Substructures ate + e − colliders

We review, update and propose tests of a possible substructure of leptons, quarks andW ^±,Z bosons for the next generation ofe ⁺ e ^? colliders. We successively consider the three following domains of physics: at theZ peak, out of theZ peak and in the high energy range.     

Signatures of thes-leptons andW,Z spins in polarized γe collisions

We study the gaugino +s-electron,Wv andZe photoproductions off electrons with both beams polarized. We make a systematic calculation of the spin and angular asymmetries and obtain model independent results, which allow to identify the spin and/or charge of the scalars-leptons and of the electroweak gauge bosons, either in the high energy limit or at the threshold. For example, the photon helicity asymmetries of theW andZ total cross sections have the distinct value 1 at threshold, but it is negative for the reactions γe→spinor + scalar. In the high energy limit, the same asymmetry for the differential cross sections is equal to one for spin zero boson and negative forW andZ photoproductions and Compton scattering.     

The hadronic contribution to theW andZ mass

In the framework of the standard model of weak interactions, we discuss the hadronic contribution in the radiative correction to the masses of theW andZ boson. Predictions including the nonhadronic parts are given.     

Characteristics of leptonic signals forZ boson pairs at hadron colliders

We study the production ofZ boson pairs at hadron colliders followed by their subsequent decay into muons or electrons. We take into account the processes andgg ZZ. The calculation incorporates all effects of the polarization of theZ bosons. Particular emphasis is put on the Higgs-signal where we study the angular distribution of the decay leptons, in order to determine the longitudinal polarisation fraction of theZ bosons. We also study the correlation of the decay planes of the leptons from the twoZ bosons. This correlation may be significant for light Higgs bosons.Supported by LAA, CERN, Geneva     

Production ofW-bosons in high energye + e − ande − p collisions

We study the processe ⁺ e ^?→W+hadrons from theZ ⁰-pole to the threshold region forW-pair production, keeping the widths of theZ ⁰ andW finite. Already slightly below threshold the cross section is strongly depressed. Also the total cross section at theZ ⁰-peak is very small. We present a simple model to account for this. We also give exact results to lowest order for the weak Compton processese ⁺ e ^?→e ⁺ W ^? v _e ande ^? p→pW ^? v _e and compare them with results obtained with the equivalent photon approximation.     

Charged Higgs production at hadron colliders

We study the production and decay of charged Higgs bosons,H ^±, at TEVATRON and SSC energies as a function of the top massm _t and theH ^± massm _H . We give the cross sections for events arising from bothH ^±→τν andtb decays, together with those of the competing background processes. In particular, form _t >m _H we studyH ^± W ^? andW ⁺ W ^? production and thet→bτν decay.     

The muon spectra from decays ofW- andZ-bosons produced ine + e −-collisions

The muon spectra from the decays ofW-andZ-bosons, produced ine ⁺ e ^?→W ⁺ W ^?,e ⁺ e ^?→Zγ,e ⁺ e ^?→ZZ ande ⁺ e ^?→ZH reactions have been obtained (H is the Higgs boson). It has been shown (in terms of Glashow-Weinberg-Salam theory) that the main source of muons are thee ⁺ e ^?→Zγ ande ⁺ e ^?→W ⁺ W ^? processes (over theW-boson production threshold). The contribution of thee ⁺ e ^?→ZZ ande ⁺ e ^?→ZH reactions to the inclusive muon spectra is small. It has been also shown, that it is possible to distinguish contributions of thee ⁺ e ^?→Zγ ande ⁺ e ^?→W ⁺ W ^? reactions if the decay muons move at a small angle to the initial electron momentum.     

Weak boson plus jet production in 2nd-order QCD

We calculate cross sections for the production ofW ⁺ andZ bosons in association with 1 and 2 jets at \(p\bar p\) collider energies. The expected rates for these processes in second-order QCD are presented as a function of the cuts on the transverse momenta of the jets and are compared with jet rates measured by UA1.     

