光子-双轻子径向流层析成像的物理解释及其局限

中文摘要 AI 辅助

热光子和双轻子提供了相对论性重离子碰撞中产生的物质温度与集体膨胀的互补信息。它们的组合已被提议作为径向流的电磁探针：利用一个相对对流动不敏感的双轻子不变质量逆斜率来推断在没有横向流动情况下预期的光子逆斜率，并将其与观测到的光子斜率进行比较。本文通过一个受控的膨胀火球计算，检验了这一构造的物理基础及其主要局限。双轻子与无流动光子的逆斜率之间存在紧密关联，因为它们对底层热标度变化的响应相似，尽管数值关系依赖于谱窗口和电磁源。流动引起的光子逆斜率变化与沿光子动量的光子发射加权速度分量的相关性，强于其与体状径向流平均值的相关性。预热源变化可能使推断的无流动光子参考产生偏差，并即使在直接光子谱-流动信号消失时也能产生表观流动，而多个光子和双轻子窗口提供了独立的响应模式，有助于诊断这种源模糊性。这些结果阐明了光子-双轻子径向流层析成像所测量的内容，以及其解释所需的源一致性。

英文摘要

Thermal photons and dileptons provide complementary information on the temperature and collective expansion of matter created in relativistic heavy-ion collisions. Their combination has been proposed as an electromagnetic probe of radial flow: a comparatively flow-insensitive dilepton invariant-mass inverse slope is used to infer the photon inverse slope expected without transverse flow and compared with the observed photon slope. Here the physical basis and leading limitation of this construction are examined using a controlled expanding-fireball calculation. The dilepton and flow-free photon inverse slopes are tightly correlated because they respond similarly to changes of the underlying thermal scale, although the numerical relation depends on the spectral window and electromagnetic source. The flow-induced change of the photon inverse slope correlates more strongly with the photon-emission-weighted velocity component along the photon momentum than with a bulk-like radial-flow average. Prethermal source variations can bias the inferred flow-free photon reference and generate apparent flow even when the direct photon spectral-flow signal vanishes, while multiple photon and dilepton windows provide independent response patterns that can help diagnose this source ambiguity. These results clarify both what photon--dilepton radial-flow tomography measures and the source consistency required for its interpretation.

发表机构

• University of California, Berkeley（加州大学伯克利分校）
• Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）

机构由 AI 辅助整理，请以论文原文为准。

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13 pages, 5 figures