*Dr Catalina Oana Curceanu, National Institute of Nuclear Physics, Laboratori Nazionali di Frascati
Parnell (7), Rm 222, 11 am*

Abstract: One of the main pillars of our understanding of Nature and Universe is the quantum theory (QT), which, in spite of its tantalizing success, still generates many debates, rooted in its puzzles, which trigger efforts towards a deeper understanding of the underlying mechanisms. What we know about the world is based on QT, but what precisely do we know, and how do we learn it? We see a series of “events” – we measure them. What we define as an “event” is the result of an observation, of a measurement process. The measurement process, however, is hiding one of the deepest mysteries of QT and, more generally, of science. In QT we have the “measurement problem”, generated by how (even whether) the wave function describing the system collapses. We do measure a definite state, in spite of the fact that the QT describes a state as (usually) being in a linear superposition of different states. How does the wave function collapse and generates that “event” we measure/see? In the last decades huge theoretical effort was devoted to the development of consistent theoretical models aiming to solve the “measurement problem”. Among these, the Dynamical Reduction Models (DRM) provide a consistent theoretical framework for understanding how “classical world” emerges from quantum mechanics. Their dynamics practically preserves quantum linearity for the microscopic systems, but becomes strongly nonlinear when moving towards macroscopic scale. These types of models can be regarded as effective theories for the “real theory” beyond QT which is yet to be discovered.

The DRM possess the unique characteristic to be experimentally testable, thus enabling to set experimental upper bounds on the reduction rate parameter “lambda” characterizing these models. The conventional approach to test the collapse models is to generate spatial superpositions of mesoscopic systems and examine the loss of interference, while environmental noises are under control. The present day technology, however, does not allow to set stringent limits by applying this direct method. The most promising testing ground, instead, is offered by the search for the spontaneous radiation emitted by charged particles interacting with the “collapsing field”, which is predicted by the collapse models.

We shall present results coming from dedicated measurements of this spontaneous radiation performed in the low-background underground laboratory of Gran Sasso (LNGS-INFN, Italy) with the aim to put the most stringent limit on the lambda parameter ever.