The last five years in neutrino oscillations

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The last five years inneutrino oscillations

• Stan Wojcicki
• NuFact06
• Irvine, CA
• August 24, 2006

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Outline

• Introductory Comments
• Atmospheric regime
• Dominant oscillation mode
• Subdominant modes
• Solar regime
• Anomalies (LSND)

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Introductory HistoricalComments

• History of oscillations extends almost as far
  back as discovery of neutrinos (1956)
• Characterized by
• Theoretical speculations (Pontecorvo)
• Searches, ambiguous results, anomalies
• In my view the modern era of neutrino
  oscillations started with Neutrino98

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Late 80s, early 90s view
Theoretical view
1000 lb Gorilla
Any unbiased observer who has not been
brainwashed by recent speculations concerning
supersymmetry, axions, or galaxy formation would
undoubtedly conclude that the leading suspect
in the dark matter puzzle must be the light
neutrinoat the relevant mass range of 15-65 eV.
angle qtm mixes adjacent generations. It is
analogous to q23 in the quark sector. The
pattern of the charged lepton mass ratios is not
very much different from that of the quark mass
ratios. Most theoretical models expect mixing
angles to be somehow related to fermion masses.
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The Bottom Line

• Possible existence of neutrino oscillations with
  large mixing angles was viewed with scepticism
• To quote one of my colleagues
• There is no discovery potential. At best, you
  will be able to set an upper limit
• There was also scepticism about oscillations
  explaining solar anomaly - large mixing angles
  seemed to be required pre-MSW
• Most likely the solar neutrino problem has
  nothing whatsover to
• do with particle physics. It is a great
  triumph that astrophysicists
• are able to predict the number of B8
  neutrinos coming from the
• sun as well as they do, to within a factor of
  2 or 3.
• Quark mixing matrix and neutrino candidacy for
  being the dark matter explanation argued for high
  Dm2 and low sin22q

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1998 Status

• Three anomalies
• Atmospheric - too few nms
• Solar - too few nes
• LSND - appearance of ne-bars
• None of them well understood

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Nu98 - Tokayama

• This talk generated a phase transition in the
  status of neutrino oscillations
• Search for n oscillations became study of n
  oscillations
• Non-believers became believers

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Atmospheric region
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Neutrino98 - Kajita Talk

• Pre 98 atmospheric data gave strong indications
  of anomalous n behavior
• The anomalies involved m/e rates and ratios
• Angular asymmetry in nm events provided
  definitive evidence for nm disappearance

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Kajitas summary

• Contained events give best information on
  parameters
• Upgoing ms (from SuperK) give compatible
  contours
• Still very large uncertainty in Dm2

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Subsequent evolution
Higher statistics Improved analysis Better
modeling of atmospheric n flux and spectra
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Confirmation - Soudan2
Soudan2 has superior resolution over SuperK in
energy and zenith angle (hence L) That
partially compensates for much lower
statistics (1 kt vs 22.5 kt in SuperK)
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Confirmation - MACRO
FLUKA MC Prediction (no oscillation)
Suggest increase in flux normalization of 25
at high energy 12 at low energy
Oscillations with MACRO parameters
sin2(2q) 1 , Dm2 0.0023 eV2
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Parameter measurement

• In atmospheric n experiments, different data
  determine Dm223 and sin2(2q23)
• Ratio of vertical up vs down ns gives sin2(2q23)
  (relatively bias free)
• Dependence of survival probability at equatorial
  angles gives Dm223 (much more delicate
  measurement)
• In accelerator experiments position of dip in the
  spectrum (L/E) determines Dm223 (2), depth of the
  dip the value of sin2(2q23) (1)

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SuperK L/E Analysis

• By selecting events with very good measurement of
  L/E on can search for the dip in nm data/MC ratio
• This analysis gives another measurement of the
  oscillation parameters
• And provides discrimination against other
  hypotheses

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1st accelerator expt K2K
Experiment using SuperK and a nm beam from K2K
with L250km
Best fit parameters Maximum mixing Dm2 2.8 x
10-3
107 events observed 151-11 expected (no osc)
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MINOS in NuMI Beam
Design parameters 120 GeV protons
1.87 s min cycle time
10 msec extraction 4 x 1013
protons/pulse 0.4 MW
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MINOS run overview
MINOS has reported results from its first run,
May-December, 2005, based on 1.27E20 POT.
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Detector and events
Neutrino view of MINOS
nm CC NC ne CC
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Understanding the spectra
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CC/NC separation
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PID variable in ND, FD
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Fits to FD spectra
Contour includes systematics effects
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Summary of results
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Summary contour plots
New SuperK results
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Search for ?? - SuperK
Apply topological cuts designed to enhance nt

• Likelihood analysis
• - Total ? excess 138 48(stat.)
  (14.8/-31.6)(sys.) ( 2.4 sigma)
• - Expected ? excess 78.4 26(sys.)

