Daya Bay II：the Next Generation Reactor Neutrino Experiment Yifang Wang Institute of High Energy Physics

New era of neutrino experiments Since the discovery of the non-zero q13 by the Daya Bay experiment, the planning of the next generation neutrino experiments is accelerated Main focus: Mass hierarchy and CP phase What role a reactor neutrino experiment can play ? Mass hierarchy independent of the CP phase 2018/6/25

Mass Hierarchy by Reactor neutrinos S.T. Petcov et al., PLB533(2002)94 S.Choubey et al., PRD68(2003)113006 J. Learned et al., hep-ex/0612022 L. Zhan, Y. Wang, J. Cao, L. Wen, PRD78:111103, 2008 PRD79:073007, 2009 2011-10-30 Jun Cao (IHEP)

Fourier transformation of L/E spectrum Frequency regime is in fact the DM2 regime  enhance the visible features in DM2 regime Take DM2 32 as reference NH: DM2 31 > DM2 32 , DM2 31 peak at the right of DM2 32 IH: DM2 31 < DM2 32 , DM2 31 peak at the left of DM2 32 The Fourier formalism: Distinctive features No pre-condition of Dm223 L. Zhan et al., PRD78(2008)111103 4

Quantitative Features of FCT and FST To quantify the symmetry breaking, we define: RV/LV: amplitude of the right/left valley in FCT P/V: amplitude of the peak/valley in FST For asymmetric Pee NH: RL>0 and PV>0 IH: RL<0 and PV<0 Baseline: 46-72 km Sin2(2q13): 0.005-0.05 Others from global fit Two clusters of RL and PV values show the sensitivity of mass hierarchy determination L. Zhan et al., PRD78:111103,2008

In reality Unfortunately, DM221 / DM223 ~ 3% L. Zhan, et. al., Phys.Rev.D79:073007,2009

Daya Bay-II Experiment 60 km Daya Bay II KamLAND 20-50 kton LS detector 2-3 % energy resolution Rich physics possibilities Mass hierarchy Precision measurement of 4 mixing parameters Supernovae neutrino Geoneutrino Sterile neutrino Atmospheric neutrinos Exotic searches Talk by Y.F. Wang at ICFA seminar 2008, Neutel 2011; by J. Cao at Nutel 2009, NuTurn 2012 ; Paper by L. Zhan, Y.F. Wang, J. Cao, L.J. Wen, PRD78:111103,2008; PRD79:073007,2009

Easier now with a large q13 Smaller detector ? Relaxed resolution ? Requirement on baseline ? New default parameters: Detector size: 20kt Energy resolution: 3% Thermal power: 36 GW Baseline 58 km 3 years 2 s 6 years 3 s 8

Site Candidate Overburden >1500 MWE 128.9 km 58 km 58 km Lufeng NPP Daya Bay New exp. 128.9 km 58 km 58 km Lufeng NPP planned 6x2.9GW Huizhou NPP planned 6x2.9GW Daya Bay NPP 6x2.9GW

Optimum baseline ? Optimum at the oscillation maximum of q12 Multiple reactors may cancel the oscillation structure We are still working on Different fitting methods(c2, Fourier transformation, …) Understand effects of multiple baselines Optimum site selection q12 maximum 2018/6/25

Other Scientific Goals Neutrino Mass hierarchy Precision measurement of mixing parameters: q12, D M212, DM231  test the unitarity of the mixing matrix Supernova neutrinos Geo-neutrinos Exotics searches Sterile neutrinos Monopoles, Fractional charged particles, …. Target for neutrino beams Atmospheric neutrinos Solar neutrinos High energy cosmic-rays & neutrinos Point source: GRB, AGN, BH, … Diffused neutrinos Dark matter

Precision measurement of mixing parameters Fundamental to the Standard Model and beyond Probing the unitarity of UPMNS to ~1% level ! Current Daya Bay II Dm212 3% < 1% Dm223 5% sin2q12 6% Sin2q23 20% - sin2q13 14% 4% To be elaborated

