Model of n¯ annihilation in experimental searches for n

Abstract

Searches for baryon number violation, including searches for proton decay and neutron-antineutron transformation ( → ̅), are expected to play an important role in the evolution of our understanding of beyond Standard Model physics. The → ̅ is a key prediction of certain popular theories of baryogenesis, and the experiments such as the Deep Underground Neutrino Experiment and the European Spallation Source plan to search for this process with bound-and free-neutron systems. Accurate simulation of this process in Monte Carlo will be important for the proper reconstruction and separation of these rare events from background. This article presents developments towards accurate simulation of the annihilation process for use in a cold, free neutron beam for → ̅ searches from ̅ annihilation, as 6 12 is the target of choice for the European Spallation Source's NNBar Collaboration. Initial efforts are also made in this paper to perform analogous studies for intra-nuclear transformation searches in 18 40 nuclei.I.

Future searches for free and bound n → n̅ transformations

“…It has also become clear to our group 40 18 Ar 's nuclear density distribution in black (approximated by the blue stepped histogram), the approximate radial annihilation probability distribution of extranuclear annihilation on 40 18 Ar in yellow (assuming similarity with [32]), and the same for an intranuclear annihilation in orange [33]. These distribution are shown as used in our group's internal intranuclear n →n MC simulations, and represent extensions of our current work for the ESS NNBar collaboration in modeling of the free (extranuclear) transformation and subsequent annihilation on carbon [31,33]. Most pertinent to DUNE, the figure effectively shows differences between the current assumptions of [27], wherein the transformation and subsequent annihilation are supposed to occur along the density profile of the nucleus, and our modeling of the intranuclear annihilation position [30,32,33].…”

“…While it is true that future DUNE data will indeed test and resolve theoretical nuclear physics models used in MC for 40 18 Ar , presently these models can arguably only be tested by their overall consistency between and among themselves, effectively requiring a combination of various theoretical approaches. Regarding these, there exist a number of of perogatives for our group's future MC simulation work beyond [31,33]. In continuation of similar efforts discussed in [34], it is necessary that the simulation of new, reliable, ν atm background samples within the DUNE ten kiloton LArTPC detector modules utilize cross sections for electron and ν scattering developed at LANL/ANL from ab-initio quantum Monte Carlo calculations.…”

The effect of collisions with the wall on neutron-antineutron transitions

“…In different models the imaginary part of the optical potential differs by almost an order of magnitude [20]. An attempt has been undertaken recently [21] to develop a model forn 12 6 C interaction. Carbon is a material which served as a target in the ILL experiment [5] and will be used in the ESS project [7].…”

Plan of NNbar experiment at the WWR-M reactor

“…Special simulations were carried out to model the nuclear processes associated with annihilation events in Ni and Mo nuclei (for a more detailed description of the model see Ref. [11]). We used the generated events to develop the detector system and estimate the detector efficiency.…”