Weak effects in e±e± → e±e±

The prediction for the cross section of e^±e^± → e^±e^± is given, assuming one photon and W^o exchange. Pure W^o terms and transverse and longitudinal beam polarizations are included.     

Detailed W0 effects in e+e− → e+e−

The predicted cross section for the reaction e⁺e^?→e⁺e^? is presented assuming one photon and W⁰ exchange. Pure W⁰ terms and the W⁰ width are included.     

One-loop corrections to e+e− → e+e− in the weinberg model

Radiative corrections to Bhabha scattering are calculated in the simplest example of non-Abelian gauge theories. A detailed analysis of the higher-order effects is presented and the total differential cross section including weak corrections is evaluated at different angles in an energy range up to 70 GeV per beam. The effects of weak interactions appear to be negligible up to the production of the neutral vector boson.     

QED to lowest order ine + e −→e + e −γγγ

We calculate the cross-section for the production ofe ⁺ e ^?γγγ ine ⁺ e ^? annihilation. The results are in agreement with the first observation of such a process by the ASP experiment at SLAC. The calculation also provides another example of the power of ‘spinor techniques’ in calculating Feynman amplitudes.     

(e, 2e) spectroscopy

We present a detailed treatment of the theoretical and experimental aspects of the symmetric (e, 2e) reaction in atoms, molecules and solids. Two experimental arrangements are described for measuring angular correlations and separation energy spectra. the one arrangement employing coplanar and the other noncoplanar symmetric kinematics. The latter arrangement is shown to be particularly suitable for extracting structure information. The basic approximation, the factorized distorted-wave off-shell impulse approximation with fully distorted waves, is shown to correctly describe the reaction in some test cases, as does the phase distortion approximation. At energies of the order of 1200 eV the simple eikonal and plane wave approximations adequately describe the valence shell cross sections for light atoms and molecules containing first row elements. Energy independent structure information is obtained on: (a) shapes and magnitudes of the square of the momentum space wave functions for individual electron orbitals; (b) separation energies for individual ion eigenstates; (c) the characteristic orbital of each state; and (d) spectroscopic factors describing the probability that an eigenstate contains the principal configuration of a hole in the characteristic orbital for each eigenstate. Comparison is made with photoelectron spectroscopy and Compton scattering, since they separately yield some of the information obtained by the (e, 2e) method. A brief summary is given of other electron-electron coincidence experiments.     

Properties of anomalous eμ events produced in e+e− annihilation

We present the properties of 105 events of the form e⁺ + e^? → e^+- + μ^? + missing energy, in which no other charged particles or photons are detected. The simplesthypothesis compatible with all the data is that these events come from the production of a pair of heavy leptons, the mass of the lepton being in the range 1.6 to 2.0 GeV/c²     

Analyzing thee + e −→e + e − angular distibution at LEP

The analysis of the lepton angular distribution at LEP is reviewed and the specific concerns in the case ofe ⁺ e ^– final state are singled out. Studies of the physical information contained in thee ⁺ e ^– angular distribution are shown to justify the need for a new approach. Two different solutions that enable the complete use of the angular distribution information for the extraction of theZ parameters are presented. We show that these approaches have accuracies well above the future experimental needs.     

Virtual LSPs at e+ e− colliders

Currently popular search strategies for supersymmetric particles may be significantly affected due to relatively light sneutrinos which decay dominantly into invisible channels. In certain cases the second lightest neutralino may also decay invisibly leading to two extra carriers of missing energy (in addition to the lightest supersymmetric particle (LSP) ) — the virtual LSPs (VLSPs). A tree lavel calculation shows that if the sneutrino mass happens to be in the small but experimentally allowed range (m _≈ν ≈ 45–55 GeV), these particles together with neutralino pairs may contribute significantly to the missing energy in the process e⁺e^? → γ+ E at LEP-2 energies as an enhancement over the Standard Model or the conventional MSSM predictions. It is further shown that a much larger region of the parameter space can be scanned at a high luminosity e⁺e^? collider at 500 GeV like the proposed NLC machine. Moreover, at both LEP-2 and NLC this process may play a complementary role to direct chargino searches, which may fail due to a near mass degeneracy of the chargino and the sneutrino. Formulae for the cross sections taking into account full mixings of the charginos and the neutralinos are derived. The signal remains observable even in the context of more restricted models based onN=1 SUGRA with common scalar and gaugino masses. A preliminary study of the QED radiative corrections due to soft multiple photon emission as well as hard collinear bremsstrahlung indicates that these corrections play a crucial role in estimating the background.     

