Showing papers by "Yang Gao published in 1996"
TL;DR: In this article, the polarization of Λ baryons from Z decays with the Aleph apparatus is studied with the first time, and the measured longitudinal Λ polarization is PLΛ = −0.32 ± 0.07 for z = p p beam > 0.3.
80 citations
TL;DR: In this article, a comparison of gluon and mixed-flavoured quark jets with the same energy, 24 GeV, was performed using the ALEPH detector.
52 citations
TL;DR: In this paper, the authors performed searches for supersymmetric particles produced in e+e− collisions at centre-of-mass energies of 130 and 136 GeV in a data sample of 5.7 pb−1 collected in the autumn of 1995 by the ALEPH detector at LEP.
50 citations
15 Feb 1996-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
41 citations
41 citations
TL;DR: In this article, the reaction e + e − → HZ ∗ was used to search for the standard model Higgs boson in the H ν ν and the Hl + l − channels.
40 citations
TL;DR: In this article, the Lambda(b) polarization in hadronic Z decays is measured in semileptonic decays from the average energies of the charged lepton and the neutrino.
34 citations
TL;DR: In this article, a lower limit on the oscillation frequency of the Bs0 B s0 system is obtained from approximately four million hadronic Z decays accumulated using the ALEPH detector at LEP from 1991 to 1995.
28 citations
26 citations
TL;DR: In this article, a complete and consistent set of tau hadronic branching ratios is presented for 18 exclusive modes. And a detailed study of the systematics entering the pi(o) reconstruction is also given.
Abstract: From 64492 selected tau-pair events, produced at the Zeta(o) resonance, the measurement of the tau decays into hadrons from a global analysis using 1991, 1992 and 1993 ALEPH data is presented. Special emphasis is given to the reconstruction of photons and pi(o)'s, and the removal of fake photons. A detailed study of the systematics entering the pi(o) reconstruction is also given. A complete and consistent set of tau hadronic branching ratios is presented for 18 exclusive modes. Most measurements are more precise than the present world average. The new level of precision reached allows a stringent test of tau - mu universality in hadronic decays, g(tau)/g(mu) = 1.0013 +/- 0.0095, and the first measurement of the vector and axial-vector contributions to the non-strange hadronic tau decay width: R(tau,V) = 1.788 +/- 0.025 and R(tau,A) = 1.694 +/- 0.027. The ratio (R(tau,V) - R(tau,A))/(R(tau,V) + R(tau,A)), equal to (2.7 +/- 1.3) %, is a measure of the importance of QCD non-perturbative contributions to the hadronic tau decay width.
26 citations
TL;DR: In this paper, a search for the strange b baryon Ξb with a study of Ξ-lepton correlations was performed with a data sample of approximately four million hadronic Z decays recorded with the ALEPH detector from 1990 to 1995, and the measured product branching ratio is Br(b → Ξ b ) × Br(Ξ b → X c Xl − ν l − Ξ − X′) = (5.4±1.1(stat) ± 0.15(syst) ps.
TL;DR: In this paper, a search for the radiative decay of excited charged leptons, l∗, and for radiative and weak decays of excited electron neutrinos, ν e ∗, was performed, using the 5.8 pb−1 of data collected by ALEPH at 130-140 GeV.
TL;DR: In this article, the four-jet final state is analyzed to search for hadronic decays of pair-produced heavy particles, and the properties of these events are studied and compared to the expectations from standard processes and to pair production hypotheses.
Abstract: The four-jet final state is analyzed to search for hadronic decays of pair-produced heavy particles. The analysis uses the ALEPH data collected at LEP in November 1995 at centre-of-mass energies of 130 and 136 GeV, corresponding to a total integrated luminosity of 5.7 pb(-1). An excess of four-jet events is observed with respect to the standard model predictions. In addition, these events exhibit an enhancement in the sum of the two di-jet masses around 105 GeV/c(2). The properties of these events are studied and compared to the expectations from standard processes and to pair production hypotheses.
TL;DR: In this article, the authors measured the production of charmed particles in Z → b b decays from the yield of D0, D+, Ds+ and Λc+ decays in a sample of q q events with high b purity collected with the ALEPH detector.
TL;DR: In this article, the authors analyzed angular correlations between the two quarks and the gluon in three-jet events and measured the differential two-jet rate, finding no signal of anomalous CP violation.
TL;DR: Hadronic and leptonic cross-sections and forward-backward asymmetries were measured using 5.7 pb−1 of data taken with the ALEPH detector at LEP at centre-of-mass energies of 130 and 136 GeV as discussed by the authors.
TL;DR: In this paper, the production of final states involving one or more energetic photons from e+e− collisions at high energies is studied using data collected by the ALEPH detector at LEP.
TL;DR: In this paper, the branching fractions for tau decays into electrons and muons were measured with emphasis on the study of systematic effects from selection, particle identification and decay classification.
Abstract: A sample of 62249 tau-pair events is selected from data taken with the ALEPH detector in 1991, 1992 and 1993. The measurement of the branching fractions for tau decays into electrons and muons is presented with emphasis on the study of systematic effects from selection, particle identification and decay classification. The results obtained are: B-e=17.79+/-0.12(stat)+/-0.06(syst)(%) and B-mu=17.31+/-0.11(stat)+/-0.05(syst)(%). Combined with the most recent ALEPH determination of the tau lifetime, these results provide a relative measurement of the leptonic couplings in the weak charged current for transverse W bosons: g(mu)/g(e)=1.0002+/-0.0051 and g(tau)/g(mu)=0.9943+/-0.0065.
