1 Using the pHE data to measure the beam e ’s from  + decay David Jaffe and Pedro Ochoa April 12 th 2007  Reminder  Systematic from background  Horn 1 systematics  Conclusion

2 Reminder x parLE (  + ) pHE ( ,K) pHE - ( ,K) LE x parHE (  + ) LE  Procedure: - Take pHE-LE difference. Correct for - Fit using MC shapes. Scale (  + ) LE and (  + ) pHE by parameters parLE and parHE.  Recent study showed that this procedure yields a ~13% statistical error when applied to the ~2x10 19 POT of existing pHE data (doc-2783)  Need to assess systematics associated with this measurement. Two main concerns:  C= ( ,K) pHE - ( ,K) LE correction.  Background in nubar selection. both addressed in this talk

3  Expanded feasibility study to include background: Background in pHE and LE samples obtained with the nubar-PID cut at 0.9 (mostly CC neutrinos; see doc 2783) (  + ) pHE (  + ) LE (  ,K - ) pHE (  ,K - ) LE Bkgd. pHE Bkgd. LE Systematic from background Please note that vertical scale is not the same in all 6 plots

4  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 +2%-2%+7%-7%+12%-13%-2%+3%-8%+8%-13%+13% Bias in parHE -0%+0%-0%+0%-0%+0%+3%-2%+7%-7%+12%-12% Background shifted by  +10%-10%+30%-30%+50%-50% Bias in parLE -0%+0%-1%+0%-1%+1% Bias in parHE +2%-2%+7%-7%+11%-12%  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)

5  It seems background is not that big of a problem.  Tools like the MuonChopper may assist us in determining this error. (minos-doc 2841)  Main concern is C = ( ,K) pHE - ( ,K) LE :  Work by David suggests differences are due mostly to geometry, as one would expect: Note: nomenclature and drawing follow scheme for focussing Horn 1 systematics

6 Ex: horn1 current increase by 2% in pHE neutrino beam  First obtained ratios of spectra with systematics over nominal spectra: Recommended in minos-doc-1283 Used for this study horn 1 offset1.0 mm4.0 mm horn 1 angle0.2 mrad0.4 mrad horn current offset1.0 %2.0 %  Using gnumi, looked at the effect of varying the following horn1 parameters:  Then converted these ratios to reconstructed energy using the ntuples:  Good agreement with pbeam Ex: horn1 current increase by 2% in pHE antineutrino beam Note: scale is different than above Convert to E reco Might have been too pessimistic. See conclusion

7  The obtained ratios for the antineutrinos with hadron parents are:  The ratios are smoothed due to lack of statistics. LE-10 pHE

8 LE-10 pHE  But also have to consider effect on antineutrinos with muon parents:  Large effect !  + ’s depend directly on focusing.

9  Applied these systematics in our feasibility study:  The nominal spectra are used to do the fit.  Assume infinite pHE and LE statistics.  Horn current shift -2%: Systematics: Results of fit: (  + ) pHE (  + ) LE (  ,K - ) pHE (  ,K - ) LE with systematics result of fit (  + ) pHE (  + ) LE fit pHE-LE corrected for background and nominal C  Bias of -18.0%  Bias of -21.9% with systematics nominal

10  Horn current shift of +2%: Systematics: (  + ) pHE (  + ) LE (  ,K - ) pHE (  ,K - ) LE Results of fit: with systematics nominal with systematics result of fit (  + ) pHE (  + ) LE fit pHE-LE corrected for background and nominal C  Bias of -26.8%  Bias of -67.2%

11  Horn angle shift by 0.4mrad:  Bias of -7.2%  Bias of -16.9% Systematics: (  + ) pHE (  + ) LE (  ,K - ) pHE (  ,K - ) LE Results of fit: with systematics nominal with systematics result of fit (  + ) pHE (  + ) LE fit pHE-LE corrected for background and nominal C

12  Horn offset by 4mm:  Bias of -35.7%  Bias of -66.1% Systematics: (  + ) pHE (  + ) LE (  ,K - ) pHE (  ,K - ) LE Results of fit: with systematics nominal with systematics result of fit (  + ) pHE (  + ) LE fit pHE-LE corrected for background and nominal C

13  It seems that worse sources of systematics are increase in horn current and horn offset:  Also need to add the error associated with hadron production. Work is in progress to assess it. Horn I -2%Horn I +2%Horn angle 0.4mrHorn offset 4mm Bias in parLE-18.0%-26.8%-7.2%-35.7% Bias in parHE-21.9%-67.2%-16.9%-66.1%  This assumed same horn conditions for pHE and LE running. If that is not the case need to blend with other combinations & scenarios: Horn I -2%Horn I +2%Horn angle 0.4mrHorn offset 4mm Applying systematics to LE beam only Bias in parLE+4.8%-9.1%-2.0%-19.8% Bias in parHE+9.5%-4.5%-2.6%-7.6% Applying systematics to pHE beam only Bias in parLE-24.9%-24.8%-4.7%-17.8% Bias in parHE-34.7%-46.9%-14.2%-58.8% + recently discovered target z position offset of ~1cm between the two LE-10 datasets

14  The geometric systematics associated with the measurement of (  + ) LE seem to be very large. However, a recent discussion between Sacha and David revealed that the assumed horn 1 systematics were too pessimistic. Study will have to be repeated using horn 1 offset of 1mm and horn current shift of ±1%  In addition, maybe can improve situation by modifying fit:  Ignore GeV region where systematics which pull parLE (and parHE) down are largest?  Use information at > 30 GeV to constrain the fit?  Add an extra parameter to scale the C correction up and down? Summary & Ongoing work  Measurement of (  + ) pHE seems severely hampered by systematics. Fortunately we don’t care.