The SpinQuest (E1039) experiment’s polarized target system

The SpinQuest experiment at Fermilab aims to measure the Sivers asymmetry for the light sea quarks in the longitudinal momentum fraction range of 0.1 < xB < 0.5 from the Drell-Yan process. A nonzero Sivers asymmetry measurement would be indicative of a nonzero orbital angular momentum contribution from the sea quarks. The SpinQuest experiment uses the proton beam from Fermilab's 120 GeV main injector, which will provide about 10¹¹ protons per second during a 4.4-second spill. The SpinQuest polarized target uses a superconducting split-pair magnet with an operating magnetic field of 5T with transversely polarized NH₃ or ND₃ targets (8cm long target cells). The maximum intensity that the target can handle will be determined during beam-target commissioning. As proposed SpinQuest will be the highest integrated proton beam luminosity, around 2 × 10⁴²cm⁻², ever on a solid polarized target. The helium-4 evaporation refrigerator operates at 1 Kelvin using high-powered evaporation from a roots stack with a pumping rate of nearly 17,000 m³/hr. The anticipated average target polarization of 80% for protons and 32% for deuterons will be measured using three NMR coils equally spaced apart in the target cell.