Effects of the extra Z-boson in e+e−→W+W− reactions

We calculate the total and differential cross sections for the process e⁺e⁻→W⁺W⁻ including the effects of the extra Z-boson coming from the E₈⊗E₈ superstring. It is pointed out that the observation of the total and differential cross sections can determine the relative sign of the Weinberg angle τ_w and the mixing angle τ_e between Z^'₀ and Z _E.     

Delayed unitary cancellation and heavy particle effects in e+e−→W+W−

We examine one-loop radiative corrections to e⁺e⁻→W⁺W⁻ in the standard model with one Higgs doublet, concentrating on the effects of very heavy fermions. These disturb the delicate unitarity cancellation between s- and t-channel diagrams, raising the cross section even well below the fermion threshold and giving a clear experimental signature for the heavy sector.     

How gluon bremsstrahlung inW-decays distorts the experimental signature ofe + e −→W + W −

The effect of gluon bremsstrahlung in the decays of theW-bosons on the measurement of the reactione ⁺ e ^?→W ⁺ W ^?→ hadrons is discussed. From simulation studies we find a substantial fraction of events with high jet multiplicities. At energies of \(\sqrt s = 200\) GeV this leads to probabilities of 25% or higher to misassign a jet to aW-boson when a realistic resolution of a detector is assumed. Some implications on the measurement of the decay and production properties of theW's are discussed.     

Effective field theory analysis of new physics in e + e −→W + W − at a linear collider

The effective Lagrangian with scalar and vector resonances that might result from new strong physics beyond the SM is formulated and studied. In particular, the scalar resonance representing the recently discovered 125-GeV boson is complemented with the SU(2) _L+R triplet of hypothetical vector resonances. Motivated by experimental and theoretical considerations, the vector resonance is allowed to couple directly to the third quark generation only. The coupling is chiral-dependent and the interaction of the right top quark can differ from that of the right bottom quark. To estimate the applicability range of the effective Lagrangian the unitarity of the gauge boson scattering amplitudes is analyzed. The experimental fits and limits on the free parameters of the vector resonance triplet are investigated.     

Electroweak radiative corrections toe + e −→HZ

The cross section fore ⁺ e ^–HZ with arbitrary lepton andZ-boson polarizations is calculated within the electroweak standard model including the completeO() virtual and soft photonic corrections. These were obtained using the computer-algebra packagesFeynArts andFeynCalc. We list the relevant analytical results and discuss the influence of the weak radiative corrections on the unpolarized as well as the polarized cross sections. For LEP200 energies the weak radiative corrections amount to several per cent. For higher energies the corrections are usually of the same order for the total unpolarized cross section. However, for large values of the Higgs mass or for the suppressed cross section of transversely polarizedZ-bosons they reach +30% and –40%, respectively. The differential cross section in the forward and backward directions gets even larger corrections for high energies, where the box diagrams constitute the dominant part of the radiative corrections.     

There is no equivalence between ϱ′(1250) and inelastic effects in e+e−→π+π−

The analysis of all existing pion form factor data by a model respecting the fundamental principles, including (770), (1250) and (1600) contributions without inelastic effects and depending just on the physical parameters is carried out. The comparison of the obtained results with a previous analysis performed by means of a model with only (770) and (1600) contributions and inelastic effects confirmes the conclusions of Novosibirsk experimental group that the (1250) contribution and inelastic effects in e⁺e^–+– are indistinguishable. However, theoretically predicted behaviours of the P-wave isovector phase shift and the inelasticity from both models and their comparison with existing data unambiguously favour the model with (770), (1600) and inelastic contributions.We are indebted to Dr. D. Krupa who called our attention to the concise (in comparison with our original diagrammatized presentation) and transparent algebraic proof, given in the text by (30)–(33). One of us (A. Z. D.) would like to thank Professor Abdus Salam, the International Atomic Energy Agency and UNESCO for hospitality at the International Centre for Theoretical Physics in Trieste.     

