Shell model calculations applied to the gamma ray spectroscopy of light Lambda hypernuclei
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73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
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Effects of the two-body and three-body hyperon-nucleon interactions in Λ hypernuclei
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Lonardoni, D.↗
High-Resolution Hypernuclear Spectroscopy at JLab Hall A. Results and perspectives
Hypernuclear spectroscopy via electromagnetic induced reactions is a valuable and powerful way to study hypernuclei, hadronic systems with non-zero strangeness content, providing an alternative to the hadron induced reactions mainly studied so far. Electron-induced hypernuclear spectroscopy has been studied in Hall A at Je!erson Lab [1] on three nuclei, 12C, 16O, and 9Be with unprecedented resolution and with an improved particle identification system, using a RICH detector, in order to unambiguously identify kaons, thus allowing the measurement of high-quality, almost backgroundfree, hypernuclear spectra. Two superconducting septum magnets were added to the existing apparatus in order to permit particle detection at very forward angle providing a reasonable counting rate. These studies have provided the first quantitative information on core-excited states in hypernuclei. In the case of oxygen, a waterfall target has been employed allowing for the simultaneous measurement of hypernuclear production on oxygen and of elementary kaon-? electro-production on protons: a crucial measurement to disentangle the contribution of the elementary reaction from the measured hypernuclear production cross section, yielding direct access to the nucleus-hypernucleus transition structure. A ? binding energy value for 16 ?N calibrated against the elementary (e, e?K+) reaction on hydrogen, has been obtained. Final results for 12C, 16O, 9Be will be presented [1-3]. Results of Hall C experiments will be presented in another talk in this Conference. Since it is essential for further theoretical study of hypernuclei to collect enough information about L production on nucleons and about excitation spectra of a wide variety of ? hypernuclei, a continuation of the successful hypernuclear program at JLab is very desirable. For these reasons Hall A and Hall C Jefferson Lab hypernuclear collaborations decided to merge and propose a new layout for the 12 GeV Jefferson Lab era that has the advantages of both the experimental setups. In fact the new experimental design not only widens and deepens the physics range but also dramatically improves production yield and efficiency allowing to study both mass spectroscopy on a wide range of nuclei (from few body to 208Pb) and pion decay spectroscopy at the same time [4]. Figs.1, 2 show the results obtained for 12C and 16O. Fig. 3 shows the new layout.
Garibaldi, Franco↗
Measurements of H Λ 3 and H Λ 4 Lifetimes and Yields in Au + Au Collisions in the High Baryon Density Region
We report precision measurements of hypernuclei $^3_ΛH$ and $^4_ΛH$ lifetimes obtained from Au + Au collisions at $\sqrt{sNN}$ = 3.0 GeV and 7.2 GeV collected by the STAR experiment at the Relativistic Heavy Ion Collider, and the first measurement of $^3_ΛH$ and $^4_ΛH$ midrapidity yields in Au + Au collisions at $\sqrt{sNN}$ = 3.0 GeV. $^3_ΛH$ and $^4_ΛH$, being the two simplest bound states composed of hyperons and nucleons, are cornerstones in the field of hypernuclear physics. Their lifetimes are measured to be 221 ± 15 (stat) ± 19 (syst) ps for $^3_ΛH$ and 218 ± 6 (stat) ± 13 (syst) ps for $^4_ΛH$. The p T -integrated yields of $^3_ΛH$ and $^4_ΛH$ are presented in different centrality and rapidity intervals. It is observed that the shape of the rapidity distribution of $4_ΛH$ is different for 0%–10% and 10%–50% centrality collisions. Thermal model calculations, using the canonical ensemble for strangeness, describes the $^3_ΛH$ yield well, while underestimating the $^4_ΛH$ yield. Transport models, combining baryonic mean-field and coalescence (jam) or utilizing dynamical cluster formation via baryonic interactions (phqmd) for light nuclei and hypernuclei production, approximately describe the measured $^3_ΛH$ and $^4_ΛH$ yields. Our measurements provide means to precisely assess our understanding of the fundamental baryonic interactions with strange quarks, which can impact our understanding of more complicated systems involving hyperons, such as the interior of neutron stars or exotic hypernuclei.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Observation of the antimatter hypernucleus $^4_{\bar{\Lambda}}\overline{\hbox{H}}$
