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Showing papers by "Yang Gao published in 1997"


Journal ArticleDOI
TL;DR: In this paper, the spectral functions of the dominant two-and four-pion tau decay channels are compared to published results of ece-annihilation experiments via isospin rotation.
Abstract: A measurement of the spectral functions of non-strange tau vector current final states is presented, using 124 358 tau pairs recorded by the ALEPH detector at LEP during the years 1991 to 1994. The spectral functions of the dominant two-and four-pion tau decay channels are compared to published results of ece-annihilation experiments via isospin rotation. A combined fit of the pion form factor from tau decays and e(+)e(-)data is performed using different parameaizations. The mass and the width of the rho(+/-)(770) and the p(0)(770) are separately determined in order to extract possible isospin violating effects. The mass and width differences are measured to be M

133 citations


Journal ArticleDOI
D. Buskulic1, I. De Bonis1, D. Decamp1, Philippe Ghez1  +400 moreInstitutions (25)
TL;DR: In this article, the 132 pbt -1 of data collected by ALEPH from 1991 to 1994 have been used to analyze η and ω production in τ decays and the following branching fractions have been measured:
Abstract: The 132 pbt - 1 of data collected by ALEPH from 1991 to 1994 have been used to analyze η and ω production in τ decays. The following branching fractions have been measured: \(B\left( {{\tau ^ - } \to { u _\tau }\omega {h^ - }} \right) = \left( {1.91 \pm 0.07 \pm 0.06} \right) \times {10^{ - 2}},\)\(B\left( {{\tau ^ - } \to { u _\tau }\omega {h^ - }{\pi ^0}} \right) = \left( {4.3 \pm 0.6 \pm 0.5} \right) \times {10^{ - 3}},\)\(B\left( {{\tau ^ - } \to { u _\tau }\eta {K^ - }} \right) = \left( {2.9_{ - 1.2}^{ + 1.3} \pm 0.7} \right) \times {10^{ - 4}},\)\(B\left( {{\tau ^ - } \to { u _\tau }\eta {h^ - }{\pi ^0}} \right) = \left( {1.8 \pm 0.4 \pm 0.2} \right) \times {10^{ - 3}}\) and the 95% C.L. limit B(τ− → ντηπt -) < 6.2 × 10t - 4 has been obtained. The ωπt- and ηπt -π0 rates and dynamics are found in agreement with the predictions made from e+e∼ - annihilation data with the help of isospin invariance (CVC).

54 citations


Journal ArticleDOI
D. Buskulic, H.Y. Kim1, A. S. Thompson2, Giuseppe Zito  +401 moreInstitutions (33)
TL;DR: In this paper, an analysis of the properties of hadronic final states produced in electron-positron annihilation at center-of-mass energies of 130 and 136 GeV is presented.
Abstract: An analysis of the properties of hadronic final states produced in electron-positron annihilation at centre-of-mass energies of 130 and 136 GeV is presented. The measurements are based on a data sample of 5.7 pb(-1) collected in November 1995 with the ALEPH detector at LEP. Inclusive charged particle distributions, jet rates and event-shape distributions are measured and the results are compared with the predictions of QCD-based models. From the measured distributions quantities are determined for which the dependence on the centre-of-mass energy can be predicted by QCD, including the mean multiplicity of charged particles, the peak position of the inclusive distribution of xi = - 1nx(p) (x(p) = p/p(beam)), and the strong coupling constant alpha(s). The QCD predictions are tested by comparing with corresponding measurements at E(cm) = 91.2 GeV and at lower energies.

52 citations


Journal ArticleDOI
D. Buskulic1, I. De Bonis1, D. Decamp1, Philippe Ghez1  +396 moreInstitutions (27)
TL;DR: In this paper, two samples of exclusive semileptonic decays, 579 events and 261 events, were selected from approximately 3.9 million hadronic Z decays collected by the ALEPH detector at LEP.

46 citations


Journal ArticleDOI
R. Barate1, D. Buskulic1, D. Decamp1, Philippe Ghez1  +396 moreInstitutions (26)
TL;DR: In this paper, the LEP 1 data sample was updated using a lifetime tag and a tag based on the b c hadron mass difference was used to reconstruct the event primary vertex.

