Observation of meson central production in baryon exchange processes

The central production of ⁰,f ₂ and ₃ ⁰ mesons is observed for the first time in processes which are originated by ⁺ p reactions proceeding via baryon exchange mechanism. The data come from the CERN WA56 experiment designed to separate the baryon exchange reactions in ⁺ p-collisions at 20 GeV/c. We report on the measured integral and differential cross sections and also give the density matrix elements of the meson resonances observed.     

Photon-deuteron diffractive scattering

One expects a similarity of the energy dependence of the difference _tot(*p)– _tot(*n) for virtual (deep inelastic scatteringQ ²m ²) and real (Q ²=0) photons. Previous analysis of D structure functions with allowence for nuclear shadowing (NS) in the deuteron has led to conclusion that _tot(*p)– _tot(*n)<0>x<0.015. the=" early=" evidence=" from=" the=" real=" photoproduction=" data="> _tot(p)– _tot(n)<0. we=" critically=" reexamine=" determinations=" of=" the="> _tot(p)– _tot(n), using more accurate calculations of NS correction to _tot(D), and discuss a possibility of _tot(n) _tot(p) at moderately high energies.     

Isotonic and isobaric dependencies of nuclear charge radii for rare-earth nuclei

Isotonic and isobaric dependencies of nuclear charge radii in the region between Z=54 and Z=70 are obtained from the analysis of isotope shift data r² and muonic and electron scattering data on r². They are compared with the predictions of the droplet model and the Hartree-Fock calculations. The isobaric dependencies of r² have proven to be especially sensitive to the choice of an effective nucleon-nucleon interaction.     

Heavy-quark bound states in potentials with the Bethe-Salpeter equation

The spinless Bethe—Salpeter equation is solved for three attractive static quark-antiquark potentials of the form V(r)=–ar^–+br+c, 01, and the effective non-Coulombic power-law potential of the formV(r)=ar ^0.1+c to obtain the spin-averaged energy levels in bottomonium (b ) and charmonium (c ) families. The shifted 1/N expansion technique is used. Calculations of the energy eigenvalues are carried out up to third order and parameters of each potential are adjusted to obtain the best agreement with the experimental spin-averaged data (SAD). Flavor-dependent and flavor-independent cases are considered in this work.     

A unified formalism for γγ→meson and ψ-γX with possible tests for hybrid and gluonic hadrons

The couplings of conventional and hybrid mesons to (real and virtual) and their production amplitudes in M are described in a unified manner. Existing results for heavy quarks are recovered, extensions to light quarks and to virtual couplings are made and phenomenological applications discussed. In particular we discuss relativistic corrections to 0⁺, 1⁺, 2⁺ for both real and virtual photons and offer a resolution to a long standing puzzle in perturbative QCD concerning the helicity structure of 2⁺⁺. We suggest that the production off ₂ (1720) involves gluons in an essential way or that this meson hasJ2.     

Study of theπ + π − γ system centrally produced in the reactionpp→p f (π + π − γ)p s at 300 GeV/c

The reactionppp _f ( ^{+ –} )p _s , where the ^{+ –} system is centrally produced, has been studied at 300 GeV/c. The ^{+ –} mass spectrum shows evidence for a ⁰ decay mode of the (958) andf ₁ (1285). The branching ratio (f ₁(1285) ^{+ +})/(f ₁(1285) ⁰ ) is found to be 5.0±0.7. No evidence is found for a ⁰(770) decay mode of theE/f ₁ (1420) for which an upper limit BR (E/f ₁(1420) ⁰ )<0.08 at=" 95%=" cl=" is=">     

Excited levels of111In and113In

Levels and transitions in¹¹¹In and¹¹³In have been studied in the¹¹¹Cd(p, n)¹¹¹In and¹¹³Cd(p, n)¹¹³In reactions. By means of- coincidences,-angular distributions, relative excitation functions and conversion electron measurements more than 20 levels below 2 MeV have been established in each nucleus. Several negative-parity states were found above 1 MeV. Two low-spin positive-parity states with features similar to the possible rotational band in the heavier In nuclei are observed below 1,400 keV in both nuclei.     

