1. April 1, 20061 Beam measurement with -Update - David Jaffe & Pedro Ochoa 1)Reminder of proposed technique 2)Use of horn-off data 3)Use of horn2-off data? 4)Effect of correcting for KL3 branching fractions and matrix elements 5)Summary & Ongoing work

2. April 1, 20062 1) Brief reminder ● Concept: Measurement of low energy can be used to constrain the flux, since: So look for whose father is a ! True energy of true at the ND No from  above this energy (Ecut) E cut ● 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. April 1, 20063 2) Use of Horn-off data We made a first pass at C by studying its energy dependence: C(E). So the procedure we followed was to: Step 1) Calculate C(E) from the horn-off data and MC. Step 2) Test C(E) on the horn-on data and MC for E > E cut =10GeV. 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. How? Horn-off data gives us a direct handle: Horn Off no mu+

4. April 1, 20064 Step 1: Obtaining C(E) from horn-off data First, two words on antineutrino selection: ● Selected events that satisfy some “basic” cuts: At least 1 track Track passes fit UV asym < 6 / ndf < 20 PID > -0.2 ● Used “NuBar-PID” cut at 0.27 (ref. doc-1657): Evaluating the selection on the horn-off MC gives 94.6% purity and 61.2% overall efficiency. Horn-off MC ● Selected events in fiducial volume: 1<vtxz<5 & vtxr < 1.0m Background composition

5. April 1, 20065 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. The right plot is our estimate of C(E). Step 2 is to test it ! Data MC data/MC Horn-off Please note that (ref. slide 3) and therefore that, with infinite MC statistics, we have

6. April 1, 20066 ● 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 Horn-on ● 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 > E cut ) Step 2: Testing C(E) in horn-on data straight line ! --------------------------

7. April 1, 20067 Tried 3 different approaches when “fitting” C(E) and scaling MC: Data Scaled MC 1) 5 th degree pol. 2) 2 constants Data Scaled MC 3) Bin by bin Data Scaled MC Horn-on Horn-off data/ Scaled MC C(E) apply C(E) apply C(E) apply C(E) take ratio take ratio take ratio

8. April 1, 20068 We observe that: ● The 3 fits perform similarly at E < E high ~ 16 GeV and the results are encouraging in that region. Furthermore, C(E) seems to be consistent with a constant from E cut < E < E high. Need to understand why this is. ● This suggests the following methods for estimating C: i) Estimate C = C H for the horn-on or horn-off data/MC: where H denotes events with Ecut < E < Ehigh. ii) Similarly, estimate C L with the horn-off data: where L denotes events with 0 < E < Ecut. iii) The degree of agreement between the 3 estimates (C H (on), C H (off) and C L (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 H HHC  /  ● ME & HE data may be very useful in understanding C, since the mu+ component should be the only one focussed.

9. April 1, 20069 Normal Horn-2 off Normal Horn-2 off component all other components (π,K) ● 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. 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: Units are flux per m2 per 5e5 POT.

10. April 1, 200610 Negligible systematic effect of Kl3 corrections on C(E) and method to extract the  flux from  O(5%) effect on total  e 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. April 1, 200611 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  component of    flux. There appears to be a modest effect on the beam e flux. Need corrected gnumi (or equivalent) for definite conclusions. Improving the purity of the low energy  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?