Showing papers by "German Martinez published in 1996"
TL;DR: In this article, the authors studied hadronic events produced at LEP at center-of-mass energies of 130 and 136 GeV and compared the predictions of several Monte Carlo models and analytic QCD calculations.
Abstract: We have studied hadronic events produced at LEP at centre-of-mass energies of 130 and 136 GeV. Distributions of event shape observables, jet rates, momentum spectra and multiplicities are presented and compared to the predictions of several Monte Carlo models and analytic QCD calculations. From fits of event shape and jet rate distributions to\({\mathcal{O}}(\alpha _s^2 ) + NLLA\) QCD calculations, we determineαs(133 GeV)=0.110±0.005(stat.)±0.009(syst.). We measure the mean charged particle multiplicity 〈nch〉=23.40±0.45(stat.) ±0.47(syst.) and the position ζ0 of the peak in the ζp = ln(1/xp) distribution ζ0=3.94±0.05(stat.)±0.11(syst.). These results are compared to lower energy data and to analytic QCD or Monte Carlo predictions for their energy evolution.
85 citations
36 citations
TL;DR: In this article, the production of weakly decaying charmed hadrons was measured by summing the partial contributions from each of these states and the partial width for Z0 decays into a c-bar c pair.
Abstract: Measurements of the production of the weakly decaying charmed hadrons: D0, D+, Ds+ andΛc+ in both\(Z^0 \to c\bar c\) and\(Z^0 \to b\bar b\) events are reported. By summing the partial contributions from each of these states we measure the partial width for Z0 decays into a\(c\bar c\) pair as:
$$\frac{{\Gamma _{c\bar c} }}{{\Gamma _{had} }} = 0.167 \pm 0.011(stat) \pm 0.011(sys) \pm 0.005(br)$$
where the errors are statistical, systematic and due to the uncertainties in the charmed hadron branching ratios, respectively. The relative production rates for the formation of the charmed hadrons from primaryc quarks is found to be in good agreement with continuum e+e− data at √s≈10 GeV.
35 citations
TL;DR: In this paper, the first observation of W boson pair production at a centre-of-mass energy s =161 GeV in the OPAL detector at LEP is described, where a total of 28 events have been selected for an integrated luminosity of 9.89±0.06 pb −1.
33 citations
TL;DR: In this article, the first direct test of those calculations is presented, showing that the results are only weakly dependent on a jet finding algorithm, which is in general agreement with the prediction of a recent analytic calculation which incorporates energy conservation into the parton shower branching processes, but is considerably smaller than analytic predictions which do not incorporate energy conservation.
32 citations
TL;DR: In this paper, a search for charginos and neutralinos, predicted by supersymmetric theories, has been performed using a data sample of 2.6 pb−1 at a centre-of-mass energy of S=130 GeV and 2.1 pb −1 at 136 GeV collected with the OPAL detector at LEP during November 1995.
29 citations
TL;DR: In this article, the authors measured the spin composition of Λ Λ, ΛΛ, Λ ǫ and Λǫ pairs at low invariant mass values with the OPAL detector at LEP.
27 citations
TL;DR: In this article, the Bose-Einstein correlations between like charged track pairs have been studied using a sample of approximately 3.6 million multihadronic Z0 decays collected with the OPAL detector at LEP.
Abstract: Bose-Einstein correlations between like charged track pairs have been studied using a sample of approximately 3.6 million multihadronic Z0 decays collected with the OPAL detector at LEP. The radius of the emitting sourceR and the chaoticity parameterλ were studied using two parametrisations, the Goldhaber (G) parametrisation and the one-dimensional Kopylov-Podgoretskii (KP) parametrisation. The radiiR
G andR
KP are found to increase linearly with the average observed charged multiplicityn
ch
, with changes with respect to a unit increase inn
ch
of
$$\begin{gathered} \frac{1}{{\langle R_G \rangle }}\frac{{\Delta R_G }}{{\Delta n_{ch} }} = (3.6 \pm 0.6) \cdot 10^{ - 3} and \hfill \\ \frac{1}{{\langle R_{KP} \rangle }}\frac{{\Delta R_{KP} }}{{\Delta n_{ch} }} = (3.4 \pm 1.0) \cdot 10^{ - 3} . \hfill \\ \end{gathered} $$
where the 〈R〉 are the radius values measured in the inclusive event sample. The chaoticity parametersλ
G andλ
KP decrease with increasing charged multiplicity. It is shown that the increase ofR with multiplicity may be connected with differences between two- and three-jet events.
