Abstract
An observation of neutron-antineutron oscillations (n-n[over ¯]), which violate both B and B-L conservation, would constitute a scientific discovery of fundamental importance to physics and cosmology. A stringent upper bound on its transition rate would make an important contribution to our understanding of the baryon asymmetry of the Universe by eliminating the postsphaleron baryogenesis scenario in the light quark sector. We show that one can design an experiment using slow neutrons that in principle can reach the required sensitivity of τ_{n-n[over ¯]}∼10^{10} s in the oscillation time, an improvement of ∼10^{4} in the oscillation probability relative to the existing limit for free neutrons. The improved statistical accuracy needed to reach this sensitivity can be achieved by allowing both the neutron and antineutron components of the developing superposition state to coherently reflect from mirrors. We present a quantitative analysis of this scenario and show that, for sufficiently small transverse momenta of n/n[over ¯] and for certain choices of nuclei for the n/n[over ¯] guide material, the relative phase shift of the n and n[over ¯] components upon reflection and the n[over ¯] annihilation rate can be small enough to maintain sufficient coherence to benefit from the greater phase space acceptance the mirror provides.
Highlights
An especially interesting class of models collectively referred to as postsphaleron baryogenesis (PSB) [34] can generate the baryon asymmetry below the electroweak
A stringent upper bound on its transition rate would make an important contribution to our understanding of the baryon asymmetry of the Universe by eliminating the postsphaleron baryogenesis scenario in the light quark sector
We show that one can design an experiment using slow neutrons that in principle can reach the required sensitivity of τn−n ∼ 1010 s in the oscillation time, an improvement of ∼104 in the oscillation probability relative to the existing limit for free neutrons
Summary
Possibility in experiments [58,59,60,61] using ultracold neutrons (UCNs) [62,63] is the subject of active studies [64]. Reflection of n − nwas considered already in 1980 for UCNs [8,12,74,75] for experiments constraining τn−n , we extend this approach to higher energies (slow n that can be confined in neutron guides), point out conditions for suppressing the phase difference for n and n , quantify the low transverse momenta of n=nrequired, and make new choices for the nuclei composing the guide material. This approach can preserve both the very low antineutron detector backgrounds that have been achieved in free n oscillation searches and the ability to confirm a nonzero signal by applying a small external magnetic field on the beam to split the n and nstates by ΔE 1⁄4 2μB enough to suppress the oscillation probability It does not require the same level of detail in the understanding of the ndynamics and the subsequent annihilation products needed to interpret the underground detector nannihilation experiments. Note that the diverging part contributes to the n − nsensitivity provided the n=nincidence angles are small
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