Future Sterile Neutrino Searches from Stopped Pions and Muons SNAC 11 VPI September 26-28, 2011 Gerry Garvey Los Alamos Nat. Lab.

Outline Introduction- Sterile Neutrino Searches with Stopped π + and μ + LSND Scope and Relevant Parameters for necessary improvement over LSND Possible Future Ventures o Osc-SNS o SK + Ga +1 GeV Acc. o NOVA +1 GeV Acc o LENA + 1 GeV Acc o ???

Why a Stopped Pion and Muon Source for Sterile Neutrinos? Stopping Time ~ sec production π absorption μ absorption All E ν < m μ c 2 L/E for phase change =π/2

Oscilla tion App. Or Dis Reaction in a CH 2 Detector A A D D D At L=0, ν μ τ= s, ν μ,ν e τ= s 12 B(gs) 12 N(gs) 12 C(gs) 12 C(15.11) Important: All cross sections for the processes listed above are known. The flux can also be established to <5%. The charged current interactions allow the incident neutrino energy to be determined. All different from 1GeV/1km experiments.

Need kiloton scale detectors and a several hundred kilowatt beam of ≈1GeV protons Scale of Detector Mass x 1 GeV Proton Flux

Cosmic Ray Background 1 kiloton detector ≈10 3 m 3 A≈10 2 m 2 μ CR rate at sea level = 10 2 x160=16,000 s -1 20% stop in detector creating Michel electrons Need small accelerator duty factor ( 1ktwe) Consider SNS: 60 H with 0.65μs/pulse.5 mA x 1kt produces 10 3 ν μ ν e events/year or 2x10 -6 /pulse With a 5μs trigger window there are 24 x 10 6 CR Michels triggers/y Need rejection of.5 x10 -5 (not difficult) At 1ktwe underground the CR rate is down by more than 10 3

Neutrino Time and Energy Distributions from Decay at Rest at SNS (0.69μs x 60H) Time (μs) Energy (MeV)

LSND found an excess of ν e from ν μ from a stopped μ + source at 33M. Signature: Cerenkov light from e + with delayed n-capture (2.2 MeV) Excess: 87.9 ± 22.4 ± 6.0 (3.8 σ ) The data was analysed under a two neutrino mixing hypothesis* — — KARMEN at a distance of 17 meters saw no evidence for an excess →low Δm 2 The LSND Excess Remains!!

Energy and Angular Distribution of Electrons in LSND 18x10 22 pot 8.3mx5.7mD 70 ton fiducial volume E e threshold 20 MeV mostly 12 C(ν e, e) 12 N(gs) Note νe elastic

OscSNS (low beam duty factor) Sterile Neutrino Oscillation Signals : White paper study to install upgraded version of the MiniBooNE detector at the SNS Beamstop (2008) Increased coverage, 1280 to ” pmts. 25% Add 31mg/l of butal-PPD for scint. 800 tons of mineral oil 60 m from beam dump to proton beam Relevant SNS design Parameters

OcsSNS (flux &CS) σ(cm 2 ) x E ν (MeV) neutrino- 12 C css E ν (MeV) x Un-oscillated neutrino fluxes: Through a 6m radius circle 60 m from the SNS target. Assume 2.7x10 23 protons per year Larger because 1.3 GeV and Hg target. No problem τ μ- =76ns in Hg ] M. Fukugita et al, Phys. Lett. B 212, 139 (1988).

OscSNS (event rates) 1 year, Fiducial volume cut at r=5M, ε=0.5, L=60M, osc. probability

OscSN (disapearance sensitivity) 1 year3 years

OscSNS (apearance sensitivity) 1 year3 years

Going Underground Sanjib K. Agarwalla, Patrick Huber: Physics Letters B 696 (2011) 359–361 Gd doped Super K to pursue the LSND appearance signal via sterile neutrino Neutron capture on Gd required to identify the reaction in H 2 O Super K is a water Cherenkov detector with 22.5 Kt cylindrical fiducial volume, r=14m, h=36m; with 2.7 kmwe overburden 300kW of 1 GeV protons to create the π + and μ + decay at rest provided via the Conrad and Shaevitz Daeδalus cyclotron scheme. A Δm 2 ~ 1ev 2 oscillation will be observed within the detector!

