共查询到20条相似文献,搜索用时 15 毫秒
1.
P. Abreu et al. 《The European Physical Journal C - Particles and Fields》1999,11(3):383-407
The data collected with the DELPHI detector at centre-of-mass energies between 130 and 172 GeV, during LEP operation in 1995
and 1996, have been used to determine the hadronic and leptonic cross-sections and leptonic forward–backward asymmetries.
In addition, the cross-section ratios and forward–backward asymmetries for flavour-tagged samples of light (uds), c and b
quarks have been measured. No significant deviations from the Standard Model expectations are found. The results are interpreted
by performing S-matrix fits to these data and to the data collected previously at the energies near the resonance peak (88-93 GeV). The results are also interpreted in terms of physics beyond the Standard Model: contact interactions,
R-parity violating SUSY particle exchange and of possible Z bosons.
Received: 9 February 1999 / Published online: 14 October 1999 相似文献
2.
P. Abreu et al. 《The European Physical Journal C - Particles and Fields》2000,14(4):613-631
A precise measurement of the strange quark forward-backward asymmetry used 3.2M multihadronic events around the Z peak collected by the DELPHI experiment from 1992 to 1995. The ring imaging Cherenkov detectors in the barrel and end-cap
regions identify high energy charged kaons which tag the s quark. The s quark asymmetry was measured at different centre-of-mass
energies; in particular at the Z pole
taking the expected d and u quark asymmetries from the Standard Model. The quark flavour fractions are assumed from the Standard
Model and the fragmentation process is modelled by JETSET. From the s quark pole asymmetry the electroweak mixing angle was
determined:
The parity violating coupling of the s quark to the Z was determined to be:
Received: 8 October 1999 / Revised version: 23 February 2000 / Published online: 18 May 2000 相似文献
3.
P. Abreu et al. 《The European Physical Journal C - Particles and Fields》2000,14(4):585-611
The polarisation has been studied with the data collected by the DELPHI detector at LEP in 1993, 1994 and 1995 around the Z resonance firstly through the exclusive
decay channels , , , and and secondly with an inclusive hadronic analysis which benefits from a higher efficiency and a better systematic precision.
The results have been combined with those previously published on 1990 to 1992 DELPHI data, to produce results which reflect
the full LEP-1 statistics. The fit of the polarisation dependence on the production angle yielded the polarisation parameters and . From these results the ratio of the vector and axial-vector effective couplings and have been derived, compatible with e universality. With the assumption of lepton universality, the ratio of vector to axial-vector effective couplings for leptons
was obtained, implying a value of the effective weak mixing angle .
Received: 1 December 1999 / Revised version: 2 February 2000 / Published online: 14 April 2000 相似文献
4.
G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》2001,19(4):587-651
This final analysis of hadronic and leptonic cross-sections and of leptonic forward-backward asymmetries in collisions with the OPAL detector makes use of the full LEP 1 data sample comprising of integrated luminosity and selected Z decays. An interpretation of the data in terms of contributions from pure Z exchange and from Z interference allows the parameters of the Z resonance to be determined in a model-independent way. Our results are in good
agreement with lepton universality and consistent with the vector and axial-vector couplings predicted in the Standard Model.
A fit to the complete dataset yields the fundamental Z resonance parameters: GeV, GeV, nb, , and . Transforming these parameters gives a measurement of the ratio between the decay width into invisible particles and the
width to a single species of charged lepton, . Attributing the entire invisible width to neutrino decays and assuming the Standard Model couplings for neutrinos, this
translates into a measurement of the effective number of light neutrino species, . Interpreting the data within the context of the Standard Model allows the mass of the top quark, GeV, to be determined through its influence on radiative corrections. Alternatively, utilising the direct external measurement
of as an additional constraint leads to a measurement of the strong coupling constant and the mass of the Higgs boson: and GeV.
Received: 1 December 2000 / Published online: 6 April 2001 相似文献
5.
These final results on
production cross-section measurements at LEP2 use data collected by the DELPHI detector at centre-of-mass energies up to 209 GeV. Measurements of total cross-sections, W angular differential distributions and decay branching fractions, and the value of the CKM element |Vcs| are compared to the expectations of the Standard Model. These results supersede all values previously published by DELPHI.Received: 13 November 2003, Revised: 21 January 2004, Published online: 9 March 2004 相似文献
6.
P. Abreu et al. 《The European Physical Journal C - Particles and Fields》1999,10(3):415-442
The partial decay width of the Z to quark pairs has been measured by the DELPHI detector at LEP using data taken in the years 1992 to 1995. Decays of b-hadrons
were tagged by several methods using tracks with large impact parameters and/or reconstructed secondary vertices, complemented
by event shape variables. Combining these methods in a multivariate analysis the value was obtained, where the production fraction was fixed to its Standard Model value.
