第２回MeVガンマ線天文学研究会

GRAMSプロジェクトでのダークマター探索とMeVガンマ線観測
TSUGUO ARAMAKI, SLAC

outline
Dark Matter Search with Antimatter
Current status and recent results of indirect dark matter search
Why is antimatter survey important?
Antimatter-based dark matter search with GRAMSMeV Gamma-Ray Observations
Current status of MeV gamma-ray observations
Why are MeV gamma-ray observations important?
MeV gamma-ray observations with GRAMS

Summary
GRAMS First Paper
accepted in Astroparticle Physics
Aramaki et al., 2019

Dark MatterSearchINDIRECT Dark Matter SEARCH!4

MEASURE DM ANNIHILATION/DECAY PRODUCTSDMq , h , W,

_ _ _DMaPOSITRON:AMS-02, PAMELA, DAMPE…
GAMMA RAY:FERMI-LAT, VERITAS, CTA, GRAMS…
NEUTRINO:ICECUBE, ANTARES…

e + , γ, ν, p , d , n …

ANTIPROTON:AMS-02, PAMELA, BESS, GAPS, GRAMSANTIDEUTERON:AMS-02, BESS, GAPS, GRAMSANTIHELIUM:
AMS-02, GAPS, GRAMSCOMPLEMENTARY SEARCHES WITH DIFFERENT DETECTION METHODS ANDBACKGROUND MODELS ARE CRUCIAL TO VALIDATE DM SIGNATURES

Recent Results from fermi-lat!5Launched in June 2008, targeting 20MeV - 300GeV gamma-rays
Possible DM signatures from Galactic Center Region (GCE)
Inconsistent with dwarf spheroidal galaxy (dSph) observations(recent observations for new dSphs show some small excess)Daylan et al., 2016

10-24

— Fermi Dwarf Galaxy Observation(Ackermann et al., 2015)10-25<σv > [cm3/s]

gamma-ray excess observed

Excluded

Thermal Relic Cross Section(Steigman et al., 2012)

10-26

FERMI GALACTIC CENTER EXCESS (GCE)~50GeV DM or astrophysical objects?

Propagation model: MEDb̄b

Fermi Galactic Center Excess— Calore et al., 2014
— Daylan et al., 2014
— Abazajian et al., 2015

<latexit sha1_base64="mn4t03Afz1AIdBXox69qkMUN1ZQ=">AAAB8XicbVDLSsNAFL3xWeur6tLNYCm4KokIdllw47KCfWAbymR60w6dTMLMRCihf+HGhSJu/Rt3/o2TNgttPTBwOGcu99wTJIJr47rfzsbm1vbObmmvvH9weHRcOTnt6DhVDNssFrHqBVSj4BLbhhuBvUQhjQKB3WB6m/vdJ1Sax/LBzBL0IzqWPOSMGis9DgKqsmBOgvKwUnXr7gJknXgFqUKB1rDyNRjFLI1QGiao1n3PTYyfUWU4EzgvD1KNCWVTOsa+pZJGqP1skXhOalYZkTBW9klDFurviYxGWs8im6wWUTPRq14u/uf1UxM2/IzLJDUo2XJRmApiYpKfT0ZcITNiZgllitushE2ooszYkvISvNWT10nnqu5Zfn9dbTaKOkpwDhdwCR7cQBPuoAVtYCDhGV7hzdHOi/PufCy/bjjFzBn8gfP5A8wCkEs=</latexit>

10-27

10100mᵪ [GeV]

1000

DIFFICULT TO VERIFY DM SIGNATURES DUE TO MIMIC SIGNAL FROM BACKGROUNDNEED A NEW APPROACH/EXPERIMENT TO VALIDATE THE RESULTS

Recent Results from ams-02
Launched in May 2011, targeting cosmic-rays including antiparticles

Ek2Flux (GeV m-2 s-1 sr-1)

Possible DM detection in antiproton measurements
Possible detection of antiheliums and antideutrons
101
100~50GeV DM?

bkgdm
AMS-02

10-1
10-2
10-3

10-4
10-1

Cui et al. 2016)
100

101
Ek (GeV)102

103_ _So far, 6 3 He, 2 4 He candidate events reported

Antiproton excess: ~50GeV DM (consistent with Fermi GCE) or cosmic-rayinteraction?
PLANCK▶ Antiheluim detection:▶ If from DM, a large excess should be seen in the antiproton/antideuteron fluxes?
▶ antimatter clouds in our galaxy?
▶

NEED A NEW APPROACH, EXPERIMENT TO VALIDATE THE RESULTS!6WHY ANTIDEUTERONS?

