Measurement of triple gauge boson couplings from W $^+$ W $^-$ production at LEP energies up to 189 GeVal., G. Abbiendi et
doi: 10.1007/s100520100597pmid: N/A
Abstract. A measurement of triple gauge boson couplings is presented, based on W-pair data recorded by the OPAL detector at LEP during 1998 at a centre-of-mass energy of 189 GeV with an integrated luminosity of 183 pb\(^{-1}\). After combining with our previous measurements at centre-of-mass energies of 161–183 GeV we obtain \(\kappa=0.97_{-0.16}^{+0.20}\), \(g^{\mathrm{z}}_1=0.991^{+0.060}_{-0.057}\) and \(\lambda=-0.110_{-0.055}^{+0.058}\), where the errors include both statistical and systematic uncertainties and each coupling is determined by setting the other two couplings to their Standard Model values. These results are consistent with the Standard Model expectations.
Study of dimuon production in photon-photon collisions and measurement of QED photon structure functions at LEPal., P. Abreu et
doi: 10.1007/s100520100592pmid: N/A
Abstract. Muon pair production in the process \(e^+e^-\to e^+e^-\mu^+\mu^-\) is studied using the data taken at LEP1 (\(\sqrt{s}\simeq m_Z\)) with the DELPHI detector during the years 1992-1995. The corresponding integrated luminosity is 138.5 pb\(^{-1}\). The QED predictions have been tested over the whole \(Q^2\) range accessible at LEP1 (from several GeV\(^2/c^4\) to several hundred GeV\(^2/c^4\)) by comparing experimental distributions with distributions resulting from Monte Carlo simulations using various generators. Selected events are used to extract the leptonic photon structure function \(F_2^\gamma\). Azimuthal correlations are used to obtain information on additional structure functions, \(F_A^\gamma\) and \(F_B^\gamma\), which originate from interference terms of the scattering amplitudes. The measured ratios \(F_A^\gamma/F_2^\gamma\) and \(F_B^\gamma/F_2^\gamma\) are significantly different from zero and consistent with QED predictions.
Search for sleptons in ${\mathrm e}^+{\mathrm e}^- $ collisions at $\sqrt{s} = $ 183 to 189 GeVal., P. Abreu et
doi: 10.1007/s100520100595pmid: N/A
Abstract. Data taken by the DELPHI experiment at centre-of-mass energies of 183 GeV and 189 GeV with a total integrated luminosity of 212 pb\(^{-1}\) have been used to search for the supersymmetric partners of the electrons, muons, and taus in the context of the Minimal Supersymmetric Standard Model (MSSM). The decay topologies searched for were the direct decay (\({\mathrm {\tilde \ell}}\rightarrow\ell{\mathrm{\tilde \chi_1^0}}\)), producing acoplanar lepton pairs plus missing energy, and the cascade decay (\({\mathrm {\tilde \ell}} \rightarrow \ell{\mathrm{\tilde \chi_2^0}}\rightarrow \ell\gamma{\mathrm{\tilde \chi_1^0}}\)), producing acoplanar lepton and photon pairs plus missing energy. The observed number of events is in agreement with Standard Model predictions. The 95% CL excluded mass limits for selectrons, smuons and staus are \(m_{\tilde e} \le 87 \mathrm{GeV}/c^2, m_{\tilde{\mu}} \le 80 \mathrm{GeV}/c^2\) and \(m_{\tilde{\tau}} \le 75 \mathrm{GeV}/c^2\), respectively, for values of \(\mu=-200 \mathrm{GeV}/c^2\) and tan\(\beta\)=1.5.
High sensitivity 2 $\beta $ decay study of $^{116}$ Cd and $^{100}$ Mo with the BOREXINO counting test facility (CAMEO project)Bellini, G.;Caccianiga, B.;Chen, M.;Danevich, F.A.;Giammarchi, M.G.;Kobychev, V.V.;Kropivyansky, B.N.;Meroni, E.;Miramonti, L.;Nikolayko, A.S.;Oberauer, L.;Ponkratenko, O.A.;Tretyak, V.I.;Zdesenko, S.Yu.;Zdesenko, Yu.G.