37 citations


Journal ArticleDOI
R. Barate1, D. Buskulic1, D. Decamp1, Philippe Ghez1  +395 moreInstitutions (26)
TL;DR: A measurement of Rb using five mutually exclusive hemisphere tags has been performed by ALEPH using the full LEP1 statistics as discussed by the authors, which is in agreement with the electroweak theory prediction of 0.2158 ± 0.0003.

36 citations


Journal ArticleDOI
R. Barate, D Buskulic, D Decamp, P Ghez  +404 moreInstitutions (32)
TL;DR: In this paper, a measurement of the color factor ratios C-A/C-F and T-F/C -F and the strong coupling constant = C-F alpha(s), (M-Z)/(2 pi) was performed by fitting theoretical predictions simultaneously to the measured differential two-jet rate and angular distributions in four-jet events.
Abstract: Using data collected from 1992 to 1995 with the ALEPH detector at LEP, a measurement of the colour factor ratios C-A/C-F and T-F/C-F and the strong coupling constant = C-F alpha(s), (M-Z)/(2 pi) has been performed by fitting theoretical predictions simultaneously to the measured differential two-jet rate and angular distributions in four-jet events. The result is found to be in excellent agreement with QCD.C-A/C-F = 2.20 +/- 0.09 (stat) +/- 0.13 (syst),T-F/C-F = 0.29 +/- 0.05 (stat) +/- 0.06 (syst).Fixing C-A/C-F and T-F/C-F to the QCD values permits a determination of alpha(s) (M-Z) and n(f), the number of active flavours. With this measurement the existence of a gluino with mass below 6.3 GeV/c(2) is excluded at 95% confidence level.

36 citations


Journal ArticleDOI
R. Barate1, D. Buskulic1, D. Decamp1, Philippe Ghez1  +390 moreInstitutions (25)
TL;DR: In this paper, the LEP centre-of-mass energy was raised to 161 GeV and pair production of W bosons in e+e− collisions was observed for the first time by LEP experiments, where an integrated luminosity of 11 pb−1 was recorded in the ALEPH detector, in which WW candidate events were observed.

35 citations


Journal ArticleDOI
D. Buskulic, I. De Bonis, D. Decamp, P. Ghez  +406 moreInstitutions (30)
TL;DR: In this paper, a sample of 3.6 million hadronic Z decays recorded between 1991 and 1995 with the ALEPH detector at LEP is used to investigate semileptonic decays of B mesons into final states involving orbitally excited charm mesons.
Abstract: A sample of 3.6 million hadronic Z decays recorded between 1991 and 1995 with the ALEPH detector at LEP is used to investigate semileptonic decays of B mesons into final states involving orbitally excited charm mesons. Topological vertex criteria are used to search for decays involving narrow D$^{**}$ states as well as wide D$^{**}$ resonances and non-resonant D$^{(*)}\pi$ final states. The sum of the branching ratios for these processes is measured to be \begin{eqnarray*} \lefteqn{{\mathrm{Br}}({\overline {\mathrm{B}}} \to {\mathrm{D}}\pi\ell^-\overline u) +{\mathrm{Br}}({\overline {\mathrm{B}}} \to {\mathrm{D}}^*\pi\ell^-\overline u)}\\ & & = (2.26\pm 0.29(\mathrm{stat}) \pm 0.33(\mathrm{syst}))\%, \end{eqnarray*} which accounts for a significant fraction of the deficit between inclusive measurements and the sum of exclusive semileptonic B decay modes.

31 citations


Journal ArticleDOI
R. Barate1, D. Buskulic1, D. Decamp1, Philippe Ghez1  +390 moreInstitutions (25)
TL;DR: In this article, the reaction e(+)e(-) --> HZ is used to search for the Standard Model Higgs boson, the data sample consists of integrated luminosities of 10.9 pb(-1), 1.1 pb (-1), and 9.5 pb(1) collected by the ALEPH experiment at LEP during 1996, at centre-of-mass energies of 161, 170 and 172 GeV, respectively.

