I made 90 posts about physics at this blog in 2020. A few topics dominated the discussion, and I collect some of those posts.
There were many increasingly accurate measurements of Standard Model physical constants. I tracked these results against some speculative theoretical expectations, but the uncertainties in the top quark mass measurement which won't be dramatically better for the foreseeable future, and to a lesser extent, some of the other measurements limited the extent to which these expectations could be meaningfully confirmed.
The neutrino data, in particular, strongly disfavors the sterile neutrino hypothesis although it hasn't quite put a nail in the coffin of that conjecture and continues to favor a "normal mass hierarchy" for neutrinos with no evidence of Majorana neutrinos such a neutrinoless double beta decay. Efforts to determine the CP violating phase in neutrino oscillation have confirmed that there is some CP violation in this process and favors near maximal CP violation in neutrino oscillation, but has large margins of error. These measurements are likely to improvement meaningfully in the coming year.
Modified gravity approaches to explaining dark matter and dark energy continued to be successful, while the paradigmatic lambdaCDM theory of cosmology continued to fall short. Demonstration of violations of the strong equivalence principle towards the end of the year topped the list. Advances of modified gravity and dings for lambdaCDM in the area of early cosmology were also significant.
A variety of experimental anomalies and measurement tensions were explored.
The biggest one that is that there will be two new muon g-2 measurements, the last of which was fifteen years ago and the next of which will be announced early this year. The new measurement (and the new theoretical prediction) will be much more accurate than the last, in which the measurement which differed by about three sigma (about 2 parts per million) from the theoretically expected value. The calculation of muon g-2 is sensitive in a global way to almost all aspects of Standard Model physics and can be calculated and measured with extreme precision. The closer that the experimentally measured value of muon g-2 is, the less room there is for new physics beyond the Standard Model. On the other hand, big differences would be strong evidence that scientists are missing something in the Standard Model.
Another area where there have been tensions is in suggestions that premise of charged lepton universality (i.e., that the electron, muon and tau lepton are identical apart from mass) is violated. The tensions have appeared in B meson decays, but not in other kinds of decays that should implicate the same properties.
The Xenon1T experiment reported some anomalous outcomes that were almost immediately determined to be meaningless because the results failed to consider an important source of background contamination in its results, although that hasn't prevented theorists for coming up with esoteric and unlikely theoretical explanations for it.
A Hungarian group has argued that there is a beyond the Standard Model X17 particle, but that hasn't been panning out either (see also a lengthy discussion with citations to journal articles in the comments to this post).
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