W ± Z 0 signals from the strongly interacting symmetry breaking sector

We study the possibilities of unraveling the underlying dynamics of the symmetry breaking sector through the scattering of longitudinal weak bosons inpp collisions.W ^± Z ⁰ channels are considered in the context of a general approach based on chiral perturbation theory, supplemented by a unitarization procedure. The channels considered here are the relevant ones for symmetry breaking sector dynamics such as technicolor, where aI=J=1 resonance appears in the spectrum. DirectWZ production from quark annihilation viap _tc-W mixing is also considered and compared withWZ production from theWZ fusion mechanism.     

Phenomenology of composite colored weak bosons

In composite models of quarks, leptons and weak bosons whereW-constituents are colored objects, color octet partners ofW ^± andZ ⁰ are predicted. We study in detail the phenomenology of these particles. Independent of the specific model one expects a color octet isotriplet of vector bosons (W ₈ ^± ,Z ₈ ⁰ ) with mass in the range of 100–200 GeV, and a color octet isosinglet vector bosonV ₈ ⁰ with substantially larger mass, due to mixing with the gluon. Moreover, relatively light color octet excitations of the leptons appear, while the existence of “color exotic” partners of the quarks is model dependent. These particles decay mainly into a lepton (quark) and a gluon. We construct the couplings ofW ₈ ^± ,Z ₈ ⁰ andV ₈ ⁰ to ordinary and “color exotic” fermions. The signals of color octet weak bosons in low energy weak reactions are explored in detail. The production cross section ofW ₈ ^± (Z ₈ ⁰ ) in hadron-hadron collisions is calculated for \(0.54TeV \leqq \sqrt s \leqq 20TeV\) . Various decay modes of colored weak bosons are studied. The most prominent decay signatures ofW ₈ ^± andZ ₈ ⁰ are events of the type (l ^+-: charged lepton;j: hadronic jet; : missing transverse momentum). The present CERN \(p\bar p\) collider data on such events are discussed in the light ofW ₈ ^± andZ ₈ ⁰ decays. If colored weak bosons are not found with a mass less than ～250 GeV composite model building will be strongly restricted.     

Searching for supersymmetry at LEP/LHC

For theep collider at LEP/LHC, we study the production and the signal coming from sleptons and squarks for several processes. We show how the supersymmetric signal can be extracted from the Standard Model background processes. In particular the large backgrounds due to singleW andZ production are considered. All the results are based on exact calculations of the matrix elements at tree level. Total cross sections and various kinematical distributions are presented.     

Composite weak bosons in neutrino-lepton scattering

We study effects due to a compositeW or/andZ boson in four different leptonic processes where deviations from the standard model (SM) of electroweak unification may be observed. Compositeness is considered through a simple modification of theW andZ gaugeboson propagator, by a form factor depending on a composition scale parameter. We found that all the four processes point out that this type of propagator modification gives an indication of compositeness if Λ≦400 GeV. For Λ>400 GeV, deviation from SM is negligible.     

Anomalously interacting new extra vector bosons and their first LHC constraints

In this review phenomenological consequences of the Standard Model extension by means of new spin-1 chiral fields with the internal quantum numbers of the electroweak Higgs doublets are summarized. The prospects for resonance production and detection of the chiral vector Z* and W*^± bosons at the LHC energies are considered on the basis of quantitative simulations within the CompHEP/CalcHEP package. The Z* boson can be observed as a Breit-Wigner resonance peak in the invariant dilepton mass distributions in the same way as the well-known extra gauge Z?? bosons. However, the Z* bosons have unique signatures in transverse momentum, angular and pseudorapidity distributions of the final leptons, which allow one to distinguish them from other heavy neutral resonances. In 2010, with 40 pb^?1 of the LHC proton-proton data at the energy 7 TeV, the ATLAS detector was used to search for narrow resonances in the invariant mass spectrum of e ⁺ e ^? and ??⁺??^? final states and high-mass charged states decaying to a charged lepton and a neutrino. No statistically significant excess above the Standard Model expectation was observed. The exclusion mass limits of 1.15 and 1.35 TeV/c ² were obtained for the chiral neutral Z* and charged W* bosons, respectively. These are the first direct limits on the W* and Z* boson production. Based on the above, a novel strategy for the chiral boson search in the LHC dijet data is discussed. For almost all currently considered exotic models the relevant signal is expected in the central dijet rapidity region y _1,2 ? 0 and |y ₁ ? y ₂| ? 0. On the contrary, the chiral bosons do not contribute to this region but produce an excess of dijet events far away from it. In particular, for these bosons the appropriate kinematical restrictions lead to a dip in the centrality ratio distribution over the dijet invariant mass instead of a bump expected in the most exotic models.     

