Eta Production Research Articles

Simulation of photon-nucleon interactions Part I. An event generator from the pion threshold up to 4 GeV

We describe an event generator that reproduces the photon-nucleon interaction from the pion threshold up to 4 GeV accounting to a large extent for the total photoabsorption cross section. Many reaction channels on the nucleon have been considered: namely single pion production, eta production, multipion production and some hyperon production channels. Compatibility with the GEANT and PAW software packages has been assured throughout. The extension to reactions on two and three nucleon systems is discussed.

Statistical description of π, K+, K−, η-meson and antiproton production from absolute threshold to 2 GeV/nucleon

The production of pions, K±, η-mesons and antiprotons at the energy region from absolute threshold to 2 Gev/nucl. is discussed in the frame of a statistical approach with finite particle number and quantum statistics effects. For antiprotons and strangeness particle production we take into account the associative character of these particles formation and for eta production we take into consideration the contribution of resonances N(1440)P11 and N(1535)S11. When calculating the cross-sections of K±, η-mesons and antiprotons we used the value of the thermalization degree of nuclear matter obtained from pion data. The results of our calculations show quite good agreement with experimental data. The model predictions of the K±, η, p̄-production cross-sections from 0.2 to 2 GeV/nucl. are presented.

Subthreshold η-production in pion-nucleus collision

We study subthreshold eta production in terms of the first collision model. The calculation was made taking into account the high energy component of nuclear nucleon momentum distribution as well as Hulthen and Fermi distributions. We obtain fine description of Los Alamos experimental data, both subthreshold eta production cross sections and the energy spectra. The eta reabsorption inside the nucleus is discussed.

Next to leading order eta production at hadron colliders

Inclusive eta production at hadron colliders is considered, based on the evaluation of the eta fragmentation functions at next to leading order. Absolute predictions at LHC and SSC are presented, including the ratio η/π0, together with the estimate of the theoretical uncertainty, as a possible neutral background to theH→γγ detection.

Pion interaction with the trinucleon up to the eta production threshold.

Pion elastic, charge exchange scattering, and induced eta production on the trinucleon systems are investigated in a coupled-channels approach in momentum space with Faddeev wave functions. The channel [pi][ital N][r arrow][eta][ital N] is included using an isobar model with [ital S]-, [ital P]-, and [ital D]-wave resonances. While the coherent reactions like [sup 3]He([pi],[pi])[sup 3]He can be reasonably well reproduced up to [ital T][sub [pi]]=500 MeV, large discrepancies appear for the incoherent processes [sup 3]He([pi][sup [minus]],[pi][sup 0])[sup 3]H and [sup 3]He([pi][sup [minus]],[eta])[sup 3]H at backward angles and energies above [Delta] resonance. In the forward direction, the ([pi],[eta]) calculations underestimate the experimental measurements very close to threshold, but agreement with the data improves with increasing pion energy. Predictions are made for the asymmetries of the various reactions on polarized [sup 3]He.

ETA and dilepton production in heavy-ion reactions

We present a nonperturbative dynamical study of η-meson and pion production in heavy-ion collisions from 1 to 2 GeV/A bombarding energy. The dynamical evolution of the nucleus-nucleus collision is described by a transport equation of the Boltzmann-Uehling-Uhlenbeck type evolving phase-space distribution functions for nucleons, Δ's, N(1440)'s, N(1535)'s, pions and η's with their isospin degrees of freedom. We also study the effect of pion and Δ selfenergies on the pion dynamics. Though quite substantial medium modifications are incorporated, the pion spectra and yields show only a weak sensitivity on the in-medium effects. Furthermore, we present results for differential dilepton yields in heavy-ion collisions at bombarding energies of 1 and 2 GeV/A incorporating all known sources for dilepton production. We investigate in particular the sensitivity of the calculated yields to predicted changes of the ρ meson in dense matter and discuss the feasibility to measure the time-like electromagnetic form factor of hadrons and their medium-dependence through the observation of dileptons.

