Regular Series

Vol. 28 (1997), No. 6, pp. 1271 – 1508

\(W\) Boson Physics at the Fermilab Tevatron

Acta Phys. Pol. B 28, 1271 (1997)

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We present electroweak physics results from the DO and CDF experiments using data from \(p \ barp\) collisions at \(\sqrt {s}= 1.8\) TeV. Measurements of the cross sections times branching ratios for \(W\) and \(Z\) production, the inclusive width of the \(W\) boson and the \(W\) boson mass are presented. Direct tests of the \(WW\gamma \) and \(WWZ\) trilinear gauge boson couplings are also presented based on studies of diboson production.

New Results from the L3 Collaboration

Acta Phys. Pol. B 28, 1287 (1997)

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We report on the measurement of \(W\)-boson pair-production with the L3 detector at LEP at a centre-of-mass energy of 161.34 GeV and preliminary results at 172.13 GeV. In a data sample corresponding to a total luminosity of 11 pb\(^{-1}\) at 161.34 6eV and 10.25 pb\(^{-1}\) at 172.13 GeV, we select four-fermion events with high invariant masses of pairs of hadronic jets or leptons. Experimental results are given for the \(W\)-boson mass, cross sections and anomalous couplings.

New Results from ALEPH in \(e^+e^-\) Annihilations at \(\sqrt {s}=\) 161–172 GeV

Acta Phys. Pol. B 28, 1303 (1997)

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After the energy upgrade of CERN’s LEP electron–positron collider, an integrated luminosity of 22 p\(^{-1}\) has been collected by the ALEPH experiment during the 1996 data taking period, with a centre-of-mass energy of 161 and 172 GeV. With this data, new studies of the standard electroweak theory and of quantum chromodynamics observables are presented and, most notably, precision measurements of \(m_W\) are obtained from the first observation of \(W\) pair decays. No evidence of Higgs boson production, nor any signal of supersymmetry or other new physics has been found in the data so that limits are derived, in the framework of the SM and of its minimal supersymmetric extension. The anomalous four jet production excess that was reported at lower centre-of-mass energies of 130–436 GeV is partially confirmed with the new data, though the origin of such excess in not yet well understood and necessitates further studies. All the presented ALEPH results are preliminary and subject to modifications.

Recent LEP2 Results from OPAL

Acta Phys. Pol. B 28, 1327 (1997)

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In 1996, after another set of upgrades, LEP began running for the first time at centre-of-mass energies above the \(W\)-pair threshold. This new energy regime offers a wide array of physics topics including tests of the Standard Model at higher energy scales, search physics, and \(W\) physics. We summarize the recent results from OPAL using 9.9 pb\(^{-1}\) of data collected at \(\sqrt {s}=\) 161.3 GeV from June to August 1996.

Standard and Non-Standard Precision Tests of the Standard Model

Acta Phys. Pol. B 28, 1349 (1997)

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The present status of the Standard Model Precision Tests is shortly reviewed.

\(W\)-Mass Reconstruction from Hadronic Events in LEP2: Bose–Einstein Effect

Acta Phys. Pol. B 28, 1363 (1997)

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We discuss several aspects of the \(W\)-pair production and decay into quarks, taking hadronization into account. We touch upon the influence of the so-called Bose–Einstein effect and colour reconnection on the reconstructed mass of the \(W\) boson. The initial-state radiation effect is also revisited. The numerical studies are done using the KORALW Monte Carlo event generator. We find that the Bose–Einstein effect, which we implement using the “weighting method”, has a negligible influence, below 30 MeV, on the reconstruction of the \(W\) mass.

