arXiv subjects

Suman Bharti

Publications and source records attributed to Suman Bharti.

4 recordsLinked to original sources

arXiv2020

Matter vs. vacuum oscillations at long baseline accelerator neutrino experiments

The neutrino oscillation probabilities at the long-baseline accelerator neutrino experiments are expected to be modified by matter effects. We search for evidence of such modification in the data of T2K and NO$ν$A, by fitting the data to the hypothesis of (a) matter modified oscillations and (b) vacuum oscillations. We find that vacuum oscillations provide as good a fit to the data as matter modified oscillations. Even extended runs of T2K and NO$ν$A, with 5 years in neutrino mode $(5 ν)$ and five years in anti-neutrino mode $(5 \barν)$, can {\bf not} make a $3~σ$ distinction between vacuum and matter modified oscillations. The proposed experiment DUNE, with neutrino and anti-neutrino runs of 5 years each $(5 ν+ 5 \barν)$, can rule out vacuum oscillations by itself at $5~σ$ if the hierarchy is normal. If the hierarchy is inverted, a $5~σ$ discrimination against vacuum oscillations requires the combination of $(5 ν+ 5 \barν)$ runs of T2K, \nova and DUNE.

hep-ph↗

arXiv2020

Tensions between the appearance data of T2K and NOvA

The long baseline neutrino experiments, T2K and NOvA, have taken significant amount of data in each of the four channels: (a) $ν_μ$ disappearance, (b) $\barν_μ$ disappearance (c) $ν_e$ appearance and (d) $\barν_e$ appearance. There is a mild tension between the disappearance and the appearance data sets of T2K. A more serious tension exists between the $ν_e$ appearance data of T2K and the $ν_e / \barν_e$ appearance data of NOvA. This tension is significant enough that T2K rules out the best-fit point of NOvA at $95\%$ confidence level whereas NOvA rules out T2K best-fit point at $90\%$ confidence level. We explain the reason why these tensions arise. We also do a combined fit of T2K and NOvA data and comment on the results of this fit.

hep-ph↗

arXiv2018

Understanding the degeneracies in NO$ν$A data

The combined analysis of $ν_μ$ disappearance and $ν_e$ appearance data of NO$ν$A experiment leads to three nearly degenerate solutions. This degeneracy can be understood in terms of deviations in $ν_e$ appearance signal, caused by unknown effects, with respect to the signal expected for a reference set of oscillations parameters. We define the reference set to be vacuum oscillations in the limit of maximal $θ_{23}$ and no CP-violation. We then calculate the deviations induced in the $ν_e$ appearance signal event rate by three unknown effects: (a) matter effects, due to normal or inverted hierarchy (b) octant effects, due to $θ_{23}$ being in higher or lower octant and (c) CP-violation, whether $δ_{CP} \sim - π/2$ or $δ_{CP} \sim π/2$. We find that the deviation caused by each of these effects is the same for NO$ν$A. The observed number of $ν_e$ events in NO$ν$A is equivalent to the increase caused by one of the effects. Therefore, the observed number of $ν_e$ appearance events of NO$ν$A is the net result of the increase caused by two of the unknown effects and the decrease caused by the third. Thus we get the three degenerate solutions. We also find that further data by NO$ν$A can not distinguish between these degenerate solutions but addition of one year of neutrino run of DUNE can make a distinction between all three solutions. The distinction between the two NH solutions and the IH solution becomes possible because of the larger matter effect in DUNE. The distinction between the two NH solutions with different octants is a result of the synergy between the anti-neutrino data of NO$ν$A and the neutrino data of DUNE.

hep-ph↗

arXiv2016

Hierarchy sensitivity of NO$ν$A in light of T2K $ν_e$ appearance data

The $ν_e$ appearance data of T2K experiment has given a glimpse of the allowed parameters in the hierarchy-$δ_{CP}$ parameter space. In this paper, we explore how this data affects our expectations regarding the hierarchy sensitivity of the NO$ν$A experiment. For the favourable combinations of hierarchy and $δ_{CP}$, the hierarchy sensitivity of NO$ν$A is unaffected by the addition of T2K data. For the unfavourable combinations, NO$ν$A data gives degenerate solutions. Among these degenerate solutions, T2K data prefers IH and $δ_{CP}$ in the lower half plane over NH and $δ_{CP}$ in the upper half plane. Hence, addition of the T2K data to NO$ν$A creates a bias towards IH and $δ_{CP}$ in the lower half plane irrespective of what the true combination is.

hep-ph↗