Flavour anti-$k_\text{T}$ algorithm applied to $Wb\bar{b}$ production at the LHC

TL;DR

This work advances precision in $pp \to W b\bar{b}$ predictions at the LHC by applying the flavoured anti-$k_T$ jet algorithm to NNLO QCD calculations in the 5-flavour scheme, and by comparing to flavour-$k_T$ and CMS data. The study shows that NNLO corrections are large and crucial for matching the CMS measurements, with notable algorithm-dependent differences driven by the small $\Delta R_{bb}$ region where gluon splitting to $b\bar{b}$ is important. The flavoured anti-$k_T$ approach reduces unfolding uncertainties and provides a direct path to experimental comparisons, while the NLO+ merging captures much of the NNLO effect but does not fully substitute for the complete NNLO result. The findings have implications for precision background modeling in $W$-associated processes and inform jet-flavour treatment in LHC analyses.

Abstract

We apply the recently proposed flavoured anti-$k_{\text{T}}$ jet algorithm to $Wb\bar{b}$ production at the Large Hadron Collider at $\sqrt{s}=8$ TeV. We present results for the total cross section and differential distributions at the next-to-next-to-leading order (NNLO) in QCD. We discuss the effects of the remaining parametric freedom in the flavoured anti-$k_{\text{T}}$ prescription, and compare it against the standard flavour-$k_{\text{T}}$ algorithm. We compare the total cross section results against the CMS data, finding good agreement. The NNLO QCD corrections are significant, and their inclusion substantially improves the agreement with the data.

Figures (7)

• Figure 1: Distribution of $\Delta R_{b\bar{b}}$ at NLO for $\operatorname{W}^+b\bar{b}$, calculated with different jet algorithms: flavour-$k_\text{T}$, standard $k_\text{T}$ and anti-$k_\text{T}$, and flavoured anti-$k_\text{T}$ with a selected set of values for the tuneable parameter $a$. The coloured bands show the scale uncertainty using the standard 7-point variation scheme for the calculations based on the flavour-$k_\text{T}$ and standard anti-$k_\text{T}$ algorithms. All calculations were performed simultaneously using the same Monte-Carlo seed.
• Figure 2: Comparison between CMS data from Ref. CMS:2016eha and the theoretical predictions using the flavoured anti-$k_\text{T}$ jet algorithm with different $a$-parameters in the exclusive setup for the $\mathrm{W^+}$ and $\mathrm{W^-}$ combined signature. The theoretical uncertainty is estimated by the standard 7-point scale variation (thick band). At NLO and NNLO we also show the theoretical uncertainty calculated using the uncorrelated prescription as described in the text (thin band). The multiplicative hadronisation and additive DPI correction factors are taken into account in all theoretical predictions. Additionally, we include (in quadrature) uncertainties on the DPI factor and hadronisation corrections CMS:2016eha to the uncorrelated theoretical uncertainties via a dotted extension to the bands.
• Figure 3: Distribution of $\Delta R_{b\bar{b}}$ and $\Delta \phi_{b\bar{b}}$ for inclusive $pp\to\operatorname{W}^+(\to\ell^+\nu)b\bar{b}$ production. The second panel shows the ratio of all setups to the flavoured-$k_\text{T}$ algorithm. The coloured bands define scale uncertainty for two calculations: flavour-$k_\text{T}$, and flavoured anti-$k_\text{T}$ with $a=0.1$. The last two panels show the $K$-factors at NNLO and NLO, correspondingly. The vertical bars define the statistical uncertainty. All calculations were performed simultaneously using the same Monte-Carlo seed.
• Figure 4: Distribution of invariant mass (left) and transverse momentum (right) of the $b\bar{b}$-pair for inclusive $pp\to\operatorname{W}^+(\to\ell^+\nu)b\bar{b}$ production. The individual plot structure is the same as in Figure \ref{['fig:jetalgos_dRbb_dphibb']}.
• Figure 5: Distribution of the $\mathrm{W^+}$-boson transverse mass (left) and of the positively charged lepton transverse momentum (right) for inclusive $pp\to\operatorname{W}^+(\to\ell^+\nu)b\bar{b}$ production. The individual plot structure is the same as in Figure \ref{['fig:jetalgos_dRbb_dphibb']}.