  We experimentally demonstrate cooling of trapped ions by collisions with
co-trapped, higher mass neutral atoms. It is shown that the lighter
$^{39}$K$^{+}$ ions, created by ionizing $^{39}$K atoms in a magneto-optical
trap (MOT), when trapped in an ion trap and subsequently allowed to cool by
collisions with ultracold, heavier $^{85}$Rb atoms in a MOT, exhibit a longer
trap lifetime than without the localized $^{85}$Rb MOT atoms. A similar cooling
of trapped $^{85}$Rb$^{+}$ ions by ultracold $^{133}$Cs atoms in a MOT is also
demonstrated in a different experimental configuration to validate this
mechanism of ion cooling by localized and centered ultracold neutral atoms. Our
results suggest that cooling of ions by localized cold atoms holds for any mass
ratio, thereby enabling studies on a wider class of atom-ion systems
irrespective of their masses.
