Using Reactor Anti-Neutrinos to Measure sin22?13

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Using Reactor Anti-Neutrinos to Measure sin22?13
Byron, Illinois
Jonathan Link Columbia University Fermilab Long
Range Planning Committee, Neutrino
Session November 7, 2003
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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
Distance
1200 to 1800 meters
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Nuclear Reactors as a Neutrino Source

• Nuclear reactors are a very intense sources of
  ?e deriving from the b-decay of the neutron-rich
  fission fragments.
• Each fission liberates about 200 MeV of energy
  and generates about 6 electron anti-neutrinos.
  So for a typical commercial reactor (3 GW
  thermal energy)
• 3 GW 21021 MeV/s ? 61020 ne/s

From Bemporad, Gratta and Vogel
Arbitrary
Observable n Spectrum
Cross Section
Flux
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Reactor Neutrino Event Signature
The reaction process is inverse ß-decay (Used by
Reines and Cowan in the neutrino discovery
experiment) Two part coincidence signal is
crucial for background reduction. Minimum energy
for the primary signal of 1.022 MeV from ee-
annihilation at process threshold. Positron
energy spectrum implies the anti-neutrino
spectrum In pure scintillator the neutron would
capture on hydrogen Scintillator will be doped
with gadolinium which enhances capture
ne p? en n capture
E? Ee 0.8 MeV ( mn-mpme-1.022)
n H ? D g (2.2 MeV)
n mGd ? m1Gd gs (8 MeV)
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Detector Design Basics

• Larger version of CHOOZ (or smaller KamLAND)
• Homogenous Volume
• Viewed by PMTs (coverage of 20 or better)
• Gadolinium Loaded, Liquid Scintillator Target
  (50 tons)
• Pure Mineral Oil Buffer (To shield the
  scintillator from radioactive isotopes in the PMT
  glass)

Detector
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What is the Right Way to Design the
Experiment? Start with the dominate systematic
errors from previous experiments and work
backwards
CHOOZ Systematic Errors, Normalization
Near Detector
Vogel and Beacom have reduced this theoretical
error since CHOOZ
Identical Near and Far Detectors
The combination of these two plus a complex
analysis gives you the anti-neutrino flux
Movable Detectors
(All normalization errors reduce to one
measurable, relative efficiency error)
CHOOZ Background Error BG rate
0.9
Muon Veto and Neutron Shield (MVNS)
Statistics may also be a limiting factor in the
sensitivity, but we should design the experiment
to avoid this.
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Movable Detectors to Control Systematics
The far detector spends about 10 of the run at
the near site where the relative efficiency of
the two detectors is measured head-to-head.
Build in all the calibration tools needed for a
fixed detector system and verify them against the
head-to-head calibration.
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Reducing Background

1. Go as deep at you can (300 mwe ? 0.2 BG/ton/day
   at CHOOZ)

1. Veto ms and shield neutrons (Big effective
   depth)
2. Measure the recoil proton energy and extrapolate
   into the signal region. (Understand the BG that
   gets through and subtract it)

6 meters
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Characterizing BG with Vetoed Events
Matching distributions from vetoed events outside
the signal region to the non-veto events will
provide an estimate of correlated backgrounds
that evade the veto.

• Other Useful Distributions
• Spatial separation prompt and delayed events
• Faster neutrons go farther
• Radial distribution of events
• BGs accumulate on the outside of the detector.

n interactions
Proton recoils
?
From CHOOZ
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Sensitivity vs. ?m2
This is a full shape plus rate analysis, and
includes all sources of systematic error. At the
Super-K preferred ?m2 of 2?10-3, the sensitivity
to sin22?13 is 0.01 at 90 CL.
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Discovery Potential vs. Time
Rate only analysis
3s Discovery Potential
Preferred ?m2 from Super-K
After one year, the discovery potential is below
the 90 CL limit from Minos (sin22?13lt 0.06).
After three years the discovery potential is down
to 0.02 to 0.03.
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Is this program a good match for Fermilab?

• Detector Experience
• The detectors will be similar to the MiniBooNE
  detector.
• Tunneling Experience
• The size of the tunnel and the geology are
  similar to the NuMI beam line tunnel.
• Future machines at the lab will require deep
  tunnels and this project will help to maintain
  that expertise.
• Physics Parameters
• The value of sin22?13 is an important input for
  designing the future neutrino oscillation
  experimental program (e.g. NuMI Off-axis).

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Is this program a good match for Fermilab?
Top 30 U.S. Sites by Power Performance

• Overlap with Lab Theorists
• Stephen Parke, Boris Kayser, John Beacom, etc.
  have done a lot of work in this area.
• Administrative Structure
• Project management, safety training, etc. would
  have to be replicated for this project.
• Proximity to Reactor Sites
• Many of the best reactor sites in the U.S. are
  located in Illinios.

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Location of Reactors Near Fermilab
Byron
80 km
50 km
60 km
La Salle
Braidwood
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Experiment Timeline
2003
2004
2005
2006
2007
2008
2009
2010
2011
Years
Site Selection
Run
Construction
Proposal
1 year 2 years 2 years
3 years (initially)

• JHF-SK and NuMI Off-axis are both slated to
  start in 2009.
• This timeline could slip by 6 months and a well
  executed reactor experiment would still make the
  first observation of non-zero ?13.
• Even if its not first, a precise reactor
  measurement helps to resolve the degeneracies
  inherent in the off-axis experiments.

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Conclusions and Recommendation

• Nuclear reactors are an excellent source of
  anti-neutrinos to use for a ?e disappearance
  search related to sin22?13.
• Sensitivity to sin22?13 at the 0.01 level is
  possible if steps are taken to control systematic
  errors.
• Many of the best reactor sites in the U.S. are
  located in Illinois (and we have the support of
  Exelon to study the feasibility of an experiment
  at these reactors!)
• The reactor experiment is a good match to the
  physics and capabilities of the lab.

Recommendation Fermilab should participate in a
reactor based sin22?13 experiment, and should
pursue locating the experiment at an Illinois
reactor.