CYGNUS HD10 A low-mass dark matter search with directional sensitivity via charge cloud tomography Sven Vahsen (University of Hawaii) for the U.S. and U.K. CYGNUS Collaborators 3/23/17 U.S. Cosmic Visions: New Ideas in Dark Matter 1
The CYGNUS Collaboration • Recently, many of the groups working on directional dark matter detection formed a new international proto-collaboration: CYGNUS • 44 signed members from the US, UK, Japan, Italy, Spain, China • Steering group: • Neil Spooner (Sheffield, UK) • Sven Vahsen (Hawaii, USA) • Kentaro Miuchi (Kobe, Japan) • Elisabetta Baracchini (Frascati, Italy) • Elisabetta Barberio (Melbourne, Australia) • Four working groups, monthly meetings: https://indico.phys.hawaii.edu/categoryDisplay. py?categId=34 • Outcome and namesake of bi-annual CYGNUS workshop on directional dark matter detection, held since 2007. • This year, in Xichang, Sichuan, China The dark matter wind is expected to http://www.tir.tw/conf/cygnus2017/ come from the constellation Cygnus. 3/23/17 U.S. Cosmic Visions: New Ideas in Dark Matter 2
CYGNUS vision and long-term goal • Build large-scale (>1000 m 3 ) nuclear recoil detector capable of CYGNUS • Observing Dark Matter via diurnal directional oscillation ( ó Dipole in galactic coordinates) • Detecting solar neutrinos • Efficiently penetrating the ν floor • Measuring DM particle properties and physics • WIMP astronomy • A review of the discovery reach of directional Dark Matter detection , Physics Reports 627 (2016) but most costly and challenging 3D readout w/ head-tail requires the fewest events to identify the recoil dipole. • Of order 10 events (versus order 1000/100 for 1D/2D) • 3/23/17 U.S. Cosmic Visions: New Ideas in Dark Matter 3
Detecting the Neutron Wind - in 3D Source Absent Cf-252 Cf-252 Source Present 27-sigma evidence for “neutron wind” in Hawaii! Recoils point back to source, in 3D. 3/23/17 U.S. Cosmic Visions: New Ideas in Dark Matter 4
Types of directionality: 1D, 2D, 3D • 3D recoil reconstruction also best for penetrating the neutrino floor, though advantage here is smaller • Caveat: Such studies typically do not include energy dependence of detector performance (such as angular resolution, efficiency, head/tail reconstruction). • These are major effects. CYGNUS collaboration working on a comprehensive technology comparison. Anticipating the outcome of this work, we propose CYGNUS HD10… Readout strategies for directional dark matter detection beyond the neutrino background Ciaran A. J. O'Hare, Anne M. Green, Julien Billard, Enectali Figueroa-Feliciano, Louis E. Strigari 3/23/17 U.S. Cosmic Visions: New Ideas in Dark Matter 5
CYGNUS HD10: Experimental Approach • Gas Time Projection Chamber, 10 m 3 • Gas mixture: SF 6 : 4 He, p~1 atm • Possibility of switching from atmospheric pressure (search mode) operation to low pressure operation for (improved) directional confirmation of WIMP signal E • Reduced diffusion via negative Ion drift (SF 6 ) SF 6 : 4 He gas • Charge amplification via Micromegas WIMP • HD – high resolution charge readout via x/y strips (200 µm pitch) for improved central cathode • 3D directionality with head-tail sensitivity • Electron event rejection • Fiducialization recoil (track) • Redundant 3D fiducialization ionization • SF 6 minority carriers E • charge cloud profile • Helium target • Improved sensitivity to low mass WIMP • Longer recoil tracks, extending electron event gas vessel discrimination to lower energies through Helium target neutron + gamma shielding 3/23/17 U.S. Cosmic Visions: New Ideas in Dark Matter 6
CYGNUS HD10: Proponents • CYGNUS P.I.s from U.S. and U.K. • James Battat – Wellesley • Dinesh Loomba – New Mexico • Neil Spooner – Sheffield • Dan Snowden-Ifft – Occidental • Sean Paling – Boulby Underground Laboratory • Sven Vahsen – Hawaii 3/23/17 U.S. Cosmic Visions: New Ideas in Dark Matter 7
CYGNUS HD10: SD Sensitivity 10 7 • Search mode: p=1 atm DAMA Allowed NAIAD (2005) ZEPLIN − III (2009) 10 6 DMTPC (2010) COUPP (2012) PICASSO (2012) KIMS (2012) • 200 torr SF 6 , 600 torr 4 He 10 5 DRIFT (2012) XENON100 (2013) SIMPLE (2014) DRIFT (2015) NEWAGE (2015) 10 4 LUX (2016) • SD sensitivity due to Fluorine PICO − 2L (2016) WIMP − proton SD cross section (pb) PICO − 60 (2016) DRIFT (2016) 10 3 CYGNUS 200 Torr SF6, 3 yrs, 10 m^3, 10 keVee CYGNUS 200 Torr SF6, 3 yrs, 10 m^3, 1 keVee 10 2 • 3 years of running time 10 • Potential for SD reach slightly 1 better than LZ / PICO-60 10 − 1 projections (not shown) 10 − 2 10 − 3 • But will depend on discrimination 10 − 4 threshold (see later slide) Highly 10 − 5 • Discoveries can be investigated preliminary - 10 − 6 likely to 10 − 7 with improved directionality in change 10 − 8 low-pressure mode (~0.1 atm) 1 10 100 1000 10000 WIMP Mass (GeV/c 2 ) 3/23/17 U.S. Cosmic Visions: New Ideas in Dark Matter 8
