FNAL-E-1039()
SpinQuest: Drell-Yan Experiment with a Polarized Proton Target
()
- Proposed: Jun, 2013,
- Approved: Jun, 2013,
- Started: 2018,
- Still Running
Predecessor Experiment:
SpinQuest Collaboration
The proton and neutron each have “spin” and an associated magnetic field. A great mystery that is not understood: How do the quarks and gluons inside the nucleon create this state of “spin”? In total, the “spin” of the nucleon must arise from a combination of the “spin” of the quarks, anti-quarks, and gluons, as well from orbital motion of those same particles about the center of the nucleon. It has been determined from other experiments that the “spin” of the nucleon does not arise solely from the “spin” of the quarks and anti-quarks. SpinQuest will investigate whether the sea quarks are orbiting around the center of the nucleon by exploring the nucleon in a particular way. A beam of protons is created by an accelerator at Fermilab, called the Main Injector, and this beam of protons is directed at a target also containing protons. The protons in the target, however, are arranged so that the axis of the “spin” of most of the protons point all in the same direction; we say the protons in the target are “spin polarized” and we say we have a “polarized target.” When the protons in the beam interact with the protons in the target, we look for a special process where a quark in the beam proton and an anti-quark in the target proton combine to form a single particle of light, a photon. This is a special kind of photon that is unstable and does not travel very far, and it quickly decays into another particle and anti-particle pair. This special process is called the Drell-Yan process, after two scientists who figured out it must be going on in such collisions of protons. We look for the particle and anti-particle pair (in our case we look for a muon–anti-muon pair) in a special detector constructed just for this purpose, and we study the relationship between the angles at which those particles were emitted compared to the direction in which the target is polarized; this reveals key information about how the quarks and anti-quarks are behaving inside the protons
Loading ...
Loading ...