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arXiv 2003.06201hep-ph
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在具有$k_T$ -因子分解的NRQCD中的底胞产生和极化。II:$Υ(2S)$和$χ_b(2P)$介子

Bottomonia production and polarization in the NRQCD with $k_T$-factorization. II: $Υ(2S)$ and $χ_b(2P)$ mesons

N. A. Abdulov, A. V. Lipatov

摘要:

在$k_T$ -因子分解方法的框架下研究了高能下$Υ(2S)$的产生和极化.我们的考虑是基于非相对论QCD形式主义的束缚态的形成和离壳生产振幅硬部分子过程。考虑了直接产生机制、辐射$χ_b(3P)$和$χ_b(2P)$衰变的反馈贡献以及$Υ(3S)$衰变的贡献。由Ciafaloni-Catani-Fiorani-Marchesini演化方程和Kimber-Martin-Ryskin公式导出了质子中与横动量有关的胶子密度。用多极辐射理论处理非微扰色八重态跃迁,从CMS和ATLAS合作组在LHC能量$\sqrt s = 7$和$13$ TeV下测量的$Υ(2S)$横动量分布和LHCb合作组在$\sqrt s = 7$和$8$ TeV下测量的相对产生率$R^{χ_b(2P)}_{Υ(2S)}$的组合拟合中,我们提取了相应的$Υ(2S)$和$χ_b(2P)$介子的非微扰矩阵元。然后,我们应用提取的值来研究偏振参数$λ_θ$,$λ_ϕ$和$λ_{θϕ}$,这决定了$Υ(2S)$自旋密度矩阵。我们的预测有一个很好的协议与目前可用的数据在理论和实验的不确定性。

英文摘要:

The $Υ(2S)$ production and polarization at high energies is studied in the framework of $k_T$-factorization approach. Our consideration is based on the non-relativistic QCD formalism for bound states formation and off-shell production amplitudes for hard partonic subprocesses. The direct production mechanism, feed-down contributions from radiative $χ_b(3P)$ and $χ_b(2P)$ decays and contributions from $Υ(3S)$ decays are taken into account. The transverse momentum dependent gluon densities in a proton were derived from the Ciafaloni-Catani-Fiorani-Marchesini evolution equation as well as from the Kimber-Martin-Ryskin prescription. Treating the non-perturbative color octet transitions in terms of the mulitpole radiation theory, we extract the corresponding non-perturbative matrix elements for $Υ(2S)$ and $χ_b(2P)$ mesons from a combined fit to $Υ(2S)$ transverse momenta distributions measured by the CMS and ATLAS Collaborations at the LHC energies $\sqrt s = 7$ and $13$ TeV and from the relative production rate $R^{χ_b(2P)}_{Υ(2S)}$ measured by the LHCb Collaboration at $\sqrt s = 7$ and $8$ TeV. Then we apply the extracted values to investigate the polarization parameters $λ_θ$, $λ_ϕ$ and $λ_{θϕ}$, which determine the $Υ(2S)$ spin density matrix. Our predictions have a good agreement with the currently available data within the theoretical and experimental uncertainties.

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