Abstract
An observation of neutron-antineutron oscillations (n - n¯), which violate both B and B - L by 2 units, would constitute a fundamental discovery and contribute to our understanding of the baryon asymmetry of the universe. A sufficiently stringent upper constraint on this process would also make a major contribution by ruling out the possibility of post-sphaleron baryogenesis (PSB) involving first-generation quarks, which would mean that sphaleron transitions at the electroweak scale are essential for baryogenesis within the Sakharov paradigm. We show that one can design an experiment with free n using existing or projected neutron sources that can reach the sensitivity needed to rule out PSB if one allows the n and n¯, with sufficiently small tangential velocity, to coherently reflect from n/n¯ mirrors composed of certain nuclei. We show that the sensitivity of a future experiment can be greatly improved, and a more compact and less expensive apparatus can be realized. A sensitivity gain of ~ 104 in the oscillation probability relative to the existing free-n limit can be reached if one is willing to adopt a long flight path with a horizontal guide viewing a cold neutron source, or a significantly shorter flight path with a vertical guide viewing a very cold neutron source.
Highlights
The possibility to conduct a much more sensitive search for ∆B = 2 violating processes, especially with ∆(B − L) = 2, such as n − noscillations, has started to attract more attention both from theory and experiment. The latter processes are important for cosmological arguments, which use the well-known Sakharov criteria [2] to generate the baryon asymmetry of the universe starting from a B = 0 initial condition
A baryon asymmetry generated in the early universe from B-violating processes, which come from new physics above the electroweak phase transition and conserves B − L, such as the simplest ∆B = 1 and ∆L = 1
Any set of experiments which are able to rule out post-sphaleron baryogenesis (PSB) would be of fundamental importance for cosmology as in this case one would be able to conclude that an understanding of the electroweak sphaleron transitions in the early universe is necessity for understanding the baryon asymmetry within the Sakharov paradigm
Summary
The possibility to conduct a much more sensitive search for ∆B = 2 violating processes, especially with ∆(B − L) = 2, such as n − noscillations, has started to attract more attention both from theory and experiment The latter processes are important for cosmological arguments, which use the well-known Sakharov criteria [2] to generate the baryon asymmetry of the universe starting from a B = 0 initial condition. Recent studies have investigated in greater depth the limits of the so-called quasifree condition for the evolution of the n/namplitudes described below [62] These developments in theory and experiment show that the subject of ∆B = 2 processes has become more interesting and that the experimental approach described in this paper is of general interest to the physics community.
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