Received: 18 December 1998 / Revised version: 26 April 1999 / Published online: 3 August 1999 相似文献
7.
The determination of the centre-of-mass energies from the LEP1 data for 1993, 1994 and 1995 is presented. Accurate knowledge
of these energies is crucial in the measurement of the Z resonance parameters. The improved understanding of the LEP energy
behaviour accumulated during the 1995 energy scan is detailed, while the 1993 and 1994 measurements are revised. For 1993
these supersede the previously published values. Additional instrumentation has allowed the detection of an unexpectedly large
energy rise during physics fills. This new effect is accommodated in the modelling of the beam-energy in 1995 and propagated
to the 1993 and 1994 energies. New results are reported on the magnet temperature behaviour which constitutes one of the major
corrections to the average LEP energy. The 1995 energy scan took place in conditions very different from the previous years.
In particular the interaction-point specific corrections to the centre-of-mass energy in 1995 are more complicated than previously:
these arise from the modified radiofrequency-system configuration and from opposite-sign vertical dispersion induced by the
bunch-train mode of LEP operation. Finally an improved evaluation of the LEP centre-of-mass energy spread is presented. This
significantly improves the precision on the Z width.
Received: 25 March 1998 / Revised version: 3 August 1998 / Published online: 29 October 1998 相似文献
8.
Production of events with hadronic and leptonic final states has been measured in collisions at centre-of-mass energies of 130–172 GeV, using the OPAL detector at LEP. Cross-sections and leptonic forward-backward
asymmetries are presented, both including and excluding the dominant production of radiative Z events, and compared to Standard Model expectations. The ratio of the cross-section for production to the hadronic cross-section has been measured. In a model-independent fit to the Z lineshape, the data have
been used to obtain an improved precision on the measurement of -Z interference. The energy dependence of has been investigated. The measurements have also been used to obtain limits on extensions of the Standard Model described
by effective four-fermion contact interactions, to search for -channel contributions from new massive particles and to place limits on gaugino pair production with subsequent decay of
the gaugino into a light gluino and a quark pair.
Received: 30 July 1997 / Published online: 10 March 1998 相似文献
9.
J. Abdallah et al. 《The European Physical Journal C - Particles and Fields》2006,45(2):273-289
The production of single charged and neutral intermediate vector bosons in e + e- collisions has been studied in the data collected by the DELPHI experiment at LEP at centre-of-mass energies between 183
and 209 GeV, corresponding to an integrated luminosity of about 640 pb-1. The measured cross-sections for the reactions, determined in limited kinematic regions, are in agreement with the Standard
Model predictions.
Arrival of the final proofs: 21 November 2005 相似文献
10.
This paper presents DELPHI measurements and interpretations of cross-sections, forward-backward asymmetries, and angular distributions,
for the
process for centre-of-mass energies above the Z resonance, from
-207 GeV at the LEP collider. The measurements are consistent with the predictions of the Standard Model and are used to study
a variety of models including the S-Matrix ansatz for
scattering and several models which include physics beyond the Standard Model: the exchange of Z′ bosons, contact interactions
between fermions, the exchange of gravitons in large extra dimensions and the exchange of
in R-parity violating supersymmetry.
This paper is dedicated to the memory of Alan Segar. 相似文献
11.
Muon pair production in the process is studied using the data taken at LEP1 () with the DELPHI detector during the years 1992-1995. The corresponding integrated luminosity is 138.5 pb. The QED predictions have been tested over the whole range accessible at LEP1 (from several GeV to several hundred GeV) by comparing experimental distributions with distributions resulting from Monte Carlo simulations using various generators.
Selected events are used to extract the leptonic photon structure function . Azimuthal correlations are used to obtain information on additional structure functions, and , which originate from interference terms of the scattering amplitudes. The measured ratios and are significantly different from zero and consistent with QED predictions.
Received: 23 February 2000 / Revised version: 7 December 2000 / Published online: 23 February 2001 相似文献
12.
G. Abbiendi et al. 《The European Physical Journal C - Particles and Fields》2003,26(3):331-344
The process is studied using data collected by the OPAL detector at LEP between the years 1997 and 2000. The data set corresponds to
an integrated luminosity of 672.3 pb-1 at centre-of-mass energies lying between 181 GeV and 209 GeV. Total and differential cross-sections are determined and found
to be in good agreement with the predictions of QED. Fits to the observed angular distributions are used to set limits on
parameters from several models of physics beyond the Standard Model such as cut-off parameters, contact interactions of the
type , gravity in extra spatial dimensions and excited electrons. In events with three photons in the final state the mass spectrum
of photon pairs is investigated. No narrow resonance is found and limits are placed on the product of the production cross-section and branching ratio.
Received: 22 July 2002 / Published online: 8 November 2002 相似文献
13.
