Abstract
Prompt double-J/psi production at high-energy hadron colliders can be considered as a golden channel to probe double parton scatterings (DPS)—in particular to study gluon–gluon correlations inside the proton—and, at the same time, to measure the distribution of linearly-polarised gluons inside the proton. Such studies, however, require a good control of both single parton scatterings (SPS) and DPS in the respective regions where they are carried out. In this context, we have critically examined two mechanisms of SPS that may be kinematically enhanced where DPS are thought to be dominant, even though they are either at higher orders in the strong-coupling or velocity expansion. First, we have considered a gauge-invariant and infrared-safe subset of the loop-induced contribution via colour-singlet (CS) transitions. We have found it to become the leading CS SPS contributions at large rapidity separation, yet too small to account for the data without invoking the presence of DPS yields. Second, we have surveyed the possible colour-octet (CO) contributions using both old and up-to-date non-perturbative long-distance matrix elements (LDMEs). We have found that the pure CO yields crucially depend on the LDMEs. Among all the LDMEs we used, only two result into a visible modification of the NRQCD (CS+CO) yield, but only in two kinematical distributions measured by ATLAS, those of the rapidity separation and of the pair invariant mass. These modifications, however, do not impact the control region used for their DPS study.
Highlights
The role of multiple parton interactions in proton–proton collisions is believed to become increasingly important when one explores the energy frontier in particle physics
We have explicitly computed that the parton-distribution functions (PDFs) uncertainty from NNPDF3.0 is less than 20%, whereas the difference between CTEQ6M and NNPDF3.0 PDF sets is below 15% at 13 TeV in the LHCb acceptance, which lies within the estimated NNPDF PDF uncertainty
Since the main PDF uncertainty is from the least constrained low-x gluon density, we anticipate that the PDF uncertainty should be less than 15% in the ATLAS and CMS acceptance which correspond to larger x and larger scales
Summary
The role of multiple parton interactions in proton–proton collisions is believed to become increasingly important when one explores the energy frontier in particle physics. Since DPS are higher-twist effects in total cross sections compared to the conventional single parton scatterings (SPS), quantitative studies of DPS remain challenging though not impossible both on the theoretical and experimental sides. The first calculation of triple-J/ψ production showed that it can help us probe both DPS and triple parton scatterings (TPS) [52] In this context, we focus in this paper on the di-J/ψ case with the aim to improve the existing perturbative QCD calculations for the SPS. Our analysis follows the lines of a similar study for J/ψ + Υ production [42] Such contributions appear at next-to-next-to-leading order (NNLO) in αS but could be enhanced at large rapidity differences and high invariant masses of the J/ψ pair because of the presence of topologies with double t-channel gluon exchanges between both charm–anticharm-quark lines. Appendix B collects additional plots relevant for further theory-data comparisons
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