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     

Experimental study of π− π+ system at low invariant-masses

We report on results of an experiment to study the reaction ^– p ^{– +} in the incident pion momentum region between 295 and 450 MeV/c. A departure from phase space was observed in invariant-mass spectra and angular distributions which cannot be explained with and resonance production. It indicates aI=0,J ^P = 0^{+ – +} final-state interaction.Deceased     

On the possibilities to study the exotic state 1−+ in photoproduction of the πη, πη′ systems

We show that photoproduction experiments provide propitious conditions to study the exotic state 1^–+ in the and channels. For unpolarized photons contributions from natural and unnatural parity exchanges do not interfere with each other, a fact which permits to estimate the correctness of phase shift analyses. In photoproduction of the ⁺ system in the mass range ofa ₂(1320) a more stringent limit on the product (1^–+)Br(1^–+) can be obtained than in experiments on Primakoff production on nuclei. Particularly favourable is the study of the state 1^–+ in the coherent photoproduction of the ⁰ and ⁰ systems on nuclei, with significantly enlarged statistics and a simplified phase shift analysis.     

Inelastic production of neutral pions in the4He(γ, πℴp)3H reaction

The yield of the⁴He(, p)³H reaction has been studied in a bremsstrahlung beam of photons with a maximum energy of 450 MeV. The measurements were made on an experimental setup consisting of a total absorption Cerenkov gamma spectrometer and a helium streamer chamber. A kinematic analysis is made of the angular distributions of the disintegration products of the⁴He nucleus to study the mechanism of inelastic photoproduction of neutral pions. The relatively high event density in the region of small proton-triton separation angles is attributable to the quasielastic mechanism of the reaction in which pion photoproduction is accompanied by excitation of the⁴He nucleus.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 51–56, September, 1989.     

Photofission of235U and238U at intermediate energies: absolute cross sections and fragment mass distributions

The total photofission cross section _,F for²³⁵U and²³⁸U has been measured in the energy range 50E 800 MeV at the 855 MeV Mainz Microtron MAMI using energy and time tagged photons (Glasgow Tagger) and a 4 arrangement of position sensitive fragment detectors. Besides the absolute photofission cross section _F , which almost completely exhausts the total photon absorption cross section for these nuclei, fragment mass distributions in this energy domain were determined via time of flight techniques (TOF). The results for the total photofission cross sections _,F normalized to the atomic numberA for both isotopes coincide, and agree in the-resonance region, within the systematic errors, with the socalledUniversal Curve _,T /A of the total photon absorption cross section _,T . At higher energies the cross sections exhibit a smooth behaviour. In particular, it is shown for the first time that there isno resonance-like shape near the D₁₃ resonance (at 710 MeV) as observed for the free proton. This complete suppression of the D₁₃ resonance in complex nuclei is not yet understood on a microscopic level. The fragment mass distributions show a predominantly mass symmetric fission. However, contributions from mass asymmetric fission at some photon energies may give a hint of an increased mass asymmetric fission after the onset of the pion and two pion channels.Excerpt from D26 Supported by the Deutsche Forschungsgemeinschaft, SFB 201 Mainz     

The new element 111

In an experiment carried out to identify element 110, we have observed an-decay chain, that can be unambiguously assigned to²⁶⁹110. In a scries of preexperiments the excitation functions of the fusion reactions⁵⁰Ti +²⁰⁸Pb²⁵⁸104^* and⁵⁸Fe +²⁰⁸Pb²⁶⁶108^* were measured with high precision in order to get the optimum projectile energies for the production of these heavy elements. The cross-section maxima of the 1n evaporation channels were observed at excitation energies of 15.6 MeV and 13.4 MeV, respectively. These data result in an optimum excitation energy of 12.3 MeV of the compound nucleus for the production of²⁶⁹110 in the reaction⁶²Ni +²⁰⁸Pb²⁶⁹110 + 1n. In irradiations at the corresponding beam energy of 311 MeV we have observed a decay chain of 4 subsequent a decays. This can be assigned to the isotope with the mass number 269 of the element 110 on the basis of delayed - coincidences. The accurately measured decay data of the daughter isotopes of the elements 108 to 102, obtained in the previous experiments, were used. The isotope²⁶⁹110 decays with a hair-life of (270 _-120 ⁺¹³⁰⁰ ) s by emission of (11.132±0.020) MeV alpha particles. The production cross-section is (3.3 _-2.7 ^+6.2 ) pb.     

AssociateJ/ψ+γ production: a clean probe of gluon densities

Production of strange and charm particles by hadron-proton collisions is analyzed in terms of a fire-ball (FB) model assuming the multiplicity of secondaries of a given massm, to be proportional to the FB mass: n(m)M ^*, the FB kinematics being determined by the Feynman-Yang scaling, as in the case of production. It is found that (m)1/m ² and that, using this property together with the scaling, no-free-parameter fits to currently available data of strange and charm particles frompp and p collisions are satisfactory, as well as for the photoproduction of charm mesonD and charm hyperon _c .