Abstract
An accurate knowledge of nuclear parton distribution functions (nPDFs) is an essential ingredient of high energy physics calculations when the processes are involving nuclei in the initial state. It is well known now that the prompt photon production both in hadronic and nuclear collisions is a powerful tool for exploring the parton densities in the nucleon and nuclei especially of the gluon. In this work, we are going to perform a comprehensive study of the isolated prompt photon production in $ p $-Pb collisions at backward rapidities to find the best kinematic regions in which the experimental measurements have most sensitivity to the nuclear modifications of parton densities. Most emphasis will be placed on the antishadowing nuclear modification. To this aim, we calculate and compare various quantities at different values of center-of-mass energy covered by the LHC and also different rapidity regions to realize which one is most useful.
Highlights
Our main goal is performing a comprehensive study of the isolated prompt photon production in p-Pb collisions to find the best kinematic regions for constraining the antishadowing nuclear modifications of parton distribution functions (PDFs), we study the nuclear parton distribution functions (nPDFs)
First of all, focusing on each result obtained for Rηγ at various energies, we find that the sensitivity of this quantity to the antishadowing nuclear modification is decreased as the bins with higher value of absolute rapidity are considered in the numerator as pγT increases, Rηγ moves towards the of Rηγ . isospin baseline which means that the nuclear modifications in the numerator and denominator of Rηγ have neutralized each other
Because of the lack of experimental data on nuclei in the initial state compared with the case of free nucleons which are suitable for use in a global analysis, our knowledge of nuclear modifications of parton densities is not as good as for PDFs
Summary
Besides the parton distribution functions (PDFs), whether unpolarized [1,2,3,4,5,6,7,8,9,10,11] or polarized [12,13,14,15,16,17,18], and fragmentation functions (FFs) [19,20,21,22,23], the nuclear modifications of PDFs [24,25,26,27,28,29,30,31] are important ingredients of high energy physics calculations, in particular for processes involving nuclei in the initial state. Despite all these experimental efforts, another kind of measurement that is very important for achieving accurate information of the gluon nuclear modifications is the measurement of the prompt photon production in p-A collisions, especially at higher values of the center-of-mass energy and forward rapidities [39].
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