Abstract
The LHCb collaboration has recently performed a measurement of the production rate of inclusive B hadron production (pp → BX) at both 7 and 13 TeV centre-of-mass (CoM) energies. As part of this measurement, the ratio of these two cross section measurements has been presented differentially in B hadron pseudorapidity within the range of ηB ∈ [2.0, 5.0]. A large tension (4σ) is observed for the ratio measurement in the lower pseudorapidity range of ηB ∈ [2.0, 3.0], where the data is observed to exceed theoretical predictions, while consistency is found at larger ηB values. This behaviour is not expected within perturbative QCD, and can only be achieved by introducing ad-hoc features into the structure of the non-perturbative gluon PDF within the region of x ∈ [10−3, 10−4]. Specifically, the gluon PDF must grow extremely quickly with decreasing x within this kinematic range, closely followed by a period of decelerated growth. However, such behaviour is highly disfavoured by global fits of proton structure. Further studies of the available LHCb B and D hadron cross section data, available for a range of CoM energies, indicate systematic tension in the (pseudo)rapidity region of [2.0, 2.5].
Highlights
It comes as a quite a surprise that significant tension is observed for the B hadron ratio data with respect to the corresponding theoretical predictions
At the LHC, inclusive B hadron production is dominated by the gluon-fusion heavy quark pair production subprocess, and the predictions of the distributions of B hadrons can be obtained by convoluting the partonic cross section for heavy quark pair production with input PDFs and the relevant heavy quark fragmentation functions
While the discussion is focussed towards B hadron production, the predictions for D hadron production proceed in essentially the same way
Summary
At the LHC, inclusive B hadron production is dominated by the gluon-fusion heavy quark pair production subprocess, and the predictions of the distributions of B hadrons can be obtained by convoluting the partonic cross section for heavy quark pair production with input PDFs and the relevant heavy quark fragmentation functions. The current state-of-the-art for differential cross section predictions is the next-to-leading order (NLO) partonic cross section [10,11,12,13,14], where predictions can be further improved by matching this massive calculation to a parton shower or a massless calculation. The theoretical set-up for providing B hadron predictions will be provided. The partonic kinematics relevant for forward B hadron measurements in the LHCb acceptance are discussed. While the discussion is focussed towards B hadron production, the predictions for D hadron production proceed in essentially the same way
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