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Low Energy Accelerator Neutrino Experiments Zelimir Djurcic Low Energy Accelerator Neutrino Experiments Zelimir Djurcic Argonne National Laboratory Instrumentation Frontier Community Meeting (CPAD), Argonne, January 9-11, 2012 1 -Low Energy Accelerator Neutrino Experiments are DAEδALUS-like experiments. -What are the DAEδALUS-like experiments? Those that use decay-at-rest sources of (anti) neutrinos i.e. pion/muon decay-at-rest or isotope decay-at-rest. Pion/muon decay-at-rest π+ Search for νμ –> νe µ+ + + νµ Protons→ π (stop)→ µ + νµ + + µ → e + νe + νµ → π- (captures before decay) _ νµ µ+ νe e+ Isotope decay-at-rest Example: 8Li decay neutron proton 8 8 - Li → Be + e + νe electron antineutrino electron Produce a very pure νe beam But only a few isotopes have endpoints > 3MeV above environmental backgrounds. 2 The DAR beams can be detected via Inverse Beta Decay Isotopes Pion/muon e+ νe p n Reactors • Scintillator or Gd-doped water detector • prompt positron signal followed by neutron capture • 3 DAEδALUS approach to determine δCP -Use νµ → νe and exploit the L/E dependence in absolute event rates. (-) (-) Oscillation probability P(νμ −> νe) in a vacuum (modified in matter): } } Want to find If δ ≠ 0 CP terms depending on terms depending on mixing angles mass splittings Details: arXiv:1006.0260 -Different from conventional long-baseline neutrino beam approach. 4 Proton Source for DAEδDALUS: Cyclotron System -Under Development. DAR Target-Dump ' H + Ion' 2 3 Source (about 6x6x9 m )' 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. 5 0.06 "CP = (/2 0.05 0.04 DAE"ALUS Concept = 0 0.03 0.02 Oscillaon Probability 0.01 0 0 5 10 15 20 25 30 Kilometers Constrains rise Constrains Osc. maximum of probability Initial flux at ~40 MeV wave Use a planned >50 kton detector (LENA, HyperK, MEMPHYS…) 6 #$ #$ #$ #e #e #e #$ #$ #$ Constrains rise Constrains of probability Osc. maximum Initial flux wave -Three identical pion/muon decay-at- rest at three different distances. -Only need to know relative normalization. 7 IsoDAR Experiment at Large Detector _ -Use this low-energy pure #e source to search for sterile neutrinos (as a part of staged approach). This is injector cyclotron 1 kton LS detector for DAE"ALUS 16.5 m Details: arXiv:1205.4419 -Potential locations: KamLAND, SNO+, Daya BayII. 8 General Instrumentation Issues for DAE"ALUS/isoDAR -The detectors need to be underground because we don't have beam timing to reject cosmic rays (use CW mode of operation). The idea of pairing with an underground detector presents unique issues for beams. -Proximity – DAR sources are isotropic, though you are helped by a signal that rises with L Nevertheless, these are 10 m to few km experiments -Space – if the accelerator goes underground, space is a limitation. -Infrastructure – though many mines and tunnels have a lot of power and water, MW of beam will be an issue. -Radiation – always an issue with beams, but even harder when not located at an accelerator laboratory site! 9 Detector Instrumentation Issues Water Cerenkov Detector for DAE"ALUS: -For water Cerenkov detector one needs similar PMT coverage as for the solar studies (~40%, or more) in order to see the Cerenkov light from the electrons from the Gd photon Compton scattering. + -IBD interactions are identified via a coincidence signal: IBD νe + p → e + n process. Prompt signal is from e+’s Cerenkov ring. The second signal is from n capture on proton. -The signal from n capture on p is a single 2.2 MeV gamma, and is usually too faint to be efficiently observed in a large Cerenkov detector => needs doping water with gadolinium (Gd) to see the Cerenkov light from the electrons from the Gd photon (total ~8 MeV) Compton scattering, and provide a high capture rate and a short n capture time (~30 $s). SK studies indicate that multiple photons with a total ~8MeV energy may be observed with 67% efficiency, with 40% PMT coverage. -Related to the PMT-coverage are issues of energy threshold and energy resolution. - - For example, when extracting νe + e → νe + e sample with E#>10 MeV one introduces a 1% error on flux normalization assuming 2.1% energy resolution in SK example. -Examples of proposed water Cerenkov detectors are SK with Gd, Hyper-K, MEMPHYS. 