• Neural Net analysis
• - Total ? ?excess 134 48(stat.)
  (16/-27.2)(sys.) (2.4sigma)
• - Expected ? excess 78.4 27(sys.)

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Limits on sterile n
Sterile ns would give a signature of depletion
of NC interactions
Limit from SuperK lt25 Consistent with no
nsterile
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Subdominant mode nm-gtne (q13)
SuperK atmospheric n data is not very sensitive
here because the two transitions, nm-gtne and
ne-gtnm almost cancel each other ? Need to go to
other technique reactor flux measurement
CHOOZ result
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Subdominant mode - status
From Heeger Nu06
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Solar Region
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Solar anomaly
3 solutions - Smirnov 98
Pre-SuperK Neutrino96
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SuperK ne -gt ne
Identification of ne events Measurement
of 8B spectrum
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SNO Basic Idea(initially proposed by Herb Chen)

• Use deuterons (heavy water) as target
• This allows three separate measurements
• ne d -gt e- p p gives Fcc Fe
• nx d -gt nx p n gives Fnc Fe (Fm Ft)
• nx e- -gt nx e- gives Fes Fe .154(Fm
  Ft)
• Each measurement gives a line in the space
  defined by Fe and (Fm Ft)
• In MSW picture, the ratio Fcc/FNC is equal to
  sin2q12

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SNO Results Summary
SNO n e
SuperK n e
CC
NC
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SNO Flux Results
FNC Ftot 4.94 .21(st).38-.34(sys)
FCC 1.68 .06.08-.09(sys)
sin2q12 FCC/ Ftot ne 0.5 NOT maximal mixing
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KamLAND Experiment

• 1 kton liq. Scint. Detector
• 1300 17 fast PMTs
• 700 20 large area PMTs
• 30 photocathode coverage

Source Reactors
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KamLAND Results (Rate)

• In 766.3 ton-yr exposure, there are
• 258 observed events
• 365 - 24 expected if
• no oscillations
• 17.8- 7.3 background events
• Observed energy spectrum is distorted

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KamLAND Spectrum
Observed/Expected
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SNO and KamLAND are complementary
SNO measures well sin2q12 KamLAND measures well
Dm212
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Combined Solar/KamLAND Fit
Solar
Solar KamLAND
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LSND Anomaly LSND Experiment
Results MiniBooNE
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LSND Experiment
Signal p ? e n n p ? d ? (2.2MeV)
Saw an excess of??e 87.9 22.4 6.0
events. With an oscillation probability of
(0.264 0.067 0.045). 3.8 s significance for
excess.
Oscillations?
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MiniBooNE Overview
12m diameter sphere 950,000 l mineral oil 10
PMT coverage 1280 inner PMTs Prompt Cerenkov
light Delayed scintillator light
500 m earth
Target and horn
P beam
Booster
Decay region
Detector
Secondary - hadrons
Tertiary - ns
Primary - p
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MiniBooNE Sensitivity
MiniBooNE aims to cover LSND region. Almost
there, with ongoing work on -accurate prediction
of rate -improved detector modeling -analysis of
misID-ed ?0 measurement in place
?
LSND best fit sin22? 0.003 ?m2 1.2 ev2
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Detector Checks
!
Michel electrons from ? decay E calibration
at low energy (52.8 MeV),
?0 mass peak energy scale resolution at medium
energy (135 MeV), reconstruction

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Check on ne/nm separation
There is a significant flux of ns from the NuMI
beam that intercept the MiniBooNE detector (at
100-250 mr) These contain a significant number
of nes from 3-body K decays
ne - like?
? nm - like
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Potential signal and background
Full data sample 5.3 x 1020 POT

• Oscillation ?e
• Example oscillation signal
• ?m2 1 eV2
• sin22? 0.004
• Fit for excess as function of reconstructed ?e
  energy

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Final Remarks

• Lot of progress in the last 8 years
• Neutrino oscillations appear to be established as
  dominant process responsible for original n
  anomalies
• We are in a phase of precision measurements of
  parameters
• There are still a number of unknowns ? the next
  talk

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SNO Results Summary
SuperK n e
Hime, Nu06
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KamLAND Spectrum
Observed/Expected
L0 180km
L0/E (km/MeV)
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KamLAND Results (Rate)

• In 766.3 ton-yr exposure, there are
• 258 observed events
• 365 - 24 expected if
• no oscillations
• 17.8- 7.3 background events
• Observed energy spectrum is distorted