Electron-positron annihilation above 2 GeV and the new particles

This paper reviews the experimental and phenomenological aspects of electron-positron annihilation into hadrons at center-of-mass energies above 2 GeV. The behavior of the total cross section for hadron production as a function of energy is described; and the important parameter R - the ratio of this cross section to the muon-pair production cross section - is discussed. Data on charged particle multiplicities, particle production ratios, and single particle inclusive distributions is also summarized. The paper than summarizes our knowledge of the newly discovered ψ particles; and examines the various theories as to their nature and their relation to conventional hadronic physics.     

Observation of antideuteron production in electron-positron annihilation at 10 GeV center of mass energy

The production of antideuterons has been observed in electron-positron annihilations at center-of-mass energies around 10 GeV. Antideuterons have been identified unambiguously by their energy loss in the drift chamber, their time-of-flight and the pattern of their energy deposition in the shower counters of the ARGUS detector. The production rate in the momentum range (0.6?1.8) GeV/c is (1.6_?0.7^+1.0) × 10^?5 per hadronic event.     

Supersymmetric three-jets in electron-positron annihilation

The bremsstrahlung of gluons and gluinos off quarks and squarks is studied in e⁺e^? annihilation for longitudinally polarized beams. The contribution of a given supersymmetric state is found to be 11–27% of the conventional gluon bremsstrahlung. With all supersymmetric channels open this adds up to 90–100% of the q$\text{q}$g contribution. Dalitz-plot and angular distributions are investigated. A pronounced forward-backward asymmetry is found for gluino bremsstrahlung. Characteristic features are also exhibited by the angular distribution of the normal to the event plane.     

Gluino production in electron-positron annihilation

We discuss the pair production of gluinos in electron-positron annihilation at LEP, in a model with soft supersymmetry breaking, allowing for mixing between the squarks. In much of the parameter space of the Minimal Supersymmetric Model (MSSM) the cross section corresponds to aZ branching ratio above 10^–5, even up to 10^–4. A non-observation of gluinos at this level restricts the allowed MSSM parameter space. In particular, it leads to lower bounds on the soft mass parameters in the squark sector.     

Senile scaling in electron-positron annihilation

An important difference is pointed out between the approach to scaling behaviour in deep inelastic scattering and annihilation. In the framework of the massive quark model a quantitative analysis of the breaking terms is carried out for the total and the one-particle inclusive cross-sections. Good agreement with available data is found.     

Spinless bosons in electron-positron annihilation

The contributions to the processes \(e^ + e^ - \to \mu ^ + \mu ^ - ,q\bar q,\gamma \gamma ,e^ + e^ - \) , mediated by scalar and/or pseudoscalar bosons are calculated. The constraints on their coupling constants and their masses are investigated as they arise from the radiative decayZ ⁰→⁺ e ^? γ and from the experimental data for the annihilation processes into lepton, photon and quark pairs. Data one ⁺ e ^?→μ⁺ μ^?, γγ ande ⁺ e ^? seriously reduce the domain of coupling constants to leptons and photons still allowed by the probable value of the width ofZ ⁰→e ⁺ e ^? γ. Experimentse ⁺ e ^?→μ⁺ μ^?, γγ,e ⁺ e ^? at 45 GeV c.m.s. energy with a sensitivity of 10% will decide about the existence of a heavy spinless boson with the presumed phenomenological couplings to leptons and photons. Assuming universality of the coupling to leptons and quarks a conservative bound on the contribution toR arising from spinless boson exchange is already in conflict with the presumed radiative width ofZ ⁰→e ⁺ e ^? γ.     

Gluino pair production in electron-positron annihilation

We summarize the effects of some unknown supersymmetry breaking mechanism by the addition to the super-QCD lagrangian of explicit, and different, mass terms for the scalar superpartners of quarks and antiquarks. Allowing also a possible Majorana mass for the gluino, we then calculate cross sections for e⁺e^? → two gluinos, a process which may be observable if the gluino is sufficiently long-lived.     

Hunting for glueballs in electron-positron annihilation

We calculate the cross section for the exclusive production of J(PC)=0(++) glueballs G0 in association with the J/psi in e(+)e(-) annihilation using the perturbative QCD factorization formalism. The required long-distance matrix element for the glueball is bounded by CUSB data from a search for resonances in radiative Upsilon decay. The cross section for e(+)e(-)-->J/psi+G0 at sqrt[s]=10.6 GeV is similar to exclusive charmonium-pair production e(+)e(-)-->J/psi+h for h=eta(c) and chi(c0), and is larger by a factor of 2 than that for h=eta(c)(2S). As the subprocesses gamma(*)-->(cc)(cc) and gamma(*)-->(cc)(gg) are of the same nominal order in perturbative QCD, it is possible that some portion of the anomalously large signal observed by Belle in e(+)e(-)-->J/psiX may actually be due to the production of charmonium-glueball J/psiG(J) pairs.     

