Neutrino Oscillations: The Next Steps?

1
Neutrino Oscillations The Next Steps?

• M. Shaevitz
• Columbia University
• WIN 05 Workshop
• Introduction
• MiniBooNE and LSND
• Determining q13 Reactor Oscillation Experiments
• (Next talks Feldman Long baseline
  oscillation experiments NovaMondal Next
  generation atmospheric exp. INO )

2
Possible New Surprises in the Next Step

• Sterile Neutrinos
• New type of neutrino
• No weak interactions (effectively no
  interactions)
• Produced by mixing with normal neutrinos
• Expected in many extensions to the standard model
  
• They would give a whole new spectrum of mass
  states and mixings
• ? MiniBooNE and follow-ups are key
• Probing for CP violation (and the mass
  hierarchy)
• CP violation comes about when a process has a
  different rate for particles and anti-particles
• CP violation in the neutrino mixing couldbe a
  key ingredient for explaining the
  matter-antimatter asymmetry in the universe
• Then look at ?n versus n oscillations to measure
  d
• ? New long baseline and reactor experiments are
  key

3
Possibility 1 The LSND Experiment ? Sterile
Neutrinos ?
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 evidence for
oscillation.
Oscillations?
LSND took data from 1993-98 - 49,000 Coulombs
of protons - L 30m and 20 lt Enlt 53 MeV
4
Why Sterile Neutrinos?

• Possible explanations
• One of the experimental measurements is wrong
• Explanations other that n osc.
• Additional sterile neutrinos involved in
  oscillations

Need better measurement in LSND region ?
MiniBooNE

• (M.Sorel, J.Conrad, M.Shaevitz, PRD
  70(2004)073004 (hep-ph/0305255) )

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Booster Neutrino Experiment(MiniBooNE)
Use protons from the Fermilab 8 GeV booster ?
Neutrino Beam ltEngt 1 GeV
MiniBooNE designed to check LSND signal by
searching for ne appearance in a nm beam at
Fermilab.
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MiniBooNE Neutrino Exp. At Fermilab
8 GeV Proton Beam Transport
50 m
One magnetic Horn, with Be target
Detector
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MiniBooNE Collaboration
Y. Liu, I. Stancu Alabama S. Koutsoliotas
Bucknell E. Hawker, R.A. Johnson, J.L. Raaf
Cincinnati T. Hart, R.H. Nelson, E.D. Zimmerman
Colorado A. Aguilar-Arevalo, L.Bugel, L.
Coney, J.M. Conrad, Z. Djurcic, J. Link, J.
Monroe, K. McConnel, D. Schmitz, M.H.
Shaevitz, M. Sorel, G.P. Zeller Columbia D.
Smith Embry Riddle
L.Bartoszek, C. Bhat, S J. Brice, B.C. Brown,
D.A. Finley, R. Ford, F.G.Garcia, P.
Kasper, T. Kobilarcik, I. Kourbanis, A.
Malensek, W. Marsh, P. Martin, F. Mills, C.
Moore, P. Nienaber, E. Prebys, A.D. Russell,
P. Spentzouris, R. Stefanski, T. Williams
Fermilab D. C. Cox, A. Green, H.-O. Meyer, R.
Tayloe Indiana G.T. Garvey, C. Green, W.C.
Louis, G.McGregor, S.McKenney, G.B. Mills, H.
Ray, V. Sandberg, B. Sapp, R. Schirato, R.
Van de Water, D.H. White Los Alamos R.
Imlay, W. Metcalf, M. Sung, M.O. Wascko
Louisiana State J. Cao, Y. Liu, B.P. Roe, H.
Yang Michigan A.O. Bazarko, P.D. Meyers,
R.B. Patterson, F.C. Shoemaker, H.A.Tanaka
Princeton B.T. Fleming Yale
MiniBooNE consists of about 70 scientists from 13
institutions.
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The MiniBooNE Detector

• 12 meter diameter sphere
• Filled with 950,000 liters (900 tons) of very
  pure mineral oil
• Light tight inner region with 1280
  photomultiplier tubes
• Outer veto region with 241 PMTs.
• Oscillation Search Method Look
  for ne events in a pure nm beam

(?? ? ?e and ??? ???e )
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Particle Identification

• Separation of ne from nm events
• Exiting nm events fire the veto
• Stopping nm events have a Michel electron after a
  few msec
• Cerenkov rings from outgoing particles
• Shows up as a ring of hits in the phototubes
  mounted inside the MiniBooNE sphere
• Pattern of phototube hits tells the particle type

Stopping muon event
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Muon Identification Signature m ? e nm
ne after 2msec
Charge (Size)
Time (Color)
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NuMI Beam Events in MiniBooNE(Worlds 1st
Offaxis Neutrino Measurement !!)

