Predictions for all processes ee → fermions + γ

The complete matrix elements for e⁺e⁻ → 4 and e⁺e⁻ → 4fγy are calculated in the Electroweak Standard Model for polarized massless fermions. The matrix elements for all final states are reduced to a few compact generic functions. Monte Carlo generators for e⁺e⁻ → 4f and e⁺e⁻ → 4fγ are constructed. We compare different treatments of the finite widths of the electroweak gauge bosons; in particular, we include a scheme with a complex gauge-boson mass that obeys all Ward identities. The detailed discussion of numerical results comprises integrated cross sections as well as photon-energy distributions for all different final states.     

Composite scalars in ee collisions and radiative Z decays

Starting point is the hypothesis that the observed Z→e⁺e⁻γ decays are mediated by a (composite) spin 0 boson X with 40m_X50 GeV. The consequences for e⁺e⁻→e⁺e⁻, e⁺e⁻→γγ and e⁺e⁻→ hadrons at PETRA are explored. PETRA experiments turn out to be sensitive up to masses m_X50 GeV; the best indicator for m_X 48 GeV is the angular distribution of Bhabha scattering.     

Hadronic production by ee collisions at the energy 990 MeV with the Orsay storage ring

Data were taken at the energy 2E = 990 MeV to search for multibody events, with the same large solid angle detector which has been used for the measurement of the , ω andφ production by e⁺e⁻ annilations. Assuming a π⁺π⁻π⁰π⁰ production by the quasi two-body process e⁺e⁻ → → ωπ⁰ we give the correspondi ng cross section σ(e⁺e⁻ → π⁺π⁻π⁰π⁰) = (1.1 ± 0.5) 10⁻³² cm². Since no events with 3 and 4 charged pions have been observed σ(e⁺e⁻ → π⁺π⁻π⁰π⁻) 1.5 × 10⁻³³ cm².     

The decay ω(782)→5π in chiral theory.

The arguments are put forward that the many pion decays ω→2π⁺2π⁻π⁰ and π⁺π⁻3π⁰ provide an ideal test site for testing the predictions of chiral models of the vector meson decays into many pions. Using the approach based on the Weinberg Lagrangian or, in a new language, the Lagrangian of hidden local symmetry added with the term induced by the anomalous Lagrangian of Wess and Zumino, the partial widths of these decays are evaluated, and their excitation curves in e⁺e⁻ annihilation are obtained. The discussed are the perspectives of the experimental study of the decays ω→5π in e⁺e⁻ annihilation and photoproduction.     

A search for neutral heavy leptons

In e⁺e⁻ annihilations at SPEAR we have searched for narrow neutral resonances in the eπ and μπ channels for masses between 0.5 GeV/c² and 1.5 GeV/c². No evidence for such states has been found. Under standard theoretical assumptions for production cross sections and decay branching ratios of heavy leptons a lower limit of 1.2 GeV/c² can be set on the mass.     

Weak and radiative asymmetries

It is shown that the weak amplitude must also be radiatively corrected for a satisfactory analysis of the neutral current in e⁺e⁻→μ⁺μ⁻. Radiative asymmetry can be of possible help in isolating the weak effect provided the symmetric cross section can be measured to 1% accuracy at PEP/PETRA energies.     

A new upper limit for the decay μ→eee

A search for the decay μ⁺→e⁺e⁺e⁻, in which no candidate was found, yields a new upper limit for the branching ratio R_μ→3e<1.6×10⁻¹⁰ (90% confidence). A total of 16 decays were observed, in agreement both in number and momentum distribution with V - A theory.     

Identifying heavy flavours with vertex detectors via unusual decay topologies

Although top-flavoured hadrons decay too quickly to leave detectable tracks, multibranch cascade decays offer distinctive topological signatures with multiple b-, c- and τ-decay vertices emanating from a top decay. These modes are relatively copious for and systems produced at e⁺e⁻ and hadron colliders, and should be recognizable by micro-vertex detectors with impact distance resolutions of order 20 μm or better. Multibranch cascade decay topologies are also relevant to the study of b-quarks and possible heavy quarks, charged leptons and neutrinos of the fourth generation; they occur too in multiple heavy quark production via jet fragmentation or Higgs bremsstrahlung.     

Restrictions on possible early weak gauge boson from petra QED cut-off

Data on μ pair production in the presently accessible e⁺e⁻ energy range put nontrivial restrictions on low mass weak gauge boson properties.     

Supersymmetric left-right model and its tests in linear colliders

We investigate phenomenological implications of a supersymmetric left-right model based on SU(2)_L × SU(2)_R × U(1)_B–L gauge symmetry testable in the next generation linear colliders. We concentrate in particular on the doubly charged SU(2)_R triplet higgsino , which we find very suitable for experimental search. We estimate its production rate in e⁺e⁻, e⁻e⁻, e⁻γ and γγ collisions and consider its subsequent decays. These processes have a clear discovery signature with a very low background from other processes.     

Three-jet event orientation in ee annihilation: new tests of the Standard Model

We discuss the orientation of e⁺e⁻ → q g events in terms of the polar and azimuthal angles of the event plane w.r.t. the electron beam direction. We define an asymmetry of the azimuthal-angle distribution which, along with the left-right forward-backward polar-angle asymmetry, is sensitive to parity-violating effects in three-jet events; these have yet to be explored experimentally. We have evaluated these observables at O(_s) in perturbative QCD and present their dependence on longitudinal beam polarisation and c.m. energy. We also define a moments analysis in terms of the orientation angles that allows a new and more detailed test of QCD by isolating the six independent helicity cross-sections.     

