Abstract
In this paper, we indicate a possibility of utilizing the intense chromium source ($\sim 370 PBq$) in probing the neutrino nature in low energy neutrino experiments with the ultra-low threshold and background real-time Borexino detector located near the source ($\sim 8 m$). We analyze the elastic scattering of electron neutrinos (Dirac or Majorana, respectively) on the unpolarized electrons in the relativistic neutrino limit. We assume that the incoming neutrino beam is the superposition of left-right chiral states. Left chiral neutrinos may be detected by the standard $V A$ and non-standard scalar $S_L$, tensor $T_L$ interactions, while right chiral ones partake only in the exotic $V + A$ and $S_R, T_R$ interactions. Our model-independent study is carried out for the flavour (current) neutrino eigenstates. We compute the expected event number for the standard $V-A$ interaction of the left chiral neutrinos using the current experimental values of standard couplings and in the case of left-right chiral superposition. We show that the significant decrement in the event number due to the interference terms between the standard and exotic interactions for the Majorana $\nu_e$'s may appear. The $90 \%$ C. L. sensitivity contours in the planes of corresponding exotic couplings are also found. The presence of interferences in the Majorana case gives the stronger constraints than for the Dirac neutrinos, even if the neutrino source is placed outside the detector.
Highlights
IntroductionThis detector seems to be an appropriate tool to test the ν nature, i.e. whether ν’s are the Dirac or Majorana fermions
Have already been utilised to calibrate GALLEX and SAGE experiments [12,13,14,15,16], where a deficit in the rate of ν interactions has been found [17,18]
Concerning interacting right chiral (RCh) ν’s, the suitable non-standard models seem to be the left–right symmetric models (LRSM) [78,79,80,81,82,83], composite models (CM, where tensor and scalar interactions are generated by the exchange of constituents) [84,85,86], models with extra dimensions (MED) [87], the unparticle models (UP) [88,89,90,91,92,93,94,95,96,97,98,99,100]
Summary
This detector seems to be an appropriate tool to test the ν nature, i.e. whether ν’s are the Dirac or Majorana fermions. A lot of non-standard schemes with the Majorana (and Dirac) ν’s, time reversal violation (TRV) exotic interactions, mechanisms explaining the origin of fermion generations, masses, mixing and smallness of ν mass appeared They include a non-standard ν interactions (NSI) changing and conserving ν flavour [54,55,56,57], which may be generated by the mechanisms of massive neutrino models [58,59,60,61,62]. There is a constant necessity of improvement of the precision of the present tests at low energies, and on the other hand, the precise measurements of new observables including the linear terms from the exotic couplings would be required In this context the theoretically possible scenario of the measurement of the azimuthal asymmetry of recoil electrons as signature of the nature of ν has been considered [101]. We find the 90 % C.L. sensitivity contours in the planes of proper exotic couplings for both scenarios
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