Testing perturbative QCD calculations with beauty-meson production in proton-proton collisions with ALICE

TL;DR

This paper reports on the measurement of B0-meson production in proton-proton collisions at 13.6 TeV by ALICE, providing a test of perturbative QCD calculations through comparison with advanced theoretical models.

Contribution

First measurement of B0-meson production at 13.6 TeV in pp collisions, testing pQCD predictions with new experimental data.

Findings

Measured B0 production cross section agrees with pQCD calculations within uncertainties.

Provides data at low transverse momentum for improved theoretical constraints.

Validates the factorisation theorem in high-energy proton-proton collisions.

Abstract

Measurements of the production cross section of beauty hadrons in proton-proton (pp) collisions provide excellent tests of perturbative quantum chromodynamics (pQCD) calculations. Theoretical approaches based on the factorisation theorem allow for the calculation of differential cross sections for hadron production as functions of transverse momentum ($p_{\mathrm{T}}$) and rapidity ($y$). Measurements down to low transverse momenta are also fundamental ingredients for the estimation of the $\mathrm{b\overline{b}}$ production cross section. In this contribution, the measurement of $\mathrm{B^{0}}$-meson production in pp collisions at $\sqrt{s}=13.6$ TeV collected by the ALICE experiment during LHC Run 3 is presented. The $\mathrm{B^{0}}$ mesons are fully reconstructed via their decay channels into a D meson and a charged pion. The measured production cross section is compared with state-of-the-art pQCD calculations with next-to-leading order accuracy plus all-order resummation of next-to-leading logarithms.

Full text

In this contribution, the measurement of $\mathrm{B^{0}}$-meson production in pp collisions at $\sqrt{s}=13.6$ TeV collected by the ALICE experiment during LHC Run 3 is presented. The $\mathrm{B^{0}}$ mesons are fully reconstructed via their decay channels into a D meson and a charged pion. The measured production cross section is compared with state-of-the-art pQCD calculations with next-to-leading order accuracy plus all-order resummation of next-to-leading logarithms.

1 Introduction

Because of their large mass, heavy quarks (i.e., charm and beauty) are exclusively produced in processes with large transferred momentum, and hence their production can be computed with pQCD calculations. The measurement of the production of heavy-flavour hadrons in pp collisions is therefore an excellent test of pQCD calculations. Calculations at the Next-to-Leading Order plus Next-to-Leading Log approximation successfully describe the measurements of both beauty hadron production LHCb:2017vec ; CMS:2024vip and of non-prompt charm hadrons ALICE:2024xln (i.e. those produced from the decay of a beauty hadron) in pp collisions at the LHC. While open beauty production in pp collisions at LHC energies has been measured in a wide $p_{\mathrm{T}}$ range by the LHCb Collaboration LHCb:2017vec at forward rapidity, and at high $p_{\mathrm{T}}$ ($p_{\mathrm{T}}>5$ $\mathrm{GeV}/c$) by the CMS Collaboration CMS:2024vip at midrapidity, the production of open beauty hadrons down to low $p_{\mathrm{T}}$ at midrapidity was never directly measured.

2 Measurement of the production cross section of $\mathrm{\mathbf{B^{0}}}$ mesons in pp collisions at $\mathbf{\sqrt{s}=13}$ TeV

Exploiting the large dataset collected during the LHC Run 3 data-taking period, the ALICE Collaboration was able to perform the first measurement of the $\mathrm{B^{0}}$ production cross section at midrapidity ($|y|<0.5$) down to $p_{\mathrm{T}}=1\leavevmode\nobreak\ \mathrm{GeV}/c$ at LHC energies ALICE-PUBLIC-2025-004 .

