QCD anatomy of photon isolation

Journal of High Energy Physics

Regular Article - Theoretical Physics

Thomas Becher¹  Xiaofeng Xu¹  Samuel Favrod¹ 

[1] Albert Einstein Center for Fundamental Physics, Institut für Theoretische Physik, Universität Bern, Sidlerstrasse 5, CH-3012, Bern, Switzerland;

关键词: Effective Field Theories of QCD;    Factorization;    Renormalization Group;    Jets and Jet Substructure;    Resummation;   

DOI  :  10.1007/JHEP01(2023)005

 received in 2022-08-04, accepted in 2022-11-28,  发布年份 2022

来源: Springer

【 摘 要 】

To separate the energetic photons produced in hard scattering processes from those from other sources, measurements impose isolation requirements which restrict the hadronic radiation inside a cone around the photon. In this paper, we perform a detailed factorization analysis of the QCD effects associated with photon isolation. We show that for small cone radius R, photon isolation effects can be captured by a fragmentation function describing the decay of a parton into a photon accompanied by hadronic radiation. We compute this fragmentation function for different isolation criteria and solve the associated renormalization group equations to resum logarithms of R. For small isolation energy, the cone fragmentation function factorizes further, into collinear functions describing energetic quarks and gluons near the cone boundary and functions encoding their soft radiation emitted into the cone. Based on this factorization we also resum the non-global logarithms of the ratio of the photon energy and the isolation energy, so that we control all logarithmically enhanced terms in the cross section. In this limit, we provide a simple formula to convert NNLO cross section results from smooth-cone isolation to fixed-cone isolation.

【 授权许可】

Unknown   
© The Author(s) 2023

【 图 表 】

41116_2022_35_Article_IEq361.gif

41116_2022_35_Article_IEq359.gif

Fig. 2

41116_2022_35_Article_IEq356.gif

41116_2022_35_Article_IEq355.gif

41116_2022_35_Article_IEq353.gif