Search

Cosmic-ray antideuterons could be a key for the discovery of exotic phenomena in our Galaxy, such as dark-matter annihilations or primordial black hole evaporation. Unfortunately the theoretical predictions of the antideuteron flux at Earth are plagued with uncertainties from the mechanism of antideuteron production and propagation in the Galaxy. We present the most up-to-date calculation of the antideuteron fluxes from cosmic-ray collisions with the interstellar medium and from exotic processes. We include for the first time the antideuteron inelastic interaction cross section recently measured by the ALICE collaboration to account for the loss of antideuterons during propagation. In order to bracket the uncertainty in the expected fluxes, we consider several state-of-the-art models of antideuteron production and of cosmic-ray propagation.

The possibility of antihelium production in interaction of cosmic rays with the interstellar gas is studied using large-scale Monte Carlo simulations. For this purpose, an energy-dependent coalescence mechanism developed previously is extended to estimate the production of light antinuclei (${}^3\overline{\text{He}}$ and ${}^4\overline{\text{He}}$). The uncertainty in the coalescence parameter and its effect on the expected antiparticle flux is also investigated. The simulated background antihelium fluxes are found to be lower than the fluxes predicted by simplified models using numerical scaling techniques., Comment: 16 figures

The precise measurement of cosmic-ray antiparticles and antinuclei serves as important means for identifying the nature of dark matter and other beyond-standard-model physics. Recent years showed that identifying the nature of dark matter with cosmic-ray positrons and antiprotons is difficult, and has lead to a significantly increased interest in cosmic-ray antideuteron and antihelium searches. Antideuterons and antihelium nuclei may also be generated in dark matter annihilations or decays, offering a potential breakthrough in unexplored phase space for dark matter. Low-energy antinuclei are an important approach because the flux from dark matter interactions exceeds the background flux by orders of magnitude in the low-energy range for a wide variety of models without relying on any boosting mechanisms. This talk summarizes the results of the ``2nd Cosmic-ray Antideuteron Workshop" that was held in March 2019 and brought together theorists and experimentalists in the field to discuss the current status, perspectives, and challenges for cosmic-ray antinuclei searches. It will review the motivation for antinuclei searches, the experimental status and its interpretation, as well as discuss some of the theoretical and experimental uncertainties of antinuclei production and propagation in our Galaxy.

The General Antiparticle Spectrometer (GAPS) is an Antarctic balloon-borne detector designed to measure the low energy (< 0.25 GeV/n) antideuteron cosmic ray component as a distinctive signal from dark matter annihilation or decay in the Galactic halo. The detector consists of a tracker, made up by ten planes of lithium-drifted silicon Si(Li) detectors, surrounded by a plastic scintillator time-of-flight system. GAPS uses a novel particle identification method based on exotic atom capture and decay with emission of pions, protons and atomic X-rays from a common annihilation vertex. The resulting "nuclear star" topology provide sufficient rejection power to suppress any non-antiparticle cosmic ray background. Here we present results for a preliminary reconstruction algorithm that has been tested on simulated events. The GAPS simulation software is based on GEANT4 and fully reproduce the detector geometry. Various technique like Kalman filter, Hough-3D transform, Least Squares minimization were combined in order to precisely reconstruct the topology of the "nuclear star". The performance of the final algorithm in reconstructing the annihilation vertex position and the secondary pions will be discussed.

The study of the cosmic-ray deuteron and antideuteron flux is receiving increasing attention in current astrophysics investigations. For both cases, an important contribution is expected from the nuclear interactions of primary cosmic rays with intergalactic matter. In this work, deuteron and antideuteron production from 20 to $2.6\ifmmode\times\else\texttimes\fi{}{10}^{7}\text{ }\text{ }\mathrm{GeV}$ beam energy in $\mathrm{p}+\mathrm{p}$ and $\mathrm{p}+\mathrm{A}$ collisions were simulated using EPOS-LHC and Geant4's FTFP-BERT Monte Carlo models by adding an event-by-event coalescence model afterburner. These estimates depend on a single parameter (${p}_{0}$) obtained from a fit to the data. The ${p}_{0}$ for deuterons in this wide energy range was evaluated for the first time. It was found that ${p}_{0}$ for antideuterons is not a constant at all energies as previous works suggested and, as a consequence, the antideuteron production cross section can be at least 20 times smaller in the low-collision-energy region than earlier estimations.

Experiments aiming to directly detect dark matter (DM) particles have yet to make robust detections, thus underscoring the need for complementary approaches such as searches for new particles at colliders, and indirect DM searches in cosmic-ray spectra. Low energy (< 0.25 GeV/n) cosmic-ray antiparticles such as antideuterons are strong candidates for probing DM models, as the yield of these particles from DM processes can exceed the astrophysical background by more than two orders of magnitude. The General Antiparticle Spectrometer (GAPS), a balloon borne cosmic-ray detector, will perform an ultra-low background measurement of the cosmic antideuteron flux in the regime < 0.25 GeV/n, which will constrain a wide range of DM models. GAPS will also detect approximately 1000 antiprotons in an unexplored energy range throughout one long duration balloon (LDB) flight, which will constrain < 10 GeV DM models and validate the GAPS detection technique. Unlike magnetic spectrometers, GAPS relies on the formation of an exotic atom within the tracker in order to identify antiparticles. The GAPS tracker consists of ten layers of lithium-drifted silicon detectors which record dE/dx deposits from primary and nuclear annihilation product tracks, as well as measure the energy of the exotic atom deexcitation X-rays. A two-layer, plastic scintillator time of flight (TOF) system surrounds the tracker and measures the particle velocity, dE/dx deposits, and provides a fast trigger to the tracker. The nuclear annihilation product multiplicity, deexcitation X-ray energies, TOF, and stopping depth are all used together to discern between antiparticle species. This presentation provided an overview of the GAPS experiment, an update on the construction of the tracker and TOF systems, and a summary of the expected performance of GAPS in light of the upcoming LDB flight from McMurdo Station, Antarctica in 2020., 4 pages, 3 figures, The 39th International Conference on High Energy Physics (ICHEP2018), Seoul, Korea