!7BACKGROUND-FREE DM SEARCH AT LOW-ENERGY
Antideuteron Flux [m- 2 s -1 sr -1 (GeV/n) -1 ]10 -3
BESS upper limit

10 -4

GAPS

AMS-02— DM, mᵪ = 30GeV— background
AMS-02PRIMARY FLUXDM ANNIHILATION/DECAY
DM

10 -5

DM

10 -6 GRAMS

Aramaki et al., 2016

q,h,W…

DARK MATTERANNIHILATION_d_p_n

HADRONIZ ATION COALESCENCEPROCESSPROCESS (P C )~ 400x

10 -710 -810 -90.1

LSP: Donato et al., 2008
BKG: Ibarra et al., 2013

110Kinetic Energy per Nucleon [GeV/n]

SECONDARY FLUXCOSMIC RAY INTERACTION ___100p (CR) +H (ISM)→ p + H + p + n + p + n

GAPS FIRST SCIENCE FLIGHT IS SCHEDULED FROM ANTARCTIC IN 2021
GRAMS: NEXT GENERATION EXPERIMENTdGRAMS Antimatter Detection Concept!8MEASURE ATOMIC X-RAYS AND ANNIHILATION PRODUCTS_dπ-

TOF Plastic Scintillator

ATOMIC TRANSITIONSEXOTIC ATOM

X-ray

Auger e-_dno,loRefilling e-

n=nK~40π+pX- rayπ+π-

X-rayAr

X-RAYLAr TPCX-RAY

X-RAYπ-A time of flight (TOF) system tags
candidate events and records velocity
The antiparticle slows down & stops,
forming an excited exotic atom
De-excitation X-rays provide signature

n=2M* ⎛ 1 1 ⎞Eγ = (zZ ) * RH ⎜⎜ 2 − 2 ⎟⎟me ⎝ nf ni ⎠0π
2π+ππ+n=1

pπ-

NUCLEAR
ANNIHILATION
Aramaki et al., 2013

Annihilation products provide additional
background suppression

Concept proven with accelerator beam test
Cascade model developed for X-ray yields

GRAMS antideuteron identification techniqueCR p, e ± REJECTION: ANTIPROTON AND ANTIDEUTERON SELECTION
Select slow particles with TOF
Simultaneous detection of secondary/annihilation products (pions/protons)▸ Slow CR p and e ± may not be able to produce secondary particles
ANTIDEUTERON IDENTIFICATION FROM ANTIPROTONSAtomic X-rays from exotic atom
▶ different energy: 58, 97 keV for antiproton, 74, 114 keV for antideuterons
Pion/proton multiplicity▶ antideuterons produce more pions and protons
Stopping range (depth sensing)▶ antideuterons with the same velocity go deeper before stopping
dE/dX energy deposit in LArTPC
PLANCK▶ antideuterons with the same velocity deposit more energy

EXPECTED BACKGROUND/MIMIC EVENTS ~0.01!9

GRAMS Detector Design!10LARTPC DETECTOR SURROUNDED BY PLASTIC SCINTILLATORSLARTPC MEASURES SCINTILLATION LIGHT AND IONIZATION ELECTRONSπ-

Plastic Scintillator

Anode wires/pads(X-Y plane)

140x140x20cm
X-ray

π+

X- rayX-rπ-π+pati
Scintillo n Li gSegmentation

ction EleazinoIht

E-FIELD_dtrons

LAr TPCayπ-SiPMs

LArTPC

Plastic Scintillators: TOF - measure velocity and incoming angle
LArTPC: Calorimeter and particle tracker▶ Scintillation light at SiPMs to trigger events▶ Wires/pads on anode plane (X, Y), drift time (Z) to provide a 3D image/track▶ Well-studied, widely-used in large-scale DM/neutrino experiments
Scintillation light localized by segmentation to reduce coincident backgroundGRAMS Sensitivity in DM Parameter SpaceSTRONG TENSIONS WITH FERMI GCE/DSPHS AND AMS-02!1110-24

