RED-100 detector for the first observation of the elastic coherent

neutrino scattering off xenon nuclei

On behalf of the COHERENT collaboration

Alexander KhromovNational Research Nuclear University

MEPhI

International conference on particle physics and astrophysics 5-10 October 2015, Moscow

Coherent neutrino-nucleus elastic scattering

(CENNS)

Z0

D.Z. Freedman PRD 9 (1974)A. Drukier & L. Stodolsky, PRD 30, 2295 (1984)

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§

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flavor blind, no threshold

predicted by the SM

high cross-section

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Neutrino elastically scatters off a nucleus via Z0 exchange

Neutrinos with energies up to 50 MeV satisfy coherence condition

GF – Fermi constant

F(Q2) – form factor at four-momentum Q

QW=N −(1−4 sin2(θW))Z – weak charge for a nucleus with N and Z, θW – weak mixing angle; sin2(θW)≈0.22 => QW~N;

σ~N2

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

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, 2006J. Barranco et al., JHEP0512:021, 2005

Why measure CENNS?

Two-phase emission detector

S1 - scintillationS2 -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)

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

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

Thermosyphon control

LN2 Dewar

Xe storage

purification

electronics

Ti cryostat

break-out-box

Spallation Neutron Source at Oak Ridge National Laboratory

ν flux at 30 m (all 3 types):~7 х 106 ν/cm2/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

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 μs < T dr max < 16.7 ms

Timing is possible only with S1

Without duty factor

With duty factor 1/1600 and with selection S1 ≥ 2 phe

Gamma background simulation at SNS basement

No neutron shield

Radial cut – 163 mm

Exposition – 9 months

With duty factor~1/1600, withselection 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

νμ prompt component is lost in

this case

Neutron background simulation at SNS basement

based on measured neutron flux

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

Backups

RED-100 assembling

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