BORIS Theses

BORIS Theses
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QCD anatomy of photon isolation

Favrod, Samuel (2023). QCD anatomy of photon isolation. (Thesis). Universität Bern, Bern

23favrod_s.pdf - Thesis
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Energetic photons are a short-distance probe to search for new physics and test the standard model at colliders. In order to differentiate photons from different origins at hadron colliders, it is necessary to impose isolation requirements. These requirements restrict the hadronic radiation inside a cone around the photon. In this thesis, we present a factorization theorem for 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. For small isolation energy, the cone fragmentation function factorizes further into jet and soft functions. Using renormalization-group methods, we resum the leading logarithms of R and the non-global logarithms of the ratio εγ of the isolation energy and the photon energy, so that we control all logarithmically enhanced terms in the cross section. Finally, in the limit of small R and small εγ, we provide a simple formula to convert NNLO cross-section results from smooth-cone isolation to fixed-cone isolation.

Item Type: Thesis
Dissertation Type: Single
Date of Defense: 9 January 2023
Subjects: 500 Science > 530 Physics
Institute / Center: 08 Faculty of Science > Institute of Theoretical Physics
Depositing User: Hammer Igor
Date Deposited: 06 Feb 2023 07:50
Last Modified: 09 Jan 2024 23:25

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