Possible Clues:

• Quark-binding particle
• Particle binding quarks together
• Tiny binder supposedly at first getting lost under old notepaper
• Aptly named particle that binds quarks together
• Particle to attach firmly, we're told
• Sticky-sounding particle
• Cut down on binding agent?
• Hypothetical particle
• 56-Down-binding particle
• Binding elementary particle