1. A precision measurement of d2 on the neutron
Hall A Experiment E06-014
A 4.7 and 5.9 GeV polarized electron beam scattering off a polarized 3He target
Measure unpolarized cross section for reaction in conjunction with the parallel asymmetry and the transverse asymmetry for 0.23 < x < 0.65 with 2 < Q2 < 5 GeV2.
Asymmetries measured by BigBite at a single angle: q = 45°
Absolute cross sections measured by L- HRS
Experimental Overview

2. A precision measurement of d2 on the neutron
d2 represents an averaged transverse force acting on the struck quark
connected to the color field response to the polarized neutron
E,B: “color electric & magnetic polarizabilities”
Provides a benchmark test for theory (lattice QCD).
we can achieve a statistical uncertainty of ∆d2n = 5 x 10-4
four times better then existing world average!
Analysis is in preliminary stages, stay tuned...
Dark green stripe indicates expected uncertainty from E Light blue strip is uncertainty for present world value.
Lattice QCD

3. BigBite Cerenkov Design Parameters
Dimensions: 200cm x 60cm x 60cm
sandwiched between wire chambers
Radiator gas: C4F8O
 threshold: 2.51 GeV/c
We measured ~8 photo-electrons/track
About ½ of initial design model, reduction is now understood:
lower collection eff. due to installation of improved mag. shielding (needed to handle larger BB fringe field at PMTs)
losses due to lower mirror reflectivity in UV than in vendor specs (based on CERN meas.)
Performance still met min. design goals for d2n
For RHRS side, electron efficiency: >80%
For beamline side, electron efficiency: 60-70%
Rough estimate of online π:e rejection ratio:
>50:1 on RHRS side
~30:1 on beamline side
(near calorimeter)
Backside

4. BigBite Cerenkov Performance During E06-014
BigBite Cerenkov ADC Spectra for production 3He run
Blue is background, Red are good electrons
Upper 10 plots are beamline side, lower 10 are RHRS side (less BG)

5. BB Cerenkov During Assembly (viewed from rear)
Spherical Mirrors
Flat Mirrors
- The missing mirror on the lower left was courtesy of the coating vendor breaking 2 of the 21 that were sent for coating. Replacements arrived and were installed after this photo was taken.
- The small white light above the 'm' in "Reflected images..." served as an effective target during alignment. Rays from the light were focused on the paper targets. The light was moved to 4 different spacial locations which represent 4 different electron momenta of (0.6 through 1.4 GeV) -- this roughly spans the range of interest for d2n/Transversity. The images associated with these positions were confirmed to lie well within the acceptance of each PMT.
- The "paper target" mentioned in the slide represents the front face of the 5" PMT that mates with the narrow side of the conical mirror. There are bull's eye circles on it used for alignment. The targets were (of course) removed when the PMTs were installed.
Reflected images of conical mirror and a paper target at 5” PMT location