Searching for Sterile Neutrinos with an Isotope β-decay Source: The IsoDAR Experiment

Transcription

1 1 Searching for Sterile Neutrinos with an Isotope β-decay Source: The IsoDAR Experiment Mike Shaevitz - Columbia University Aspen Winter Workshop--New Directions in Neutrino Physics February 8, 2013

2 Where Are We With Sterile Neutrinos? 2 Several hints of oscillations through sterile neutrino state with Δm 2 1 ev 2 LSND / MiniBooNE ν e / ν e appearance Some difficulty for fits with one or two Reactor ν e disappearance ( Reactor Anomaly ) sterile neutrino models Radioactive source ν e disappearance - App vs Disapp But still no indication of ν µ disappearance - ν vs ν Establishing the existence of sterile neutrinos would be a major result for particle physics but.. Need definitive experiments Significance at the > 5σ level Observation of oscillatory behavior within detector Several directions for next generation experiments Multi-detector accelerator neutrino beam experiments Very short baseline (VSBL) experiments with compact neutrino sources

3 Has ν e Disappearance Been Observed? Reactor Antineutrino Anomaly 3 ν e ν s? 3 ν 4 ν RENO Daya Bay near detectors Region to Explore for Sterile Neutrinos Older Reactor Exps at Close Distances R = ± (3.0 σ ) Current Reactor Experiments Red: 3ν sin 2 (2θ 13 ) = 0.15 Blue: 4ν m 2 new = 2 ev2 and sin 2 (2θ new )=0.12, with sin 2 (2θ 13 ) = arxiv:

4 Very-short Baseline Oscillation Experiments 4 ν - Source Radioactive Source or Isotope Source or Reactor Source or Proton into Dump Source ν - Detector 1 / L 2 flux rate modulated by Prob osc = sin 2 2! " sin 2 (#m 2 L / E) Can observe oscillatory behavior within the detector if neutrino source has small extent. Look for a change in event rate as a function of position and energy within the detector Bin observed events in L/E (corrected for the 1/L 2 ) to search for oscillations Backgrounds produce fake events that do not show the oscillation L/E behavior and can be separated from signal

5 Possible Sources for VSBL Experiments 5 Need experiments with L/E ~ 1 m/mev Reactor sources E ν ~ 3 MeV optimum distance around 3 to 20 m Reactor core size can also be an issue Radioactive sources E ν ~ few MeV see oscillations with wavelengths ~ 1m Compact source can be placed directly into detector or just outside Isotope neutrino source E ν ~ 8 MeV (typical of short lived isotopes, i.e. 8 Li) Distance to source can be longer 10m to 20m Compact source that can be set up near an existing large detector Beam can be turned off periodically to measure background Higher energy neutrinos with less background

6 6 IsoDAR Experiment Isotope Decay-at-Rest Neutrino Source ( ν e Disappearance )

7 DAEδDALUS 800 MeV Cyclotron System (Under Development) 7 H 2 + Ion Source DAR Target-Dump (about 6x6x9 m 3 ) IsoDAR Cyclotron Injector Cyclotron (Resistive Isochronous) Ring Cyclotron (Superconducting) Isochronous cyclotron where mag. field changes with radius, but RF does not change with time. This can accelerate many bunches at once.

8 8 Columbia, Huddersfield, IBA, Maryland, MIT, PSI, INFN-Catania, INFN Legnaro, RIKEN, Wisconsin Academics: Neutrino Physicists, Accelerator Physicists And also Scientists at a Corporation Submitted to NIM

9 9 Phase I: The Ion Source Ion source Injector Superconducting Ring Cyclotron Target/ Dump

10 10 source solenoid lens slits & diagnostics

11 Beam to be characterized at Best Cyclotrons, Inc, Vancouver This spring (NSF funded) 11 Results to be available by Cyclotrons 13 Conference, Sept 2013, Vancouver

12 12 We have a workable ion source for a Phase II Ion source Injector Superconducting Ring Cyclotron Target/ Dump IsoDAR: A sterile neutrino experiment On its own!

