Study of Neutral-Current Four-Fermion and ZZ Production in e+e−e^+ e^- Collisions at s\sqrt{s}= 183 GeV

Study of Neutral--Current Four--Fermion and ZZ \\ Production in $\rm e^+ e^-$ Collisions at $\rm \sqrt{s}=$ 183 GeV A study of neutral--current four--fermion processes is performed using a data sample corresponding to 55.3~pb$^{-1}$ of integrated luminosity collected by the L3 detector at LEP at an average centre--of--mass energy of 183~\GeV. The neutral--current four--fermion cross sections for final states with a pair of charged leptons plus jets and with four charged leptons are measured to be consistent with the Standard Model predictions. Events with fermion pair masses close to the Z boson mass are selected in all observable final states and the ZZ production cross section is measured to be %\begin{center} $\rm \sigma_{ZZ} = 0.30 ^{+0.22\,\,+0.07}_{-0.16\,\,-0.03}\,\mathrm{pb},$ %\end{center} in agreement with the Standard Model expectation. No evidence for the existence of anomalous triple gauge boson ZZZ and ZZ$\gamma$ couplings is found and limits on these couplings are set

Heavy Quarkonium Production in Z Decays

We report measurements of the inclusive production of heavy quarkonium states in $\mathrm {Z}$ decays based on the analysis of 3.6 million hadronic events collected by the L3 detector at LEP. The measurement of inclusive J production and an improved $95\%$ confidence level upper limit on $\Upsilon$ production are presented. In addition, two independent measurements of the ratio, $f_{\mathrm{p}}$, of prompt J mesons to those from B decay are made using two different isolation cuts to separate prompt J mesons from J mesons produced in the decays of b hadrons. The results are: % \begin{eqnarray} \mathrm{Br}(\mathrm{Z} \rightarrow \mathrm{J} + \mathrm{X}) & = & (3.21 \pm 0.21 \; \mathrm{(stat.)} \; ^{+ 0.19}_{- 0.28} \; \mathrm{(sys.)} ) \times 10^{-3} \; , \nonumber \\ \mathrm{Br}(\mathrm {Z} \rightarrow \Upsilon(\mathrm{1S} + X) & < & 4.4 \times 10^{-5} \; , \nonumber \\ %% f_{\mathrm{p}} & = & (7.1 \pm 2.1 \; \mathrm{(stat.)} \; \pm 1.2 \; \mathrm{(sys.)} \; ^{+1.5}_{-0.8} \;\mathrm{(theo.)} ) \times 10^{-2} \; . \nonumbe

Inclusive Charm Production in Two-Photon Collisions at LEP

The cross section of charm production in $\mathrm{\gamma \gamma}$ collisions $\mathrm{\sigma (e^+e^- \rightarrow e^+e^-c\bar{c} X)}$ is measured at LEP with the L3 detector at centre of mass energies from 91 GeV to 183 GeV. Charmed hadrons are identified by electrons and muons from semi-leptonic decays. The direct process $\mathrm{\gamma \gamma \rightarrow c \bar{c}}$ is found to be insufficient to describe the data. The measured cross section values and event distributions require contributions from resolved processes, which are sensitive to the gluon density in the photon

Infectious complications in patients receiving ticagrelor or clopidogrel before coronary artery bypass grafting.

The antiplatelet agent ticagrelor has recently been found to have bactericidal activity, demonstrated in vitro and in an in vivo mouse model, which warrants further clinical investigations. The aim of this study was to evaluate infectious complications after coronary artery bypass grafting in patients pre-operatively treated with ticagrelor or clopidogrel. In a multi-centre trial, all adult patients who were pre-operatively treated with ticagrelor or clopidogrel prior to isolated primary coronary artery bypass grafting were eligible. Propensity score matching was used. Outcome measures were any sternal wound infection, deep sternal wound infection, and any in-hospital use of postoperative antibiotics. Of 2311 patients who were included, 1293 (55.9%) received clopidogrel and 1018 (44.1%) ticagrelor pre-operatively. In both overall and propensity score matched analyses, ticagrelor was associated with a similar incidence of infectious complications compared to clopidogrel. Our findings do not support a clinically relevant bactericidal effect of ticagrelor in patients undergoing coronary artery bypass grafting

Search for R-parity Violating Chargino and Neutralino Decays in e+e−e^+ e^- Collisions up to s\sqrt{s}= 183 GeV

A search for chargino and neutralino pair production in $\mathrm{ e^+e^-}$ collisions at center-of-mass energies between 161~\textrm{Ge\kern -0.1em V} and 183~\textrm{Ge\kern -0.1em V} is performed under the assumptions that R-parity is not conserved and that only purely leptonic or hadronic R-parity violating decays are allowed. No signal is found in the data. Limits on the production cross sections, on the Minimal Supersymmetric Standard Model parameters and on the masses of the supersymmetric particles are derived

