Hard photon corrections for Bhabha scattering

Numerical results for the α³ differential cross section for e⁺e^? → e⁺e^? are presented for the case of e⁺e^? colliding beams. Special care is given to the hard photon corrections. Acoplanarity distributions for e⁺e^? → e⁺e^?γ are also presented. Attention is drawn to experimental conditions which require the calculation of still higher order corrections.     

Z boson effects in electron positron scattering at epic energies at 14 GeV

We discuss the problem of testing the intermediate vector boson effects in the reactions e^?e⁺ → e^?e⁺ + hadrons, e^?e⁺ → e^?e⁺ + μ^?μ⁺, e^?p → e^?x with the next generation of accelerators, and conclude that these reactions must be considered. The differential cross sections for the one lepton at large four-momentum transfer are obtained, and a significant contribution of Z effects is found.     

ee Annihilation into two hadrons in the energy interval 1400–2400 MeV

The proof is given for the existence of the reaction e⁺e⁻ → h^±h^? in the energy range 1400–2400 MeV, and its energy dependence is compared with that of e⁺e⁻ → e^±e^?, in the same experimental conditions of observation. The exponent of the s-dependence of the ratio α = (e⁺e⁻ → h^±h^?)/ (e⁺e⁻ → e^±e^?) is measured to be n = 2.08 ± 0.45, in the s-range (1.96 − 5.76) GeV², on the basis of 51 e⁺e⁻ → h^±h^? events and 8918 e⁺e⁻ → e^±e^? events observed.     

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.     

Study of the η'→Ve~+e~- decay with hidden local symmetry model

Within the hidden local symmetry framework, the Dalitz decay η→Ve+e-is studied with the vector meson dominance model. It is found that the partial width Γ(η→ωe+e-)≈40 e V and branching ratio B(η→ωe+e-)≈2×10-4, and Γ(η→ρe+e-)≈10Γ(η→ωe+e-) and B(η→ρe+e-)≈10B(η→ωe+e-). The maximum position of the dilepton distribution is m e+e-≈1.33 Me V. These decays are measurable with the advent of high statistic ηexperiments.     

Approximations for high-energy photon-photon scattering in two-photon processes and double bremsstrahlung

Presented are some approximation formulae for the processese ⁺ e ^? →e ⁺ e ^?γ^*γ^* →e ⁺ e ^?γγ (e ⁺ e ^?) scattering with intermediate γγ scattering) ande ⁺ e ^?→e ⁺ e ^?γγ (double bremsstrahlung) at high energies for forwarde ⁺ e ^? scattering, using not only the usual equivalent-photon approximation method but also direct approximations under certain kinematic conditions. In both cases the outgoing photons can be polarized. Their numerical check is examined by comparing these results with those of the exact calculations obtained in a recent paper. The agreement of both results is quite satisfactory if the required conditions are satisfied.     

Screening effect of the coulomb interaction on the energy levels of atomic and molecular systems

The energies of atomic and molecular systems with a screened Coulomb interaction are expressed in terms of properties of the system with a conventional Coulomb interaction to the third order in the screening constant. The energy levels of an H atom, an H^? ion, and nonadiabatic systems, namely, the positronium ion e ⁺ e ^? e ^? and the positronium molecule e ⁺ e ⁺ e ^? e ^?, are calculated for screened Coulomb interactions of charged particles. It is demonstrated that, as the screening constant of the Coulomb interaction increases, the stability of the hydrogen atom, the H^? ion, and the positronium molecule e ⁺ e ⁺ e ^? e ^? decreases, whereas the stability of the positronium ion e ⁺ e ^? e ^? increases after a slight decrease.     

Measurement of the ω, ρ → π0 e + e − branching fractions

The e ⁺ e ^? → ω, ρ → π⁰ e ⁺ e ^? processes have been investigated in the experiments with Spherical Neutral Detector at the VEPP-2M e ⁺ e ^? collider. The measurements provide the probability ?(ω → π⁰ e ⁺ e ^?) = (0.761 ± 0.053 ± 0.064) × 10^?3 of the ω → π⁰ e ⁺ e ^g- conversion decay and the upper limit ?(ρ → π⁰ e ⁺ e ^?) < 1.2 × 10^?5 (at 90% CL) for the ρ → π⁰ e ⁺ e ^? decay. The transition form factor was measured at three values of the 4-momentum transfer squared.     

