Beyond first observation of PeV-energy
neutrinos with IceCube
石原安野（Aya Ishihara)
aya@hepburn.s.chiba-u.ac.jp
千葉大学

Aya Ishihara 2013年3月15日 宇宙ニュートリノ研究会 柏の葉

The High Energy Deep Universe Mystery
The fisrt star
million years

Big Bang

The first galaxy
800million years

Present

Gamma-ray burst
AGN – Massive BH•

起源のわからない高エネルギー粒子が宇宙から地球に飛来している。どこから？
エネルギーはLHC加速器の１０００万倍以上に達する（１００EeV＝１０keV(x-ray) x 10,000,000,000,000,000!)•

巨大ブラックホールである活動銀河核（AGN)や宇宙で最も激しい爆発現象であるガンマ線爆発（GRB)といった極限爆発現象は遠方（若い）宇宙に分布• Was young Universe more active? why? how high energy they can produce?
3/15/2013

Aya Ishihara2•

解明に向けた障壁

地球で観測される最高エネルギー粒子は電荷を持っているため宇宙磁場に曲げられてきており来た方向が分からない。

•

高エネルギー深宇宙を直接光で観測することが出来ない。
o

ガンマ線は３Kの宇宙背景輻射と反応してしまい、エネルギーを失ってしまうo

PeV宇宙を見られる範囲は10万光年（天の川銀河の直径）ほどo

ハドロン・レプトン起源に対するambiguity

ガンマ線＞１００TeV

宇宙背景輻射
e+
e－

e－

荷電粒子
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Aya Ishihara

3Ultra-high Energy - IceCube’s sweet spot
PeV and above•

Cosmic frontier - PeV

gamma-ray horizon
limited to a few tens ofkpc (our galaxy radius)•

Energies above

dominant atmospheric
neutrinos•

Cosmogenic neutrino
production is a‘guaranteed’ n source
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Aya Ishihara

4

The highest energy neutrinos
cosmogenic neutrinos induced by the interactions of cosmic-ray and CMB photons
Off-Source (<50Mpc) astrophysical neutrino production via
GZK (Greisen-Zatsepin-Kuzmin) mechanism

p >100EeV

+

nm

0

m+

nm
ne

e+

The main energy range: En ~ 108-10 GeVp 2.7 K     X  m   n  e  n ' sCarries important physics• Location of the cosmic-ray
sources• Cosmological evolution of the
Variouscosmic-ray sources
GZK n• Cosmic-ray spectra at sources
models • The highest energy of thecosmc-rays• Composition of the cosmicrays• Particle physics beyond theenergies accelerators canreach
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Aya Ishihara

5どのような宇宙ニュートリノ検出器が必要か？
ニュートリノ流量のエネルギー分布

超新星1987

大気ニュートリノ
宇宙ニュートリノ

超新星爆発ニュートリノ
1987年2月23日にIMB実験とカミオカ
ンデ実験により初めて観測（小柴昌俊氏
が2002年にノーベル物理学賞）爆発的天体現象でニュートリノが出来ることがわ
かった

初の宇宙ニュートリノ発見以来、さまざまな実験によって超新星爆発ニュートリノエネルギーを超える,他の天体からの宇宙ニュートリノの検出研究が続けられているが、25年間観測されていない。
何故か？
９桁以上のエネルギー領域にわたって
背景事象となる大気ニュートリノの量が宇宙ニュートリノ量より何桁も多く、宇宙ニュートリノを区別して観測することが出来ない！

High energy neutrino telescopes in the worldSince 1976 DUMAND, Lake Baikal. NESTOR, ANTARES, and NEMO…

ICECUBE at
the South Poleandtime to see
cosmic ν！
We arehere!

AMANDA/IceCube

The first test bed
in 1991/1992
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Aya Ishihara

7

The IceCube Collaboration
http://icecube.wisc.edu

36 institutions, ~270 members
CanadaUniversity 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

SwedenGermany

Universität Mainz
Uppsala Universitet
Stockholms Universitet DESY-Zeuthen
Universität Dortmund
Universität Wuppertal
UK
Humboldt-Universität zu Berlin
Oxford University
MPI Heidelberg
Japan
RWTH Aachen
Chiba
Universität Bonn
University
Ruhr-Universität Bochum

Belgium
Université Libre de Bruxelles
Vrije Universiteit Brussel
Universiteit Gent
Université de Mons-Hainaut

Switzerland
EPFL, Lausanne

Barbados

New Zealand

University of West Indies

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The first
results fromthe full
IceCube

ANTARCTICA
Amundsen-Scott Station

University of Canterbury

8

Aya Ishihara

The Largest Neutrino Detector in the world:

The IceCube Detector
1km

1.5km

Array of 78 sparseand 8 dense strings
5160
opticalsensors

South Pole Dome (old station)

Amundsen-Scott
South Pole station

1km
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検出原理

暗く、しかし光をよく通す巨大なマテリアルνll,W, Z νlhadronic
showerm, t or cascades
チェレンコフ光

光電子増倍管の格子
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Aya Ishiharan10

from MC simulation

Ultra-high Energy Signal Events
20PeV muon

Track

300PeV nu induced cascade

CascadeNot flavor sensitive except some special cases, however, we distinguish muon/tau
tracks induced by nu mu, nutau CC and cascades induced by nu e CC and NC by 3
flavors of neutrinos
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Comparison between IceCube’s 3D events• 丸一つ一つが光電子増倍管
and SK 2D events••super-KAMIOKANDE
検出器の大きさ40m x 40mx40m>15,000倍

丸の大きさが観測された光の強さ
色が光が届くタイミングICECUBE
検出器の大きさ
1000m x 1000m x 1000m

2Dから3Dへ
事象の大きさ6m x 6m

ICECUBE
事象の大きさ800m x 300m x 300m

A big challenge: IceCube検出器の建設
2006年に建設開始2010年末に建設終了 IC86 = full IceCube (2011~)

IC79 (2009-2010)

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IC59 (2008-2009)

Aya Ishihara

IC40 (2007-2008)

IC22 (2006-2007)13

Event rates
Strings

Data(year)

Livetime

AMANDAII(19) 2000-2006 3.8 years(Hz)HE ν rate(per day)100~5 / daytrigger rate

IC40

2008-09375 days

1100~40/ day

IC59

2009-10350 days

1900~70/ day

IC79

2010-11320 days

2250~100/dayIC86-I2011- 2012 360 days

2700

~120/day2700

running

IC86-II

current

IC86 achieving ~ 99% uptime
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Neutrino Example

With 40 strings, 2009 May

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15

IceCube Events
With 40 strings, 2008 Dec

With 79 strings, 2010 June

Energy threshold ~10 GeV>108 muons/day>100 neutrinos/day

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With 22 strings
2007

Aya Ishihara
130TeV

Cascade-like

16

Waveform
examplesfrom spe to
10000 pesingle pe level

Digitized
Waveform

25 cm PMT

7V

O(10000)peSC

4

2012/11/30

10

NPE = Integrated charge/PMT gain

Aya Ishihara

17

UHE neutrino analysis 2010-2012
Data samples Effective livetime of 670.1days
2010-2011 - 79 strings config.
May/31/2010-May/12/2011
Effective livetime 319.9days

2011-2012 – 86 strings config
May/13/2011-May14/2012
Effective livetime 350.1 days

9 strings (2006)
22 strings (2007)
40 strings (2008)
59 strings (2009)79 strings (2010)
86 strings (2011)

IceCube has been in astable operation for morethan 5 years

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BackgroundAtmospheric muons(downward going andvery energetic,

dominated in number)andAtmospheric neutrinos(full angle, lessenergetic, smaller inrate)

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19

Signal and Background events
Signal Track

Muon bundles

MC

data
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Aya Ishihara

Burn sample
NPE~ 1x105
μ bundle with ~ 3PeV

data

20

A Strategy for search for ultra-high energy
neutrinos

GZK signal

Atmospheric m
background(CORSIKA)
3/15/2013

Background energy smaller thansignalBackground is vertical downwardgoing while signal comes near horizon

Aya Ishihara

21

Atmospheric neutrinos in PeV••••

Conventional atmospheric neutrinos from decays of pion and kaons
Prompt atmospheric neutrinos form decays of heavy flavor short lived mesons(charm)
Prompt harder than conventional still steeper than astronomical spectra
Transition around 3 x 105 GeV depending on the models

No clear evidence of prompt atmospheric n observed so far

Prompt Slope= 2.7

Physics of heavy flavor particle production

ourdefault
relatively
high but
notexcluded
Conventional Slope = 3.7
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Aya Ishihara

22pair-creation

The Energy estimation

e+e-

photo-nuclear
m and t tracks lose their energy byradiative processes

m



e+e-


dE
E
dx

bremsstrahlung

channel # > 300

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23

Analysis Level ZA Distributions
cos zenith angle distributions comparisons with burn sample

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Analysis Level NPE Distributions
NPE distributions comparisons with burn sample

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Analysis Level NPE vs ZA
IC86