26 citations
TL;DR: In this article, a new measurement of the τ lifetime is presented, which uses data collected with the Opal detector during 1994, which almost doubled the size of the OPAL τ sample.
25 citations
24 citations
TL;DR: In this paper, a search for scalar particles and neutralinos such as those predicted by supersymmetric models has been performed using a data sample of 4.4 million hadronic Z 0 decays recorded by the OPAL detector at the e + e − collider LEP.
TL;DR: In this paper, the authors measured the cross-sections and leptonic forward-backward asymmetries of hadronic and lepton events with different energy levels at the OPAL detector at LEP.
Journal Article•
TL;DR: In this article, the first observation of W boson pair production at a centre-of-mass energy root s = 161.3 GeV in the OPAL detector at LEP is described.
TL;DR: The radiative channel of pion-nucleon interaction, involving subthreshold pions produced in the nuclear medium, dominates all other processes considered for the production of the very energetic photons.
Abstract: We report on the first measurement in heavy-ion collisions of hard photons of extremely high energies that extend the photon spectrum to 5 times the beam energy per nucleon. The photon spectrum was measured for the systems {sup 86}Kr+{sup nat}Ni at 60 {ital A} MeV and {sup 181}Ta+{sup 197}Au at 40 {ital A} MeV. The data are interpreted using the Dubna cascade model. The radiative channel of pion-nucleon interaction {pi}+{ital N}{r_arrow}{ital N}+{gamma}, involving subthreshold pions produced in the nuclear medium, dominates all other processes considered for the production of the very energetic photons. This channel was never considered so far at beam energies below the pion threshold. {copyright} {ital 1996 The American Physical Society.}
TL;DR: The 95% C.L.L lower limit on the lightest chargino mass in the Minimal Supersymmetric Standard Model is 78.5 GeV if the universal scalar mass m0 is greater than 1 TeV, and 62.0 GeV for the smallest m0 compatible with slepton and sneutrino mass limits obtained at centre of mass energies near the Z peak as mentioned in this paper.
TL;DR: In this paper, the authors measured cross-sections and angular distributions for the production of events with single and multiple photons from data recorded with the OPAL detector at the recently upgraded LEP collider.
TL;DR: In this article, a search was described to detect charged Higgs bosons via the process Z0 → H+H−, using data collected by the OPAL detector at LEP which correspond to an integrated luminosity of approximately 110 pb−1.
TL;DR: In this paper, the authors presented evidence for the production of prompt J/psi mesons in hadronic Z(0) decays using a sample of 36 million hadronic events, and 24 candidates were identified from their decays into e(+)e(-) and mu(+)mu(-) pairs.
TL;DR: In this article, the authors used a sample of 3.7 million hadronic events and identified eight Y candidates from their decays into e+e− and μ+μ− pairs.
TL;DR: In this paper, the OPAL detector data collected during 1990-1994 were used to measure the time dependence of mixing and a sample of 348 D*± candidates with a lepton in the opposite hemisphere were reconstructed, of which 167±25 are expected to be from B d 0 decays.
Abstract: Data collected with the OPAL detector during 1990–1994 are used to measure the time dependence of\(B_d^0 \leftrightarrow \bar B_d^0 \) mixing. A sample of 348 D*± candidates with a lepton in the opposite hemisphere are reconstructed, of which 167±25 are expected to be from B d 0 decays. The B d 0 oscillation frequency is measured to be
$$\Delta m_d = 0.567 \pm 0.089(stat)_{ - 0.023}^{ + 0.029} (syst) ps^{ - 1} .$$
. A previously published analysis ofΔm d using D*± and lepton candidates in the same hemisphere and jet charge is also updated with a larger data sample. From 1200 D*±l∓ candidates, of which 778±84 are expected to be from B d 0 decays, we find a value of:
$$\Delta m_d = 0.539 \pm 0.060(stat) \pm 0.024(syst) ps^{ - 1} .$$
. The combined result of these two analyses is
$$\Delta m_d = 0.548 \pm 0.050(stat)_{ - 0.019}^{ + 0.023} (syst) ps^{ - 1} .$$
.
