100 research outputs found
Bose-Einstein correlations in the hadronic decays of the Z0
No full textBose-Einstein correlations between pairs of like-sign charged particles produced in e+e- annihilations near the Z0 peak have been studied using data taken with the DELPHI detector at LEP. An enhancement is found in the production of pairs of identical pions of similar momenta, with respect to a reference sample. Under the hypothesis that the pions are emitted by a spherically symmetrical source with gaussian density, the data indicate a radius of the source of r = 0.62 +/- 0.04(stat.) +/- 0.20(syst.) fm. The large systematic uncertainty reflects the sensitivity of r to the choice of the reference sample
A MEASUREMENT OF B-MESON PRODUCTION AND LIFETIME USING DL- EVENTS IN Z(0) DECAYS
No full textA study of B meson decays into D l- X final states is presented. In these events, neutral and charged D mesons originate predominantly from B+ and B0 decays, respectively. The dilution of this correlation due to D** production has been taken into account. From 263700 hadronic Z0 decays collected in 1991 with the DELPHI detector at the LEP collider, 92 D0 --> K- pi+, 35 D+ --> K- pi+ pi+ and 61 D*+ --> D0 pi+ followed by D0 --> K- pi+ or D0 --> K- pi+ pi+ pi-, are found with an associated lepton of the same charge as the kaon. From the D0 l- and D*+ l-, the probability f(d) that a b quark hadronizes into a B- (or B0BAR),meson is found to be 0.44 +/-0.08 +/-0.09, corresponding to a total (B(s) + LAMBDA(b)) hadronization fraction of 0.12(-0.12)+0.24 .By reconstructing the energy of each B meson, the b quark fragmentation is directly measured for the first time. The mean value of the B meson energy fraction is: [X(E)(B)] = 0.695+/-0.015(stat.)+/-0.029(syst.) Reconstructing D-lepton vertices, the following B life-times are measured: tau(B) = 1.27(-0.18)+0.22(stat.)+/-0.15(syst.) ps, where bBAR --> D0 l- X, tau(B) = 1.18(-0.27)+0.39(stat.)+/-0.15(syst.) ps, where BBAR --> D+ l- X, T(B) = 1.19(-0.19)+0.25(stat.)+/-0.15(syst.) ps where BBAR --> D*+ l- X, and an average tau(B) = 1.23(-0.13)+0.14(stat.)+/-0.15(syst.) ps is found. Allowing for decays into D** l- vBAR, the B+ and B0 lifetimes are: tau(B+)= 1.30(0.29)+0.33(stat.)+/-0.15(syst. exp.) +/-0.05(syst. D**) ps, tau(B0)= 1.17(-0.23)+0.29(stat.)+/-0.15(syst. exp.) +/-0.05 (syst. D**) ps, tau(B+)/tau(B0) = 1.11(0.39)+0.51(stat.)+/-0.05(syst. exp.) +/-0.10(syst. D**) ps
MEASUREMENT OF THE AVERAGE LIFETIME OF B-HADRONS
No full textThe average lifetime of B hadrons produced in hadronic Z0 decays has been measured with the DELPHI detector at LEP. The measurement is based on the analysis of the impact parameter distribution of high p(t) muons and hadrons. The resulting mean B lifetimes are tau(B) = (1.30 +/- 0.10 +/- 0.08) ps and tau(B) = (1.27 +/- 0.04 +/- 0.12) ps respectively, giving a combined value of tau(B) = (1.28 +/- 0.10) ps. The hadronic sample was also used to measure the partial Z0 width GAMMA(bbBAR)/GAMMA(h) and gave a value of 0.222(-0.031)+0.033 +/- 0.017
MEASUREMENT OF THE TRIPLE-GLUON VERTEX FROM 4-JET EVENTS AT LEP
No full textFrom the combined data of 1990 and 1991 of the DELPHI experiment at LEP, 13057 4-jet events are obtained and used for determining the contribution of the triple-gluon vertex. The relevant variables are the generalized Nachtmann Reiter angle theta(NR)* and the opening angle of the two least energetic jets. A fit to their two-dimensional distribution yields C(A)/C(F)=2.12+/-0.35 and N(C)/N(A)=0.46+/-0.19, where C(A)/C(F) is the ratio of the coupling strength of the triple-gluon vertex to that of gluon bremsstrahlung from quarks, and N(C)/N(A), the ratio of the number of quark colours to the number of gluons. This constitutes a convincing model-independent proof of the existence of the triple-gluon vertex, since its contribution is directly proportional to C(A)/C(F). The results are in agreement with the values expected from QCD: C(A)/C(F)=2.25, and N(C)/N(A)=3/8
FIRST EVIDENCE OF HARD SCATTERING PROCESSES IN SINGLE TAGGED GAMMA-GAMMA-COLLISIONS
No full textFor the first time, multihadronic production from single tagged gamma gamma collisions has been studied, where one of the scattered leptons was tagged at very low virtual photon absolute mass squared ([Q(2)] = 0.06 (GeV/c(2))(2)). Data collected during 1991 and 1992 in the DELPHI experiment at LEP are shown to agree well with predictions which included the non-perturbative vector meson dominance model in which the interacting photons are assumed to have converted into a vector meson (rho, omega or pi), a quark-parton model which describes direct photon interactions and a QCD-based model which considers the photon to have quark and gluon structure functions. Five different parametrizations of these structure functions were used and the predictions compared with the data. This study confirms recent results from no-tag experiments in requiring a QCD-based component to successfully describe the data, indicating that the photon has a significant partonic content
