1 Beam e ’s from antineutrinos – Update – David Jaffe, Pedro Ochoa November 13 th 2006  Part 1: from  + reweighing  Part 2: New ideas

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

3  Suggested in last collaboration meeting.  Used carrot and thus required mupi trees (thanks Chris!) from  + reweighting from  + raw MC reweighed MC raw MC  Used SKZP “a la Boston” to reweigh the  + and K + parents of the  + : Raw MCReweighed MC #events (1.93x10 19 POT)

4 pzpz ptpt    Why so little change?  pzpz ptpt  Plotted  +,  + weights as a function of p t, p z to make sure no error:  The  + parents get weights very close to 1:    parents (# events)  + parent type (  + ~ 96%)

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

6 Current status (see minos-doc 2218) from  + decay E < E cut data-(Fit or Scaled) MC, E cut < E < 30 GeV raw MC375.8 ± 15.1 (stat)72.8 ± 6.5 (stat) reweighed MC373.4 ± 15.1 (stat)99.1 ± 9.1 (stat) Scale method ± (stat) Scale method ± (stat) Stan’s method654.8 ± (stat) ± (stat) Scale method ± (stat)132.4± (stat) Fit method546.4 ± (stat)-21.4 ± (stat)  “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 p t,p z space.  Considerable fraction of antineutrinos not produced in target (cf. minos-docs 2042 and 2376) Should be real nubars from  + if data/MC from horn-off is trust- worthy in this region Should be ~0 by construction Should be real nubars from  + Expected to be highly negative by construction Note: le010z185i data POT=1.93x10 19 le010z000i data POT=2.77x10 18

7 New ideas  How about using the pHE data?  Antineutrinos from  + are the only ones affected by focusing (?)  Can do pHE-LE and extract the two  + components that way (?)  K K L  + Plots scaled to 1.0x10 20 POT All plots until slide 10 are true E of true antineutrinos. All available stats for pHE LE pME pHE

8  But also significant differences in the other components: from  -,K - : LE pHE LE/pHE ratio from  + LE ME pHE  Indeed  + component is considerably affected by focusing: from  -,K -

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

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

11 What about using the pME data? from  -,K - LE pME  Antineutrinos from  -,K - are almost identical in LE and 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 nubar-PID in pME all NC Selected events at 1.9x10 19 POT from  -,K - pME - LE

12 from  -,K - LE pME (reweighed)  Checked with SKZP reweighing, just in case: Selected events at 1.9x10 19 POT  Idea is to take (pME-LE) data difference and fit with MC shapes using two scaling parameters “parLE” and “parME”: from  + pME from  + LE pME-LE Fit from  -,K - pME – LE

13 How well could this work?  Use fitted shapes instead of histograms: from  -,K - from  + pME LE Selected events at 1.0x10 18 POT

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

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

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

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

20  What about systematics?  One systematic is our assessment of  from  -,K - ) ME - ( from  -,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.  Other systematics (cross-sections, … etc) could be assessed by varying shape of spectra.  Had a preliminary look by not correcting for at all: pME POT1e192.5e195e197.5e191e20 shift in parLE shift in parME  from  -,K - ) ME - ( from  -,K - ) LE

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

22 Backup slides

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

24 Then we have: thus giving: Let be the fraction of  + in the spectrum (Data) Let be the fraction of  + in the spectrum (MC) But if then  This method implied assuming f DATA = f MC

25 Antineutrino provenance: