New constraints on muon-neutrino to electron-neutrino transitions in MINOS

This paper reports results from a search for ${\nu }_{\mu }\to {\nu }_e$ transitions by the MINOS experiment based on a $7\times {10}^{20}$ protons-on-target exposure. Our observation of 54 candidate ${\nu }_e$ events in the far detector with a background of $49.1\pm 7.0(\mathrm{stat})\pm 2.7(\mathrm{syst})$ events predicted by the measurements in the near detector requires $2{sin}^2(2{\theta }_{13}){sin}^2{\theta }_{23}<0.12(0.20)$ at the 90% C.L. for the normal (inverted) mass hierarchy at ${\delta }_{CP}=0$. The experiment sets the tightest limits to date on the value of ${\theta }_{13}$ for nearly all values of ${\delta }_{CP}$ for the normal neutrino mass hierarchy and maximal ${sin}^2(2{\theta }_{23})$.

Figure 1

Reconstructed near detector energy spectra of the ${\nu }_e\mathrm{\text{−}}\mathrm{CC}$ selected events (bold solid lines). Also shown is the decomposition of this spectrum into neutral current (dotted lines), ${\nu }_{\mu }$ charged current (dashed lines), and beam ${\nu }_e\mathrm{\text{−}}\mathrm{CC}$ (light solid lines) components determined using the multiple beam configuration method. The sum of the three background components is constrained to agree with the data. Uncertainties on the data are statistical and are not visible on this scale; uncertainties on the components are systematic.

Figure 2

Distribution of the ANN selection variable for preselected events in the far detector. Black points show data with statistical error bars. The nonshaded histogram shows the expected background. The shaded region shows the additional ${\nu }_e$ charged current events allowed from the best fit to the oscillation hypothesis as described in the text.

Figure 3

Reconstructed energy spectrum of the events in the far detector which pass all ${\nu }_e$ charged current selection criteria, with the exception of the energy cut. Black points show data with statistical error bars. The nonshaded histogram shows the expected background. The shaded region shows the additional ${\nu }_e$ charged current events allowed by the best fit to the oscillation hypothesis.

Figure 4

Values of $2{sin}^2(2{\theta }_{13}){sin}^2{\theta }_{23}$ and ${\delta }_{CP}$ that produce a number of candidate events in the far detector consistent with the observation for the normal hierarchy (top) and inverted hierarchy (bottom). Black lines show those values that best represent our data. Red (blue) regions show the 90% (68%) C.L. intervals. The CHOOZ limit is drawn for $\Delta m_{32}^2=2.43\times {10}^{-3}{\mathrm{eV}}^2$, ${sin}^2(2{\theta }_{23})=1.0$.