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Physics program > Hypernuclei

The λ hypernucleus is a long-lived baryonic system (t=10-10s). The λ is not affected by the Pauli principle and can penetrate deeply inside the nucleus permitting measurements of the system’s response to the stress imposed on it. Unknown properties of the baryonic interaction may manifest themselves in hypernuclei, providing information on the flavor SU(3) basis for baryonic systems. Spectroscopic investigation of  λ hypernuclei, provides a unique tool to study the LN interaction, since direct LN scattering experiments are difficult. λ hypernuclei feature narrow states commonly described by coupling of low-lying core states to a λ in low level shell states. This makes spectroscopic studies possible. The comprehension of Baryon-Baryon interactions is fundamental in order to understand our world and its evolution. An effective LN interaction can be determined from the hypernuclear spectra obtained from various reactions and be used to discriminate between the different YN and YY potentials. The knowledge of the LN interaction is important. It provides a check of various generalized models of the baryon-baryon interaction. More precise knowledge of the YN and YY interactions can shed some light on the role of strange quarks in the dynamics of baryonic systems.

Hyperons are believed to appear in the interior of neutron stars at around 2-3 times nuclear saturation density. Quantitative information on YN, YNN and YY interactions is indispensable to understand the high-density phases of neutron star matter, the occurrence of which may dramatically affect both the equilibrium and non-equilibrium properties of the star. Most theoretical models predict that the appearance of hyperons brings the maximum mass of a stable neutron star down to values incompatible with the recent observation of a star of about two solar masses. While there are indications that this problem may be overcome including the effect of YNN interactions, it may also signal the presence of a non-hadronic phase, i.e. of deconfined quark matter, in the inner core of the star. A large body of data came from two types of highly complementary hypernuclear spectroscopy techniques: reaction based spectroscopy (with hadron probes) and  gamma spectroscopy. Both these powerful techniques have limitations, first limited energy resolution and small spin-flip amplitudes, and second the access only to hypernuclear states below nucleon emission threshold. The advantage of being able to simultaneously observe, by (e, e'K+) spectroscopy, more complete structures, as well as to provide precise absolute binding energy is obvious.

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