Fermi Galactic Center ExcesDaylan et al., 2016
Abazajian et al., 2016
Calore et al., 2015b̄b

M, mᵪ = 30GeVackground<latexit sha1_base64="mn4t03Afz1AIdBXox69qkMUN1ZQ=">AAAB8XicbVDLSsNAFL3xWeur6tLNYCm4KokIdllw47KCfWAbymR60w6dTMLMRCihf+HGhSJu/Rt3/o2TNgttPTBwOGcu99wTJIJr47rfzsbm1vbObmmvvH9weHRcOTnt6DhVDNssFrHqBVSj4BLbhhuBvUQhjQKB3WB6m/vdJ1Sax/LBzBL0IzqWPOSMGis9DgKqsmBOgvKwUnXr7gJknXgFqUKB1rDyNRjFLI1QGiao1n3PTYyfUWU4EzgvD1KNCWVTOsa+pZJGqP1skXhOalYZkTBW9klDFurviYxGWs8im6wWUTPRq14u/uf1UxM2/IzLJDUo2XJRmApiYpKfT0ZcITNiZgllitushE2ooszYkvISvNWT10nnqu5Zfn9dbTaKOkpwDhdwCR7cQBPuoAVtYCDhGV7hzdHOi/PufCy/bjjFzBn8gfP5A8wCkEs=</latexit>

10-25<σv > [cm3/s]

Excluded

Thermal Relic Cross Section(Steigman et al., 2012)

10-26
GAPS

AMS-02 Antiproton Excess
Cui et al., 2016

GRAM

S

Fermi Dwarf Galaxy Observation
Ackermann et al., 2015

10-27
100
10 Aramaki et al., 2019

GeV/n]

100mᵪ [GeV]1000

GRAMS COULD DEEPLY INVESTIGATE FERMI GCE, AMS-02 ANTIPROTON EXCESSCURRENTLY EVALUATING ANTIHELIUM SENSITIVITYMeV Gamma-RayObservation

Current Status of MeV Gamma-Ray Observations
GAMMA-RAYS IN MEV REGION POORLY EXPLORED = “MEV GAP”

!13

Takahashi et al., 2013

Compton scattering process dominates in MeV
Good energy & spacial resolution required

MeV-gap

Previous experiments: COMPTEL and COSICOMPTEL(The Imaging Compton Telescope)

!14

COSI
(The Compton Spectrometer and Imager)

Liquid Scintillator

cm

~1.6m

~8NaI Crystalm~ 8c

Z. AndreasNASAlaunched into space in 1991
▶ installed on Compton Gamma-Ray Observatory▶ energy range: 0.75 - 30 MeV▶ spacial resolution: ~ 40cm 3▶ Detected ~30 sources▶

12 HPGe crystals (2x2x3), double-sided stripped▶ energy range: 0.2 - 5 MeV▶ spacial resolution: ~ 2mm 3▶ 1st balloon flight from Antarctica in 2014
▶ 2nd flight from New Zealand in 2016▶

MeV Gamma-Ray Science!15

GAMMA-RAY SPECTRUM
Extreme objects▶ Neutron stars: high matter density▶ Magnetars: strong magnetic field▶ AGNs/Blazars: powerful jets
▶ Transition of physical processes▶ Cosmic MeV gamma-ray background▶

GAMMA-RAY LINES

Gamma-ray lines

Transition of physicalprocesses
MeV-gapInoue et al., 20190.1

1

10E [MeV]

100

Positron annihilation: 511 keV▶ Nuclear lies are typically in ~MeV
▶ Radioactive isotopes provide physical condition during nucleosynthesis▶ SNe: 26 Al (1809keV), 60 Fe (1173keV, 1333keV), 44 Ti (1157keV), 56 Co (847keV)▶ Neutron capture: 2 H (2223keV), Cosmic-ray interactions: 12 C* (4438keV)▶

