Detecting the Directionality of Dark Matter via “Columnar Recombination” (CR) Technique An attractive, natural candidate for Dark Matter is the WIMP – Assume WIMPs are, on average, at rest in the galactic frame. – The sun’s galactic velocity is about 230 km/sec, so WIMPS are perceived as a “wind” from the direction of Cygnus. Direct WIMP detection: A Unique Directionality Signature  Directionality of recoil not determined by track imaging, but rather by recombination signal along the ionization column in the presence of an E-field  Use high pressure gas to get statistics in a ~ ton-sized detector, add a suitable molecule (TMA) to cool electrons, enhancing the recombination signal  With E-field providing a reference direction, get 12 hour oscillation of DM signal due to earth’s rotation  3 order of magnitude increased sensitivity over other direct detection methods  Can be used to reduce backgrounds in Direct DM searches such as Detector noise, radioactivity, neutrons Seasonal variations Can extend discovery reach beyond the “neutrino floor” caused by atmospheric neutrinos LDRD Brainstorming 2015

WIMP Directionality and Detection Detector with E field along x WIMP halo -> WIMP wind Solar system orbit (-230 km/s) Annual rate modulation (DAMA, etc.) Earth orbit (±30 km/s -> few % effect) Backgrounds may also be annually modulated Sidereal direction modulation (Our Proposal) Angle between WIMP wind and E-field has 24hr period Directionality signature (unique to WIMPS) “Control” detectors could be used for example: fixed on a telescope mount, aimed at Cygnus Expect order of magnitude rate variation between positions May be most robust signature of the WIMP nature of DM E is parallel to WIMPS E is perpendicular to WIMPS

The Eventual Detector 10 bar Xe density 0.05 g/cm**3 – 2,000 liter volume ( 2 cubic meters)  100 kg mass, which is competitive with LUX (purely calorimetric) Xe recoils produce highly dense ionization tracks A few % of TMA: Key Ingredient to make this work – Cools ionized electrons to keep them in track vicinity – Transfer of energy from Xe* and Xe + to ionize TMA Reduces photon production from prompt recombination and de-excitation (independent of E) Enhances Columnar Recombination (depends on E) Radiates ~ 300 nm, as opposed to VUV, so easier to detect This should work, in principle. It must be demonstrated.

Columnar Recombination: More photons, fewer ions High ionization density is needed Electric field pulls electrons and ions past each other, causing recombination Nuclear recoil makes a column of ions and electrons α : angle between electric field and recoil direction Recoil directionality D o D = R/I R = recombination signal (photons) I = ionization signal (drifted electrons) o Diffusion of electrons as they drift to anode doesn’t degrade D o D is determined locally, after drift length of microns, not centimeters Electric Field time

LDRD to study Columnar Recombination Goal: Design, build and test a detector that is capable of using sources and test beams to demonstrate the Proof of Principle signals of columnar recombination can be seen in a high pressure gas mixture of Xe + few % of molecular additive TMA. Procedure: Test and select the best gas mixture electron position sensors photodetectors Stage 1 – Desktop tests to study CR development -Design and build pressure vessel (commercially available) with feedthroughs -Build test prototypes to fit inside vessel -Photodetectors: SiPMs or PMTs -Drift electron detector: (GEMs, micromegas, MCP hybrid) to study column development -Build Xe purification, TMA filter system -Test with cosmic ray muons, alpha source (Am-241) Stage 2 – Test Beam (probably beyond this LDRD) -Move test device to test beam facility (ANL Atlas ion beams, FNAL test beam )

Backup Slides

Concept of a Prototype Additional Equipment Cosmic ray telescope External radioactive sources (beta) Internal collimated alpha source

HP Xe 30 keV Recoils: Higher target mass but impossible to image short tracks.

ATLAS Low Energy Ion Beam

Possible Technique to Study CR 10 GeV pion beam Grazing scattering angle FNAL test beam with Si telescope Xe recoils perpendicular to beam up or down scatter  max CR in or out of page  min CR HV cathode (foil), anode (miromegas, mcp, gem or wires) Photodetectors (SiPM or PMT) are also inside gas volume, but not shown here

Competing Experiments Cryogenic solid state: CDMS II (finished), Super CDMS, EDELWEISS II, CRESST II, TEXONO, CDEX and CoGeNT. Feature: the mK experiments (all but the last three) use phonons and ionization to discriminate in favor of recoils (vs electron background) Liquid Xenon: ZEPLIN III (finished), XMASS-1, XENON 100, LUX, PandaX-1. Feature: scintillation/ionization yield is powerful discriminant for recoils. Not used by XMASS-1. Liquid Argon: Dark Side-50, ArDM, miniCLEAN, DEAP Features (1) 39Ar is naturally occurring radioactive background, not able to remove. Seek Ar with low levels of 39. (2) scintillation/ionization is powerful discriminant for recoils. (3) Scintillation pulse shape is strong discriminant for identifying recoils. Superheated liquids (bubbles): COUPP-60, PICASSO III, SIMPLE Phase III: Feature: sensitive to Spin-dependent WIMP coupling due to Fluorine nucleus. Crystal : DAMA/LIBRA, KIMS, others coming on line. Annual Modulation of recoils. Directional Detection: DRIFT II-d, DM-TPC. Features: (1) image track of recoil, which should correspond to WIMP wind direction (requires much less data than annual modulation). (2) Low mass ~100 g (50 mbar), lower sensitivity.

Benefits of this Research Proof of principle of the Columnar Recombination method (both ionization and drift signals seen, correlation with recoil direction as measured in test beam) - from stages 1,2 Columnar Recombination signal strength vs theory in gaseous medium (high pressure Xe + molecular additive TMA) (references on this) - from stage 1 Development of an electron drift and amplification sensor for use in high pressure gas (GEMs, micromegas, hybrid device using MCP + micromegas pad readout) - from stages 1,2 By-product - detector properties and operating parameters ~identical to that needed for next-generation neutrino less double beta decay detector!