mlesiakbzdak miami2012 final - university of miami · 2012. 12. 31. · honda: prd 75 (2007) 043006...

Results of the extraterrestrial and atmospheric neutrino-induced cascade

searches with IceCube

Mariola Lesiak-Bzdak Stony Brook University for the IceCube Collaboration

Outline: }  Motivation }  The IceCube detector }  Atmospheric cascade neutrino searches }  Extraterrestrial cascade neutrino

searches }  Summary

Geographic South Pole"

Amundsen-Scott "South Pole Station"

1

IceCube detector

Mariola Lesiak-Bzdak, Miami 2012

Cosmogenic Neutrinos }  Cosmic rays lose their energy due

to interactions with cosmic microwave background (CMB)

}  Above 1019 eV Greisen-Zatsepin-Kuzmin cut-off : p + γ CMBà Δ+ à π+ + n à νµ + µ+ + n

à π0 + p à γ γ + p

}  Neutrinos: }  straight line propagation }  unabsorbed }  not GZK supressed

Mariola Lesiak-Bzdak, Miami 2012 2

Greisen, Zatsepin, and Kuzmin (1966)

GZK cutoff"

€

Ep > 6×1019eV

Searches for a Diffuse Neutrino Flux

3

Diffuse Flux = effective sum from all (unresolved) extraterrestrial sources (e.g. AGNs)

}  Signal: }  Extraterrestrial ν from ~E-2 sources

}  Background: }  Atmospheric µ }  Atmospheric ν

}  Sensitive to all three ν flavors }  Energy information used to

separate signal from background


Northern sky

Southern sky

GRBs AGNs Energy

Atmospheric ν, µ Harder

Spectrum ν (E-2)

Atmospheric Neutrinos

4 Mariola Lesiak-Bzdak, Miami 2012

Northern sky

Southern sky

}  Signal: }  Conventional atm. ν flux:

}  Originates from decays of pions and kaons

}  ~ E-3.7

}  Prompt atm. ν flux: }  Decay of charmed mesons

}  ~ E-2.7

}  No measurement of prompt neutrinos yet

}  Background: }  Atmospheric µ

}  Astrophysical ν: }  ~E-2 (model)

IceCube Detector


9 strings (2006) 22 strings (2007) 40 strings (2008) 59 strings (2009) 79 strings (2010) 86 strings (2011) For more see talk by

Kurt Woschnagg Insta

lla'on com

pleted: De

c, 2010

Opera'on

of IC86 sta

rted: May 13

th, 2011

Neutrino Event Signatures

6

νμ N è μX

Color coding: red – earliest blue - latest


νe Nè cascade

IC79 data

Cascades §  e-m and hadronic cascades

§  energy resolution ~ 35% §  used for diffuse flux searches

€

νe(τ ) + N →e(τ ) + Xν l + N →ν l + X l = e, µ,τ

νe(τ)(CC) νl(NC)

Tracks with length ~1km §  angular resolution <1o

§  energy resolution log(E) ~ 0.2 §  used for point source searches and diffuse flux searches

€

νµ +N→µ + XN - target nucleon X - hadronic shower

νµ (CC)

This talk


}  Signal: }  Atmospheric ν e CC and (ν e + ν µ) NC

}  Background: }  Atmospheric µ and ν µ CC

}  281 days of IC79 DeepCore data

Atmospheric Cascades with IC79 DeepCore


}  Signal: }  Atmospheric ν e CC and (ν e + ν µ) NC

}  Background: }  Atmospheric µ and ν µ CC

}  281 days of IC79 DeepCore data }  Analysis strategy:

}  Demand spherical light distribution pattern and its reconstructed vertex to be contained inside the fiducial volume

}  Combination of cut variables in Boosted Decision Tree

}  Selection criteria developed on 10% of the data (burn sample) More on DeepCore - see talk by Kurt Woschnagg



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First observation of atmospheric neutrino-induced cascades in DeepCore Mariola Lesiak-Bzdak, Miami 2012

(90% of IC79 data) }  Found 1029 events in 281

days of IC79 data

Bartol: PRD 70 (2004) 023006 Honda: PRD 75 (2007) 043006

IceCube Collaboration, arXiv: 1212.4760


}  Found 1029 events in 281 days of IC79 data

}  Observed 496 ± 66(stat) ±

88(syst) cascade signal events (4.5 σ)

}  Energy range between 80

GeV and 6 TeV

10

First observation of atmospheric neutrino-induced cascades in DeepCore Mariola Lesiak-Bzdak, Miami 2012

(90% of IC79 data)

