2015/06/02 T. Asada Nagoya University The performance and status of directional dark matter search with the nuclear emulsion 2015/06/02 T. Asada Nagoya University

Collaboration Nagoya University T. Naka , T. Asada , T. Katsuragawa , M. Yoshimoto , A. Umemoto , S. Furuya , S. Machii , H. Ichiki , O. Sato , Y. Tawara University of Napoli G. de Lellis , A. Di Crescenzo , A. Aleksandrov , V. Tioukov University of Padova C. Sirignano LNGS N. D’Ambrossio , N. Di Marco , F. Pupilli Rome University G. Rosa, P. Monacelli Japanese people are mainly take charge of detector study, and Italian people are take charge of underground experiment design. readout system are developed both on Japan and Italy in parallel

topic Introduction Emulsion detection performance background theoretical performance readout performance & calibration ideal sensitivity background electron BG noise BG plan of underground experiment

Directional search with emulsion Light & heavy component Good scalability Solid state & good uniformity Large scale production Self production ( ~ 10 kg / month) high scanning power ~ g /day at current R&D, and many large scale experiments Good Angular resolution ~ 20 deg (1 sigma) including scattering DM direction sensitivity with equatorial telescope atom Mass fraction % H 1.63 C 10.12 O 7.40 N 2.68 S 0.03 Ag 44.07 Br 32.20 I 1.87 cygnus WIMP Fine crystal nuclear emulsion NIT Direction recognizing

The situation and strategy MSSM region search: AgBr targets are almost dominant high energy deposit →high background rejection power will be expected ton scale is required→difficult DAMA region search: scale is possible (~ 10 kg) CNO targets are sensitive CNO has relative low energy deposit → background rejection study Minimal Supersymmetric Standard Model Our First target should be DAMA region

detector performance

Detection process of Emulsion particle 43 nm Silver grain Ag core Development electron- dissolved Silver Bromide crystal in gelatin film Intrinsic detection threshold is estimated about two times of crystal size (~ 40 nm) But the exact relativity between micro construction of crystal and detected track were not studied. → realistic simulation with micro construction

Intrinsic performance of Emulsion We construct new simulation which calculate geometrical effect of each 1 crystal. Then we combine the simulation to SRIM. →the intrinsic performance of particle detection 300 nm 100 200 NIT (43nm) imaginal crystal arrangement particle simulation by SRIM

The result of Intrinsic tracking sensitivity tracking efficiency (simulation) angular resolution (simulation) old estimation range > 150 nm (Energy > 28keV) 2 2 Carbon Energy [keV] Carbon Energy [keV] XENON100 Leff (relative scintillation efficiency) efficiency: previous is just cut the threshold, but new simulation gives the curve as a function of energy. efficiency curve of Xenon 100 experiment angle : such low energy can be detect as “track”. scattering is dominant Efficiency curve of XENON 100 experiment. they have sensitivity until several keV, but the efficiency is not so high. Emulsion can serch near region in theory. Emulsion can detect a track with a order of keV as “track”. → How do we readout such low energy tracks? Aprile et al. (XENON100) PRD 88, 012006 (2013)

readout concept Optical microscope X-ray microscope Scalability is OK, resolution is not enough 486nm lined silver grain can be seen as … fuzzy picture clear picture X-ray microscope good resolution scalability is not enough

readout concept Combination of multi methods Optical microscope The signals are unchanged and read any time Optical microscope Scalability is OK, resolution is not enough 486nm X-ray microscope good resolution scalability is not enough Further analysis

Optical readout system : trigger of signal Nagoya (Japan) 1st unit Napoli (Italy) new LNGS (Italy) new Nagoya (Japan) 2nd unit upgrade Introduction of Optical readout system. We had used left up machine, but recently we constructed new machines. New scanning machines (improved optical system, ~ g/day speed) are ready ! → calibration study is in progress

X-ray microscope : confirmation Optical microscope candidate selection SPring-8 @ Japan confirmation 486nm 8keV X-ray Zone plate Zernike phase plate X-ray microscope etc. X-ray microscope is already established technique

Cal.1 : Optical readout efficiency Optical readout use Ellipticity We associate it with track range optical readout efficiency Track Range (on X-ray) [nm] Rate [Optical / X-ray event] Optical Track recognition efficiency Optical selected events X-ray all track events = Recognition threshold ~ 150 nm curve function is available for exact efficiency

Cal.2 : Optical signal selection performance ion direction emulsion film 11µm Ion implantation system (Nagoya univ) gas source : Kr, Ar+CO2, N2, BF4 → Main target (C, N, O) are available acceleration voltage : 5 - 200keV monochromatic energy parallel angle beam contour fit angle ellipticity cut 15

signal selection performance (Carbon) signal selection efficiency Elli cut 1.25 Elli cut 1.40 Elli cut 1.60 Energy [keV] Preliminary Efficiency xy projected angle [rad] 100 keV result of calibration signal selection efficiency depends on energy color means signal selection cut in typical cut, we can detect 60 keV signals as directional tracks 60 keV At least, > 60 keV Carbon are detectable Angular resolution(1sigma) :~ 20 deg (60 - 100 keV) Detail : Katsuragawa’s talk (tomorrow)

Comparison between simulation (intrinsic) and calibration (readout) scattering red line is simulation data calibration 1 ; optical readout efficiency is applied to simulation data, drawn by blue line. and calibration 2 ; data of ion implantation calibration is drawn by green line. black line of angular resolution is SRIM data of scattering. see blue and green line. ― SRIM estimation ― new simulation ― efficiency calibrated simulation ― optical calibration data the simulation result is consistent with calibration data angular resolution of readout system is smaller than error

