Strange dibaryons in neutron stars and in heavy-ion collisions

Abstract

The formation of dibaryons with strangeness are discussed for the interior of neutron stars and for central relativistic heavy-ion collisions. We derive limits for the properties of H-dibaryons from pulsar data. Signals for the formation of possible bound states with hyperons at BNL's Relativistic Heavy-Ion Collider (RHIC) are investigated by studying their weak decay patterns and production rates. HYPERONS AND DIBARYONS IN NEUTRON STARSThere has been a lot of speculations about the appearance of new particles in the interior of neutron stars. A traditional neutron star consists of neutrons, protons, and leptons only. Cameron suggested first in 1959, that hyperons will also appear at high baryon density [1]. A possible phase transition to quark matter was conjectured shortly after the quark model was introduced [2]. Pion condensation [3] as well as kaon condensation were considered later [4]. Finally, strange stars, built out of absolutely stable strange quark matter, have been studied within the MIT bag model [5,6]. The appearance of one or the other exotic phase in the core of neutron stars is still a matter of active debates. Nevertheless, recent developments in the field indicate, that hyperons are probably the first exotic particle to appear in neutron star matter at twice normal nuclear density. This result was consistently derived within various, different models: nonrelativistic potential models [7], quark-meson coupling model [8], relativistic mean-field models [9-11], relativistic Hartree-Fock [12], Brueckner-Hartree-Fock models [13,14], and chiral effective Lagrangians [15]. Hence, the onset of hyperons at 2ρ 0 seems to be rather insensitive to the underlying details of the hyperon-nucleon interaction used.If there are a lot of hyperons in the interior of neutron stars, then it might be also possible to form dibaryons with strangeness. Besides the famous H-dibaryon proposed by Jaffe [16] built out of six quarks, the most recent version of the Nijmegen potential predicts the existence of deeply bound states of two hyperons, involving the Σ's and Ξ's with maximum isospin [17]. Their results can be understood in terms of the underlying SU(3) symmetry for the baryon-baryon interactions (see [17]).Let us assume in the following, that there exist bound states with hyperons. What would be the consequences for the properties of dense matter, as present in the interior of neutron stars? Bound systems in dense matter have been discussed before in connection * I thank RIKEN, BNL, and the U.S. Department of Energy for providing the facilities essential for the completion of this work.

Novel Mechanism ofH0Dibaryon Production in Proton-Proton Interactions from Parton-Based Gribov-Regge Theory

“…More recently, QCDinspired models predict di-baryons with strangeness S = 0, -1, and -2. The invariant masses range between 2000 and 3000 MeV [5][6][7][8][9][10][11][12]. Unfortunately, masses and widths of the expected 6-quark states differ considerably for these models.…”

“…Metastable exotic multihypernuclear objects (MEMOs), for example, consists of nucleons, Λ's, and Ξ and are stabilized due to Pauli's principle, blocking the decay of the hyperons into nucleons. Only few investigations about the weak decay of di-baryons exist so far (see [12] for a full discussion and new estimates for the weak nonleptonic decays of strange di-baryons): In [16], the H-di-baryon was found to decay dominantly by H → Σ − + p for moderate binding energies. While the (ΛΛ) bound state, which has exactly the same quantum numbers as the H-di-baryon, was studied in [17].…”

Strangeness at the international Facility for Antiproton and Ion Research

“…MEMOs consist of nucleons, Λ's, and Ξ and are stabilised due to Pauli's principle, blocking the decay of the hyperons into nucleons. Only a few investigations about the weak decay of di-baryons exist so far (see [14] for a full discussion and new estimates for the weak nonleptonic decays of strange di-baryons). The (ΛΛ) bound state, which has exactly the same quantum numbers as the H-di-baryon, was studied in [15].…”

Strangeness at the International Facility for Antiproton and Ion Research

“…MEMOs consist of nucleons, 's, and and are stabilized due to Pauli's principle, blocking the decay of the hyperons into nucleons. Only few investigations about the weak decay of dibaryons exist so far (see [14] for a full discussion and new estimates for the weak nonleptonic decays of strange di-baryons). The ( ) bound state, which has exactly the same quantum numbers as the H-di-baryon, was studied in [15].…”