doi: 10.1007/s100520100594pmid: N/A
Abstract. The unique features (super-low background and large sensitive volume) of the CTF and BOREXINO set ups are used in the CAMEO project for a high sensitivity study of \(^{100}\)Mo and \(^{116}\)Cd neutrinoless 2\(\beta \) decay. Pilot measurements with \(^{116}\)Cd and Monte Carlo simulations show that the sensitivity of the CAMEO experiment (in terms of the half-life limit for \( 0\nu 2\beta \) decay) is \(\approx 4\times 10^{24}\) yr with a 1 kg source of \(^{100}\)Mo and \(\approx 10^{26}\) yr with \(\approx \)100 kg of enriched \( ^{116}\)CdWO\(_4\) crystals placed in the liquid scintillator of the CTF. The last value corresponds to a limit on the neutrino mass of \(m_\nu \leq 0.06\) eV. Similarly with 1000 kg of \(^{116}\)CdWO\(_4\) crystals located in the BOREXINO apparatus the neutrino mass limit can be pushed down to \(m_\nu \leq 0.02\) eV.
The heavy neutral Higgs signature in the $\gamma \gamma \to Z Z $ processGounaris, G.J.;Porfyriadis, P.I.;Renard, F.M.
doi: 10.1007/s100520100589pmid: N/A
Abstract. If the standard model (SM) Higgs particle is sufficiently heavy, then its contribution to \(\gamma \gamma \to Z Z\) should be largely imaginary, interfering with the also predominantly imaginary SM “background” generated by the W loop. For standard model Higgs masses in the region \(200\lesssim m_H \lesssim 500\) GeV, this interference is found to be constructive and increasing the Higgs signal. In the minimal SUSY case an interference effect should also appear for the contribution of the heavier CP-even neutral Higgs boson \(H^0\), provided it is sufficiently heavy. The effect is somewhat reduced, though, by the smallness of the \(H^0\) width and the \(\gamma\gamma\) and ZZ branching ratios. The interference is again found to be constructive for part of the parameter space corresponding to sfermion masses at the TeV scale and maximal stop mixing. For both the SM and the SUSY case, regions of the parameter space exist, though, where the interference may be destructive. It is therefore essential to take these effects into account when searching for possible scalar Higgs-like candidates. To this aim, we present the complete analytic expressions for both resonance and background amplitudes.
On the determination of the polarized sea distributions of the nucleonGlück, M.;Hartl, A.;Reya, E.
doi: 10.1007/s100520100576pmid: N/A
Abstract. The possibilities to determine the flavor structure of the polarized sea (antiquark) distributions of the nucleon via vector boson \((\gamma^*, W^{\pm}, Z^0)\) production at high energy polarized hadron–hadron colliders, such as the Relativistic Heavy–Ion Collider (RHIC), are studied in detail. In particular the perturbative stability of the expected asymmetries in two representative models for the (un)broken flavor structure are investigated by confronting perturbative QCD leading order predictions of the expected asymmetries with their next–to–leading order counterparts.
Charge and transition form factors of light mesons in LFQMHwang, C.-W.
doi: 10.1007/s100520100584pmid: N/A
Abstract. The charge and transition form factors of pions (\(F_\pi\), \(F_{\pi\gamma}\), and \(F_{\pi\gamma^*}\)) are studied in the light-front quark model (LFQM). We find that our results for \(F_\pi\) and \(F_{\pi\gamma}\) agree well with experiment. Furthermore, the mixing of \(\eta\) and \(\eta'\) is considered. We also calculate \(F_{\eta\gamma}\) and \(F_{\eta'\gamma}\) and compare them with the data.
Quark-confinement mechanism for SU(2) Yang–Mills theory in abelian gaugeSu-Peng, Kou
doi: 10.1007/s100520100557pmid: N/A
Abstract. By dimensional reduction in the sense of Parisi and Sourlas (PS), the gauge fixing term in the abelian gauge of the SU(2) Yang–Mills field is reduced to a two-dimensional O(3) nonlinear \(\sigma \) model. The confinement potential is obtained from magnetic monopoles and frame fluctuations. But the source of quark confinement is frame fluctuations and not magnetic monopoles. Because the frame \(T^a\) cannot be regarded as a fixed one, the abelian projected SU(2) Yang–Mills field turns into a \({\mathrm{U(1)}} \times{\mathrm{U(1)}}\) gauge field – one group element being \(\exp (\mathrm i\varphi ^3T^3)\) with fixed frame \(T^3\), another group gauging the frame \(T^3\). The nonperturbative part \(\varpi _\mu (x) \) becomes a dynamical gauge field in two dimensions, giving rise to the short range linear potential.