Search for EHE neutrinos with the Ice Cube

Search for EHE neutrinos with the Ice. Cube detector Aya Ishihara Chiba University 1

EHE Neutrino Underground atmospheric flux Target GZKmuon neutrino above 106　 Ge. Vrange is very Surface energy 8 < Log(E/Ge. V) uncertain < 12 Surface n fluxes (energy at depth ~ 6 -7 < Log(E/Ge. V) < 10 -11) atm m Fluxes at the Ice. Cube depth main signal GZK neutrino induced leptons background Atmospheric muon EGZK >> EAtm m 2 Simple energy cut works! S. Yoshida et. al. (2004) Phys. Rev. D 69 103004

Energy ? ! m and t tracks loose their energy by Te. V 9100 Ee. V radiative processes pair-creation e+e- photo-nuclear m g p m e+e- bremsstrahlung 3

The 9 -string real sample 2006 Example Bright Events 20 m. V digital optical module waveform 0 m. V [ns] 4 NPE = integral of waveforms / single charge

NPE and Energy Correlation with 2006 Ice. Cube configuration Visible Energy vs. NPE correlation up to log 10 NPE ~ 4. 5 then, early saturation effect diffuse them m log ( m Energy / Ge. V ) t log ( t Energy / Ge. V ) 5

Atmospheric Muon Bundles Model m m log Cosmic-Ray Energy Number of muon in a shower above threshold Energy Ethres (Elbert parameterization) This relation - CR energy and energy contributes to muons in shower and CR flux intensity gives atmospheric m bundle flux 6 Nagano, Watson: Reviews of Modern Physics Vol 72 No 3 (689)

Background simulation experimental data atmospheric m simulation model 1 atmospheric m simulation model 2 log 10 NPE cos q 4 < log 10 NPE < 5 7

Atmospheric fluxes at Ice. Cube depth #2 Model a Ethres[Ge. V] 1 1. 9 300 2 2. 0 1500 #1 without GZK cutoff with GZK cutoff !! #1 #1 8

log (m Bundle Energy at Depth [Ge. V]) Comparison with CORSIKA Atmospheric m empirical model Proton Iron QGSJET 01 log (Primary CR Energy [Ge. V]) overestimate underestimate m bundle energy 1 Pe. V 10 Pe. V m bundle energy 100 Te. V 9 log (Primary CR Energy [Ge. V])

Event Selection and Numbers Cut Level GZK n events ne+nm+nt Atmospheric m model 1 Atmospheric m model 2 1 (dotted brown) 0. 055 0. 003 0. 006 2 (solid red) 0. 046 < 10 -4 3 (dotted black) 0. 036 < 10 -4 4 (solid brown) 0. 024 < 10 -4 10

Sensitivity for 2006 E 2 fcut 2 (106. 5 < E < 109. 5) ~ 10 -6 [Ge. V cm-2 sr-1 sec-1] 90 % C. L. all n flavor added assuming 1: 1: 1 11

Neutrino Effective Area Cut 2 12

l l l Summary The Ice. Cube 9 string array provided physics data sample in 2006 MC shows 9 string Ice. Cube is capable of EHE neutrino search but early saturation and reduced bin numbers limits capability For BG estimation, Related EHE CR fluxes and surface m bundle energy relation from experimental sample expressed in terms of Elbert formula The obtained empirical model gives good agreement with data Cut candidates are selected according to the model Effective area, sensitivity for 2006 Ice. Cube EHE region is obtained 13