
A simple approximate expression for the electron lifetime() in metals is rederived and discussed for different dimensions. In the 3D-case we get the well known Drude behaviour, i.e. a constant. In one dimension() is strongly frequency-dependent in the IR. The 2D-case is intermediate to the preceding ones. These results are essentially due to the different form of the Fermi surface for an electron gas in one, two and three dimensions. 相似文献
12.
We consider a semi-infinite 3-dimensional Ising system with a rough wall to describe the effect of the roughness r of the substrate on wetting. We show that the difference of wall free energies (r)=
AW(r)–
BW(r) of the two phases behaves like (r)r(1), where r=1 characterizes a purely flat surface, confirming at low enough temperature and small roughness the validity of Wenzel's law, cos (r)r cos (1), which relates the contact angle of a sessile droplet to the roughness of the substrate 相似文献
13.
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
14.
15.
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
16.
M. Loewenhaupt Th. Reif R. R. Arons E. Gratz M. Rotter B. Lebech 《Zeitschrift für Physik B Condensed Matter》1995,96(4):491-496
We investigated the magnetic structure of NdCu2 by means of neutron diffraction as a function of temperature between 1.5 K and 8 K in zero external field. The diffraction data were obtained on two single crystals with different orientations using the triple-axis-spectrometer TAS6 at the DR-3 reactor at Risø. Two magnetic phases were observed between 1.5K andT
N
=6.5K. From 1.5 K to 4.1 K the magnetic reflections can be described by the commensurate wave vector =(3/5 0 0) and its higher harmonics 3 and 5. Below 2.5K the structure is completely squared-up. For 4.1 KT6.5 K the magnetic structure is incommensurate with the chemical lattice and can be described by the wave vector=(3/5 0 0) and its higher harmonies 3 and 5M. Below 2.5 K the structure is completely squared-up. For 4.1 K T 6.5 K the magnetic structure is incommensurate with the chemical lattice and can be described by the wave vector
*=(0.62 0.044 0). In both phases the Nd-moments are oriented along the easyb-direction. 相似文献
17.
Abraham Boyarsky 《Journal of statistical physics》1988,50(1-2):213-229
Let : [0, 1][0, 1] be a piecewise monotonie expanding map. Then admits an absolutely continuous invariant measure. A result of Kosyakin and Sandler shows that can be approximated by a sequence of absolutely continuous measures
n
invariant under piecewise linear Markov maps itn. Each itn is constructed on the inverse images of the turning points of . The easily computable measures
n
are used to estimate the Liapunov exponent of . The idea of using Markov maps for estimating the Liapunov exponent is applied to both expanding and nonexpanding maps. 相似文献
18.
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
19.
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
20.
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