MULTI-MESSENGER ASTRONOMY
EM counterparts of NS-NS mergers▶ r-process in NS mergers/remnants▶

DARK MATTER SEARCH▶

Wu et al., 2019

MeV gamma rays from DM annihilation

GRAMS Detection Concept: MeV Gamma-rays!16

LARTPC DETECTOR SURROUNDED BY PLASTIC SCINTILLATORSLARTPC MEASURES SCINTILLATION LIGHT AND IONIZATION ELECTRONS
Anode wires/pads(X-Y plane)

Gamma-Ray
Compton Scattering Event

Charged Particle

Segmentation

E-FIELDθSiPMsGamma-RayPair Production Event
TOF Plastic Scintillator

ee-eeee+e-LArTPC

Compton “Event Circles”

Plastic Scintillators: Veto incoming charged particles
LArTPC: Compton camera and calorimeter (for pair-production)▶ Scintillation light at SiPMs to trigger events▶ Wires/pads on anode plane (X, Y), drift time (Z) to provide a 3D image/track
Signal localized by segmentation to reduce coincident background
Neutron events can be separated based on the pulse shapeLARTPC vs. semiconductor detector
LArTPC

Anode wires/pads!17

Semiconductor Detector (Si/Ge)
Si/Ge

PreampFrameZYx

LArTPC

SiPMs
LArTPC

Semiconductor (Si/Ge)ρ (g/cm3)

1.4

2.3/5.3

Toperation~80K~240K/~80K

Cost$$$$

Signalscintillation light + Ionization electrons

electrons, holes

X, Y Positions

wires on anode plane (X-Y)

double-sided strips

Z position

from drift timefrom layer ## of Layers

1 layer

multi-layers# of Electronics####Dead Volumealmost no dead volume

detector frame, preamps

Neutron bkg

Identified with pulse shape

No rejection capability

LARTPC IS COST-EFFECTIVE AND EASILY EXPANDABLE TO A LARGER-SCALE,
MUCH LESS CHANNELS/ELECTRONICS REQUIRED, ALMOST NO DEAD VOLUMEGRAMS MeV Gamma-ray Continuum sensitivity
Takahashi et al., 2013

Aramaki et al., 2019SINGLE BALLOON FLIGHT: AN ORDER OF MAGNITUDE IMPROVEDSATELLITE MISSION: COMPARABLE (BETTER) TO FUTURE MISSIONS!18

Future Prospects!19

R&D FOR PROOF OF CONCEPT – IN A FEW YEARSValidate detection concept with a small-scale prototype detector▶ Develop event reconstruction technique▶

FIRST BALLOON FLIGHT - IN 5-10 YEARSMeV gamma-ray observations focusing on bright objects, nuclear lines▶ Antimatter-based indirect DM search▶ Possibly detect antideuterons from DM in the first flight▶ Investigate Fermi/AMS-02 results▶

TPC DESIGN UPGRADE/DEVELOPMENT - IN 10 YEARS▶

Improve energy/position resolutions, event reconstruction▶ Finer pitch of anode wires/pads to track Compton scattered electrons▶ Add calorimeters to improve the performance of Energy measurement

SATELLITE MISSION - IN > 10 YEARSAll sky survey in the MeV energy domain▶ MeV gamma-rays from NS-NS mergers▶ Cosmic MeV gamma-ray background▶ Antimatter-based (including antihelium) DM search▶

“Event Circle”
becomes “Event Arc”

Summary!20GRAMS is the first experiment to target both gamma-ray observations in thepoorly explored MeV energy band and antimatter-based dark matter search.
▶ With a cost-effective, large-scale, LArTPC detector, the sensitivity to MeV
gamma rays can be more than an order of magnitude improved compared toprevious experiments.
▶ GRAMS antineutron measurements can provide an essentially background-freedark matter signature while deeply investigating and validating the possible dark
matter detection indicated in Fermi GCE and AMS-02 antiproton measurements.
▶ The project is currently in the R&D phase and will demonstrate the detection
concept using a small-scale prototype detector.
▶ Project will then become a balloon-borne experiment, as a step forward to asatellite mission with detector upgrades.
▶