Diffuse high-energy neutrino searches in AMANDA-II and IceCube 9 strings Kotoyo Hoshina for the IceCube Collaboration TAUP 2007 in Sendai
★ down going Event Detection Strategy Cosmic Ray θ • Target neutrinos : up going + + π → µ + ν Muon µ e + + ν + ν e µ − K , (similar for ) ± π Atmospheric • Detect muons generated from Neutrino neutrinos via Charged Current interaction Astrophysical • Choose up going events to Neutrino (signal) Cosmic Ray reject atmospheric muons (apply quality cuts)
Detection Mechanism Ice Direct Hit Cherenkov Hit Digital Optical Module radiation (DOM) for IceCube Observables Used for track reconstruction, • Hit timing (Direct Hit, Hit) Number of Direct Hit (Ndir) indicates reconstruction quality • Number of Hit OMs (Nch) Used as energy estimator • Charge / waveform waveform can be used for track reconstruction (not this analysis)
What is Diffuse Neutrino Search ? • Astrophysical point source search (See T.Montaruli’s talk in this session) • Observe multiple events from same source • Needs good angle resolution • Atmospheric Neutrino study (see P .Desiati’s talk on Thursday) • Uses low energy sample • Need statistics • Diffuse high-energy source search • Uses energy-related parameter to investigate excess from Atmospheric Neutrino events • Event selection : optimized to extract high-energy sample fewer Atmospheric Neutrino event in final sample
Analysis Strategy True Neutrino Number of Hit OMs (Nch) Energy Distribution (observable) (not observable) Signal spectrum is harder than Atms.Neutrino 350 Arbitrary Unit Atmospheric Nu 300 2 10 Atmospheric Nu Astrophysical Nu All Monte-Carlo -2 (test flux 1.0e-6 E ) 250 Astrophysical Nu -2 (test flux: 1.0e-6 E ) All Monte-Carlo 200 10 150 count event above 100 Nch > Nch cut 1 50 0 -1 0 1 2 3 4 5 6 7 8 9 10 Log (true Energy[GeV]) � µ 10 0 20 40 60 80 100 Nch Nch cut Nch i. Reject all background muons then Search best Nch cut ii.Apply Nch cut (Nch>Nch cut ) then compare number of survived events with Monte-Carlo prediction
AMANDA-II 807days multi-year 1500m analysis 677 OMs 500m 200m
Event selection : Preparing neutrino induced events Quality cuts (examples) Data 2000 - 2003 Data 2000 - 2003 Data 2000 - 2003 Data 2000 - 2003 • Require enough Uncertainty in atms. Uncertainty in atms. Uncertainty in atms. Uncertainty in atms. ! ! ! ! Barr et al. atms. Barr et al. atms. Barr et al. atms. Barr et al. atms. ! ! ! ! number of Direct Hit Honda et al. atms. Honda et al. atms. Honda et al. atms. Honda et al. atms. ! ! ! ! which close to the CORSIKA atms. CORSIKA atms. CORSIKA atms. CORSIKA atms. ! ! ! ! -6 -2 2 2 -6 -2 2 -6 -6 -2 -1 -1 E 2 = 10 GeV cm -2 -1 s -1 -1 sr -1 E E " " = 10 = 10 GeV cm GeV cm -1 s s sr -1 sr E " " = 10 GeV cm s sr expected hit time for sig sig sig sig the reconstructed track Events Events 4 4 10 10 level 5 Data (Nch < 100) (Ndir cut) horizontal 3 3 10 10 • Hits should distribute events removed 2 2 10 10 smoothly along with the reconstructed track 10 10 • Require long enough 1 1 track -1 -1 10 10 level of final analysis • Remove horizontal -2 -2 10 10 -1 -1 -0.8 -0.8 -0.6 -0.6 -0.4 -0.4 -0.2 -0.2 -0 -0 events Cosine of Reconstructed Zenith Angle Cosine of Reconstructed Zenith Angle upgoing horizontal
AMANDA-II 807days Diffuse Analysis Nch distribution after final selection Data 2000 - 2003 Uncertainty in atmospheric ! Events Barr et al. atms. + prompt ! ! Honda et al. atms. + prompt ! ! 2 10 -6 2 -2 -1 -1 E = 1.0 x 10 GeV cm s sr " signal -8 2 -2 -1 -1 E = 7.4 x 10 GeV cm s sr " signal 10 final event sample 1 -1 10 atms. rescaled ! -2 10 0 20 40 60 80 100 120 140 160 Number of OMs hit (N ) ch at Nch > 100, 6 events observed no significant excess from background
AMANDA-II 807days Diffuse Analysis Upper Limit Paper Published! Physical Review D 76, E -2 < 7.4 x 10 -8 GeV cm -2 s -1 sr -1 042008 (2007) -4 10 ] -1 AMANDA-II 2000 atms. data (prelim.) ! ! sr Barr et al. atms. + prompt atms. ! ! -1 s Honda et al. atms. + prompt atms. ! ! -2 dN/dE [GeV cm -5 10 Max uncertainty in atms. ! Frejus MACRO AMANDA B-10 1997 diffuse ! -6 ! 10 AMANDA-II 2000 Cascades (all-flavor / 3)* AMANDA B-10 1997 UHE (all-flavor / 3)* 2 Baikal 1998 - 2002 ( all-flavor / 3 )* E -7 10 RICE 1999-2005 ( all-flavor / 3 )* AMANDA-II 2000 unfolding (prelim.) AMANDA-II 2000-2002 UHE limit (prelim.) AMANDA-II 2000-3 limit -8 ! 10 ! W&B limit/2 (transparent sources) Full IceCube 1 yr * assumes a 1:1:1 flavor ratio at Earth -9 10 3 4 5 6 7 8 9 log [E (GeV)] ! 10
