Lambda-hypernuclear production in stopped (K-,pion) reactions reexamined

DWIA calculations of Lambda-hypernuclear production rates in stopped K- reactions on several p-shell targets used recently in experiments by the FINUDA Collaboration are reported. Chirally motivated K- + N -> pion + Lambda in-medium transition amplitudes are employed and the sensitivity of the calculated rates to the initial K- atomic wavefunctions and final pion distorted waves is studied. The calculated rates are compared with measured rates, wherever available, confirming earlier observations that (i) the calculated rates are generally lower than the measured rates, and (ii) the deeper the K- nuclear potential, the worse is the discrepancy. The A dependence of the calculated 1s Lambda hypernuclear production rates is discussed for the first time, providing a useful tool in resolving the issue of depth of the K- nuclear potential near threshold.Comment: matches published version, including the dubious change of `revisited' in the title to `reexamined' upon PRC Editor's insistenc

The A(Kstop−,π±Σ∓)A′A(K^-_{stop},\pi^\pm\Sigma^\mp)A' reaction on p-shell nuclei

This letter is concerned with the study of the $K^-_{stop}A\rightarrow \pi^\pm\Sigma^\mp A'$ reaction in p-shell nuclei, i.e., $^{6,7}Li$, $^9Be$, $^{13}C$ and $^{16}O$. The $\pi^\pm\Sigma^\mp / K^-_{stop}$ emission rates are reported as a function of $A$. These rates are discussed in comparison with previous findings. The ratio $\pi^-\Sigma^+/\pi^+\Sigma^-$ in p-shell nuclei is found to depart largely from that on hydrogen, which provides support for large in-medium effects possibly generated by the sub-threshold $\Lambda(1405)$. The continuum momentum spectra of prompt pions and free sigmas are also discussed as well as the $\pi^\pm\Sigma^\mp$ missing mass behavior and the link with the reaction mechanism. The apparatus used for the investigation is the FINUDA spectrometer operating at the DA$\Phi$NE $\phi$-factory (LNF-INFN, Italy).Comment: 14 pages, 5 figures, accepted for publication in Phys. Lett.

K- absorption in nuclei by two and three nucleons

It will be shown that the peaks in the (Lambda p) and (Lambda d) invariant mass distributions, observed in recent FINUDA experiments and claimed to be signals of deeply bound kaonic states, are naturally explained in terms of K- absorption by two or three nucleons leaving the rest of the original nuclei as spectator. For reactions on heavy nuclei, the subsequent interactions of the particles produced in the primary absorption process with the residual nucleus play an important role. Our analyses leads to the conclusion that at present there is no experimental evidence of deeply bound K- state in nuclei. Although the FINUDA experiments have been done for reasons which are not supported a posteriori, some new physics can be extracted from the data.Comment: 6 pages, 5 figures. Talk presented at the International Conference on Exotic Atoms "EXA 2008", Vienna, Austria, September 15-18, 200

Neutron Rich Hypernuclei in Chiral Soliton Model

The binding energies of neutron rich strangeness $S=-1$ hypernuclei are estimated in the chiral soliton approach using the bound state rigid oscillator version of the SU(3) quantization model. Additional binding of strange hypernuclei in comparison with nonstrange neutron rich nuclei takes place at not large values of atomic (baryon) numbers, $A=B\leq\sim 10$. This effect becomes stronger with increasing isospin of nuclides, and for "nuclear variant" of the model with rescaled Skyrme constant $e$. Total binding energies of (Lambda)He-8 and recently discovered (Lambda)H-6 satisfactorily agree with experimental data. Hypernuclei (Lambda)H-7, (Lambda)He-9 are predicted to be bound stronger in comparison with their nonstrange analogues H-7, He-9; hypernuclei (Lambda)Li-10, (Lambda)Li-11, (Lambda)Be-12, (Lambda)Be-13, etc. are bound stronger in the nuclear variant of the model.Comment: 8 pages, 4 tables; amendments made, data on binding energy of (Lambda)He-8 and references added; prepared for the conferences Quarks-2012 and HYP201

KiDS0239-3211: A new gravitational quadruple lens candidate

We report the discovery of a candidate to quadrupole gravitationally lensed system KiDS0239-3211 based on the public data release 3 of the KiDS survey and machine learning techniques

