Photoproduction ofη-MesicHe3

Abstract

The photoproduction of eta-mesic 3He has been investigated using the TAPS calorimeter at the Mainz Microtron accelerator facility MAMI. The total inclusive cross section for the reaction gamma3He-->etaX has been measured for photon energies from threshold to 820 MeV. The total and angular differential coherent eta cross sections have been extracted up to energies of 745 MeV. A resonancelike structure just above the eta production threshold with an isotropic angular distribution suggests the existence of a resonant quasibound state. This is supported by studies of a competing decay channel of such a quasibound eta-mesic nucleus into pi(0)pX. A binding energy of (-4.4+/-4.2) MeV and a width of (25.6+/-6.1) MeV is deduced for the quasibound eta-mesic state in 3He.

η-PHOTOPRODUCTION OFF 3He: SEARCH FOR η-MESIC NUCLEI

“…The total cross sections of the two decay modes (2γ and 6γ) are in good agreement with results from [30]. The cross section has a maximum of about 29 µb at an incident photon beam energy of 825 MeV.…”

“…Thresh Figure 9.11: η coherent cross section. The expected shape of the resonance like structure is plotted (with a FWHM of 39 MeV see [30])above threshold in continue black line, below threshold in dotted black line.…”

“…Photoproduction of η-meson o 3 He was studied via the η →2γ and η →3π 0 decay modes at the tagged photon beam of the Mainz MAMI accelerator using the combined 4π Crystal Ball/TAPS calorimeter. In a previous experiment, Pfeier et al [30] had reported evidence (although at low statistical signicance) for the formation of a quasi-bound η-nucleus state. The present experiment aimed at an improved statistical quality.…”

Search for η-mesic 3He in non-mesonic final state

“…Previous indirect experimental studies of near threshold η production in pd → 3 Heη reaction [48,49] show that probably there is a pole in the production amplitude at excitation energy of Q 0 = [(−0.36±0.11±0.04)±i(0.19±0.28±0.06)] M eV that is in agreement with data for γ 3 He → η 3 He reaction [50,51]. The experimental search for η-mesic 3 He provided by COSY-11 collaboration [56,57] resulted in the cross section upper limit of 70 nb for pd → ( 3 Heη) bound → 3 Heπ 0 reaction.…”

Systematic few-body analysis of ηd, ηHe3 , and ηH

“…In the second group of experiments [15][16][17][18][19][20][21][22][23][24] one detects the η-nucleus system with low relative kinetic energy E ηA . Here the key point is that attractive forces between the meson and the nucleus tend to hold them in the region where the primary 'photoproduction interaction' acts.…”