《Zeitschrift fur Physik C Particles and Fields》1997,73(2):229-242
Inclusive charged particle and event shape distributions are measured using 321 hadronic events collected with the DELPHI experiment at LEP at effective centre of mass energies of 130 to 136 GeV. These distributions are presented and compared to data at lower energies, in particular to the precise Z data. Fragmentation models describe the observed changes of the distributions well. The energy dependence of the means of the event shape variables can also be described using second order QCD plus power terms. A method independent of fragmentation model corrections is used to determine αs from the energy dependence of the mean thrust and heavy jet mass. It is measured to be: $$←pha _s(133 {? GeV})={0.116}pm {0.007}_{exp-0.004theo}^{+0.005}$$ from the high energy data. 相似文献
14.
P. Abreu et al. 《The European Physical Journal C - Particles and Fields》1999,10(2):219-237
A measurement of the forward–backward asymmetry of and on the Z resonance is performed using about 3.5 million hadronic Z decays collected by the DELPHI detector at LEP in the years 1992 to 1995. The heavy quark is tagged by the exclusive reconstruction
of several D meson decay modes. The forward–backward asymmetries for c andb quarks at the Z resonance are determined to be: The combination of these results leads to an effective electroweak mixing angle of:
Received: 9 February 1999 / Revised version: 26 April 1999 / Published online: 3 August 1999 相似文献
15.
A search for charginos with masses close to the mass of the lightest neutralino is reported, based on the data collected
with the DELPHI detector at LEP from 1995 to 1997 at centre-of-mass energies between 130 and 183 GeV. The signature of a photon
at high transverse momentum radiated from the initial state reduces the two-photon background to acceptable rates, thus making
the mass differences between a few hundred MeV/c and 3 GeV/c detectable. In very nearly degenerate scenarios, the lifetime of the chargino can be large enough to produce either visible
secondary vertices or decays outside the detector; therefore, quasi-stable heavy charged particles and displaced decay vertices
were also searched for. No excess of events with respect to the Standard Model expectations was observed, and limits in the
plane of chargino-neutralino mass difference versus chargino mass are given.
Received: 20 March 1999 / Published online: 8 September 1999 相似文献
16.
The production of single photons has been studied in the reaction at centre-of-mass energies of 183 GeV and 189 GeV. A previously published analysis of events with multi-photon final states
accompanied by missing energy has been updated with 189 GeV data. The data were collected with the DELPHI detector and correspond
to integrated luminosities of about 51 pb and 158 pb at the two energies. The number of light neutrino families is measured to be . The absence of an excess of events beyond that expected from Standard Model processes is used to set limits on new physics
as described by supersymmetric and composite models. A limit on the gravitational scale is also determined.
Received: 28 January 2000 / Revised version: 27 April 2000 / Published online: 26 July 2000 相似文献
17.
DELPHI data collected at centre-of-mass energies up to 208 GeV have been analysed to search for charginos, neutralinos and sfermions in the framework of the Minimal Supersymmetric Standard Model (MSSM) with R-parity conservation. No evidence for a signal was found in any of the channels. The results of each search were used to derive limits on production cross-sections and particle masses. In addition, the combined result of all searches excludes regions in the parameter space of the constrained MSSM, leading to limits on the mass of the Lightest Supersymmetric Particle and other supersymmetric particles.Received: 22 February 2003, Revised: 24 July 2003, Published online: 12 November 2003 相似文献
18.
LEP运行的第一年,OPAL,ALEPH,L3和DELPHI四个实验已收集和分析了不少于五十万个Z°粒子衰变。这些实验的主要目的之一是通过精确测量Z°参数来检验标准模型。本文通过介绍L3实验的结果,说明LEP实验已达到的精度,和标准模型对这些参数的预言与测量值符合的程度。 相似文献
19.
The branching ratios of the decay of the lepton to five charged hadrons have been measured with the OPAL detector at LEP using data collected between 1991 and 1995
at centre-of-mass energies close to the resonance. The branching ratios are measured to be
where the first error is statistical and the second systematic.
Received: 4 June 1998 / Published online: 11 March 1999 相似文献
20.
P. Abreu et al. 《The European Physical Journal C - Particles and Fields》2000,16(2):229-252
This paper describes a measurement of the Michel parameters, , , , , and the average helicity, , in lepton decays together with the first measurement of the tensor coupling in the weak charged current. The pairs were produced at the LEP collider at CERN from 1992 through 1995 in the DELPHI detector. Assuming lepton universality in the decays of the the measured values of the parameters were: , , , , . The strength of the tensor coupling was measured to be . The first error is statistical and the second error is systematic in all cases. The results are consistent with the structure of the weak charged current in decays of the lepton.
Received: 14 February 2000 / Revised version: 7 March / Published online: 8 May 2000 相似文献