Beam measurement with -Update -

1. Beam measurement with -Update - • Reminder of proposed technique • Use of horn-off data • Use of horn2-off data? • Effect of correcting for KL3 branching fractions and matrix elements • Summary & Ongoing work David Jaffe & Pedro Ochoa

2. True energy of true at the ND So look for whose father is a ! 1) Brief reminder Ecut ●Concept: Measurement of low energy can be used to constrain the flux, since: No from m+ above this energy (Ecut) ● The technique is: where The most critical aspect of this measurement lies in the uncertainty of the correction factor C. (doc-1663, doc-1605)

3. 2) Use of Horn-off data We made a first pass at C by studying its energy dependence: C(E). How? Horn-off data gives us a direct handle: Horn Off no mu+ Ansatz: C(E) is the same for horn-off and horn-on data. This may actually be true if the differences between data and MC lie only in things that affect both situations (horns on & off) the same, like cross-sections. So the procedure we followed was to: Step1) Calculate C(E) from the horn-off data and MC. Step2) Test C(E) on the horn-on data and MC for E > Ecut=10GeV.

4. Horn-off MC Step 1: Obtaining C(E) from horn-off data First, two words on antineutrino selection: At least 1 track Track passes fit UVasym < 6 / ndf < 20 PID > -0.2 ●Selected events in fiducial volume: 1<vtxz<5 & vtxr < 1.0m ●Selected events that satisfy some “basic” cuts: ●Used “NuBar-PID” cut at 0.27 (ref. doc-1657): Background composition Evaluating the selection on the horn-off MC gives 94.6% purity and 61.2% overall efficiency.

5. Horn-off data and MC comparison for antineutrinos: ●Used all available MC and data (2.77e18 POT, taken in February). MC was scaled to the data. ● Uncertainty is dominated by data statistics. Data MC data/MC Horn-off Horn-off The right plot is our estimate of C(E). Step 2 is to test it ! Please note that (ref. slide 3) and therefore that, with infinite MC statistics, we have

6. Step 2: Testing C(E) in horn-on data ● Used same cuts as for horn-off data. Evaluation in horn-on MC gives 86.6% purity and 61.2% efficiency (including all cuts). ●Checked efficiency and purity as a function of energy to make sure that we are not affected by background at high energies (E > Ecut) ● Used 1.9e19 POT of R1.18.2 data (January 2006). MC was scaled to the data. ● Observe similar deficit of MC with respect to data, like in the horn-off case. Data MC data/MC -------------------------- straight line ! Horn-on Horn-on

7. Tried 3 different approaches when “fitting” C(E) and scaling MC: Horn-on Horn-off data/ Scaled MC Data Scaled MC C(E) apply C(E) take ratio 1) 5th degree pol. data/ Scaled MC C(E) Data Scaled MC apply C(E) take ratio 2) 2 constants Data Scaled MC data/ Scaled MC C(E) apply C(E) take ratio 3) Bin by bin

8. i) Estimate C = CHfor the horn-on or horn-off data/MC: • where H denotes events with Ecut < E < Ehigh. • ii) Similarly, estimate CL with the horn-off data: • where L denotes events with 0 < E < Ecut. • iii) The degree of agreement between the 3 estimates (CH(on), CH (off) and CL(off)) provides an estimate of the systematic uncertainty in C with a statistical uncertainty of a few percent from the horn-off data statistics of 2.77e18 POT. = MC C H / H m n H We observe that: ● The 3 fits perform similarly at E < Ehigh ~ 16 GeV and the results are encouraging in that region. Furthermore, C(E) seems to be consistent with a constant from Ecut < E < Ehigh. Need to understand why this is. ●This suggests the following methods for estimating C: ● ME & HE data may be very useful in understanding C, since the mu+ component should be the only one focussed.

9. component 3) Horn-2 OFF Flux Generation ●Idea was brought up by Milind that the mu+ may be getting focused mainly by the second horn. If so, horn2-off data can be an extra tool for constraining C(E). ●In order to answer this, generated 1e7 POT of horn2-off flux: all other components (π,K) Normal Horn-2 off Normal Horn-2 off Units are flux per m2 per 5e5 POT. ●It seems that the second horn focuses about ~3/5 of the mu+, but the rest is done by the first horn. This is less than we expected. ●The spectrum’s disruption is too severe for the non-mu+ components to use this data.

10. Negligible systematic effect of Kl3 corrections on C(E) and method to extract the nm flux from m O(5%) effect on total ne flux of corrections for Kl3 Br and ME 4) Corrections for Kl3 matrix elements and branching fractions ●In doc-1652, Stan noted that Kl3 matrix elements were not implemented correctly in gnumi. Implications of correcting for Kl3 Br and ME were analyzed: _

11. Summary & Ongoing Work • Preliminary check with horn-off data is encouraging: • C(E) appears to be the same for horn-on/off for the region Ecut < E < Ehigh • Comparison of C from the different data sets will provide an estimate of the systematic uncertainty in C. Use of ME, HE should improve understanding. • Need to take NC and neutrino bkgd into account in estimation of C. • No motivation for Horn2-off running in this analysis. • Kl3 corrections do not appear to have significant impact on extraction of m component of nm flux. There appears to be a modest effect on the beam ne flux. Need corrected gnumi (or equivalent) for definite conclusions. • Improving the purity of the low energy nm sample is difficult. Current work on nubar selection: (Alternative: Measure purity with decays of stopped muons? doc-1571) Which one of these tools is/are most suited for high purity at low energy?