Puzzle with the precession of the neutron spin? More perplexing news about the neutron spin in this recent Nature Physics publication: arxiv.org/abs/2103.03333 The authors collaboration (more than 100 authors) report a newly experimentally found large discrepancy on the precession of the Neutron from the theoretical predictions.
However, this is too much technical for me. This discrepancy seem to be localized only at a specific energy range they call low $Q^2$ region.
Can you please explain to me what this region is and what is this all about?
 A: Since this question was not answered by PSE for a relative long time now, I did my own investigation in collider physics and regarded it as useful to report back my findings. This required actually quite a lot of digging.
The $Q$ variable is used in particle collider physics such us deep inelastic scattering of electrons or muons with protons and their constituents like quarks. Of  course these type of quantum collisions are not the same we have in classical terms where two objects get in actual contact when colliding but instead the electron or muon interacts with the quark via a virtual photon. $Q$ variable is called virtuality of this intermediate photon responsible for transferring the collision momentum.
Physical Meaning of $Q$:
Using the Uncertainty principle it teaches us
that
$\Delta p \Delta l \approx \hbar$
which means that the photon probes the proton at the distances of the order $(\hbar=1)$
$$
\Delta l \sim \frac{1}{Q}
$$
Large Momentum Q = Short Distances Probed

So, the factor $Q^2$ in particle collider physics actually refers to the surface spatial resolution of the collider or magnification analogue to a conventional microscope. The larger this term is the smaller areas we can probe for example inside a proton. Higher $Q^2$ means also higher collision energies.
However, the higher $Q^2$ we use in an experiment the larger the uncertainty of the measurement we obtain and our measurement disturbs more strongly the measured quantum state. That is why the low $Q^2$ value used in the experiment referenced in this question thread is actually meant to be an advantage when higher spatial resolution is not needed for the conclusions of an experiment.
The above information was taken from a presentation of Prof. Yuri Kovchegov. You can watch his presentation in the link below:
https://www.youtube.com/watch?v=NIQ6FfKHSbI