Search for Scalar Leptons in e+e−e^+ e^- collisions at s\sqrt{s}= 183 GeV

We report the result of a search for scalar leptons in $\mathrm{ e^+ e^-}$ collisions at 183 GeV centre-of-mass energy at LEP. No evidence for such particles is found in a data sample of 55.2 pb$^{-1}$. Improved upper limits are set on the production cross sections for stable as well as unstable scalar leptons. New exclusion contours in the parameter space of the Minimal Supersymmetric Standard Model are derived, as well as new lower limits on scalar lepton masses

Measurement of the cross-section for the process γ∗γ∗→\gamma^* \gamma^* \to hadrons at LEP

Measurements of the two-photon interaction e+e- --> e+e- hadrons at sqrt(s) = 91 GeV and sqrt(s) = 183 GeV are presented. The double-tag events, collected with the L3 detector, correspond to integrated luminosities of 140 pb-1 at 91 GeV and 52 pb-1 at 183 GeV. The cross-section of gamma*gamma* collisions has been measured at = 3.5 GeV^2 and = 14 GeV^2. The data agree well with predictions based on perturbative QCD, while the Quark Parton Model alone is insufficient to describe the data

χc2\chi_{c2} formation in two-photon collisions at LEP

Two-photon formation of the charmonium resonance $\chi_{{\rm c}2}$ has been studied with the L3 detector at LEP. The $\chi_{{\rm c}2}$ is identified through its decay $\chi_{{\rm c}2} \rightarrow \gamma {\rm J}$, with a subsequent decay ${\rm J} \rightarrow {\mathrm{e^+ e^-}}$ or ${\rm J} \rightarrow {\mathrm{\mu^+ \mu^-}}$. With an integrated luminosity of 140 pb$^{-1}$ at $\sqrt{s} \simeq$ 91~\textrm{Ge\kern -0.1em V} and 52 pb$^{-1}$ at $\sqrt{s} \simeq$ {Ge\kern -0.1em V}, we measure the two-photon width of the $\chi_{{\rm c}2}$ to be \begin{center} \Gamma_{\gamma\gamma}(\chi_{{\rm c}2})=1.02 \pm 0.40 \mbox{\;(stat.)} \pm 0.15 \mbox{\;(sys.)} \pm 0.09(\rm{BR.}) {\mathrm{\ ke\kern -0.1em V}}

The Q2^2 evolution of the Hadronic Photon Structure Function F2γF^\gamma_2 at LEP

New measurements at a centre-of-mass energy of 183 GeV of the hadronic photon structure function F2(x) in the Q2 interval, 9 GeV2 < Q2 < 30 GeV2, are presented. The data, collected in 1997, with the L3 detector, correspond to an integrated luminosity of 51.9 pb-1. Combining with the data taken at centre-of-mass energies of 91 GeV, the evolution of F2 with Q2 is measured in the Q2 range from 1.2 GeV2 to 30 GeV2. F2 shows a linear growth with ln(Q2); the value of the slope (alpha-1)dF2(Q2)/dln(Q2) is measured in two x bins from 0.01 to 0.2 and is higher than predictions

Measurement of the e+e−→Z→bb‾e^+ e^- \to Z \to b\overline{b} forward-backward asymmetry and the B0B‾0B^{0}\overline{B}^0 mixing parameter using prompt leptons

The time-integrated $\mathrm{B}^{0}\bar{\mathrm{B}}^{0}$ mixing parameter and the forward-backward charge asymmetry in the process $\mathrm{e}^{+}\mathrm{e}^{-} \rightarrow \mathrm{b}\bar{\mathrm{b}}$ are measured in hadronic \Z events containing prompt muons or electrons, collected by the L3 experiment in the years 1990 to 1995. The total sample of 3.3 million hadronic $\mathrm{Z}$ events with a mean centre-of-mass energy of 91.26 GeV yields: \begin{eqnarray*} \mbox{$A_{\mathrm{FB}}^{\mathrm{b} }$} & = & 0.0960 \pm 0.0066(stat.) \pm 0.0033(sys.) \,, \\ %corel-6 \mbox{$\chi_{\mathrm{b}}$} & = & 0.1192 \pm 0.0068(stat.) \pm 0.0051(sys.) \,. % \end{eqnarray*} %%% %%% %%% %%% This asymmetry measurement together with measurements at energies away from the $\mathrm{Z}$ pole energy yield a pole asymmetry and corresponding effective electroweak mixing angle of: \begin{eqnarray*} \mbox{$A_{\mathrm{FB}}^{0,\mathrm{b}}$} & = & 0.1015 \pm 0.0064(stat.) \pm 0.0035(sys.) \,, \\ %corel-6.nb \mbox{$\sin^{2}\bar{\theta}_{\mathrm{W}}$} & = & 0.2318 \pm 0.0013 \, .\\ %sin2tw-3.nb \end{eqnarray*