# Understanding forward $B$ hadron production

## TL;DR

The paper investigates discrepancies between LHCb measurements of $B$ hadron production ratios at different energies and theoretical predictions, revealing tensions that challenge current understanding of gluon PDFs in perturbative QCD.

## Contribution

It highlights a significant tension in $B$ hadron production data that cannot be explained by standard perturbative QCD models, suggesting the need for revised gluon PDF models in specific kinematic regions.

## Key findings

- Large 4σ discrepancy in $B$ production ratio at low pseudorapidity.
- Data exceeds theoretical predictions in the $x$ region of $10^{-3}$ to $10^{-4}$.
- Systematic tension observed across multiple $B$ and $D$ hadron measurements.

## Abstract

The LHCb collaboration has recently performed a measurement of the production rate of inclusive $B$ hadron production ($pp\to BX$) 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 $\eta_B \in [2.0,5.0]$. A large tension ($4\sigma$) is observed for the ratio measurement in the lower pseudorapidity range of $\eta_B \in [2.0,3.0]$, where the data is observed to exceed theoretical predictions, while consistency is found at larger $\eta_B$ 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 $x\in[10^{-3},10^{-4}]$. 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 to 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 $[2.0,2.5]$.