Beam n e ’s from antineutrinos – Update –

1. Part 1: n from m+ reweighing • Part 2: New ideas Beam ne’s from antineutrinos – Update – David Jaffe, Pedro Ochoa November 13th 2006

2. Nearly all come from m+→ e+ + ne + nm True energy of true nm at the ND Reminder • One of the backgrounds in neanalysis: intrinsic beam ne‘s • Need to tag antineutrinos coming from m+ decay: Ecut This is what we are trying to measure Very little contribution from µ+ above this energy (Ecut) • The technique: E (GeV) Need high purity at low E

3. n from m+ reweighting reweighed MC n from m+ raw MC raw MC reweighed MC • Suggested in last collaboration meeting. • Used SKZP “a la Boston” to reweigh the p+ and K+ parents of the m+: (1.93x1019 POT) • Used carrot and thus required mupi trees (thanks Chris!)

4. pt pt p+ K+ pz pz Why so little change? • Plotted p+,K+ weights as a function of pt, pz to make sure no error: • The m+ parents get weights very close to 1: p+ p+parents(# events) m+parent type (p+ ~ 96%) K+

5. Current status (see minos-doc 2218) • Overall technique: • Main idea of scaling methods (cf. minos-doc 1971) is: No reweighting applied to the MC • Scale method 1: C(E) from horn-off data/MC ratio, Ecut < E < Ehigh • Scale method 2: C(E) from horn-off data/MC ratio, Elow < E < Ecut • Stan’s method: C(E) from horn-off data/MC ratio, all E • Scale method 4: C(E) from horn-on data/MC ratio, E > Ecut • Scale method 5 (retired): C(E) from horn-on data/MC ratio, all E • Main idea of fit method is: Results in next slide were obtained with Ecut = 10 GeV, Elow = 4 GeV and Ehigh = 16 GeV

6. Current status (see minos-doc 2218) Expected to be highly negative by construction Should be real nubars from m+ if data/MC from horn-off is trust- worthy in this region Should be ~0 by construction Note: le010z185i data POT=1.93x1019 le010z000i data POT=2.77x1018 Should be real nubars from m+ • “Scale method 5” was removed. See first two backup slides for more details. • Fit method needs to be revisited: • SKZP “a la Boston” not very appropriate for antineutrinos since not much variation in pt,pz space. • Considerable fraction of antineutrinos not produced in target (cf. minos-docs 2042 and 2376)

7. New ideas • How about using the pHE data? • Antineutrinos from m+ are the only ones affected by focusing (?) • Can do pHE-LE and extract the two m+ components that way (?) p- K KL m+ pME LE Plots scaled to 1.0x1020 POT All plots until slide 10 are true E of true antineutrinos. All available stats for pHE pHE

8. n from p-,K-: n from m+ n from p-,K- LE ME pHE • Indeed m+ component is considerably affected by focusing: • But also significant differences in the other components: LE pHE LE/pHE ratio

9. Where are the p-,K- differences coming from? (See backup slide on antineutrino provenance for more information) Plots made by A. Himmel from Caltech

10. LE/pHE ratio for plots in previous slide: Note: error bars are probably wrong Plots made by A. Himmel from Caltech

11. all n from p-,K- n from p-,K- NC What about using the pME data? nubar-PID in pME • Checked that nubar-PID selection does as good in pME as in LE: For now neglecting ~0.3% difference in purity between LE and pME • Antineutrinos from p-,K- are almost identical in LE and pME ! pME - LE LE pME Selected events at 1.9x1019 POT

12. n from p-,K- n from p-,K- n from m+ n from m+ • Checked with SKZP reweighing, just in case: pME – LE LE pME (reweighed) Selected events at 1.9x1019 POT • Idea is to take (pME-LE) data difference and fit with MC shapes using two scaling parameters “parLE” and “parME”: pME-LE Fit pME LE

13. n from p-,K- n from p-,K- n from m+ n from m+ How well could this work? • Use fitted shapes instead of histograms: LE pME Selected events at 1.0x1018 POT LE pME

14. n from p-,K- n from m+ infinite MC statistics (pME and LE) infinite LE data statistics • Assume: • Create fake pME data set for 1e18 POT by fluctuating smooth histograms with Poisson stats. For example: pME fluct Sum of these two is fake pME data set fluct pME

15. (pME-LE) fake data set as a function of pME POT: (pME-LE)FAKE at 1e18 POT (pME-LE)SMOOTH at 1e18 POT pME POT (pME-LE)FAKE at 1e20 POT (pME-LE)FAKE at 1e19 POT

16. (n from p-,K-)ME (n from p-,K-)LE n from m+ n from m+ • Used TMinuit with MIGRAD for the fit, with two parameters “parLE” and “parME” • Used • parLE and parME are started at 1.0 and cannot be negative. Fit fake data set with pME LE This is an example for pME-POT=1e18

17. Fake data set and fit are repeated 5,000 times. • Could this work with our current amount of pME POT ~ 1e18 ? • Does not work at this POT !

18. What about 1e19 POT ?

19. At other values of pME POT: 2.5e19 POT 5e19 POT 1e20 POT 7.5e19 POT

20. What about systematics? • One systematic is our assessment of (n from p-,K-)ME - (n from p-,K-)LE: • Need to get this from MC and not from fit (need more pME stats) • Proper way to estimate error might be looking how much variation with reweighing. • Had a preliminary look by not correcting for at all: (n from p-,K-)ME - (n from p-,K-)LE • Other systematics (cross-sections, … etc)could be assessed by varying shape of spectra.

21. Almost no variation observed when reweighted n from m+ Summary & Ongoing work • Have our 5 semi-independent methods for assessing n’s from m+: • Fit method needs more work. Currently trying to converge on the best fit for antineutrinos in nubar group. • New idea of using the MC shapes to fit the (pME-LE) difference: • Allows to cancel many unknowns in n’s from p-,K- • Preliminary study shows measurement is possible to ~20% with ~2.5e19 POT of pME data • pME data may be useful for other analyses • Need more pHE MC statistics to see if we can do something similar with the pHE data.

22. Backup slides

23. Why “Scaling method 5” was thrown away: Overall method: Main idea of scaling methods is:  In Scale Method 5 C(E) was approximated with Pol 4th deg

24. Let be the fraction of m+ in the n spectrum (Data) Let be the fraction of m+ in the n spectrum (MC) Then we have: thus giving: But if then This method implied assuming fDATA = fMC

25. Antineutrino provenance: