Improved limits on β− and β−β− decays of 48Ca

New limits on 48Caβ− and β−β− decays to excited states of 48Ti have been obtained using a 400 cm3 low-background HPGe detector and an external source of 24.558 g enriched CaF2 powder (9.822 g of 48Ca). The limits for β− decay to the 6+ ground state and excited 5+ and 4+ states in 48Sc are 1.6×1020 yr, 2.5×1020 yr, and 1.9×1020 yr at the 90% confidence level. For the β−β− decay to 48Ti, the limits to the first 2+, second 2+, and first 0+ excited states are 1.8×1020 yr, 1.5×1020 yr, and 1.5×1020 yr, again at the 90% confidence level.