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CAP Congress 2025

The IceCube Neutrino Observatory

Select results and current efforts

Daniel Durnford

On behalf of the IceCube Collaboration

June 9^th 2025

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The IceCube neutrino observatory

Neutrino physics, oscillation measurements

Ongoing efforts

IceCube Upgrade

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Neutrino physics

Daniel Durnford

CAP Congress 2025

1/30

Rev. Mod. Phys. 92, 045006

Natural and artificial sources of neutrinos

Energies far exceeding that of collider experiments

Unhindered by astronomical foregrounds

Fundamental particle physics

Astrophysics

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Neutrino physics

Daniel Durnford

CAP Congress 2025

2/30

Natural and artificial sources of neutrinos

Energies far exceeding that of collider experiments

Unhindered by astronomical foregrounds

The original motivation for neutrino telescopes:

Fundamental particle physics

Astrophysics

Rev. Mod. Phys. 92, 045006

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Neutrino as cosmic messengers

Daniel Durnford

CAP Congress 2025

3/30

J.A. Aguilar & J. Yang, Multi-messengers

from hadronic accelerators

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Neutrino as cosmic messengers

Daniel Durnford

CAP Congress 2025

3/30

J.A. Aguilar & J. Yang, Multi-messengers

from hadronic accelerators

See talk by Professor Nahee Park, session R2-6!

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Neutrino physics

Daniel Durnford

CAP Congress 2025

4/30

IceCube can also study fundamental physics with neutrinos

Fundamental particle physics

Astrophysics

Rev. Mod. Phys. 92, 045006

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The IceCube neutrino observatory

Daniel Durnford

CAP Congress 2025

Image source

5/30

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Neutrino interactions

Daniel Durnford

CAP Congress 2025

6/30

Mainly deep inelastic scattering with individual quarks

Two main types of interactions: charged current (W^±) and neutral current (Z)

Charged particles travelling faster than c in the medium produce Cherenkov radiation

Cone-shaped wave front (opening angle ~41°)

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1/30

Muon track

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Neutrino interactions

Daniel Durnford

CAP Congress 2025

8/30

Track events

(high energy 𝜇)

Cascade events

(hadronic and electromagnetic showers)

TeV-scale and up

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Daniel Durnford

CAP Congress 2025

9/30

GeV-scale:

Sparse PMT hits, reconstruction is difficult!

Neutrino interactions

Track events

(high energy 𝜇)

Cascade events

(hadronic and electromagnetic showers)

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Select neutrino physics results

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Daniel Durnford

CAP Congress 2025

10/30

Neutrino inelasticity measurement with atmospheric neutrinos

Inelasticity: fraction of neutrino energy

transferred to hadronic system:

Neutrino interaction inelasticity

Canadian contribution

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Daniel Durnford

CAP Congress 2025

10/30

Phys. Rev. D 111, 112001 (2025)

Neutrino inelasticity measurement with atmospheric neutrinos

Inelasticity: fraction of neutrino energy

transferred to hadronic system:

Neutrino interaction inelasticity

Canadian contribution

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Daniel Durnford

CAP Congress 2025

11/30

Cross-section measurement

Phys. Rev. D 104, 022001 (2021)

Measurement of all-flavour neutrino cross-section with diffuse HE neutrinos: use the Earth as a target!

Flux ratio IceCube:Surface, assuming nominal cross-section

𝛳

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Daniel Durnford

CAP Congress 2025

11/30

Cross-section measurement

Phys. Rev. D 104, 022001 (2021)

Measurement of all-flavour neutrino cross-section with diffuse HE neutrinos: use the Earth as a target!

Flux ratio IceCube:Surface, assuming nominal cross-section

𝛳

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Neutrino oscillations

Daniel Durnford

CAP Congress 2025

12/30

Neutrino oscillations: 3 (known) flavour states and mass states

Oscillations parameterized by:

3 mixing angles (e.g. sin²𝜃₂₃)
2 mass differences
1 CP-violating phase
Whether or not the 3rd mass state is heavier or lighter than the first 2 (normal vs. inverted hierarchy)

J. Phys. G: 43 (8), 084001 (2016)

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Neutrino oscillations

Daniel Durnford

CAP Congress 2025

12/30

Neutrino oscillations: 3 (known) flavour states and mass states

Oscillation probability depends on path length L, energy E (also matter effects)

Oscillations parameterized by:

3 mixing angles (e.g. sin²𝜃₂₃)
2 mass differences
1 CP-violating phase
Whether or not the 3rd mass state is heavier or lighter than the first 2 (normal vs. inverted hierarchy)

J. Phys. G: 43 (8), 084001 (2016)

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Atmospheric neutrino measurements

Daniel Durnford

CAP Congress 2025

13/30

Atmospheric neutrinos provide are abundant source for IceCube to study

Use the entire Earth as a shield! Upgoing events from neutrinos, downgoing from neutrinos + atm. muons

