Introduction Science Experiment 2012 pGAPS Flight Papers & Talks GAPS Team Internal


A rendering of the detector design.


An Indirect Dark Matter Detector

GAPS (General Antiparticle Spectrometer) is a proposed experiment to search for the anti-deuteron particle in the cosmic rays. Astrophysically produced anti-deuterons have never been detected and so the unambiguous detection of even a single event would be very significant. Anti-deuterons may also be a tell-tale signature of dark matter annihilations.

GAPS, initially configured as a long-duration balloon experiment, will detect anti-deuterons with an effectively background-free method. Anti-deuterons produced by the annihilation of weakly interacting massive particles (WIMPs), a well-motivated dark matter candidate, will be captured in the GAPS target material, resulting in an exotic atom in an excited state. This exotic atom will then quickly decay, producing X-rays of precisely defined energies and a correlated pion signature from nuclear annihilation.

The method of detection uses a time-of-flight (TOF) system, which tags candidate events and particle velocities and planes of pixillated Si(Li) detectors, which serve as the target material and tracking detector. The Si(Li) detectors provide both excellent X-ray energy resolution and good particle tracking. The GAPS method has already been successfully tested in an accelerator environment at KEK in 2004 and 2005. A balloon-borne prototype experiment with a TOF system and 6 Si(Li) detectors was successfully flown in June 2012.

At low energies, antideuteron is rarely
produced by cosmic rays while dark
matter models present a high flux,
resulting in an effectively background
free experiment.


Neutralino Self-annihilation

Approximately 90% of the mass in the universe is dark matter and discovering its nature is one of the most pressing goals in science. It is hypothesized to be a new particle which is both cold and non relativistic, a WIMP (weakly interacting massive particle). A leading WIMP dark matter candidate is the hypothetical neutralino. The neutralino is predicted by the supersymmetric (SUSY) extension to the standard model and is a heavy, stable particle with the WIMP energy scale.

In contrast to direct searches and accelerator experiments, GAPS will look for the antideuterons that result from neutralino self-annihilation. These resultant particles should be detectable from areas with high dark matter density. In addition, GAPS will also explore other antideuteron sources, such as evaporating primordial black holes.

Antideuteron detection is a novel approach to the dark matter hunt. While antiprotons are more copiously produced in neutralino-neutralino annihilation, they are difficult to distinguish from cosmic ray antiprotons. Cosmic rays, however, rarely produce antideuterons below 1 GeV. Furthermore, dark matter models predict a relatively high antideuteron flux in this energy range. Thus, at low energies, antideuteron detection is effectively a background free signture of dark matter.


Previous Experiments

A GAPS prototype was tested at the KEK accelerator in 2004 and 2005. When antiprotons were dumped into the target, X-ray events with multiple signatures were detected. Furthermore, pion stars provided additional antiparticle identification and non antiparticle background was clearly identified and rejected. These experiments successfully demonstrated the multi X-ray and pion detection method to identify antiparticles. Furthermore, the absolute X-ray transition yields for antiprotons were measured for the first time in several target material.

The prototype instrument

Based on the accelerator testing and extensive design studies, we have designed a flight instrument capable of reaching deep into the parameter space of many CDM models. The heart of the instrument consists of layers of coarsely pixilated Si(Li) detectors that function as both a target in which exotic atoms are formed and a detector of the subsequent atomic transition X-rays. The Si(Li) detectors also serve as a particle tracker for the incoming antiparticle as well as the annihilation pions. An array of plastic scintillators surrounding the Si(Li) detectors serves as a time of flight (TOF) trigger, providing a measurement of the incoming antiparticle velocity.

Si(Li) detectors


GAPS provides a nearly background free technique of identifying antideuterons by using three different methods of detection for every event. Initially, a plastic time of flight (TOF) system tags the particle and records the velocity. This will distinguish antideuterons from lighter particles, such as antiprotons. The particle then slows down and stops in the target, forming an excited exotic atom. This atom then deexcites and releases both X-rays and a pion star.

Si(Li) wafers will be hexagonally packed into ten layers as the detectors. These have a timing of 50 ns and a 2 keV energy resolution while only requiring a 2 X-ray coincidence for detection. Because the X-ray energy only depends on the mass and charge of the particle, X-ray energy signatures precisely determine the type of antiparticle detected as it makes transitions to lower states. The pion star, the third layer of detection, provides greater background suppression.

2012 pGAPS Flight

Prototype GAPS (pGAPS) Flight

The pGAPS payload was built to test all the components and techniques necessary for a full size GAPS experiment including Si(Li) detectors with a radiator-based cooling system, a scintillator-based TOF system, and readout and control electronics.