Correction of scattering effect tracking detection efficiency ion implantation total detected usual event reflected event ion z y x some events go outside range [nm] DM situation 10 ~ 20 % improve 100 keV Carbon green line is scattered event. reflected means that the end point of track is outside of emulsion. red line events are stopped inside emulsion. With this correction, the efficiency will be improve about from 10 to 20 % in DM event situation. Spectrum of calibration data is distorted. Correct spectrum should be used for DM calculation

The experiment performance the calibration result in 60~100 keV Carbon is consistent with simulation extrapolate the simulation to other energy, nuclei ↓ estimation of experiment performance

Ideal sensitivity of experiment Cross Section Limit (0 BG 25 kg・year 90%CL) ― --- Cut 1.6 ― --- Cut 1.4 ― --- Cut 1.25 ■■ DAMA In the ideal condition, we can cover DAMA region with simply scale-up experiment. the error of non-calibrated regions (a order of keV) cause strong effect to the performance, so further calibration study is necessary. preliminary

Background

background study status The detection performance was determined next step background sensitivity rejection study

electron background 106 rejection power for electrons is required Ge spectroscopy in LNGS (Italy) Type gelatin AgBr crystal some atom is not mBq, Bq please see the 110mAg, it is dominant of all atom. In addition it, gelatin include carbons, so natural abundance of 14C should be large population. These two are dominant electron background. 228Ra, 40K (0.4 – 6.2) × 104 /kg/day 110Ag 2.5 × 105 /kg/day 14C 1.7 × 106 /kg/day (NA) 106 rejection power for electrons is required

Background rejection - cryostat chamber - temperature dependence of emulsion sensitivity (not NIT) 241Am γ-ray sensitivity room & LN2 temperature pumped down to 0.02 atm preliminary result Sample # grains / 1000 mm3 Exposed at 300 K 43  4 Exposed at 83 K 0.19  0.02 Unexposed at 300 K 0.25  0.03 This is one candidate of electro rejection. Emulsion detection sensitivity usually have temperature dependence. This result is first test of the dependence of fine crystal emulsion. *g–electron developing possibility upper limit : < 2×10-3 (90% C.L.) BG sensitivity is controllable ! B. Maglic et al, Phys. Rev. 123.1444 (1961)

Background rejection - chemical treatment - Tetrazolium-compounds new chemical treatment for electron rejection preliminary test result high electron rejection power electron developing possibility → < 3×10-3 (90 % C.L.) ⇒we can expect the background rejection power with readout more than > 106 2. High detection efficiency 30 keV C ions → 100 % consistent high S / low N will be possible! 2,3-di(methoxyphenyl) -5-phenyltetrazolium We can use use it by just mixing to gel This is another solution of electron rejection. the concept is direct control of each crystal sensitivity. These are just intrinsic efficiency. The more rejection power will be achieved with readout selection. combine them, we plan 106 rejection.

noise from other origin 10um alpha-ray noise brightness comparison on analysis mean brightness α-rays elements signal / noise noise type Generated by Development blue event is not particle source, not dusts, the origin is unknown. ― : alpha ― : non-exposed ― : developed ― : non-developed (same to non-exposed) → dusts mean brightness

Kind of events source Signal event (recoiled nuclei) hole+ electron- Signal event (recoiled nuclei) de/dx : 100~1000 keV/um Cores become strong(big) and many Background event (electron) de/dx : 1~10 keV/um Cores become small and few Noise event (not from particle, unknown) Core may be bigger than signal’s one. ?

Kind of events source after developing hole+ electron- The difference may appear in detail of readout signals →plasmon analysis (Umemoto’s talk, 3rd day) non-tracking rejection will be possible ! developing plasmon analysis X axis Y axis Y axis X axis 58 nm 58 nm ? ?

Nuclear recoil induced by neutrons neutron background Neutron from inside Nuclear recoil induced by neutrons ( > 100 nm tracks) ⇒ 0.065/kg/y neutron from Outside Studies of the flux measurement and shielding plan are in progress

plan of underground experiment

experiment design preparation for underground exposure required underground facility Detector production facility film production (pouring) underground gel production clean room dev room shield equatorial telescope the plan will submit to LNGS committee on this month. Hall B

Production of Emulsion Production system (Nagoya, Japan) R&D machine Scale: 200 g/day Semi mass production machine Scale: 600 g/day →Production ability ~ 10 kg / month Stable & enough emulsion production is already possible projects for underground run : film construction in underground emulsion production in underground 100nm

Experimental set-up: a possible design Passive shielding PE 50 cm Radon box Plexiglass Equatorial Telescope NIT sample Cu 14 cm 2 m Pb 20 cm 3 m all elements put inside the shield

Other case of design the case that equatorial telescope become serious BG source → put on the equatorial telescope several ton pay load is easy compatible with cryostat ?

schedule signal calibration BG calibration readout upgrade 2019 2016 2017 Understanding of the detector scale up study large scale run signal calibration BG calibration readout upgrade S/N improve study long term stability detector production facility plasmon analysis study equatorial telescope shield construction mini-run for BG measurement large scale run

summary We aim to search DAMA region with CNO detection and good BG rejection experiment. Detector calibration started. It shows good angular resolution (~20˚) and lower energy sensitivity (< 60 keV). New detector simulation are in good agreement with the experimental data. BG measurement and rejection study started. We try to archive 106 rejection power combination with detector intrinsic and readout technique. Underground experiment was scheduled. We will begin mini-scale run soon, and plan to start large scale in 2019.

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