2. Backgrounds for HAPPEx Ryan Snyder April 7, 2006

3. Contributions to Background 1. Quasielastic fraction 2. Aluminum end caps of target cells 3. Rescattering 4. Poletip -- Bob Michaels

4. Sliding Momentum Cut Compare E_meas to E_calc: E_calc = energy of elastically scattered electron E_meas = P_o + dp (in MeV) Numbers don’t compare directly due to precision of spectrometer angles and calibration of spectrometer Thus, a Delta offset is used to move the difference between calculated and measured energies to zero So, a cut is applied on (P_o + dp + Delta) - E_calc < -15 MeV

5. Run # LDelta RDelta Beam Current(uA) 2271 -0.06 3.51 0.52366 2366 -2.24 0.02 0.392367 2367 -2.96 0.44 0.662509 2509 -1.63 0.62 0.582689 2689 -1.46 0.68 0.622690 2690 -1.7 0.31 0.6122780 2780 -0.25 3.29 0.282781 2781 -0.09 3.22 0.6

8. With -15 MeV cut, averages work out to be Left Arm = 0.206 % Right Arm = 0.401% Both = 0.303 % % quasielastic = 0.15 +/- 0.15 % A_qe_He = -2ppm (+/- 50%) Overall correction ~ 11 ppb

9. Aluminum Background - He Integrating mode: He production run: L-arm = det1/bcm1 = 3.556 R-arm = det1/bcm1 = 3.558 Al dummy target run: L-arm = 0.222 R-arm = 0.234 Using “xt” factor of 0.278, get background fractions L-arm = 1.74% R-arm = 1.83% Bkgrnd_Al = 1.8 +/- 0.18% Total Correction = 39 ppb

11. Aluminum Background - H “xt” factor of 0.125 Integrating Mode: Det1 = 0.64% Det2 = 0.72% Det3 = 0.60% Det4 = 0.79% Total = 0.7% Front window is thicker than back window so this will be a bit higher, but no more than 50%

12. Rescattering From positive dp scan, get relative rates From negative dp scan, get fraction relative to elastic peak Then, from each section of inelastic spectrum, do (Fraction relative to elastic) x (Relative rate) = Rescattering percentage Add each section up to calculate total rescattering fraction

13. Helium

14. Rescatter fraction = 0.45 + 0.44 + 0.027 = 0.92%

15. Rescat_He = 0.25 +/- 0.15 % A_qe_rescat = -2 +/- 3 ppm Total Correction = 13 ppb

16. Hydrogen

17. Rescatter = 0.07 + 0.03 ~0.1% A_Delta = 10 +/- 5 ppm