The GAPS experiment a search for cosmic-ray antinuclei from dark - - PowerPoint PPT Presentation
The GAPS experiment a search for cosmic-ray antinuclei from dark matter M. Kozai (ISAS/JAXA) on behalf of the GAPS collaboration 1 The GAPS Experiment International collaboration between US, Japanese, and Italian institutes 2
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International collaboration between US, Japanese, and Italian institutes
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General Anti-Particle Spectrometer
➢ High-sensitivity survey for low-energy antinuclei in cosmic-rays Balloon experiment ➢ Instrument size : ~4 m x 4 m x 4 m ➢ Payload mass : 3.5 t NASA long duration balloon (LDB) flight from Antarctica ➢ Suitable for observation of low-rigidity particles ➢ ~35 days/flight ➢ Nominal 3 flights are proposed ➢ The first flight is
scheduled in late 2021 GAPS Payload
NASA
GAPS < 0.25 GeV
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➢ Antiproton ✓ Below ~0.3 GeV/n is unexplored
✓ Helpful constraints on cosmic-ray propagation/source ➢ Antideuteron (our primary target) Background-free signal from dark matter in galactic halo if dark matter is WIMPs (weakly interactive massive particles) ➢ Antihelium ✓ “Candidate” events by AMS-02 ✓ Complementary search by GAPS
Antiproton spectra
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➢ Background ഥ 𝐄 (known physics) ✓ Cosmic-ray collision with interstellar medium ✓ Kinematics & cosmic-ray soft spectrum → Suppressed below several GeV ➢ Signal ഥ 𝐄 (beyond-the-standard-model physics) ✓ WIMP annihilation/decay at rest ✓ Soft spectrum peaking <1 GeV for O(10) GeV WIMPs → 103 - 104 signal/background ratio ✓ GAPS will provide the highest sensitivity ✓ GAPS is also sensitive to O(100) GeV ~ O(1) TeV WIMPs in certain models Predicted ഥ 𝐄 fluxes
Antideuteron (ഥ 𝐄) as a dark matter signal
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Silicon detector array Time-of-Flight system (plastic scintillator paddles)
i. Characteristic X-rays are emitted by ladder deexcitation
→ Identifying cosmic-ray antinucleus Novel detection concept utilizing exotic atom
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Lithium drifted silicon (Si(Li)) detector
Silicon detector is optimal for exotic-atom technique ➢ Low atomic number (14) of Si → Appropriate energy distribution of characteristic X-rays ➢ Sufficient energy resolution to distinguish characteristic X-ray energies Thick sensitive layer can be obtained with relatively low cost → Suitable for GAPS silicon detector array which functions as a particle degrader ➢ Energy resolution <4 keV FWHM for 60 keV X-rays at ~-40℃ ➢ Thickness 2.5 mm (sensitive layer >90%), Diameter 10 cm, 8 readout strips ➢ Mass production of >1000 detectors Goal design
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➢ Leakage current suppression ✓ ~0.5 nA/cm2 at -35℃ achieved ➢ Below 4 keV FWHM for 60 keV at ~-40℃ X-ray achieved ➢ Collaboration with Shimadzu corp. and SUMCO corp. ➢ Detailed design and fabrication process fixed ➢ Mass production of >1000 detectors started from Jan., 2019 ➢ ~70 Detectors/month, Yield ~90% ➢ Uniform Li drift into large-area (~10cm) wafer ✓ Si ingot optimized for Si(Li) detector ✓ Li evaporation and drift methods
copper-stained cross section Li-drifted region Energy spectrum with X-ray sources at -41C
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Silicon detector Integration
4 detectors/module Polyethylene foam 36 modules Tracker : 10 layers
Front-End Electronics
for both X-rays and particles (10 keV – 100 MeV) ➢ Test modules and test boards have been fabricated ➢ Integration/performance tests are under way
Our challenge: Cooling silicon detector using a passive cooling system ➢ Unprecedent challenge in balloon experiment ➢ High albedo in Antarctic flight makes it more difficult New heat pipe system for GAPS ➢ Transferring heat input from preamp to radiator ➢ 2-phase coolant fluid → Large heat transfer and uniform temperature distribution ➢ Drivers of coolant : Gravity and pressure difference → Basically passive and low-power system ➢ Developments ✓ Study of self-excited flow ✓ Some technical elements 2-phase coolant, Reservoir, Check-valve, Auxiliary pump and heater ➢ Tests with the engineering model (EM) in thermal chamber
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Silicon detector cooling
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Thermal analysis of the entire payload
GAPS Radiator tests 2018 & 2019 Scaled radiator
Balloon experiment (piggy back) to demonstrate the utmost cooling (<-55℃) of radiator
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Time-of-Flight system
➢ ~200 scintillator paddles (T6.5 mm x W16 cm x L1.2~1.8 m) ➢ Both-sides-readout → position information in each paddle ➢ Requirements ✓ Timing resolution <500 ps ✓ Charge reconstruction <0.25e ➢ 6 SiPMs on each side of paddle ✓ Custom preamplifier with built-in SiPMs ✓ Custom DAQ board with DRS4 ASIC ➢ Performance test with prototype system is under way Achieved 340 ps timing resolution and dynamic range ➢ Construction of scintillator paddles already started
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Simulation study
➢ Geant 4 model ✓ Implementing full payload designs ✓ Validation of physical processes ➢ Particle detection/identification scheme ✓ Trajectory reconstruction algorithm ✓ Likelihood analysis among beta, dE/dx, stopping range, etc. ✓ Neural network techniques
Trajectory reconstruction
G4 model
ഥ 𝐄 sensitivity estimation : 2 x 10-6 (m2 s sr GeV/n)-1 for 105 days flight
(T. Aramaki et al., 2016 Astropart. Phys. 74, 6-13)
➢ More precise implementation of simulation code ➢ Improvement of analysis algorithm
Low-energy cosmic-ray antideuteron provides a clean channel for dark matter search. GAPS experiment
➢Survey for unexplored low-energy region of antinuclei spectra with high sensitivity ➢Search for antideuterons as a smoking gun signature of WIMP DM.
