Searches for the superheavy hydrogen isotope 7H in the absorption of stopped π − mesons

Experimental searches for the superheavy hydrogen isotope ⁷H were performed in reactions involving the absorption of stopped π ^? mesons on ⁹Be and ¹¹B nuclei. In the reaction ⁹Be(π ^?, pp)X, the missing-mass spectrum shows evidence for the formation of ⁷H states, that of E _r = 16 ± 1 MeV and Γ ? 2 MeV and that of E _r = 21 ± 1 MeV and Γ ? 5 MeV (E _r is the resonance energy with respect to breakup into a trition and four neutrons, and Γ is the observed level width).     

Spectroscopy of the <Superscript>5</Superscript>H superheavy hydrogen isotope

The formation of the ⁵H superheavy hydrogen isotope was experimentally sought in the reactions induced by stopped π^? mesons absorbed by ⁹Be nuclei. Peaks in missing-mass spectra were observed in two reaction channels, ⁹Be(π^?, pt)X and ⁹Be(π^?, dd)X, and were attributed to the ⁵H resonance states. The lowest state has parameters Er=5.5±0.2 MeV and Г=5.4±0.5 MeV [E_r is the resonance energy measured from the (triton + two neutrons) threshold]. Therefore, ⁵H is bound more weakly than ⁴H. Excited states of ⁵H were also observed. All three resonance levels (E_1r=10.6±0.3 MeV, Г_1r=6.8±0.5 MeV; E_2r=18.5±0.4 MeV, Г_2r=4.8±1.3 MeV; E_3r=26.7±0.4 MeV, Г_3r=3.6±1.3 MeV) can decay into five free nucleons.     

Search for superheavy hydrogen isotopes <Superscript>6</Superscript>H and <Superscript>7</Superscript>H in stopped π-absorption reactions

Experimental search for superheavy hydrogen isotopes ⁶H and ⁷H was performed in the stopped pion absorption on ⁹Be and ¹¹B nuclei. The structures in the missing-mass spectra were observed in the reaction channels ⁹Be(π^-, pd )X and ¹¹B(π^-, p⁴He)X . Four states of ⁶H were proposed. Evidences for ⁷H formation were obtained in the reaction channels ⁹Be(π^-, pp)X and ¹¹B(π^-, p³He)X .     

Search for superheavy hydrogen isotopes <Superscript>4,5</Superscript>H in reactions of pion absorption by <Superscript>10,11</Superscript>B nuclei

The results of searching for production of superheavy hydrogen isotopes ^4,5H in reactions of absorption of stopped π^? mesons by ^10,11B nuclei are reported. A peak near 3 MeV was observed in the missing mass spectra measured in the reactions ^10,11B(π^?, t⁴He)X, ¹⁰B(π^?, d⁴He)X, and ¹⁰B(π^?, t³He)X. A structure caused by two ⁵H states with the resonance energies E _R = 5.2 and 10.4 MeV was observed in the missing mass spectra measured in the reactions ¹¹B(π^?, d⁴He)X, ¹¹B(π^?, t³He)X, and ¹⁰B(π^?, d³He)X.     

The formation of the superheavy hydrogen isotope <Superscript>6</Superscript>H in the absorption of stopped π<Superscript>−</Superscript>-mesons by nuclei

An experimental search for the superheavy hydrogen isotope ⁶H was conducted through studying the absorption of stopped π^?-mesons by ⁹Be and ¹¹B nuclei. A structure in the missing mass spectrum caused by the resonance states of ⁶H was observed in three reaction channels, namely, ⁹Be(π^?, pd)X, ¹¹B(π^?, d³He)X, and ¹¹B(π^?, p⁴He)X. The parameters of the lowest state E_r=6.6±0.7 MeV and Γ=5.5±2.0 MeV (E_r is the resonance energy with respect to the disintegration into the triton and three neutrons) are evidence that ⁶H is a more weakly bound system than ⁴H and ⁵H. Three excited states of ⁶H were observed. Their resonance levels (E_1r=10.7±0.7 MeV, Γ_1r=4±2 MeV, E_2r=15.3±0.7 MeV, Γ _2r=3±2 MeV, and E_3r=21.3±0.4 MeV, Γ_3r=3.5±1.0 MeV) are energetically capable of disintegrating into six free nucleons.     

Spectroscopy of superheavy hydrogen isotopes <Superscript>4</Superscript>H and <Superscript>5</Superscript>H

The superheavy hydrogen isotopes ⁴H and ⁵H have been investigated in the stopped pion absorption on ⁹Be. Three states of ⁴H were proposed in the reaction channel ⁹Be( ^{{ - }}, dt)X. Four states of ⁵H were proposed in the reaction channels ⁹Be(^{{ - }}, pt)X and ⁹Be(^{{ - }}, dt)X. The excited states of ⁵H can decay into free nucleons.     

