P. Hawranek

Search for η-mesic nuclei in a recoil-free transfer reaction

We have studied the reaction p+{sup 27}Al {yields} {sup 3}He+p+{pi}{sup -}+X at recoil-free kinematics. An {eta} meson possibly produced in this reaction would be thus almost at rest in the laboratory system and could therefore be bound with high probability, if nuclear {eta} states exist. The decay of such a state through the N*(1535) resonance would lead to a proton-{pi}{sup -} pair emitted in opposite directions. For these conditions we find some indication of such a bound state. An upper limit of {approx_equal}0.5 nb is found.

High resolution study of the Λp final state interaction in the reaction p+p→K++(Λp)

The reaction pp ! K + + (�p) was measured at Tp = 1.953 GeV and � = 0 ◦ with a high missing mass resolution in order to study thep final state interaction. The large final state enhancement near thep threshold can be described using the stan- dard Jost-function approach. The singlet and triplet scattering lengths and effective ranges are deduced by fitting simultaneously thep invariant mass spectrum and the total cross section data of the freep scattering.

Magnetic spectrometer Big Karl for studies of meson production reactions

Abstract The paper describes modifications of the Julich magnetic spectrometer Big Karl needed to study meson production and especially to investigate charge symmetry breaking effects—an experiment that requires a high-precision measurement. New elements that have been added to Big Karl have extended the spectrometer capabilities to a much wider momentum range. The new features also facilitate simultaneous detection of particles with very different rigidities. The experimental methods for improving background and determining relative acceptance of the spectrometer at various rigidities are presented.

Cross section and tensor analysing power of the dd→ηα reaction near threshold

The angular distributions of the unpolarised differential cross section and tensor analysing power A xx A x x of the d → d → α η reaction have been measured at an excess energy of 16.6 MeV. The ambiguities in the partial-wave description of these data are made explicit by using the invariant amplitude decomposition. This allows the magnitude of the s -wave amplitude to be extracted and compared with results published at lower energies. In this way, firmer bounds could be obtained on the scattering length of the ηα system. The results do not, however, unambiguously prove the existence of a quasi-bound ηα state.

Upper limits for a narrow resonance in the reaction p + p to K^++ (Lambda p)

The reaction pp -> K^+ + (Lambda p) has been measured at T_p = 1.953 GeV and \Theta = 0 deg with a high missing mass resolution in order to study the Lambda p final state interaction. Narrow S = -1 resonances predicted by bag model calculations are not visible in the missing mass spectrum. Small structures observed in a previous experiment are not confirmed. Upper limits for the production cross section of a narrow resonance are deduced for missing masses between 2058 and 2105 MeV/c^2.

Detailed comparison of the pp→π+pn and pp→π+d reactions at 951 MeV

The positively charged pions produced in proton–proton collisions at a beam momentum of 1640 MeV/c were measured in the forward direction with a high resolution magnetic spectrograph. The missing mass distribution shows the bound state (deuteron) clearly separated from the pn continuum. Despite the very good resolution, there is no evidence for any significant

Experimental study of the p + 6Li → η + 7Be reaction 11.3 MeV above threshold

The cross section for the reaction

Precision measurements of the pp ->pi(+)pn and pp ->pi(+)d reactions: Importance of long-range and tensor force effects

p+^6\text{Li}\to\eta+^7\text{Be}

SEARCH FOR η-NUCLEUS BOUND STATE AT COSY

was measured at an excess energy of 11.28 MeV above threshold by detecting the recoiling

Study of p + d → 3A + π reactions in the Δ-resonance region

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