Speaker
Description
We study production of three isolated photons at the energy of Large Hadron Collider [1] in the Parton Reggeization Approach [2,3], which is based on high-energy factorization, Lipatov effective theory [4] and new unintegrated PDFs, obtained in modified multi-Regge kinematics approximation for QCD scattering amplitudes [5]. It is shown that data from ATLAS Collaboration can be described after merging of LO and NLO in strong coupling constant contributions, which are going via partonic subprocesses, $Q + \bar Q\to 3 \gamma$ and $Q+R\to 3\gamma+q$, where $R$ is the Reggeized gluon and $Q(\bar Q)$ is the Reggeized quark (antiquark). We found that contribution of subprocess $Q+\bar Q \to 3\gamma +g$ is very small. We demonstrate also agreement between calculation with analytical amplitudes obtained via Feynman rules of the Lipatov effective theory and calculation using Monte-Carlo generator Katie [6].
[1] ATLAS Collaboration, Measurement of the production cross section of three isolated photons in pp-collisions at √s=8TeV using the ATLAS detector. Phys. Lett. B781 (2018) 55-76
[2] A.V. Karpishkov, M.A. Nefedov and V.A. Saleev, $B\bar B$ angular correlations at the LHC in parton Reggeization approach merged with higher-order matrix elements, Phys. Rev. D96 (2017) no.9, 096019.
[3] M. Nefedov and V. Saleev, Diphoton production at the Tevatron and the LHC in the NLO approximation of the parton Reggeization approach, Phys. Rev. D 92 (2015) no.9, 094033.
[4] L.N. Lipatov, Gauge invariant effective action for high-energy processes in QCD, Nucl. Phys. B452 (1995), 369-400
[5] M.A. Nefedov and V.A. Saleev, High-Energy Factorization for Drell-Yan process in $pp$ and $p\bar p$ collisions with new Unintegrated PDFs, Phys. Rev. D102 (2020), 114018
[6] A. van Hameren, KaTie : For parton-level event generation with $k_T$-dependent initial states,
Comput. Phys. Commun. 224 (2018), 371-380
