Evidence for modification of $b$ quark hadronization in high-multiplicity $pp$ collisions at $\sqrt{s} = 13$ TeV

Information

LHCb-PAPER-2022-001
CERN-EP-2022-062
arXiv:2204.13042 [PDF]

(Submitted on 27 Apr 2022)
Phys. Rev. Lett. 131 (2023) 061901
Inspire 2072869

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Abstract

The production rate of $B^{0}_{s}$ mesons relative to $B^{0}$ mesons is measured by the LHCb experiment in $pp$ collisions at a center-of-mass energy $\sqrt{s} = 13$ TeV over the forward rapidity interval $2<y<4.5$ as a function of the charged particle multiplicity measured in the event. Evidence at the 3.4$\sigma$ level is found for an increase of the ratio of $B^{0}_{s}$ to $B^{0}$ cross-sections with multiplicity at transverse momenta below 6 GeV/$c$, with no significant multiplicity dependence at higher transverse momentum. Comparison with data from $e^{+}e^{-}$ collisions implies that the density of the hadronic medium may affect the production rates of $B$ mesons. This is qualitatively consistent with the emergence of quark coalescence as an additional hadronization mechanism in high-multiplicity collisions.

Figures and captions

Distribution of the number of VELO tracks and backward tracks for NoBias events (red) and $ B ^0 $ signal events (blue), each with only one primary vertex. The vertical scale is arbitrary.	back_v[..].pdf [28 KiB] HiDef png [282 KiB] Thumbnail [213 KiB] *.C file
Measured $ { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- $ invariant mass distributions and fit projections in the multiplicity ranges a) $30<\mathrm{N}_{\mathrm{tracks}}^{\mathrm{VELO}} \leq40$ and b) $100<\mathrm{N}_{\mathrm{tracks}}^{\mathrm{VELO}} \leq125$.	Fig2.pdf [36 KiB] HiDef png [249 KiB] Thumbnail [192 KiB] *.C file
Ratio of cross sections $\sigma_{ B ^0_ s }/\sigma_{ B ^0 }$ versus the normalized multiplicity of a) all VELO tracks, and b) backward VELO tracks. The vertical error bars (boxes) represent point-to-point uncorrelated (fully correlated) uncertainties. The horizontal bands show the values measured in $e^{+}e^{-}$ collisions.	Fig3.pdf [17 KiB] HiDef png [415 KiB] Thumbnail [200 KiB] *.C file
Ratio of cross sections $\sigma_{ B ^0_ s }/\sigma_{ B ^0 }$ versus normalized multiplicity in the transverse momentum ranges a) $0< p_{\mathrm{T}} <6$ GeV/$c$, b) $6< p_{\mathrm{T}} <12$ GeV/$c$, and c) $12< p_{\mathrm{T}} <20$ GeV/$c$. The vertical error bars (boxes) represent point-to-point uncorrelated (fully correlated) uncertainties. The horizontal bands show the values measured in $e^{+}e^{-}$ collisions and the horizontal lines show PYTHIA calculations with and without (w/o) color reconnection.	Fig4.pdf [28 KiB] HiDef png [380 KiB] Thumbnail [161 KiB] *.C file
Animated gif made out of all figures.	PAPER-2022-001.gif Thumbnail