Two-particle momentum correlation functions as measured in heavy ion collisions or in high-energetic proton–proton collisions are studied. Special emphasis is put on systems like ΛΛ or K−p where ...effects from the coupling to other channels could be relevant. In both cases other channels open at relatively low momenta or are already open at the reaction threshold. To have a solid basis, realistic coupled-channel interactions for ΛΛ−ΞN−ΛΣ−ΣΣ and πΛ−πΣ−K¯N are utilized in the actual calculations. It is found that the opening of the ΞN channel leaves a trace in the ΛΛ correlation function that could be detectable in experiments. Should the proposed H-dibaryon be located close to or below the ΞN it will have a very pronounced effect. The presence of open channels in systems like Ξ−p or K−p does influence the correlation functions significantly at low momenta and will certainly complicate any dedicated analysis.
The
Λ
N
and
Σ
N
interactions are considered at next-to-leading order in SU(3) chiral effective field theory. Different options for the low-energy constants that determine the strength of the contact ...interactions are explored. Two variants are analysed in detail which yield equivalent results for
Λ
N
and
Σ
N
scattering observables but differ in the strength of the
Λ
N
→
Σ
N
transition potential. The influence of this difference on predictions for light hypernuclei and on the properties of the
Λ
and
Σ
hyperons in nuclear matter is investigated and discussed. The effect of the variation in the potential strength of the
Λ
N
-
Σ
N
coupling (also called
Λ
-
Σ
conversion) is found to be moderate for the considered
Λ
3
H
and
Λ
4
He
hypernuclei but sizable in case of the matter properties. Further, the size of three-body forces and their relation to different approaches to hypernuclear interactions is discussed.
Results from an ongoing study of baryon–baryon systems with strangeness S=−1 and −2 within chiral effective field theory are reported. The investigations are based on the scheme proposed by Weinberg ...which has been applied rather successfully to the nucleon–nucleon interaction in the past. Results for the hyperon–nucleon and hyperon–hyperon interactions obtained to leading order are reviewed. Specifically, the issue of extrapolating the binding energy of the H-dibaryon, extracted from recent lattice QCD simulations, to the physical point is addressed. Furthermore, first results for the hyperon–nucleon interaction at next-to-leading order are presented and discussed.
The reaction e+e−→Λ¯Λ is investigated for energies close to the threshold. Specific emphasis is put on the role played by the interaction in the final Λ¯Λ system which is taken into account ...rigorously. For that interaction a variety of Λ¯Λ potential models is employed that have been constructed for the analysis of the reaction p¯p→Λ¯Λ in the past. The enhancement of the effective form factor for energies close to the Λ¯Λ threshold, seen in pertinent experiments, is reproduced. Predictions for the Λ electromagnetic form factors GM and GE in the timelike region and for spin-dependent observables such as spin-correlation parameters are presented.
Scattering of charmed baryons on nucleons Haidenbauer, J.; Krein, G.
The European physical journal. A, Hadrons and nuclei,
11/2018, Letnik:
54, Številka:
11
Journal Article
Recenzirano
Odprti dostop
.
Chiral effective field theory is utilized for extrapolating results on the
Λ
c
N
interaction, obtained in lattice QCD at unphysical (large) quark masses, to the physical point. The pion-mass ...dependence of the components that constitute the
Λ
c
N
potential up to next-to-leading order (pion-exchange diagrams and four-baryon contact terms) is fixed by information from lattice QCD simulations. No recourse to
SU
(3) or
SU
(4) flavor symmetry is made. It is found that the results of the HAL QCD Collaboration for quark masses corresponding to
m
π
=
410 - 570 MeV imply a moderately attractive
Λ
c
N
interaction at
m
π
=
138
MeV with scattering lengths of
a
≈
-
1
fm for the
1
S
0
as well as the
3
S
1
partial waves. For such an interaction the existence of a charmed counterpart of the hypertriton seems unlikely but four- and/or five-baryons systems with a
Λ
c
baryon could be indeed bound.
.
