Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userNonmaximal $theta_{23}$ mixing at NOvA from neutrino decoherence
79
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
In study of muon neutrino disappearance at 810 km, the NOvA experiment finds flavor mixing of the atmospheric sector to deviate from maximal ($sin^2theta_{23} = 0.5$) by 2.6 $sigma$. The result is in tension with the 295-km baseline measurements of T2K which are consistent with maximal mixing. We propose that $theta_{23}$ is in fact maximal, and that the disagreement is harbinger of environmentally-induced decoherence. The departure from maximal mixing can be accounted for by an energy-independent decoherence of strength $Gamma = (2.3 pm 1.1) times 10^{-23}$ GeV.
rate research
Read More
This Letter reports new results on muon neutrino disappearance from NOvA, using a 14 kton detector equivalent exposure of $6.05times10^{20}$ protons-on-target from the NuMI beam at the Fermi National Accelerator Laboratory. The measurement probes the muon-tau symmetry hypothesis that requires maximal mixing ($theta_{23} = pi/4$). Assuming the normal mass hierarchy, we find $Delta m^2 = (2.67 pm 0.11)times 10^{-3}$ eV$^2$ and $sin^2 theta_{23}$ at the two statistically degenerate values $0.404^{+0.030}_{-0.022}$ and $0.624^{+0.022}_{-0.030}$, both at the 68% confidence level. Our data disfavor the maximal mixing scenario with 2.6 $sigma$ significance.
Considerable information has been obtained about neutrino mixing matrix. Present data show that in the particle data group (PDG) parameterization, the 2-3 mixing angle and the CP violating phase are consistent with $theta_{23} = pi/4$ and $delta_{PDG} = -pi/2$, respectively. A lot of efforts have been devoted to constructing models in realizing a mixing matrix with these values. However, the particular angles and phase are parameterization convention dependent. The meaning about the specific values for mixing angle and phase needs to be clarified. Using the well known 9 independent ways of parameterizing the mixing matrix, we show in detail how the mixing angles and phase change with conventions even with the 2-3 mixing angle to be $pi/4$ and the CP violating phase to be $-pi/2$. The original Kaobayashi-Maskawa and an additional one belong to such a category. The other 6 parameterizations have mixing angles and phase very different values from those in the PDG parameterization although the physical effects are the same. Therefore one should give the specific parameterization convention when making statements about values for mixing angles and phase.
Present global fits of world neutrino data hint towards non-maximal $theta_{23}$ with two nearly degenerate solutions, one in the lower octant ($theta_{23} <pi/4$), and the other in the higher octant ($theta_{23} >pi/4$). This octant ambiguity of $theta_{23}$ is one of the fundamental issues in the neutrino sector, and its resolution is a crucial goal of next-generation long-baseline (LBL) experiments. In this letter, we address for the first time, the impact of a light eV-scale sterile neutrino towards such a measurement, taking the Deep Underground Neutrino Experiment (DUNE) as a case study. In the so-called 3+1 scheme involving three active and one sterile neutrino, the $ u_mu to u_e$ transition probability probed in the LBL experiments acquires a new interference term via active-sterile oscillations. We find that this novel interference term can mimic a swap of the $theta_{23}$ octant, even if one uses the information from both neutrino and antineutrino channels. As a consequence, the sensitivity to the octant of $theta_{23}$ can be completely lost and this may have serious implications in our understanding of neutrinos from both the experimental and theoretical perspectives.
Among all neutrino mixing parameters, the atmospheric neutrino mixing angle theta_{23} introduces the strongest variation on the flux ratios of ultra high energy neutrinos. We investigate the potential of these flux ratio measurements at neutrino telescopes to constrain theta_{23}. We consider astrophysical neutrinos originating from pion, muon-damped and neutron sources and make a comparative study of their sensitivity reach to theta_{23}. It is found that neutron sources are most favorable for testing deviations from maximal theta_{23}. Using a chi^2 analysis, we show in particular the power of combining (i) different flux ratios from the same type of source, and also (ii) combining flux ratios from different astrophysical sources. We include in our analysis ``impure sources, i.e., deviations from the usually assumed initial (1 : 2 : 0), (0 : 1 : 0) or (1 : 0 : 0) flux compositions.
We investigate the prospects for determining the octant of $theta_{23}$ in the future long baseline oscillation experiments. We present our results as contour plots on the ($theta_{23}-45^circ$, $delta$)--plane, where $delta$ is the CP phase, showing the true values of $theta_{23}$ for which the octant can be experimentally determined at 3$,sigma$, 2$,sigma$ and 1$,sigma$ confidence level, in particular, the impact of the non-unitarity of neutrino mixing.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
