Historic Information

During SMC the measurement of the N14 polarization was performed[1], also shown in earlier measurements [2]. The measurement indicated that equal spin temperature (EST) is obeyed.  With coupled systems like this that obey EST one knows what the polarization is given the other.  So no real need to measure the polarization in real-time if you know what the proton polarization is. At SLAC, a measurement of N15 where the ammonia spin is carried by the proton also found agreement with EST.  N15D3 was used for the measurement of the spin structure of the neutron. Because the spin of N15 is carried by the proton there is reduced background subtraction for observables like g1 and g2.  For this reason, ammonia that uses nitrogen-15 is a better target and the corrections for an example observable can be found in [3,4].  This approach is very reasonable given some knowledge of the nitrogen cross-section for the process of interest.  For DIS both the cross-section and the partonic effect of the nuclei polarization to the overall asymmetry were known enough to make these corrections to the asymmetry after the experiment.  These corrections in general are just a couple of percent (relative) to the overall asymmetry.

A modern Approach

For processes where the cross-section of nitrogen is not known corrections are harder to apply.  It's still possible to get nitrogen cross-section information from a generator like MCFM but this is theoretical in nature and likely, not the best option.  The other issue is the lack of theoretical and even conceptual understanding of how polarized nuclei change the scale of an observable like the Sivers asymmetry.  Unlike the standard colinear probing processes, TMDs from either Drell-Yan or Semi-inclusive DIS may have large correlations induced by partonic dynamics from nuclei in close proximity.  More experimental information is needed.  It's possible to estimate the contribution in this regard in a similar vein as before but this requires some pretty big assumptions.  Another approach is to use the modern tools available in RF and NMR technology.  The most basic approach is to modulate across the NMR signal of the nitrogen at high RF power, forcing transitions to mitigate polarization during the DNP process of the protons in the target.  Such tools were first suggested in [6] and later experimentally tested in [7].  These tools require additional RF coils at the target and amplification.  Such tools can be fully integrated into an NMR system for fast sweep control, but such a system is not presently set up for SpinQuest.  In this case, not being a priority at the moment a measure of the nitrogen-14 cross-section would be beneficial for the initial runs.

References

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