Gadolinium Doped Water Cherenkov Detectors

Gadolinium Doped Water Cherenkov Detectors David Hadley University of Warwick NuInt-UK Workshop 20th July 2015

Water Cherenkov Detector Super-Kamiokande 22.5 kt fiducial mass 2

Physics with Large Scale WC Proton Decay Neutrinos Solar Supernova Accelerator Atmospheric Broad physics topics, wide energy range 3

Water Cherenkov Technique Muon 4

Water Cherenkov Technique Muon Electron 5

Water Cherenkov Technique Muon Electron Neutral Pion 6

Water Cherenkov Technique Muon Electron π 0 Count 100 90 80 70 60 50 40 30 e μ 20 10 0-1000 -800-600 -400-200 0 200 400 600 800 1000 Likelihood 7 Excellent PID performance Accelerator νe background is dominated by irreducible intrinsic νe.

Why Water Cherenkov? Scalability Water is cheap, non-toxic, liquid at room temperature long attenuation length achievable in pure water (SK > 100m at 400nm) Proven technology many years of experience (eg Super-K 1996 to date) low risk Excellent performance for charged particles above Cherenkov threshold 8

Neutron Capture on Hydrogen νe + p e + + n νē p n + p d + γ n Number of events / 10 µs 900 arxiv:1311.3738 [hep-ex] 800 700 600 500 400 e + p γ 300 200 100 Initial charged lepton signal Delayed γ signal 200 μs capture time Eγ = 2.2 MeV Low light yield Close to or below trigger threshold Low detection efficiency (~18%) 10 ) -1 MeV s -1-2 flux upper limit (cm ν e 2 10 10 1-1 10-2 10 100 200 300 400 500 600 700 800 T (µs) SK with n-tag SK w/o n-tag 14 16 18 20 22 24 26 28 30 Neutrino energy (MeV)

Neutron Capture on Gadolinium νe + p e + + n νē p n Number of Events arxiv:0811.0735 [hep-ex] 35 30 25 20 15 (a) E = 4.3 ± 0.1 MeV Bar: Data Hatched: MC e + Gd Initial charged lepton signal Delayed γ signal 20 μs capture time Eγ ~ 8 MeV cascade (~4 MeV visible) γ Number of Delayed Signals 10 5 0 10 2 10 0 1 2 3 4 5 6 7 8 9 10 Energy [MeV] (c) Data τ = 21.2 ± 6.1 µs Fast capture time (small ΔT window) Higher energy γ signal 1 0 100 200 300 400 500 T [µs] 11

Neutron Capture on Gadolinium Cross section for neutron capture: Gd (49,700 b), H (0.3 b) Fraction of captures on Gd 0.001% 0.01% 0.1% 1% Percentage of Gd by mass in Water 0.1% Gd fraction gives 90% neutrons captured on Gd. 12

Applications: Supernova Relic Neutrinos A low energy example Directly observable local supernova are all too rare Alternative is to measure diffuse supernova background DSNB/SRN Very low rate Large backgrounds Events/2MeV/0.56Mton/10years 900 800 700 600 500 400 300 200 100 spallation B.G. SRN+B.G. inv.mu B.G. total B.G. 0 10 15 20 25 30 35 40 45 50 arxiv:1109.3262 [hep-ex] No neutron tagging atmsph.! e Energy (MeV) 13

Applications: Supernova Relic Neutrinos A low energy example Directly observable local supernova are all too rare Alternative is to measure diffuse supernova background DSNB/SRN Very low rate Large backgrounds Removed by requiring coincidence with neutron 200 180 SRN+B.G.(inv.mu 1/5) 160 140 120 100 80 60 with neutron 40 tagging 20 0 10 15 20 25 30 35 40 45 50 arxiv:1109.3262 [hep-ex] Events/2MeV/0.56Mton/10years A few clean events per year in SK 14 total B.G. inv.mu(1/5) atmsph.! e Energy (MeV) ~100s per year in HK

Applications: Accelerator based long baseline neutrino oscillations A high energy example T2K / T2HK neutrino beam energy ~ 0.6 GeV Signal: ν CCQE: ν + n l - + p ν CCQE: ν + p l + + n events 60000 50000 40000 30000 ν µ ν µ ν µ ν µ p-ccqe p-mec n-ccqe n-mec Multi-nucleon: ν + (nn) l - + p + n ν + (p p/n) l + + n + p/n 15 20000 10000 0 0 1 2 3 4 5 6 7 8 9 10 num. of nucleon Neutron multiplicity gives an additional observable with which to isolate interaction modes. Complimentary to LAr proton measurements

Applications: Accelerator based long baseline neutrino oscillations Tagging neutron reduces wrong-sign background in anti-neutrino mode N events [arbitrary units] 60000 50000 40000 30000 20000 ν µ ν e ν µ ν e NC No neutron selection N events [arbitrary units] 50000 40000 30000 20000 ν µ ν e ν µ ν e NC With neutron selection 10000 10000 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 QE E ν [GeV] 16 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Impact on sensitivity being evaluated by Hyper-K Gd-doped Near Detector (TITUS) working group QE E ν [GeV]

EGADs (Evaluating Gadolinium s Action on Detector Systems) 200 t instrumented Water Cherenkov detector to test introduction of a water soluble Gadolinium in a Gd(SO4)3 ;. arxiv:1201.1017 [physics.ins-det] 17

