After choosing between two alternatives, people perceive the chosen alternative as more attractive and the rejected alternative as less attractive. This postdecisional dissonance effect was eliminated by cleaning one’s hands. Going beyond prior purification effects in the moral domain, physical cleansing seems to more generally remove past concerns, resulting in a metaphorical “clean slate” effect.
Here’s the actual paper. The numbers are kind of weird. If the rating difference was .14 for one group and .68 for another, both before choice, that suggests to me that the samples were way too small.