1. RED-100 detector for the first observation of the elastic coherent neutrino scattering off xenon nuclei On behalf of the COHERENT collaboration Alexander Khromov National Research Nuclear University MEPhI International conference on particle physics and astrophysics 5-10 October 2015, Moscow

2. Coherent neutrino-nucleus elastic scattering (CENNS) Z0 D.Z. Freedman PRD 9 (1974) A. Drukier & L. Stodolsky, PRD 30, 2295 (1984) § § § flavor blind, no threshold predicted by the SM high cross-section § Neutrino elastically scatters off a nucleus via Z0 exchange Neutrinos with energies up to 50 MeV satisfy coherence condition G F – Fermi constant F(Q 2 ) – form factor at four-momentum Q Q W =N −(1−4 sin 2 (θ W ))Z – weak charge for a nucleus with N and Z, θ W – weak mixing angle; sin 2 (θ W )≈0.22 => Q W ~N; σ~N 2 For heavy nuclei Cross-section is two orders of magnitude higher for ν-e scattering and one order of magnitude higher for IBD Tiny nuclear recoil energies in keV region for spallation sources; in sub-keV region for nuclear reactors

3. Possible application: monitoring of nuclear reactors Test of the SM, probe of neutrino NSI Important in supernova processes & detection J.R. Wilson, PRL 32 (74) 849 Dark-matter direct-detection background K. Scholberg, Phys.Rev.D73:033005, 2006 J. Barranco et al., JHEP0512:021, 2005 Why measure CENNS?

4. Two-phase emission detector S1 - scintillation S2 -proportional scintillation(electroluminescence): measurement of e- charge extracted from the liquid to the gas S2/S1 ratio depends on the recoil type Position sensitivity: -X and Y from the S2 light distribution across the PMT array -Z from drift time (delay between S1 and S2) LXe is very attractive (self-shielding, high Z, high density, no intrinsic backgrounds)

5. RED-100 is a two-phase noble gas emission detector. Contains ~250 kg of LXe, ~100 kg in FV. The sensitive volume ~ 45 cm in diam ~ 45 cm in height, is defined by the top and bottom optically transparent mesh electrodes and field-shaping rings. PMTs are Hamamatsu R11410-20 (low-background); 38 in total (2 x 19) Drift field is ~ 0.5 ÷ 1 kV/cm; Field in EL region is ~ 7 ÷ 10 kV/cm (in the gas phase). Size of the EL region – 1 cm. The expected number of photoelectrons per one electron extracted to the gas phase ~ 80. Titanium cryostat Top PMT array Electrodes & field shaping rings Bottom PMT array LXe sensitive volume

6. LXe response for ER and NR is well-known in the region of interest

7. Thermosyphon control LN2 Dewar Xe storage purification electronics Ti cryostat break-out-box

8. Spallation Neutron Source at Oak Ridge National Laboratory ν flux at 30 m (all 3 types): ~7 х 10 6 ν/cm 2 /sec Collaboration( ~ 60 members from 14 institutions ) was established in March 2014 with the goal to discover CENNS with three different detector techniques at SNS. COHERENT has applied for $4M from DOE

9. Basement hallway is neutron-quite (beam-related neutrons four orders of magnitude lower compared to the experimental floor) In addition 8 m.w.e. overburden Experimental site

10. 10 μs < T dr max < 16.7 ms Timing is possible only with S1

11. Without duty factor With duty factor 1/1600 and with selection S1 ≥ 2 phe Gamma background simulation at SNS basement

12. No neutron shield Radial cut – 163 mm Exposition – 9 months With duty factor ~1/1600, with selection S1 ≥ 2 phe With duty factor ~1/1600, with selection S1 ≥ 2 phe, and with time selection > 1 μs after start of the SNS pulse ν μ prompt component is lost in this case Neutron background simulation at SNS basement based on measured neutron flux

13. CENNS was predicted more than 40 years ago but has never been observed Spallation Neuron Source at Oak Ridge is an excellent site for the first CENNS observation Performed simulations for the SNS basement showed that CENNS can be discovered with RED-100 two-phase liquid detector RED-100 is fully assembled and getting started now at NRNU MEPhI We plan to ship RED-100 to SNS in the near future Conclusion

14. Backups

15. RED-100 assembling

16. All 3-inch low-background Hamamatsu R11410-20 PMTs were characterized before implementing in the arrays Cryogenics is based on thermosyphon technology Voltage divider (18.5 MΩ) boards are made of Cirlex Purification is achieved by continuously passing Xe gas through a heated getter using a circulation pump To prevent deterioration of the photocathodes due to the intense illumination by cosmic muons a blocking pulse is sent to the PMTs D.Akimov et al., Instruments and Experimental Techniques, 57 (2014), 615 RED-100 is fully assembled and under commissioning now at NRNU MEPhI