Matter-antimatter asymmetry is a research topic of fundamental interest, as it is the basis for the existence of the matter world, which survived annihilation with antimatter in the early Universe. High energy nuclear collisions create conditions similar to the Universe microseconds after the Big Bang, with comparable amounts of matter and antimatter. Much of the antimatter created escapes the rapidly expanding fireball without annihilation, making such collisions an effective experimental tool to create heavy antimatter nuclear objects and study their properties. In this paper, we report the first observation of the antimatter hypernucleus $^4_{\bar{\Lambda}}\overline{\hbox{H}}$, composed of an $\bar{\Lambda}$, an antiproton and two antineutrons. The discovery was made through its two-body decay after production in ultrarelativistic heavy ion collisions by the STAR experiment at the Relativistic Heavy Ion Collider. In total, 15.6 candidate $^4_{\bar{\Lambda}}\overline{\hbox{H}}$ antimatter hypernuclei are obtained with an estimated background count of 6.4. Lifetimes of the antihypernuclei $^3_{\bar{\Lambda}}\overline{\hbox{H}}$ and $^4_{\bar{\Lambda}}\overline{\hbox{H}}$ are measured and compared with lifetimes of their corresponding hypernuclei, testing the symmetry between matter and antimatter. Various production yield ratios among (anti)hypernuclei and (anti)nuclei are also measured and compared with theoretical model predictions, shedding light on their production mechanism.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
The third generation (e,e'K+) hypernuclear spectroscopic experiment at JLab Hall-C
We carried out a Lambda hypernuclear spectroscopic experiment at Jefferson Lab in 2009, aiming at precise spectroscopy of {Lambda} hypernuclei in the wide-mass region up to A = 52. The experiment has been successfully carried out and now we are in data analysis phase. The most important point of the analysis is precision mass scale calibration by comparing mass spectra of Lambda hypernuclei and Lambda and {Sigma}{sup 0} hyperons in the same setup with {Lambda} hypernuclear spectroscopic experiment. We show a preliminary result of the calibration analysis with {sup 12}{sub {Lambda}}B spectrum.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Formation of Hyper Hydrogen isotopes in light p-shell nuclei
Recent experiment by A1 Collaboration at Mainz, namely identification of {sub Λ}{sup 4}H hyperfragment from primary {sub Λ}{sup 9}Li hypernucleus produced in reaction (e, e′K{sup +}), stirred renewed interest in baryonic decay of hypernuclei. The important role of s{sup −1}s{sub Λ} excitation in p-shell hypernuclei as well as the existence of selection rules connected with [f] (Young diagram) was noted earlier within Translational Invariant Shell Model (TISM). The particular conditions of the present experiment (reaction is not selective and produces highly excited states) dictate extension of the simplest TISM: expansion of the harmonic oscillator basis space and compression of multiplets (to only (λμ) for L and [f] for S, T). Such modified TISM explains abundance production of {sub Λ}{sup 4}H hyperfragment and predicts production of another Hyper Hydrogen {sub Λ}{sup 6}H.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Strange Light Nuclei
"Strange" means 1) unusual or surprising, especially in a way that is difficult to explain or understand or 2) having strangeness degree of freedom. Light nuclear systems with strangeness, light hypernuclei, are perfect playground to study baryon force which would be a bridge between well established nuclear force in low energy region and QCD, the first principle of the strong interaction. Overview of study of light hypernuclei is given and recent experimental findings are reviewed.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Position reconstruction in fission fragment detection using the low pressure MWPC technique for the JLab experiment E02-017
When a lambda hyperon was embedded in a nucleus, it can form a hypernucleus. The lifetime and its mass dependence of stable hypernuclei provide information about the weak decay of lambda hyperon inside nuclear medium. This work will introduce the Jefferson Lab experiment (E02-017) which aims to study the lifetime of the heavy hypernuclei using a specially developed fission fragment detection technique, a multi-wire proportional chamber operated under low gas pressure (LPMWPC). Presented here are the method and performance of the reconstruction of fission position on the target foil, the separation of target materials at different regions and the comparison and verification with the Mote Carlo simulation.