Precise Predictions for the \(W\)-Boson Mass

Acta Phys. Pol. B 28, 1381 (1997)

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Recent results for higher-order corrections to the relation between the vector-boson masses in the Standard Model and Supersymmetry are summarized. In the Standard Model, the Higgs-mass dependence of the two-loop contributions to \(\Delta r\) is studied. Exact results are given for the Higgs-dependent contributions associated with the top quark, i.e. no expansion in the masses has been made. Good agreement is found with the results of the expansion up to next-to-leading order in the top-quark mass. In Supersymmetry, the two-loop QCD corrections to the stop- and sbottom-loop contributions to the \(p\) parameter are presented. The two-loop corrections modify the one-loop contribution by up to 30%: the gluino decouples for large masses. Contrary to the SM case where the QCD corrections are negative and screen the one-loop value, the corresponding corrections in the supersymmetric case are in general positive, increasing the sensitivity in the search for scalar quarks through their virtual effects in high-precision electroweak observables.

In Search of SUSY

Acta Phys. Pol. B 28, 1395 (1997)

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Electroweak precision tests of the SM and MSSM as well as Searches for Supersymmetric Particles and Higgs bosons at LEP II and their significance within the MSSM are discussed.

\(M_W\) and Supersymmetry

Acta Phys. Pol. B 28, 1419 (1997)

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Various aspects of the link between the weak gauge boson masses and supersymmetry are discussed.

Supersymmetric \(W\) Boson Decays as a Means to Search for Charginos and Neutralinos

Acta Phys. Pol. B 28, 1437 (1997)

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If the sneutrino mass is below the chargino mass, the dominant decay mode of the lightest chargino is via a two-body decay channel \(\chi _1^{\pm } \to \bar \nu +l^{\pm }\). Sneutrinos are invisible in \(R\)-parity conserving supersymmetric models and, if the mass gap \(m(\chi _1^{\pm })-m(\bar \nu )\) is sufficiently small, the soft decay lepton may escape detection leading to invisible chargino decays. This “blind spot” of the supersymmetry parameter space would jeopardize the chargino search at LEP2. We point out that such a scenario can be tested by searching for single \(W\) events in \(e^+e^- \to W^+W^-\), with one \(W\) boson decaying to visible leptons or quark jets, and the second \(W\) boson decaying to invisible charginos and neutralinos.

\(W\) Production at LEP2

Acta Phys. Pol. B 28, 1445 (1997)

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We present some analyses for \(W\) physics at LEP2 regarding \(W\) mass measurement in fully hadronic and semileptonic channels. We also analyze distributions for measuring possible anomalous gauge couplings. We finally discuss some possible uncertainties and open problems.

Physics of the \(W\) Boson at Future Linear Colliders

Acta Phys. Pol. B 28, 1461 (1997)

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A survey is given of the various aspects of \(W\)-boson physics at the next generation of linear colliders. In particular, it is indicated how the \(W\) boson can help us improve our understanding of the mechanism of mass generation and the structure of the non-abelian gauge-boson interactions. Also the topics of radiative corrections and gauge invariance are briefly addressed.

\(W\) Pair Production in \(e^-e^-\) Collisions

Acta Phys. Pol. B 28, 1483 (1997)

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The discovery potential of the \(e^-e^-\) option of a new linear collider is discussed. The standard model processes of \(W^-W^-\), \(W^-Z^0\) and \(Z^0Z^0\) production in \(e^-e^-\) collisions are studied as potential sources of background to ‘new physics’ reactions, in particular, to the \(W^-\) pair production through the lepton number violating reaction \(e^-e^- \to W^-W^-\). The possibility of probing anomalous quartic vector boson couplings in \(e^-e^-\) collisions with highly polarized beams is demonstrated.

QCD Structure of \(W\) Boson and Electron Structure Function

Acta Phys. Pol. B 28, 1493 (1997)

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The QCD structure of the \(W\) boson is constructed and compared with that of the photon. A new concept of the electron structure function is also defined. The leading order splitting functions of electron into quarks are extracted, showing an important contribution from \(\gamma -Z\) interference. Leading logarithmic QCD evolution equations are constructed and solved in the asymptotic region where log\(^2\) behaviour of the parton densities is observed. Possible applications with clear manifestation of ‘resolved’ photon and weak bosons are discussed.


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