• MiniBooNE sees n events in the 8 ms NuMI beam
  window that agree with expectation.

? NuMI Offaxis beam will be a calibration
beam for MiniBooNE ( and we can look at
electron neutrino interactions)
(NuMI offaxis beam analysis done by Alexis
Aguilar-Arevalo)
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MiniBooNE Run Plan

• At the current time have collected
• 5.6 1020 protons on target (original goal
  was 1 1021)
• 600k neutrino candidates (worlds largest sample
  in the 1 GeV region)
• Blind analysis Hide possible ne candidates
  other 90 events are openPlan is to open the
  ne appearance box when the analysis has been
  substantiated and when sufficient data has been
  collected for a definitive result
  ? Current estimate is sometime in Late 2005

Next Step
Signal
No SignalLimit
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The Next Step

• If MiniBooNE sees no indications of oscillations
  with nm ? Need to run with?nm since
• LSND signal was?nm??ne (Indications
  of CP violation)

• If MiniBooNE sees an oscillation signal? Many
  ?m2 and mixing angles plus CP violation to
  determine
• ? BooNE Experiment (with ? and??) Add another
  detector to MiniBooNE at 1-2 km distance
  (Also nt appearance searches.)

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Possibility 2 CP Violation in Neutrino Mixing
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What do we know?
Solar ?12 30
Atmospheric ?23 45
sin2 2?13 lt 0.2 at 90 CL(or ?13 lt 13)
What is ?e component of ?3 mass eigenstate?
These two differentmass schemesare calledMass
HierarchyProblem
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Key questions

• What is value of ?13?
• What is mass hierarchy?
• Do neutrino oscillations violate CP symmetry?
• May give hints about possible Leptogenesis

CP violating phase ?sin? ? 0 ? CP Violation
sin ?13

• Why are quark and neutrino mixing matrices so
  different?

Value of ??3 central to these questions it sets
the scale for experiments needed to resolve mass
hierarchy and search for CP violation.
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Methods to measure sin22?13

• Long-Baseline Accelerators Appearance (nm?ne) at
  ?m2?2.5?10-3 eV2

NO?A ltE?gt 2.3 GeV, L 810 km
T2K ltE?gt 0.7 GeV, L 295 km
Currently pursued Offaxis Exps.

• Reactors Disappearance (?ne??ne) at ?m2?2.5?10-3
  eV2

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Reactor and Offaxis Exps. Are Complementary

• Reactor experiment needed for determining q13 ?
  Is q13 large enough?
• Then offaxis studies of n and?n give sensitivity
  to CP violation

Reactor Exp. Best for Determining q13
Reactor Can Lift q23 Degeneracy (Example sin22
?23 0.95 ? 0.01)
90 CL
?m2 2.510-3 eV2 sin22q13 0.05
McConnel /Shaevitzhep-ex/0409028
90 CL
?m2 2.510-3 eV2 sin22q13 0.05
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Reactor and Offaxis Exps. (contd)
Far future Precision Osc. Parameter
Measurements

• Other Guidance
• In many models, q13 could be very small ?
  sin22q13 lt 0.01 seems to be a dividing level for
  both theory and exp.
• Such a low level might imply a new underlying
  symmetry or change in theory paradigm
• Require longer baseline experiments to measure CP
  and mass hierarchy
• Measuring the full set of mixing parameters (q12,
  q13, q23, and d) is needed for addressing
  quark-lepton unification models.

90 CL
(Add Reactor)
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• Consensus Recommendation 2 (of 3)
• An expeditiously deployed multi-detector reactor
  experiment with sensitivity sin22q130.01
• A timely accelerator experiment with comparable
  sensitivity
• A proton driver with an appropriate very large
  detector

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Long History of ReactorNeutrino Measurements The
original neutrino discovery experiment, by Reines
and Cowan, used reactor anti-neutrinos
Reines and Cowan at the Savannah River Reactor
The first successful neutrino detector
The??e interacts with a free proton via inverse
ß-decay
Later the neutron captures giving a coincidence
signal. Reines and Cowan used cadmium to capture
the neutrons (modern exp. use Gadolinium)
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Reactor Measurements of ?13

• Nuclear reactors are a very intense sources of??e
  with a well understood spectrum
• 3 GW ? 61020?ne/s700 events / yr / ton at 1500
  m away
• Reactor spectrum peaks at 3.7 MeV
• Oscillation Max. for Dm22.5?10-3 eV2 at L near
  1500 m

