Purpose Purpose

Purpose

• Purpose

• Provide almost-free neutron target to improve our understanding of neutron structure.

Purpose

• Purpose

• Neutron Structure-function measurements unencumbered by Final-State Interaction Effects

Measure slow protons

• Measure slow protons

• Identify spectator protons to tag e-d events in which the neutron was struck.

Angular distribution is isotropic. Backwards proton almost certain to be a spectator.

• Angular distribution is isotropic. Backwards proton almost certain to be a spectator.
• Momentum distribution favors low values.
• Tracks are 20x - 50x minimum ionizing.

Time Projection Chamber (TPC)

• Time Projection Chamber (TPC)

• Just a box of gas
• Readout elements only on the surfaces.
• Windows can be made thin.

Uses standard 10cm x 10cm GEMs.

• Uses standard 10cm x 10cm GEMs.

• Drift region similar to planned final detector.

• Uses 3x 3M GEMs to allow tracking cosmics (min-I).

• At present, tests are performed using 80/20 Ar/CO2.

Cosmic tracks easily recognized.

• Cosmic tracks easily recognized.

• Position resolution would be better with charge sharing over ≥3 pads.

• Gain ~ 303

Heavily Ionizing Protons from TUNL’s Tandem

• Heavily Ionizing Protons from TUNL’s Tandem

Specialized spectator proton detector developed

• Specialized spectator proton detector developed

• First use of GEMs at JLab

• First application of Curved GEMs

• Experiment Run

• More to come