31 citations


Journal ArticleDOI
R. Barate, D Buskulic, D Decamp, P Ghez  +387 moreInstitutions (22)
TL;DR: In this paper, a search for pair-production of long-lived, heavy, singly-charged particles has been performed with data collected by the ALEPH detector at a centre-of-mass energy of 172 GeV.

Journal ArticleDOI
R. Barate, D. Buskulic, D. Decamp, P. Ghez  +390 moreInstitutions (25)
TL;DR: In this paper, the process e(+)e(-) --> hA is used to search for the Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM), in the b (b) over bar b(b), over bar and tau(+)tau(-)b(b)over bar final states, and no candidate events are found in either of the final states.

Journal ArticleDOI
R. Barate1, D Buskulic1, D Decamp1, P Ghez1  +390 moreInstitutions (25)
TL;DR: In this paper, the ALEPH detector at LEP has been used to search for scalar top and bottom quarks with data collected by the LEP detector, and a limit of 67 GeV/c 2 has been set on the scalar quark mass, independent of the mixing angle between the supersymmetric partners of the left and right-handed states of the top quark.

Journal ArticleDOI
R. Barate1, D. Buskulic1, D. Decamp1, Philippe Ghez1  +394 moreInstitutions (26)
TL;DR: In this article, a new measurement of the mean lifetime of the tau lepton is presented and three different analysis methods are applied to a sample of 90000 tau pairs, collected in 1993 and 1994 with the ALEPH detector at LEP.

Journal ArticleDOI
R. Barate1, D. Buskulic1, D. Decamp1, Philippe Ghez1  +394 moreInstitutions (26)
TL;DR: In this paper, a search for the B c meson decaying into the channels J ψπ + and Jπl + ν l (l = e or μ ) is performed in a sample of 3.9 million hadronic Z decays collected by the ALEPH detector.

Journal ArticleDOI
D. Buskulic, I. De Bonis, D. Decamp, P. Ghez  +398 moreInstitutions (1)
TL;DR: In this paper, the ALEPH experiment at LEP was used to measure the time dependence of the decaying $b$ quark and its decay time using three techniques, two of which are updates of previous measurements, and the third method uses a lepton in each hemisphere.
Abstract: The time dependence of $B^0_d--\bar{B}^0_d$ oscillations is measured by the ALEPH experiment at LEP, using three techniques, two of which are updates of previous measurements. In all cases the charge of the decaying $b$ quark and its decay time are measured in one hemisphere of the event the quark charge at production is tagged mainly using the opposite hemisphere. The first method uses the charge correlation between a $D^{*-}$ and a lepton in the opposite hemisphere; if no lepton is present, the produced quark charge is determined from the hemisphere charges. In the second method, the decay time is measured using a lepton in one hemisphere and the initial state is inferred from the opposite-hemisphere jet charge. The third method uses a lepton in each hemisphere. The data used were collected from 1991 to 1994. The combined result is $\Delta m_d = 0.436\pm 0.033\, {\rm ps}^{-1}$

Journal ArticleDOI
R. Barate1, D. Buskulic1, D. Decamp1, Philippe Ghez1  +394 moreInstitutions (26)
TL;DR: In this paper, the branching fraction for D0 → K−π+ was measured with statistics collected by ALEPH from 1991 to 1994, based on the comparison between the reconstructed D ∗+ → D 0 π +, D 0 → K −π+ decay chain and the rate for inclusive soft pion production at low transverse momentum with respect to the nearest jet.


Journal ArticleDOI
R. Barate1, D. Buskulic1, D. Decamp1, Philippe Ghez1  +386 moreInstitutions (25)
TL;DR: In this paper, the ALEPH experiment at LEP at center-of-mass energies of 161 GeV and 172 GeV were analysed to search for sleptons, the supersymmetric partners of leptons.

Journal ArticleDOI
R. Barate1, D. Buskulic1, D. Decamp1, Philippe Ghez1  +388 moreInstitutions (26)
TL;DR: In this paper, the total cross section and the forward-backward asymmetry for the process e+e− → μ+μ−(nγ) are measured in the energy range 20 −136 GeV by reconstructing the effective centre-of-mass energy after initial state radiation.