Cosmological production of vector bosons and cosmic microwave background radiation

An intensive cosmological production of vector W and Z bosons is considered within a cosmological model that involves a relative scale of measurement. Field-theory models are studied in which cosmic microwave background radiation and baryon matter may appear as products of the decay of such primordial bosons.     

Z boson pair production and compositeness at large hadron colliders

Z boson pair production at LHC and SSC provides an opportunity to study possible effects due to compositeness in a very high energy domain. We discuss several sources of anomalous effects and give the corresponding bounds on the appropriate compositeness scale. The best bounds are obtained for contact interactions implying longitudinal components of theZ's and for the anomalous couplings of three neutral vector bosons.     

Effects of a non-standardW ± magnetic moment inW ± production via deep inelastice −P scattering

We calculate the production of charged bosons in deep inelastice ^?P scattering in the context of an electroweak model in which the vector boson self interactions may be different from those prescribed by the electroweak standard model. We present results which show the dependence of the cross section on the anomalous magnetic dipole moment κ of theW ^±. We find for energies available at HERA that even small deviations from the standard model value of κ imply observable deviations in theW ^± production rates. We also show that the contributions from heavy boson exchange diagrams are very important.     

Deep inelastic production of charged vector bosons at HERA energies

We discuss the production of gauge bosons in polarized and unpolarized deep inelastice P-scattering in the context of the standard modelSU(3)×SU(2)×U(1) of the strong and electroweak interactions. We present results for the total and the differential cross sections as functions of the parameters of the outgoing lepton for energies available at HERA in the near future. Besides the γ-exchange diagrams we also have included the contributions ofW- andZ-exchange. We find that they cannot be neglected especially for the processe ^? P→v _e W ^? X.     

Spin asymmetries in large-pT production of gauge bosons based on quantum chromodynamics and electroweak gauge model

We make predictions for spin asymmetries in the production of gauge bosons, such as Z⁰, Wsu± and γ, at large p_T from the collision of longitudinally polarized hadrons using QCD perturbation theory and the electroweak gauge model in the framework of a hard scattering model. Asymmetries typically at the 20% and 4% level are predicted for the weak bosons and photon, respectively. Experimental tests should be possible in the near future, e.g., at Fermilab, ISABELLE and colliding SPS.     

Polarization density matrix forZ decay intoWff' with generalZWW couplings

We give the polarization density matrix ofZ andW for the decay processZ ⁰→Wff' with generalZWW couplings. The matrix elements are expressed in terms of kinematical invariants so that they can be readily used in \(p\bar p \to Z^0 W\) as well. Using these formulas, we analyze the possibilities of probing theZWW couplings through the decay of polarizedZ ⁰.     

Same-sign W pair production as a probe of double-parton scattering at the LHC

We study the production of same-sign W boson pairs at the LHC in double parton interactions. Compared with simple factorised double parton distributions (dPDFs), we show that the recently developed dPDFs, GS09, lead to non-trivial kinematic correlations between the W bosons. A numerical study of the prospects for observing this process using same-sign dilepton signatures, including W ^± W ^± jj, diboson and heavy flavour backgrounds, at 14 TeV centre-of-mass energy is then performed. It is shown that a small excess of same-sign dilepton events from double parton scattering over a background dominated by single scattering W ^± Z(γ ^*) production could be observed at the LHC.