Speaker
Summary
The Roper resonance has been a puzzle ever since its detection in πN
phase shifts. In most investigations no apparent resonance signatures
could be found in the observables. Not only its nature has been a
matter of permanent debate, also its resonance parameters show a big
scatter in their values.
In the pp → npπ+ reaction measured at CELSIUS-WASA at several
energies a pronounced resonance structure at M_nπ+≈ 1350 MeV with
Γ ≈ 140 MeV has been found. These numbers agree very favourably
with recent SAID πN phase shift results for the Roper pole as well as
with the very recent BES results from J/ψ → NbarN. With the pole
position being roughly 100 MeV below the previously believed value
of the N(1440), also its decay branchings (defined at the pole posi-
tion) change dramatically. From near-threshold two-pion production,
when Roper excitation is the only significant process, we find the decay
N→ Nσ to be the by far dominant process pointing to a breathing
mode nature of the Roper resonance.
supported by BMBF (06 TU 261), DFG (Europ. Grad. School), COSY-FFE
