Historical clue formulations

• Accelerator particles — 2019-10-05
• Some subatomic particles — 2019-05-10
• Accelerator particles — 2018-03-16
• Quark-plus-antiquark particles — 2015-05-28
• Accelerator particles — 2013-08-08
• Quark/antiquark pairs — 2009-03-22
• Quark/antiquark particles — 1997-12-14