10 Detector Instrumentation Issues Hyper-Kamiokande detector, arXiv:1109.3262 11 Detector Instrumentation Issues Liquid Scintillator Detector for DAE"ALUS: -An optimal detector would be LSND-like (lightly doped scintillator). In this case the experiment may use about a factor of 3 less tonnage than water because there is no invisible muon background (from atmospheric muon neutrinos). In the same time one can reconstruct Cerenkov rings which is a benefit. -Example of planned large liquid scintillator detector is LENA (highly doped scintillator for enhanced light yield). The detector is optimized for low energy neutrinos (geo-neutrinos and astro-physical neutrinos) it would be a highly efficient (~90%) for detection of 2.2 MeV gamma ray + from IBD νe + p → e + n process. 12 - 12 In addition one may use it for an efficient detection of process νe + C → e + Ng.s. process (important for a short-baseline of ~10m accelerator based experiment). 12 Detector Instrumentation Issues -Proposed LENA (Low Energy Neutrino Astronomy) detector, see arXiv:1104.5620. 13 Detector Instrumentation Issues IsoDAR experiment (intermediate step in DAE"ALUS program): -Liquid scintillator is optimal. Gd doping would be an addition but isn't necessary for a detector a high light yield with low background. -Prosed detector (LENA) would do the job, but also existing detectors such as KamLAND would be optimal. Inverse Beta Decay Permits e+ Well- reconstructed E #e # is essential, … p n … along with spatial resolution. The next generation of oscillation experiments Should demonstrate the oscillation “wave” 14 Detector Instrumentation Issues -IsoDAR experiment at KamLAND site 15 -IsoDAR paper appeared in PRL and it was chosen as a “highlight”. 16 Conclusion -A brief overview of the low energy accelerator experiments i.e. those that use either pion/muon decay-at-rest or isotope decay-at-rest is provided. -DAE"ALUS/isoDAR are examples of the concept. -Other DAR (decay-at-rest) concepts and detectors: mostly short-baseline sterile neutrino searches. Examples are OscSNS at Oak Ridge and an DAR accelerator at Gd-loaded SK. -All detectors for the low energy accelerator experiments require: -large detector mass (~1kT up to ~1MT). -high PMT coverage (translates into enhanced energy resolution and optimal reconstruction capabilities for identifying signal and rejecting backgrounds). -reasonable low cost (dictates use of water or liquid scintillator equipped with photo-multiplier tubes). -These requirements are the major challenges: getting an efficient massive detector requires effective light collection so the advances in the area of the photon-detection are expected to make performance/cost ratio more optimal. 17 Backup Slides 18 Neutrino Beam Production Time Sequence Beam Off Beam Off 400µs 400µs 1.5 km' 100µs 100µs 100µs Accelerator 400µs 400µs 8 km' 100µs 100µs 100µs Accelerators 20 km' 100µs 400µs 100µs 400µs 100µs Accelerators Constrains rise Constrains Osc. maximum of probability Initial flux wave One needs to know which source is providing the beam. So they have to turn on/off. The duty factor is flexible, But beam-off time is needed. 19 How can we know the normalization? Along with the signal: We will also have scattering from electrons: - e+ # e # # #e e p n - e- e- e #e The #-e cross section is known to <1% due to precision measurements of weak interaction parameters Extract normalization from #-e rate. 20 Where can one run such beam? Large proton-based detectors w/ neutron detection exist SNO+ Borexino KamLAND Planned ~10-100 kt: SK with Gd LENA, HyperK MEMPHYS These detectors are deep underground, So reducing cosmic background by duty factor will not be necessary. 21 Detector Instrumentation Issues Other DAR (decay-at-rest) concepts and detectors: mostly short-baseline sterile neutrino Searches. Examples are OscSNS at Oak Ridge and an DAR accelerator at Gd-loaded SK. -OscSNS experiment, see arXivL1211.5199. -as mentioned already neutrinos from pion/muon decay-at-rest with well known spectrum provide a source for an oscillation search. -in past LSND experiment deployed this concept in #$ → #e oscillation search at a short beseline (~30 m) proving L/E~1 m/MeV, and resulted in 3.8* signal excess consistent with #e appearance. -Spallation Neutron Source at Oak Ridge National Laboratory is 1MW pion and muon DAR source. It may be combined with a LSND-style detector to directly probe the LSND signal excess with lower background and higher beam power. -Such experiment could reconstruct appearance and disappearance oscillation waves across a long detector. -OscSNS detector with ∼3000 8-inch phototubes, based on the LSND and MiniBooNE de- tectors, can be built for ∼ $20M (or < $20M if the MiniBooNE oil and phototubes are reused). 22 Detector Instrumentation Issues -Potential oscSNS detector shares common neutrino detector issues: need large detector mass, high PMT coverage (enhanced energy resolution and reconstruction capabilities), low cost. 23 .
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