New measurements of the size of a proton, using a new method of muon interactions with protons rather than electron interactions for protons, reveals a ~4% discrepancy in the proton radius between the two methods. Physicists are trying to figure out if this is due to some mistake being made with the muon experiment, or possibly some misunderstanding of systematic uncertainties in the experiment, or other 'boring' explanations for the difference. The story can be found here.
However, if this result and difference hold after all the investigations are completed and are statistically significant, then this could be an indication of new physics beyond the current Standard Model theory, which is the foundational theory in particle physics for the past five decades. Time will tell as the current experiments, as well as new experiments being designed and run to check these results, are completed over the next 5-10 years.
This is a wonderful example of how science works. Experimental results are published in peer-reviewed journals, and are scrutinized by the scientific community. When a discrepancy comes up with well established and well tested ideas over long periods of time, one needs to seriously and open-mindedly look at all possible explanations for the discrepancy. Results must be reproducible by independent groups. Possible new explanations must be considered and tested and debated. It is a slow process, but the goal is to uncover the truths in Nature, if at all possible, based on physical evidence. This makes for the excitement that scientists encounter in their research programs!