M. Lesiak

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.

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}

Three-nucleon interaction dynamics studied via the deuteron-proton breakup

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

SEARCH FOR η-NUCLEUS BOUND STATE AT COSY

^7

SEARCH OF η-NUCLEUS BOUND STATE FORMATION IN RECOIL FREE TRANSFER REACTIONS

Be nuclei. A dedicated set of focal plane detectors was built for the magnetic spectrograph Big Karl and was used for identification and four momentum measurement of the

SEARCH FOR BOUND η-NUCLEUS STATES

^7