1.  Expand feasibility study to include background: Beam e measurement from antineutrinos Background in pHE and LE samples obtained with the nubar-PID cut at 0.9 (mostly CC neutrinos) (  + ) pHE (  + ) LE (  ,K - ) pHE (  ,K - ) LE Bkgd. pHE Bkgd. LE

2.  Create fake data in which background level is shifted by a given amount. Fit is done assuming nominal background levels:  Results: Shifting only LE backgroundShifting only pHE background Background shifted by  +10%-10%+30%-30%-50%+50%+10%-10%+30%-30%+50%-50% Bias in parLE +3%-3%+7%-8%+9%-13%-4%+6%-10%+13%-16%+25% Bias in parHE -1%+1%-1%+1%-2%+1%+3%-4%+9%-11%+14%-22% Background shifted by  +10%-10%+30%-30%+50%-50% Bias in parLE -2%+3%-4%+6%-5%+7% Bias in parHE +3%-4%+8%-11%+13%-20%  If shift is in same proportion & direction for the two backgrounds then bias in parLE is considerably reduced: Example: parHE background shifted up by 10% (  + ) pHE (  + ) LE (  ,K - ) pHE (  ,K - ) LE Bkgd. pHE Bkgd. LE (These are scaled to 2.0x10 20 POT)

3. |(y low -y)/y||(y high -y)/y| Applying in feasibility study, lower envelope Note: scale is different than above Applying in feasibility study, higher envelope