experimental evidence reference would be good perhaps a reference should be added to the value of years the paper given k hagiwara et al particle data group current best estimates of proton lifetime phys rev d isbn dates from and is presumably from the super kamiokande results you will be aware that the average non specialist reader will have seen years or just years and this is the value that other google sources bring up from the same super kamiokande experiment e g the hyperphysics phy astr gsu edu site as of it seems that the proton lifetime has been pushed out to at least years which point isn't strictly equal to