BEXCO - Room F(201/202/203/204)
[CRD048] Seasonal Variations for Multiple Muon Events in MINOS and NOvA
Maury Goodman for the NOvA collaboration Seasonal variations of cosmic ray muons have been well-measured by a number of underground experiments at a variety of overburdens and it has been found that the rate of muons increases in the summer and decreases in the winter. This is understood from the properties of the atmosphere as the temperature varies. We have measured with large statistics the seasonal variation of multiple muons in the MINOS ND (225 mwe), the MINOS (2100 mwe) and the NOvA ND (225 mwe). We find that rates in the 225 mwe detectors increase in the winter and decrease in the summer. This is opposite to the result for single muons and was not expected. For the deeper MINOS FD, we separate the muons by distance of closest approach. The muons separated by less than 5 m exhibits a modulation that peaks in the winter, while the muons separated by more than 8 m exhibit a modulation that peaks in the summer. Several hypotheses for this unexpected result are considered, but the effect is not currently explained. The newer NOvA data will be used to study the situation further.