Abstract
Background: The LHCb Collaboration has studied a number of kinematic correlations between $B$-hadron pairs through their subsequent decays to $J/\psi$ pairs at 7 and 8 TeV for four minimum values of the $J/\psi$ $p_T$. Purpose: In this work, these measurements are compared to calculations of $b \bar b$ pairs and their hadronization and inclusive decays to $J/\psi J/\psi$ are compared to the same observables. Potential cold matter effects on the $b \bar b$ pair observables are discussed to determine which are most likely to provide insights about the system and why. Methods: The calculations, employing the exclusive HVQMNR code, assume the same intrinsic $k_T$-broadening and fragmentation as in [R. Vogt, Phys. Rev. C {\bf 98} (2018) 034907]. The pair distributions presented by LHCb are calculated in this approach, both for the parent $b \bar b$ and the $J/\psi J/\psi$ pairs produced in their decay. The sensitivity of the results to the intrinsic $k_T$ broadening is shown. The theoretical uncertainties due to the $b$ quark mass and scale variations on both the initial $b \bar b$ pairs and the resulting $J/\psi$ pairs are also shown. Possible effects due to the presence of the nucleus are studied by increasing the size of the $k_T$ broadening and modification of the fragmentation parameter. Results: Good agreement with the LHCb data is found for all observables. The parent $b \bar b$ distributions are more sensitive to the $k_T$ broadening than are the final-state $J/\psi$ pairs. Conclusions: Next-to-leading order calculations with $k_T$ broadening, as in [R. Vogt, Phys. Rev. C {\bf 98} (2018) 034907], can describe all correlated observables. Multiple measurements of correlated observables are sensitive to different nuclear effects which can help distinguish between them.
Highlights
Heavy flavor pair production has long been of interest in elementary p + p and p + p collisions as a way to test perturbative QCD
Measurements of heavy flavor correlations provide information about how heavy quark pairs are produced in perturbative QCD, much more information that can be gained from single inclusive heavy flavor production alone
In Ref. [15], the LHCb Collaboration compared their data to PYTHIA [19,20] and POWHEG [21] calculations as well as simulations of uncorrelated bb production [22,23] based on the transverse momentum and rapidity distributions for single b → J/ψX decays measured by LHCb
Summary
The LHCb Collaboration has studied a number of kinematic correlations between B-hadron pairs through their subsequent decays to J/ψ pairs in p + p collisions at 7 and 8 TeV for four minimum values of the J/ψ pT. Purpose: In this work, these measurements are compared to calculations of bb pairs and their hadronization and inclusive decays to J/ψJ/ψ are compared to the same observables. The pair distributions presented by LHCb are calculated in this approach, both for the parent bb and the J/ψJ/ψ pairs produced in their decays. The sensitivity of the results to the intrinsic kT broadening is shown. The parent bb distributions are more sensitive to the kT broadening than are the final-state J/ψ pairs. Multiple measurements of correlated observables are sensitive to different nuclear effects which can help distinguish between them
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