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

11/7/2003Jonathan Link, Columbia University FLRPC Neutrino Public Meeting νeνe νeνe νeνe νeνe νeνe νeνe Distance Probability ν e 1.0 E ν ≤ 8 MeV 1200 to 1800 meters Sin 2 2θ 13 Reactor Experiment Basics Unoscillated flux observed here. Well understood, isotropic source of electron anti-neutrinos. Oscillations observed as a deficit of ν e. sin 2 2θ 13

11/7/2003Jonathan Link, Columbia University FLRPC Neutrino Public Meeting Nuclear Reactors as a Neutrino Source Arbitrary Flux Cross Section Observable Spectrum The observable spectrum is the product of the flux and the cross section. The spectrum peaks at ~3.7 MeV. From Bemporad, Gratta and Vogel Nuclear reactors are a very intense sources of ν e deriving from the  -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 ≈ 2×10 21 MeV/s → 6×10 20 e /s

11/7/2003Jonathan Link, Columbia University FLRPC Neutrino Public Meeting 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 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 e p→ e + n n capture Reactor Neutrino Event Signature n H → D  (2.2 MeV) n m Gd → m+1 Gd  ’s (8 MeV) E ν = E e MeV ( =m n  m p +m e  1.022)

11/7/2003Jonathan Link, Columbia University FLRPC Neutrino Public Meeting Detector 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 Design Basics

11/7/2003Jonathan Link, Columbia University FLRPC Neutrino Public Meeting 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 CHOOZ Background Error BG rate 0.9% Statistics may also be a limiting factor in the sensitivity, but we should design the experiment to avoid this. Identical Near and Far Detectors Movable Detectors Muon Veto and Neutron Shield (MVNS) (All normalization errors reduce to one measurable, relative efficiency error) Vogel and Beacom have reduced this theoretical error since CHOOZ The combination of these two plus a complex analysis gives you the anti-neutrino flux

11/7/2003Jonathan Link, Columbia University FLRPC Neutrino Public Meeting 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.

11/7/2003Jonathan Link, Columbia University FLRPC Neutrino Public Meeting Veto Detectors p n   n 1.Go as deep at you can (300 mwe → 0.2 BG/ton/day at CHOOZ) Reducing Background 2.Veto  ’s and shield neutrons (Big effective depth) 3.Measure the recoil proton energy and extrapolate into the signal region. (Understand the BG that gets through and subtract it) 6 meters

11/7/2003Jonathan Link, Columbia University FLRPC Neutrino Public Meeting From CHOOZ  interactions ? 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. Proton recoils 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.

11/7/2003Jonathan Link, Columbia University FLRPC Neutrino Public Meeting Sensitivity vs. Δm 2 This is a full shape plus rate analysis, and includes all sources of systematic error. At the Super-K preferred Δm 2 of 2  10 -3, the sensitivity to sin 2 2θ 13 is 0.01 at 90% CL.

11/7/2003Jonathan Link, Columbia University FLRPC Neutrino Public Meeting Discovery Potential vs. Time After one year, the discovery potential is below the 90% CL limit from Minos (sin 2 2θ 13 < 0.06). 3σ Discovery Potential Rate only analysis Preferred Δm 2 from Super-K After three years the discovery potential is down to 0.02 to 0.03.

11/7/2003Jonathan Link, Columbia University FLRPC Neutrino Public Meeting 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 sin 2 2θ 13 is an important input for designing the future neutrino oscillation experimental program (e.g. NuMI Off-axis).

11/7/2003Jonathan Link, Columbia University FLRPC Neutrino Public Meeting Top 30 U.S. Sites by Power Performance Is this program a good match for Fermilab? 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.

11/7/2003Jonathan Link, Columbia University FLRPC Neutrino Public Meeting Braidwood La Salle Byron 80 km 60 km 50 km Location of Reactors Near Fermilab

11/7/2003Jonathan Link, Columbia University FLRPC Neutrino Public Meeting Site Selection 2010 Run 2011 Experiment Timeline Construction Years 1 year 2 years 2 years 3 years (initially) JHF-SK and NuMI Off-axis are both slated to start in This timeline could slip by 6 months and a well executed reactor experiment would still make the first observation of non-zero θ 13. Even if it’s not first, a precise reactor measurement helps to resolve the degeneracies inherent in the off-axis experiments. Proposal

11/7/2003Jonathan Link, Columbia University FLRPC Neutrino Public Meeting Conclusions and Recommendation Nuclear reactors are an excellent source of anti-neutrinos to use for a ν e disappearance search related to sin 2 2θ 13. Sensitivity to sin 2 2θ 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 sin 2 2θ 13 experiment, and should pursue locating the experiment at an Illinois reactor.