Probing the Structure of Halo Nuclei

Our understanding of halo nuclei has so far relied on high-energy scattering and reactions, but a number of uncertainties remain. I discuss in general terms the new range of observables which will be measured by experiments around the Coulomb barrier, and how some details of the reaction mechanisms still need to be clarified.Comment: Proceedings of FUSION97 conference (March 1997), South Durras, Australia. Submitted to J. Physics G: special issue `Heavy ion collisions at near barrier energies'. No figures; uses IOPConf.sty (included

New experimental limit on Pauli Exclusion Principle violation by electrons (the VIP experiment)

The Pauli Exclusion Principle is one of the basic principles of modern physics and is at the very basis of our understanding of matter: thus it is fundamental importance to test the limits of its validity. Here we present the VIP (Violation of the Pauli Exclusion Principle) experiment, where we search for anomalous X-rays emitted by copper atoms in a conductor: any detection of these anomalous X-rays would mark a Pauli-forbidden transition. ] VIP is currently taking data at the Gran Sasso underground laboratories, and its scientific goal is to improve by at least four orders of magnitude the previous limit on the probability of Pauli violating transitions, bringing it into the 10**-29 - 10**-30 region. First experimental results, together with future plans, are presented.Comment: To appear in proceedings of the XLVI International Winter Meeting on Nuclear Physics, Bormio, Italy, January 20-26, 200

Preliminary study of the 19F(7Li,7Be)19O reaction at 52 MeV with MAGNEX

The 19F(7Li,7Be)19O charge-exchange reaction at 52 MeV incident energy has been performed at INFN-LNS in Catania using the MAGNEX spectrometer. The use of an algebraic ray-reconstruction technique has allowed to extract the 19O excitation energy spectrum and the experimental angular distributions obtained with a single angular setting of the spectrometer

Observation of a baryon resonance with positive strangeness in K+ collisions with Xe nuclei

The status of our investigation of low-energy $K^+$Xe collisions in the Xenon bubble chamber DIANA is reported. In the charge-exchange reaction $K^+Xe \to K^0 p Xe'$ the spectrum of $K^0 p$ effective mass shows a resonant enhancement with $M = 1539 \pm 2$ MeV/c$^2$ and $\Gamma \le 9 MeV/c$^2$. The statistical significance of the enhancement is near$4.4\sigma$. The mass and width of the observed resonance are consistent with expectations for the lightest member of the anti-decuplet of exotic pentaquark baryons, as predicted in the framework of the chiral soliton model.Comment: 9 pages, 4 figure

New experimental limit on Pauli Exclusion Principle violation by electrons (the VIP experiment)

The Pauli exclusion principle (PEP) represents one of the basic principles of modern physics and, even if there are no compelling reasons to doubt its validity, it still spurs a lively debate, because an intuitive, elementary explanation is still missing, and because of its unique stand among the basic symmetries of physics. A new limit on the probability that PEP is violated by electrons was estabilished by the VIP (VIolation of the Pauli exclusion principle) Collaboration, using the method of searching for PEP forbidden atomic transitions in copper. The preliminary value, {1/2}\beta^{2} \textless 4.5\times 10^{-28}, represents an improvement of about two orders of magnitude of the previous limit. The goal of VIP is to push this limit at the level of $10^{-30}$.Comment: submitted to Journal of Physics: Conference Series, by the Institute of Physic

The DEAR experiment on DAΦNE

DEAR is one of the first experiments at the new DAΦNE Ø-factory at the Laboratori Nazionali di Frascati dell'INFN. The objective of the DEAR experiment is to perform a precision measurement of the strong interaction shifts and widths of the K-series lines in kaonic hydrogen and the first observation of the same quantities in kaonic deuterium. The aim is to obtain a precise determination of the isospin-dependent kaon-nucleon scattering lengths which will represent a breakthrough in KN low-energy phenomenology and will allow us to determine the kaon-nucleon sigma terms. The sigma terms give a direct measurement of chiral symmetry breaking and are connected to the strangeness content of the proton. First results on background measurements with the DEAR NTP setup installed on DAΦNE are reported

First measurement of kaonic helium-3 X-rays

The first observation of the kaonic 3He 3d - 2p transition was made using slow K- mesons stopped in a gaseous 3He target. The kaonic atom X-rays were detected with large-area silicon drift detectors using the timing information of the K+K- pairs of phi-meson decays produced by the DAFNE e+e- collider. The strong interaction shift of the kaonic 3He 2p state was determined to be -2+-2 (stat)+-4 (syst) eV.Comment: Accepted for publication in Phys. Lett.

A New Measurement of Kaonic Hydrogen X rays

The $\bar{K}N$ system at threshold is a sensitive testing ground for low energy QCD, especially for the explicit chiral symmetry breaking. Therefore, we have measured the $K$-series x rays of kaonic hydrogen atoms at the DA$\Phi$NE electron-positron collider of Laboratori Nazionali di Frascati, and have determined the most precise values of the strong-interaction energy-level shift and width of the $1s$ atomic state. As x-ray detectors, we used large-area silicon drift detectors having excellent energy and timing resolution, which were developed especially for the SIDDHARTA experiment. The shift and width were determined to be $\epsilon_{1s} = -283 \pm 36 \pm 6 {(syst)}$ eV and $\Gamma_{1s} = 541 \pm 89 {(stat)} \pm 22 {(syst)}$ eV, respectively. The new values will provide vital constraints on the theoretical description of the low-energy $\bar{K}N$ interaction.Comment: 5 figures, submitted to Physics Letters

Measurements of the reaction pˉp→ϕη\bar{p}p \to \phi \eta of antiproton annihilation at rest at three hydrogen target densities

The proton-antiproton annihilation at rest into the $\phi\eta$ final state was measured for three different target densities: liquid hydrogen, gaseous hydrogen at NTP and at a low pressure of 5 mbar. The yield of this reaction in the liquid hydrogen target is smaller than in the low-pressure gas target. The branching ratios of the $\phi\eta$ channel were calculated on the basis of simultaneous analysis of the three data samples. The branching ratio for annihilation into $\phi\eta$ from the $^3S_1$ protonium state turns out to be about ten times smaller as compared to the one from the $^1P_1$ state.Comment: 10 pages, 3 Postscript figures. Accepted by Physics Letters

New data on OZI rule violation in bar{p}p annihilation at rest

The results of a measurement of the ratio R = Y(phi pi+ pi-) / Y(omega pi+ pi-) for antiproton annihilation at rest in a gaseous and in a liquid hydrogen target are presented. It was found that the value of this ratio increases with the decreasing of the dipion mass, which demonstrates the difference in the phi and omega production mechanisms. An indication on the momentum transfer dependence of the apparent OZI rule violation for phi production from the 3S1 initial state was found.Comment: 11 pages, 3 PostScript figures, submitted to Physics Letter