论文标题
在$ \ sqrt {s _ {\ mathrm {nn}}}} = 5.02 $ tev with atlas中的超疗法pb+pb碰撞中的独家dimuon生产
Exclusive dimuon production in ultraperipheral Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV with ATLAS
论文作者
论文摘要
超疗法碰撞（UPC）中的独家二酮产生是由碰撞高能铅核的强电磁场中的光子 - 光子相互作用产生的，$ \ mathrm {pbpb}（γγ） （\ mathrm {pb}^{（\ star）} \ mathrm {pb}^{（\ star）}）$，使用$ \ mathcal {l} _ {\ mathrm {intrm {int}} = 0.48 $ \ sqrt {s_ \ mathrm {nn}} = 5.02 $ tev铅铅碰撞数据与Atlas检测器。 Dimuon对测量在基准区域$ P _ {\ Mathrm {t}μ}> 4 $ GEV，$ |η_μ| <2.4 $，不变的质量$ m_ {μμ}> 10 $ gev，$ p _ {\ mathrm {t，μμ}}} <2 $ gev。使用模板拟合技术从数据中提取了单分离过程中的主要背景。差分横截面作为$ M_ {μμ} $的函数，绝对对快速度（$ | y_ {μμ} | $），dimuon休息框架中的散射角（$ | \ cos \ cos \ cos \ vartheta^{\ star} _ {\ star} _ {_ {μμμ} | $）和碰撞光子colding Photon Elolgies。 UPC $γγ\rightarrowμ^{+}μ^{ - } $进程的总横截面的测量为$σ_{\ Mathrm {fid}}}^{μμμ} = 34.1 \！ \ pm \！ 0.3 \ mathrm {（stat。）} \！ \ pm \！ 0.7 \ Mathrm {（Syst。）} $ $ $ $ \ MATHRM {B} $。通常，与Starlight的计算发现了良好的一致性，该计算结合了前阶BREIT-wheeler过程，没有最终状态效应，尽管观察到测量和理论期望之间的差异。特别是，发现数据较大的横截面的数据比计算大约要大约10-20％，这表明在初始状态下存在较大的光子通量。还研究了在前进和/或向后中子产生的情况下修改Dimuon横截面的，并发现与更难的传入光子谱相关，与期望一致。
Exclusive dimuon production in ultraperipheral collisions (UPC), resulting from photon-photon interactions in the strong electromagnetic fields of colliding high-energy lead nuclei, $\mathrm{PbPb}(γγ) \rightarrow μ^+μ^- (\mathrm{Pb}^{(\star)}\mathrm{Pb}^{(\star)} )$, is studied using $\mathcal{L}_{\mathrm{int}} = 0.48$ nb$^{-1}$ of $\sqrt{s_\mathrm{NN}}=5.02$ TeV lead-lead collision data at the LHC with the ATLAS detector. Dimuon pairs are measured in the fiducial region $p_{\mathrm{T}μ} > 4$ GeV, $|η_μ| < 2.4$, invariant mass $m_{μμ} > 10$ GeV, and $p_{\mathrm{T,μμ}} < 2$ GeV. The primary background from single-dissociative processes is extracted from the data using a template fitting technique. Differential cross sections are presented as a function of $m_{μμ}$, absolute pair rapidity ($|y_{μμ}|$), scattering angle in the dimuon rest frame ($|\cos \vartheta^{\star}_{μμ}|$) and the colliding photon energies. The total cross section of the UPC $γγ\rightarrow μ^{+}μ^{-}$ process in the fiducial volume is measured to be $σ_{\mathrm{fid}}^{μμ} = 34.1 \! \pm \! 0.3 \mathrm{(stat.)} \! \pm \! 0.7 \mathrm{(syst.)}$ $μ\mathrm{b}$. Generally good agreement is found with calculations from STARlight, which incorporate the leading-order Breit-Wheeler process with no final-state effects, albeit differences between the measurements and theoretical expectations are observed. In particular, the measured cross sections at larger $|y_{μμ}|$ are found to be about 10-20% larger in data than in the calculations, suggesting the presence of larger fluxes of photons in the initial state. Modification of the dimuon cross sections in the presence of forward and/or backward neutron production is also studied and is found to be associated with a harder incoming photon spectrum, consistent with expectations.
