Higgss-channel production ine + e − collisions below theW + W − threshold

The cross section for direct neutral Higgs production in the reaction is calculated in theE _CM energy range of 40 to 160 GeV and compared to the corresponding Electro-Weak (EW) process . Neglecting radiation effects, a signal of the order of 10^–4 to 10^–3 over the EW can be expected outside theZ ⁰ region for the Minimal Standard Model Higgs in its decay to a state. For \sqrt s - M_Z $$ " align="middle" border="0"> , thes-channel Higgs formation can surpass the Bjorken Bremsstrahlung process and thus may afford at LEP 2 a realistic search method for high mass, say 100 GeV Higgs, given enough luminosity. For a non-Standard Model Higgs, in some cases, significantly higher signals are expected. The effects of initial state radiation and-machine energy resolution are evaluated and the gain in using longitudinal polarized electron beams is discussed.Supported in part by the Israel Ministry for Science and Technology     

Magnetic properties of Nd3+ in Nd−Ba−Cu−O-compounds

Neutron diffraction, neutron spectroscopy and magnetization measurements have been employed to study the structural, electronic, and magnetic behavior of eleven compounds with the general formula Nd_1+y Ca _v Ba_2–y–v Cu₃O _x (0y0.5; 0v0.25; 6x7). The structure turned out to react to oxygen reduction similar as other 123-compounds, yielding discontinuities close to the metal-insulator-transition and the well-known relations of bond lengths as a function ofT _c. The crystalline electric field (CEF) interaction, splitting the 10-fold degenerate ground-state J-multiplet of the Nd³⁺-ions into five doublet states, was investigated by neutron spectroscopy. The derived CEF parameters have been used to determine changes in the electronic surroundings of the Nd³⁺ ions. In addition, with the help of the CEF parameters the thermodynamic magnetic properties of these compounds were calculated which turn out to be in good agreement with the experimental data.     

Duality ine + e − annihilation

With the help of a relativistic generalization of the formula for the leptonic width of quarkonium in the semiclassical approximation it is shown that for any confinement potential nonsingular at the origin the sum of total cross sections for the production of the heavy quarkonium states \((Q\bar Q)_n\) with masses \(M_n \leqq \sqrt s\) ine ⁺ e ^?-annihilation is equal to the cross section at givens for the production of the free quark-antiquark pair \(Q\bar Q\) . We obtain also a family of dual sum rules for quarkonium which are in agreement with the available experimental data on charmonium and beautionium within experimental errors.     

Thrust ine + e −-annihilation

The thrust distribution ine ⁺ e ^–-annihilation is analysed in perturbative QCD. Proper account is taken of multiple emission of gluons. Scaling holds for this quantity in the sense that its energy dependence comes only through the change in the QCD effective coupling. It thus provides an ideal means to determine the value of the QCD mass scale experimentally. From the data atW=91 GeV by the ALEPH collaboration at LEP, we obtain .     

Effect of weak neutral currents in the process e− + p → e− + γ + X

Polarization effects in the inclusive process e^– + p e^– + + X due to the neutral current are studied in the framework of the Weinberg-Salam model. Expressions for the asymmetry parameters and the degree of circular polarization of the photons are obtained in the quark-parton picture. It is shown that measurement of such quantities gives additional information about the quark structure of the hadronic weak neutral current.Paper presented at the scientific session of the nuclear physics branch, USSR Academy of Sciences and the Moscow State University on Electromagnetic and Weak Interactions (Moscow, January 16–20, 1979).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 96–99, January, 1981.     

W+W−γ production in e+e− annihilation in the TeV region

The reaction e⁺e⁻→γW⁺W⁻ has been studied at TeV energies as a possible background to Higgs production. Our results differ significantly from previous estimates and show that the ratio signal/background can be kept reasonably large.     