MEASUREMENT OF THE PARTIAL WIDTH OF THE Z0 INTO B(B)OVER-BAR FINAL-STATES USING THEIR SEMILEPTONIC DECAYS
No full textThe spectra of prompt electrons and muons from the semi-leptonic decays of heavy hadrons produced in Z0 decays have been used to measure the coupling of the Z0 to b quarks weighted by the B hadrons mean semi-leptonic branching fraction, giving a value: BR(sl)b*GAMMA(bbBAR)/GAMMA(H)=0.0221+/-0.0015. The data has also been used to measure the value of the fragmentation parameter, defined in the context of the LUND PS Model, version 7.2, giving: epsilon(b)=(8(+5/-3)+/-2) 10(-3). The corresponding value of the mean fraction of the beam energy taken by a B hadron in the fragmentation of a b quark is: X(E)bBAR=0.69(+0.02/-0.03)+/-0.01. If the values of GAMMA(bbBAR) and GAMMA(H) are taken from the Standard Model, the following value is obtained for the mean semi-leptonic braching fraction of B hadrons: BR(sl)b=(10.1+/-0.7)%. Taking the value of GAMMA(bbBAR)/GAMMA(H) from an independent analysis of DELPHI data based on the use of the boosted sphericity product, a value: BR(sl)b=(10.1+/-1.3)% is obtained
PRODUCTION CHARACTERISTICS OF K-0 AND LIGHT MESON RESONANCES IN HADRONIC DECAYS OF THE Z(0)
No full textAn analysis of inclusive production of KO and the meson resonances K*(+/-)(892), rho(0)(770), f(0)(975) and f(2)(1270) in hadronic decays of the Z(0) is presented, based on about 973,000 multihadronic events collected by the DELPHI detector at LEP during 1991 and 1992. Overall multiplicities have been determined as 1.962 +/- 0.060 K-0 mesons, 0.712 +/- 0.067 K*(+/-)(892) and 1.21 +/- 0.15 rho(0)(770) per hadronic Z(0) decay. The average multiplicities of f(0)(975) for scaled momentum, x(p) = p/p(beam), in the range 0.05 less than or equal to x(p) less than or equal to 0.6 and of f(2)(1270) for 0.05 less than or equal to x(p) less than or equal to 1.0 are 0.098 +/- 0.016 and 0.170 +/- 0.043 respectively. The f(0)(975) and rho(0)(770) x(p)-spectra have p similar shapes. The f(2)(1270)/rho(0)(770) ratio increases with x(p). The average multiplicities and the differential cross sections are compared with the JETSET Parton Shower model. The model with default parameters fails to reproduce the experimental K-0 momentum spectrum at low momentum, describes the K*(+/-)(892) and rho(0)(770) x(p)-spectrum shapes, but significantly overestimates their production rates
The reaction e+ e- ---> gamma gamma (gamma) at Z0 energies
No full textThe total and differential cross-sections for the reaction e+e- → γγ(γ) are measured at centre of mass energies around 91 GeV using an integrated luminosity of 4.7 pb-1. The aggreement with QED prediction is good. Consequently there is no evidence for non-standard channels which would have the same experimental signature. The lower limits on the QED cuttoff parameters are Λ+ > 113 GeV and Λ- > 95 GeV. An upper limit on the effective coupling between a possible excited electron and the gamma is derived. At 95% confidence level the branching ratios for Z0 decay into π0γ, ηψ and γγγ are below 1.5 × 10-4, 2.8 × 10-4 and 1.4 × 10-4 respectively.0info:eu-repo/semantics/publishe
A Precision measurement of the average lifetime of B hadrons
No full textThe average lifetime of B 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 for B hadrons of {Mathematical expression} The second method was based on a new technique, which used inclusively reconstructed secondary vertices to measure {Mathematical expression} Taking into account both the statistical and systematic corelations, the results of these two methods were combined to give an average lifetime for B hadrons of {Mathematical expression} © 1994 Springer-Verlag
Search for pair produced heavy scalars in Z0 decays
No full textA search for charged Higgs bosons decaying into quarks is described, based on statistics of around 1.7 million hadronic Zo decays detected in DELPHI. Despite the very high background from standard hadronic decays of the Zo, masses in the range up to 43.5 GeV/c2 are excluded at the 95% confidence level. After combination with a search for leptonic decays, this mass limit is extended to cover all branching ratios. A similar analysis sets new limits on the possible production of any pair-produced heavy scalar decaying into a pair of jets, such as neutral Higgs bosons in a two doublet scheme and diquarks. © 1994 Springer-Verlag.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe
- …
