Choose timezone
Your profile timezone:
Seminars
Highlights on n-rich $\Lambda$-Hypernuclei from the FINUDA experiment
→
Asia/Tokyo
Main Research Bldg. 2F Rom 213 (RIKEN Wako)
Main Research Bldg. 2F Rom 213
RIKEN Wako
Description
Date & Place: Aug. 28 (2013), 13:30- @ RIKEN main building, 213
Lecturer: Ellena Botta (INFN - Sezione di Torino and Torino University)
Title: Highlights on n-rich $\Lambda$-Hypernuclei from the FINUDA experiment
Abstract:
Lambda-hypernuclei are long lived systems in which the lambda-hyperon acts as constituent nucleon. The strangeness degree of freedom of the hyperon makes the Pauli exclusion principle ineffective on it and allows the lambda to populate sharp single particle shell model states down to the lambda(1s) ground state.
In lambda-hypernuclei, then, a strong contribution to the total binding energy is added by the lambda, with the possibility of producing bound systems containing unstable core nuclei (glue-like role of the lambda). lambda-hypernuclei are thus suitable tools for investigating neutron-rich (proton-rich) systems, even beyond the neutron (proton) drip line.
The study of neutron-rich lambda-hypernuclei is one the main topics of the scientific program of the FINUDA experiment which has completed its operation at DA \Phi NE, the INFN-LNF (e+, e-) collider working at the \Phi(1020) center of mass energy. FINUDA has performed an extensive search for bound neutron-rich lambda-hypernuclear states. In the first data taking (2003-2004), ^6_Lambda H, ^7_Lambda H and ^{12}_Lambda Be have been investigated by looking at the pi^+
from the double charge exchange (K^-_stop, pi^+) production reaction; upper limits for the production rates have been reported [1]: R_pi^+(^6_Lambda H) < (2.5 \pm 0.4_stat ^{+0.4}_{-0.1syst})\cdot 10^{-5}/K^-_stop, R_{pi^+}(^7_Lambda H) < (4.5 \pm 0.9_stat^{+0.4}_{-0.1syst})\cdot 10^{-5}/K^-_stop and R_{pi^+} (^{12}_Lambda Be) < (2.0 \pm 0.4_stat^{+0:3}_{0.1syst})\cdot 10^{-5}/K^-_stop.
In the second data taking (2006-2007) a \sim 5 times larger statistics has been collected and a new analysis technique has been applied for the search of bound ^6_Lambda H and ^9_Lambda He, based on the coincidence between a pi^+ from the (K^-_stop, pi^+) production reaction and a pi^- from the two body mesonic weak decay of the hypernucleus to pi^- + ^6He_{g.s}. With this method the existence of ^6_Lambda H as a bound state has been assessed, based on 3 clearly identified events, with a binding energy B_Lambda=(4.0 \pm 1.1) MeV, with respect to ^5H+Lambda; and a production rate R_{pi^+}(^6_Lambda H)= (5.9\pm 4.0)\cdot 10^{-6}/K^-_stop [2,3] has been evaluated. Indications on the structure of the ^6_Lambda H energy levels have been obtained from a systematic difference among the ^6_Lambda H mass
evaluated from production and decay reactions.
The same method has been applied to the search for bound ^9_Lambda He, which is interesting since it could be a neutron-halo Hypernucleus. No event was found and an upper limit for its production, R_{pi^+}(^9_Lambda He) (5.0\pm 4.1)\cdot 10^{-6}/K^-_stop, was deduced [4]. In the presentation a review of all observed neutron-rich Lambda-hypernuclei will be given, with particular emphasis on the FINUDA results and on their discussion.
[1] M. Agnello, et al., Physics Letters B 640 (2006) 145.
[2] M. Agnello et al., Physical Review Letters 108 (2012) 042501.
[3] M. Agnello et al., Nuclear Physics A 881 (2012) 269.
[4] M. Agnello et al., Physical Review C 86 (2012) 057301.
SNP seminars