The production of a pair of τ leptons via photon–photon fusion, γγ→ττ, is observed for the first time in proton–proton collisions, with a significance of 5.3 standard deviations. This observation is based on a data set recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb⁻¹. Events with a pair of τ leptons produced via photon–photon fusion are selected by requiring them to be back-to-back in the azimuthal direction and to have a minimum number of charged hadrons associated with their production vertex. The τ leptons are reconstructed in their leptonic and hadronic decay modes. The measured fiducial cross section of γγ→ττ is σobsfid=12.4−3.1+3.8fb. Constraints are set on the contributions to the anomalous magnetic moment ( aτ) and electric dipole moments ( dτ) of the τ lepton originating from potential effects of new physics on the γττ vertex: aτ=0.0009−0.0031+0.0032 and |dτ|<2.9×10−17ecm (95% confidence level), consistent with the standard model.

中文翻译：

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质子-质子碰撞中γγ→ττ的观测及τ轻子反常电磁矩的限制


首次在质子-质子碰撞中观察到通过光子-光子融合产生一对 τ 轻子，γγ→ττ，其显着性为 5.3 个标准差。该观测基于 LHC 的 CMS 探测器在 13 TeV 的质心能量下记录的数据集，对应于 138 fb ^-1的积分光度。通过光子-光子融合产生一对 τ 轻子的事件被选择，要求它们在方位角方向上背靠背，并且具有与其产生顶点相关的最小数量的带电强子。 τ 轻子以轻子和强子衰变模式重建。 γγ→ττ 的测量基准横截面为 σobsfid=12.4−3.1+3.8fb。对 τ 轻子的反常磁矩 (aτ) 和电偶极矩 (dτ) 的贡献设置约束，这些反常磁矩 (aτ) 和电偶极矩 (dτ) 源于新物理学对 γττ 顶点的潜在影响：aτ=0.0009−0.0031+0.0032 和 |dτ|<2 .9×10−17ecm（95%置信水平），与标准模型一致。