Next-to-leading-order results for five, six, and seven jets in electron-positron annihilation

We present next-to-leading order corrections in the leading color approximation for jet rates in electron-positron annihilation up to seven jets. The results for the two-, three-, and four-jet rates agree with known results. The NLO jet rates have been known previously only up to five jets. The results for the six- and seven-jet rate are new. The results are obtained by a new and efficient method based on subtraction and numerical integration.     

Single weak boson production in electron-positron annihilation

The cross sections for the process,e ⁺ e ^?→W ^±+hadrons are estimated extensively at the lowest order in the minimal gauge theory ofSU(2) _L ×U(1). It is pointed out that our result on the angular distribution is not compatible with the result reported by Neufeld.     

Three-photon annihilation of the electron-positron pairs

Three-photon annihilation of the electron-positron pairs (=(e⁻,e⁺)-pairs) is considered in the electron rest frame. The energy of the incident positron can be arbitrary. The analytical expression for the cross-section of three-photon annihilation of the (e⁻,e⁺)-pair has been derived and investigated.     

Four jet event shapes in electron-positron annihilation

We report next-to-leading order perturbative QCD predictions of 4 jet event shape variables for the process obtained using the general purpose Monte Carlo EERAD2. This program is based on the known `squared' one loop matrix elements for the virtual parton contribution and squared matrix elements for 5 parton production. To combine the two distinct final states numerically we present a hybrid of the commonly used subtraction and slicing schemes based on the colour antenna structure of the final state which can be readily applied to other processes. We have checked that the numerical results obtained with EERAD2 are consistent with next-to-leading order estimates of the distributions of previously determined four jet-like event variables. We also report the next-to-leading order scale independent coefficients for some previously uncalculated observables; the light hemisphere mass, narrow jet broadening and the 4 jet transition variables with respect to the JADE and Geneva jet finding algorithms. For each of these observables, the next-to-leading order corrections calculated at the physical scale significantly increase the rate compared to leading order (the K factor is approximately 1.5–2). With the exception of the 4 jet transition variables, the published DELPHI data lies well above the predictions. The renormalisation scale uncertainty is still large and in most cases the data prefers a scale significantly smaller than the physical scale. This situation is reminiscent of that for three jet shape variables, and should be improved by the inclusion of power corrections and resummation of large infrared logarithms. Received: 17 November 1998 / Revised version: 26 January 1999 / Published online: 7 April 1999     

The hadronic cross section of electron-positron annihilation at 9.5 GeV and the ϒ and ϒ′ resonance parameters

The reaction e⁺e^?→ hadrons has been measured in the ? and ?′ region using the DASP detector at the DESY storage ring DORIS. The following final results are obtained: R_had(9.5 GeV)=3.73±0.16±0.28, Γ_ee(?)=(1.23 ± 0.08 ± 0.12) keV, B_μμ(?)=(3.2±1.3±0.3)%, $\text{Γ}{}_{\mathrm{<mtext>ee</mtext>}}\text{Γ}{}_{\mathrm{<mtext>had</mtext>}}\text{Γ}{}_{\mathrm{<mtext>tot</mtext>}}\text{(?′)=(0.55±0.11 ±0.06)}\text{keV}$, and M(?′)?M(?)=(556 ±10) MeV.     

Double vector-charmonium production in electron-positron annihilation into two photons at $$\sqrt s = 10.6$$ GeV

In experimentally studying the exclusive production of two \(c\bar c\) mesons in electron-positron annihilation, the BELLE Collaboration obtained results that differ substantially from theoretical predictions. Recently, it was assumed that a significant part of this discrepancy can be explained by the process e⁺e^? → 2γ* → 2J/ψ, and its cross section was published. It is shown here that these results are incorrect (the cross sections are overestimated). The correct values of the cross sections for the double production of various vector charmonia are given.     

Recent results on antiproton annihilation in 4He

With experimental data of ${\bar p}$ annihilation at rest on nuclei of ⁴He, collected by the Obelix spectrometer (LEAR, CERN), we have studied a number of reactions with 4 and 5 charged particles in the final state, distinguishing the annihilations on more than one nucleon, and with strangeness production. The main results of our observations are: (a) a higher (up to 20 times) strangeness production in ⁴He than in H; (b) the evidence of a possible signature of a $\overline{K}pp$ ( $\overline{K} ppn$ ) bound state; (c) a measurement of a double strangeness production (2K ⁺) and a hint for some production yields of double-strange bound systems like 2K ^?2n; (d) a signal compatible with the baryonic $\Theta^+(1530)$ resonance, interpreted as a pentaquark system.     

Pion-nucleon charge exchange amplitudes above 2 GeV

The amplitudes for the pion-nucleon charge exchange reaction of the Karlsruhe-Helsinki and the George-Washington-University partial-wave analyses are compared with those of a Regge-cut model with the aim to explore the possibility to provide high-energy constraints for theoretical baryon resonance analyses in the energy region above 2GeV.