Graviton-induced bremsstrahlung at e + e - colliders

We consider graviton-induced bremsstrahlung at future e ⁺ e ^- colliders in both the ADD and RS models, with emphasis on the photon perpendicular momentum and angular distribution. The photon spectrum is shown to be harder than in the standard model, and there is an enhancement for photons making large angles with respect to the beam. In the ADD scenario, the excess at large photon perpendicular momenta should be measurable for values of the cut-off up to about twice times the CM energy. In the RS scenario, radiative return to graviton resonances below the CM energy can lead to large enhancements of the cross section.Received: 28 March 2004, Published online: 3 June 2004     

F-meson production in e+e− annihilation

The F-meson production rate is calculated on the ψ(4414) resonance using non-relativistic multipole expansion techniques. The results are compared with the available data.     

Toponium production in e+e− collisions

We study the properties of toponium states and their production in e⁺e^? collisions with special emphasis on the mass region accessible to SLC and LEP. A formalism for toponium -Z mixing is developed that is applicable for arbitrary mass differences between Z and the toponium state. It is shown that simple lowest-order perturbation theory is equivalent to the mixing formalism up to an accuracy better than one percent in the entire energy range we investigate. The results are illustrated by calculations performed in the framework of two QCD-inspired potential models which predict about 10 narrow states in the mass range around the Z. The mixing effects on the properties of Z are small even in the case of degenerate Z and toponium masses. The effect of electroweak interferences on and around toponium are studied, and analytic forms for cross sections and asymmetries before and after energy smearing are presented. We show that high radial excitations of toponium states below threshold may be difficult to disentangle from the continuum states. A brief survey of the properties of heavy bottom-type quarkonia concludes the paper.     

Event shapes in e+e− annihilation

We present a complete set of rotationally invariant observables (H_l) which characterizes the ‘shapes’ of final states in e⁺e^? annihilation. They are infrared stable when calculated in QCD perturbation theory. We compare the ‘shapes’ of final states from the processes $\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{→}\text{q}\text{q}\text{,}\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{→}\text{q}\text{q}\text{(}\text{G}\text{)}$ and from the three-gluon decays of heavy vector mesons. We also consider the production and decay of heavy quarks and leptons. Using a realistic model for the development of hadron jets, we find that for c.m. energies above about 10 GeV, these processes may be clearly distinguished by their distributions in the H_l. We indicate how our analysis may be extended to deep inelastic lepton-hadron interactions and hadron-hadron collisions involving large transverse momenta.     

e+e− → γ + Hadrons

We give the spectrum in momentum and angle of directly produced γ's in e⁺e^? → γ + hadrons, and show that in QCD if p_⊥² of the recoil hadron jet relative to the photon is large, the leading logarithmic corrections to the lowest order result are absent. This process is therefore of great value in learning whether QCD actually governs quark dynamics.     

6Li(e,e′α) and (e,e′d) reactions

The correlation cross sections for the quasifree scattering in the ⁶Li(e,e′α) and (e,e′d) reactions are calculated in the microscopic model. The internal momentum distributions of clustering particles play an important role for explaining experimental data.     

Heavy vector mesons and the anomalous eμ events in e+e− annihilation

As a possible explanation of the SLAC anomalous eμ events, we computed the cross section for e⁺ + e^? → V⁺ + V^? → μ^± + e^± + neutrinos, taking into account the spin correlations of V^±. If one assumes that the vector meson has an anomalous magnetic moment (κ ≈ 1), the spin effects are considerable. The V^± production hypothesis seems to be a viable alternative to that of the heavy lepton production.     

Observations on K-production in e+e− collisions

We examine recent K-production data in e⁺e^? collisions in the framework of a heavy quark bound state model for the new resonances. If the rise in R is due to the production of new particles which are bound states of a heavy quark and an ordinary quark, we deduce that approximately half of the time the weak decays of these particles will contain a K-meson. Theoretical consequences of this fact are discussed. We also use the K-production rate at the ψ and ψ' resonances to calculate the branching ratio of these states to ?π and K¹$\text{K}$. The number obtained for the ψ, where it is measured, is in satisfactory agreement with experiment.