Production of singleW bosons ine + e − ande − p collisions

The production ofW bosons in electronpositron colliding beams below theW ⁺ W ^? threshold is discussed. The corresponding reactions \(e^ + e^ - \to l^ \pm W^ \mp \mathop {\nu _l }\limits^{( - )} \) yield total cross-sections of the order of 10^?37 cm² (forl=e) and 10^?38 cm² (forl=μ). The total cross-sections as well as the angular and energy distributions of theW boson in \(e^ + e^ - \to e^ \pm W^ \mp \mathop {\nu _e }\limits^{( - )} \) are sensitive to the magnetic moment of theW. So, with this reaction, not onlyW bosons can be produced but also the gauge nature of the interaction can be tested. The decay \(Z^0 \to l^ \pm W^ \mp \mathop {\nu _l }\limits^{( - )} \) is discussed in view of its observation ine ⁺ e ^? experiments. Finally the crosssections ofe ^- p→ν _e W ^- X ⁺ are computed. They are of the order of 10^?38 cm² for \(\sqrt s \simeq 200\) GeV.     

Rapidity distribution ine + e − annihilation

A method to systematically calculate the rapidity distribution of hadrons in a high-energy jet is formulated in terms of an integral equation for the multiplicity. The distribution has the following properties at high energies: (i) a translational invariance; (ii) an increasingly steep distribution with a width proportional to \(\sqrt {\ln s} \) , but without a widening “central plateau”; (iii) if the rapidity is scaled by \(\sqrt {\ln s} \) , it approaches to a universal exponential curve. In the large rapidity region, however, the translational invariance is broken because of the recoil of the quark by the emission of soft gluons. It is also discussed that a gluon jet has a wider angular distribution.     

Annihilation mechanisms of e+e− and μ+μ− production in relativistic nuclear collisions

We revise the μ⁺μ^? and $q\bar q$ annihilation mechanisms of dilepton production during relativistic nuclear collisions. We focus on the modifications caused by the specific features of in-medium pion and quark states rather than by medium modification of the ρ-meson spectral density. The main ingreditent emerging in our approach is a form-factor of the multi-pion (multi-quark) system. Replacing the usual delta-function the form-factor plays the role of distribution which, in some sense, “connects” the total 4-momenta of the annihilating and outgoing particles. The difference between the c.m.s. velocities attributed to annihilating and outgoing particles is a particular consequence of this replacement and results in the appearance of a new factor in the formula for the lepton pair production rate. We obtained that the form-factor of the multi-pion (multi-quark) system causes broadening of the rate which is most pronounced for small invariant masses, in particular, we obtain a growth of the rate for the invariant masses below two masses of the annihilating particles.     

Study of theK + K − π+ π− system centrally produced in the reactions π+ p→π+(K + K − π+ π−)p andpp→p(K + K − π+ π−)p at 85 GeV/c

The reactions π⁺ p→π⁺(K ⁺ K ^? π⁺ π^? p andpp→p(K ⁺ K ^? π⁺ π^?)p where the (K ⁺ K ^? π⁺ π^?) system is centrally produced have been studied at 85 GeV/c. 48% of the final state proceeds through single or double vector meson resonant production i.e.,K ^*0(890) (37%), ? (4%),ρ ⁰ (7%). Evidence is found for associatedK ^*0 (890) \(\bar K\) ^*o (890) production (6.4±1.1%) with a cross section ten times higher than that found for associated ? ? production in the same experiment.     

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.     

Comparative study of Z′ searches in e+e− and e−e− scattering

We consider indirect searches for additional neutral vector bosons in e⁺e⁻ and e⁻e⁻ collisions, and compare these two linear collider modes with similar analysis procedures and assumptions. Discovery limits and resolving power are discussed in a model-independent way.     

An improved upper limit on the ντ-mass from the decay π−→π−π−π−π+π+ντ

Using the ARGUS detector at the e⁺e⁻ storage ring DORIS II, we have observed the decay τ⁻→π⁻π⁻π⁻π⁺π⁺ν_τ in tau-pair events produced at center-or-mass energies between 9.4 and 10.6 GeV. From the 5π invariant mass distribution we derive an upper limit of m(ν_τ)<35 MeV/c² at the 95% confidence level. The branching ratio for this decay channel is found to be (0.064±0.023±0.01)%.     

