Nucleon Decay Searches in DUNE Viktor P , The University of - - PowerPoint PPT Presentation

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Nucleon Decay Searches in DUNE Viktor P , The University of - - PowerPoint PPT Presentation

Jan 22, 2023 567 likes •760 views

Nucleon Decay Searches in DUNE Viktor P , The University of Sheffield for the DUNE collaboration BLV 2019, Madrid October 22nd, 2019 Deep Underground Neutrino Experiment (DUNE) Location SURF, 1.5 km underground, Lead, South Dakota,

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SLIDE 1

Nucleon Decay Searches in DUNE

Viktor Pěč, The University of Sheffield for the DUNE collaboration BLV 2019, Madrid October 22nd, 2019

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SLIDE 2

Deep Underground Neutrino Experiment (DUNE)

  • Location
  • SURF, 1.5 km underground, Lead, South Dakota,
  • 1300 km from source
  • Neutrino source - beam @ Fermilab, Chicago, Illinois
  • powerful new beam of neutrinos

2

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SLIDE 3

Experimental Halls at SURF

  • 4 modules, 17.5 kt/10 kt fiducial LAr each
  • Modules
  • Cryostats 18.9 m (W) x 17.8 m (H) x 65.8 m (L), 17.5 kt of LAr

3

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SLIDE 4

DUNE Physics Programme

  • Neutrino oscillation (CP violation and mass hierarchy, mixing

parameters)

  • Supernova neutrinos
  • Nucleon decay and nn̅ oscillations

this talk

  • Planned to start with 1st module in 2026, remaining 3 modules

will be added sequentially

←

4

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SLIDE 5

Cathode Plane

Edrift

U V Y

Liquid Argon TPC Y wire plane waveforms V wire plane waveforms Sense Wires

t

I n c

  • m

i n g N e u t r i n

  • Charged Particles

X

X

γ γ γ γ γ

C C

Liquid Argon Time Projection Chamber — LArTPC

Basics of operation

  • electric field applied across drift volume
  • ionising particles create free charge — electrons drift

towards anode planes

  • multiple anode planes with readout wires with different
  • rientation → position in transversal plane
  • drift time + wire plane location → 3D reconstruction of

energy depositions

  • signal proportional to deposited energy → dE/dx

measurement — particle ID Anode planes

  • induction plane wires — electrons pass through
  • collection plane wires — last plane, all ionisation

electrons collected DUNE

  • collection plane (C) wires vertical
  • induction plane (U,V) wires 37.5º from vertical
  • wire pitch 5 mm

5

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SLIDE 6

Advantage of LArTPC

  • Can reconstruct tracks
  • Sees dE/dx profile
  • Can identify K in nucleon-to-K decays
  • Can classify different event topologies

6

Wire number Drift time C U V µ+ K+ e+ p → K+ + ¯ ν K+ → μ+ + νμ μ+ → e+ + ¯ νμ

  • Example of crisp proton-decay

event display

  • in 3 wire views

MC Simulation Signal

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SLIDE 7

Nucleon Decays

  • Potential of DUNE for some nucleon decays investigated:
  • ,

,

  • Backgrounds: atmospheric neutrino CC and NC interactions

p→ K𝛏̅

Key features

  • K Bragg peak near its decay
  • K-decay particles create unique tracks

Difficulties

  • proton decays in Ar → K may undergo Final State Interactions (FSI)

inside the nucleus

  • K loses energy and it is more difficult to reconstruct

p → K+¯ ν n → e−K+ p → e+π0

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SLIDE 8

Effect of FSI on K Track

  • Left: kinetic energies of kaons leaving Ar nucleus without and with FSI
  • Right: current tracking efficiency of kaons: reconstruction switches on
  • nly at about 40 MeV
  • Room for improvement

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50 100 150 200 250 300 Kaon Kinetic Energy (MeV) 100 200 300 400 500 600 700 800 Events

+

Primary K

+

Final State K 20 40 60 80 100 120 140 160 180 200 Kaon Kinetic Energy (MeV) 0.2 0.4 0.6 0.8 1 Tracking Efficiency