Supersymmetric Box Contributions toe + e −→Z 0 h 0 ande + e −→A 0 h 0

Within the MSSM we calculate the electroweak 1-loop box contributions to the processese ⁺ e ^–Z ⁰ h ⁰ ande ⁺ e ^–Z ⁰ h ⁰. We present detailed results for c.m. energies and as well as for tan =2 and tan =50. The box contributions to the processe ⁺ e ^–Z ⁰ h ⁰ are, depending on and tan , of the order –2 to –20% and toe ⁺ e ^– A ⁰ h ⁰ of 2 to 10%.     

Antiproton-proton annihilation at rest intoπ + π − η ′ andπ + π − η from atomicS andP states

We have measured the branching ratios for \(\bar pp\) annihilation at rest intoπ ⁺ π ^? η andπ ⁺ π ^? η′ in hydrogen gas in two data samples that have different fractions ofS-wave andP-wave initial states. The branching ratios are derived from a comparison with the topological branching ratio for \(\bar pp\) annihilations into four charged pions of (49±4)% and the branching ratio intoπ ⁺ π ^? π ⁺ π ^? π ⁰ of (18.7±1.6)%. We find a significant reduction of the branching ratios fromP-states for \(\bar pp \to \pi ^ + \pi ^ - \eta \) andπ ⁺ π ^? η′ in comparison toS-state annihilation. $$\begin{gathered} BR(S - wave \to \pi ^ + \pi ^ - \eta ) = (13.7 \pm 1.46) \cdot 10^{ - 3} \hfill \\ BR(P - wave \to \pi ^ + \pi ^ - \eta ) = (3.35 \pm 0.84) \cdot 10^{ - 3} \hfill \\ BR(S - wave \to \pi ^ + \pi ^ - \eta ') = (3.46 \pm 0.67) \cdot 10^{ - 3} \hfill \\ BR(P - wave \to \pi ^ + \pi ^ - \eta ') = (0.61 \pm 0.33) \cdot 10^{ - 3} . \hfill \\ \end{gathered} $$ In a partial wave analysis of theπ ⁺ π ^? η Dalitz plot we find the following contributions: Phase space, \(a_2^ + (1320)\pi ^ \mp \) ,ηρ⁰ andf ₂(1270)η: $$\begin{gathered} BR(S - wave \to \pi ^ + \pi ^ - \eta PS) = (6.31 \pm 1.22) \cdot 10^{ - 3} \hfill \\ BR(P - wave \to \pi ^ + \pi ^ - \eta PS) = (0.47 \pm 0.26) \cdot 10^{ - 3} \hfill \\ BR(^1 S_0 \to a_2^ \pm (1320)\pi ^ \mp ) = (2.59 \pm 0.73) \cdot 10^{ - 3} \hfill \\ BR(^3 S_1 \to a_2^ \pm (1320)\pi ^ \mp ) = (1.31 \pm 0.48) \cdot 10^{ - 3} \hfill \\ BR(P - wave \to a_2^ \pm (1320)\pi ^ \mp ) = (1.31 \pm 0.69) \cdot 10^{ - 3} \hfill \\ BR(^3 S_1 \to \rho \eta ) = (3.29 \pm 0.90) \cdot 10^{ - 3} \hfill \\ BR(^1 P_1 \to \rho \eta ) = (0.94 \pm 0.53) \cdot 10^{ - 3} \hfill \\ BR(^1 S_0 \to f_2 (1270)\eta ) = (0.083 \pm 0.086) \cdot 10^{ - 3} \hfill \\ BR(P - wave \to f_2 (1270)\eta ) = (0.64 \pm 0.26) \cdot 10^{ - 3} . \hfill \\ \end{gathered} $$ We find a 2 σ effect for the reaction \(\bar pp \to a_0^ \pm (980)\pi ^ \mp \) , \(a_0^ \pm \to \eta \pi ^ \pm \) , with a branching ratio of (0.13±0.07)·10^?3. For η' production we give a branching ratio of \(\bar pp \to \rho \eta '\) of (1.81±0.44)·10^?3 from³ S ₁. We estmate a contribution of about 0.3·10^?3 for ρη' fromP-states. The ratio of ρη and ρη' rpoduction is used to test the validity of the quark line rule. In theπ ⁺ π ^? π ⁺ π ^? γ final state we do not observe the reaction \(\bar pp \to \pi ^ + \pi ^ - \omega \) , ω→π ⁺ π ^? λ and derive an upper limit of 3·10^?3 for decay modeω→π ⁺ π ^? λ.     

