Mixing of toponium and Z° boson in elastic e+ − annihilation

If toponium with a mass close to the mass of a Z meson exists, it could be studied on the basis of the interference pattern which would be produced in the differential cross section for elastic e⁺e^– annihilation with unpolarized initial beams. The energy and angular dependence of the quantity which determines the relative contribution of vector toponium to the differential cross section for the process e⁺e^– e⁺e^– has been studied.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika,No. 10, pp. 38–42, October, 1988.     

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.     

A direct measurement of theZ0 invisible width by single photon counting

The OPAL detector at LEP is used to measure the branching ratio of theZ ⁰ into invisible particles by measuring the cross section of single photon events ine ⁺ e ^– collisions at centre-of-mass energies near theZ ⁰ resonance. In a data sample of 5.3 pb^–1, we observe 73 events with single photons depositing more than 1.5 GeV in the electromagnetic calorimeter, with an expected background of 8±2 events not associated with invisibleZ ⁰ decay. With this data we determine theZ ⁰ invisible width to be 0.50±0.07±0.03 GeV, where the first error is statistical and the second systematic. This corresponds to 3.0±0.4±0.2 light neutrino generations in the Standard Model.     

Polarization effects in the photoproduction of a fermion pair and a gamma quantum on nuclei

Integration of the cross section of the process+(Ze)(Ze)+₁+e^–+e⁺ over the angles of emission of the electron and positron was carried out, and the angular, energy, and spin dependences of the cross section were obtained. The cross section for photoproduction of a lepton-antilepton pair and a quantum on nuclei in the case where the emitted photon moves in the same direction as the incident quantum can exceed the Bethe-Heitler cross section for ordinary photoproduction of an e^–e⁺ pair. The probabilities of some electron and positron spin states are analyzed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 106–110, June, 1972.In conclusion I express my thanks to A. A. Sokolov and A. I. lViukhtarov for valuable advice.     

Search for contact interactions in the reactionse+e?→l+l? ande+e?→γγ

Contact interactions are searched for using the differential cross sections for the reactionse ⁺ e ^–e ⁺ e ^–,e ⁺ e ^–µ ⁺ µ ^–,e ⁺ e ^{– + –} ande ⁺ e ^– measured at 12 energies around theZ peak and corresponding to about 20 pb^–1 of cumulated luminosity. Four-fermion contact term models assuming various chiralities of lepton currents are fitted to the lepton data and lower limits on the energy scale of such terms are set at 95% c.l. The limits vary in the range 0.9–4.7 TeV, depending on the model and on the lepton flavour. Theee contact terms are searched for assuming various chiralities. Limits on the energy scale between 79 and 130 GeV are extracted from the data. The results are compared and combined with those reported at lower energies.Deceased     

Limits on electron compositeness from Bhabha scattering

We have studied the reactione ⁺ e ^–e ⁺ e ^– using data taken by the CELLO detector at 35 GeV centre of mass energy with an integrated luminosity of 86 pb^–1. The differential cross section is found to agree with the Standard Model and is used to set limits on possible deviations from the pointlike structure of the electron. The lower limits obtained for the compositeness scale range from 0.8 to 6.0 TeV (95% C.L.), depending on the structure of the current.     

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.     

Solution of three-dimensional Faddeev equations for three-body Coulomb bound states

A new method of directly solving the three-dimensional Faddeev equations in the total-angular-momentum representation for the pure Coulomb bound-state problem is developed. The method is based on the tri-quintic Hermite spline expansion of the Faddeev components. The ground states of thee ^– e ^– e ⁺ system and thepp ^– mesic molecule are calculated.     

Inverse muon decay in a steady external field

A standard Weinberg-Salam model has been used to calculate the cross section of +e »v _e+ in steady crossed fields (EH=E ²–H ²=0). The asymptotic behavior of the cross section has been examined as a function of the kinematic and dynamic (field) invariant parameters.M. V. Lomonosov Moscow State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 106–111, December, 1992.     

Branching Fraction Measurements of the SM Higgs with a Mass of 160 GeV at Future Linear e + e − Colliders

Assuming an integrated luminosity of 500 fb^–1 and a center-of-mass energy of 350 GeV, we examine the prospects for measuring branching fractions of a Standard Model-like Higgs boson with a mass of 160 GeV at the future linear e⁺e^–collider TESLA when the Higgs boson is produced via the Higgsstrahlung mechanism, e⁺e^– HZ. The Higgs boson mass chosen close to the W pair threshold covers a mass regime with complicated background structures. We study in detail including some detector responds the precisions achievable for the branching fractions of the Higgs boson into WW^(*), ZZ^* and , whereas the measurement of BF(H ) remains a great challenge. Expectations for the total Higgs width are discussed using either the BF(Z ZZ^*) measurement of this study and the expected error for the inclusive Higgsstrahlung cross section or in addition the precise cross section expected for the weak boson fusion process, e⁺e^– v H, or W,Z-universality.     

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%.     

