Neutrino masses and mixings: Status of known and unknown 3ν parameters

Abstract

Within the standard 3ν mass-mixing framework, we present an up-to-date global analysis of neutrino oscillation data (as of January 2016), including the latest available results from experiments with atmospheric neutrinos (Super-Kamiokande and IceCube DeepCore), at accelerators (first T2K ν and NOνA ν runs in both appearance and disappearance mode), and at short-baseline reactors (Daya Bay and RENO far/near spectral ratios), as well as a reanalysis of older KamLAND data in the light of the "bump" feature recently observed in reactor spectra. We discuss improved constraints on the five known oscillation parameters (δm 2 , |∆m 2 |, sin 2 θ 12 , sin 2 θ 13 , sin 2 θ 23 ), and the status of the three remaining unknown parameters: the mass hierarchy [sign(±∆m 2 )], the θ 23 octant [sign(sin 2 θ 23 − 1/2)], and the possible CP-violating phase δ. With respect to previous global fits, we find that the reanalysis of KamLAND data induces a slight decrease of both δm 2 and sin 2 θ 12 , while the latest accelerator and atmospheric data induce a slight increase of |∆m 2 |. Concerning the unknown parameters, we confirm the previous intriguing preference for negative values of sin δ (with best-fit values around sin δ −0.9), but we find no statistically significant indication about the θ 23 octant or the mass hierarchy (normal or inverted). Assuming an alternative (so-called LEM) analysis of NOνA data, some δ ranges can be excluded at > 3σ, and the normal mass hierarchy appears to be slightly favored at ∼ 90% C.L. We also describe in detail the covariances of selected pairs of oscillation parameters. Finally, we briefly discuss the implications of the above results on the three non-oscillation observables sensitive to the (unknown) absolute ν mass scale: the sum of ν masses Σ (in cosmology), the effective ν e mass m β (in beta decay), and the effective Majorana mass m ββ (in neutrinoless double beta decay).

A study of invisible neutrino decay at DUNE and its effects on θ23 measurement

“…The neutrino oscillation parameters -namely the two mass squared differences ∆m 2 21 = m 2 2 − m 2 1 and |∆m 2 31 | = |m 2 3 − m 2 1 |, m 1 , m 2 , m 3 being the mass states and the three mixing angles θ 12 , θ 13 and θ 23 have been determined with considerable precision by global oscillation analysis of world neutrino data [1,2]. The unknown oscillation parameters are: (i) the neutrino mass hierarchy i.e whether m 3 > m 2 > m 1 leading to normal hierarchy (NH) or if m 3 < m 2 ≈ m 1 resulting in inverted hierarchy (IH); (ii) the octant of θ 23 -if θ 23 < 45 • it is said to be in the lower octant (LO) and if θ 23 > 45 • it is in the higher octant (HO); (iii) the CP phase δ CP .…”

Can nonstandard interactions jeopardize the hierarchy sensitivity of DUNE?

“…Current data determines the two mass squared differences (∆m 2 21 = m 2 2 − m 2 1 , |∆m 2 31 | = |m 2 3 − m 2 1 |, m 1 , m 2 , m 3 being the mass states) and three leptonic mixing angles (θ 12 , θ 23 , θ 13 ) with considerable precision [1]. This leaves determination of neutrino mass hierarchy i.e.…”

“…whether m 3 > m 2 > m 1 (normal hierarchy (NH)) or m 3 < m 1 ≈ m 2 (inverted hierarchy (IH)), octant of θ 23 i.e whether θ 23 < π/4 and lies in lower octant (LO) or it is > π/4 and is in the higher octant (HO) and measurement of δ CP as the major objectives of ongoing and future experiments. Recently, the on-going T2K experiment [2] and global analysis of data [1] have hinted that the Dirac CP phase is maximal i.e. δ CP = −π/2 although at 3σ the full range (0 − 2π) remains allowed.…”

“…The experimental specifications and other numerical details are taken from [21] except that this analysis is done for 40 kt detector mass. The true values that we have considered are, sin 2 θ 12 = 0.297, sin 2 2θ 13 = 0.085, θ 23 = 45 • , δ CP = −π/2, ∆m 2 21 = 7.37 × 10 −5 eV 2 and ∆m 2 31 = 2.50 × 10 −3 eV 2 [1]. Different true values of NSI parameters are as mentioned in the fig.…”

Broken S 3L × S 3R flavor symmetry and leptonic CP violation

“…Although the normal ordering of neutrino masses (i.e., m 1 < m 2 < m 3 ) is slightly favored and there is a preliminary hint of a nearly-maximal CP -violating phase δ ≈ 261 • or equivalently δ ≈ −99 • , the possibility of an inverted mass ordering (i.e., m 3 < m 1 < m 2 ) and CP conservation in the leptonic sector has not yet been excluded [6]. See also the independent global-fit results from two other groups [7][8][9]. An unambiguous determination of neutrino mass ordering and a robust discovery of leptonic CP violation in neutrino oscillations are two primary goals of future medium-baseline reactor (e.g., JUNO [10] and RENO-50 [11]) and long-baseline accelerator neutrino experiments (e.g., T2K [12], NOνA [13] and LBNF-DUNE [14]).…”