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1.
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
2.
P. Abreu W. Adam T. Adye E. Agasi I. Ajinenko R. Aleksan G. D. Alekseev P. P. Allport S. Almehed S. J. Alvsvaag et al. 《Zeitschrift fur Physik C Particles and Fields》1995,68(3):353-362
The decayB
*B
has been observed with the DELPHI detector at LEP, where theB
* meson is produced inZ boson decays. The combination of inclusively reconstructedB mesons with well-measured converted photons yields a measurement of the flavour-averagedB
*-B mass difference of 45.5±0.3 (stat.) ±0.8 (syst.) MeV/c2. 95% confidence level upper limits at 6 MeV/c2 are placed on both the isospin (i.e.B
+-B
0) and theB
s
-B
ud
splitting of the mass difference. The production ratio ofB
* toB mesons inZ decays is measured to be 0.72±0.03 (stat.) ±0.06 (syst.). Limits on the production cross-section of other hypothetical excitedB hadron states decaying radiatively are established. The differentialB
* cross section has been measured to be in good agreement with the averageb fragmentation, yielding an average fractionalB
* energy of x
E
=0.695±0.009 (stat.) ±0.013 (syst.). From the decay angular distribution the relative contribution of longitudinalB
* polarisation states is measured to be L/(L + T) = 0.32 ± 0.04 (stat.) ±0.03 (syst.).CICYT_AEN93-0832 相似文献
3.
P. Abreu W. Adam F. Adami T. Adye G. D. Alexeev P. Allen S. Almehed F. Alted S. J. Alvsvaag U. Amaldi et al. 《Zeitschrift fur Physik C Particles and Fields》1991,50(2):185-194
This paper presents an analysis of the multiplicity distributions of charged particles produced inZ
0 hadronic decays in the DELPHI detector. It is based on a sample of 25364 events. The average multiplicity is n
ch>=20.71±0.04(stat)±0.77(syst) and the dispersionD=6.28±0.03(stat)±0.43(syst). The data are compared with the results at lower energies and with the predictions of phenomenological models. The Lund parton shower model describes the data reasonably well. The multiplicity distributions show approximate KNO-scaling. They also show positive forward-backward correlations that are strongest in the central region of rapidity and for particles of opposite charge. 相似文献
4.
P. Abreu W. Adam T. Adye E. Agasi R. Aleksan G. D. Alekseev P. Allport S. Almehed F. M. L. Almeida Junior S. J. Alvsvaag et al. 《Zeitschrift fur Physik C Particles and Fields》1994,63(1):3-15
The average lifetime ofB hadrons was measured using data collected with the DELPHI detector at the LEP collider during 1991 and 1992. The measurement was performed using two different anayses. The first method was an improvement on a previous technique, which used charged particle impact parameter distributions. This analysis measured an average lifetime forB hadrons of
相似文献
5.
《The European Physical Journal C - Particles and Fields》2007,52(4):767-785
From a total data sample of 701.1 pb-1 recorded with e+e- centre-of-mass energies of 161–209 GeV with the OPAL detector at LEP, 11693 W-pair candidate events are selected. These data are used to obtain measurements
of the W-pair production cross sections at 10 different centre-of-mass energies. The ratio of the measured cross sections
to the standard model expectation is found to be: , where the uncertainties are statistical, experimental systematics and theory systematics respectively. The data are used
to determine the W boson branching fractions, which are found to be consistent with lepton universality of the charged current
interaction. Assuming lepton universality, the branching ratio to hadrons is determined to be 67.41±0.37(stat.)±0.23(syst.)%,
from which the CKM matrix element |Vcs| is determined to be 0.969±0.017(stat.)±0.012(syst.). The differential cross section as a function of the W- production angle is measured for the qqeν and qqμν final states. The results described in this paper are consistent with
the expectations from the standard model.
This paper is dedicated to the memory of Ben Shen. 相似文献
6.
M. Berggren J. Guy P. -O. Hulth G. T. Jones U. F. Katz P. Marage E. Matsinos S. W. O'Neale E. Simopoulou K. E. Varvell A. Vayaki W. Venus W. Wittek 《Zeitschrift fur Physik C Particles and Fields》1991,50(3):427-440
TheW andQ
2 dependence of the transverse momentum of the forward-going hadrons in deep inelastic neutrino charged current interactions on neon is studied. The data were obtained by exposing BEBC filled with a Ne/H2 mixture to the CERN SPS wide-band neutrino beam. The data on average transverse momentum are compared to a model which includes first order QCD, intrinsic quark momentum in the nucleon and Fermi motion, as well as a simple model for hadronization. The model is found to describe the data well. Values of
s
=0.16±0.02(stat)±0.02(syst.)±0.03(frag.) at an averageQ
2 of 15.4±0.4 GeV2/c2 and
(stat.)
–90
+100
(syst.)
–90
+130
, (frag.) MeV/v for three flavours are extracted. 相似文献
7.
《The European Physical Journal C - Particles and Fields》2006,47(2):309-335
The mass of the W boson is determined from the direct reconstruction of W decays in WW→qq̄qq̄ and WW→ℓνqq̄ events in e+e- collisions at LEP. The data sample corresponds to an integrated luminosity of 683 pb-1 collected with the ALEPH detector at centre-of-mass energies up to 209 GeV. To minimise any effect from colour reconnection
a new procedure is adopted in which low energy particles are not considered in the mass determination from the qq̄qq̄ channel.
The combined result from all channels is
where FSI represents the possible effects of final state interactions in the qq̄qq̄ channel and LEP indicates the uncertainty
in the beam energy. From two-parameter fits to the W mass and width, the W width is found to be
相似文献
8.
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
9.
