Study of the N* momentum distribution for experimental eta-mesic 3He searches
N. G. Kelkar, D. Bedoya Fierro, H. Kamada, M. Skurzok
abstract
The proximity of the etaN threshold to the mass of the N*(1535) allows us to consider the eta-nucleus interaction below the eta threshold as a series of excitations, decays of the N* on the constituent nucleons and the eventual decay of the N* to a nucleon and a pion. Experimental searches for eta-mesic nuclei rely on this model in their analysis of data where an eta-mesic nucleus could have been formed. However, the momentum distribution of an N* is often approximated to be the same as that of a nucleon inside the nucleus. Our aim is to obtain an estimate of the error introduced by this assumption and hence we calculate the momentum distribution of the N* formed inside 3He. This distribution is found to be narrower than that of a nucleon inside 3He. The latter affects the outgoing particles kinematics and reduces the determined acceptance of their experimental registration by the detection setup. This reduction is crucial for the determination of cross sections in the search for eta-mesic helium.
N-N-N* model calculations for experimental eta-mesic 3He searches
N. G. Kelkar, H. Kamada, M. Skurzok
abstract
The possibility for the existence of the exotic NNN* states is explored with the objective of calculating the N* momentum distribution inside such nuclei. Even though the latter is an essential ingredient for the analysis of the experimental data on the pd->pdpi0, pd->ppppi- and pd->pnnpi+ reactions aimed at finding an eta-mesic 3He, the data analysis is usually performed by approximating the N* momentum distribution by that of a nucleon. Here, we present calculations performed by solving the three-body Faddeev equations to obtain the momentum distribution of the N* inside possible (N* )+np, (N* )0np and (N* )+-d states. The N*
momentum distributions are found to be much narrower than those of the nucleons and influence the data selection criteria.
Constraining the optical potential in the search for eta-mesic 4He
M. Skurzok, P. Moskal, N.G. Kelkar, S. Hirenzaki, H. Nagahiro, N. Ikeno
abstract
A consistent description of the dd-> 4He eta and dd-> (4He-eta)bound X cross sections was recently proposed with a broad range of real (V0) and imaginary (W0), eta-4He optical potential parameters leading to a good agreement with the d d -> 4He eta data. Here we compare the predictions of the model below the eta production threshold, with the WASA-at-COSY excitation functions for the dd -> 3He N pi reactions to put stronger constraints on (V0, W0). The allowed parameter space (with |V_0| < sim 60 MeV and |W_0| < sim 7 MeV estimated at 90% CL ) excludes most optical model predictions of eta-4He nuclei except for some loosely bound narrow states.
On Quasibound N*-Nuclei
N. G. Kelkar, D. Bedoya Fierro, P. Moskal
abstract
The possibility for the existence of unstable bound states of the S11 nucleon resonance N?(1535) and nuclei is investigated. These quasibound states are speculated to be closely related to the existence of the quasibound states of the eta mesons and nuclei. Within a simple model for the NN? interaction involving a pion and eta meson exchange, N??nucleus potentials for N??3He and N??24Mg are evaluated and found to be of a Woods?Saxon-like form which supports two to three bound states. In the case of N??3He, one state bound by only a few keV and another by 4 MeV is found. The results are however quite sensitive to the NN?? and NN?? vertex parameters. A rough estimate of the width of these states, based on the mean free path of the exchanged mesons in the nuclei, leads to very broad states with ? ? 80 and 110 MeV for N??3He and N??24Mg respectively.