Key techniques for the novel detection concept utilizing the exotic atom had been developed and validated. Full scale system testing will be demonstrated in early 2020.
➢Silicon detectors integrated into detector modules ➢Time-of-Flight paddles with SiPMs ➢DAQ/PS system
The first balloon flight from Antarctica is scheduled in late 2021.
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Antideuteron (ഥ 𝐄) as a DM signal
Interstellar medium (H, He, ...) ഥ 𝐪 ഥ 𝐨 Coalescence ഥ 𝐪 ഥ 𝐨 ഥ 𝐄 Cosmic-ray origin ഥ 𝐄 (background, known physics) Cosmic-ray (p, He, ...)
p, n, γ, ν, ...
Collision Dark matter origin ഥ 𝐄 (signal, exotic physics) ഥ 𝐪 ഥ 𝐨 Coalescence ഥ 𝐪 ഥ 𝐨 ഥ 𝐄
p, n, γ, ν, ...
DM annihilation/decay ➢ Cosmic-ray energy threshold for the particle productions ➢ Steeply falling cosmic-ray energy spectrum Suppressed ഥ D flux below several GeV
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GAPS sensitivity as a function of DM mass
into u-ubar
for DM mass below 100 GeV in the MAX propagation model (favored by AMS-02 antiproton; Brauninger, 2009) dbar is also detectable for heavy DM (0.5-20 TeV) In MAX propagation and certain DM models such as:
AMS-02 positron and antiproton data
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Exotic atom
nucleus
non-electron particle (antiproton, antideuteron…)
1. Target material degrades incoming antinucleus. 2. Antinucleus is captured by atomic orbit of the target material. 3. Generation of the exited exotic atom
Decay of the exited exotic atom
Auger transition
Ladder deexcitations → characteristic X-rays Annihilation with nucleus → multiple π/p emissions Characteristic X-rays and π/p emissions → Detection and identification of incoming antinucleus
Energy level
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➢ Background ഥ 𝐄 (Ibarra&Wild, 2013) ➢ Signal ഥ 𝐄 from several 10 GeV WIMP models (Donato+ 2008, Dal&Raklev 2014, Baer+ 2005) ✓ SUSY model
✓ Extra-dimensional GUT
neutrino (LZP) ✓ Shaded regions : Galactic propagation uncertainties ✓ Boost factor for DM annihilation Effect of density clump Set minimum = 1 → Conservative estimation Predicted ഥ 𝐄 spectrum
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➢ Leakage current suppression
✓ Guard-ring structure ✓ Surface treatment ✓ New contact structure ➢ Detailed design and fabrication process fixed ➢ Mass production started from Jan., 2019 ➢ ~70 Detectors/month, Yield ~90% ~0.5 nA/cm2 at -35℃ achieved
➢ Uniform Li drift into large-area (~10cm) wafer
✓ Si ingot optimized for Si(Li) detector ✓ Li evaporation and drift apparatuses/methods copper-stained cross section Li-drifted region Energy spectrum with X-ray sources at -41C <4 keV FWHM for 60 keV X-ray achieved ➢ Collaboration with Shimadzu corp. and SUMCO corp.
Silicon detector array Radiator
Heat pipes
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Our challenge: Cooling silicon detector using a passive cooling system
➢ Unprecedent challenge in balloon experiment ➢ High albedo in Antarctic flight makes it more difficult
New heat pipe system for GAPS
➢ Transferring heat input from preamp to radiator ➢ 2-phase coolant fluid → Large heat transfer and uniform temperature distribution ➢ Drivers of coolant : Gravity and pressure difference → Basically passive and low-power system
Silicon detector cooling
GAPS heat pipe concept
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➢Requirement for TOF ➢Timing resolution for MIP : <500 ps ➢Photoelectrons >50 for MIP ➢Δβ/β < 0.12 ➢Charge reconstruction < 0.25e ➢Angle resolution < ±5°for vertical ➢Position resolution < ±10 cm ➢Discriminate >80% of incoming tracks from outgoing particles (i.e. annihilation products)