The Science component of the payload consisted of 3 layers of crossed scintillator paddles (16 paddles total) with PMT readout on both ends of each paddle (32 total PMT readouts) as well as six 10cm Si(Li) detectors with active cooling (down to ~40C operationg temperature).

Other ballon-craft components of the payload such as the balloon, rotator ballast, GPS, gyro, datalink , and the battery power were provided by JAXA.

Before Launch
The science payload
Balloon Filling
Before Launch
Preparing the payload for launch
Payload on launcher

On June 3rd, 2012, the pGAPS experiment was successfully flown on a high-altitude scientific balloon. The flight took place from the Taiki Aerospace Research Field operated by JAXA and located on the east coast of Hokkaido Prefecture, Japan.

Before Launch
Ready for launch
Balloon released

The total flight was over 6 hours long, with more than 3 hours (the maximum expected) of operation of float altitude (~33km). Over one million cosmic-ray triggers were recorded, and the instrument was operated in several trigger modes to allow for a through testing of all different detector systems. Both the time-of-flight system and Si(Li) systems performed well in-flight with no PMT failures or any evidence of high-voltage corona discharge.

After cut-down, the payload was recovered within several minutes of touch-down in the ocean and was brought back to the balloon facility for cleaning and packing for shipment back to the US. The flight data copied from the gongola within 1 hour of the payload returning to the base.

Retrieving the payload
Before Launch
Recovered Payload

The goals for this flight were to measure the cosmic-ray and x-ray background and rate, test our thermal model, and demonstrate the operation of Si(Li) detectors in a high-altitude environment. More analysis of the data still remains, but we are confident that all of our goals have been met.

2012 pGAPS Flight Team

Click here for more pictures and video of the flight!

Papers and Talks

Antideuteron Sensitivity for the GAPS Experiment - arXiv
T. Aramaki, C.J. Hailey, S.E. Boggs, P. von Doetinchem, H. Fuke, S.I. Mognet, R.A. Ong, K. Perez, J. Zweerink, (June 2015).

Review of the theoretical and experimental status of dark matter identification with cosmic-ray antideuterons - arXiv
T. Aramaki, S. Boggs, S. Bufalino, L. Dal, P. von Doetinchem, F. Donato, N. Fornengo, H. Fuke, M. Grefe, C. Hailey, B. Hamilton, A. Ibarra, J. Mitchell, I. Mognet, R. A. Ong, R. Pereira, K. Perez, A. Putze, A. Raklev, P. Salati, M. Sasaki, G. Tarle, A. Urbano, A. Vittino, S. Wild, W. Xue, K. Yoshimura, (May 2015).

Potential for Precision Measurement of Low-Energy Antiprotons with GAPS for Dark Matter and Primordial Black Hole Physics - arXiv
T. Aramaki, S. E. Boggs, P. von Doetinchem, H. Fuke, C. J. Hailey, S. A. I. Mognet, R. A. Ong, K. M. Perez, J. Zweerink, Astroparticle Physics Volume 59, July–August 2014, Pages 12–17.

The Flight of the GAPS Prototype Experiment - arXiv
P. von Doetinchem, T. Aramaki, N. Bando, S. E. Boggs, H. Fuke, F. H. Gahbauer, C. J. Hailey, J. E. Koglin, S. A. I. Mognet, N. Madden, S. Okazaki, R. A. Ong, K. M. Perez, T. Yoshida, J. Zweerink, Astroparticle Physics Volume 54, February 2014, Pages 93-109.

GAPS: A Dedicated Search for Anti-Deuterons in the Cosmic Rays - PDF
Rene A. Ong, Snowmass 2013, Cosmic Frontiers 6 Subgroup, SLAC Workshop (March 2013).

The General AntiParticle Spectrometer - PDF
Philip von Doetinchem, Snowmass 2013, Cosmic Frontiers 6 Subgroup, SLAC Workshop (March 2013).

The Prototype GAPS (pGAPS) Experiment - arXiv
S. A. I. Mognet, T. Aramaki, N. Bando, S. E. Boggs, P. von Doetinchem, H. Fuke, F. H. Gahbauer, C. J. Hailey, J. E. Koglin, N. Madden, K. Mori, S. Okazaki, R. A. Ong, K. M. Perez, G. Tajiri, T. Yoshida, J. Zweerink, Nuclear Instruments and Methods in Physics Research Section A, Volume 735, 21 January 2014, Pages 24–38.