Bringing the “Accelerator to the Detector ” Detector underground, cyclotron constructed adjacent

1 GeV High Intensity Proton Accelerators SBL Workshop, Janet Conrad, MIT, May 14 Maybe??

Target Cnfiguraon Optimal Target Design for Minimum μ - /μ + Target Z SBL Workshop, Janet Conrad, MIT, May 14 Light target in heavy stopping material (cooled). Don’t stop μ - in C!! Proton Energy (GeV) E p =0.8 GeV ??

signal Δm eS 2 =2eV 2 sin 2 2θ eS =10 -3 background Sanjib K. Agarwalla, Patrick Huber : Physics Letters B 696 (2011) 359–361 1 year 5σ limit Oscillation visible within detector !! ΔL=1.0m, ΔE=15% Cherenkov light allows observation of ν e disappearance via e(ν e,ν e )e

Oscillation searches with Large Scintillation Detectors Agarwalla, Conrad ad Shaevitz: arXiv: v1 [hep-ph] Discuss the physics that can be done bringing cyclotrons to two large scintillation detectors NOVA (2013) and LENA(2020) Look to discriminate between 1 and 2 sterile neutrino scenarios. Appearance: 2 sterile 1 sterile Disappearance: 2 sterile 1 sterile

LENA – NOVA Comparison

M Shaevitz at SBWS FNAL May 2011

Cyclotron Co-located with Far NOVA Detector Detector to be completed in KT, 30% PV, CH 2 scintillator, 15.7 x 15.5 x 67 m 3 Segmented detector elements Overburden only 3m of earth Heavy CR rate Only go for ν e disappearance via ν e + 12 C e N(gs), 12 N(gs) e + +ν e + 12 C, τ 1/2 =11ms Backgrounds are Michel decays and 12 B decays Use visible energy threshhold of 20 MeV for trigger corresponds to E νe =38 MeV

Cyclotron Co-located with Far NOVA Detector 1 year of data M Shaevitz at SBWS FNAL May 2011 Results with new flux

arXiv: v2 M Shaevitz at SBWS FNAL May 2011

LENA Detector (Continued) In Addition: Light yield 50 times that of water Cherenkov Particle id and direction possible using first photon light front Going for 30% optical coverage With appropriate beam duty factor LENA could presumably see every reaction associated with stopped π + source!!

M Shaevitz at SBWS FNAL May 2011 The neutrino “flux” is ≈0.1 the proton flux

M Shaevitz at SBWS FNAL May 2011

Not a great deal better than with NOVA, but note lower flux

In conjunction with a LENA like detector the cyclotrons apparently can produce far more neutrinos than needed. Why not reduce the p flux by reducing the duty factor to isolate the ν μ s from π + μ + + ν μ decay. This could be accomplished by gating the ion source, for example 0.6 μs x3000H=1.8 x10 -3 Time (μs) Look for: Cross sections small because E νμ =29.8 MeV CC: 5x cm 2, ≈3000/y* NC: 2.5 x ≈1500/y* NCe: 4.74x Don’t see how they can be extracted without use of timing. A suggestion to measure everything * 1ma at 1.8x10 -3 duty factor

Conclusions Stopped π/μ neutrino sources can provide definitive information on the oscillation of to ≈1 eV sterile neutrinos. The fluxes and cross sections are well known. Assigning the incident neutrino energy in charged current reactions is unambiguous Significant improvement on the earlier LSND observation requires a kiloton x milliamp x year scale experiment. Going underground or exploiting duty factor of the beam is required to deal with CR backgrounds. The development of GeV cyclotrons show promise as a compact, movable, affordable (?) sources of stopped π + /μ +. Simulations showing 5σ results are impressive and I believe achievable. However any results are years (>5) away.

12 m