Soft gluon radiation ine + e −→4-jets

The amplitude of a 4-jet process ine ⁺ e ^? annihilation can be used to compute the associated flux of low energy particles due to the emission of soft gluons. I calculate the radiation pattern for the two contributing process, \(e^ + e^ - \to q\bar qgg\) and \(e^ + e^ - \to q\bar qq'\bar q'\) , in a form suitable for comparison with the experimentally observed distribution of inter-jet hadrons. It is found that the dependence of the soft background radiation on the overall colour structure of the jet process can be used to differentiate between the two processes, and thus probe the 3-gluon coupling. I also suggest a suitable initial equation for extending the 4-parton cross-section to higher order gluon emission in a Monte Carlo parton shower algorithm and compare the spectrum so produced with results obtained on the parton level.     

An inclusive approach to scanning e + e −→π+π− cross section below 1 GeV by the radiative-return method

An inclusive approach to measuring e ⁺ e ^?→π⁺π^? cross section by the radiative-return method is discussed. This approach is substantially based on the choice of selection rules that exclude three-pion events and reduce the radiation background in the final state. Radiative corrections in the process with emission in the initial state are calculated for the DAPHNE conditions by treating the cross section form and the kinematics of the radiative process in the quasi-real electron approximation.     

A comparison of\bar pp annihilations into charged particles,e + e −→hadrons ande + e −→Ψ, Γ→hadrons

A comparison of multiplicity distributions and \(\left\langle {P_T^2 } \right\rangle of \bar pp\) annihilation reactions at two energies ande ⁺ e ^?→hadrons leads to a model for \(\bar pp\) annihilation into gluons. The \(\bar pp\) data are consistent with the QCD predictions for the ratio of the moments of the fragmentation functions given for isolated gluon jets. The energy dependence of the ratio of the moments is also consistent with the predictions.     

Comparative study of Z′ searches in e+e− and e−e− scattering

We consider indirect searches for additional neutral vector bosons in e⁺e⁻ and e⁻e⁻ collisions, and compare these two linear collider modes with similar analysis procedures and assumptions. Discovery limits and resolving power are discussed in a model-independent way.     

Loop corrections to the ϱ-parameter; the magnetic moment of the W± and e+e−→W+W−

Vector-boson loop corrections to the ϱ-parameter are considered for vector-boson self-interactions following from global SU(2)_WI broken by electromagnetism. Minimizing the degree of divergence of the ϱ-parameter restricts the free trilinear vector-boson self-couplings to a single one, the anomalous magnetic dipole moment, κ, of the W^+-. The analysis of e⁺e⁻ → W⁺W⁻ shows that this process is well suited for accurately determining this remaining free parameter, κ.     

Determination of the branching ratio ofρ 0→+μ− in the coherent dissociation π−→μ+μ−π− and π−→π+π−π−

In the diffraction dissociation of π^? into μ⁺μ^?π^? on a Cu nucleus at 50 GeV/c, the cross section \(\sigma _{\mu ^ + \mu ^ - \pi ^ - } \) for the 1⁺S(ρ⁰π) wave was measured. The branching ratio of ρ⁰→μ⁺μ^? could be calculated from the ratio of this and the corresponding cross sections in the diffraction dissociation of π^? into π⁺π^?π^?. The obtained value \(BR_{\rho ^0 \to \mu ^ + \mu ^ - } = (4.6 \pm 0.2_{stat^ \pm } \pm 0.2_{syst} )10^{ - 5} \) is in good agreement with the branching ratio \(BR_{\rho ^0 \to e^ + e^ - } \) , as expected ifeμ universality holds.     

Jet masses in e+e− annihilation

We calculate heavy (M _H ² /s) and light (M _L ² /s) jet masses up toO(α _s ² ) in perturbative Quantum Chromodynamics (QCD). The sensitivity of these quantities to radiative corrections, quark masses, fragmentation effects as well as their infrared stability properties, are investigated and compared to those exhibited by other jet measures. A comparison with recent Mark II data is also presented.