Search for neutron-hidden neutron interbrane transitions with MURMUR, a low-noise neutron passing-through-walls experiment

Abstract

Multi-braneworld universe is at the heart of many scenarios of physics beyond the Standard Model and the cosmological model $\Lambda CDM$. It is thus an important concern to constrain these scenarios which also allow for experiments below the GeV scale. MURMUR is a new neutron-passing-through-walls experiment designed to constrain neutron-hidden neutron transitions in the context of braneworlds scenarios. As our visible universe could be a 3-brane embedded in a multidimensional bulk, adjacent hidden 3-branes are often expected. Their existence can be constrained as matter exchange between braneworlds must occur with a swapping probability $p$. A neutron $n$ can convert into a hidden neutron $n^{\prime }$ when scattered by a nucleus with cross section $\sigma (n\to n^{\prime })$ $\propto$ ${\sigma }_E(n\to n)p$, where ${\sigma }_E$ is the usual elastic cross-section. Hidden neutrons could therefore be generated in the moderator medium of a nuclear reactor, where high-flux neutrons undergo many elastic collisions. All the theoretical and technological keys of this experiment soon to be installed at the nuclear research reactor BR2 (SCK.CEN, Mol, Belgium) are introduced.

5 pages, 7 figures, final version to be published in EPJ Web of Conferences - PPNS 2018 - International Workshop on Particle Physics at Neutron Sources (Grenoble, France, May 24 - 26, 2018)