The pGAPS experiment: an engineering balloon flight of prototype GAPS - arXiv
Hideyuki Fuke, Rene A Ong, Tsuguo Aramaki, Nobutaka Bando, Steven E Boggs, Philip v Doetinchem, Florian H Gahbauer, Charles J Hailey, Jason E Koglin, Norm Madden, Samuel Adam I Mognet, Kaya Mori, Shun Okazaki, Kerstin M Perez, Tetsuya Yoshida, Jeffrey Zweerink (March 2013) .

Development of a meter-scale U-shaped Oscillating Heat Pipe for GAPS - PDF
Shun Okazaki, Hideyuki Fuke, Hiroyuki Ogawa, Takuma Okubo, Yoshiro Miyazaki (July 2012).

UCLA Dark Matter Conference:Search of Antideuteron With GAPS - PDF
P. Von Doetinchem (February 2012).

Poster: Dark Matter Search Using Cosmic-Ray Anitdeuterons - PDF
P. Von Doetinchem (April 2011).

Poster from INPAC 2011 - PDF
S. A. I. Mognet (2011).

APS Talk - PDF
S. A. I. Mognet (2011).

UC Berkely pGAPS Presentation - PDF
P. Von Doetinchem (October 2010).

Development of the General Antiparticle Spectrometer - PDF
R.A. Ong, AAS 2009 Meeting (Long Beach) (2009).

Antideuterons as an Indirect Dark Matter Signature: Si(Li) Detector Development and a GAPS Balloon Mission (Paper) - PDF
T. Aramakia et al. (November 2008) .

Antideuterons as an Indirect Dark Matter Signature: Si(Li) Detector Development and a GAPS Balloon Mission - PDF
T. Aramaki (November 2008).

Development of large format Si(Li) detectors for the GAPS dark matter experiment - PDF
T. Aramakia et al. (August 2008) .

Antideuterons as an Indirect Dark Matter Signature: Design and Preparation for a Balloon-born GAPS Experiment - PowerPoint
Oral presentation, The Hunt for Dark Matter: a Symposium on Collider, Direct and Indirect Searches (May 2007).

Current status and future plans for the general antiparticle spectrometer (GAPS) - PDF
Fuke, H.; Koglin, J. E.; Yoshida, T.; Aramaki, T.; Craig, W. W.; Fabris, L.; Gahbauer, F.; Hailey, C. J.; Jou, F. J.; Madden, N.; Mori, K.; Yu, H. T.; Ziock, K. P. (February 2007).

Antideuterons as an Indirect Dark Matter Signature: Design and Preparation for a Balloon-born GAPS Experiment - PowerPoint
J.E. Koglin et al., submitted for publication in the Journal of Physics: Conference Series, the proceedings for the 10th International Conference on Topics in Astroparticle and Underground Physics (TAUP 2007).

Antideuterons as an Indirect Dark Matter Signature: Design and Preparation for a Balloon-born GAPS Experiment - PDF
J.E. Koglin, T. Aramaki, S. E. Boggs, W.W. Craig, H. Fuke, F. Gahbauer, C.J. Hailey, N. Madden, K. Mori, R.A. Ong, T. Yoshida, H. T. Yu, and K.P. Ziock, submitted for publication in the proceedings for the 30th International Cosmic Ray Conference (2007).

Indirect Dark Matter Search with Antideuterons: Progress and Future Prospects of GAPS - PDF
J.E. Koglin el al., Nuclear Physics B (Proceedings Supplements for the 7th UCLA Symposium: Sources and Detection of Dark Matter and Dark Energy in the Universe) (2007).

Accelerator testing of the general antiparticle spectrometer; a novel approach to indirect dark matter detection - PDF
Hailey, C. J.; Aramaki, T.; Craig, W. W.; Fabris, L.; Gahbauer, F.; Koglin, J. E.; Madden, N.; Mori, K.; Yu, H. T.; Ziock, K. P. (January 2006).

Indirect Dark Matter Search with Antideuterons: Progress and Future Prospects of GAPS - PowerPoint
Oral presentation, New Views on the Universe, Kavli Institute Inaugural Symposium in Honor of David Schramm (December 2005).


Columbia University
T. Aramaki, C.J. Hailey (P.I.), N. Madden, K. Mori, Florian Gahbauer

Haverford College
K. Perez

University of California, Berkeley
S.E. Boggs

University of Hawaii, Manoa
P. Von Doetinchem

University of California, Los Angeles
R.A. Ong, J. Zweerink, S. A. I. Mognet, K. Fuller

Lawrence Livermore National Laboratory 
W.W. Craig

Institute of Space & Astronautical Science, Japan Aerospace Exploration Agency
N. Bando, H. Fuke, T. Yoshida