Search for Antideuterons of Cosmic Origin Using the BESS-Polar II Magnetic-Rigidity Spectrometer.

Area of Science:

• * Particle astrophysics and cosmology
• * Cosmic ray physics

Background:

• * Cosmic rays contain various particles, including potential antimatter components.
• * Antideuterons (d[over ¯]s) are predicted by some theories, such as supersymmetry, and their detection could indicate new physics.
• * Previous experiments have searched for antideuterons, but with limited sensitivity.

Purpose of the Study:

• * To search for antideuterons (d[over ¯]s) in cosmic ray data.
• * To establish an upper limit on the antideuteron flux.
• * To test theoretical predictions for antideuteron production in the galaxy.

Main Methods:

• * Analysis of 4.7×10⁹ cosmic-ray events collected during the BESS-Polar II flight (2007-2008) at solar minimum.
• * Utilized a sensitive detector to identify and distinguish antideuterons from other cosmic ray particles.
• * Calculated a 95% confidence level (C.L.) upper limit on the antideuteron flux.

Main Results:

• * No antideuteron candidates were detected in the observed cosmic ray events.
• * A 95% C.L. upper limit on the antideuteron flux was determined to be 6.7×10⁻⁵ (m² s sr GeV/n)⁻¹ for energies between 0.163 and 1.100 GeV/n.
• * This limit represents a significant improvement, over 14 times lower than previous limits from the BESS97 experiment.

Conclusions:

• * The BESS-Polar II experiment sets the most stringent upper limit on the antideuteron flux to date.
• * This result achieves the sensitivity required to constrain current theoretical models of antideuteron production.
• * The lack of detected antideuterons places constraints on theories predicting their abundance in cosmic rays.