Hadronic vacuum polarization effects in Bhabha and Moller scattering

Effects of hadronic vacuum polarization in the reactions e⁺e^? → e⁺e^? and e^±e^± → e^±e^± are discussed. The cross sections with spin polarization are given. Measurements of these effects could directly determine in the hadronic vacuum polarization at spacelike momentum transfers and could improve tests of quantum electrodynamics.     

The π N → e +e−N reaction close to the vector-meson production threshold

The π^? p→e ⁺ e ^? n and π⁺ n→e ⁺ e ^? p reaction cross sections are calculated below and in the vicinity of the vector-meson (?⁰,ω) production threshold. These processes are largely responsible for the emission of e ⁺e^? pairs in pion-nucleus reactions and contribute to the dilepton spectra observed in relativistic heavy ion collisions. They are dominated by the decay of low-lying baryon resonances into vector-meson-nucleon channels. The vector mesons materialize subsequently into e ⁺ e^? pairs. Using πN→?⁰ N and πN→ωN, amplitudes calculated in the center of mass energy interval 1.4 < √s<1.8 GeV, we compute the π^? p→e ⁺ e ^? n and π⁺ n→e ⁺ e ^? p reaction cross sections in these kinematics. Below the vector-meson production threshold, the π⁰?ω interference in the e ⁺ e^? channel appears largely destructive for the π^? p→e ⁺ e ^? n cross section and constructive for the π⁺ n→e ⁺ e ^? p cross section. The pion beam and the HADES detector at GSI offer a unique possibility to measure these effects. Such data would provide strong constraints on the coupling of vector-meson-nucleon channels to low-lying baryon resonances.     

Determination of the radiative widths of the η′ and A2 from two-photon exchange production

From the two-photon exchange processes e⁺e^? → e⁺e^?η' (958) → e⁺e^??⁰γ and e⁺e^? → e⁺e^?A₂ (1310) → e⁺e^?π⁺π^?π⁰ observed using the CELLO detector at PETRA the radiative widths of the η' and A₂ have been determined with the results: Γ_γγ(η') = 5.4 ± 1.0[stat.] ± 0.7[syst.] keV; Γ_γγ(A₂) = 0.59 ± 0.14[stat.] _?0.08^+0.31[syst.] keV.     

Leptonic polarization asymmetries ate + e − colliders inE 6 theories

We examine the left-right and azimuthal polarization asymmetries of lepton pairs produced ine ⁺ e ^? ande ^? e ^? interactions as probes of new physics resulting fromE ₆ theories. The asymmetries are calculated and compared for the processese ⁺ e ^?→µ ⁺ µ ^?,e ⁺ e ^?→e ⁺ e ^?,e ^? e ^?→e ^? e ^?, ande ⁺ e ^?→L ⁺ L ^? whereL is either anE ₆ exotic, mirror, or fourth generation heavy lepton. Our results show that lepton polarization asymmetries can be used to easily distinguish differentE ₆ models and can be used to distinguish among possible new heavy leptonsL.     

Limits for short-lived neutral particles emitted in μ+ or π+ decay

In the data taken for the μ⁺ → e⁺e⁺e^- and π⁺ → e⁺νe⁺e^- experiments a search was made for neutral particles φ produced in the decay μ⁺ → e⁺φ or π⁺ → e⁺νφ with subsequent decay φ → e⁺e^-. No candidates were found, Upper limits for the branching ratios are given as a function of their masses and lifetimes. For lifetimes below 10⁻¹⁰ s limits down to 2 × 10⁻¹² are obtained.     

A search for excited electrons in the e+e− reactions up to the √s of 56 GeV

Excited electrons, e^1's, have been searched for by making use of the processes e⁺e⁻→e⁺e⁻γγ and eγ(e) (quasi-real Compton scattering). From the former process, we have obtained the lower limit for the mass of e^1', 27.9 GeV/c. A good agreement with QED is observed in the latter process, and new upper limits have been set for the coupling strength λ as a function of the mass of e¹.     