Investigating highly excited states of the 8Li isotope

Highly excited states of the ⁸Li isotope are sought in absorption reactions of π^? mesons stopped by ^10,11B isotopes. The ground and three excited states of the ⁸Li isotope are observed in inclusive measurements of reactions ¹⁰B(π^?, d)X and ¹¹B(π^?, t)X. The states with excitation energies E _x ≈ 8.7 and 10.1 MeV are observed for the first time in correlation measurements of reactions ¹⁰B(π^?, dt)X and ¹¹B(π^?, tt)X.     

Strangeness exchange reaction on nuclei

Population of hypernuclear states has been observed in recoiless Λ production of the strangeness exchange reaction (K^?, π^?) on ⁹Be, ¹²C, ¹⁶O, ³²S and ⁴⁰Ca.     

Search for superheavy hydrogen isotopes in pion absorption reactions

Review of the experimental results on the search for and the spectroscopy of the superheavy hydrogen isotopes ^4–7H obtained in stopped π^?-meson absorption by ⁹Be and ¹¹Be nuclei is presented. Study of light neutron-rich nuclei is a principal line in developing modern views on the properties of nuclear forces and determination of nuclear properties near the drip line. The present method of investigation relies on precision measurements of energy of charged particles emitted after pion absorption by nuclei. Important advantages of this method are the practically accurate initial state energy and momentum, as well as the possibility to study a wide range of excitation energy. In the frames of this method new results were obtained on level structures of the isotopes ^4–6H and indications on ⁷H production. Comparison with other experimental and theoretical results is performed.     

Production of Heavy Helium <Superscript>5</Superscript>Hе in the Absorption of Stopped Pions by <Superscript>10,11</Superscript>B Nuclei

Helium ⁵Hе states are sought in missing-mass (MM) spectra from reactions of the absorption of stopped pions: ¹⁰В(π^?, dt)Х and ¹¹В(π^?, tt)Х. The experiment is conducted using the LANL accelerator equipped with a two-arm semiconductor charged-particle spectrometer. The parameters of the ground state agree with the literature data. The best fit for the first excited level is obtained at E_r = 1.8(5) MeV and Γ = 4.7(7) MeV. Neither of the two reactions produce statistically significant evidence for the presence of highly excited (E_x ≥ 20 MeV) states of ⁵Hе.     

Searching for rare cluster configurations of <Superscript>14</Superscript>C nuclei in the pion absorption reaction

Analysis of the two-dimensional Dalitz plot measured in the reaction ¹⁴C(π^–, pd)X allows us to follow the absorption of pions by cluster ³p and identify signs of the configuration ³p + ¹¹Li in the ¹⁴C nucleus. The highly excited state of ^12,13Be beryllium isotopes with excitation energies E* ≈ 30 MeV and which decay with the emission of hydrogen isotopes is observed for the first time: ¹²Be* → p + ¹¹Li and ¹³Be* → d + ¹¹Li.     

Spectroscopy of 7Li in stopped pion absorption reactions

The structure of excited levels in the ⁷Li isotope is studied via inclusive and correlation measurements in the stopped π^? meson absorption reactions ¹⁰B(π^?, t)X and ¹²C(π^?, dt)X, respectively. The experiment is conducted using a low-energy pion beam at the LAMPF meson factory. Analysis of the missing mass spectra reveals ⁷Li states with the resonance parameters (E _x , Γ) (4.7, 0.1), (6.6, 0.9), (7.3, 0.1), (9.1, 2.8), and (9.6, 0.4) MeV. A highly excited state with E _x ≈ 11.2 MeV (i.e., an isobar analog of ⁷He) is observed in the ¹⁰B(π^?,t)X reaction. An excited state with E _x = 10.3 ± 0.1 MeV and γ = 1.8 ± 0.4 Mev is observed for the first time in the ¹²C(π^?,dt)X reaction.     

Electroexcitation of isovector magnetic dipole and quadrupole transitions in 18O and their relation to radiative pion capture

In a high-resolution ¹⁸O(e, e′) experiment sharp states at E_X=16.38±0.01 MeV (J^π=2^?, ground state analogue of and at E_X=18.86±0.01 MeV (J^π=1⁺) and clustering of strength (possibly with J^π=1^?, 2^?) at E_X≈23.7 MeV have been observed and compared to theoretical predictions. The transition strengths for the narrow states are B(M2) ↑ = 58± 8 μ_K² fm² and B(M1) ↑ = 0.28± 0.04 μ_K², respectively. These results agree qualitatively with the resu lts from the analogous ¹⁸O(π^?, γ)¹⁸N reaction.     

