Showing papers by "Jie Zhang published in 1997"

A study of tau decays involving eta and omega mesons

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).

Studies of QCD in e(+)e(-)->hadrons at E(cm)=130 and 136 GeV

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.

Production of orbitally excited charm mesons in semileptonic B decays

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.

Fertility, Growth, and Public Investments in Children

Abstract: In this paper, it is shown how subsidies for education and for the number of children affect economic growth, fertility, and welfare in an endogenous growth model with altruistic agents. Subsidizing education has not only a direct positive effect on growth but also an indirect positive effect on growth through reducing fertility. After some finite periods, future generations will gain in welfare in the education-subsidy regime. In contrast, subsidizing the number of children increases fertility, depresses growth, and reduces all generations' welfare.

Government Debt, Human Capital, and Endogenous Growth

Abstract: The effect of government debt on capital accumulation has been debated for more than a century. The debate has focused on the validity of the Ricardian equivalence hypothesis which asserts that the mix of government debt and nondistorting taxes to finance government expenditures has no real effect on an economy. In models with infinitely-lived agents, government bonds increase private assets by the full amount that offsets the rise in future tax liabilities for interest payments and the retirement of public debt. Even in a model with finitely-lived agents, Barro [1] showed that government debt is neutral when private intergenerational transfers are positive and when the rate of growth is lower than the interest rate. With operative intergenerational transfers, Carmichael [4] extended the debt neutrality into a regime where the rate of growth is greater than the interest rate while suggesting some sources of nonneutrality of public debt such as heterogeneous tastes and uncertainty. Moreover, Drazen [6] argued that when intergenerational transfers take the form of investments in human capital which have higher marginal returns than investments in physical capital, government bonds affect the equilibrium solution and increase welfare. In contrast, assuming that private intergenerational transfers are zero, van der Ploeg and Alogoskoufis [10] argued that an increase in government debt depresses real growth through reducing savings in an endogenous growth, overlapping-generations model.' With constant population, the models mentioned above ignore possible responses of fertility to changes in government debt. In an overlapping-generations model with operative bequests, Becker and Barro [3] showed that the neutrality of social security needs modification if fertility is endogenous. Lapan and Enders [9] extended the insight of Becker and Barro [3] to examine the effects of government debt and found that a rise in government debt reduces fertility and raises capital intensity through increasing bequests which are part of the cost of having children. Wildasin [11] also obtained similar results. While endogenizing fertility, none of these models has endogenous growth of per capita income.

Improved measurement of the $B^0_d$--$\overline{B}^0_d$ Oscillation frequency

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 $\Delta m_d = 0.436\pm 0.033\, {\rm ps}^{-1}$

Synthesis of BaKBiO superconductor at 260°C by direct precipitation from KOH melts

Abstract: Ba K Bi O superconductor was synthesized at a temperature as low as 260°C by direct precipitation from KOH melts. Oxidizers were added into the melts for oxidation of active elements. The resulting Ba K Bi O material with Tc=31.5K was characterized by using XPS, XRD and magnetic method.

Fluorescence Properties of BDD Molecules Doped in Si-Ti Binary Oxide Systems by the Sol-Gel Method

Abstract: The characteristics of the fluorescence spectra of 2,5-bis(4-diethyl-aminophenyl)-1,3,4-oxadiazole(BDD) doped in Si-Ti binary oxides by the sol-gel method were investigated as a function of time in...

Inclusive production of neutral pions in hadronic Z decays

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).

Search for the decay τ-→4π-3π+(π0)ντ

Abstract: A search for the decay of the τ lepton to five charged and two neutral pions is performed using data collected by the BABAR detector at the PEP-II asymmetric-energy e^+e^- collider. The analysis uses 232 fb^(-1) of data at center-of-mass energies on or near the Υ(4S) resonance. We observe 10 events with an expected background of 6.5_(-1.4)^(+2.0) events. In the absence of a signal, we set the limit on the branching ratio B(τ-→3π^-2π^+2π^0ν_τ)<3.4×10^(-6) at the 90% confidence level. This is a significant improvement over the previously established limit. In addition, we search for the decay mode τ-→2ωπ-ν_τ. We observe 1 event with an expected background of 0.4+1.0/-0.4 events and calculate the upper limit B(τ-→2ωπ-ν_τ)<5.4×10^(-7) at the 90% confidence level. This is the first upper limit for this mode.

Electrochemical syntheses of BaKBiO crystals in hot alkaline solution and water rich melts

Abstract: Non-superconducting and superconducting Ba K Bi O crystals were synthesized electrochemically from hot aqueous solution and water rich melts over a range of temperatures (80–210°C). The resulting Ba K Bi O crystals were characterized by using XPS, XRD and magnetic method.

Preparation and magnetic measurements of BaKPbO and BaKMPbO (M = Tl, Sb) crystals

Abstract: BaKPbO(BKPO) single crystals and BaKMPbO(BKMPO,M= Tl, Sb) crystals were prepared by the molten salt electrochemical method. The resulting BKPO and BKMPO samples were characterized by magnetic susceptibility measurements. We suggested that the superconductivity observed in several BKPO and BKMPO samples is not due to BKPO or BKMPO phase itself, but may be due to the impurity BaKBiO(BKBO) or BaKBiPbO(BKBPO) phase.

A comparative study of intravenous accelerated streptokinase dose regimen with conventional dose regimen for coronary thrombolysis.

Abstract: The aim of this study is to test the patency rate and safety of the accelerated streptokinase dose regimen for coronary thrombolysis compared with the conventional one One hundred and four patients entering three hospitals up to 12 hours after the onset of definite acute myocardial infarction were randomizely treated with intravenous accelerated streptokinase dose regimen (15 million units/30 min) (group A, 47 cases) and conventional dose regimen (15 million units/60 min) (group B, 57 casese) The reperfusion rate of infarct-related arteries determined by clinical evidence of reperfusion was 766% (36/47) in group A VS 614% (35/57) in group B There was significant difference in reperfusion rates among patients within 6 hours after the onset of chest pain: 879% (29/33) in group A VS 674 (29/43) in group B (P < 005) The incidence of mild bleeding, allergic reaction, hypotension was 128% (6/47), 43% (2/47), 128 (6/47) respectively in group A vs 211 (12/57), 35 (2/57), 175% (10/57) respectively in group B Compared to conventional dose regimen, intravenous accelerated streptokinase dose regimen for coronary thrombolysis seems to improve reperfusion rate markedly without increasing adverse events such as bleeding, allergic reaction and hypotension It suggests that accelerated streptokinase therapy deserves more extensive investigation

Measurement of the tau lepton lifetime with the three-dimensional impact parameter method

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 .

Transverse momentum correlations in hadronic Z decays

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.