# Evidence in favor of Single Parton Scattering mechanism in $\Upsilon$ and $D$ associated production at the LHC

## TL;DR

This paper investigates the production of $mbda(1S)$ and $D$ mesons at the LHC, providing evidence that Single Parton Scattering significantly contributes to the process, challenging the assumption that Double Parton Scattering dominates.

## Contribution

The study applies the Parton Reggeization Approach and NRQCD-factorization to show that Single Parton Scattering accounts for over half of the observed cross-section, reducing the expected role of Double Parton Scattering.

## Key findings

- Single Parton Scattering explains over 50% of the cross-section.
- Good agreement with LHCb data for most distributions.
- Discrepancy in azimuthal angle difference spectra at small angles.

## Abstract

Associated production of prompt $\Upsilon(1S)$ and $D^{+,0}$ mesons has been proposed as a golden channel for the search of Double Parton Scattering, because Single Parton Scattering contribution to the cross-section is believed to be negligible on a basis of leading order calculations in the Collinear Parton Model. We study this process in the leading order approximation of the Parton Reggeization Approach. Hadronization of $b\bar{b}$-pair into bottomonium states is described within framework of the NRQCD-factorization approach while production of $D$ mesons is described in the fragmentation model with scale-dependent fragmentation functions. We have found good agreement with LHCb data for various normalized differential distributions, except for the case of spectra on azimuthal angle differences at the small $\Delta\varphi$ values. Crucially, the total cross-section in our Single Parton Scattering model accounts for more than one half of observed cross-section, thus dramatically shrinking the room for Double Parton Scattering mechanism.