Title:
Beam Commissioning Result of Polarized Target at SpinQuest

Authors:
Kenichi Nakano (UVA)

Abstract: 
SpinQuest is a fixed-target experiment at Fermilab to measure the Drell-Yan process using transversely polarized NH_3 and ND_3 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 intensity of the proton beam is as high as 10^12 protons/second, in order to accumulate the required statistics of Drell-Yan events.
The polarized target system at SpinQuest has been has been carefully designed to accommodate such a high beam intensity.
It is equipped with an evaporation refrigerator with a cooling power of 3 W at ~1 K.
The target temperature is maintained at 1 K even under heat load caused by the proton beam and the DNP microwave.
The target system and the spectrometer were commissioned with the proton beam from May through July 2024, where we studied, for example, the effects of the beam heating on the superconducting magnet.
In this talk the experimental setup of SpinQuest and the performance of the target system during the beam commissioning will be presented.