Data

Background sum

SignalIC79

Data

Background sum

Signal

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26

Effective Area
Two years average

3 Flavors (1:1:1)sum• A factor of 2 increase from IC40
• NPE threshold difference changes the response below PeV• Larger for cascades than for track below 10PeV
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Background event rates per effective livetime
Contribution

IC79

IC86

Total
(615.9days)

Atm mu0.02960.00810.0377conv Atm nu

0.00740.00440.0118Atm mu andconv Atm nu

0.03700.01250.0495prompt0.01910.01370.0328Atm mu, conv
Atm nu andprompt

0.05610.02620.0823GZK n Signal Event Rates

Models

IceCube2010-2012per 615.9days

IceCube2008-2009
Phys. Rev D83 092003(2011)
333daysAll
contributions(B)Contributi
on> 100 PeVGZK (Yoshida m=4)*

0.57

2.0

1.9

GZK (Ahlers max) **

0.89

3.0

2.9

GZK (Ahlers best fit) **

0.43

1.5

1.4

GZK (Kotera, dip FRII) ***

4.2

2.7

GZK (Kotera, dip SFR1)***

0.9

0.6

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29

After unblind - Observation of 2 events
Run118545-Event63733662
NPE 6.9928x104
GMT time: 2012/8/8 12:23:18

Run119316-Event36556705
NPE 9.628x104
GMT time: 2012/1/3 9:34:01

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Background NPE distributions

Two events observed
over an atmosphericbackground of
0.0823 events/livetime

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Background Errors
convention
al Atm. m,n(%)
prompt (%)

The largest uncertainty is on theprompt (charm) n model (a factor of 2
in3/15/2013
pQCD model, up to a factor of 5 Aya Ishihara
from nonpQCD)

Sources
Statistical
error
±7.3
±1.1
DOM
efficiency+63.7, −30.8 +21.3, −18.9
Ice property
and detector
responses −48.0−29.8
Cosmic-ray
flux variation +24.0, −39.0 ±30.0
Cosmic-ray
composition −61.0
Hadronic
interaction ＋13.5
nu yield fromcosmic-ray
nucleon± 3.5±7.3(stat) ±1.1(stat)+69.5−92.5( +36.8−46.4(
Total
sys)
sys) 32

P-values as a counting experimentconventional atm nu and atm muo

BG 0.00495, observed 2o

BG errors assumes a flat distribution between +0.028 and −0.047op-value with sys FC (BG=0.049500 observed=2)= 9.0x10-4o3.13 sigma equivalent

conventional and prompt atm nu and atm muo

BG 0.00823, observed 2o

BG errors assumes a flat distribution between +0.039 and −0.055op-value with sys FC (BG=0.082300 observed=2)=2.8x10-3o2.77 sigma equivalentE-2 signal flux NPE distribution
With different cut off energies< 109 GeV
total 8 events< 107 GeV
total 4 events

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34

The two event properties
Side view

CC/NC interactions in the detector

MC

Top view

No indicationthat they are instrumental
artifactsthat they are cosmic-ray
muon induced
we can use dedicatedcascade hypothesis to thereconstructions of these special
events35

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The highest Charged String Positions

Well
contained
events

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36

Event from Aug-2011
Calibrated ATWD waveform above and below the highest charged DOM (S53-23)“Bert”

S53-D23 and above

S53-D23 and below

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Aya Ishihara37• Maximizing the Poisson likelihood
based on the recorded waveforms• Charges and timing information

Estimated Energy Deposit
Preliminary• Jan 2012 event 1.1 PeV• Aug 2011 event 1.0 PeV
Error of +- ~35% including absolute, ice, stat errors

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Neutrino Energy
ne  e + X (CC reaction) energy deposit = neutrino energy
nx  nx + X (NC reaction) energy deposit = a partial neutrino energy

CC
NC

Both events: ~1 PeV < En < ~4 PeV at the IceCube depth = in-ice energy
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Neutrino Energy at the Earth surface
The in-earth neutrino propagation effects taken into
account assuming the primary n spectrum (En) ~ En-2
“Ernie”“Bert”

Note: Systematic errors included

90% confidence interval of810TeV-3.6PeV and 930TeV-5.9PeV
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40Implication to the highest energy cosmic-ray
originobservation

modelsthe GZK neutrino

Kotera ”Dip”

varied cosmologicalevolution
parameters

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41

Two model tests
1. KS tests + full range event counting
Consistency check with the 2 event observation

c2 = -2 ln (pE) – 2 ln (Poisson(N=2,m))
The rate term
The energy term: p-value to the expected energy distribution
predicted by each of the cosmic n models
Use the Kolmogorov-Smirnov statistics

p-value = dlogE 
Bert(logE Bert) dlogE Ernie  Erine(logE Ernie) PKS(logE Bert, logE Ernie)