Properties of the proposed τ charged lepton

The anomalous eμ and 2-prong μx events produced in e⁺e⁻ annihilation are used to determine the properties of the proposed τ charged lepton. We find the τ mass is 1.90 ± 0.10 GeV/c²; the mass of the associated neutrino, ν_τ, is less than 0.6 GeV/c² with 95% confidence; V - A coupling is favored over V + A coupling for the τ − ν_τ current; and the leptonic branching ratios are 0.186 ± 0.010 ± 0.028 from the eμ events and 0.175 ± 0.027 ± 0.030 from the μx events where the first error is statistical and the second is systematic.     

Observation of inclusive η production in ee annihilation at CM energies of 34 GeV

The inclusive production of η mesons at CM energies around 34 GeV has been studied for e⁺e⁻ annihilation into hadrons. The average number of η-mesons per event is found to be 0.72 ± 0.10 (stat.) ± 0.18 (syst.). The abundance of η's is studied as a function of event shape parameters and it is compared to the corresponding π⁰ rates.     

Single c- and b-quark production in charm and B-meson ee factories

We examine single c- and b-quark production in e⁺e⁻ collisions with the standard model in charm and B-meson factories working on the ψ and the √ region respectively. Expected inclusive cross sections are estimated at resonant production closely below the threshold for associated open charm and bottom production, and in the nearby continuum.     

Two-component picture of ee inclusive processes

From the hypothesis that the characteristics of hadronic production in e⁺e⁻ are those seen in transverse distributions of hadron-hadron collisions we are led to consider the inclusive distributions in e⁺e⁻ annihilation as composed of two contributions, a cluster component which contains the e⁺e⁻ resonances and a parton component. The decay of the cluster is described by the same production radii as those observed in hadron-hadron collisions. The parton component obeys asymptotically Bjorken scaling and the approach to scaling is set by a mass of 1.2 GeV. Within this picture we give a simple explanation of the energy dependence of the average charged energy and the multiplicity.     

Photino mass and selectron production in unpolarized and polarized ee annihilation

Selectron production in unpolarized e⁺e⁻ collisions is reconsidered for supersymmetric theories with massive photinos. Near threshold the cross section is enhanced by a strong s-wave component enabling, in principle, also the determination of the photino mass. Polarized e⁺e⁻ annihilations into selectron and photino pairs would provide not only an independent and direct measurement of the photino mass but also a clean experimental separation of the two selectrons accompanying the left- and right-handed electron.     

Angular distribution of lepton-pairs and QCD

The recently measured angular distribution of one of the leptons produced in π⁻N → μ⁺μ^-+… is compared with theoretical calculations done in the framework of QCD.     

A search for charged Higgs bosons at tristan

We searched for pair production of charged Higgs bosons via e⁺e⁻ annihilation, using data (23.3 pb⁻) collected by the TOPAZ detector in the energy range . We observed no evidence for charged Higgs pair production and extended the excluded region in the M_H^±---BR (hadron) plane. The 95% CL lower mass limit is the most stringent for BR (hadron) = 0.6, giving m_H^±<22 GeV.     

The Li(K, π)ΣH reaction and narrow Σ states

Small-angle cross sections are calculated for ⁶Li(K⁻, π⁺)_Σ⁶H at 720 MeV/c, in order to intepret the data of the preceding paper. Due to the spin-isospin selectivity of ΣN → ΛN conversion, the substitution 1s_N → 1s_Σ leads to a narrow resonance high in the Σ continuum. Further tests of selectivity with ^3,4He targets are suggested. The energy shifts of Σ states which arise from the spin-isospin dependence of the ΣN interaction are discussed.     

Single and double dissociation in πp collisions at 11 and 16 GeV/c

The reactions π⁻p → 2π⁻π⁺p, π⁻p → 2π⁻π⁺π^op and π⁻p → 2π⁻2π⁺n are analysed at 11 and 16 GeV/c using longitudinal phase space (LPS) plots. The weighted LPS distributions for π⁻p → 2π⁻π⁺p is dominated by two well separated structures corresponding to single diffraction dissociation of the pion, π⁻p → (2π⁻π⁺)p, and of the proton, π⁻p → π⁻(π⁻π⁺p). The former is more abundant than the latter, and both are approximately constant with energy. In contrast, processes of type π⁻p → (2π)(πp) decrease with increasing energy.

In the five-body reactions the weighted LPS distribution reveals especially at 16 GeV/c a maximum for single dissociation of the proton into 3πp, namely π⁻p → π⁻(π⁻π⁺π^op); this process is likely to be diffractive. The neutron channel has a corresponding maximum displaced toward a multiperipheral configuration π⁻p → π⁻(π⁻2π⁺)n. Another strong maximum corresponds to the pion dissociation π⁻p → (2π⁻π⁺π^o)p. This is interpreted to be an ω-exchange process because no analogous structure occurs in π⁻p → (2π⁻2π⁺)n. Finally, a broad structure reveals double dissociation of both incident particles; it occurs in the two channels π⁻p → (2π⁻π⁺)(π^op) and π⁻p → (2π⁻π⁺)(π⁺n), being stronger in the latter. Further analysis of this process in terms of isospin exchange suggests that it is partially diffractive. Factorization is also discussed.

An appendix gives general aspects of the LPS analysis for the asymptotic study of n-body collisions at very high energy.