H. Döbbeling

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.

Real-to-imaginary ratio of the pp forward elastic scattering amplitude in the momentum range between 180 and 590 MeV/c

Abstract The real-to-imaginary ratio of the p p forward elastic scattering amplitude has been measured at the LEAR facility of CERN by the Coulomb-nuclear interference method at seven beam momenta between 181 and 590 MeV/c. The ratio is positive at 590 MeV/c, becomes negative below 500 MeV/c, reaches a minimum at 260 MeV/c and then crosses zero again at about 230 MeV/c.

Antiproton-proton elastic cross sections in the momentum range between 180 and 600 MeV/c

Abstract Differential cross sections for pp elastic scattering have been measured in the full angular range for the p momenta between 180 and 600 MeV/ c . It is found that s- and p-wave scattering is dominant below 300 MeV/ c . The s-wave component in the total cross section is 40–60% below 300 MeV/ c , in contrast to the NN scattering where it is about 90%. The s-, p- and d-wave scattering amplitudes are derived.

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.

Measurement of the p̄p → n̄n cross section at low p̄ momenta

First measurements of the differential cross section are presented for pp → nn at LEAR in the momentum range between 180 and 600 MeV/c. The differential cross sections show a forward peaking followed by a smooth drop-off. No indication of the “bump-dip” structure reported at higher momenta has been observed. The angle-integrated charge-exchange cross sections are determined down to Enncm = 6.6 MeV.

Measurement of the neutron and the proton F2 structure function ratio

The ratio of the structure function F2n/F2p (x) has been measured in deep inelastic scattering of 274 GeV muons on hydrogen and deuterium targets exposed simultaneously to the beam. The results were obtained from 0.3 (0.6) million events from hydrogen (deuterium) in the range 0.004 <x< 0.8 and 1 <Q2< 190 GeV2. At x < 0.25 both the statistical and the systematic error is below 2%. Implications for parton distributions and for the σw/σz production cross section ratio in pp collisions are discussed. When compared to other results obtained at lower energies, the data indicate a Q2 dependence of the ratio.

Search for a narrow resonance in antiproton-proton annihilation cross sections in the beam momentum range between 400 and 600 MeV/c

Abstract A measurement of the p p annihilation cross section in the beam momentum region between 400 and 600 MeV/c has been performed with a mass resolution of 1 MeV/c2 and statistical precision generally better than 1%. No evidence for the X(1935) resonance is found. The upper limit at the 90% confidence level is 5 mb MeV/c2 for a width of 2 MeV/c2.

Search for narrow baryonium states near the NN threshold

Abstract The reactions p p →π − X and p d → pX earch for narrow baryonium states in the mass region between 1.6 and 2.0 GeV/c2. No such state has been observed. In the first reaction the upper limit for the production of narrow baryonium states is 8μb/sr for a 3 standard deviation signal with 4 MeV/c2 width. In the second reaction this limit is 10 μb/sr. The second reaction is rather insensitive for observation of baryonium states as it is dominated by quasi-free contributions.

An apparatus for the measurement of antiproton-proton cross sections at low momenta

An experiment which aims at a precise measurement of pp cross sections at low momenta is presented. Its design and performance are described with emphasis on the particle identification capabilities. A calorimeter-like detector array which serves for the detection of antineutrons is discussed in some detail. Its properties were measured in a test experiment and are compared to Monte Carlo calculations.

A measurement of the π0 decay of Λ 12 C and Λ 11 B hypernucleihypernuclei@@@Иэмерения π0 распада гиперядер Λ 12 C и Λ 11 B

SummaryWe made a direct measurement of the π0 weak decay branching ratio of theΛ12C hypernucleus for the first time. The branching ratio is estimated to beΓπ0/Γ=0.166±0.055 from the measurement. The branching ratio agrees fairly with a theoretical calculation with a realistic pion distorted wave function, but is inconsistent with a calculation with a free π0 wave function. An upper limit of the π0 decay branching ratio of theΛ11B hypernucleus was also estimated to beΓπ0/Γ<0.291 (90% confidence level).RiassuntoÈ stata misurata direttamente la frazione di decadimento (debole) dell’ipernucleoΛ12C in π0 per la prima volta. Dalla misura risulta cheΓπ0/Γ=0.166±0.055. Il rapporto coincide con il calcolo teorico con una funzione d’onda distorta realistica pionica, ma non è in accordo con il calcolo con la funzione d’onda libera del pione. Anche il limite superiore stimato del rapporto di decadimento pionico dell’ipernucleoΛ11B èΓπ0/Γ<0.291 (livello di confidenza 90%).РеэюмеВпервые проводится прямое иэмерение отнощение ветвей π0 слабого распада гиперядерΛ12C. Иэ иэмерения оценивается отнощение ветвей, которое составляетΓπ0/Γ=0.166±0.055. Отнощение ветвей совпадает с теоретическим расчетом, испольэуюшим искаженную волновую функцию реального пиона, но не согласуется с вычислением для волновой функции свободного π0. Также оценивается верхний предел отнощения ветвей π0 распада гиперядраΛ11B, который составляетΓπ0/Γ<0.291 (с достоверностью 95%).