Neutron scattering systems for calibration of dark matter search and low-energy neutrino detectors A.Bondar, A.Buzulutskov, A.Burdakov, E.Grishnjaev, A.Dolgov, A.Makarov, S.Polosatkin, A.Sokolov, S.Taskaev, L.Shekhtman Novosibirsk State University Budker Institute of Nuclear Physics SB RAS Novosibirsk State Technical University International conference: Dark matter, dark energy and their detection, July 2013

Outline: A problem of calibration of WIMP detectors Neutron scattering systems for liquid noble gas detector calibration - based on DD generator - based on DD generator - based on p 7 Li generator - based on p 7 Li generator International conference: Dark matter, dark energy and their detection, July 2013

WIMPs (weakly interacting massive particles) are a one possible candidate for Dark Matter Theoretical models predict a mass of WIMPs in the range GeV/c 2 WIMPs expected to interact with matter by elastic scattering with production on recoil nucleus with energies ~1-100 keV, the recoil spectrum depend on mass of the WIMP and detector velocity in the Galaxy frame Recoils spectrum measurements are required for estimation of WIMP mass and interpretation of experimental data International conference: Dark matter, dark energy and their detection, July 2013 R.W.Schnee, arXiv: v1 - most probable WIMP incident energy

Recoil spectrum measurements require calibration that is establishing of energy scale of detector response Such calibration can be done by measuring of detector response from particles produced recoil nucleus with know energy International conference: Dark matter, dark energy and their detection, July 2013 A response to electrons and recoil nucleus is different for ionization and scintillation detectors This difference often specified by quenching factor L eff : E e [keV ee ] = L eff × E r [keV nr ] e+A  e+A*  e  A+h e+A + +e R+A  R+A*  R+A+h R+A + +e R+A’ Electrons (gammas)Nucleus

Data of ionization and scintillation quenching factors below 10 keV for liquid noble gases are insufficient and controversial International conference: Dark matter, dark energy and their detection, July 2013 D.Gastler et al. // Phys. Rev. C V A.Manzur et al. // Phys. Rev. C V Lippincott W.H. et al. // Phys. Rev. C V ArXeNe Scintillation quenching factors

International conference: Dark matter, dark energy and their detection, July 2013 The project of two-phase avalanche cryogenic detector suitable for DM search have proposed in Budker INP The prototype of the detector is constructed in the Laboratory of Cosmology and Elementary Particle Physics of NSU The prototype will be applied for measurements of quenching factors in the noble gases for recoil energy range keV A.Buzulutskov et al. // this conf. Volume: 50 l Working gases: Ar, Xe, Ne, He Sensitivity: up to single electron (~100 eV) Spatial resolution: ~1 mm Measurements: both scintillation (bottom PTMs) and ionization (side PMTs) CrAD detector of dark matter

International conference: Dark matter, dark energy and their detection, July 2013 Primary recoil nucleus required for detector calibration can be produced by neutrons Recoils is produced by elastic scattering on neutrons A source of neutrons with constant energy and low divergence is required Neutron source Liquid argon Scintillation detector of scattered neutrons  Scattering event DM detector calibration scheme

International conference: Dark matter, dark energy and their detection, July 2013 Isotopes ( 252 Cf)Isotopes ( 252 Cf) Nuclear reactorNuclear reactor DD neutron generator (2.45 MeV)DD neutron generator (2.45 MeV) p 7 Li neutron generatorp 7 Li neutron generator Neutron sources Wide spectrum of neutrons

International conference: Dark matter, dark energy and their detection, July 2013 Utilizes nuclear fusion reaction D(D,n) 3 He (E n =2.45 MeV) Industrial neutron generators with neutron yield 10 6 n/s is produced for geophysical applications Neutron spot size ~1 mm DD neutron generator (produced by Budker INP) DD neutron generator

International conference: Dark matter, dark energy and their detection, July 2013 DD neutrons scattering Elastic scattering: n+Ar  n+Ar rec Inelastic scattering: n+Ar  n+Ar*  n+Ar rec +  (1.46 MeV) Scattering angle, deg. Recoil energy, keV Energy of Ar recoils Scattering angle, deg. Cross-section, barn Cross-section of scattering

