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Using Reactor Anti-Neutrinos to Measure sin 2 2 θ 13

Using Reactor Anti-Neutrinos to Measure sin 2 2 θ 13. Byron, Illinois. Jonathan Link Columbia University Fermilab Long Range Planning Committee, Neutrino Session November 7, 2003. Sin 2 2 θ 13 Reactor Experiment Basics. ν e. ν e. ν e. ν e. ν e. ν e. sin 2 2 θ 13.

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Using Reactor Anti-Neutrinos to Measure sin 2 2 θ 13

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  1. Using Reactor Anti-Neutrinos to Measure sin22θ13 Byron, Illinois Jonathan Link Columbia University Fermilab Long Range Planning Committee, Neutrino Session November 7, 2003

  2. Sin22θ13 Reactor Experiment Basics νe νe νe νe νe νe sin22θ13 Well understood, isotropic source of electron anti-neutrinos. Oscillations observed as a deficit of νe. Eν≤ 8 MeV 1.0 Unoscillated flux observed here. Probability νe Distance 1200 to 1800 meters Jonathan Link, Columbia University FLRPC Neutrino Public Meeting

  3. The observable n spectrum is the product of the flux and the cross section. • The spectrum peaks at ~3.7 MeV. Nuclear Reactors as a Neutrino Source • Nuclear reactors are a very intense sources of νe 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 ≈ 2×1021 MeV/s → 6×1020ne/s From Bemporad, Gratta and Vogel Arbitrary Observable n Spectrum Cross Section Flux Jonathan Link, Columbia University FLRPC Neutrino Public Meeting

  4. Reactor Neutrino Event Signature The reaction process is inverse β-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 e+e−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 nep→ e+n ncapture Eν = Ee + 0.8 MeV ( =mn-mp+me-1.022) nH → Dg (2.2 MeV) nmGd → m+1Gdg’s (8 MeV) Jonathan Link, Columbia University FLRPC Neutrino Public Meeting

  5. Detector Design Basics • Larger version of CHOOZ (or smaller KamLAND) • Homogenous Volume • Viewed by PMT’s (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 Jonathan Link, Columbia University FLRPC Neutrino Public Meeting

  6. 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 rate0.9% 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. Jonathan Link, Columbia University FLRPC Neutrino Public Meeting

  7. 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. Jonathan Link, Columbia University FLRPC Neutrino Public Meeting

  8. Veto Detectors p n n m m Reducing Background • Go as deep at you can (300 mwe → 0.2 BG/ton/day at CHOOZ) • Veto m’s and shield neutrons (Big effective depth) • Measure the recoil proton energy and extrapolate into the signal region. (Understand the BG that gets through and subtract it) 6 meters Jonathan Link, Columbia University FLRPC Neutrino Public Meeting

  9. 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 Jonathan Link, Columbia University FLRPC Neutrino Public Meeting

  10. Sensitivity vs. Δm2 This is a full shape plus rate analysis, and includes all sources of systematic error. At the Super-K preferred Δm2 of 210-3, the sensitivity to sin22θ13 is 0.01 at 90% CL. Jonathan Link, Columbia University FLRPC Neutrino Public Meeting

  11. Discovery Potential vs. Time Rate only analysis 3σ Discovery Potential Preferred Δm2 from Super-K After one year, the discovery potential is below the 90% CL limit from Minos (sin22θ13< 0.06). After three years the discovery potential is down to 0.02 to 0.03. Jonathan Link, Columbia University FLRPC Neutrino Public Meeting

  12. 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 sin22θ13 is an important input for designing the future neutrino oscillation experimental program (e.g. NuMI Off-axis). Jonathan Link, Columbia University FLRPC Neutrino Public Meeting

  13. 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. Jonathan Link, Columbia University FLRPC Neutrino Public Meeting

  14. Location of Reactors Near Fermilab Byron 80 km 50 km 60 km La Salle Braidwood Jonathan Link, Columbia University FLRPC Neutrino Public Meeting

  15. Experiment Timeline 2003 2004 2005 2006 2007 2008 2009 2010 2011 Years Site Selection Proposal Construction Run 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 θ13. • Even if it’s not first, a precise reactor measurement helps to resolve the degeneracies inherent in the off-axis experiments. Jonathan Link, Columbia University FLRPC Neutrino Public Meeting

  16. Conclusions and Recommendation • Nuclear reactors are an excellent source of anti-neutrinos to use for a νe disappearance search related to sin22θ13. • Sensitivity to sin22θ13 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 sin22θ13 experiment, and should pursue locating the experiment at an Illinois reactor. Jonathan Link, Columbia University FLRPC Neutrino Public Meeting

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