*Assuming normal hierarchy

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Daniel Durnford

CAP Congress 2025

14/30

Atmospheric neutrino measurements

Phys. Rev. D 108, 012014 (2023)

𝝼_𝝻

𝝻

Typical analysis procedure:

Event selection to suppress backgrounds
Classify events, apply reconstructions (energy, zenith)
Forward-folding analysis: produce MC for proposed sin²𝜃₂₃ and ∆m₂₃, apply same selection and reconstructions
Binned fit of data (in energy, zenith, and PID bins)

Canadian contribution

22 of 65

Daniel Durnford

CAP Congress 2025

15/30

Atmospheric neutrino measurements

Event PID:

Track-like

Cascade-like

Typical analysis procedure:

Event selection to suppress backgrounds
Classify events, apply reconstructions (energy, zenith)
Forward-folding analysis: produce MC for proposed sin²𝜃₂₃ and ∆m₂₃, apply same selection and reconstructions
Binned fit of data (in energy, zenith, and PID bins)

Canadian contribution

23 of 65

Daniel Durnford

CAP Congress 2025

16/30

Atmospheric neutrino measurements

Typical analysis procedure:

Event selection to suppress backgrounds
Classify events, apply reconstructions (energy, zenith)
Forward-folding analysis: produce MC for proposed sin²𝜃₂₃ and ∆m₂₃, apply same selection and reconstructions
Binned fit of data (in energy, zenith, and PID bins)

Canadian contribution

24 of 65

Daniel Durnford

CAP Congress 2025

17/30

Atmospheric neutrino measurements

Observed events at final level:

Phys. Rev. D 108, 012014 (2023)

Typical analysis procedure:

Event selection to suppress backgrounds
Classify events, apply reconstructions (energy, zenith)
Forward-folding analysis: produce MC for proposed sin²𝜃₂₃ and ∆m₂₃, apply same selection and reconstructions
Binned fit of data (in energy, zenith, and PID bins)

Canadian contribution

25 of 65

Daniel Durnford

CAP Congress 2025

18/30

Atmospheric neutrino measurements

Cascade-like

Track-like

arXiv:2405.02163

(accepted in PRL)

Typical analysis procedure:

Event selection to suppress backgrounds
Classify events, apply reconstructions (energy, zenith)
Forward-folding analysis: produce MC for proposed sin²𝜃₂₃ and ∆m₂₃, apply same selection and reconstructions
Binned fit of data (in energy, zenith, and PID bins)

Canadian contribution

26 of 65

Daniel Durnford

CAP Congress 2025

19/30

Atmospheric neutrino measurements

Results competitive with long baseline accelerator measurements

Two separate analyses

Complementary to other experimental methods:

Higher energy regime
Include tau lepton contribution
Different systematics

Phys. Rev. D 108, 012014 (2023)

Canadian contribution

K. DeHolton (Lake Louise Winter Institute 2025)

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Daniel Durnford

CAP Congress 2025

20/30

Atmospheric neutrino measurements

Results competitive with long baseline accelerator measurements

Two separate analyses

Complementary to other experimental methods:

Higher energy regime
Include tau lepton contribution
Different systematics

arXiv:2405.02163

K. DeHolton (Lake Louise Winter Institute 2025)

Canadian contribution

28 of 65

Daniel Durnford

CAP Congress 2025

21/30

Atmospheric neutrino measurements

Complimentary approach: tau appearance

Signal appears as excess of upgoing cascade-like events -> normalization factor

Phys. Rev. D 99, 032007 (2019)

Tau neutrino contribution

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Daniel Durnford

CAP Congress 2025

21/30

Atmospheric neutrino measurements

Complimentary approach: tau appearance

Signal appears as excess of upgoing cascade-like events -> normalization factor

11% 1σ sensitivity with DeepCore data

Phys. Rev. D 99, 032007 (2019)

IceCube: Work in Progress

Tau neutrino contribution

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Daniel Durnford

CAP Congress 2025

21/30

Atmospheric neutrino measurements

Complimentary approach: tau appearance

Signal appears as excess of upgoing cascade-like events -> normalization factor

11% 1σ sensitivity with DeepCore data

Phys. Rev. D 99, 032007 (2019)

Tau neutrino contribution

IceCube: Work in Progress

Where does IceCube go from here? How to improve on these results?