Bert

2. Counting events above 100 PeV

Constraint on cosmological evolution parametersooMost of the EHE n models predicts n with energies >100PeV
Probability of two 2events being >100PeV is small

N 100(1   )%   PnNn,(100   )%N 100(1   )%1
mn  m BG

3/15/2013n 0

Pn probability of n events above 100 PeVAya Ishihara

p-value

42

The KS test
“Standard” GZK

The predicted En cumulative
probability“Low Energy Enhanced” GZK

Data

p-values O(1%)

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Results from KS tests + full range event counting
2事象の観測はどのGZKモデルともconsistentではない

Neutrino
Model

Combined with IC40

KS TestPE

Expected
Event Rate

PoissonSignificanceFinalp-values

6.0x10-2

2.8

5.5x10-1

1.5x10-1

GZK
Yoshida/Teshima

m=4, Zmax=4

Marginally excluded

GZK
AhlersFermi Best

6.0x10-2

GZK
KoteraFR-II

3.4x10-2

GZK
KoteraGRB

4.4x10-2

3/15/2013

2.1

7.3x10-1

1.8x10-1
Marginally excluded

5.9

3.8x10-2

1.0x10-2
Excluded by 95% C.L.

1.1

4.2x10-1

9.2x10-2
Excluded by 90% C.L.

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44

Event rates(>100 PeV) and p-valuesnTopdown
GUT

GZK
Y&T

GZK
Sigl

GZK
Ahler

GZK
Ahler

GZK
KoteraGZK
Koteram=4,zmax=4

m=5, zmax=3

Fermi Best

Fermi Max

FR-II

SFR/GRB

2.6

4.0

2.0

4.1

3.8

0.6

5.0

Model
Rejection
Factor

0.98

0.65

1.27

0.64

0.69

3.6

0.53

p-value

9.6x10-2

2.4x10-2

1.6x10-1

2.3x10-2

3.1x10-2

6.7x10-1

<10-2

Model

Rate
>100PeV

Excluded
Mildly Excluded
Consistent
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Aya Ishihara45最高エネルギー宇宙線源のEvolution
parameterに対する制限
ρ ~ (1+z)m0<z<zmax

A strongly evolved
astronomical
object (like FR-II radiogalaxy)is disfavored
Any sources evolved
stronger than SFR
will soon be ruled out by
IceCube or to be observed!

Yoshida andIshihara, PRD
85, 063002(2012)
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46

Model Independent Upper limit(Systematics included )90% C.L. upperlimit
F-C Upper fluctuation•••

A factor of ~4 improved
from the previous IceCube
results
The world’s best
sensitivity!
Will constrain theneutrino fluxes down to
mid-strong cosmologicalevolution models

Still at least a factor of two
improvement to come in
1-2 years

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47

PeV事象のFollow up analysis
Starting Event Analysis• Bright (>6000pe)• Outer veto cut to reject backgroundo

Events started in detector

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48

より低いエネルギー領域からのスキャン
Improvements in 100TeV region from the starting event analysis

new window

4
3/15/2013

5

log E
[GeV]

6

7
Aya Ishihara

49

Summary from recent 2012 results••

IceCubeが完成し、初のデータ解析を行った

特に2つのDiffuse ν解析、PeV以上のニュートリノ解析とそこから検出された2事象の研究、その事象にOPTIMIZEした１００TeV以上の事象を調べる

FOLLOWUP解析による進展•

それぞれ３σレベルの大気背景事象を超えるニュートリノ事象が観測。２つの解析からの結果を統合すると約4σレベルの*EVIDENCE*••

詳細な2＋26事象の研究を行っている
今のところ、この28事象の特徴を全て説明できるシグナル・バックグラウンドモ

デルは存在していない•

1論文はほぼ完成3月中にSUBMIT, 2論文は4月中にSUBMITを予定

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50近い今後について – 2013•

初めの解析のラウンドとしては、1)どのようなシグナルが出てくるかわからない

ため、2)出来る限り不定性などに影響を受けないよう、3)早く解析を行うため、
比較的ロバストな、詳細な事象再構築等によらないシンプルな解析を行ってきた•

2013は事象トポロジーでオプティマイズしたミューオンやカスケードの特徴による解析結果が期待。これらの解析は違ったチャンネルのエネルギー領域を観測することが可能•

オンライン解析の充実 – Collaboration with photons•

宇宙ニュートリノがほぼ見つかった。統計量には限界があるがそこにチャレンジしてその特性を調べていく - その先は、unpredictable

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