Discovery Potential for Directional Dark Matter Detection with the - - PowerPoint PPT Presentation

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Discovery Potential for Directional Dark Matter Detection with the NEWSdm Experiment

Valerio Gentile 54rd Rencontres de Moriond - Electroweak 2019

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NEWSdm COLLABORATION

https://arxiv.org/pdf/1604.04199.pdf news-dm.lngs.infn.it

Website: Letter of intent:

70 physicists 14 institutes

JAPAN Chiba Nagoya

RUSSIA LPI RAS Moscow, JINR Dubna SINP MSU Moscow, INR Moscow Yandex School of Data Analysis

TURKEY METU Ankara SOUTH KOREA

Gyeongsang

ITAL Y

INFN e Univ. Bari, INFN e Univ. Napoli, INFN e Univ. Roma LNGS

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NEWSdm PRINCIPLE

Nuclear Emulsions for WIMP Search with directional measurement 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

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NANO IMAGING TRACKERS

• Nuclear emulsions: AgBr crystals in organic gelatine
• Latent image: produced by the passage of charged particles
• Metallic silver grains: Chemical treatment
• New kind of emulsion for

DM search: NIT

• Smaller crystal size

(~40 nm or ~20nm U-NIT) 500 nm C 100 keV [ P T E P 6 ( 2 1 7 ) 6 3 H 1 ]

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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

• 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] Nucl.Instrum.Meth. A680 (2012) 12-17

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PLASMON ANALYSIS

∆s ~ 68 nm Φ ~ 5° < ∆φ > ~ 15° pol angle ∆s ~ 14 nm Φ ~ 27.5° < ∆φ > ~ 90°

Grains visualized at 8 difgerent polarization angles (α) with an angular step of 22.5°

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BREAKTHROUGHS

The position accuracy is defjned for each coordinate as the standard deviation of xα(yα) coordinates from their barycenter Barycenter shift threshold: x accuracy y accuracy 2D Angular distribution A track length threshold is obtained at (120 ± 5) nm T est on Carbon 30 keV implanted ions <LSRIM> ~ 80 nm

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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

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BACKUP SLIDES

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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

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NANO IMAGING TRACKERS

Ag-Br-I: sensitive elements Organic gelatin: retaining structure PVA: to stabilise the crystal growth Lighter nuclei (longer range at same recoil energy) Each nucleus gives a difgerent contribution to the overall sensitivity Sensitivity to low WIMP mass Energy deposit in NIT emulsions

HEAVY NUCLEI (HN) LIGHT NUCLEI (LN)

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SUMMARY SIMULATION RESULTS

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 Nuclear recoils (internal sources)

• expected to be about 0.6 per ten kilograms per year

[Astropart. Phys. 80 (2016) 16-21]

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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 = (σ2

intrinsic + σ2 scattering )0.5 = 360 mrad

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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) μm2
• Liquid Crystal Polarization Rotator (LPR-200-0405-C)

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SRIM SIMULATION

Expected track length distribution by SRIM:

• Infjnite resolution
• Granularity not included

C10keV_V C100keV_H C60keV_H C30keV_H

A schematization is needed to account for granularity of the emulsions and the response of optical microscopes

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CRYSTAL MODEL

Simulation of crystals in μm3 of NIT Crystal radius generated with a gaussian distribution (22.04, 3.43) nm Occupancy in μm3 ~ 45 % Each event generated by SRIM has been translated in the crystal framework

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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

• btained by the data with the

CDF obtained by the model it is possible to evaluate the track length threshold achieved with plasmon analysis A track length threshold is obtained at (120 ± 5) nm Further threshold lowering using U-NIT with larger granularity

C30keV