The in-medium properties of a
Ξ
N
potential derived within chiral effective field theory up to next-to-leading order are investigated. The considered
Ξ
N
interaction includes the coupling to other ...baryon-baryon channels in the strangeness
S
=
-
2
sector (
Λ
Λ
,
Σ
Σ
and is in line with available empirical constraints on the
Λ
Λ
S
-wave scattering length and on
Ξ
N
elastic and inelastic cross sections. In particular, there are no near-threshold bound states in the
Ξ
N
system. A
G
-matrix calculation for this interaction is performed and reveals that the single-particle potential of the
Ξ
-hyperon in nuclear matter is moderately attractive as suggested by recent experimental evidence for the existence of
Ξ
-hypernuclei.
.
Brueckner theory is used to investigate the in-medium properties of a
Λ
-hyperon in nuclear and neutron matter, based on hyperon-nucleon interactions derived within
SU
(3) chiral effective field ...theory (EFT). It is shown that the resulting
Λ
single-particle potential
U
Λ
(
p
Λ
=
0
,
ρ
)
becomes strongly repulsive for densities
ρ
of two-to-three times that of normal nuclear matter. Adding a density-dependent effective
Λ
N
-interaction constructed from chiral
Λ
N
N
three-body forces increases the repulsion further. Consequences of these findings for neutron stars are discussed. It is argued that for hyperon-nuclear interactions with properties such as those deduced from the
SU
(3) EFT potentials, the onset for hyperon formation in the core of neutron stars could be shifted to much higher density which, in turn, could pave the way for resolving the so-called hyperon puzzle.
Results for the ΛN and ΣN interactions obtained at next-to-leading order in chiral effective field theory are reported. At the order considered there are contributions from one- and ...two-pseudoscalar-meson exchange diagrams and from four-baryon contact terms without and with two derivatives. SU(3) flavor symmetry is imposed for constructing the hyperon–nucleon interaction, however, the explicit SU(3) symmetry breaking by the physical masses of the pseudoscalar mesons (π, K, η) and of the involved baryons is taken into account. An excellent description of the hyperon–nucleon system can be achieved at next-to-leading order. It is on the same level of quality as the one obtained by the most advanced phenomenological hyperon–nucleon interaction models.
Cross sections for the charm-production reactions p¯p→Λ¯c−Σc+, Σ¯cΣc, Ξ¯cΞc, and Ξ¯c′Ξc′ are presented, for energies near their respective thresholds. The results are based on a calculation performed ...in the meson-exchange framework in close analogy to earlier studies of the Jülich group on the strangeness-production reactions p¯p→Λ¯Σ, Σ¯Σ, Ξ¯Ξ by connecting the two sectors via SU(4) flavor symmetry. The cross sections are found to be in the order of 0.1–1 μb at energies of 100 MeV above the respective thresholds, for all considered channels. Complementary to meson exchange, where the charmed baryons are produced by the exchange of D and D* mesons, a charm-production potential derived in a quark model is employed for assessing uncertainties. The cross sections predicted within that picture turn out to be significantly smaller.
.
A qualitative discussion on the range of the potentials as they result from the phenomenological meson-exchange picture and from lattice simulations by the HAL QCD Collaboration is presented. For ...the former pion- and/or
η
-meson exchange are considered together with the scalar-isoscalar component of correlated
π
π
/
K
K
¯
exchange. It is observed that the intuitive expectation for the behavior of the baryon-baryon potentials for large separations, associated with the exchange of one and/or two pions, does not always match with the potentials extracted from the lattice simulations. Only in cases where pion exchange provides the longest ranged contribution, like in the
Ξ
N
system, a reasonable qualitative agreement between the phenomenological and the lattice QCD potentials is found for baryon-baryon separations of
r
≳
1
fm. For the
Ω
N
and
Ω
Ω
interactions where isospin conservation rules out one-pion exchange a large mismatch is observed, with the potentials by the HAL QCD Collaboration being much longer ranged and much stronger at large distances as compared to the phenomenological expectation. This casts some doubts on the applicability of using these potentials in few- or many-body systems.
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