Measurement of thee + e −→π + π − π 0 ande + e −→ωπ + π − reactions in the energy interval 1350–2400 MeV

The cross sections fore ⁺ e ^?→π ⁺ π ^? π ⁰ ande ⁺ e ^?→ωπ ⁺ π ^? have been measured in the 1.35 ≦ \(\sqrt s \) ≦2.4 GeV range from 1900 nb^?1 collected by DM2 at DCI. The second process proceeds via a resonant state at ≈- 1660 MeV/c², ≈- 280 MeV/c² wide. The first one is larger than a VDM extrapolation from the ω-? peaks and, although does not show any clear structure, is compatible with the presence of the above resonance.     

Study of the process e + e − → π+π− in the energy region 400 < \sqrt s < 1000 MeV^\P

The cross section of the process e ⁺ e ^? → π⁺π^? was measured in the spherical neutral detector experiment at the VEPP-2M collider in the energy region $400 < \sqrt s < 1000 MeV$ . This measurement was based on about 12.4 × 10⁶ selected collinear events, which include 7.4 × 10⁶ e ⁺ e ^? → e ⁺ e ^?, 4.5 × 10⁶ e ⁺ e ^? → π⁺π^?, and 0.5 × 10⁶ e ⁺ e ^? → μ⁺μ^? selected events. The systematic uncertainty of cross section determination is 1.3%. The ρ-meson parameters were determined as m _ρ = 774.9±0.4±0.5 MeV, Γ _ρ = 146.5±0.8±1.5 MeV, and σ(ρ → π⁺π^?) = 1220 ± 7 ± 16 nb and the parameters of the G-parity suppressed decay ω → π⁺π^? as σ(ω → π⁺π^?) = 29.9 ± 1.4 ± 1.0 nb and φ_ρω = 113.5±1.3±1.7°.     

Q^2 \to A\sqrt s Scaling law fore + e −→hadrons andpp collisions at high energy

It has been conjectured recently that multiparticle production in low momentum transfer hadronic collisions is due to gluon bremsstrahlung off highly virtual (mass \(\mu ^2 \sim \sqrt s \) ) quarks. The model gives a new scaling law: \(Q^2 \to A\sqrt s \) , for comparinge ⁺ e ^?→hadrons andpp non-diffractive inelastic data. The scaling law is tested for average multiplicities, plateau height and 〈p ₂ ^⊥ 〉. Fore ⁺ e ^? annihilation a parametrization of data based on perturbative QCD approach is used.     

Measurement of the e + e − → ηπ+π− cross section in the \sqrt s = 1.04–1.38-GeV energy range with a spherical neutral detector at the VEPP-2M collider

The e ⁺ e ^? → ηπ⁺π^? cross section in the η → 2γ channel has been measured in the $ \sqrt s $ = 1.04- to 1.38-GeV energy range. The data with a total integrated luminosity of 9.05 pb^?1 were collected on a spherical neutral detector at the VEPP-2M collider. The results are consistent with the BaBar and CMD2 data and have a higher statistical accuracy.     

Investigation of the reaction e+e− → ηπ+π− in the energy range up to 1.4 GeV

The reaction e⁺e⁻ → ηπ⁺π⁻ has been studied with the Neutral Detector in the CM energy range 1.05–1.40 GeV at VEPP-2M. At the maximum energy the cross section exceeds the prediction of the vector dominance with one ϱ(770). The following upper limits for the electron width times branching ratio into ηπ⁺π⁻ have been obtained for a resonance with a mass of 1.28 GeV and width of 0.08 GeV observed with the Omega-spectrometer at CERN: Λ_ee·B_ηππ < 9 eV, and for a ϱ′(1250) with a mass of 1.26 GeV and width of 0.125 GeV: Λ_ee·B_ηππ < 14 eV at 90% confidence level.     

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.     

Baryon pairs production ine + e − annihilation at\sqrt s = 2.4 GeV

Search for baryon pairs production ine ⁺ e ^? annihilation at \(\sqrt s = 2386 MeV\) is reported. The data relate to a luminosity of 161 nb^?1 collected by the DM2 experiment at DCI, the Orsay colliding ring. First measurements of directe ⁺ e ^? annihilation into \(\Lambda \bar \Lambda \) and ofe ⁺ e ^?→ \(p\bar p\) at this energy are presented. First observation of a goode ⁺ e ^?→ \(n\bar n\) candidate is reported and upper limits are given fore ⁺ e ^?→ \(n\bar n, \Lambda \bar \sum ^0 + c.c.\) and \(\Sigma ^0 \bar \Sigma ^0 \) .     

Study of the K − → e − νπ 0 decay

The decay K ^? → e ^? νπ ⁰ has been studied using in-flight decays detected with the ISTRA₊ setup working at the 25-GeV negative secondary beam of the U-70 PS. About 130K events were used for the analysis. The λ ₊ parameter of the vector form factor has been measured: λ ₊=0.0293±0.0015(stat.)±0.002(syst.). The limits on the possible tensor and scalar couplings have been derived: f _T/f ₊(0)=?0.045±0.060(stat.) and f _S/f ₊(0)=?0.019 _?0.016 ^+0.025 (stat.).     