13 Overview IsoDAR ν e Disappearance Exp 13 High intensity ν e source using β-decay at rest of 8 Li isotope IsoDAR 8 Li produced by high intensity (10ma) proton beam from 60 MeV cyclotron being developed as prototype injector for DAEδALUS cyclotron system Put a cyclotron-isotope source near one of the large (kton size) liquid scintillator/water detectors such as KAMLAND, SNO+, Borexino, Super-K. cyclotron protons Target Blanket/ Shield Detector Physics measurements: ν e disappearance measurement in the region of the LSND and reactorneutrino anomalies. Measure oscillatory behavior within the detector as a function of L and E. Phys Rev Lett (2012) arxiv:

14 IsoDAR Neutrino Source and Events 14 p (60 MeV) + 9 Be 8 Li + 2p plus many neutrons since low binding energy n + 7 Li (shielding) 8 Li 8 Li 8 Be + e + ν e Mean ν e energy = 6.5 MeV ν e / yr arxiv: Example detector: Kamland (900 t) Use IBD ν e + p e + + n process Detector center 16m from source ~160,000 IBD events / yr 60 MeV 10ma rate Observe changes in the IBD rate as a function of L/E 5 yrs

15 IsoDAR at Kamland Potential Location of ν Source Currently working with the Kamland collaboration on the details of siting and installation of the cyclotron, beamline, and neutrino source. 15

16 Detect ν e Events using Inverse Beta Decay (IBD) 16

17 IsoDAR ν e Disappearance Oscillation Sensitivity (3+1) 17 ν e ν e 5σ 5 yrs

18 IsoDAR Measurement Sensitivity 18

19 Oscillation L/E Waves in IsoDAR 19 Observed/Predicted event ratio vs L/E including energy and position smearing ν e ν e ν e ν e 5 yrs 5 yrs IsoDAR s high statistics and good L/E resolution has potential to distinguish (3+1) and (3+2) oscillation models

20 Possibility to Probe Lower Δm 2 using Super-K 20

21 21 Beyond Oscillations: IsoDAR sin 2 θ W Measurement

22 ν e e Elastic Scattering Measure sin 2 θ W 22 NuTeV weak mixing angle measurement using neutrino neutral current scattering differs from expectation by 3σ Is there something special with neutrinos or difficulty in NuTeV analysis? Use IsoDAR/Kamland to measure sin 2 θ W with pure lepton process antineutrino-electron elastic scattering: ν e + e ν e + e

23 Kamland Backgrounds to ν e e Signal 23 Backgrounds are large since signal is single outgoing electron Visible energy is low since outgoing ν e takes away energy Cuts: - Evis > 3 MeV - θ (to source) < 25 0 Reduce isotropic bkgnd by x2 electron kinematics From L. Winslow Use large sample of IBD events to constrain normalization to 0.2%

24 IsoDAR sin 2 θ W Measurement Sensivity 24 5yr data (7200 evts with E vis >3MeV) IsoDAR/Kamland: δsin 2 θ W = (~3%) Not as good as NuTeV: sin 2 θ W = ± (0.7%) But would be best ν e e elastic scattering measurement (See 3% band below)

25 Final Comments 25 Establishing the existence of sterile neutrinos would be a major result for particle physics Several hints in the Δm 2 ~1 ev 2 region Some tension with lack of ν µ disappearance signals Many proposals and ideas for sterile neutrino searches New experiments to have better sensitivity (~5σ level) with capabilities to see oscillatory behavior. IsoDAR could make a definitive search for sterile neutrinos Advantage over reactor and radioactive sources in having neutrinos with x3 higher energy Source is compact with a very well understood energy spectrum and can be setup near an existing large detector Combined L and E analysis can isolate the oscillatory behavior and reduce backgrounds Can turn beam off to measure background R&D is well underway to produce a high-intensity compact 60 MeV cyclotron to drive the neutrino source (See talk by Matt Toups)