Energy spectra and energy correlations in the decayH→ZZ→μ+μ−μ+μ−

It is shown that in the sequential decay $H \to ZZ \to (f_1 \bar f_1 ) + (f_2 \bar f_2 )$ , the energy distribution of the final state particles provides a simple and powerful test of theHZZ vertex. For a standard Higgs boson, the energy spectrum of any final fermion, in the rest frame ofH, is predicted to be dΓ/dx～1+β⁴?2(x?1)², with $\beta = \sqrt {1 - 4m_Z^2 /m_H^2 } $ and 1?β≤x=4E/m _H ≤1+β. By contrast, the spectrum for a pseudoscalar Higgs is dΓ/dx～β²+(x?1)². There are characteristic energy correlations betweenf ₁ andf ₂ and betweenf ₁ andf ₂. These considerations are applied to the “gold-plated” reactionH→ZZ→μ⁺μ^?μ⁺μ^?, including possible effects ofCP-violation in theHZZ coupling. Our formalism also yields the energy spectra and correlations of leptons in the decay $H \to W^ + W^ - \to l^ + v_l l^ - \bar v_l $ .     

Two-jet cross section ine + e − annihilation

We calculate the two-jet cross section in order α _s ² in the framework of massless perturbative QCD, using for jet resolution the jet mass. We derive results for two different approaches. One approach is based on the singularity structure of the various contributions. The other one is adjusted to the methods used in three- and four-jet calculations so that the total cross section can be reconstructed.     

Jet masses in e+e− annihilation

We calculate heavy (M _H ² /s) and light (M _L ² /s) jet masses up toO(α _s ² ) in perturbative Quantum Chromodynamics (QCD). The sensitivity of these quantities to radiative corrections, quark masses, fragmentation effects as well as their infrared stability properties, are investigated and compared to those exhibited by other jet measures. A comparison with recent Mark II data is also presented.     

A study of K−π+ scattering in the reaction K−p→K−π+n at 11 GeV/c

Results from a high statistics study of the reaction K⁻p→K⁻π⁺n are presented. These results are based on data obtained with an 11 GeV/c beam using the LASS spectrometer at SLAC. The mass dependence of the spherical harmonic moments provides clear evidence for the production of the complete leading orbitally excited K¹ series up through J^P = 5⁻. These moments are used to perform an energy independent partial wave analysis of the K⁻π⁺ system from threshold to 2.6 GeV/c² using a t-dependent parametrization of the production amplitudes. The amplitudes corroborate the leading K¹(892), K₂¹(1430), K₃¹(1780), K₄¹(2060), and K₅¹(2380) resonances observed directly in the moments, and also provide new evidence for underlying states. The 0⁺ amplitude contains the K₀¹(1350) and a second 0⁺K¹(1950) at higher mass. The 1⁻K¹(1790) seen earlier two and three-body analyses is confirmed, and evidence is provided for suppressed K⁻π⁺ decay mode of a second 1⁻ state, the K¹(1410), which has been seen in earlier three-body analyses.     

Anomalous magnetic moment of theW-bosons and non-standardZ 0 W + W − coupling in polarizede − e + collisions

We study quantitatively the reactions \(e^ + e^ - \to W^ + e\bar \nu _e \) ,e _R ^? e ⁺ and the rare decay \(Z^0 \to W^ \pm l^ \mp \mathop {\nu _e }\limits^{( - )} \) forl=e, μ and τ, as a test for anomalous γW ⁺ W ^? andZ ⁰ W ⁺ W ^? structure. If κ denotes the anomalous magnetic moment of theW-boson and ω its anomalous coupling to theZ ⁰, values of |ω|>2.5 and |κ|>1.5 can be ruled out at LEP and SLC rather easily. This will put constraints on composite model building.