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

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 constrain these scenarios which also allow for experiments below the GeV scale. MURMUR is a new neutron-passing-through-walls experiment designed 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 $nu0027$ when scattered by a nucleus with cross section $sigma (n to nu0027)$ $propto$ $sigma_E (n to n) p$, 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 be installed at the nuclear research reactor BR2 (SCK.CEN, Mol, Belgium) are introduced.