Abstract
We report on an analysis of the impact of available experimental data on hard processes in proton–lead collisions during Run I at the large hadron collider on nuclear modifications of parton distribution functions. Our analysis is restricted to the EPS09 and DSSZ global fits. The measurements that we consider comprise production of massive gauge bosons, jets, charged hadrons and pions. This is the first time a study of nuclear PDFs includes this number of different observables. The goal of the paper is twofold: (i) checking the description of the data by nPDFs, as well as the relevance of these nuclear effects, in a quantitative manner; (ii) testing the constraining power of these data in eventual global fits, for which we use the Bayesian reweighting technique. We find an overall good, even too good, description of the data, indicating that more constraining power would require a better control over the systematic uncertainties and/or the proper proton–proton reference from LHC Run II. Some of the observables, however, show sizeable tension with specific choices of proton and nuclear PDFs. We also comment on the corresponding improvements as regards the theoretical treatment.
Highlights
One of the key factors in interpreting the p–Pb data are the nuclear parton distribution functions [3,4]
We report on an analysis of the impact of available experimental data on hard processes in proton–lead collisions during Run I at the large hadron collider on nuclear modifications of parton distribution functions
It is more than three decades ago that, unexpectedly, large nuclear effects in deeply inelastic scattering were first found, which were later on shown to be factorisable into the PDFs [6]
Summary
One of the key factors in interpreting the p–Pb data are the nuclear parton distribution functions (nPDFs) [3,4]. The aim of this paper is, on the one hand, to chart the importance of nPDFs in describing the data (both globally and separately for individual data sets) and, on the other hand, to estimate the quantitative constraints that these data render. The latter question would have traditionally required a complete reanalysis adding the new data on top of the old ones. In contrast to p–Pb collisions, the precision of these data is inferior, the constraining power smaller by construction in the symmetric Pb–Pb case [19], and a higher computational load would be involved For these reasons we do not include Pb–Pb data in the present analysis.
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