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Improved event classification

Daniel Durnford

CAP Congress 2025

22/30

More topological/geometry information that can be exploited for better event classification

Event PID:

Track-like

Cascade-like

Canadian contribution

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Improved event classification

Daniel Durnford

CAP Congress 2025

22/30

The Cryosphere, 18, 75–102, 2024

More topological/geometry information that can be exploited for better event classification

E.g. varying reconstruction quality because of dust layer

Dust

Canadian contribution

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Improved event classification

Daniel Durnford

CAP Congress 2025

22/30

PoS-ICRC2023-1003

The Cryosphere, 18, 75–102, 2024

More topological/geometry information that can be exploited for better event classification

E.g. varying reconstruction quality because of dust layer

Dust

Canadian contribution

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Improved event classification

Daniel Durnford

CAP Congress 2025

22/30

PoS-ICRC2023-1003

The Cryosphere, 18, 75–102, 2024

More topological/geometry information that can be exploited for better event classification

E.g. varying reconstruction quality because of dust layer

See talk by Akanksha Katil, immediately!

Canadian contribution

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IceCube calibration efforts

Daniel Durnford

CAP Congress 2025

23/30

J. Geophys. Res., 111:D13203, 2006

Ice optical models originally based on AMANDA measurements, assuming homogeneous light scattering and absorption in X-Y plane…

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IceCube calibration efforts

Daniel Durnford

CAP Congress 2025

24/30

Ice model details:

E. Bourbeau (2017)

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IceCube calibration efforts

Daniel Durnford

CAP Congress 2025

24/30

Still missing: an absolute, in situ calibration of the PMT efficiency

E. Bourbeau (2017)

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IceCube calibration efforts

Daniel Durnford

CAP Congress 2025

24/30

E. Bourbeau (2017)

Still missing: an absolute, in situ calibration of the PMT efficiency

Solution: atmospheric muons as calibration source

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PMT efficiency with muons

Daniel Durnford

CAP Congress 2025

25/30

The MINIONS [MINimum Ionizing muONS] sample:

A small subset of really nice muon events that are well reconstructed

Two “anchor features”; indicate that the track passed close to/through the PMT

Data event:

MINIONS reco

Endpoint

Anchor PMTs

Canadian contribution

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A small subset of really nice muon events that are well reconstructed

Two “anchor features”; indicate that the track passed close to/through the PMT

PMT efficiency with muons

Daniel Durnford

CAP Congress 2025

26/30

The MINIONS [MINimum Ionizing muONS] sample:

Data event:

MINIONS reco

Endpoint

Anchor PMTs

MC events: Track-anchor distance

Canadian contribution

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PMT efficiency with muons

Daniel Durnford

CAP Congress 2025

27/30

PMT efficiency measurement: simulate those specific muons with varying PMT efficiency values, compare to the real event

Data event:

MINIONS reco

Endpoint

Anchor PMTs

Simulated events

Canadian contribution

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IceCube Upgrade

Daniel Durnford

CAP Congress 2025

28/30

IceCube Upgrade: An in-fill expansion of the existing detector

7 additional strings in the core of the detector
3m vertical optical module spacing (compared to 7m for DeepCore)
Multi-PMT modules, dedicated calibration instruments including calibrated light sources, and cameras to observe the re-frozen ice in the deployment hole

Deployment is underway now! Expected completion during the next Antarctic summer season

PoS-ICRC2019-1031

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IceCube Upgrade

Daniel Durnford

CAP Congress 2025

39/30

Denser instrumentation will improve sensitivity to ~10 GeV atmospheric neutrinos (and improve reconstruction)

Greatly improved sensitivity for neutrino oscillation parameters after a few years of operation

arXiv:2307.15295

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Summary and outlook

Daniel Durnford

CAP Congress 2025

30/30

The IceCube neutrino observatory is a powerful tool for both astrophysics and particle physics research

Atmospheric neutrino measurements: competitive results for sin²𝜃₂₃ and ∆m₂₃, tau neutrino and neutrino mass ordering studies…

Future directions of improvement:

Calibration efforts to understand the ice and optical properties of the detector
ML event reconstruction algorithms
The IceCube Upgrade is being installed, will significantly improve both detector understanding and physics reach for oscillations studie

See talk by Prof. Kurahashi Neilson!

[Friday plenary]

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Extra slides

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Daniel Durnford

CAP Congress 2025

Construction took place over 5 years, completed in 2010

A deployment hole is made with a hot water drill, 2.5km into the ice sheet

The string, with 60 DOMs, is lowered on into the hole, which then refreezes

Image source

The IceCube neutrino observatory

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The IceCube neutrino observatory

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Astrophysics with IceCube

Daniel Durnford

CAP Congress 2025

Multi-messenger observation of

blazar TXS 0506+056:

Neutrinos can be used to identify and study astrophysical sources, provide early detection warnings to other observatories

Science, Vol 361, Issue 6398 (2018)

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Astrophysics with IceCube

Daniel Durnford

CAP Congress 2025

Measurement of the diffuse astrophysical neutrino flux

Phys. Rev. D 110, 022001 (2024)

Glashow resonance event

(~ 6 PeV neutrino)

Nature volume 591,

pg. 220–224 (2021)

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Daniel Durnford

CAP Congress 2025

Phys. Rev. D 111, 112001 (2025)

Neutrino inelasticity measurement with atmospheric neutrinos

Neutrino physics

Canadian contribution

52 of 65

Daniel Durnford

CAP Congress 2025

Neutrino physics

Phys. Rev. D 104, 022001 (2021)

Measurement of all-flavour neutrino cross-section with diffuse HE neutrinos; use the Earth as a target!

