(1405) measurement through the decay to 0 0, resulting from K􀀀 meson absorption on 4He and 12C : with the KLOE detector

Abstract

This work is dealing with the study of the low-energy interactions of the negatively charged kaons with light nuclei. Such type of physics, extremely important for the understanding of the non-perturbative QCD in the strangeness sector, has important consequences, going from the particle and nuclear physics to astrophysics. We investigated the 0 0 channel, generated by K􀀀 absorptions on bound protons in 4He and 12C. 0 0 is the privileged, but still poorly explored, channel to explore the yet unsolved structure of the (1405) resonance, since it is free from the dominant (1385) background. The (1405) plays a central role in various aspects of hadron and nuclear strangeness physics. Due to its intimate connection with the strongly attractive KN channel, this state can be considered as the "key ingredient" for understanding the few body-antikaon systems and their possible exotic properties predicted in some theories, but non existent in others. The quest for low-energy K􀀀 hadronic interactions with KLOE detector at the DA NE collider is based on few, but essential features: the DA NE collider is a unique source of low-momentum monocromatic kaons produced in the decay almost at rest, the large acceptance of the KLOE detector, the excellent performances in charged particles detection, the high e ciency and resolution of the KLOE calorimeter for photons, render KLOE an ideal apparatus for the low-energy kaon-nucleon/nuclei research, dedicated studies were performed using the standard KLOE Monte Carlo simulation, GEANFI, for the conditions of the 2004-2005 runs, to which data presented in this work belong. A fraction of stopped K􀀀 in the KLOE drift chamber entrance wall (mainly Carbon) of 2% was found and of 0:1% in the drift chamber gas (mainly Helium). Apart this, there are kaons interacting in ight giving rise to the 0 0 nal state. The work is organized as follows. In Chapter 1 the scienti c case of the (1405) is presented; the status of the theoretical and experimental search is outlined, with particular care to its implications in the strangeness nuclear physics. Chapter 2 is devoted to a brief description of the DA NE collider and the KLOE detector. The details of particle identi cation and of the events selection procedure are given in Chapter 3. The core of the performed analysis of K􀀀 absorptions in Carbon and Helium are reported in Chapters 4 and 5, respectively, with a similar structure to highlight the symmetries of the obtained results for the two target nuclei. In Chapter 6 the outcome of the performed ts will enable the comparison of the measured spectra with theoretical predictions and previous results from similar experimental conditions measurements. Thanks to a careful comparative study of the relevant kinematical variables spectra with bubble chamber and emulsion experiments, a clear understanding of the di erent kinematical regimes contributing to the observed events will be achieved. The in ight K􀀀 nuclear absorptions, accessing a higher invariant mass region above the threshold imposed by the proton binding energy, will be characterized in this study for the rst time, sheding new light on the (1405) behaviour in nuclear environment. A nal Chapter 7, dedicated to conclusions, ends this work, showing how the KLOE detector at DA NE can perform, with enormous success, rst-class studies in the eld of low energy QCD in the strangeness sector.