VEXAS: VISTA EXtension to Auxiliary Surveys -- Data Release 2: Machine-learning based classification of sources in the Southern Hemisphere

We present the second public data release (DR) of the VISTA EXtension to Auxiliary Surveys (VEXAS), where we classify objects into stars, galaxies and quasars based on an ensemble of machine learning algorithms. The aim of VEXAS is to build the widest multi-wavelength catalogue, providing reference magnitudes, colours and morphological information for a large number of scientific uses. We apply an ensemble of 32 different machine learning models, based on three different algorithms and on different magnitude sets, training samples and classification problems on the three VEXAS DR1 optical+infrared (IR) tables. The tables were created in DR1 cross-matching VISTA near-IR data with WISE far-IR data and with optical magnitudes from the Dark Energy Survey (VEXAS-DESW), the Sky Mapper Survey (VEXAS-SMW), and the PanSTARRS (VEXAS-PSW). We assemble a large table of spectroscopically confirmed objects (415 628 unique objects), based on the combination of 6 different spectroscopic surveys that we use for training. We develop feature imputation to classify also objects for which magnitudes in one or more bands are missing. We classify in total ~90 million objects in the Southern Hemisphere. Among these,~62.9M (~52.6M) are classified as 'high confidence' ('secure') stars, ~920k (~750k) as 'high confidence' ('secure') quasars and ~34.8M (~34.1M) as 'high confidence' ('secure') galaxies, with probabilities $p_{\rm class}\ge 0.7$ ($p_{\rm class}\ge 0.9$). The density of high-confidence extragalactic objects varies strongly with the survey depth: at $p_{\rm class}\ge 0.7$, there are 111/deg$^2$ quasars in the VEXAS-DESW footprint and 103/deg$^2$ in the VEXAS-PSW footprint, while only 10.7/deg$^2$ in the VEXAS-SM footprint. Improved depth in the midIR and coverage in the optical and nearIR are needed for the SM footprint that is not already covered by DESW and PSW.Comment: 25 pages, 18 figures, 8 tables. Accepted for publication on A&A. The VEXAS tables are publicly available through the ESO Phase 3 here: https://archive.eso.org/scienceportal/home?data_collection=VEXAS. The DR2 tables update the DR1 with the addition of imputed magnitudes and membership probabilities to each of the three classe

Coulomb corrections to low energy antiproton annihilation cross sections on protons and nuclei

We calculate, in a systematic way, the enhancement effect on antiproton-proton and antiproton-nucleus annihilation cross sections at low energy due to the initial state electrostatic interaction between the projectile and the target nucleus. This calculation is aimed at future comparisons between antineutron and antiproton annihilation rates on different targets, for the extraction of pure isospin channels.Comment: 18 pages, 4 figures (latex format

Cadmium induces the expression of specific stress proteins in sea urchin embryos

Marine organisms are highly sensitive to many environmental stresses, and consequently, the analysis of their bio-molecular responses to different stress agents is very important for the understanding of putative repair mechanisms. Sea urchin embryos represent a simple though significant model system to test how specific stress can simultaneously affect development and protein expression. Here, we used Paracentrotus lividus sea urchin embryos to study the effects of time-dependent continuous exposure to subacute/sublethal cadmium concentrations. We found that, between 15 and 24 h of exposure, the synthesis of a specific set of stress proteins (90, 72-70, 56, 28, and 25 kDa) was induced, with an increase in the rate of synthesis of 72-70 kDa (hsps), 56 kDa (hsp), and 25 kDa, which was dependent on the lengths of treatment. Recovery experiments in which cadmium was removed showed that while stress proteins continued to be synthesized, embryo development was resumed only after short lengths of exposure

Structural relaxation of E' gamma centers in amorphous silica

We report experimental evidence of the existence of two variants of the E' gamma centers induced in silica by gamma rays at room temperature. The two variants are distinguishable by the fine features of their line shapes in paramagnetic resonance spectra. These features suggest that the two E' gamma differ for their topology. We find a thermally induced interconversion between the centers with an activation energy of about 34 meV. Hints are also found for the existence of a structural configuration of minimum energy and of a metastable state.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let