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تسجيل مستخدم جديدIs the first excited state of the $alpha$-particle a breathing mode?
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The isoscalar monopole excitation of 4He is studied within a few-body ab initio approach. We consider the transition density to the low-lying and narrow 0+ resonance, as well as various sum rules and the strength energy distribution itself at different momentum transfers q. Realistic nuclear forces of chiral and phenomenological nature are employed. Various indications for a collective breathing mode are found: i) the specific shape of the transition density, ii) the high degree of exhaustion of the non-energy-weighted sum rule at low q and iii) the complete dominance of the resonance peak in the excitation spectrum. For the incompressibility K of the alpha-particle values between 20 and 30 MeV are found.
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In this contribution we review and clarify the arguments which might allow the interpretation of the isoscalar monopole resonance of $^4$He as a collective breathing mode.
The fragmentation of quasi-projectiles from the nuclear reaction $^{40}Ca$+$^{12}C$ at 25 MeV/nucleon was used to produce excited states candidates to $alpha$-particle condensation. The methodology relies on high granularity 4$pi$ detection coupled t
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The first excited state in neutron-rich 23O was observed in a (2p1n) knock-out reaction from 26Ne on a beryllium target at a beam energy of 86 MeV/A. The state is unbound with respect to neutron emission and was reconstructed from the invariant mass
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All the time since its discovery the N$^*$(1440) baryon state, commonly known as Roper resonance, has been a state with many question marks - despite of its 4-star ranking in the particle data book. One reason is that it does not produce any explicit
resonance-like structures in the observables of $pi$N or $gamma$N reactions. Only in partial wave analyses of $pi$N scattering data a clear resonance strcuture gets obvious in the $P_{11}$ partial wave. Very recent measurements of the J/$Psi$ decay by the BES collaboration and of the $pp to nppi^+$ reaction at 1.3 GeV by the CELSIUS-WASA collaboration show for the first time a clear resonance structure in the invariant $npi^+$ mass spectrum for the Roper resonance at M $approx$ 1360 MeV with a width of about 150 MeV. These values agree very favorably with the pole position results of recent $pi$N phase shift analyses. In consequence of this very low-lying pole postion, which is roughly 100 MeV below the nominal value, the decay properties have to be reinvestigated. From our two-pion production data we see that the decay mainly proceeds via N$^* to $N$sigma$, i.e. a monopole transition as expected for the breathing mode of the nucleon.
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