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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
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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
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
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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?
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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)
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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
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LXe response for ER and NR is well-known in the region of interest
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Thermosyphon control
LN2 Dewar
Xe storage
purification
electronics
Ti cryostat
break-out-box
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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
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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
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10 μs < T dr max < 16.7 ms
Timing is possible only with S1
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Without duty factor
With duty factor 1/1600 and with selection S1 ≥ 2 phe
Gamma background simulation at SNS basement
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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
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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
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Backups
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RED-100 assembling
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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