Pion-Nucleus potentials in the energy range of 0–80 MeV

Data for the elastic scattering of 30–80 MeV positive and negative pions by a wide range of nuclei is analysed with an Ericson-Ericson MSU type optical potential. By use of consistent sets of data for π⁺ and π⁻ and of experimental results for total reaction cross sections we obtain for the first time optical potentials that describe well all the data without the need of introducing non-standard charge-dependent effects.     

Study of hadronic events inpp collisions at\sqrt s = 62GeV and comparison with hadronic events ine + e − collisions

We present an analysis of minimum bias events from proton-proton collisions at \(\sqrt s = 7GeV\) in the CERN ISR. We remove the effects of both the leading protons and compare theB=0 mesonic residue of the events to the hadronic events of similar energy produced ine ⁺ e ^? collisions. This comparison is presented in terms of the standard jet-type analyses involving quantities such as sphericity and aplanarity. We find significant differences between these data and the data frome ⁺ e ^? annihilations. The data of this experiment are consistent with the predictions of a longitudinal phase space model.     

Proc ess es e+ e− → cccc and e+ e− → J/ψ + gg at $$\sqrt s = 10.59 G eV$$

Experimental data obtained by the BELLE Collaboration for inclusive J/ψ production in the processes e⁺e^? → J/ψ + gg and e⁺e^? → J/ψ + cc are discussed. These data are compared with the predictions of perturbative QCD that were obtained by two methods, that which employs information about the J/ψ wave function and that which relies on the hypothesis of quark-hadron duality exclusively. Both computational methods yield results that disagree with the experimental data considerably. The dependence of the cross section for the process e⁺e^? → J/ψ + gg on the effective gluon mass is studied. The cross section for the production of doubly charmed baryons Ξ _cc ^* is estimated.     

Photofission of americium isotopes in the energy range 6–12 MeV

By means of the reference method, the cross sections for the fission of the ²⁴¹Am, ^242m Am, and ²⁴³Am isotopes were measured at the microtron of the Institute of Physics and Power Engineering (Obninsk). These measurements, which employed the cross section for ²³⁸U photofission as a reference, covered the energy range 6–12 MeV scanned with a variable step of 50 to 200 keV. Data on ^242m Am photofission in the energy range 6–12 MeV and ²⁴³Am photofission in the region between 6 and 7 MeV were obtained for the first time. New results for ²⁴¹Am reveal that the cross sections for ²⁴¹Am photofission from previous studies of the present author were exaggerated. The new results for this isotope comply well with data of other authors. It is not confirmed that the fissility of ²⁴¹Am is less than the fissility of ²⁴³Am. The energy dependences of the fissilities of the americium isotopes from photofission data are compared with those that were obtained for these fissilities from data on direct reactions like ²⁴⁰Pu(³He, df)²⁴¹Am. The results of this comparison show that the observed fission thresholds and the plateaulike dependences at energies above 7.5 MeV from the two types of studies comply well. The present data show evidence that, in the energy region around 6 MeV, the photofission cross section has a maximum, which is associated, in all probability, with the low-energy resonance structure in the cross section for dipole photoabsorption.     

Determination of the CP properties of the Higgs boson from data on tau-lepton-decay products in the process e + e − → τ + τ − ν \bar \nu

The process e ⁺ e ^? → τ ⁺ τ ^? v $ \bar \nu $ , which is highly sensitive to anomalous Hττ interaction, is investigated within a model involving a new pseudoscalar Higgs boson. It is shown that the problem of separating the contributions of the scalar and pseudoscalar states of the Higgs boson can be solved via taking into account the polarizations of final-state particles. The inclusion of cascade tau-lepton decays makes it possible to determine reliably the CP state of the Higgs boson and to pinpoint the magnitude and sign of respective coupling constants.     

More on the τ-μ-e problem: The process e+e−→l+l− in the region of the z-resonance

Theoretical and experimental aspects of the study of the e-- problem in effects of neutral weak currents in colliding e⁺e^– beams in the region of the Z resonance are discussed. Quantities that describe the degree of violation of e-- universality are analyzed. In particular, it is shown that by measuring the spin asymmetry for angles 160° it is possible to determine the degree of violation ofl-e universality =g _A ^e g _V ^l –g _V ^e g _A ^l to an accuracy of up to 0.01.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 88-91, May, 1989.     

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.     

Modeling the efficiency of neutron detection scintillators in the energy range of 5–70 MeV

The instrumental functions for neutron godoscope detectors used in studying the nd-breakup reaction are obtained. The effect on light output of contributions from different processes that occur in a scintillator under the effect of neutrons is examined at different energies of the incident neutrons. The relationship between the detector??s efficiency and neutron energies ranging from 5 to 70 MeV is obtained for different thresholds.     

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.