Ab initio Calculations of Charge Symmetry Breaking in the A=4 Hypernuclei

Study of Charge Symmetry Breaking in A = 4 hypernuclei in √SNN = 3 GeV Au+Au collisions at RHIC

In this paper, we present the measurement of the charge symmetry breaking in A = 4 hypernuclei in Au+Au collisions at √SNN = 3 GeV. The signal reconstruction and binding energy measurement of Λ4H and Λ4He, including corrections and systematic uncertainty evaluation, are discussed. Combined with the energy levels of excited states, our preliminary result of Λ binding energy difference for excited states is ΔBΛ(1+) = −190±130(stat.)±70(syst.) keV which shows a negative value and its magnitude is comparable to the result of ground states ΔBΛ(0+) = 130 ± 130(stat.) ± 70(syst.) keV. These results are compared with previous measurements and theoretical model calculations.

Study of charge symmetry breaking in A = 4 hypernuclei in √sNN = 3 GeV Au+Au collisions at RHIC

In these proceedings, we present the measurement of the charge symmetry breaking in A = 4 hypernuclei in Au+Au collisions at √sNN = 3 GeV. The signal reconstruction and binding energy measurements of 4ΛH and 4ΛHe, including corrections on momentum, are discussed. Our result of Λ binding energy difference for ground states is ΔBΛ(0+) = 0.16 ± 0.14(stat.) ± 0.10(syst.) MeV. Combined with the energy levels of excited states, the difference for excited states is ΔBΛ(1+) = −0.16 ± 0.14(stat.) ± 0.10(syst.) MeV which shows a negative sign with a magnitude comparable to the result of ground states. These results are compared with previous measurements and theoretical model calculations.

Resolving the Λ Hypernuclear Overbinding Problem in Pionless Effective Field Theory

We address the Λ hypernuclear "overbinding problem" in light hypernuclei which stands for a 1-3 MeV excessive Λ separation energy calculated in _{Λ}^{5}He. This problem arises in most few-body calculations that reproduce ground-state Λ separation energies in the lighter Λ hypernuclei within various hyperon-nucleon interaction models. Recent pionless effective field theory (πEFT) nuclear few-body calculations are extended in this work to Λ hypernuclei. At leading order, the ΛN low-energy constants are associated with ΛN scattering lengths, and the ΛNN low-energy constants are fitted to Λ separation energies (B_{Λ}^{exp}) for A≤4. The resulting πEFT interaction reproduces in few-body stochastic variational method calculations the reported value B_{Λ}^{exp}(_{Λ}^{5}He)=3.12±0.02  MeV within a fraction of MeV over a broad range of πEFT cutoff parameters. Possible consequences and extensions to heavier hypernuclei and to neutron-star matter are discussed.

Induced Hyperon-Nucleon-Nucleon Interactions and the Hyperon Puzzle

We present the first ab initio calculations for p-shell hypernuclei including hyperon-nucleon-nucleon (YNN) contributions induced by a similarity renormalization group transformation of the initial hyperon-nucleon interaction. The transformation including the YNN terms conserves the spectrum of the Hamiltonian while drastically improving model-space convergence of the importance-truncated no-core model, allowing a precise extraction of binding and excitation energies. Results using a hyperon-nucleon interaction at leading order in chiral effective field theory for lower- to mid-p-shell hypernuclei show a good reproduction of experimental excitation energies while hyperon separation energies are typically overestimated. The induced YNN contributions are strongly repulsive and we show that they are related to a decoupling of the Σ hyperons from the hypernuclear system, i.e., a suppression of the Λ-Σ conversion terms in the Hamiltonian. This is linked to the so-called hyperon puzzle in neutron-star physics and provides a basic mechanism for the explanation of strong ΛNN three-baryon forces.