Bartol: PRD 70 (2004) 023006 Honda: PRD 75 (2007) 043006

IceCube Collaboration, arXiv: 1212.4760

Prompt ν from decay of charm not yet measured

}  First measurement in the energy range 80 GeV - 6 TeV

}  Consistent with current models of atmospheric neutrino flux, within current uncertainties


IC79 DeepCore νe

First observation of atmospheric neutrino-induced cascades in DeepCore


IceCube Diffuse Neutrino-Induced Cascade Searches

}  Look for neutrino events at high energy, above the rapidly falling atmospheric neutrino spectrum }  Signal: (ν e and ν τ ) CC and ν µ,τ,e NC }  Background: atmospheric µ and ν µ CC



}  IC22 (25% of IceCube final size): }  No excess above µ backgr. observed }  257 days of IC22-string data }  Energy range 24 TeV < E < 6.6 PeV

}  Flux limit: E2Φ90%CL < 3.6 x 10-7 GeV· cm-2· s-1 · sr-1 }  Published: PRD84 (2011) 072001


90% of IC22 data






IC22 blind sample data events





}  IC40 (46% of IceCube final size): }  332 days of IC40-string data (next slides)


IC22 blind sample data events


}  Method: }  combination of cut variables in

Boosted Decision Tree

}  Two branches: }  Low energy (>1.8 TeV) sample

aimed at detection of atm. ν }  High energy (>100 TeV) sample

aimed at detection of astrophysical ν }  Energy used to separate signal and

background


BDT vs reconstructed energy for combined branches in 100% of data

Energy

Atmospheric ν, µ Harder

Spectrum ν (E-2) Low energy sample High energy sample

IC40 Diffuse ν-induced Cascade Searches

IC40 Diffuse ν-induced Cascades Results, Low Energy Sample

}  Observed 67 events with 2.8σexcess over atm. µ considering statistical background uncertainty


17

17

Atm. µ

Atm. Conv. ν

Atm. Conv. + Prompt ν

Predicted νSignal 1.4 10-8 GeV s-1cm-2 sr-1 E-2 (IC59 νµ

diffuse limit)

IC40 DATA (90%) Low Energy Sample

Total Number of Events in 332 days

41.1 20.8 23.1 7.1 67

Background contributions

Atm. Conv. (Honda): PRD 75 (2007) 043006 Atm. Conv+Prompt: Honda + PRD 78 (2008) 043005


}  Reconstructed energy distribution of the full (burn sample + blind sample) low-E sample.


18

(100% of the IC40 data)

18


}  Reconstructed energy distribution of the full (burn sample + blind sample) low-E sample.


19


19

Excess not significant → results compatible with background

IC40 Diffuse ν-induced Cascades Results, High Energy Sample

}  Found 3 events in a final blind sample in a total lifetime of 332 days


Burnsample event

Blind sample

events

224 TeV 114 TeV

114 TeV 135 TeV


}  Found 3 events in a final sample (after all cuts) in a total livetime of 332 days }  2.75σ excess over atm. µ based on a background estimate from

extrapolation }  2.40σ excess over atm. µ and ν (including prompt)

}  Systematic studies ongoing Mariola Lesiak-Bzdak, Miami 2012

21

21

Atm. μ

Atm. Conv. ν

Atm. Conv. + Prompt ν

Predicted νSignal 1.4 10-8 GeV s-1cm-2 sr-1 E-2 (IC59 νµ

diffuse limit)

IC40 DATA (90%) Low Energy Sample

Total Number of Events in 332 days

0.36 0.03 0.2 3.6 3



}  Reconstructed energy distribution of the full (burn sample + blind sample) high energy sample


22


22


}  Reconstructed energy distribution of the full (burn sample + blind sample) high energy sample


23


23

Excess not significant → results compatible with background

IC79+IC86 EHE Neutrinos

}  Search for Extremely High Energy events (energy >109GeV)

}  Sensitive to all ν flavors }  Combine data from IC79-string and

IC86-string (very similar detector configurations)

}  Effective lifetime of 670.1 days: }  IC-79: 5/2010 – 5/2011 (319.07days) }  IC-86: 5/2011 – 5/2012 (353.67days)


Strings not present in IC79 configuration

IC79+IC86 EHE Neutrinos, Event Selection

}  Selection of events based on deposited energy and direction: }  Search for track-like and

cascade-like events

}  Deposited energy (Cherenkov photons) }  Number of recorded

photoelectrons }  Number of triggered DOMs

(>300)

}  Straight line fit to the hit pattern (àZenith angle)


dow

ngoi

ng

Background MC

cos(

Zeni

th)

log10(NPE)

upgo

ing

IC79+IC86 EHE Neutrinos, Passing Events

}  Two events in 670.1 days pass all the selection criteria


}  Two events in 670.1 days pass all the selection criteria

}  Expected number of events and significance not including systematic uncertainties: }  0.057 events from atm. µ and conventional ν background (2.9 σ)

