Search

In recent years, several experiments using magnetic spectrometers provided high precision results in the field of Hypernuclear Physics. In particular, the accurate determination of the Lambda-binding energy, B(Lambda), contributed to stimulate considerably the discussion about the Charge Symmetry Breaking effect in Lambda-hypernuclei isomultiplets. We have reorganized the results from the FINUDA experiment and we have obtained a series of B(Lambda) values for Lambda-hypernuclei with A, Comment: 22 pages, 5 figures

The analysis of the first FINUDA paper on the emission of Λp pairs following the K − absorption at rest on 6Li, 7Li, 12C nuclei has been revised by using a much larger data set and an updated analysis techniques. The preliminary results regarding the Be 9 ( K stop − , Λ p ) X reaction are discussed.

The advent of high purity germanium (HPGe) crystals more than 40 years ago represents a fundamental milestone in experimental Nuclear Physics: the new detectors, capable of featuring an energy resolution superior by more than an order of magnitude with respect to other devices, led to a new level of γ-ray spectroscopy data quality. In the last few years it has been experimentally proven that hypernuclear spectroscopy can benefit from the same advantages as well [1, 2].

A short review of the more interesting new results presented at the HYP-X Conference is given, with emphasis on the perspectives of the field, in particular at the new complex of machines J-PARC.

This contribution describes a recent experimental study of the A ( K s t o p − , π ± Σ ∓ ) A ′ reaction on light nuclei, Li 6 , 7 , Be 9 , C 13 and O 16 . Final π ± Σ ∓ pairs arise from π + π − n events. For some nuclei, the π + momentum spectrum presents peak-strucures in the kinematical interval of formation of Σ-hypernuclear states. The apparatus used for the investigation is the FINUDA spectrometer set at DAΦNE.

The Non-Mesonic two-body decays He Λ 4 → d d , p t and He Λ 5 → d t have been studied by the FINUDA experiment. The branching ratios for these rare decay channels are given.

We experimentally investigated the dependence of the K + and K − production on the number of nucleons involved in the annihilation process at rest on 3He and 4He gas targets comparing the results with \(\overline p^1H\) and \(\overline p^2H\) annihilation data: all events were collected by the Obelix experiment, in operation at LEAR until 1996. Events with and without production of neutral mesons and with and without emission of fast neutrons (that is neutrons involved in the annihilation process) are recognized. The results are consistent with our previous ones on a more restricted sample of annihilation reactions on 4He and put in evidence that the strangeness production is lower or higher depending on the reaction channel. As a general trend, the strangeness production is higher in events with the involvement of a higher number of nucleons. The maximum K + production is observed in the reaction \(\overline p ^4He \rightarrow K^+ 2\pi^+ 2\pi^- 3n\) (with the involvement of 3–4 nucleons): compared with the reaction on hydrogen \(\overline p p \rightarrow K^+ 2\pi^+ 2\pi^- \) the production on 4He is higher by a factor of 31.7 ± 5.5. In the light of some theoretical speculations this enhancement is too high to be explainable in terms of hadronic interactions and could be interpreted as a signature of quark deconfinement or possibly of QGP formation.

The possibility of producing and detecting at DAΦNE a new hydrogen isotope formed by a (K + e − ) bound system (Kaium) is addressed, considering a dedicated, and relatively simple experiment of short duration. If Kaium will be detected, it could in perspective pave the way for a series of highly sophisticated experiments focused on the precision measurement of several observables, as the K + − K − mass difference, strictly related to CPT invariance.

Experimental results recently obtained by OBELIX on the possible production of Kaonic Nuclear Clusters by \(\overline{p}\) annihilation on 4He are critically revised and compared with analogous results from experiments with stopped K −. The use of \(\overline{p}\) instead than K − at rest on nuclei in the search of the existence and properties of such objects seems better, both from the experimental side and the discovery potential.

Recent results on mesonless absorption of stopped K − by 2,3,4 nucleons are discussed. It is possibly related to the existence of antikaon–nuclear quasibound states. Short reviews of the theoretical effort and on results from measurements with other reactions are presented. An outlook of the information that should be obtained in the near future is finally given.

The dependence of the K + and K − production on the number of nucleons involved in the annihilation process is investigated experimentally in the p ¯ annihilation at rest on hydrogen, deuterium, 3He and 4He gas targets. Annihilations with any number of prongs (charged pions and kaons, protons and deuterons) are analyzed. Events with and without production of neutral mesons and with and without emission of fast neutrons (that is neutrons involved in the annihilation process) are recognized. The results are consistent with our previous ones on a more restricted sample of annihilation reactions and put in evidence that the strangeness production is lower or higher depending on the reaction channel. As a general trend, the strangeness production is higher in events without neutral mesons and still higher in events with the involvement of a higher number of nucleons. Both K + and K − productions increase with the number of involved nucleons, but K + much more. The maximum K + production is observed in the reaction K + 2 π + 2 π − 3 n on 4He (with the involvement of 3–4 nucleons); compared with the production on hydrogen in the reaction K + π + 2 π − , the production on 4He is higher by a factor of 31.7 ± 5.5 . In the light of some theoretical speculations, this enhancement factor is too high to be explainable in terms of hadronic interactions and could be interpreted as a signature of quark deconfinement and of formation of a quark–gluon plasma.