Optimal Hamiltonian of internal motion of an atomic-molecular system in a magnetic field

The effect of a uniform magnetic field on the state of an atomic-molecular system considered as a united system of N particles (without separation of the motion of acoelightac and particles) is analyzed. It is shown that the Hamiltonian of the internal motion of the system in the magnetic field contains (N-1)(N-2)/2 arbitrary parameters corresponding to the coefficients of the gauge transformation of the vector potential. A method of calculation of the optimal values of these coefficients based on the requirement for the minimum diamagnetic correction to the energy is proposed. New formulas for the diamagnetic susceptibility of atomic-molecular systems are obtained that take into account the simultaneous perturbing effect of the magnetic field on the motion of all particles. The theory is applied for calculation of the diamagnetic susceptibilities of the H, He, Li, and Be atoms; the muonic analogues of helium atoms ^∞He²⁺µ^? e ^?,⁴He²⁺µ^? e ^?, and ³He²⁺µ^? e ^?; and the positron-containing systems t ⁺ e ⁺ e ^? e ^?, d ⁺ e ⁺ e ^? e ^?, p ⁺ e ⁺ e ^? e ^?, µ⁺ e ⁺ e ^? e ^?, and e ⁺ e ⁺ e ^? e ^?, with regard for the motion of all particles.     

Separation of electrons and pions in the SND detector calorimeter

A method is developed for discriminating between e⁺e^? → e⁺e^? and e⁺e^? → π⁺π^? events in the center-of-mass (cms) energy range of 0.5 to 1.0 GeV by energy deposition in the electromagnetic calorimeter of the SND detector using a machine learning algorithm. Identification efficiencies for e⁺e^? → e⁺e^? and e⁺e^? → π⁺π^? events are 99.6 and 99.8%, respectively.     

Study of conversion decays φ→ηe+e− and η→γe+e− in the experiment with SND detector at VEPP-2M collider

The conversion decays φ→ηe⁺e⁻ and η→γe⁺e⁻ were studied by the SND detector using φ-meson production in e⁺e⁻-annihilation at VEPP-2M collider. The branching ratios of these decays were measured: Br(φ→ηe⁺e⁻)=(1.19±0.19±0.07)×10⁻⁴ and Br(η→γe⁺e⁻)=(5.15±0.62±0.39)×10⁻³. The e⁺e⁻-pair mass spectra and transition form factors were also studied.     

Measurements of the absolute branching fractions for D→K̄πe+νe, D→K̄*e+νe and determination of Γ(D+→K̄*0e+νe)/Γ(D+→K̄0e+νe)

Using the data of about 33 pb^-1 collected at and around 3.773 GeV with the BES-II detector at the BEPC collider, we have studied the exclusive semileptonic decays D⁺→K^-π⁺e⁺ν_e, D⁰→K̄⁰π^-e⁺ν_e, D⁺→K̄^*0e⁺ν_e and D⁰→K^*-e⁺ν_e. The absolute branching fractions for the decays are measured to be BF(D⁺→K^-π⁺e⁺ν_e)=(3.50±0.75±0.27)%, BF(D⁰→K̄⁰π^-e⁺ν_e)=(2.61±1.04±0.28)%, BF(D⁺→K̄^*0e⁺ν_e)=(5.06±1.21±0.40)% and BF(D⁰→K^*-e⁺ν_e)=(2.87±1.48±0.39)%. The ratio of the vector to pseudoscalar semileptonic decay rates Γ(D⁺→K̄^*0e⁺ν_e)/Γ(D⁺→K̄⁰e⁺ν_e) is determined to be 0.57±0.17±0.02.     

Searching for the process e+e- → K+K-π0 in experiments with the spherical neutral detector at VEPP-2M

We have searched for the process e⁺e^- → K⁺K^-π⁰ at energies up to 1.38 GeVin an experiment with the spherical neutral detector at the VEPP-2M e⁺e^- collider. The upper limits of the cross sections for the processes σ(e⁺e →; φπ: → K⁺K^-π⁰) < 0.023 nb and σ(e⁺e^- → KK*(892) → K⁺K^-π⁰) < 0.059 nb have been established at a 95% confidence level.     

Constraints on couplings of a fast decaying axion

Constraints are imposed on the couplings of an axion-like pseudoscalar particle φ that decays into e⁺e⁻ and γγ. The electron g−2 sets a severe bound not only on the φe⁺e⁻ coupling but also on the φγγ coupling. The most reliable bound on the φ coupling to the light quarks comes from the decay ∑⁺ → pe⁺e⁻ which was measured in a hydrogen bubble-chamber experiment with good sensitivity and resolution covering the entire range of e⁺e⁻ mass practically down to 2m_e. These upper bounds, together with a constraint from the decay K⁺→π⁺γγ, reinforce arguments against the particle-physics interpretation of the anomalous positrons in heavy-ion collisions, since the couplings are by orders of magnitude smaller than needed to produce e⁺e⁻ pairs at the observed level by known mechanisms.