IceCube IceCube Amanda y IceCube [ m ] 9 strings 137days analysis 59 11 12 13 18 200 8 BC 1 50 6 7 14 19 DL2 5 49 4 3 2 100 15 10 9 40 16 17 SC1 39 38 0 30 29 -100 ~125m 540 DOMs 21 -200 DL1 (IC9) 200 300 400 500 600 x IceCube [ m ]
IC9 IceCube 9 (IC9) vs AMANDA Amanda • 3~4 times larger detector volume 500m • 3~4 times wider string intervals 1km • Similar number of Optical Sensors 200m 2~4 times larger effective area (10 5 ~ 10 6 GeV) 250m 375m 90% energy range shifts to higher energy Muon Neutrino After final event selection -0.8 > cos(true zenith) >= -1.0 ] True Neutrino Effective Area 2 7 10 Atms.Nu before Nch cut area [cm -0.6 > cos(true zenith) >= -0.8 -0.4 > cos(true zenith) >= -0.6 energy 4 (after Nch cut) Atms.Nu after Nch cut 10 -0.2 > cos(true zenith) >= -0.4 6 0.0 > cos(true zenith) >= -0.2 -2 10 1e-6xE Nu before Nch cut 0.2 > cos(true zenith) >= 0.0 3 10 ν Effective -2 1e-6xE Nu after Nch cut 5 10 2 10 1m 2 90% signal region 10 4 10 1 3 10 -1 10 2 10 Amanda 90% signal reg. -2 10 2 3 4 5 6 7 8 2 3 4 5 6 7 8 Log (E /GeV) Log10(primary Nu energy [GeV]) 10 ν
Event selection : Preparing neutrino induced events Data Nch < 46 is already unblinded for Atms.Nu study Low Nch data sample is compared with MC Number of event after final cut (Nch<46) Data + Atms. Mu Data : 52 event + Double Mu Background MC : 60 + 5 (Bartol) + Atms. Nu +1e-6 E -2 Nu (54 + 4 : Honda 2006) 4 10 preliminary 2 10 2 10 3 10 10 10 2 10 1 10 1 -1 1 10 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 after angle CosZenith CosZenith CosZenith after Ndir cut after final cut resolution cut
Nch distribution After final selection 10 Atms. Neutrino MC Signal Neutrino MC -2 (test flux 1e-6 E ) 1 -1 10 0 20 40 60 80 100 120 140 160 180 200 Nch
IceCube 9 string ~ 137days Scale factor of test flux vs Nch cut threshold • Scale factor is mrf mrf Model Rejection Factor Entries Entries 150 150 Mean 77.97 Mean 77.97 very flat between 1 RMS 37.46 RMS 37.46 Best mrf(bottom) = 0.126009 Best cut at Nch=33 (bin 17) Nch cut ~30 and Best Integrated Bgd = 4.79439 Int. Bgd (<bestcut) = 61.4359 0.8 50 Best Integrated Sig = 40.5372 --------------------------------- mrf at cut = 0.129037 0.6 Cut Nch=46 (bin 24) Best Integrated Bgd = 1.06569 Int. Bgd (<cut) = 60.625 Best Integrated Sig = 25.7652 0.4 Choose Nch cut = 46 Nch cut = 46 0.2 Min. 0.13 to get sensitivity 0 20 40 60 80 100 120 Nch
Diffuse Muon Neutrino Sensitivity of IC9 137 days (2006) E -2 < 1.3 x 10 -7 GeV cm -2 s -1 sr -1 -4 10 ] AMANDA-II 2000 atms. data (prelim.) -1 � µ sr Barr et al. atms. + prompt atms. � � AMANDA-II -1 s Honda et al. atms. � + prompt atms. � -2 807days upper limit dN/dE [GeV cm -5 Max uncertainty in atms. � 10 Frejus MACRO AMANDA B-10 1997 � diffuse µ -6 10 AMANDA-II 2000 Cascades (all-flavor / 3)* AMANDA B-10 1997 UHE (all-flavor / 3)* Baikal 1998 - 2002 ( all-flavor / 3 )* 2 E RICE 1999-2005 ( all-flavor / 3 )* -7 10 AMANDA-II 2000 unfolding (prelim.) AMANDA-II 2000-2002 UHE limit (prelim.) AMANDA-II 2000-3 limit � µ -8 10 W&B limit/2 (transparent sources) Full IceCube 1 yr * assumes a 1:1:1 flavor ratio at Earth IceCube 9 strings 137days -9 10 3 4 5 6 7 8 9 log [E (GeV)] � 10 IC9 137days sensitivity is factor 2 above AMANDA-II 807days in 2007 integrated IceCube exposure exceeds AMANDA-II 4yr
Summary • AMANDA-II 807days upper limit on the diffuse flux of muon neutrino with a A const E -2 spectrum for the energy range 16 TeV to 2.5PeV is E -2 < 7.4 x 10 -8 GeV cm -2 s -1 sr -1 • Monte-Carlo verification for IceCube 9 string has done with Nch<46 low energy data. MC data shows reasonable agreement with the data sample. • The sensitivity of IceCube 9 string 137days on the diffuse flux of muon neutrino with a A const E -2 spectrum for the energy range from 25T eV to 10PeV is E -2 < 1.3 x 10 -7 GeV cm -2 s -1 sr -1 which is factor 2 above AMANDA-II 807days.
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