International conference: Dark matter, dark energy and their detection, July 2013 DD scattering system Neutron generator Water-filled tank Active region of WIMP detector Scintillation detectors of scattered neutrons Neutron generator: 10 6 n/s Scintillators: slilbene Water shield: 40 cm Baseline: 80 cm Count rate of scattering events ~0.1 min -1 Recoil energy, keV Count rate, keV -1 Pulse height spectrum (90  scattering)

International conference: Dark matter, dark energy and their detection, July 2013 Background suppression Neutron background (random coincidence): - Neutron collimation - Neutron collimation Cosmic ray background: - Pulse shape discrimination (scintillation detector) - Pulse shape discrimination (scintillation detector) Neutron generator Water-filled tank Active region of WIMP detector Scintillation detectors of scattered neutrons

International conference: Dark matter, dark energy and their detection, July 2013 Pulse shape discrimination Scintillation pulses from gammas and neutrons in stilbene have different shape and can be effectively distinguished Time, ns w/o neutronsw/ neutrons 2.45 MeV

International conference: Dark matter, dark energy and their detection, July 2013 Calibration in low-energy range Calibration below 10 keV is a challenge: -Increase of “geometric” errors for low-angle scattering: -Failure to shield scintillation detector from neutron source Neutron generator Water-filled tank Active region of WIMP detector Scintillation detectors of scattered neutrons

International conference: Dark matter, dark energy and their detection, July 2013 Calibration in low-energy range Calibration below 10 keV is a challenge: -Increase of “geometric” errors for low-angle scattering: -Failure to shield scintillation detector from neutron source Neutron generator Water-filled tank Active region of WIMP detector Scintillation detectors of scattered neutrons

International conference: Dark matter, dark energy and their detection, July 2013 Calibration by inelastic scattering Recoils energy for inelastic scattering to small angle tend co constant value -8.3 keV Scattering angle, deg. Recoil energy, keV Energy of Ar recoils Escape of “geometric” error allow to increase solid angle of scintillation detector without loss of accuracy 100 times gain in count rate is estimated Recoils with energy 1.2 keV can be produced with 14 MeV DT neutrons Pulse height spectrum for small-angle scattering

International conference: Dark matter, dark energy and their detection, July 2013 Calibration in low-energy range Calibration below 10 keV is a challenge: -Increase of “geometric” errors for low-angle scattering: -Failure to shield scintillation detector from neutron source Neutron generator Water-filled tank Active region of WIMP detector Scintillation detectors of scattered neutrons

International conference: Dark matter, dark energy and their detection, July 2013 Generator of tagged neutrons Tagged neutron generator should provide effective trigger for suppression of random coincidence The generator of tagged neutrons in under development in Budker INP Neutron generating reaction: D+D  n (2.45 MeV) + 3 He (0.8 MeV) Recorded by build-in detector

International conference: Dark matter, dark energy and their detection, July 2013 Generator of epithermal neutrons in the reaction 11 B(p,n) 11 Be have been developed in Budker INP for medical applications (neutron cancer therapy) Tandem accelerator HV power supply H- ion source Proton beam: 1.9 MeV, 3 mA Neutron yield n/s p 7 Li neutron generator

International conference: Dark matter, dark energy and their detection, July 2013 p 7 Li neutron generator Generator of epithermal neutrons in the reaction 7 Li(p,n) 7 Be have been developed in Budker INP for medical applications (neutron cancer therapy)

p 7 Li neutron generator 7 Li(p,n) 7 Be: reaction threshold MeV Neutron energy is determined by beam energy and neutron escape direction Operation point E n =77 keV International conference: Dark matter, dark energy and their detection, July 2013 Neutron escape direction, degrees Neutron energy, keV

p 7 Li neutron generator Operation point for Ar detector calibration:  =110 , E p =2.077 MeV, En=77 keV 40 Ar have a peak of scattering cross-section on 77 keV Sulphur filter can be applied for additional monochromatization The system produces Ar recoils in the range keV Neutron energy, keV Scattering cross-section, barn International conference: Dark matter, dark energy and their detection, July 2013

Conclusion International conference: Dark matter, dark energy and their detection, July 2013 Neutron scattering systems for calibration on liquid cryogenic detectors are under development in the Laboratory of Cosmology and and Elementary Particle Physics of NSU The systems will allow to measure ionization and scintillation yield for liquid noble gases in the range of recoil energies keV