• Disappearance Measurement Look for small rate
  deviation from 1/r2 measured at a near and
  far baselines
• Counting Experiment
• Compare events in near and far detector
• Energy Shape Experiment
• Compare energy spectrum in near and far detector

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Experimental Setup

• The reaction process is inverse ß-decay (IBD)
  followed by neutron capture
• Two part coincidence signal is crucial for
  background reduction.
• Positron energy spectrum implies the neutrino
  spectrum
• The scintillator will be doped with gadolinium to
  enhance capture

Liquid Scintillatorwith Gadolinium
Shielding
E? Evis 1.8 MeV 2me
n mGd ? m1Gd gs (8 MeV)
6 meters
Signal Positron signal Neutron signal within
100 msec (5 capture times)
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Precision Reactor Disappearance Exp. Are Difficult

• Looking for a small change in the expected rate
  and/or shape of the observed event

• How to do better than previous reactor
  experiments?
• ? Reduce systematic uncertainties due to
  reactor flux and detector
• Optimize baseline
• Larger detectors ? Reduce and control
  backgrounds

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How Do You Measure a Small Disappearance?

• Use identical near and far detectors to cancel
  many sources of systematics.

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Sin22?13 Reactor Experiment Basics
Well understood, isotropic source of electron
anti-neutrinos
Oscillations observed as a deficit of ?e
E?? 8 MeV
1.0
Unoscillated flux observed here
Probability ?e
Survival Probability
Distance
1200 to 1800 meters
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How Do You Measure a Small Disappearance?

• Use identical near and far detectors to cancel
  many sources of systematics.
• Design detectors to allow simple analysis cuts
  that will have reduced systematic uncertainty.

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Detector Design Basics

• Homogenous Volume
• Viewed by PMTs
• Coverage of 20 or better
• Gadolinium Loaded, Liquid Scintillator Target
• Enhances neutron capture
• Pure Mineral Oil Buffer
• To shield the scintillator from radioactivity in
  the PMT glass.

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How Do You Measure a Small Disappearance?

• Use identical near and far detectors to cancel
  many sources of systematics.
• Design detectors to eliminate the need for
  analysis cuts that may introduce systematic
  error.
• Detector cross calibration may be used to
  further reduce the near/far normalization
  systematic error.
• Use events and sources to cross calibrate
• For example, n capture peaks
• ? Move far detectors to near site for cross
  calibration

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How Do You Measure a Small Disappearance?

• Use identical near and far detectors to cancel
  many sources of systematics.
• Design detectors to eliminate the need for
  analysis cuts that may introduce systematic
  error.
• Detector cross calibration may be used to
  further reduce the near/far normalization
  systematic error.
• Reduce background rate and uncertainty

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Backgrounds

• Backgrounds are important since the
  signal/background ratios in the near and far
  detectors are different.
• Uncorrelated backgrounds from random coincidences
  are not a problem
• Reduced by limiting radioactive materials
• Directly measured from rates and random trigger
  setups
• Correlated backgrounds from
• Neutrons that mimic the coincidence signal
• Cosmogenically produced isotopes that decay to a
  beta and neutron (9Li and 8He)
• Veto system is the prime tool for
  tagging/eliminating and measuring the rate of
  these coincidence backgrounds

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How Do You Measure a Small Disappearance?

• Use identical near and far detectors to cancel
  many sources of systematics.
• Design detectors to eliminate the need for
  analysis cuts that may introduce systematic
  error.
• Detector cross calibration may be used to
  further reduce the near/far normalization
  systematic error.
• Reduce background rate and uncertainty
• Go as deep as you can
• Veto

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Veto Background Events
Fast neutrons Veto ms and shield neutrons
9Li and 8He

• Produced by a few cosmic ray muons through
  spallation
• Large fraction decay giving a correlated ßn

Shielding
KamLAND Data
A few second veto after every muon that deposits
more than 2 GeV in the detector or veto will
reduce this rate to an acceptable level.
6 meters
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How Do You Measure a Small Disappearance?

