Measuring Oscillations with a Million Atmospheric Neutrinos

Measuring Oscillations with a Million Atmospheric Neutrinos

Illustrated tale of a hard and beautiful project

C.A. Argüelles, Pablo F., I. Martínez-Soler, Miaochen Jin 2022/11/23– XIV CPAN days

[arXiv:2211.02666]

Introduction

● Sensitivity achievable by the current and near-

future water(ice)-Cherenkov atmospheric neutrino experiments in the context of standard three-flavor neutrinos oscillations

● Perform an in-depth analysis of the current shared systematic uncertainties arising from the common flux and neutrino-water interactions

● Develop the atmospheric neutrino simulations for Super-Kamiokande (SK), with and without

neutron-tagging capabilities (SuperK-Gd), IceCube-Upgrade, and ORCA experiments

● Implement the systematic uncertainties of each experiment

Neutrino (3f) Oscillations

Atm. neutrinos are good discovery experiments, they cover ten orders of magnitude in the ratio of baseline to energy, L/E^ν

This broad range of L/E^ν and the fact that atmospheric neutrinos go through the largest amounts of matter allow them to measure neutrino osc. parameters In the 3ν scenario, neutrino evolution is described by six parameters: two

mass-squared differences, three mixing angles, and a complex phase parameterizing the violation of the CP-symmetry

This analysis focuses on the study of θ²³, Δm³¹² (including the MO) θ¹³ and δ^CP

P_νl→νl'

(

)

^∑

Neutrino (3f) Oscillations

The ordering and θ¹³

Ordering flips the MSW resonance between neutrinos (NO) and antineutrinos (IO) Position and intensity depends on θ¹³

Neutrino (3f) Oscillations

● CP-violation results in a different normalization of the probability and a shift in the oscillation phase.

Broad in energy and more relevant at sub-GeV

● In the multi-GeV scale, the neutrino oscillation is dominated by ∆m³¹ and θ²³ the oscillation

amplitude is controlled by sin²2θ²³

2

Atm. neutrino flux

Atmospheric neutrinos are produced by the collision of cosmic rays with Earth’s atmosphere

The primary spectrum of cosmic rays spans from MeV to EeV energies and is composed of free protons ( 80%) and bound nuclei ( 20%)∼ ∼

Their interaction with nuclei in the atmosphere

initiates hadronic showers on average about 20 km above the surface, producing numerous mesons Neutrinos are produced predominantly from the decay of muon, pion, and kaon;

which dominate the muon neutrino flux below 10, 100, and 10⁶ GeV

Cross-sections

All three experiments considered in this work also share the neutrino cross-sections on water

In WC detectors, mainly neutrinos interacting charged current (CC) are reconstructed. Only a small fraction of neutral current (NC) interactions can produce a

detectable signal

The flavor of CC neutrinos can be very efficiently

reconstructed through the corresponding charged-lepton, whereas in NC no flavor information can be extracted.

The wide energy range of atm neutrinos cover many interaction channels:

● Charged current quasi-elastic (CCQE)

● Resonance production (CC RES)

● Deep Inelastic Scattering (CC DIS)

Experiments: IceCube-Upgrade

IceCube is a 1 km3 ice-Cherenkov detector at the South Pole with 5160 optical sensors at depths between 1450 m and 2450 m

DeepCore is a ~10 Mton denser sub-array in the inner part of the detector

IceCube is planning an upgrade that will add strings to have a denser region, lowering the threshold to 1 GeV

There are two event morphologies:

● Tracks: propagation of muons

● Cascades: produced by the propagation of electrons, taus, or hadronic cascades

We use the official IC-Upgrade simulation published by the collaboration

Experiments: IceCube-Upgrade

Experiments: KM3NeT/ORCA

Water-Cherenkov neutrino telescope under construction in the Mediterranean sea,

KM3NeT

● ARCA: TeV-PeV neutrino astronomy

● ORCA will be a ~8 Mton detector with 64170 PMTs, achieving an energy

threshold of ~2 GeV

Already an official projection of its sensitivity to neutrino oscillations

Well advanced analysis with a third event category in addition to tracks and

cascades

Unfortunately, no public MC simulation; we produced our own by re-weighting and

extending the MC from IC-Up to reproduce their results

Experiments: KM3NeT/ORCA

Tracks

Experiments: Super-Kamiokande

Super-Kamiokande is a Japanese 50-kton cylindrical water-Cherenkov detector,

instrumented with ~11,000 20-inch PMTs facing inwards

The large photo-coverage and more

controlled medium enables a (n effective) energy threshold of 0.1 GeV for atm.

neutrinos

Now, being upgraded dissolving Gd to tag neutrons very efficiently (Nataly’s talk)

More than 15 rather complex event categories with no publicly available simulation… things get interestingly hard

Using publicly available information, we produced simulations for SK, SK with neutron tagging on H, and SK with neutron tagging on Gd

Experiments: Super-Kamiokande

δ^CP senstivity MO senstivity

Experiments: Super-Kamiokande

Results

We conservatively assume the running of SuperK until the last reported

exposure time, the SK-Gd and IceCube- Upgrade data-taking period extending from 2025 until 2030, and ORCA from 2027 to 2030

Assuming latest global fit values:

The “atmospheric” parameters

Resolving the θ²³ octant and measure Δm³¹² with great precision

Results

Sensitivity to θ¹³ comparable with

LBL experiments Synergies between experiments

most relevant in δ^CP sensitvity

Results

Measurement of the ordering

before the end of the decade Significant fraction of δ^CP excluded at 99% CL (largely depends on the actual value)

Results; present and future

Independent, comparable (even better) sensitivities than current LBL experiments (ideal for weighing in tensions)

Very valuable input for next-generation experiments and the precise measurement of the CP-phase

Results; present and future

Current ancillary measurements (both flux and cross-section) for next-generation experiments could significantly reduce relevant systematic uncertainties dragging the sensitivity to the CP-phase

Bonus: Intermediate WC Detector (IWCD)

Of particular (and biased) interest is the IWCD, within the HyperK project

● ~400 ton instrumented with ~500 mPMTs, located ~750 m from J-PARC ν-beam

● Large statistics of muon and electron (anti)neutrinos in the subGeV region

● Crucial for reducing CCQE systematics

Conclusions

First in-depth analysis of the potential of a combined fit with data from current and soon-to-operate WC atm. neutrino experiments

● Strong constraints on the atmospheric mixing parameters

– Resolves the octant of θ²³

– Precise measurement of Δm³¹

– Measurement of the mass ordering above 5σ

– Measurement of θ¹³ with similar precision as current LBL experiments

– Significant constraints on of δ^CP independently/complementary to LBL experiments

● Provides a comprehensive picture of the 3-flavor mixing and very valuable input for next-generation neutrino oscillation experiments (DUNE and HyperK)

● Ordering information also crucial for next-generation ββ0ν searches

2

Conclusions

● Provides input for the key improvements in flux and cross-section uncertainties, especially for the sensitivity to δ^CP

– Will benefit from ongoing task force systematic errors reduction towards next-generation experiments

● Machinery ready for properly including atm. neutrinos in global fits, crucial requirement for complete description of neutrino mixing with current data

● Opens the door to other very interesting analyses… (coming soon)