ΛNN\Lambda NN and ΣNN\Sigma NN systems at threshold

We calculate the hypertriton binding energy and the $\Lambda d$ and $\Sigma d$ scattering lengths using baryon-baryon interactions obtained from a chiral constituent quark model. We study consistently the $\Lambda NN$ and $\Sigma NN$ systems analyzing the effect of the $\Sigma \leftrightarrow \Lambda$ conversion. Our interactions correctly predict the hypertriton binding energy. The $(I,J)=(0,3/2)$ $\Lambda NN$ channel is also attractive and it might have a bound state. From the condition of nonexistence of a (0,3/2) $\Lambda NN$ bound state, an upper limit for the spin-triplet $\Lambda N$ scattering length is obtained. We also present results for the elastic and inelastic $\Sigma N$ and $\Lambda N$ cross sections. The consistent description of the $\Sigma N$ scattering cross sections imposes a lower limit for the corresponding spin-triplet scattering lengths. In the $\Sigma NN$ system the only attractive channels are $(I,J)=(1,1/2)$ and $(0,1/2)$, the $(1,1/2)$ state being the most attractive one.Comment: 17 pages, 6 tables, 13 figures. Accepted for publication in Phys. Rev.

Σ−p\Sigma^- p emission rates in K−K^- absorptions at rest on 6^6Li, 7^7Li, 9^{9}Be, 13^{13}C and 16^{16}O

An experimental study of the $K^-_{stop}A\rightarrow \Sigma^- p A'$ reaction on $A=^6$Li, $^7$Li, $^9$Be, $^{13}$C and $^{16}$O $p$-shell nuclei is presented. The data were collected by the FINUDA spectrometer operating at the DA$\Phi$NE $\phi$-factory (LNF-INFN, Italy). Emission rates for the reaction in the mentioned nuclei are measured and compared with the few existing data. The spectra of several observables are discussed; indications of Quasi-Free absorptions by a $(np)$ pair embedded in the $A$ nucleus can be obtained from the study of the missing mass distributions.Comment: Version accepted by PR

High luminosity interaction region design for collisions inside high field detector solenoid

An innovatory interaction region has been recently conceived and realized on the Frascati DA{\Phi}NE lepton collider. The concept of tight focusing and small crossing angle adopted to achieve high luminosity in multibunch collisions has evolved towards enhanced beam focusing at the interaction point with large horizontal crossing angle, thanks to a new compensation mechanism for the beam-beam resonances. The novel configuration has been tested with a small detector without solenoidal field yielding a remarkable improvement in terms of peak as well as integrated luminosity. The high luminosity interaction region has now been modified to host a large detector with a strong solenoidal field which significantly perturbs the beam optics introducing new design challenges in terms of interaction region optics design, beam transverse coupling control and beam stay clear requirements. Interaction region design criteria as well as the luminosity results relevant to the structure test are presented and discussed.Comment: 12 pages, 9 figures, submitted to JINS

Hypernuclei formation probability as a function of the atomic mass number A

The creation of a hypernucleus [2], that is a nucleus in which a nucleon is replaced by an hyperon, requires the injection of strangeness into the nucleus. This is possible in different ways [3], mainly using π+ or K− beams on nuclear targets; recently, also electron beams have been used. The FINUDA experiment at the DAΦNE Φ factory of the INFN “Laboratori Nazionali di Frascati” produced Λ-hypernuclei by stopping, in thin nuclear targets (0.1-0.2 g/cm2), the negative kaons originating from the Φ decay through the strangeness-exchange reaction K−st o p +A Z →AΛ Z + π − , where A Z indicates the target nucleus and AΛZ the Λ hypernucleus in which a Λ particle replaced a neutron. FINUDA, an unconventional and innovative apparatus, allowed the positioning of 8 different target modules around the interaction region. In this way different targets could be studied contemporaneously, with the same apparatus and with the same analysis technique, allowing for a direct comparison between different nuclei. In particular FINUDA could study the production of Λ-hypernuclei on 7Li, 9Be, 12C, 13C and 16O targets. Both the Λ binding energy and the hypernuclei production probabilities have been measured [1]. The new measurements on 7 Li, 9 Be, 13C and 16O, along with previous measurements on 12C, allowed for a meaningful study ΛΛΛΛ Λ of the formation of p-shell hypernuclei from the two-body capture of K− at rest, giving for the first time the possibility of disentangling the effects due to atomic wave-function of the captured K− from those due to the pion optical nuclear potential and from those due to the specific hypernuclear states [4]