Structure of neutron-rich Be and C isotopes

The structure of neutron-rich beryllium isotopes has been investigated using different heavy-ion-induced transfer reactions. In neutron transfer reactions, the population of final states shows a strong sensitivity to the chosen core nucleus, i.e., the target nuclei ⁹Be or ¹⁰Be, respectively. Molecular rotational bands up to high excitation energies are observed with ⁹Be as the core due to its pronounced 2α-cluster structure, whereas only a few states at low excitation energies are populated with ¹⁰Be as the core. For ¹¹Be, a detailed investigation has been performed for the three states at 3.41, 3.89, and 3.96 MeV, which resulted in the most probable spin-parity assignments 3/2⁺, 5/2^?, and 3/2^?, respectively. Furthermore, we have studied particle-hole states of ¹⁶C using the ¹³C(¹²C, ⁹C)¹⁶C reaction and found 14 previously unknown states. Using the ¹²C(¹²C, ⁹C)¹⁵C reaction, five new states were observed for ¹⁵C.     

Spin dipole excitations in radiative pion capture on 1p shell nuclei

Shell-model calculations for spin-dipole transitions in the (π^?,γ) reaction on ^6,7Li, ⁹Be, ¹¹B, ¹³C and ¹⁴N are compared with experimental data. The gross structure of resonance is discussed in terms of configurational splitting and symmetry considerations. Quantum numbers of resonances, total and partial yields are considered. Selected (π^?, γn) and (gp^?, γnγ′) coincidence experiments are proposed. The role of quadrupole and quasielastic excitation is also briefly discussed.     

Search for narrow four-baryon states

Highly excited (4.10?mass?5.35 GeV/c²) four-baryon resonances have been searched for in the missing-mass spectrum of the reaction π^?+⁴He→π^?+X at 5 GeV/c in the region of small four-momentum transfer (0.005?6t6?0.15 (GeV/c)²), where one of the decay products of the X is either proton or deuteron or triton. No resonance signal is seen in the mass spectrum of X. Within our limited acceptance, the cross section for the production of a narrow (Γ ～ 20 MeV/c²) four-baryon state with mass 4.9 GeV/c² is estimated to be smaller than ～ 100 nb.     

Search for light neutron-rich isotopes in stopped pion absorption

The results based on the spectroscopy of superheavy hydrogen isotopes (^4?7H), heavy helium isotopes (^6,7He), and heavy lithium isotopes (^7?12Li) produced in stopped pion absorption by light nuclei were analyzed. Search for nuclear states was performed in inclusive and correlation measurements of missing mass spectra. A broad range of excitation energies studied in correlation measurements provided the possibility of search for isobaric analog states and cluster resonances. A comparison with experimental and theoretical results of other authors was conducted.     

Pion production in 3He-nucleus interactions at 910 MeV

The (³He, π^±X) reaction has been studied at 910 MeV using the ³He⁺⁺ beam of the CERN SC. Complete π^? spectra on CH₂, CD₂, ⁹Be, ¹²C, ²⁷Al, Cd and Pb, and π⁺ spectra on CH₂, CD₂ and ¹²C targets have been measured at 0°, up or close to the kinematic limit x_F = 1. The results are compared to various theoretical calculations.     

In-beam study of excited states in80Br

Excited states of the doubly-odd nucleus⁸⁰Br have been studied via the reactions⁸⁰Se(p, n),⁸⁰Se(d,2n) and⁷⁸Se(α, pn) using in-beamγ-ray spectroscopy. A positiveparity level sequence built on aI ^π=5⁺ state at 331.04 keV has been found up to spin (10). For this 5⁺ level de-exciting to the known 5^? isomeric state and for the 6⁺ level at 357.22 keV half-lives of 0.7 and 0.4 ns, respectively, have been determined. Negativeparity states have been observed up to spin (6). For the positive-parity level sequence the configuration (πg _9/2,vg _9/2) and collective excitations are proposed. Some of the negative-parity states are tentatively interpreted as arising from the configurations (πp _3/2,vg _9/2) and (πp _3/2, (vg _9/2) ₇ ^2/3 ).     

Ξ * resonances inΞ −be interactions

In an experiment carried out in the CERN SPS hyperon beam, the diffractive dissociation of incidentΞ ^? hyperons into ΛK ^? andΞ ^?π⁺π^? final states has been observed. Several resonances are seen in the final states, including the well known Ξ(1820) which appears in both channels, and the Ξ(1680) which appears as a narrow state (M=1691.1±2.7 MeV/c², Γ<8 MeV/c²) in the ΛK^? channel and possibly also in the Ξππ channel.