Research press release


Nature Physics

Quark soup’s strangeness observed



今回ALICE Collaborationは、クォークグルーオンプラズマが形成されるとは予測されていなかった、原子核よりはるかに軽い陽子の衝突において、こうした効果を初めて観測したことを報告している。さらに、ストレンジ粒子生成量の増大に関連する、他の予想外の特徴も見いだされた。今回の観測結果によって、ストレンジクォーク生成の背後にある機構に関する手掛かりが得られ、始原的なクォークスープからどのようにしてストレンジ粒子が初めて現れたかについての理解が深まるだろう。

Observation of an unexpectedly large number of particles containing strange quarks, created by colliding protons together at the CERN Large Hadron Collider, is reported in a paper published online in Nature Physics this week.

Shortly after the Big Bang, elementary particles like protons and neutrons had yet to form, but their building blocks, quarks and gluons, roamed freely in a hot, primordial soup. This mixture, known as a quark-gluon plasma, can be recreated by colliding heavy nuclei inside particle colliders. Quarks come in several varieties: up and down quarks form ordinary matter, while strange quarks can be produced in large amounts in high-energy physics experiments. An enhanced production of strange particles is expected, and has already been observed, in nuclear collisions leading to the formation of quark-gluon plasma.

Here the ALICE Collaboration reports the first observation of this effect in the collision of the much lighter protons, where the formation of a quark-gluon plasma was not expected. Moreover, they also find other unexpected features related to the increased abundance of strange particle production. This observation will provide clues about the mechanisms behind the creation of strange quarks and improve our understanding of how strange particles first emerged from the primordial quark soup.

doi: 10.1038/nphys4111


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