Precision measurements of 2-3 oscillation parameters in the next-generation long-baseline experiments

Abstract

Over the past few decades, data from leading neutrino experiments have firmly established neutrino oscillation, implying non-zero neutrino masses and leptonic mixing and thereby providing confirmed evidence of physics beyond the Standard Model. On the backdrop of the precision era of neutrino oscillation, this thesis underscores its relevance by demonstrating the physics reach of the forthcoming long-baseline experiments -- Deep Underground Neutrino Experiment (DUNE) and Hyper-Kamiokande (Hyper-K) -- to establish non-maximal $θ_{23}$, resolve the correct $θ_{23}$ octant, and improve the precision on $θ_{23}$ and $Δm^2_{31}$ by efficiently breaking parameter degeneracies. This is enabled by DUNE's high-resolution LArTPC detector and its wide-band beam, achieving sensitivity at a high confidence level compared to the global fits of world neutrino data. The combined analysis of DUNE and Hyper-K not only significantly enhances sensitivity to these phenomenological studies but also demonstrates their capabilities at lower exposures when operated together, relative to their nominal individual exposures. In addition, we investigate the impact of flavor-dependent long-range interactions arising from anomaly-free U(1)' extensions of the Standard Model, showing that although subdominant long-range interactions can substantially influence the sensitivity and precision of oscillation parameter measurements, the complementary strengths of DUNE and Hyper-K mitigate these challenges to a large extent.

Figures (36)

• Figure 1: Neutrino oscillation probability in vacuum at two flavor case as the function of true neutrino energy (in GeV) is depicted here. The upper (lower) panel represents $\nu_\alpha\rightarrow\nu_\beta$ appearance ($\nu_\alpha\rightarrow\nu_\alpha$ disappearance) probability using Equation \ref{['eq:2 flavor app oscillation probability']}. In the left panel, we observe the oscillation probability for three choices of mixing angle $\theta\,\,i.e.,\,\,40^\circ,\,45^\circ,\,\mathrm{and}\,\,\, 55^\circ$ (shown in red, blue, and green lines), respectively, assuming $L= 1300$ km and $\Delta m^2=+2.522\times10^{-3}$ eV$^2$. In the right panel, we compute the same but for three different choices of $\Delta m^2,\,\,i.e.,\,2.436\times10^{-3}$ eV$^2,\, 2.522\times10^{-3}$ eV$^2, \mathrm{and}\,\,\, 2.605\times10^{-3}$ eV$^2$ (shown by red, blue, and green lines), respectively, assuming a given mixing angle $\theta=45^\circ$.
• Figure 2: Current $1\sigma$ (see rectangular boxes) and $3\sigma$ (see horizontal lines) allowed ranges of the neutrino oscillation parameters obtained from the global fit studies performed by Esteban $et~ al.$NuFIT, de Salas $et~ al.$deSalas:2020pgw, and Capozzi $et~ al.$Capozzi:2021fjo. The blue (red) lines and boxes represent the values for NMO (IMO). In each panel, the best-fit value of the respective oscillation parameter is shown by blue (red) dots for NMO (IMO). Vertical black dashed lines in the panels related to $\sin^2\theta_{12}$ and $\sin^2\theta_{23}$ show their corresponding values in the tri-bimaximal mixing scheme. Note that the measurements of $\sin^{2}\theta_{12}$ and $\Delta m^{2}_{\mathrm{sol}}\, (\equiv \Delta m^{2}_{21})$ are not sensitive to the choice of mass ordering.
• Figure 3: Probability as a function of $\sin^2\theta_{23}$ for $E = 2.5$ GeV, $L=1284.9$ km, and $\rho=2.848~ \rm{g/cm}^{3}$ assuming NMO. The top (bottom) panels are for the disappearance (appearance) channel. The left (right) panels are for neutrino (antineutrino). The black solid curves show the probability considering the best-fit values of oscillation parameters as given in Table \ref{['table:one']}. The three shaded blue (red) regions depict the variations in probability due to the present $1\sigma,~2\sigma,~\rm{and}~3\sigma$ allowed ranges in $\Delta m^2_{31}$ ($\delta_{\rm CP}$). The dark (light)-shaded grey area shows the currently allowed $1\sigma~ (2\sigma)$ region in $\sin^{2}\theta_{23}$ with the best-fit value of $\sin^{2}\theta_{23} = 0.455$ as shown by the vertical brown line. See Table \ref{['table:one']} for details. Note that y-ranges are different in the bottom two panels.
• Figure 4: Total event rates as a function of $\sin^2\theta_{23}$ for DUNE assuming NMO. The top (bottom) panels are for disappearance (appearance) channel. The left (right) panels are for neutrino (antineutrino) assuming 3.5 years of run. The black solid curves show the event rates considering the best-fit values of oscillation parameters as given in Table \ref{['table:one']}. The three shaded blue (red) regions show the variations in events due to present $1\sigma,~2\sigma,~ \rm{and}~3\sigma$ allowed ranges in $\Delta m^2_{31}$ ($\delta_{\rm CP}$). The dark (light)-shaded grey area shows the currently allowed $1\sigma~ (2\sigma)$ region in $\sin^{2}\theta_{23}$ with the best-fit value of $\sin^{2}\theta_{23} = 0.455$ as shown by the vertical brown line. See Table \ref{['table:one']} and related text for details. Note that y-ranges are different in all the four panels.
• Figure 5: Bi-events plot for DUNE in the plane of neutrino - antineutrino disappearance events assuming 336 kt$\cdot$MW$\cdot$years of exposure equally divided in neutrino and antineutrino modes. The blue line is obtained by varying $\Delta m^{2}_{31}$ in its 3$\sigma$ range of $[2.43 : 2.6] \times 10^{-3}~\rm{eV}^{2}$ with $\sin^2\theta_{23}=0.455$ (LO). The red line depicts the same with $\sin^2\theta_{23}=0.5$ (MM). The black dot on each line shows the disappearance events corresponding to the best-fit value of $\Delta m^2_{31} = 2.52 \times 10^{-3}$ eV$^{2}$. The values of other oscillation parameters are taken from Table \ref{['table:one']} assuming NMO. The blue (red) rectangular region on blue (red) line portrays the variation in event rates due to 3$\sigma$ range in $\Delta m^{2}_{31}$ expected from JUNO EPS-HEP-Conference2021JUNO:2015zny. The horizontal (vertical) error bars for the points [($\sin^{2}\theta_{23} = 0.455, \Delta m^{2}_{31} = 2.52 \times 10^{-3} \rm{eV}^{2}$) and ($\sin^{2}\theta_{23} = 0.455, \Delta m^{2}_{31} = 2.6 \times 10^{-3} \rm{eV}^{2}$)] show the 1$\sigma$ statistical uncertainties which are obtained by taking the square root of the $\nu \,(\bar{\nu})$ disappearance events.