RED An experiment to sense recoil directionality in LAr

THE CASE FOR A DIRECTIONAL MASSIVE DARK MATTER DETECTOR WIMPs are still excellent candidates for particle dark matter SUSY WIMPs with masses > 100 GeV and cross sections: cm 2 ton to multi-ton scale experiments in preparation will probe the full space of parameters for a WIMP scattering down to the “neutrino floor” Observation of a few WIMP- like events might not be enough to claim discovery background discrimination through the “neutrino floor” A sidereal variation of WIMP wind from Cygnus i.e. a substantial anisotropy in nuclear recoils is expected ➔ Directionality might be key to the discovery!

DIRECTIONALITY OF WIMPS WIMP halo → WIMP wind Solar system orbit (~230 km/s) Annual rate modulation Earth orbit (±30 km/s, few % effect) Background signal may be also annually modulated Sidereal direction modulation Angle between WIMP wind & E Directionality signature (unique to WIMPs) O(10) rate variation between parallel and perpendicular directions (large effect)

DIRECTIONAL SENSITIVITY IN ARGON Double differential argon recoil rate dR/dE R dΩ Directional differential recoil rate in argon integrated over the energy interval between 50 keV and 200 keV, plotted in Mollweide equal area projection maps of the celestial sphere in galactic coordinates (l, b). We assume a WIMP mass of 200 GeV and a cross section of cm 2. The colour scale is in events/100 tonne/day/sr. Ratio of horizontal WIMP induced Ar recoils to vertical ones varies of a factor O(10) over the day (acceptance ±30°) Hard for a background to mimic the directional signal (anisotropic backgrounds in lab are isotropic in Galactic rest- frame) Mollweide equal area projection map in galactic coordinates M. Cadeddu, G. Covone, G. Fiorillo M. Lissia

DM & COLUMNAR RECOMBINATION

NUCLEAR RECOILS IN LAR Energy = ̸ S1: energy deposited into 3 channels (“heat” prominent for NR, reducing their S1 & S2) Excitation and recombination lead to the S1, while escaping ionization electrons lead to the S2 Divisions at each stage are functions of particle type, electric field, and dE/dx or energy Recombination S2 S1

DIRECTIONAL SENSING FOR NUCLEAR RECOILS? Columnar Recombination may display a sensitivity to the angle between nuclear recoil direction and drift field E in a LAr TPC “Columnarity” is given by the aspect ratio between the nuclear recoil track range and the Onsager radius r O =e 2 /εKT (the distance between a positive ion and a free electron for which the potential energy is balanced by the electron kinetic energy KT) Substantial CR: more light, less charge CR small: less light, more charge LAr: r O ≃ 80 nm range of NR ≃ 60 keV track E E

DO NUCLEAR RECOILS RETAIN DIRECTIONALITY? Tracks for Argon ions entering a liquid Argon target with a 60 keV recoil energy superposition of 100 tracks of Argon ions originating in the same position and with a momentum whose initial direction is horizontal - SRIM simulation F. Calaprice, C. Galbiati - WARP internal report, 2005

COLUMNAR RECOMBINATIO N Jaffé’s theory The initial ionization charge is distributed in a ‘‘column’’ around the trajectory of the ionizing particle. Electrons and ions drift away from this column under the effect of the external drift field and of charge diffusion. N e electrons surviving recombination N i initial number of electron-ion pairs k(E) function of the electric field, depends on the diffusion and mobility coefficients θ R angle between the ionizing track and the electric field direction S1 and S2 are expected to depend on the electric field and θ R An hint for anisotropy of 57.2 keV nuclear recoils from the SCENE experiment further investigation with more precise measurements and higher energies

A MEASUREMENT CAMPAIGN TO VERIFY THE DIRECTIONAL SENSITIVITY OF LAR DETECTORS

UNINA neutron beam facility at the TTT-3 Tandem accelerator Cryolab Ar recirculation and purification Optical characterisation at low temperature Clean Room facilities GAP-TPC: an innovative LAr TPC with high performance cryogenic SiPM readout explore scintillation and ionization in LAr with low energy NR nToF spectrometer assess Columnar Recombination as a function of angle between track and field Future medical application of the new technology: 3Dπ an innovative high-definition 3D Positron annihilation vertex imager

GAP-TPC CONCEPTUAL DESIGN Compact, no dead spaces to minimise multiple scattering → quartz vessel A drift distance such as to have a good separation between S1 and S2 signals Very uniform drift field Very high light yield Stable, high efficiency, high granularity pixellated photosensors Continuous monitoring of detector response with sources and laser light G. Fiorillo, B. Rossi, H. Wang

KINEMATICS OF THE NEUTRON SCATTERING EXPERIMENT A scattering cone of aperture θ around the neutron beam axis defines events with the same recoil energy and angle, though different orientations θ R with respect to the electric field. Maximum energy transfer 4A/(1+A)2E n =0.095E n. Energy and direction of the incoming neutron beam define the phase space that can be investigated: (top) E R vs θ R for the case of a 4.5 MeV neutron beam with α=45° wrt TPC axis. (bottom) For any given energy, several different θ R can be selected by suitably choosing the azimuthal angle Φ of the scattered neutron along the cone. d(d,n) 3 He reaction allows for a larger energy of neutrons and a trigger from the associated particle ➡ investigate several recoiling angles at the same time, without having to change the detector set-up 4.5 MeV neutrons incoming at 45° degrees wrt detector electric field axis, can be produced with an horizontal deuteron beam of 2 MeV energy. A.G. Cocco, G. Fiorillo, B. Rossi

NTOF SPECTROMETER CONCEPTUAL DESIGN assume 10 5 neutrons/s and a target to TPC distance of 100 cm → flux of 20 neutrons/s into our argon test cell ~0.2 probability of producing useful interactions in the 5 cm thick LAr from preliminary Monte Carlo study → 4 evts/s need a fine granularity spectrometer with large acceptance for the scattered neutrons with 80 2” LSci detector cells, 30% detection efficiency → 220 coincidence events per hour ToF techniques to select neutron energy PSD technique to reject gamma background G. Fiorillo, B. Rossi, M. Rescigno, M. Zullo, T. Zullo

RED schedule

Participating groups: UNINA, INFN (Napoli, Cagliari, Milano, Pisa, Roma1, TIFPA), APC-IN2P3, Princeton, Temple, UCLA INFN: 29 researchers, 8.4 FTE