Discovery Potential for Directional Dark Matter Detection with the NEWSdm Experiment Valerio Gentile 54 rd Rencontres de Moriond - Electroweak 2019 1 / 60
NEWSdm COLLABORATION 70 physicists ITAL Y 14 institutes INFN e Univ. Bari, INFN e Univ. Napoli, INFN e Univ. Roma LNGS JAPAN Chiba Nagoya SOUTH KOREA Gyeongsang RUSSIA LPI RAS Moscow, JINR Dubna SINP MSU Moscow, TURKEY INR Moscow Yandex School of Data Analysis METU Ankara Website: news-dm.lngs.infn.it Letter of intent: https://arxiv.org/pdf/1604.04199.pdf 2 / 60
NEWSdm PRINCIPLE N uclear E mulsions for W IMP S earch with d irectional m easurement Nuclear Emulsion based detector acting both as target and tracking device • Aim: detect the direction of nuclear recoils produced in WIMP interactions Background reduction: shielding surrounding the target • Fixed pointing: target mounted on equatorial telescope constantly • pointing to the Cygnus Constellation Directionality: Unambiguous proof of the galactic origin of Dark Matter • Location: Gran Sasso underground laboratory • 3 / 60
NANO IMAGING TRACKERS • Nuclear emulsions: AgBr crystals in organic gelatine • Latent image: produced by the passage of charged particles • Metallic silver grains: Chemical treatment C 100 keV [ P T E P 6 ( 2 0 1 7 ) 0 6 3 H 0 1 ] 500 nm • New kind of emulsion for DM search: NIT • Smaller crystal size (~40 nm or ~20nm U-NIT) 4 / 60
READOUT STRATEGY Challenge: detect tracks a few hundred nanometers long (comparable / shorter than the optical resolution) using optical microscopes Strategy : two-steps approach 1. candidate identifjcation based on elliptical shape analysis Nucl.Instrum.Meth. A680 (2012) 12-17 • Pros: Fast scanning profjting of the improvements driven by the OPERA experiment • Limit: resolution with standard technologies ~ 200 nm 2. candidate validation performed with a new concept of optical microscope, assembled in Napoli University • Pros: allows to extend the reconstruction of tracks beyond the optical limit by exploiting the resonance efgect of polarized light [H. Tamaru et al., Appl. Phys. Lett. 80 (2002) 1826] 5 / 60
PLASMON ANALYSIS Grains visualized at 8 difgerent polarization angles (α) with an angular step of 22.5° ∆s ~ 14 nm Φ ~ 27.5° < ∆φ > ~ 90° pol angle ∆s ~ 68 nm Φ ~ 5° < ∆φ > ~ 15° 6 / 60
BREAKTHROUGHS y accuracy x accuracy The position accuracy is defjned for each coordinate as the standard deviation of x α (y α ) coordinates from their barycenter Barycenter shift threshold: T est on Carbon 30 keV implanted ions <L SRIM > ~ 80 nm 2D Angular distribution A track length threshold is obtained at (120 ± 5) nm 7 / 60
NEWSdm SENSITIVITY With mass detector of 10 kg and assuming a spin-indipendent interaction and the SHM for the local WIMP density, it is possible to cover a wide region of the DAMA/LIBRA signal by using a completely difgerent approach Unique possibility to overcome the “neutrino fmoor”, where coherent neutrino scattering creates an irreducible background 8 / 60
BACKUP SLIDES 9 / 60
NEWSdm @ LNGS Aim: - reproduce all the experimental steps (emulsion production, fjlm pouring, exposure, data analysis) - measure the background yield for a 10 g exposure to be compared with simulations - pave the way for the fjrst 10 kg per year exposure of the NEWSdm detector Experimental setup: • shield from environmental background • cooling system to ensure required temperature to NIT emulsions Polyethylene slabs 40 cm-thick to absorb environmental and cosmogenic neutrons Lead bricks 10 cm-thick to absorb environmental photons It will act as a demonstrator to further extend the mass range 1 / 60 0
NANO IMAGING TRACKERS Each nucleus gives a difgerent Lighter nuclei contribution to the overall (longer range at same recoil energy) sensitivity Sensitivity to low WIMP mass HEAVY NUCLEI (HN) LIGHT NUCLEI (LN) Energy deposit in NIT emulsions Ag-Br-I: sensitive elements Organic gelatin: retaining structure PVA: to stabilise the crystal growth 1 / 60 1
SUMMARY SIMULATION RESULTS Nuclear recoils (internal sources) • expected to be about 0.6 per ten kilograms per year [Astropart. Phys. 80 (2016) 16-21] Nuclear recoils (external sources): • expected to be lower than 0.01 for exposures up to ten grams per month • expected to be about 1 for exposures up to ten kilograms per year Electron induced background: Grain density A grain density less than 10 -3 per (10μm) 3 corresponds to a rate of background tracks less than 1 1 / 60 2
CANDIDATE IDENTIFICATION Scanning with optical microscope and shape recognition analysis: • Automatic selection of candidate signals by optical microscopy • Selection of clusters with elliptical shape • Background: spherical cluster • Resolution 200 nm (~ a factor 10 better than OPERA scanning system) Overall Angular Resolution σ = (σ 2 intrinsic + σ 2 scattering ) 0.5 = 360 mrad 1 / 60 3
OPTICAL MICROSCOPE @ NAPOLI • LED source (green, blue, violet) blue in the present work • Objective lens Nikon Oil Objective 100X, 1.45 N.A • Bonito CL/CMC-4000 ( 386 fps with 4 Mpx resolution (2320 × 1726) ) • Epi-illumination mode • Pixel size ~ 27nm • Field of view (fov): (64 x 41) μm 2 • Liquid Crystal Polarization Rotator (LPR-200-0405-C) 1 / 60 4
SRIM SIMULATION Expected track length distribution by SRIM: C10keV_V • Infjnite resolution • Granularity not included A schematization is needed to account for granularity of the emulsions and the response of optical microscopes C100keV_H C60keV_H C30keV_H 1 / 60 5
CRYSTAL MODEL Simulation of crystals in μm 3 of NIT Crystal radius generated with a gaussian distribution (22.04, 3.43) nm Occupancy in μm 3 ~ 45 % Each event generated by SRIM has been translated in the crystal framework 1 / 60 6
PLASMON EFFICIENCY C100keV_H: 48.3 % C60keV_H: 39.8 % C30keV_H: 31.4 % For C30 keV sample only the plasmon analysis contribute to n-crystals in the model Comparing the effjciency obtained by the data with the CDF obtained by the model it is possible to evaluate the track length threshold C30keV achieved with plasmon analysis A track length threshold is obtained at (120 ± 5) nm Further threshold lowering using U-NIT with larger granularity 1 / 60 7
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