Low-rigidity cosmic rays and solar particles are strongly deflected by Earth's geomagnetic field and only particles above a certain geomagnetic cutoff rigidity are able to reach space-based or balloon-borne experiments. Geomagnetic cutoff calculations utilizing the PLANETOCOSMICS software with the IGRF geomagnetic field and the Tsyganenko magnetosphere models are discussed. These calculations focus on the time from 2011 to 2015 where the AMS-02 experiment on the International Space Station (ISS) was operational and are used to compare trajectories of cosmic-ray detectors on the ISS and balloon-borne experiments. A database approach was developed that allows very quick geomagnetic cutoff calculations, and thus an easy comparison of different trajectories. During the period under study time a particle-rich event that greatly perturbed the magnetic field strength on 7 March 2012 was observed and was studied in more detail from the geomagnetic cutoff perspective. All calculations put a special emphasis on antiparticles because precise measurement of their low-rigidity fluxes have the potential of revealing exotic sources like dark matter annihilations or primordial black holes. The findings underline that geomagnetic cutoff effects have to be treated as a function of particle charge, time, location, and direction.

The GAPS experiment is foreseen to carry out a dark matter search by measuring low-energy cosmic-ray antideuterons and antiprotons with a novel detection approach. It will provide a new avenue to access a wide range of different dark matter models and masses from about 10 GeV to 1 TeV. The theoretically predicted antideuteron flux resulting from secondary interactions of primary cosmic rays is very low. Well-motivated theories beyond the Standard Model contain viable dark matter candidates, which could lead to a significant enhancement of the antideuteron flux due to annihilation or decay of dark matter particles. This flux contribution is believed to be especially large at low energies, which leads to a high discovery potential for GAPS. The GAPS low-energy antiproton search will provide some of the most stringent constraints on ~30 GeV dark matter, will provide the best limits on primordial black hole evaporation on galactic length scales, and explore new discovery space in cosmic-ray physics. GAPS is designed to achieve its goals via long duration balloon flights at high altitude in Antarctica. The detector itself will consist of 10 planes of Si(Li) solid state detectors and a surrounding time-of-flight system. Antideuterons and antiprotons will be slowed down in the Si(Li) material, replace a shell electron and form an excited exotic atom. The atom will be deexcited by characteristic X-ray transitions and will end its life by the formation of an annihilation pion/proton star. This unique event structure will deliver a nearly background free detection possibility.

Recent years have seen increased theoretical and experimental effort towards the first-ever detection of cosmic-ray antideuterons, in particular as an indirect signature of dark matter annihilation or decay. In contrast to indirect dark matter searches with positrons, antiprotons, or gamma-rays, which suffer from relatively high and uncertain astrophysical backgrounds, searches with antideuterons benefit from very suppressed conventional backgrounds, offering a potential breakthrough in unexplored phase space for dark matter. This report is a condensed summary of the article "Review of the theoretical and experimental status of dark matter identification with cosmic-ray antideuteron" [1].

The GAPS experiment is foreseen to carry out a dark matter search using a novel detection approach to detect low-energy cosmic-ray antideuterons. The theoretically predicted antideuteron flux resulting from secondary interactions of primary cosmic rays with the interstellar medium is very low. So far not a single cosmic antideuteron has been detected by any experiment, but well-motivated theories beyond the standard model of particle physics, e.g., supersymmetry or universal extra dimensions, contain viable dark matter candidates, which could led to a significant enhancement of the antideuteron flux due to self-annihilation of the dark matter particles. This flux contribution is believed to be especially large at small energies, which leads to a high discovery potential for GAPS. GAPS is designed to achieve its goals via a series of ultra-long duration balloon flights at high altitude in Antarctica, starting in 2014. The detector itself will consist of 13 planes of Si(Li) solid state detectors and a time of flight system. The low-energy antideuterons (< 0.3 GeV/n) will be slowed down in the Si(Li) material, replace a shell electron, and form an excited exotic atom. The atom will be deexcited by characteristic x-ray transitions and will end its life by forming an annihilation pion star. This unique event structure will allow for nearly background free detection. To prove the performance of the different detector components at stratospheric altitudes, a prototype flight will be conducted in 2011 from Taiki, Japan.

Intriguing signals with excesses over expected backgrounds have been observed in many astrophysical and terrestrial settings, which could potentially have a dark matter origin. Astrophysical excesses include the Galactic Center GeV gamma-ray excess detected by the Fermi Gamma-Ray Space Telescope, the AMS antiproton and positron excesses, and the 511 and 3.5 keV X-ray lines. Direct detection excesses include the DAMA/LIBRA annual modulation signal, the XENON1T excess, and low-threshold excesses in solid state detectors. We discuss avenues to resolve these excesses, with actions the field can take over the next several years., Comment: 57 pages, solicited white paper submitted to the Proceedings of the US Community Study on the Future of Particle Physics (Snowmass 2021)