However, in 2010 an international research team published a proton charge radius measurement via the Lamb shift in muonic hydrogen (an exotic atom made of a proton and a negatively charged muon). As a muon is 200 times heavier than an electron, its de Broglie wavelength is correspondingly shorter. This smaller atomic orbital is much more sensitive to the proton's charge radius, so allows more precise measurement. Their measurement of the root-mean-square charge radius of a proton is ", which differs by 5.0 standard deviations from the CODATA value of ". In January 2013, an updated value for the charge radius of a proton——was published. The precision was improved by 1.7 times, increasing the significance of the discrepancy to 7σ.