$B$-jet fragmentation with $B^{\pm} \to J/ψK^{\pm}$ decays in $\sqrt{s} = 13$ TeV $pp$ collisions at LHCb

Abstract

The collinear and transverse-momentum-dependent jet fragmentation function and the radial profile for $B^{\pm}$ mesons in jets are measured. The $B^{\pm}$ mesons are reconstructed through the $J/ψ(\to μ^{+} μ^{-}) K^{\pm}$ decay channel using proton-proton collision data collected during 2016-2018 with the LHCb detector at a center-of-mass energy of $\sqrt{s}=13$ TeV, corresponding to an integrated luminosity of $5.4$ fb$^{-1}$. The results complement recent measurements of jet fragmentation functions for heavy-flavor hadrons and suggest a growing contribution of gluon fragmentation to $B^{\pm}$ mesons as the jet transverse momentum increases.

Figures (8)

• Figure 1: Schematic of the collinear momentum fraction $z$, transverse momentum with respect to the jet axis $j_{\mathrm{T}}$, and radial profile $r$ of a ${{\mathrm{B}\xspace}\xspace^\pm}\xspace$ meson within a jet.
• Figure 2: Example of the invariant mass distribution of the $\mathinner{{{\mathrm{B}\xspace}\xspace^\pm}\xspace\!\rightarrow\xspace {{\mathrm{J}\xspace / \uppsi\xspace}}\xspace \mathinner{(\!\rightarrow\xspace {\upmu\xspace^+}\xspace {\upmu\xspace^-}\xspace)}\xspace {{\mathrm{K}\xspace}\xspace^\pm}\xspace}$ candidates within $8 < p_{\mathrm{T,}B^{\pm}}\xspace < 9$$\text{\,Ge V\!/}c$. The data points are shown as black circles while the total fit model is shown as a red curve. The blue dashed line depicts the combinatorial background model, while the green dotted and purple dash-dotted lines highlight the signal and sideband regions.
• Figure 3: Measured $z$ distributions (top panel) shown alongside simulation/data ratios (bottom panel) in each $p_{\mathrm{T,jet}}$ bin. Note that some points are outside of the displayed range in the bottom panel. In the top panels, the black points and bars correspond to the data points and statistical error bars, the shaded gray boxes correspond to the systematic uncertainties, and the blue points correspond to the prediction from Pythia 8.186. The measured quantity corresponds to the collinear JFF for ${\mathrm{B}\xspace}\xspace^\pm$ mesons.
• Figure 4: Measured $j_{\mathrm{T}}$ distributions (top panel) shown alongside simulation/data ratios (bottom panel) in each $p_{\mathrm{T,jet}}$ bin. In the top panels, the black points and bars correspond to the data points and statistical error bars, the shaded gray boxes correspond to the systematic uncertainties, and the blue points correspond to the prediction from Pythia 8.186.
• Figure 5: Measured $r$ distributions (top panel) shown alongside simulation/data ratios (bottom panel) in each $p_{\mathrm{T,jet}}$ bin. In the top panels, the black points and bars correspond to the data points and statistical error bars, the shaded gray boxes correspond to the systematic uncertainties, and the blue points correspond to the prediction from Pythia 8.186.