CYGNUS HD10: SI Sensitivity • Search mode: p=1atm • 200 torr SF 6 , 600 torr 4 He • 3 years of running time • Good SI reach for m WIMP <1 GeV due to He target • Similar to SuperCDMS HV detectors, but with electron event discrimination Highly • May see first solar neutrino events preliminary - likely to • Discoveries can be investigated change with improved directionality in low-pressure mode (~0.1 atm) 3/23/17 U.S. Cosmic Visions: New Ideas in Dark Matter 9
Three types of energy thresholds in a Gas TPC • Ionization threshold • as low as ~30 eVee - depends achievable gain, readout 10 torr of SF6 F recoil - E > 30 eVee, no direc. segmentation → capacitance → thres F recoil - E > 1 keVee 10 thres + 50 torr of He F recoil - E > 5 keVee thres F recoil - E > 10 keVee noise floor, and diffusion/drift thres 1 event detected I. Jaegle length 1000 days exposure 1 1 m 3 [pb] • Electron discrimination 60cm drift length track length / sigma(drift distance) > 3 threshold SD -1 10 N σ -2 10 • order 10 keVee (depends on I. Jaegle -2 10 gain, S/N, readout -3 10 dimensionality, segmentation, drift length, gas density, target -3 10 -4 nucleus) 10 1 10 [pb] 2 WIMP mass [GeV/c ] • Directional threshold -5 SI 10 N σ Highly • depends on same factors as preliminary - discrimination threshold -6 10 He recoil - E > 30 eVe, no direc. thres likely to He recoil - E > 1 keVee thres • but tends to be higher He recoil - E > 5 keVee thres He recoil - E > 10 keVee thres F recoil - E > 30 eVe, no direc. S recoil - E > 30 eVe, no direc. -7 thres thres change 10 F recoil - E > 1 keVee S recoil - E > 1 keVee thres thres F recoil - E > 5 keVee S recoil - E > 5 keVee thres thres F recoil - E > 10 keVee S recoil - E > 10 keVee thres thres 1 10 2 Each of these thresholds is lowest with 3D charge readout --- pixels or strips. WIMP mass [GeV/c ] 3/23/17 U.S. Cosmic Visions: New Ideas in Dark Matter 10
3D Charge Readout pixels and strips 2-D projection • • Pixel readout: ultimate in performance of ionization • 3D: 50 µm x250 µm x 40 MHz HeC0 2 gas,p=1 atm density, • Small readout pads à lower detector measured w/ capacitance à lower noise à lower charge Charge density threshold 𝛽 – particle 2x2 cm ATLAS • Can detect single electrons (30 keVee) with high efficiency at gain > 20k pixel chip • Improved separation of electron and recoil readout events à lower discrimination threshold gain ~ 3000 • Lower directional threshold • Raw data – • Fiducialization via charge cloud profile no noise hits! neutron • But • High cost – of order $100k / m 2 Charge density • Low radio-purity • Tedious to construct - each chip is only 2x2 cm à Best compromise • Resistive Micromegas readout with integrated x/y strips (available from CERN • Cost of order $10k / m 2 • Large - up to 1m x 2m! • Higher noise floor and thus ionization threshold 3/23/17 U.S. Cosmic Visions: New Ideas in Dark Matter 11
3D Fiducialization I: Minority Carriers Discovery of Multiple, Ionization-Created Anions in Gas Mixtures Containing CS2 and O2 Daniel P . Snowden-Ifft http://arxiv.org/abs/1308.0354 CS 2 -CF 4 -O 2 All BG removed! Game changer for directional WIMP search via gas TPC • Utilizes timing - works with any charge readout (1D,2D,3D) • More recently - Minority carriers also discovered in SF 6 • Incredibly lucky: SF 6 is also non-toxic, non-flammable, not corrosive, • has gain, and is a good SD target (!) 3/23/17 U.S. Cosmic Visions: New Ideas in Dark Matter 12
3D Fiducialization II: Charge Cloud Reconstruction P.Lewis • Measurement of charge- profile ( not width) of track, enables accurate measurement of transverse diffusion, which depends on drift length à obtain absolute position in drift direction Requires high resolution readout of charge density à only 2D, 3D • However, should work with any gas • Published version utilized “chopped” alphas, but has since been • extended by grad student to also work with recoil events (unpublished) 3/23/17 U.S. Cosmic Visions: New Ideas in Dark Matter 13
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