EGADs (Evaluating Gadolinium s Action on Detector Systems) Need a water filtration system that removes impurities but not water plus Gd 2 (SO 4 ) 3 from tank Gd 2 (SO 4 ) 3 plus smaller impurities (UF Product) Gd(SO4)3 Ultrafilter Nanofilter #1 Gd 2 (SO 4 ) 3 (NF#1 Reject) Scaled up design for SK sized tank Impurities larger than Gd 2 (SO 4 ) 3 trapped in UF (UF Reject flushed to drain periodically ) Impurities smaller than Gd 2 (SO 4 ) 3 (NF#2 Product) arxiv:1201.1017 [physics.ins-det] Nanofilter #2 RO RO Reject to tank (temporary for splitting test) 18 Pure water (RO product) plus Gd 2 (SO 4 ) 3 back to SK

EGADs (Evaluating Gadolinium s Action on Detector Systems) M. Vagins (6th Open HK Meeting) 19

Super Kamiokande + Gd(SO4)3 In June 2015 the Super-K collaboration approved Gd-loading. Gd is also an option for Hyper-K. 20

3556.00 [140.000 in] 2438.40 [96.000 in] ANNIE (Accelerator Neutrino Neutron Interaction Experiment) CC events at ANNIE hall, BNB Events/1E20POT/ton/50MeV 2 10 10 1 10-1 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 E ν (GeV) ν µ ν µ ν e ν e Muon Range Detector Gd loaded Water Cherenkov Detector B 101.60 [4.000 in] 787.40 [31.000 in] 3771.90 [148.500 in] 4660.90 [183.500 in] arxiv:1504.01480 [physics.ins-det] Aim to measure neutron multiplicities for neutrino interactions on Oxygen in the few GeV range 21

TITUS Proposed Intermediate Water Cherenkov Detector for T2HK TITUS Detector Maximise cancellation of uncertainties between near and far detector Identical target nucleus and detector technologies ~2 km from beam source match the flux at the far detector Magnetised Muon Range Detector Measure momentum of escaping muons. In-situ cross-check of sign selection with neutron tagging method. 22

Gadolinium Doped Water Cherenkov Detectors Neutron tagging with Gd-doped WC significantly extends the physics reach of large scale Water Cherenkov detectors. Technical implementation has been successfully demonstrated (EGADs etc). Gd-doping is the future for Super-K (and Hyper-K?). To fully exploit this new technology, we need to make measurements of neutron multiplicity for ν-oxygen interactions and build models that reproduce them. 23

Thank you for listening References sk.icrr.u-tokyo.ac.jp hyperk.org t2k-experiment.org David Hadley University of Warwick 29th May 2015 arxiv:hep-ph/0309300 arxiv:1311.3738 arxiv:0811.0735 arxiv:1109.3262 arxiv:1201.1017 arxiv:1504.01480

Backup 25

Proton Decay Limits with 2.75 2.50 Neutron Tagging p eπ 0 2.25 Hyper-K Log(τ/10 33 ) years 2 1.75 1.50 1.25 1 0.75 Super-K LBNE-LAr 100 kt water 0.50 0.25 2015 2020 2025 2030 2035 2040 2045 year 26

Super-K Measurements of Neutron Multiplicity 27

ANNIE Events CC events at ANNIE hall, BNB Events/1E20POT/ton/50MeV 2 10 10 ν µ ν µ ν e ν e 1 10-1 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 (GeV) E ν 28

ANNIE Neutron Transit 500 net neutron transit distances (inclusive) 400 300 200 transverse to the beam direction 100 beam direction 0-3000 -2000-1000 0 1000 2000 3000 mm 29

Neutron Capture on Gd 30

Kamiokande Detectors Kamiokande 680 tonne fiducial mass (1983) Super-Kamiokande 22.5kt fiducial mass (33x Kamiokande) Megaton scale Water Cherenkov detector x25 larger fiducial volume than Super-K. 31 (202X)

Physics with Large Scale WC Proton Decay p e + + π 0 >1.3x10 35 years 90% CL p ν + K + >3.2x10 34 years 90% CL Neutrinos Solar Supernova SN ~200,000 @ 10kPC SN ~30-50 @ M31 200 solar ν per day Indirect dark matter search Hyper-K Physics Accelerator Atmospheric Goals Leptonic CP violation Mass Hierarchy determination >3σ θ23 octant determination 3σ for sin 2 θ23 >0.56 or sin 2 θ23 < 0.46 Broad physics programme. 32

Near Detector Development TITUS Detector New Intermediate Water Cherenkov Detectors Maximise cancellation of uncertainties between near and far detector Identical target nucleus and detector technologies ~2 km from beam source match the flux at the far detector Neutron Capture on Gd ~20µs capture time 8MeV γ cascade N events [arbitrary units] 60000 50000 40000 30000 20000 10000 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 33 ν µ ν e ν µ ν e NC No neutron selection QE E ν [GeV] N events [arbitrary units] 50000 40000 30000 20000 10000 ν µ ν e ν µ ν e NC With neutron selection 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 QE E ν [GeV]

DSNB at GADZOOKS 10 3 Phys.Rev.Lett. 93 (2004) GADZOOKS! dn/de e [(22.5 kton) yr MeV] -1 10 2 10 1 10 0 Reactor ν e Supernova ν e (DSNB) Atmospheric ν µ ν e 10-1 10-2 0 5 10 15 20 25 30 35 40 Measured E e [MeV] 34