Journal ArticleDOI
R. Barate1, D. Buskulic1, D. Decamp1, Philippe Ghez1  +391 moreInstitutions (25)
TL;DR: In this article, the e+e−→W+W− cross section is measured in a data sample collected by ALEPH at a mean centre-of-mass energy of 172.09 GeV, corresponding to an integrated luminosity of 10.65 pb−1.

Journal ArticleDOI
R. Barate, D. Buskulic, D. Decamp, P. Ghez  +393 moreInstitutions (27)
TL;DR: In this paper, a measurement of the transverse-transverse and transverse normal τ spin correlations in the decay Z → τ+τ−, CTT and CTN, is presented based on the aplanarity angle of the decay products of both τ leptons.

Journal ArticleDOI
R. Barate, D. Buskulic, D. Decamp, P. Ghez  +405 moreInstitutions (31)
TL;DR: In this paper, a measurement of the inclusive production of pi0 mesons in hadronic Z decays is presented and compared to Monte Carlo model predictions, based on approximately 2 million hadronic events recorded with the ALEPH detector at LEP at a centre-of-mass energy of sqrt(s) = 91.2 GeV.
Abstract: A measurement of the inclusive production of pi0 mesons in hadronic Z decays is presented and compared to Monte Carlo model predictions. The analysis is based on approximately 2 million hadronic events recorded with the ALEPH detector at LEP at a centre-of-mass energy of sqrt(s) = 91.2 GeV. Neutral pions are reconstructed using photons from conversion pairs and photons measured in the electromagnetic calorimeter. The inclusive pi0 momentum spectrum is measured in the range from 0.025 < x(p) = p/p(beam) < 1 to be 4.80 +/- 0.07(stat) +/- 0.31(sys). The differential inclusive pi0 cross section has also been measured as a function of transverse momentum with respect to the event plane (p_T^in and p_T^out_T).


Journal ArticleDOI
R. Barate, D. Buskulic, D. Decamp, P. Ghez  +388 moreInstitutions (31)
TL;DR: The 3DIP method as discussed by the authors relies on the three-dimensional information from a double-sided vertex detector and on kinematic constraints for the precise measurement of the lepton decay angles.
Abstract: A new method is presented for the measurement of the mean $\tau$ lepton lifetime using events in which $\tau$'s are pair-produced and both $\tau$'s decay to hadrons and $ u_\tau$. Based on the correlation between the two $\tau$'s produced at a symmetric $e^+ e^-$ collider, the 3DIP method relies on the three-dimensional information from a double-sided vertex detector and on kinematic constraints for the precise measurement of the $\tau$ decay angles. Using the data collected from 1992 to 1994 with the ALEPH detector at LEP, a $\tau$ lifetime of $288.0 \pm 3.1 \pm 1.3 $\fs is obtained from the sample in which both $\tau$'s decay to one charged track, and $292.8 \pm 5.6 \pm 3.0 $\fs from the sample in which one $\tau$ decays to one prong and the other to three prongs. The results show small statistical correlations with those derived from other methods. When combined with the previously published ALEPH measurements, the resulting $\tau$ lifetime is $291.2 \pm 2.0 \pm 1.2 $\fs .

Journal ArticleDOI
D. Buskulic, I Debonis, D. Decamp, P. Ghez  +410 moreInstitutions (33)
TL;DR: In this article, a measure based on transverse momentum is shown to exhibit a correlation between the two halves of a hadronic event which cannot be explained by energy-momentum conservation, flavour conservation, the imposition of an event axis or imperfect event reconstruction.
Abstract: Using data obtained with the ALEPH detector at the Z resonance, a measure based on transverse momentum is shown to exhibit a correlation between the two halves of a hadronic event which cannot be explained by energy-momentum conservation, flavour conservation, the imposition of an event axis or imperfect event reconstruction. Two possible explanations based on Monte Carlo models are examined: a) ARIADNE, with the correlation forming early in the parton shower and with the transition from partons to hadrons playing only a minor part; b) JETSET, with the correlation forming at the fragmentation stage. A correlation technique based on a jet cluster analysis is used to make a comparison of the models with the data. It is concluded that both non-perturbative and perturbative effects make important contributions to the observed correlation.