First combined analysis of neutrino and antineutrino oscillations at T2K (1701.00432v1)

Abstract: T2K reports its first results in the search for CP violation in neutrino oscillations using appearance and disappearance channels for neutrino- and antineutrino-mode beam. The data include all runs from Jan 2010 to May 2016 and comprise $7.482\times10^{20}$,protons on target in neutrino mode, which yielded in the far detector 32 e-like and 135 $\mu$-like events, and $7.471\times10^{20}$,protons on target in antineutrino mode which yielded 4 e-like and 66 $\mu$-like events. Reactor measurements of $\sin^{2}2\theta_{13}$ have been used as an additional constraint. The one-dimensional confidence interval at 90% for $\delta_{CP}$ spans the range ($-3.13$, $-0.39$) for normal mass ordering. The CP conservation hypothesis ($\delta_{CP}=0,\pi$) is excluded at 90% C.L.

Combined Analysis of Neutrino and Antineutrino Oscillations at T2K

The paper "First combined analysis of neutrino and antineutrino oscillations at T2K" presents significant advancements in understanding CP violation through neutrinos. Presented by the T2K Collaboration, this research illustrates the use of appearance and disappearance channels in both neutrino and antineutrino modes, focused on detecting CP violation.

The experimental setup involves the T2K experiment using a 30 GeV proton beam from the J-PARC accelerator in Japan, which produces a muon (anti)neutrino beam upon striking a graphite target. The resulting charged pions and kaons are focused by magnetic horns, yielding beams primarily composed of muon neutrinos or antineutrinos. These beams are measured by on-axis and off-axis detectors, where the far detector is the Super-Kamiokande, located 295 km away, used for observing oscillated neutrinos.

Data and Experimental Results

Data covers the period from Jan 2010 to May 2016, with exposures of $7.482\times10^{20}$ protons on target in neutrino mode and $7.471\times10^{20}$ in antineutrino mode. The far detector analyses resulted in 32 electron-like events and 66 muon-like events in neutrino mode, and 4 electron-like events and 66 muon-like events in antineutrino mode. To constrain the oscillation parameters, reactor measurements of $\sin^{2}2\theta_{13}$ have been integrated into the analysis.

Key Findings and Analysis

One-dimensional confidence intervals at 90% for $\delta_{CP}$ range between $-3.13$ and $-0.39$, with normal mass ordering. This analysis marks a significant result: the exclusion of CP conservation hypothesis ($\delta_{CP}=0,\pi$) at 90% Confidence Level. The data illustrates sensitivity to both $\delta_{CP}$ and potential mass ordering effects, indicating a preference for $\delta_{CP}$ near $-\pi/2$, suggesting maximal CP violation.

Implications and Future Directions

The implications of this analysis are profound in the field of particle physics, potentially providing insights into the nature of baryon asymmetry in the Universe. The exclusion of CP conservation could contribute to our understanding of the standard model and open avenues for novel exploration beyond it. As data collection continues and the T2K experiment improves its sensitivity, further fortification of these findings or potential challenges to current models could be realized, paving the way for future research in neutrino physics and beyond.

The research team's robust experimental approach and thorough data analysis showcase a significant step in neutrino oscillation studies. The continued progress in this domain holds promise for elucidating CP violation mechanisms, potentially addressing broader cosmic questions related to the matter-antimatter imbalance.