TL;DR: The scalar top quark can be the lightest charged supersymmetric particle and it can be lighter than the top quarks itself in supersymmymmetric extensions of the Standard Model as mentioned in this paper.
TL;DR: In this article, the production of J/psi mesons in Z(0) decays is studied using 3.6 million hadronic events recorded by the OPAL detector at LEP.
Abstract: The production of J/psi mesons in Z(0) decays is studied using 3.6 million hadronic events recorded by the OPAL detector at LEP. The inclusive Z(0) to J/psi and b-quark to J/psi branching ratios are measured from the total yield of J/psi mesons, identified from their decays into lepton pairs. The J/psi momentum distribution is used to study the fragmentation of b-quarks. The production rate of psi' mesons, identified from their decays into a J/psi and a pi(+)pi(-) pair, is measured as well. The following results are obtained:Br(Z(0)-->J/psi X) = (3.9 +/- 0.2 +/- 0.3). 10(-3) and Br(Z(0)-->psi' X) = (1.6 +/- 0.3 +/- 0.2). 10(-3),where the first error is statistical and the second systematic. Finally the J/psi sample is used to reconstruct exclusive b-hadron decays and calculate the corresponding b-hadron branching ratios and masses.
TL;DR: In this paper, the OPAL detector at LEP was used to search for excited states of charged and neutral leptons, e∗, μ ∗, τ ∗ and ν ∗, in e+e− collisions at s =130.
TL;DR: In this article, the lower bound on the mass of unstable neutral and charged heavy leptons (L0, L±) at the OPAL detector at LEP was established.
TL;DR: In this article, four-fermion contact interaction models were fitted to the OPAL data and lower limits were obtained on the energy scale Λ at the 95% confidence level.
TL;DR: The probability for hard photon production was found to scale linearly with the transferred mass and to depend on the direction of the transfer, thus indicating the relative importance of one- and two-body dissipation in peripheral reactions.
Abstract: Hard photons were measured in coincidence with projectilelike fragments in peripheral reactions of Ar-36 + Tb-159 at E/A = 44 MeV. The probability for hard photon production was found to scale linearly with the transferred mass and to depend on the direction of the transfer, thus indicating the relative importance of one- and two-body dissipation in peripheral reactions.
TL;DR: A measurement of the τ lepton polarization and its forward-backward asymmetry at the Z0 resonance using the OPAL detector is described in this article, based on analyses of τ→ρντ, ττπ(K)ντ and τ→a1ντ.
Abstract: A measurement of theτ lepton polarization and its forward-backward asymmetry at the Z0 resonance using the OPAL detector is described The measurement is based on analyses of τ→ρντ, ττπ(K)ντ,\(\tau \to e\bar
u _e
u _\tau \),\(\tau \to \mu \bar
u _\mu
u _\tau \) andτ→a1ντ decays from a sample of 89075 e+e−→τ+τ− candidates corresponding to an integrated luminosity of 117 pb−1 Assuming that theτ lepton decays according to V-A theory, we measure the averageτ polarization at √s=MZ to be 〈P〉=(−130±09±09)% and theτ polarization forward-backward asymmetry to be ApolFB=(−94±10±04)%, where the first error is statistical and the second systematic These results are consistent with the hypothesis of lepton universality and, when combined, can be expressed as a measurement of sin2θefflept=02334±00012 within the context of the Standard Model
TL;DR: The post-print version of the final paper published in Physics Letters B is available from the link below as discussed by the authors, where the published article is available for a limited period of time.
TL;DR: In this article, the branching ratio of the radiative τ decay τ − → μ − ν μ ν τ γ has been measured using data collected with the OPAL detector at LEP.
TL;DR: The branching ratio of the τ− → e−νeντ decay mode has been measured with the OPAL detector to be (17.78 ± 0.09)% where the first error is statistical and the second is systematic as mentioned in this paper.