Xi-Yu, Qiu↗
High-resolution hypernuclear spectroscopy at Jefferson Lab, Hall A
The experiment E94-107 in Hall A at Jefferson Lab started a systematic study of high resolution hypernuclear spectroscopy in the 0 p -shell region of nuclei such as the hypernuclei produced in electroproduction on 9 Be, 12 C and 16 O targets. In order to increase counting rates and provide unambiguous kaon identification two superconducting septum magnets and a ring-imaging Cherenkov detector were added to the Hall A standard equipment. The high-quality beam, the good spectrometers and the new experimental devices allowed us to obtain very good results. Here, measurable strength with sub-MeV energy resolution was recorded for the core-excited states of $^{12}_{Λ}$B. A high-quality$^{16}_{Λ}N hypernuclear spectrum was likewise obtained. A first measurement of the Λ binding energy for Lambda 16N, calibrated against the elementary reaction on hydrogen, was obtained with high precision, 13.76 ± 0.16 MeV. Similarly, the first$^{9}_{Λ}Li hypernuclear spectrum shows general agreement with theory (distorted-wave impulse approximation with the SLA and BS3 electroproduction models and shell-model wave functions). Some disagreement exists with respect to the relative strength of the states making up the first multiplet. A Λ separation energy of 8.36 MeV was obtained, in agreement with previous results. It has been observed that the electroproduction of hypernuclei can provide information complementary to that obtained with hadronic probes and the γ-ray spectroscopy technique.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Towards the understanding of the genuine three-body interaction for p–p–p and p–p–Λ
Three-body nuclear forces play an important role in the structure of nuclei and hypernuclei and are also incorporated in models to describe the dynamics of dense baryonic matter, such as in neutron stars. So far, only indirect measurements anchored to the binding energies of nuclei can be used to constrain the three-nucleon force, and if hyperons are considered, the scarce data on hypernuclei impose only weak constraints on the three-body forces. In this work, we present the first direct measurement of the p–p–p and p–p–Λ systems in terms of three-particle correlation functions carried out for pp collisions at $\sqrt{s}$=13 TeV. Three-particle cumulants are extracted from the correlation functions by applying the Kubo formalism, where the three-particle interaction contribution to these correlations can be isolated after subtracting the known two-body interaction terms. A negative cumulant is found for the p–p–p system, hinting to the presence of a residual three-body effect while for p–p–Λ the cumulant is consistent with zero. This measurement demonstrates the accessibility of three-baryon correlations at the LHC.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Strangeness physics at Jlab
In year 2000, spectroscopic study of hypernuclei with electron beam was started at the Jefferson Lab (JLab). There were many difficulties to be overcome to explore the full potential of this new experimental technique. A decade of efforts and progress for the hypernuclear study at JLab are reviewed.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
A NEW EQUATION OF STATE FOR NEUTRON STAR MATTER WITH NUCLEI IN THE CRUST AND HYPERONS IN THE CORE
The equation of state for neutron stars in a wide-density range at zero temperature is constructed. The chiral quark-meson coupling model within relativistic Hartree-Fock approximation is adopted for uniform nuclear matter. The coupling constants are determined so as to reproduce the experimental data of atomic nuclei and hypernuclei. In the crust region, nuclei are taken into account within the Thomas-Fermi calculation. All octet baryons are considered in the core region, while only Ξ{sup –} appears in neutron stars. The resultant maximum mass of neutron stars is 1.95 M{sub ☉}, which is consistent with the constraint from the recently observed massive pulsar, PSR J1614-2230.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Equation of state for neutron stars with hyperons and quarks in the relativistic Hartree–Fock approximation
We construct the equation of state (EoS) for neutron stars explicitly including hyperons and quarks. Using the quark–meson coupling model with the relativistic Hartree–Fock approximation, the EoS for hadronic matter is derived by taking into account the strange (σ* and ϕ) mesons as well as the light non-strange (σ, ω, π, and ρ) mesons. Relevant coupling constants are determined to reproduce the experimental data of nuclear matter and hypernuclei in SU(3) flavor symmetry. For quark matter, we employ the MIT bag model with a one-gluon-exchange interaction, and Gibbs criteria for chemical equilibrium in the phase transition from hadrons to quarks. We find that the strange vector (ϕ) meson and the Fock contribution make the hadronic EoS stiff, and that the maximum mass of a neutron star can be consistent with the observed mass of heavy neutron stars even if the coexistence of hadrons and quarks takes place in the core. However, in the present calculation, the transition to pure quark matter does not occur in stable neutron stars. Furthermore, the lower bound of the critical chemical potential of the quark–hadron transition at zero temperature turns out to be around 1.5 GeV in order to be consistent with the recent observed neutron-star data.
79 ASTRONOMY AND ASTROPHYSICS↗
Electromagnetic and strange probes of dense nuclear matter at NICA/MPD: a feasibility study
The main task of the NICA/MPD physics program is a study of the properties of nuclear matter under extreme conditions achieved in collisions of heavy ions. These properties can reveal themselves through different probes, the most promising among those being the lepton-antilepton pairs and strange hadrons. In this paper the MPD performance for measuring the electron-positron pairs and strange particles (Λ, Ξ{sup –} and Ω{sup –} hyperons and their antiparticles Λ̄, Ξ̄{sup +} and Ω̄{sup +} as well as hypernuclei {sub 3}{sup Λ}Λ) in central Au + Au collisions at NICA energies is presented.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
The EOS of neutron matter, and the effect of Lambda hyperons to neutron star structure
The following topics are addressed: the model and the method; equation of state of neutron matter, role of three-neutron force; symmetry energy; Λ-hypernuclei; Λ-neutron matter; and neutron star structure. In summary, quantum Monte Carlo methods are useful to study nuclear systems in a coherent framework; the three-neutron force is the bridge between E sym and neutron star structure; and neutron star observations are becoming competitive with experiments. Λ-nucleon data are very limited, but ΛNN is very important. The role of Λ in neutron stars is far from understood; more ΛN data are needed. The author's conclusion: We cannot conclude anything with present models.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