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arXiv 2403.13631hep-ph
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HERA上大动量转移下独家衍射中质子波函数的饱和与涨落

Saturation and fluctuations in the proton wavefunction at large momentum transfers in exclusive diffraction at HERA

Arjun Kumar, Tobias Toll

AI总结:

本文提出质子几何模型,热点数量和大小随分辨率尺度演化,用单一参数描述$|t|>1.1~$GeV$^2$的非相干$t$谱,发现HERA数据对饱和尺度效应不敏感。

摘要:

我们提出了一个质子几何模型,其中质子厚度函数中胶子密度热点的数量和大小随事件的分辨率尺度(由独家衍射$ep$碰撞中的Mandelstam $t$变量给出)而演化。我们使用依赖于碰撞参数的饱和偶极子模型bSat/IPSat及其线性化(非饱和)版本bNonSat。在后者中,质子厚度有明确的厚度解释,而在前者中它直接与饱和尺度相关。由此产生的热点分裂唯象模型充分利用了早期的实验和唯象研究,能够用单一唯象参数描述$|t|>1.1~$GeV$^2$范围内的整个非相干$t$谱。我们使用先前提出的热点模型作为演化的初始条件。所得模型与部分子簇射类似,是一种分辨率尺度演化。非相干截面与质子初始态中的几何涨落成正比。热点演化引起多种逐事件涨落,如热点数量、宽度和归一化涨落,饱和尺度涨落是其直接结果。基于分辨率的演化使热点产生有效排斥。我们用热点演化模型研究$t$谱中的饱和尺度效应,发现HERA数据对此物理不敏感。

英文摘要:

We present a model of proton geometry where the number and size of gluon density hotspots in the proton's thickness function evolves with the resolution scale of the event given by the Mandelstam $t$ variable in exclusive diffractive $ep$ collisions. We use the impact-parameter dependent saturation dipole model bSat/IPSat, as well as its linearised (non-saturated) version bNonSat. In the latter the proton thickness has a clear interpretation as a thickness and in the former it is directly related to the saturation scale. The resulting phenomenological model for the splitting of hotspots, making full use of earlier experimental and phenomenological studies, is able to describe the entire incoherent $t$-spectrum for $|t|>1.1~$GeV$^2$ with a single phenomenological parameter. We use the previously suggested hotspot model as an initial condition for our evolution. The resulting model is a resolution scale-evolution in the same vein as a parton shower.The incoherent cross section is directly proportional to geometrical fluctuations in the proton's inital state. The hotspot evolution give rise to several kinds of event-by-event fluctuations such as in the hotspot number, width and normalization, and saturation scale fluctuations is a direct effect of these. A natural consequence of our resolution based evolution is that the hotspots obtain an effective repulsion. We use our hotspot evolution model to investigate saturation scale effects in the $t$-spectrum, and found that HERA data is not sensitive to this physics.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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