Longitudinal jet cross sections in order α s 2

We calculate the cross section fore ⁺ e ^–3 jets for longitudinally polarized virtual photons up to order _s ² in the quark-gluon coupling.Dedicated to the memory of Kurt Symanzik     

Probing the photon at γe-colliders

We investigate the feasibility of studying the photon structure function at a e-collider. We show that the deep inelastic probe of the real photon by a highly virtual photon in such a collider will extend significantly thex andQ ² range presently accessible ate ⁺ e ^– colliders. In addition, we study the production of large transverse momentum dijet final states to determine the sensitivity of these cross sections to different parametrisations of the quark and gluon distributions in the photon.     

Dilepton mass spectra in collisions at and the contribution from open charm

PHENIX has measured the electron–positron pair mass spectrum from 0 to 8 GeV/c² in p+p collisions at . The contributions from light meson decays to e⁺e⁻ pairs have been determined based on measurements of hadron production cross sections by PHENIX. Within the systematic uncertainty of 20% they account for all e⁺e⁻ pairs in the mass region below 1 GeV/c². The e⁺e⁻ pair yield remaining after subtracting these contributions is dominated by semileptonic decays of charmed hadrons correlated through flavor conservation. Using the spectral shape predicted by PYTHIA, we estimate the charm production cross section to be 544±39(stat)±142(syst)±200(model) μb, which is consistent with QCD calculations and measurements of single leptons by PHENIX.     

Hadronic vacuum polarization contribution to the Lamb shift in muonic hydrogen

We report on the accuracy of the measurement of the total cross section of the process e⁺e^– ZH and of the Higgs boson mass that would be achieved in a linear collider operating at a centre-of-mass energy of 350 GeV, assuming an integrated luminosity of 500 fb^–1. For that we have exploited the recoil mass off the Z using its leptonic decays into electron and muon pairs. The Higgs mass is determined with 150 MeV accuracy, the recoil mass resolution is about 1.5 GeV and the cross section is obtained with a statistical error of 3%.     

Radiative annihilation of a lepton pair to form hadrons

The electromagnetic annililation of an e^–e⁺ pair to form hadrons, accompanied by the emission of a ray, is studied. A differential cross section is derived to describe the angular and energy distributions of the bremsstrahlung photons. The possibility of determining structure functions is studied. A five-quark model is used to calculate the circular polarization of the photon, P, and the transverse asymmetry coefficienta.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 25–29, December, 1981.     

Study of the process ee→ππγ in c.m. energy range 600–970 MeV at CMD-2

The cross section of the process e⁺e⁻→π⁰π⁰γ has been measured in the c.m. energy range 600–970 MeV with the CMD-2 detector. The following branching ratios have been determined:

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and

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. Evidence for the ρ⁰→f₀(600)γ decay has been obtained:

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. From a search for the process e⁺e⁻→ηπ⁰γ the following upper limit has been obtained: at 90% CL.     

Multiplicity with a thrust cut

We evaluate the multiplicity of hadrons in thee ⁺ e ^–-annihilation at a given thrustT in the modified leading-log approximation, including corrections. The calculation is done at a large value of =1–T by the use of the factorisation which takes place in the one-particle-inclusive cross section at a given . At a small , a different type of factorisation takes place, which also enable us to evaluate the multiplicity. Two approaches are compared numerically. Measuring this quantity near =1/3, we can determine the multiplicity ratio between a gluon-jet and a quark-jet.     

A study of double pomeron exchange inπ + p andK + p interactions at 250 GeV/c

Using the ARGUS detector at thee ⁺ e ^– storage ring DORIS II at DESY, we have measured the inclusive production ofD ⁰,D ⁺ andD ^*(2010)⁺ mesons inB decays and in nonresonante ⁺ e ^– annihilation around 10.6 GeV. The inclusive branching ratios forB decays toD ⁰,D ⁺ andD ^*+ mesons are found to be (52.2±8.2±3.5)%, (27.2±6.3±3.5)% and (34.8±6.0±3.5)% respectively. Thus,D ⁰ andD ⁺ production account for about 70% of the charm produced inB decays, neglectingbu contributions to the total width. The production cross sections and momentum spectra for continuume ⁺ e ^– annihilation are also presented.Supported by the German Bundesministerium für Forschung und Technologie, under contract number 054DO51P     

Searching for light Higgs scalar bosons in the next generation of electron-positron collider at LEP

Thee ⁺ e ^–-collider facilities at LEP II, with the CM energy S in the range 100–170 GeV, may be able to detect light Higgs bosons, assuming a high luminosity. The production cross sections of a light Higgs bosonH ⁰ in association with the neutral gauge bosonZ ⁰ are calculated for varying ranges of the CM energy expected to be available to LEP II and VLEEP (Novosibirsk) and for various values of the light Higgs mass. It is found that production cross sections are sizable in comparison with those for the very massive Higgs bosons in proton-anti(proton) supercolliders, Tevatron, Sp¯pS, and SSC, respectively. The implication of this feature is pointed out. Further, prospects for light Higgs production in association with the charged gauge bosonW ^– in ultraenergetic neutrino beams are examined.