}  0.190 events from atm. µ and conventional and prompt ν background (2.2 σ)

}  Cascade-like events: }  Expected from CC and NC events


First observation of high energy (~PeV) neutrino-induced cascades in IceCube

IC79+IC86 EHE Neutrinos, Passing Events

IC79+IC86 EHE Neutrinos, Expected Number of Events

}  Two events in 670.1 days pass all selection criteria



Total Number of Background Events in 670.1 days

Atm. μ 0.036

Atm. Conventional μ

0.021

Coincidence μ 0.0006

Total 0.057

Total with prompt 0.190

Cosmogenic ν Signal Models

Event All

Rates Eν≥100 PeV

Yoshida et al. 2.1 2.0

Kotera et al. (FRII) 4.1 2.6

Ahlers et al. (maximal)

3.2 3.0

Ahlers et al. (best fit) 1.6 1.5

IceCube data 2 0

Signal events Background events

First observation of high energy (~PeV) neutrino-induced cascades in IceCube

Yoshida et al., ApJ 479 (1997) 547-559 K. Kotera et al, JCAP 10 (2010) 013 M. Ahlers et al, Astropart. Phys. 34 (2010) 106

IC79+IC86 EHE Neutrinos, Events NPE and Energy

}  Preliminary reconstructed energy estimated at 1.1 PeV and 1.3 PeV with 35% energy resolution including statistical and systematic uncertainties


Preliminary IceCube Sensitivity


}  Preliminary IceCube sensitivity to all flavor neutrino flux by the 2010-2012 ultra-high energy neutrino analysis with an effective lifetime of 670.1 days. The systematic errors are not included.

}  Cascade-like events

WB bound

Summary }  Atmospheric neutrino-induced cascade searches:

}  First observation (4.5σ) of atm. cascades in DeepCore (80 GeV < E < 6 TeV)

}  Diffuse cascade searches: }  IC22 – results compatible with background:

}  24 TeV < E < 6.6 PeV, flux=E2Φ90%CL < 3.6 x 10-7 GeV· cm-2· s-1 · sr-1

}  IC40 – results compatible with background: }  low energy sample: observed 67 events (2.8σ) (1.8 TeV < E < 100 TeV) }  high energy sample: observed 3 events (2.75σ) (100 TeV < E <1 PeV)

}  EHE search with IC79+IC86: }  2 events observed over an expected atm. µ and atm. conv. ν background

of 0.057 (with prompt 0.190) events (2.9 σ and 2.2 σ, respectively) }  First observation of cascade events with energy estimates

of 1.1 PeV and 1.3 PeV


Stay tuned! http://icecube.wisc.edu/

IceCube Collaboration

32

Canada University of Alberta US Bartol Research Institute, Delaware Pennsylvania State University University of California - Berkeley University of California - Irvine Clark-Atlanta University University of Maryland University of Wisconsin - Madison University of Wisconsin - River Falls Lawrence Berkeley National Lab. University of Kansas Southern University, Baton Rouge University of Alaska, Anchorage University of Alabama, Tuscaloosa Georgia Tech Ohio State University Stony Brook University

Sweden Uppsala Universitet Stockholms Universitet

UK Oxford University

Belgium Université Libre de Bruxelles Vrije Universiteit Brussel Universiteit Gent Université de Mons-Hainaut Switzerland EPFL, Lausanne

Germany Universität Mainz DESY-Zeuthen Universität Dortmund Universität Wuppertal Humboldt-Universität zu Berlin MPI Heidelberg RWTH Aachen Universität Bonn Ruhr-Universität Bochum

Japan Chiba University

New Zealand University of Canterbury ANTARCTICA!

Amundsen-Scott Station!

http://icecube.wisc.edu 36 institutions, ~250 members


BACKUP SLIDES


Cascade Position Reconstruction


}  Ilustration of directional reconstruction for cascade-like events

IC79+IC86 EHE Neutrinos, Event Selection

}  Deposited energy (Cherenkov photons) }  Number of recorded photoelectrons }  Number of triggered DOMs (>300)

}  Straight line fit to the hit pattern (àZenith angle)


upgo

ing

dow

ngoi

ng

Background MC Data (10%) Signal MC

cos(

Zeni

th)

cos(

Zeni

th)

cos(

Zeni

th)

log10(NPE) log10(NPE) log10(NPE)

Add selection criteria lines

log10(Energy)

log 1

0(N

PE

)

mlesiakbzdak miami2012 final - university of miami · 2012. 12. 31. · honda: prd 75 (2007) 043006...

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