R. Bertini

Hypernuclei with sigma particles

Abstract The production of Σ particles in the (K − , π − ) on 9 Be at 720 MeV/ c has been studied at the CERN proton synchrotron (PS). The missing-mass spectrum shows structures in the Σ region, which have been interpreted as belonging to hypernuclei with sigma particles. An upper limit of 8 MeV for the width of these states has been estimated.

Indication of a deeply bound and compact K- pp state formed in the pp- -> pLambdaK+ reaction at 2.85 GeV.

We have analyzed data of the DISTO experiment on the exclusive pp --> pLambdaK+ reaction at 2.85 GeV to search for a strongly bound compact K- pp(approximately = X) state to be formed in the pp --> K+ + X reaction. The observed spectra of the K+ missing mass and the pLambda invariant-mass with high transverse momenta of p and K+ revealed a broad distinct peak of 26-sigma confidence with a mass M(X)=2267+/-3(stat)+/-5(syst) MeV/c2 and a width Gamma(X)=118+/-8(stat)+/-10(syst) MeV. The enormously large cross section indicates formation of a compact K- pp with a large binding energy of B(K)=103 MeV, which can be a possible gateway toward cold and dense kaonic nuclear matter.

Spin-orbit interaction of lambda particles in nuclei

Abstract In the strangeness exchange reaction (K − , π − ) on 12 C and 16 O the most prominent transitions to hypernuclear states produced in recoilless and quasi-free Λ production have been identified. The analysis of the spectra shows that in the Λ-nucleus interaction the spin-orbit coupling is at least one order of magnitude smaller than for the nucleon-nucleus interaction.

Σ hypernuclear states in (K−, π±) reactions on 12C

Abstract Using negative kaons of momenta 400 and 450 MeV/c, Σ hypernuclear states have been produced in (K−, π−) and (K−, π+) reactions on 12C. The observed states are interpreted as the recoilless production of Σ particles on carbon. The upper limit for the widths of these states is estimated to be 5 MeV, independent of the charge of the Σ particle.

The (K−, π+) strangeness exchange reaction on 16O

Abstract Using negative kaons of 450 MeV/c momentum, Σ hypernuclear states have been produced in the (K−, π+) reaction on 16O. The observed states are interpreted as the recoilless production of Σ− particles in the p 3 2 and p 1 2 orbits of the Σ16C hypernucleus. Their energy splitting gives a constraint to the magnitude of the spin-orbit coupling for the Σ− particles in the nucleus.

Hypernuclear production in the

Abstract Cross sections for the production of hypernuclei were measured in the reaction A(K − , π − ) Λ A. on light and heavy nuclear targets, using a separated K − beam at the CERN Proton Synchrotron. The pions were detected in the forward direction. The results are compared with cross sections calculated under the assumption that the reaction took place on a single neutron. The good agreement between the measured and the calculated cross sections justifies the use of the (K − , π − ) reaction in order to obtain spectroscopic information on hypernuclei.

(K^−, π^−)

Abstract The strangeness exchange reaction (K − , π − ) on 32 S and 40 Ca has been studied. The strongest transitions are assigned to states having a configuration with the Λ particle in a 1s, 1p, 1d, 2s, and 1f orbit coupled to the nuclear core. These Λ shells are approximately equidistantly spaced, the energy spacings being about 9 MeV. In the first approximation the Λ particle behaves like a “spinless neutron” in a harmonic oscillator potential.

reaction

Abstract As part of a programme to study the spin structure of the p p→ n n channel, we have measured the analysing power A 0 n and the differential cross section at an incident antiproton beam momentum of 704 MeV/ c . The analysing power exhibits a remarkable angular dependence, which is poorly reproduced by the existing potential models.

A full set of nuclear shell orbitals for the Λ particle observed in 32ΛS and 40ΛCa

Abstract The total cross section of the reaction pp→ppK+K− has been determined for proton–proton reactions with p beam =3.67 GeV /c . This represents the first cross section measurement of the pp→ppK−K+ channel near threshold, and is equivalent to the inclusive pp→ppK−X cross section at this beam momentum. The cross section determined at this beam momentum is about a factor 20 lower than that for inclusive pp→ppK+X meson production at the same CM energy above the corresponding threshold. This large difference in the K+ and K− meson inclusive production cross sections in proton-proton reactions is in strong contrast to cross sections measured in sub-threshold heavy ion collisions, which are similar in magnitude at the same energy per nucleon below the respective thresholds.

Measurement of the analysing power and the differential cross section of the pp charge-exchange reaction at LEAR

Abstract Results are given for the analysing power of the p p→ n n charge-exchange reaction at four incident beam momenta. The measurement is part of an experimental programme to study the spin structure of this reaction at LEAR. The analyzing power shows strong angular and energy dependence, which at present is not reproduced by the existing meson-exchange potential models.