Atmospheric Neutrinos and the Quest for Neutrino Oscillations

1
Other Atmospheric Neutrino Experiments (past)
present and future
Hugh Gallagher Tufts University June 15,
2004 Neutrino 2004 College de France
2
Introduction

• In less than two decades, atmospheric neutrinos
  have gone from being anomalous to being one of
  our main tools for exploration of the lepton
  sector.
• 1980s 1990s Skepticism was rampant!
• Neutrino experiments are hard!
• Cosmic ray experiments are hard!
• Oscillation experiments are hard!

Since 1998 the experimental evidence from
SuperK, MACRO and Soudan 2 for atmospheric
neutrino oscillations has been overwhelming.
Now that neutrino oscillations are established,
is there still a role for atmospheric neutrinos
to play in the experimental study of neutrino
oscillations?
3
Experimental Goals - Present

• One set of experimental questions around the
  goal of confirming or refuting the standard
  picture of neutrino oscillations.
• Mixing between 3 active flavors of neutrinos
  through neutrino oscillations.
• No sterile mixing.
• No CPT violation.
• Majorana masses, small via see-saw mechanism.
• Experimental goals
• Confirmation with multiple independent
  measurements
• Observing oscillations
• Confirming nm? nt through nt appearance
• Ruling out mixing to sterile neutrinos
• Ruling out various alternative hypotheses
  decoherence, neutrino decay, CPT violation in the
  neutrino sector, violation of Lorentz invariance

NC detection np ? np J. Beacom and S.
Palomares-Ruiz PRD 67 (2003)
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Current Experiments

• These goals, as well as the measurement of Dm223
  and sin2(2q23), have been the focus of the
  current generation of experiments.

1. Soudan 2
2. MACRO
3. MINOS
4. SNO

Final or nearly final analyses
Preliminary analyses
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Soudan 2 The Detector
224 1m x 1m x 2.7 m modules 963 ton total
mass 5.90 fiducial kton-yr exposure
The detector is surrounded by a 1700 m2 veto
shield which provides nearly 4p coverage for the
identification of charged particles entering /
exiting the detector cavern.
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Soudan 2

Partially contained events ltEngt 6 GeV
Contained events ltEngt 1 GeV
nm multiprong
Up-stopping muons lt Engt 6.2 GeV
In-down muons ltEngt 2.4 GeV

• 3 flavor categories (ne CC, nm CC, NC)
• 2 bins of resolution (hi and low resolution)
• Data corrected for neutral backgrounds (6
• in hi-resolution samples)

ne quasi-elastic
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Soudan 2
Flavor tag
? e NC
?? 1466 46 76
?e 67 1337 72
NC 123 111 77
True flavor
Corrected for mis-id
note scale
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Soudan 2
Perform a Feldman-Cousins analysis using unbinned
maximum likelihood assuming nm ? nt. Flux
normalization and background amounts (7
parameters) allowed to float at each point in
(Dm2, sin2(2q)) plane. Nuisance
Parameters e-energy calibration 7 m-energy
calibration 3 Flux shape (1 b
En) sb 0.005 GeV-1 e/m ratio
5 Qel/inelastic s
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D ln L
sin2(2q)
log10(Dm2)
M. Sanchez et al, PRD 68, 113004 (2003)
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Soudan 2 Results
Best Fit ?m2 0.0052 eV2 sin22?
0.97 fn(data/mc) 0.90 MC ? Bartol '96
Inclusion of systematic errors and application of
Feldman- Cousins technique substantially increases
the size of the 90 CL region.
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Soudan 2 Upgoing Muons
A sample of 45 events entering or exiting the
bottom of the detector have been isolated.
Work is underway to incorporate them into the
oscillation fits.
Scan Category MC Truth (no osc.) MC Truth (no osc.) Data
Scan Category In-Down Up-Stop Data
In-down 13.31.4 0.70.2 17
Up-stop 1.90.5 58.41.9 26
Ambigs 0.90.4 3.60.5 2
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MACRO

• 5.3 kton detector located in the
• Gran Sasso laboratory
• 40 CR m ? 1989 2000
• 3 atmos n samples
• Up-throughgoing m
• In-up going
• In-down Up-stop

Scintillator layers for timing (0.5 ns) Streamer
tubes for tracking (1 cm)
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MACRO Up-going m
Produced by neutrino interactions in rock below
detector. Shape of distribution known to
5 Normalization uncertain to 25 2 independent
analyses yield consistent results.
Estimate E and
MC predictions assume oscillations with the MACRO
parameters sin2(2q) 1 , Dm2 0.0023 eV2
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MACRO m Energy Calibration
Energy estimated from muon multiple Coulomb
scattering. Use drift time in streamers to get
sx 3 mm.
Calibrated in test beam runs at the CERN PS and
SPS. Muon energy estimated using a neural
network with 7 inputs, 1 hidden layer and a
single output. Global En resolution is 150.
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MACRO
2 low energy samples
InUp Identified by topological criteria and
time-of-flight. Expect to be fully oscillated.
UpStop InDown Identified by topology UpStop ?
fully oscillated InDown ? unoscillated
Ratio InUp/ (UpStopInDown) Known to 6
FLUKA MC Prediction (no oscillation) Oscillation
s with MACRO parameters
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MACRO

• Monte Carlo studies are carried out to find
• the flux normalization independent statistics
• most senstive to oscillations.
• Vertical (cosqlt-0.7) / Horizontal (cosqgt-0.4)
• Upward Throughgoing muons
• Nlow (Enlt30 GeV) / Nhigh (Engt130 GeV)
• InUp / (InDown UpStop)