TL;DR: In this article, a search for pair production of new heavy leptons has been performed assuming different scenarios for the mixing of the new particles with Standard Model lepton, and no candidate events were found in a data sample corresponding to an integrated luminosity of 5.6 pb−1 collected by the ALEPH detector at centre-of-mass energies of 130 and 136 GeV.
TL;DR: In this article, the B 0 - B 0 average mixing parameter χ and b forward-backward asymmetry A FB 0 (b) are measured from a sample of about 4 200 000 Z → qq events recorded with the ALEPH detector at LEP in the years 1990-1995.
TL;DR: An improved measurement of the average b hadron lifetime was performed using a sample of 1.5 million hadronic Z decays, collected during the 1991-1993 runs of ALEPH, with the silicon vertex detector fully operational as mentioned in this paper.
TL;DR: In this article, the average branching ratio of weakly decaying B hadrons (a mixture of B d 0, B s 0 and Λ b weighted by their production cross sections and lifetimes, here denoted B) is measured to be Br (B → h + h − ) = (1.7 −0.3 −0 0.2) × 10 −5.
TL;DR: In this paper, the lifetimes of the B 0 and B + mesons were measured with theAleph detector at LEP, using approximately 3 million hadronic Z decays collected in the period 1991-1994.
Abstract: The lifetimes of theB 0 andB + mesons have been measured with theAleph detector at LEP, using approximately 3 million hadronic Z decays collected in the period 1991–1994. In the first of three methods, semileptonic decays ofB 0 andB + mesons were partially reconstructed by identifying events containing a lepton with an associatedD*− orD¯0 meson. The second method used fully reconstructedB 0 andB + mesons. The third method, used to measure theB 0 lifetime, employed a partial reconstruction technique to identifyB 0→D*− π + X decays. The combined results are τ0=1.55±0.06±0.03ps,τ+=1.58±0.09±0.03ps,τ+τ0=1.03±0.08±0.02.
TL;DR: In this article, the lifetimes of the B0 and B+ mesons were measured with theAleph detector at LEP using approximately 3 million hadronic Z decays collected in the period 1991-1994.
Abstract: The lifetimes of theB0 andB+ mesons have been measured with theAleph detector at LEP, using approximately 3 million hadronic Z decays collected in the period 1991–1994. In the first of three methods, semileptonic decays ofB0 andB+ mesons were partially reconstructed by identifying events containing a lepton with an associatedD*− or\(\bar D^0 \) meson. The second method used fully reconstructedB0 andB+ mesons. The third method, used to measure theB0 lifetime, employed a partial reconstruction technique to identifyB0→D*−π+X decays.
TL;DR: In this article, four Λb baryon candidates are exclusively reconstructed in the Λ b → Λc+π− channel, with the β decaying into pK−π+, p K 0, or Λπ+π+δ−π−.
TL;DR: In this article, indirect limits on the mass of the lightest neutralino were derived from the results of searches for charginos, neutralinos, and sleptons performed with data taken by the ALEPH Collaboration at centre-of-mass energies near the Z peak and at 130 and 136 GeV.
Abstract: Indirect limits on the mass of the lightest neutralino are derived from the results of searches for charginos, neutralinos, and sleptons performed with data taken by the ALEPH Collaboration at centre-of-mass energies near the Z peak and at 130 and 136 GeV. Within the context of the Minimal Supersymmetric Standard Model and when\(M_{\tilde
u } \geqslant 200 GeV/c^2 \), the boundM x > 12.8 GeV/c 2 at the 95% confidence level applies for any tanβ. The impact of lighter sneutrinos is presented in the framework of SUSY grand unified theories; a massless neutralino is allowed only for a narrow range of tanβ,μ, and the scalar mass parameterm 0. Finally, by including Higgs mass constraints and requiring that radiative electroweak symmetry breaking occur, more stringent bounds onM x as a function of tanβ are derived.
TL;DR: In this article, searches for charginos and neutralinos produced in e+e− collisions at center-of-mass energies of 130 and 136 GeV have been performed under the assumptions that R-parity is not conserved, that the dominant Rparity violating coupling involves only leptonic fields, and that the lifetime of the lightest supersymmetric particle can be neglected.
TL;DR: In this paper, four-fermion events have been selected in a data sample of 5.8 pb−1 collected with the aleph detector at centre-of-mass energies of 130 and 136 GeV.
TL;DR: In this paper, the electroweak mixing angle is determined with high precision from measurements of the mean difference between forward and backward hemisphere charges in hadronic decays of the Z with a data sample of 2.5 million hadronic Z decays recorded over the period 1990 to 1994 in the ALEPH detector at LEP.
Abstract: The electroweak mixing angle is determined with high precision from measurements of the mean difference between forward and backward hemisphere charges in hadronic decays of the Z. A data sample of 2.5 million hadronic Z decays recorded over the period 1990 to 1994 in the ALEPH detector at LEP is used. The mean charge separation between event hemispheres containing the original quark and antiquark is measured for\(b\bar b\) and\(c\bar c\) events in subsamples selected by their long lifetimes or using fastD*’s. The corresponding average charge separation for light quarks is measured in an inclusive sample from the anticorrelation between charges of opposite hemispheres and agrees with predictions of hadronisation models with a precision of 2%. It is shown that differences between light quark charge separations and the measured average can be determined using hadronisation models, with systematic uncertainties constrained by measurements of inclusive production of kaons, protons andΛ’s. The separations are used to measure the electroweak mixing angle precisely as sin2ϑweff=0.2322±0.0008(exp.stat.) ±0.0007(exp.syst.)±0.0008(sep.). The first two errors are due to purely experimental sources whereas the third stems from uncertainties in the quark charge separations.