Polarized NH₃ and ND₃ Targets at FNAL-SpinQuest

SpinQuest at Fermilab is a fixed-target experiment to measure the Drell-Yan process using transversely polarized NH₃ and ND₃ targets and unpolarized 120-GeV proton beam. In the Drell-Yan process, a quark in one scattering hadron and an anti-quark in the other hadron annihilate into a virtual photon and then decay into a muon (lepton) pair. The angular distribution of final-state muon pairs with respect to the target polarization is sensitive to the Sivers function of light anti-quarks in the nucleon, which is one of the eight Transverse Momentum Dependent (TMD) parton distribution functions. The Sivers function of each anti-up and anti-down quarks can be extracted by the use of the NH₃ and ND₃ targets for p+p and p+d reactions. The intensity of the proton beam is as high as 2*10¹² protons/second, in order to accumulate the required number of Drell-Yan events. The polarized target has been designed to accommodate this high intensity.

It is equipped with an evaporation refrigerator with a maximum cooling power of 3 W. The target temperature is maintained at 1 K under heat loads due to the proton beam and the DNP microwave. The polarization is higher than 80% for NH₃ and 32% for ND₃. The commissioning of the whole target system with the beam is planned in November 2023. The design and the performance of the polarized target will be presented.