The color dipole picture for prompt photon production in pp and pPb collisions at the CERN-LHC
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Regular Article - Theoretical Physics
The color dipole picture for prompt photon production in pp and p P b collisions at the CERN-LHC G. Sampaio dos Santos1 , G. Gil da Silveira1,2,a , M. V. T. Machado1 1 2
High Energy Physics Phenomenology Group, GFPAE IF-UFRGS, Caixa Postal 15051, CEP 91501-970 Porto Alegre, RS, Brazil Departamento de Física Nuclear e de Altas Energias, Universidade do Estado do Rio de Janeiro, CEP 20550-013, Rio de Janeiro, RJ, Brazil
Received: 29 June 2020 / Accepted: 25 August 2020 © The Author(s) 2020
Abstract A study on the prompt photon production within the QCD color dipole picture with emphasis in pp and p A collisions at the LHC energy regimes is performed. We present predictions for the differential cross section as a function of photon transverse momentum at different rapidity bins considering updated phenomenological color dipole models, which take into account the QCD gluon saturation physics. The results are directly compared to the recent experimental measurements provided by CMS and ATLAS Collaborations, showing a reasonable agreement in all rapidity bins with no free parameters. Special attention is given to the IPSAT model given its good description of the data in all rapidity bins from low- to high- pT ranges. As a result, a freeparameter approach has succeeded in describing the LHC data for prompt photon production, while new predictions for the 13-TeV data is presented in view of new data to confirm such prospect.
1 Introduction The production of photons in hadronic collisions can be understood as a superposition of different sources of production, and isolation criteria are used to reduce the contamination by photons originating from certain production mechanisms. A photon produced in a hadronic collision is considered prompt when it does not originate from the decay of a hadron, such as π 0 or η, or when produced with a large transverse momentum, pT . Moreover, the terminology isolated photons concerns to the imposition of an isolation criterion where a photon is said to be isolated if, in a cone of radius R in rapidity y γ and azimuthal angle φ γ around the photon direction, the amount of deposited hadronic transhad = (E )h , verse energy is smaller than some cut, E cut T max h had inside the region defined by the experiment (i.e., E T ≤ E cut a e-mail:
[email protected] (corresponding author)
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(y − y γ )2 + (φ − φ γ )2 ≤ R 2 ). Several data sets on prompt photon production have been collected over the years, covering a large domain of center-of-mass energy and also a wide range of photon rapidity and transverse momentum spectrum. For instance, inclusive measurements of prompt photons have been made at hadron colliders by ATLAS [1–3], CMS [4,5], CDF [6], and D∅ [7,8] Collaborations, making the comparison between predictions and experimental data a quite meaningful scenario. In addition, a detailed understanding of prompt photon production is crucial to improve the knowledge both in experimental and theoretical sides. As such, the quantu
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