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SLIDE 9

p→ K𝛏̅ Background Events

  • Example of potential background events — atmospheric neutrino CC interaction
  • BDT multi-variate analysis used to classify events:
  • Left: well discriminated by the classifier (low score)
  • Right: poorly discriminated (high score)

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Low scoring High scoring 𝛏e + n → e- + p + 𝜌0 𝛏𝜈 + n → 𝜈- + p µ- e- p

Wire number Drift time Wire number Drift time

MC Simulation Atm.neutrinos

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SLIDE 10

Sensitivity to p→ K𝛏̅

  • Current analysis predicts signal efficiency

15% with background suppression of 3x10-6 (about 1 bg event per Mton-year or 25 years

  • f data taking)
  • Current K tracking efficiency only at 58%
  • Visual scanning of signal and background

events suggests 80% K tracking eff. achievable

  • If combined with improvements in K/p

separation, signal efficiency 15% → 30%

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0.35 0.4 0.45 0.5 0.55 0.6 0.65 BDT response Arbitrary Units

signal background

Sensitivity:

  • if no signal observed in 10 years, in full 40 kt

configuration

  • limit of 1.3 x 1034 years (90%CL) on partial

proton lifetime in p → K𝛏 channel

Systematics:

  • contribution of FSI effect unknown → 2%

uncertainty on signal efficiency

  • atmospheric neutrino flux and cross-section

uncertainties → 20% uncertainty in backgrounds

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SLIDE 11

n→e-K+

  • Similar analysis to p→ K𝛏̅ decay
  • Additional electron shower
  • Invariant mass ~1 GeV
  • Background: atmospheric neutrinos
  • Signal efficiency expected 47% with 15 bg events per Mton-year
  • Limit 1.1 x 1034 years in 400 kt-year exposure with 6

background events

  • → >2 x improvement of current limits

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SLIDE 12

p → e+𝜌0

  • Signature: 3 EM showers, invariant mass ~1 GeV
  • Background: atmospheric neutrinos
  • Preliminary analysis based on MC truth
  • Reconstruction only approximated
  • 8.7x1033 years to 1.1x1034 for exposure of 400 kt-year
  • dependent on reco. approximation (energy smearing)
  • Doubling the exposure would allow reaching current SK limit

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SLIDE 13

nn̅

  • Were nn̅ oscillations possible, neutrons would transform into

antineutron and quickly annihilate with surrounding nucleons

  • Oscillation time heavily suppressed for neutrons bound in

nucleus

  • Effective conversion time

relates to free neutron oscillation time :

  • Suppression factor calculated for iron [1]

Tn−¯

n

τn¯

n

τ 2

n−¯ n = Tn−¯ n

R fferent nuclei. ThisR = 0.666 × 1023s−1

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[1] Phys. Rev. D78 (2008) 016002

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SLIDE 14

nn̅

  • Annihilation produces multiple

pions

  • FSI can yield nucleons
  • Typical star-like signal
  • Invariant mass ~2 GeV
  • Vanishing total momentum

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MC Simulation Signal

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SLIDE 15

nn̅ Backgrounds

  • Atmospheric neutrino NC interactions

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Low scoring High scoring MC Simulation Atm.neutrinos

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SLIDE 16

Nn̅ Oscillation Time Limits

  • Analysis uses similar multi-variate

methods to nucleon decay searches

  • Bound neutron: 6.45 x 1032 years

@ 90% CL with 400 kt-year exposure (~10 years in full configuration)

  • After conversion to free neutron
  • scillation time:
  • 5.53 x 108 s
  • 2x improvement over the current

limits

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0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 BDT response Arbitrary Units

signal background

e 6.9: Boosted Decision Tree response for ¯ oscillation for signal (blue) and backgrou

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SLIDE 17

Summary

  • LArTPC new technology for nucleon decay searches
  • DUNE will be the largest LArTPC with sensitivities

complementary to large water Cherenkov detectors

  • p→ K𝛏̅ — potential improvement of current limits
  • n→e-K+— factor >2 improvement expected
  • p → e+𝜌0 — preliminary study suggests current limits reached
  • nly after double the exposure
  • nn̅ — factor 2 improvement on free neutron oscillation time
  • Observation 1 event can constitute compelling evidence

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