Threshold pion photoproduction on nucleons

Pion photo- and electroproduction of the nucleon at threshold is reviewed in theory and experiment. In this region the leading S-wave amplitudes (E0+) are predicted by low-energy theorems (LET) based on current conservation and chiral symmetry. While these predictions are in agreement with the data for charged pion production, LET cannot explain the reaction p( gamma , pi 0)p over the energy range of the first 10 MeV above threshold. Present calculations involving final state interactions are difficult to reconcile with the requirements of LET and suffer from a strong model dependence due to off-shell formfactors. With the completion of the new electron accelerators with high duty factor and high intensity, new types of coincidence experiments with polarization degrees of freedom will be performed. The authors review the formalism for such reactions and present the multipole decomposition of the various response functions. The new experimental capabilities allow some of the most challenging problems of intermediate energy physics to be attacked, such as the puzzle of neutral pion production at threshold, the electric quadrupole amplitude in the region of the Delta resonance (bag deformation), the Coulomb monopole amplitude near the Roper resonance ('breathing mode'), the production of eta -mesons via the N*(1535) and the production of two pions and more to test consequences of chiral symmetry and the interaction of pions at low energies.

ETA production in heavy ion collisions

The production of η mesons and pions in intermediate energy heavy ion collisions has been calculated on the basis of a BUU calculation. We find an η to pion ratio of about 10−3 at 1 GeV/A for the primordial particles. Effects of the reabsorption of the η's through the N(1535) resonance are discussed.

Eta and eta ' production in e+e- annihilation at 29 GeV. Evidence for the Dx+/- decays into eta pi +/- and eta ' pi +/-

eta production has been investigated by the Mark II Collaboration at the SLAC e/sup +/e/sup -/ storage ring PEP. eta particles are reconstructed by their ..gamma gamma.. decay mode. The eta fragmentation function has been measured and found to be in good agreement with the Lund-model prediction. eta' production has been measured for the first time in high-energy e/sup +/e/sup -/ annihilation. There is evidence at the 3sigma level for D/sub s//sup +- / decay into eta..pi../sup +/ and eta'..pi../sup +- /.

Detection of staphylococcal exfoliative toxin by slide latex agglutination

A simple and rapid method in which slide latex agglutination was used was developed to detect the exfoliative toxin (ET) elaborated by clinical isolates. ET types A and B (ET-A and ET-B) were purified by plate gel isoelectrofocusing, and anti-ET sera were obtained by immunizing rabbits. A specific immunoglobulin G antitoxin was then prepared from the immunized rabbit sera by fast protein liquid chromatography, and latex particles were coated with the antitoxin. Of 74 staphylococcal strains isolated from patients with staphylococcal scalded skin syndrome, 61 strains were found to produce ET by the newborn mouse bioassay. All 61 strains were shown to be positive for ET-A and ET-B production by the slide latex agglutination method. The lowest concentration of ETs detected by the latex agglutination method was 0.5 microgram/ml, which was much lower than that detected by the double immunodiffusion method, with a sensitivity of 50 micrograms/ml. It is crucial to prove ET production by clinical isolates for the diagnosis and surveillance of staphylococcal scalded skin syndrome. The latex agglutination method is a sensitive, simple, and rapid test which can be used as an alternative to the newborn mouse bioassay.

Production of eta and omega mesons in tau decay and a search for second-class currents.

The production of eta and ..omega.. mesons in tau decay has been studied with the CLEO detector. A sample of 42 000 e/sup +/e/sup -/..-->..tau/sup +/tau/sup -/ events at a mean ..sqrt..s of 10.5 GeV is used in the analysis. The branching ratio B(tau/sup -/..--> omega pi../sup -/..nu../sub tau/) is measured to be (1.60 +- 0.27 +- 0.41)%. No signal for eta production from tau decay is observed, resulting in 95%-confidence-level upper limits of 1.8% for B(tau/sup -/..-->..eta..pi../sup -/..nu../sub tau/), 2.1% for B(tau/sup -/..-->..eta..pi../sup -/..pi../sup 0/..nu../sub tau/), and 2.1% for inclusive eta production in tau decay. No evidence is found for decays proceeding via second-class currents.

Enzyme-linked immunosorbent assays for Staphylococcus aureus exfoliative toxins A and B and some applications.