Events with production of two K + are observed in p ¯ He 4 annihilations at rest. They are detected in annihilation reactions with four and five prongs and are interpreted to proceed via the following intermediate states: 2 K + Σ − Σ − p s → 2 K + 2 π − ( 2 n p s ) , 2 K + Σ − Σ + n π − → 2 K + π + 2 π − ( 3 n ) , 2 K + Σ − Λ n → 2 K + p 2 π − ( 2 n ) and 2 K + K − Λ 2 n → 2 K + K − p π − ( 2 n ) with yields (lower limits) ( 0.17 ± 0.04 ) × 10 −4 , ( 2.71 ± 0.47 ) × 10 −4 , ( 1.21 ± 0.29 ) × 10 −4 and ( 0.28 ± 0.14 ) × 10 −4 , respectively. They could be the signature of different production mechanisms like rescattering cascades and formation of quark–gluon plasma and of bound K − K − -few nucleon systems. Even though the statistics is very small, signatures compatible with ( K − K − n n ) and ( K − K − n n p ) bound systems are discussed.

Correlated Λd pairs emitted after the absorption of negative kaons at rest K stop − A → Λ d A ′ in light nuclei 6Li and 12C are studied. Λ-hyperons and deuterons are found to be preferentially emitted in opposite directions. The Λd invariant mass spectrum of 6Li shows a bump whose mass is 3251 ± 6 MeV / c 2 . The bump mass (binding energy), width and yield are reported. The appearance of a bump is discussed in the realm of the [ K ¯ 3 N ] clustering process in nuclei. The experiment was performed with the FINUDA spectrometer at DAΦNE (LNF).

One of the more controversial recent issues in Hadronic Physics is the possible existence of the so-called Kaonic Nuclear Clusters (KNC), often referred to also as Deeply Bound Kaon States (DBKS). They are strange (S = −1, −2) systems composed by nucleons strongly bound to one or two . This topic is connected with the possible existence of unusual nucleon bound states like pp or ppp, with the possibility that a high-density nuclear medium will be created around the K, that could be a seed for the understanding of the dense nuclear matter in the neutron stars.

A research has been made to look for a signature of the positive-strangeness baryon resonance Θ + ( 1530 ) , which is expected to decay into p K 0 . A peak is observed in the p π + π − invariant mass distribution in antiproton– 4 He annihilation reactions at rest with production of two π + π − pairs with invariant mass close to the K S 0 mass. The annihilation reactions on 4 He can involve two to four nucleons producing an energy blob characterized by high strangeness content. The peak is centred around 1560.0 ± 3.7 MeV and its width is very narrow. The statistical significance is 2.7; this value is considered of not sufficient significance to claim support of the Θ + . The data were collected with the Obelix spectrometer at the LEAR machine of CERN.

FINUDA is the hypernuclear physics experiment carried out at DAΦNE, the e+e- ϕ-factory of the INFN Frascati Laboratory. The aim of the experiment is to study simultaneously the formation and decay of hypernuclei produced by the strangeness exchange reaction induced by the stopped K- coming from the decay of the ϕ(1020) mesons. This paper presents the first preliminary results concerning spectrometer performances, hypernuclear formation and decay from the first FINUDA data set.

The Mossbauer effect is well interpreted and understood in an ideal, infinitely stiff (mathematical) lattice. However we argue that the electrostatic forces that are usually considered in solid-state physics are not adequate to support such a «stiffness». This difficulty is seen to been surmounted by a «superradiant» behaviour of the plasma of nuclei of a crystal.

We point out that the first steps in understanding the recent results reported on cold nuclear fusion can be made by considering the important role that the coherent interactions with the quantized e.m. field play in condensed matter. Indeed we find natural mechanisms to decrease the Coulomb repulsion and to suppress the usual nuclear-fusion channels with respect to the transfer of the excess energy directly to the electrons of the metal.

The recent proposal of the ARES facility, a single-pass electron-positron collider up to 15 GeV c.m. with high luminosity, opens the possibility of producing Λc+(Λb)-hypernuclei by means of the charm (beauty) exchange reactions on nuclei. An estimation of the production cross-sections as well as experimental conditions and requirements are discussed.

Cross sections are presented for the reaction pi -p to pi -p gamma at square root s=1234 MeV.

In view of the forthcoming operation of the 0micron spectrometer at the CERN synchrocyelotron it seems to us tha t the t ime is ripe for an analysis of the nuclear physics experiments already planned, e.g. pion backward scattering and pion doublecharge exchange (DCX) (1). Theoretical aspects of pion scattering have been discussed in detail by several authors (2). Recent measurements (a) at low energy (30~

A method for calculating the efficiency of large aperture gas Cherenkov counters is presented. It is based on a careful Monte Carlo simulation of the geometrical response of the apparatus and on the measurement of the number of photoelectrons detected by the photomultipliers for some selected directions of the particles traversing the radiating volume. An application to a counter whose efficiency was systematically measured with great care is presented. The results are very satisfactory.

The recent determination of the partial decay widths for the one-proton and the two-nucleon induced Non-Mesonic Weak Decay of Λ-Hypernuclei in the A = 5 – 16 range permitted to reconstruct the full pattern of decay widths for 5 Λ He and 11 Λ B. A consistency check on 12 Λ C decay widths confirms the validity of the adopted method.