Flux ratio IceCube:Surface, assuming nominal cross-section

53 of 65

Atmospheric neutrinos

Daniel Durnford

CAP Congress 2025

54 of 65

Daniel Durnford

CAP Congress 2025

Atmospheric neutrino measurements

Phys. Rev. D 108, 012014 (2023)

Typical analysis procedure:

Event selection to suppress backgrounds
Classify events, apply reconstructions (energy, zenith)
Forward-folding analysis: produce MC for proposed sin²𝜃₂₃ and ∆m₂₃, apply same selection and reconstructions
Binned fit of data (in energy, zenith, and PID bins)

Canadian contribution

55 of 65

Daniel Durnford

CAP Congress 2025

Atmospheric neutrino measurements

Phys. Rev. D 108, 012014 (2023)

Energy reconstruction performance

Event PID:

Track-like

Cascade-like

Typical analysis procedure:

Event selection to suppress backgrounds
Classify events, apply reconstructions (energy, zenith)
Forward-folding analysis: produce MC for proposed sin²𝜃₂₃ and ∆m₂₃, apply same selection and reconstructions
Binned fit of data (in energy, zenith, and PID bins)

Canadian contribution

56 of 65

Daniel Durnford

CAP Congress 2025

Atmospheric neutrino measurements

Observed events at final level:

Cascade-like

Track-like

Mixed

arXiv:2405.02163

Canadian contribution

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IceCube calibration efforts

Daniel Durnford

CAP Congress 2025

The Cryosphere, 18, 75–102 (2024)

Ice model - fine details:

arxiv:2107.08692

Ice model includes the tilt of the ice sheet, birefringence effect from flow of the ice -> preferential refraction along the axis of flow

Modelling of the bubbly “hole ice”, from refreezing of the deployment holes

Measurement of dust layers in the ice

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PMT efficiency with muons

Daniel Durnford

CAP Congress 2025

Several kHz of atmospheric muons per second

A high rate, ~homogeneous, isotropic calibration source, of well-understood events!

Canadian contribution

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PMT efficiency with muons

Daniel Durnford

CAP Congress 2025

Step 1: Look for a small subset of really nice muon events that are well reconstructed, e.g. good spatial reconstruction, ideally no large stochastic energy losses, single muons only…

Canadian contribution

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PMT efficiency with muons

Daniel Durnford

CAP Congress 2025

Step 1: Look for a small subset of really nice muon events that are well reconstructed, e.g. good spatial reconstruction, ideally no large stochastic energy losses, single muons only…

Look for “anchor features”, cases where one PMT sees an unusually large amount of light compared to its neighbours - indicates (hopefully) that the track passed really close to the PMT

Canadian contribution

61 of 65

PMT efficiency with muons

Daniel Durnford

CAP Congress 2025

Step 1: Look for a small subset of really nice muon events that are well reconstructed, e.g. good spatial reconstruction, ideally no large stochastic energy losses, single muons only…

Look for “anchor features”, cases where one PMT sees an unusually large amount of light compared to its neighbours - indicates (hopefully) that the track passed really close to the PMT

Find two of these anchor features, spaced apart, and you have a robustly-reconstructed event!

Canadian contribution

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Minimum ionizing muons (MIMs): less energy lost to stochastic, radiative processes

These can provide a source of fairly uniform, “standard candle” calibration events!

D. Groom et al, Atomic Data and Nuclear Tables 76, 2 (2001)

Minimum ionizing muons

Daniel Durnford

CAP Congress 2025

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MINIONS events

Daniel Durnford

CAP Congress 2025

IC DOM

DC DOM

Weighted Charge Density (WCD)

Total charge in a cylindrical volume (around a given point, oriented by a given track)

DC charge scaled by 1/1.35

Normalized by # of DOMs in the volume

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MINIONS events

Daniel Durnford

CAP Congress 2025

Weighted Charge Density (WCD)

Total charge in a cylindrical volume (around a given point, oriented by a given track)

DC charge scaled by 1/1.35

Normalized by # of DOMs in the volume

Distribution of WCD for sample of single muon MC events, 200m segments with no stochastic losses

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PMT efficiency with muons

Daniel Durnford

CAP Congress 2025

Lots of MINIONS events! ~10⁵ per year

Student project: use MINIONS events to perform data-driven test of reconstruction methods

Anchor PMTs

MINIONS_reco

Canadian contribution

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