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The prompt photon production in hadronic collisions has a long history of providing information on the substructure of hadrons and testing the perturbative techniques of QCD. Some valuable information about the parton densities in the nucleon and nuclei, especially of the gluon, can also be achieved by analysing the measurements of the prompt photon production cross section whether inclusively or in association with heavy quarks or jets. In this work, we present predictions for the inclusive isolated prompt photon production in pp collisions at center-of-mass energy of 13 TeV using various modern PDF sets. The calculations are presented as a function of both photon transverse energy

From past to present, prompt photon production at hadron colliders has undergone very impressive experimental [

Inclusive prompt photon production consists of two types of photons: direct and fragmentation photons [

The production of photons in heavy-ion collisions [

Although in [

The paper is organised as follows. In Section

Theoretical and computational aspects of the inclusive isolated prompt photon production such as involved leading order (LO) and next-to-leading order (NLO) subprocesses, direct and fragmentation component of the cross section, and photon isolation requirement have been discussed in many papers (e.g., see [

There are three scales that should be set in the calculation of the cross section equation (

At LO, there are two Born-level subprocesses contributing to the prompt photon production cross section: the quark-gluon Compton scattering

For measuring the prompt photon production at hadron colliders inclusively, the background of secondary photons coming from the decays of hadrons produced in the collision should be well rejected. We can do it by imposing appropriate isolation cuts. As mentioned, the photon isolation also significantly reduces the fragmentation components of the prompt photon cross section. Actually, the reason is that the fragmentation photons are emitted collinearly to the parent parton, and on the other hand, the isolation cut discards the prompt photon events that have too much hadronic activity. Here we introduce two prescriptions of photon isolation used so far in photon production studies. The most used is the cone criterion [

There are some computer codes that can be used to calculate the prompt photon production cross section at NLO such as J

Now we are in position to predict the isolated prompt photon production in pp collisions at center-of-mass energy of 13 TeV using various modern PDF sets (CT14 [

As a first step, we calculate the NLO differential cross section of the isolated prompt photon production in pp collisions at

The NLO differential cross section of the isolated prompt photon production in pp collisions at

By virtue of the J

Same as Figure

In order to study the impact of input PDFs on the final results and estimate the order of magnitude of the difference between their predictions, we can now recalculate the differential cross sections presented in Figures

A comparison of the NLO theoretical predictions for the total differential cross section of the isolated prompt photon production as a function of

Same as Figure

In the previous section we calculated the cross section of isolated prompt photon production in pp collisions using various PDF sets. Now, it is important to calculate and study the theoretical uncertainties in the results. Since the dominant theoretical uncertainty is that arising from the scale uncertainties, in this section, we discuss only the scale uncertainties and ignore the study of PDFs uncertainties (note that the uncertainty arising from those in the PDFs amounts to 1–4%). As discussed in the previous section, the NLO calculation of the isolated prompt photon production involves all three renormalization (

In order to study the scale uncertainty of the isolated prompt photon production cross section in pp collisions at

The NLO theoretical predictions for the total differential cross section of the isolated prompt photon as a function of

Same as Figure

As we saw in the previous section, if one considers the combination of both incoherent and coherent scale variations, the resulting scale uncertainty is considerably large. Generally, the decrease of the total uncertainty origination from various sources is a very important issue in both the experimental measurements and theoretical calculations. In most cases, the expression of results as ratios can be very useful to this aim. For example, in nuclear collisions, it is well established now that the measurement of nuclear modification and forward-to-backward ratios is more suitable than single differential cross section [

A comparison of the ratio of the NLO theoretical predictions for the differential cross section of the isolated prompt photon for the rapidity region

The study of the energetic photons produced in the collision of two hadrons provides a probe of perturbative QCD and can also give us some valuable information about the parton densities in the nucleon and nuclei especially of the gluon. Photon production in heavy-ion collisions is also a powerful tool to study the cold nuclear matter effects and the fundamental properties of QGP. It is indicated that the recent ATLAS data [

The authors declare that there are no conflicts of interest regarding the publication of this paper.

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