G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》2006,45(2):291-305
The effects of the final state interaction phenomenon known as colour reconnection are investigated at centre-of-mass energies
in the range
≃ 189–209 using the OPAL detector at LEP. Colour reconnection is expected to affect observables based on charged particles
in hadronic decays of . Measurements of inclusive charged particle multiplicities, and of their angular distribution with
respect to the four jet axes of the events, are used to test models of colour reconnection. The data are found to exclude
extreme scenarios of the Sj?strand-Khoze Type I () model and are compatible with other models, both with and without colour
reconnection effects. In the context of the model, the best agreement with data is obtained for a reconnection probability
of 37%. Assuming no colour reconnection, the charged particle multiplicity in hadronically decaying W bosons is measured to
be
=19.38±0.05(stat.)±0.08(syst.).
Arrival of the final proofs: 28 November 2005 相似文献
10.
P. Abreu W. Adam F. Adami T. Adye T. Akesson G. D. Alekseev P. Allen S. Almehed F. Alted S. J. Alvsvaag et al. 《Zeitschrift fur Physik C Particles and Fields》1991,52(2):271-281
The multiplicity distributions of charged particles in restricted rapidity intervals inZ
0 hadronic decays measured by the DELPHI detector are presented. The data reveal a shoulder structure, best visible for intervals of intermediate size, i.e. for rapidity limits around ±1.5. The whole set of distributions including the shoulder structure is reproduced by the Lund Parton Shower model. The structure is found to be due to important contributions from 3-and 4-jet events with a hard gluon jet. A different model, based on the concept of independently produced groups of particles, clans, fluctuating both in number per event and particle content per clan, has also been used to analyse the present data. The results show that for each interval of rapidity the average number of clans per event is approximately the same as at lower energies.This paper is dedicated to the memory of Léon Van Hove 相似文献
11.
M. Z. Akrawy G. Alexander J. Allison P. P. Allport K. J. Anderson J. C. Armitage G. T. J. Arnison P. Ashton G. Azuelos J. T. M. Baines et al. 《Zeitschrift fur Physik C Particles and Fields》1991,50(3):373-384
The OPAL detector at LEP is used to measure the branching ratio of theZ
0 into invisible particles by measuring the cross section of single photon events ine
+
e
– collisions at centre-of-mass energies near theZ
0 resonance. In a data sample of 5.3 pb–1, we observe 73 events with single photons depositing more than 1.5 GeV in the electromagnetic calorimeter, with an expected background of 8±2 events not associated with invisibleZ
0 decay. With this data we determine theZ
0 invisible width to be 0.50±0.07±0.03 GeV, where the first error is statistical and the second systematic. This corresponds to 3.0±0.4±0.2 light neutrino generations in the Standard Model. 相似文献
12.
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
13.
《Physics letters. [Part B]》2001,510(1-4)
A new precise measurement of |Vcb| and of the branching ratio BR
) has been performed using a sample of about 5000 semileptonic decays
, selected by the DELPHI detector at LEP I by tagging the soft pion from D*+→D0π+. The results are: Vcb=(39.0±1.5 (stat.)+2.5−2.6 (syst. exp.)±1.3 (syst. th.))×10−3,
Full-size image 14.
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
15.
P. D. Acton G. Alexander J. Allison P. P. Allport K. J. Anderson S. Arcelli A. Astbury D. Axen G. Azuelos G. A. Bahan et al. 《Zeitschrift fur Physik C Particles and Fields》1992,56(4):521-535
Results are reported of a study of neutral vector meson production in multihadronicZ
0 decays in the OPAL experiment at LEP. Pions and kaons have been identified by specific ionisation energy loss andK
±
andK
+
K
– mass spectra have been fitted, in bins of the scaled momentum variablex
p
, to combinations of resonance signals and non-resonant backgrounds. Rates are given forK
*(892)° and ø(1020), and production cross sections are compared to the predictions of Monte Carlo models. Overall multiplicities have been determined as 0.76±0.07±0.06K
*(892)° and 0.086±0.015±0.010 ø(1020) per hadronicZ
0 decay (the quoted errors are respectively statistical and systematic). Momentum dependent distortions of the mass spectra, possibly associated indirectly with Bose-Einstein effects, have prevented reliable measurement of the (770)° cross section in this study. 相似文献
16.
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
17.
Hadronic events produced in e+e- collisions by the LEP collider and recorded by the OPAL detector were used to form distributions based on the number of reconstructed
jets. The data were collected between 1995 and 2000 and correspond to energies of 91 GeV, 130-136 GeV and 161-209 GeV. The
jet rates were determined using four different jet-finding algorithms (Cone, JADE, Durham and Cambridge). The differential
two-jet rate and the average jet rate with the Durham and Cambridge algorithms were used to measure in the LEP energy range
by fitting an expression in which
calculations were matched to a NLLA prediction and fitted to the data. Combining the measurements at different centre-of-mass
energies, the value of () was determined to be
αS(MZ) = 0.1177 ± 0.0006 (stat.) ± 0.0012 (expt.) ± 0.0010 (had.) ± 0.0032 (theo.). 相似文献
18.
P. Abreu W. Adam E. Agasi I. Ajinenko R. Aleksan G. D. Alekseev P. P. Allport S. Almehed F. M. L. Almeida S. J. Alvsvaag et al. 《Zeitschrift fur Physik C Particles and Fields》1995,66(3):341-354
The forward-backward asymmetries for the processes
and
at theZ resonance are measured using identifiedD
*± mesons. In 905,000 selected hadronic events, taken in 1991 and 1992 with the DEL-PHI detector at LEP, 4757D
*+D
0+ decays are reconstructed. Thec andb quark forward-backward asymmetries are determined to be:
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