Measurement of the atmospheric muon charge ratio at TeV energies with the MINOS detector
2007
The 5.4 kton
MINOSfar detector has been taking charge-separated cosmic ray
muondata since the beginning of August, 2003 at a depth of 2070 m.w.e. in the Soudan
UndergroundLaboratory, Minnesota, USA. The data with both forward and reversed magnetic field running configurations were combined to minimize systematic errors in the determination of the
underground
muoncharge ratio. When averaged, two independent analyses find the charge ratio
undergroundto be N-mu(+)/N-mu(-)=1.374 +/- 0.004(stat)(-0.010)(+0.012)(sys). Using the map of the Soudan rock
overburden, the
muonmomenta as measured
undergroundwere projected to the corresponding values at the surface in the energy range 1-7 TeV. Within this range of energies at the surface, the
MINOSdata are consistent with the charge ratio being
energy independentat the 2 standard deviation level. When the
MINOSresults are compared with measurements at lower energies, a clear rise in the charge ratio in the energy range 0.3-1.0 TeV is apparent. A qualitative model shows that the rise is consistent with an increasing contribution of kaon decays to the
muoncharge ratio.
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