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arXiv 2408.15441nucl-exhep-ex
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通过核碰撞追踪重子数

Tracking the baryon number with nuclear collisions

STAR Collaboration

AI总结:

STAR合作组通过等压核碰撞和光核碰撞实验,发现重子数与电荷数之比及净质子产额的结果不支持价夸克承载重子数的图景,为追踪重子数的替代机制提供了实验依据。

摘要:

自宇宙早期重子产生以来,重子量子数被认为是守恒的。传统上认为带分数电荷的价夸克各自携带1/3的重子数,但重子结(一种由中性胶子构成的非微扰Y形拓扑结构)也被提出作为追踪重子数的替代实体,这两种情景均未得到实验验证。STAR合作组报告了在等压核碰撞中对快度中心区域的重子数(B)与电荷数差(ΔQ)之比的测量,以及光核碰撞中沿快度的净质子产额测量。与将重子数赋予价夸克的模型预测相比,观测到更大的B/ΔQ比值和更不对称的净质子产额,这些发现与此前Au+Au碰撞中的测量结果一致,不支持价夸克图景。

英文摘要:

Baryon quantum number is believed to be conserved since baryogenesis in the early Universe. While fractionally charged valence quarks are understood conventionally to each carry a baryon number of 1/3, the baryon junction, a non-perturbative Y-shaped topology of neutral gluons, has also been proposed as an alternative entity tracing the baryon number. Neither scenario has been verified experimentally. The STAR Collaboration reports measurements at mid-rapidity of baryon number ($\boldsymbol{B}$) over the electric charge number difference ($\boldsymbol{ΔQ}$) in isobar nuclear collisions, and the net-proton yield along rapidity in photonuclear collisions. A larger $\boldsymbol{B/ΔQ}$ ratio and less asymmetric net-proton yield are observed than predicted from models assigning baryon number to valence quarks. These findings, corroborated by previous measurements in Au+Au collisions, disfavor the valence quark picture.

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