Category Ndetected Rmeassstat Rt R0s0
Vertical/ Horizontal 547.3 1.38 0.12 1.61 2.11 0.13
Nlow/ Nhigh 100.5 0.85 0.16 1.00 1.50 0.25
InUp/ (InDownUpStop) 418.4 0.60 0.06 0.56 0.745 0.06
Ambrosio et al, Measurements of Atmospheric
Muon Neutrino Oscillations, submitted to
EPJ. Ambrosio et al, Phys Lett. B 566, (2003)
35. Ambrosio et al, NIM A 492, (2002) 376.
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MACRO
10 bin angular distribution of up-through events
Use Feldman-Cousins procedure to account for
physical boundary. Best fit sin2(2q)1 --
Dm20.0023 eV2
(Nlow, Nhigh)
(InDownUpStop, InUp)
a parameters normalize the data to the
prediction in each category. Absolute rate of
the UpThrough events is not used because of the
uncertainty in the flux at high energy.
Suggest increase in flux normalization of 25
at high energy 12 at low energy
Vertical / horizontal rate sensitive to matter
effects nm ? ns excluded at 99.8 CL
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MINOS Far Detector
5.4 kton long baseline detector 2 2.7 kton
supermodules Fermilab beam on schedule for
late 2004.

• Alternating 8m octagonal planes
• 1 inch thick steel
• 192 4.1 cm x 1cm plastic
• scintillator strips with embedded
• WLS fiber

Scintillator panel veto shield
Average 1.5 T magnetic field 8-fold optical
multiplexing at face of 16 channel Hammamatsu
PMTs. Scintillator layers rotated by 45o for
3d tracking.
2-ended readout
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MINOS Cosmic Ray Data
First detector capable of separating n from n
interactions Contained events, up-going
stopping muons, and neutrino-induced throughgoing
muons. Muon energy determined by range or
curvature, track direction from timing or
curvature.
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MINOS Atmospheric Neutrinos

• Thursdays MINOS talk will include results from 2
  preliminary analyses on
• data taken September 2002 April 2004.
• throughgoing muons
• contained events (1.85 fiducial-kiloton years)

Neutrino Sky Map Muon direction for
neutrino-induced throughgoing muons.
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Sudbury Neutrino Observatory
SNO Not just a solar neutrino detector CR m,
atmospheric neutrinos, spallation products
Large overburden means that one can look for
throughgoing muons from neutrino interactions
from above the horizon.
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SNO
Analysis of 730 live-days data is proceeding.
Data above the horizon is unoscillated, Determines
the flux normalization ? Powerful lever arm for
an oscillation fit.
Normalization region
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Experimental Goals - Future
The Future Precision Measurements of the PMNS
Matrix!

• Experimental Questions include
• Better precision on masses and mixing angles
• Is sin2(2q23) different from unity?
• Determination of sin(q23 )
• Measurement of non-zero q13
• Measurement of dCP
• Normal or Inverted mass hierarchy
• Neutrino mass scales Dirac or Majorana
  particles

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Atmospheric Neutrinos -- Future

• Atmospheric neutrino experiments have sensitivity
  to all of the above experimental questions except
  those related directly to the neutrino mass.
• Measurements will be of subtle effects,
  particularly those brought about by matter
  effects.
• Future experiments will require reduction of
  experimental uncertainties through improved
  models of atmospheric neutrino fluxes and
  neutrino interaction cross sections on nuclear
  targets.
• Future detectors will be large (100kton Mton)
  and
• explore multiple physics topics
• Proton decay
• Long-baseline detectors
• Atmospheric neutrinos

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INO India-based Neutrino Observatory
A possible design
1965 first detection of atmospheric neutrinos
in the Kolar Gold Fields Phase I Atmospheric
neutrinos Phase II Very long baseline n
detector

• 30-50 kton magnetized steel
• 140 layers of 6 cm thick Fe plates
• 2.5 cm air gap containing RPCs
• ns timing for direction resolution
• 1-1.3 T magnetic field for good momentum
• resolution and charge determination
• 2 sites under consideration
• Explore mass hierarchy through n / n

25
UNO Undergound Nucleon Decay and Neutrino
Observatory
Scales up a proven technology 650 kton (440 fid)
water Cerenkov detector. 3 60 x 60 x 60 m3
optically isolated cubes. 10-40-10 PMT
coverage. Considering various underground
sites Henderson mine is leading candidate.

• Proton decay at 1035 yr sensitivity
• Atmospheric neutrinos
• Astrophysical neutrino observatory
• Supernova relic neutrino detection
• Long baseline neutrino detector
• Possible centerpiece for a
• US National Underground Lab

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Future Icarus

• An observation of atmospheric neutrino events
  with very high quality
• An unbiased, mostly systematic free, observation
  of atmospheric neutrino events
• CC/NC separation, clean e/µ discrimination, all
  final states accessible, excellent e/p0
  separation, particle identification (p/K/p) for
  slow particles
• An excellent reconstruction of incoming neutrino
  properties (energy and direction)

27
Future Icarus
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Frejus Laboratory
Considering options including 1 Mton water
Cerenkov 100 kt liquid Ar

• Site considerations
• good depth (at least 4800 mwe)
• good rock quality
• horizontal access
• good baseline for n superbeam, b beam
• centrally located

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Hyper-Kamiokande
1 Mton water Cerenkov detector follow-up to JHF
? SuperK with 4 MW superbeam
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Conclusions
90 CL intervals
Good consistency between results from SuperK,
Soudan 2, and MACRO. Non-SuperK atmospheric
neutrinos now in the hands of MINOS and
SNO. Future experiments will have sensitivity to
more of the PMNS matrix an independent check
of results from future long baseline beams with
completely different systematics.
Soudan 2
MACRO
SuperK