The production cross section of $\mathrm{B^{0}}$ mesons is measured in the rapidity range $|y|<0.5$ and the $1<p_{\mathrm{T}}<23.5$ $\mathrm{GeV}/c$ interval, and is computed from the $\mathrm{B^{0}}$ raw yields, which include particles and antiparticles, extracted in each $p_{\mathrm{T}}$ interval via a fit to the invariant mass distribution of selected candidates. They are corrected for the detector acceptance and efficiency, branching ratio $\mathrm{BR}=\mathrm{BR(\mathrm{B^{0}}\rightarrow D^{-}\pi^{+})}\times\mathrm{BR(\mathrm{D^{-}}\rightarrow\pi^{-}K^{+}\pi^{-})}=(2.35\pm 0.08)\cdot 10^{-6}$ ParticleDataGroup:2024cfk and integrated luminosity $\mathcal{L}_{\mathrm{int}}=(43\pm 4)\leavevmode\nobreak\ \mathrm{pb}^{-1}$. The cross section is shown in Fig. 1 as a function of $p_{\mathrm{T}}$, and shows a good agreement with state-of-the-art pQCD calculations Cacciari:2012ny ; Benzke:2019usl ; Helenius:2023wkn ; Barattini:2025wbo , as well as with predictions from the TAMU He:2022tod model, where the beauty-quark $p_{\mathrm{T}}$ spectrum is taken from FONLL calculations Cacciari:2012ny and a statistical approach for the description of the hadronisation process is used. The measured $p_{\mathrm{T}}$-differential production cross section is found to be consistent with all the considered theoretical predictions within uncertainties.

The rapidity dependence of the $\mathrm{B^{0}}$ meson production cross section is also studied by considering the ratio between the $\mathrm{B^{0}}$ meson production cross section measured at midrapidity by the ALICE Collaboration and the one measured for the $\mathrm{B^{+}}$ meson at forward rapidity by the LHCb Collaboration LHCb:2017vec . The ratio is shown in Fig. 2 and is found to follow different trends with $p_{\mathrm{T}}$ in the different rapidity intervals. It is well described by FONLL calculations Cacciari:2012ny . The ratio is also compared to the one measured for $\mathrm{D^{0}}$ mesons in pp collisions at $\sqrt{s}=13$ TeV ALICE:2023sgl , which shows a similar trend with $y$, suggesting the factorisation of the mass and rapidity dependence of the production cross section of heavy flavour hadrons.

The $\mathrm{b\overline{b}}$ production cross section at midrapidity ($|y|<0.5$) can be estimated starting from the total $\mathrm{B^{0}}$ production cross section and the fragmentation fractions measured in $\mathrm{p\overline{p}}$ collisions HFLAV:2019otj . The $\mathrm{B^{0}}$ production cross section can in turn be obtained by integrating the $p_{\mathrm{T}}$-differential production cross section measured in the $1<p_{\mathrm{T}}<23.5$ $\mathrm{GeV}/c$ range and by applying an extrapolation factor obtained from FONLL predictions Cacciari:2012ny . The resulting $\mathrm{b\overline{b}}$ production cross section per unit of rapidity in pp collisions at $\sqrt{s}=13.6$ TeV and $|y|<0.5$ is shown in Fig. 3, and is found to be in line with the increasing trend with energy of previous measurements at lower energies. Predictions at NNLO precision Catani:2020kkl are available for the $\mathrm{b\overline{b}}$ production cross section, and are consistent with the measured value. They are found to be in good agreement with FONLL predictions Cacciari:2012ny , while laying on the upper edge of its uncertainty band.

3 Conclusions

The first measurement of the production cross section of $\mathrm{B^{0}}$ mesons in pp collisions performed by the ALICE Collaboration was presented. The considered observables are found to be in good agreement with state-of-the-art pQCD-based calculations. This measurement provides a solid baseline for the study of beauty-hadron production in Pb–Pb collisions, where modifications due to the presence of the quark–gluon plasma are expected. Measurements of other beauty hadrons will allow the study of the relative abundances of different beauty-hadron species, providing insights about the beauty-quark hadronisation mechanisms.