Supernova neutrinos Less than 20 events observed so far Assumptions: Distance: 10 kpc (our Galaxy center) Energy: 31053 erg Ln the same for all types Tem. & energy Many types of events: ne + p  n + e+, ~ 3000 correlated events ne + 12C  13B* + e+, ~ 10-100 correlated events ne + 12C  11N* + e-, ~ 10-100 correlated events nx + 12C nｘ+ 12C*, ~ 600 correlated events nx + p  nｘ+ p, single events ne + e-  ne + e-, single events nx + e- nｘ+ e-, single events T(ne) = 3.5 MeV, <E(ne)> = 11 MeV T(ne) = 5 MeV, <E(ne)> = 16 MeV T(nx) = 8 MeV, <E(nx)> = 25 MeV Water Cerenkov detectors can not see these correlated events Energy spectra & fluxes of all types of neutrinos

Geoneutrinos Current results: KamLAND: 40.0±10.5±11.5 TNU Borexino: 64±25±2 TNU Desire to reach an error of 3 TNU: statistically dominant Daya Bay II: >×10 statistics, but difficult on systematics Background to reactor neutrinos Stephen Dye 2018/6/25

Liquid Scintillator 20 kt Detector Concept Muon tracking Stainless steel tank Water Seal Liquid Scintillator 20 kt Water Buffer 10kt Acrylic sphere：φ34.5m MO buffer6kt ~15000 20” PMTs optical coverage: 70-80% SS sphere ： φ 37 .5m 20” VETO PMTs Details to be worked out

Technical Challenges Requirements: Ongoing R&D: Large detector: >10 kt LS Energy resolution: 3%/E  1200 p.e./MeV Ongoing R&D: Low cost, high QE “PMT” Highly transparent LS: 15m  30m KamLAND Daya Bay II LS mass ~1 kt 20 kt Energy Resolution 6%/E 3%/E Light yield 250 p.e./MeV 1200 p.e./MeV

More photons, how and how many ? Highly transparent LS: Attenuation length/R: 15m/16m  30m/35m ×0.9 High light yield LS: KamLAND: 1.5g/l PPO  5g/l PPO Light Yield: 30% 45%; × 1.5 Photocathode coverage : KamLAND: 34%  ~ 80% × 2.3 High QE “PMT”： 20” SBA PMT QE: 20%  35% × 1.7 or New PMT QE ~ 40% × 2 5.3 – 7.0  (2.7 – 2.4)% /E With 1% constant term & 1% neutron recoil uncertainty, we are still OK

A new type of PMT: higher photon detection eff. Low cost MCP by accepting the following: Top: transmitted photocathode Bottom: reflective photocathode additional QE: ~ 80%*40% MCP to replace Dynodes  no blocking of photons 1. asymmetric surface; 2. Blind channels; 3. Non-uniform gains 4. Flashing channels ~ 2 improvement

Prototypes 5”MCP-PMT 8”MCP-PMT

LAB based liquid scintillator studies IHEP, Nanjing Uni. Composition of LAB：~4.5% impurities Understand light absorbers: Measure all impurities up to ppm level Use calculation techniques in solid state physics and quantum chemistry, identify structures which may absorb visible and UV light Study element traces(S,N,O,…) and their origin Study removing method Linear- Alkyl- Benzene (C6H5 -R)

How to get transparent LS ? Improve raw materials (using Dodecane instead of MO for LAB production） Improve the production process Purification LAB Atte. Length @ 430 nm RAW 14.2 m Vacuum distillation 19.5 m SiO2 column 18.6 m Al2O3 column 22.3 m 21 2018/6/25

Summary Daya Bay II was proposed a few years ago, now boosted by the large q13 Science case is strong with significant technical challenges Funding are promising Possible time schedule: Proposal to government: 2015 Construction: 2016-2020 Welcome collaborators 2018/6/25