Detection of a neutrino event at the Glashow resonance with IceCube

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Detection of a neutrino event at the Glashow resonance with IceCube

Christian Haack, TUM

Lu Lu, Tianlu Yuan, UW Madison For the IceCube Collaboration

VLVnT 2021, 21.05.2021

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Christian Haack (TUM) | VLVnT 2021 2

Production of Astrophysical Neutrinos

Accelerator (AGN, SNR, GRB, ..)

p

_or

γ

𝝅

^±

, 𝝅

^𝟎

γ γ

Pion Decays

𝜋⁺ → 𝜇⁺ + 𝜈_𝜇 → 𝑒⁺ + 𝜈_𝑒 + 𝜈_𝜇 + ҧ𝜈_𝜇 𝜋⁻ → 𝜇⁻ + ҧ𝜈_𝜇 → 𝑒⁻ + ҧ𝜈_𝑒 + ҧ𝜈_𝜇 + 𝜈_𝜇

𝜋⁰ → 𝛾𝛾

e+ν

DESY

Idealized scenarios

𝑝 + 𝑝 → 𝑋 + ൞

𝜋⁺ 1/3 𝜋⁻ 1/3 𝜋⁰ 1/3 𝑝 + 𝛾 → Δ⁺ → ൝𝑝 + 𝜋⁰ 1/3

𝑛 + 𝜋⁺ 2/3

Interaction of accelerated CR naturally leads to production of neutrinos and gamma rays

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Proton-Proton (𝒑𝒑) interactions Idealized scenario:

𝜈

_𝑒

: ҧ𝜈

_𝑒

: 𝜈

_𝜇

: ҧ𝜈

_𝜇

: 𝜈

_𝜏

: ҧ𝜈

_𝜏

= 1: 1: 2: 2: 0: 0

Astrophysical Neutrino Production

Proton-Photon (𝒑𝜸) interactions Idealized scenario:

𝜈

_𝑒

: ҧ𝜈

_𝑒

: 𝜈

_𝜇

: ҧ𝜈

_𝜇

: 𝜈

_𝜏

: ҧ𝜈

_𝜏

= 1: 0: 1: 1: 0: 0

Neutrino Oscillations

1: 1: 1: 1: 1: 1 14: 4: 11: 7: 11: 7

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The Glashow Resonance

 Resonant 𝑊⁻ -production in _𝑒ҧ𝜈 − e⁻ interactions at 6.3 PeV neutrino energy (electron at rest)

𝑒ҧ𝜈 + 𝑒⁻ → 𝑊⁻ → ቊHadrons (67%) Leptons (23%)

 > x100 increase over DIS in ҧ𝜈_𝑒 cross section

 Not observed experimentally, despite being fundamental Standard Model process

 Allows (statistical) measurement of ^ഥ^𝜈^𝑒

𝜈_𝑒 ratio -> Handle on astrophysical 𝜈 production mechanisms

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The Glashow Resonance

 Resonant 𝑊⁻ -production in _𝑒ҧ𝜈 − e⁻ interactions at 6.3 PeV neutrino energy (electron at rest)

𝑒ҧ𝜈 + 𝑒⁻ → 𝑊⁻ → ቊHadrons (67%) Leptons (23%)

 x200 increase over DIS in ҧ𝜈_𝑒 cross section

 So far not observed experimentally, despite being fundamental Standard Model process

 Allows (statistical) measurement of ^ഥ^𝜈^𝑒

𝜈_𝑒 ratio -> Handle on astrophysical 𝜈 production mechanisms

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How to Measure the Glashow Resonance

Need good energy resolution:

→ Cascade Events

From conventional event selections expect

~0.2 GR events / year

Solution: Use partially contained events Caveat: Increased contamination by

atmospheric muons

Christian Haack (TUM) | VLVnT 2021

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A Multi-PeV Uncontained Cascade

Event Vertex

The event vertex is outside the

detector and the PMTs closest to the vertex are saturated.

⇒ Challenging Reconstruction Best reconstruction achieved by

DirectFit: ABC (Approximate Bayesian Computing) method using event

resimulations.

Time

Early Late

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Event Display

Nature 591, 220–224 (2021)

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9 Christian Haack (TUM) | VLVnT 2021

Energy Reconstruction

Reject NC/CC origin with 1% p-value

Nature 591, 220–224 (2021) Nature 591, 220–224 (2021)

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Verification via Resimulation

Nature 591, 220–224 (2021)

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Muon Production in Hadronic Cascades

𝑊

⁻

𝜈

_𝑙

𝑙/𝜈

_𝑙

Mesons Muons

Hadronic Cascade (~15m length in ice)

𝑒

ҧ𝜈 𝑒

OR

Neutrino DIS

Glashow Resonance

N

^{Muons can}outrange the

hadronic cascade

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Early Pulses from Muonic Component

 Cherenkov light front propagates with 𝑐/𝑛

_𝑖𝑐𝑒

 Relativistic muons from hadronic cascade can

“outrun” cascade light front

 Resulting early hit patterns

can be used to reconstruct

muon direction

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Early Pulses from Muonic Component

Nature 591, 220–224 (2021)

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Angular Reconstruction

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Resimulation with Muonic Component

Nature 591, 220–224 (2021) Nature 591, 220–224 (2021)

Pure EM Cascade Hadronic Cascade

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Maximum Muon Energy

Number of strings with early hits correlated to leading muon energy

Nature 591, 220–224 (2021)

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Background Probability

Expect less than

𝟏𝟎^−𝟕

muon events with similar topology.

Energy losses

Muon at Surface

Propagate to detector

Deposit ~6 PeV at reconstructed vertex

Remain with ~25 GeV

Direction is well constrained.

Only possible background topology:

Stopping muon

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Background Probability

Expect less than

𝟏𝟎^−𝟕

muon events with similar topology.

Energy losses

Muon at Surface

Propagate to detector

Deposit ~6 PeV at reconstructed vertex

Remain with ~25 GeV

Direction is well constrained.

Only possible background topology:

Stopping muon

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The Astrophysical Neutrino Spectrum

Nature 591, 220–224 (2021)

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• IceCube has detected a multi-PeV uncontained hadronic cascade event

• Deposited energy is consistent with the expectation from the Glashow Resonance

• Production via CC constrained at 1% p-value.

• Muons produced in the hadronic cascade allow independent reconstruction of the event direction

& confirmation of the cascade reconstruction

• Atmospheric origin excluded at 5𝜎

• What I didn‘t talk about: Early muon reconstruction technique in principle allows to measure the inelasticity of the neutrino interaction → Further discrimination of CC/GR

• In the future GR measurements can help constrain astrophysical source scenarios

Detection of a neutrino event at the Glashow resonance with IceCube