Status of the 2000 EHE Analysis with AMANDA-II

1. Status of the 2000 EHE Analysis with AMANDA-II Lisa Gerhardt Berkeley, 2005

2. Previously • Requested unblinding for EHE analysis for 2000 year with cuts detailed at http://www.ps.uci.edu/~gerhardt/uhe/uhe.html • Evidence turned up which suggested the iterative reconstruction may be unstable for some events • Stopped unblinding to investigate this

3. Iterative Reconstruction • Iterative reconstruction refers to reconstruction which repeats the reconstruction a specified number of times (16) • Uses single Pandel reconstruction as a reference, each new iteration starts from a randomly generated track • Pandel, MPE and best downgoing fit • During the unblinding process, it was discovered that values for the iterative reconstruction fluctuated wildly • Zenith angle can change by as much as 40

4. Number Passing Cuts Also Fluctuates • Repeated processing on 20% data sample • All steps the same • Previous had no events pass cuts, now 3 events pass • Only due to fluctuations of iterative reconstruction • Similar behavior observed in MC (both BG and signal) • Cuts are tuned to a particular fluctuation of the iterative reconstruction

5. Increasing Iterations Doesn't Help Fluctuating between two values

6. MC Fluctuator Characteristics • Fluctuators in BG MC tend to have slightly higher energy primaries and to be less vertical

7. Data Fluctuator Characteristics • Spread throughout the data year and independent of number of modules hit

8. Nice afterpulse peak (15%) Possible horizontal event with large energy deposit inside array

9. 30% of hits Possible downgoing event

10. Iterative Reco. Used Throughout Analysis • Level 0 – hit cleaning • Level 1– FRAC1, nhits • Level 2 – FRAC1 • Level 3 – energy(HE), likelihood(down), NN1 • Level 4 – zenith(HE), NN2 • Level 5 – nhits, nch, zenith(down), zenith(Pan) • Level 6 – avg. hit prob.(mpe), zenith(down) Red = likelihood reconstruction

11. Strategy • Fall back to level 2 • Separate fluctuating events from non-fluctuating events • Apply cuts on previous slide to non-fluctuators • Can relax some of the cut values • Develop new cuts for fluctuators which do not use iterative reconstruction • Hit topology, first guess reconstruction • Fluctuation must be correctly modeled in BG MC

12. Strategy • Events are considered fluctuators if reconstruction iterated 16, 32, 64 and 128 times disagrees by more than 2 degrees • Check Pandel, MPE and downgoing reconstructions, if any one disagrees, event is a fluctuator • Too computationally intensive to start at level 2, so use level 3 as a test of principle while level 2 is processing • 1.4 x 105 events at level 2 versus 2300 at level 3, BG MC takes ~45 s per event, signal takes ~60 s

13. Passing Rates • Data (L3): 3100 (34%) non-fluctuators 6068 (66%) fluctuators • BG MC (L3): 2139 (28%) non-fluctuators 5612 (72%) fluctuators • Signal (L3): E-2 17% non-fluctutators E-2 83% fluctuators BG MC and data are in good agreement

14. New Cuts Promising cuts that don't depend on the iterative reconstruction have been found

15. Outlook • Cuts have been found at level 3 which leave roughly the same sensitivity (~15% worse than old analysis) • Improvement can continue while level 2 is processing • Level 2 processing should be done in a few weeks • Expect new unblinding request then