• Use identical near and far detectors to cancel
  many sources of systematics.
• Design detectors to eliminate the need for
  analysis cuts that may introduce systematic
  error.
• Detector cross calibration may be used to
  further reduce the near/far normalization
  systematic error.
• Reduce background rate and uncertainty
• Go as deep as you can
• Veto
• Use vetoed events to measure the background
• Redundant measurements to give convincing signal
• Multiple detectors at each site
• See osc. signal in both rate and spectral
  distortion

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Types of Measurements

• Counting (Rate) Measurement
• Compare total number of observed events in near
  and far detector
• Systematic uncertainty
• Relative near/far efficiency and normalization
• Fairly insensitive to relative energy
  calibrations
• Only method available for small detector exps
  (gt 300 ton-GW-yrs)

• Energy (Spectral) Shape Analysis
• Compare the energy distribution in the near and
  far detectors
• Systematic uncertainty
• Largest due to the energy calibration, offsets
  and scale
• Insensitive to relative normalization and
  efficiency
• Need large detectors in order to obtain required
  statistics(gt 2000 ton-GW-yrs)
• Need single baseline
• Multiple baselines may wash out energy variation

Best to design for both Rate and Shape
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Proposed Reactor Oscillation Experiments
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Comparisons of Proposed Reactor Oscillation
Experiments

• small sin22q130.02 to 0.03
• Goal fast experiment to explore region x3-4
  below the Chooz limit.
• Sensitivity through rate mainly
• Example Double-Chooz, Kashiwazaki experiments
  (300 GW-ton-yrs)
• medium sin22q13 0.005 to 0.01
• Make a discovery of q13 in region of interest for
  the next 10-20 year program
• Sensitivity enough to be complementary to offaxis
  measurements
• Sensitivity both to rate and energy shape
• Example Braidwood, Daya Bay (3000 GW-ton-yrs)
• large sin22q130.002-0.004??
• Measurement capability comparable to second
  generation offaxis experiments
• Sensitivity mainly through energy shape
  distortions
• MiniBooNE/Kamland sized detector (20,000
  GW-ton-yrs)

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Braidwood Reactor Experiment
Exelon Corporation - Enthusiastic and very
supportive of the project - VP has sent letter
of support to funding agencies - Security and
site access issues not a problem - Have helped
with bore holes at near/far locations
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Braidwood Experiment Design
Design Goals Flexibility, Redundancy, and
Cross Checks

• Four identical 65 ton detectors
• Outside Radius 3.5 m
• Fid. Radius 2.6 m
• Two zones (Inner Gd Scint, Outer Pure oil)
• Redundant detectors at each site
• Cross checks and flexibility
• Moveable detectors
• Allows direct cross calibration at near site
• Flat overburden at 450 mwe depth
• Optimized to use both rate and shape analysis
• Mitigate Correlated Backgroundwith extensive,
  active veto system

• Baseline Cost Estimate
• Civil Costs 34M 8.5M (Cont.)
• Detector and Veto System
  18M 5M (Cont.)
• Schedule
• 2004 RD proposal submission.
• 2005 Full proposal submission
• 2007 Project approval start const.
• 2010 Start data collection

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Braidwood90 CL Sensitivity vs Years of Data

• Information from both counting and shape fits
• Combined sensitivity for sin22q13 reaches the
  0.005 level after three years

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Braidwood Physics Reach

• For three years of Braidwood data and Dm2 gt 2.5 x
  10-3 eV2
• 90 CL limit at sin22q13 lt 0.005
• 3 s discovery for sin22q13 gt 0.013

Measurement Capability for sin22q13 0.02and
Dm2 2.5 x 10-3 eV2
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Other Physics Neutrino Electroweak Couplings

• At Braidwood can isolate about 10,000?ne e
  (elastic scattering) events in the near detector
  allowing the measurement of the neutrino gL2
  coupling to 1
• This is ?4 better than past n-e experiments and
  would give an error comparable to gL2(NuTeV)
  0.3001 ? 0.0014

gL2 - gL2(SM)

• Precision measurement possible since
• Measure elastic scattering relative to inverse
  beta decay (making this a ratio, not an
  absolute, measurement)
• Can pick a smart visible energy window (3-5 MeV)
  away from background

Braidwood is unique among q13 experiments in
having the potential to address this physics
because of having a near detector with high
shielding and high rate.
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Reactor Experiments Will Join a Strong Program
of Worldwide Neutrino Physics
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Summary

• Neutrinos have mass and flavor mixing
• Observed masses and differences are much smaller
  than charged lepton partners ??
• Mixings are very large ?? near 100 ??
• But expect small mixings if mn is from the
  See-Saw
• If all indications true, need to add more
  neutrinos (sterile, heavy?)
• Neutrinos may have an important role in producing
  the baryon-antibaryon asymmetry in the universe
• Need CP violation in the neutrino mixing
• Need sterile neutrinos (also needed for
  See-Saw)
• Are we on the verge of a next neutrino
  revolution?
• Many ideas and projects being proposed
  great time for young theorists and
  experimentalists to take the lead.

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Maybe it was the n?s !