论文标题
前向夸克Dijet生产中改进的TMD和CGC框架的比较
Comparison of improved TMD and CGC frameworks in forward quark dijet production
论文作者
论文摘要
最近在高能稀释密度碰撞中研究了小$ x $ gluon饱和度，最近提出了改进的TMD（ITMD）分解公式。在彩色玻璃冷凝物（CGC）框架中，它代表了硬尺度反向力量扩展的主要项。它包含与小Gluon的横向动量$ k_t $相关的领先TMD分解公式，但还结合了运动曲折的全阶重新召集，从而在大型$ k_t $上与高能分解相匹配。在本文中，我们定量地评估了ITMD公式的准确性，对于高能质子 - 蛋白质（$ p+p $）和Proton-Nucleus（$ p+a $）碰撞的Quark Dijet产生的情况。我们通过比较夸克式的方位角角度$δ$分布与CGC公式获得的分布来做到这一点。对于每个夸克动量$ p_t $比目标饱和量表大得多，$ q_s $大得多，ITMD公式与CGC公式的近似值较宽。由于在CGC框架中存在真正的高级阵阵贡献，因此它降低了JET $ P_T $的降低，这变得不太准确，这代表了ITMD公式中不存在多体型散射效应。我们发现，随着硬喷射动量的降低，ITMD的准确性是从小角度下降的，在高能基础化制度下，而在接近$ δϕ =π$的TMD策略中，需要$ P_T $的非常低的值才能看到CGC和ITMD公式之间的差异。此外，对于$ p+a $碰撞中的$ p_t $的较高值，与$ p+p $碰撞相比，对ITMD的真实扭曲更正变得可见，这表明它们通过目标饱和度量表增强。
For studying small-$x$ gluon saturation in forward dijet production in high-energy dilute-dense collisions, the improved TMD (ITMD) factorization formula was recently proposed. In the Color Glass Condensate (CGC) framework, it represents the leading term of an expansion in inverse powers of the hard scale. It contains the leading-twist TMD factorization formula relevant for small gluon's transverse momentum $k_t$, but also incorporates an all-order resummation of kinematical twists, resulting in a proper matching to high-energy factorization at large $k_t$. In this paper, we evaluate the accuracy of the ITMD formula quantitatively, for the case of quark dijet production in high-energy proton-proton($p+p$) and proton-nucleus ($p+A$) collisions at LHC energies. We do so by comparing the quark-antiquark azimuthal angle $Δϕ$ distribution to that obtained with the CGC formula. For a dijet with each quark momentum $p_t$ much larger than the target saturation scale, $Q_s$, the ITMD formula is a good approximation to the CGC formula in a wide range of azimuthal angle. It becomes less accurate as the jet $p_t$'s are lowered, as expected, due to the presence of genuine higher-twists contributions in the CGC framework, which represent multi-body scattering effects absent in the ITMD formula. We find that, as the hard jet momenta are lowered, the accuracy of ITMD start by deteriorating at small angles, in the high-energy-factorization regime, while in the TMD regime near $Δϕ=π$, very low values of $p_t$ are needed to see differences between the CGC and the ITMD formula. In addition, the genuine twists corrections to ITMD become visible for higher values of $p_t$ in $p+A$ collisions, compared to $p+p$ collisions, signaling that they are enhanced by the target saturation scale.