Two enzyme-linked immunosorbent assays were developed for detection of staphylococcal exfoliative toxins A and B (ETA and ETB) with a double-antibody sandwich protocol. Antibodies against both toxins were purified by affinity chromatography from sheep antisera raised against purified ETA and ETB. These affinity-purified antibodies were free of detectable amounts of antibodies to other staphylococcal antigens and neutralized the actions of ETA and ETB. Alkaline phosphatase was conjugated to these antibodies. The enzyme-linked immunosorbent assay, which could detect at least 3 ng of ETA and ETB per ml, was used to quantitate the toxins in the culture supernatant fluids of staphylococcal strains. Thus, the kinetics of ETA and ETB synthesis and of ETA and ETB release into the supernatant fluids were determined; other determinations included the roles of carbon dioxide concentration, pH, glucose concentration, temperature, and agitation on the production of ETA and ETB.

Nuclear Enhancement ofπ0andηMesons Produced at Large Transverse Momenta

The authors have measured the large-p/sub T/ inclusive cross sections for ..pi../sup 0/ and eta production near 90/sup 0/ in the center-of-mass system in 200-GeV/c ..pi../sup +/ and proton collisions with beryllium, carbon, and aluminum targets. The cross section for both ..pi../sup 0/ and eta mesons rises with increasing nucleon number (A) of the target nucleus as A/sup ..cap alpha../, with ..cap alpha..>1. The ratio of the ..pi../sup 0/ yield in pA collisions to that in ..pi../sup +/A collisions decreases with increasing p/sub T/. .AE

The role of the Nβin nucleon-exchange reactions

The authors argue that the Nbeta trajectory plays a role in nucleon-exchange reactions which, though small compared with Nalpha in pi N to N pi , provides a better understanding of SU(3)-related nucleon-exchange reactions, particularly those involving Sigma and eta production.

Measurement of InclusiveηProduction ine+e−Interactions near Charm Threshold

We have measured the inclusive cross section for eta production in e/sup +/e/sup -/ interactions near charm threshold using the Crystal Ball detector. No pronounced structure in the energy dependence is observed. By comparing cross sections above and below charm threshold we obtain the limits (90% confidence limit): R(e/sup +/e/sup -/..-->..FF-barX)Br(F..-->..etax) ..etax)<0.13 (averaged over charged and neutral D components of the psi''(3770) decays). Our results are inconsistent with a previous report of a large energy dependence of the eta cross section ascribed to the crossing the FF* and F*F* production thresholds.

Measurement of High-Energy Direct Photons inψDecays

The inclusive ..gamma.. and ..pi../sup 0/ momentum distributions at the psi have been measured. Using these data and estimates of eta production, it is found that (4.1 +- 0.8) % of psi decays contain a direct photon with energy greater than 60% of the beam energy. The expected momentum distribution for direct photons calculated to lowest order in quantum chromodynamics is qualitatively different from that observed in the data.

Isospin-½ nucleon-resonance production by aV,Aweak neutral current

A set of ratios characterizing the production of the isospin-1/2 resonances D$sub 13$(1514) and S$sub 11$(1505), as well as the isospin-3/2 resonance P$sub 33$(1232), by electromagnetic and weak (charged and neutral) currents are defined. Assuming the most general weak neutral current with V, A spatial structure, the matrix elements needed to extract the production ratios are calculated in three dynamical models for resonance production: the Born- approximation model, the nonrelativistic quark model, and the quark-bag model. For the special case of the Weinberg-Salam theory neutral current, the three models suggest that for 0 < or = sin$sup 2$theta/subW/ < or = 0.5 the ratios D$sub 13$/P$sub 33$ and S$sub 11$/P$sub 33$ observed in neutral-current $pi$$sup 0$ or eta production on a free nucleon target should be substantially smaller (by a factor of 2 to 4) than the corresponding ratios observed in charged-current $pi$$sup 0$ or eta production. An attempt is made to predict the ratios D$sub 13$/P$sub 33$ and S$sub 11$/P$sub 33$ to be expected in charged-current production from the corresponding ratios observed in electroproduction, but here the three models do not agree, and so it is possible only to state a wide possible range in which the values of the ratios may lie. The charge-exchange corrections needed for comparison with experiments on complex nuclear targets are briefly discussed; it is found that for an aluminum target the reduction factors quoted above are halved, so that in neutral-current-induced reactions the ratios D$sub 13$/P$sub 33$ and S$sub 11$/P$sub 33$ are smaller by a factor of 1 to 2 than the corresponding ratios observed in charged-current--induced reactions. (AIP)

Eta production by pions

The generalised interference model is applied to the process of eta production by pions. The model is shown to give a good description of this process at all energies.