CMS-PAS-HIN-16-016

CMS-PAS-HIN-16-016
Studies of beauty suppression via measurements of nonprompt $\mathrm{D^0}$ mesons in PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}= $ 5.02 TeV
CMS Collaboration
May 2018

Abstract: The transverse momentum spectra of $\mathrm{D^0}$ mesons from b hadron decays are measured in pp and PbPb collisions at a nucleon-nucleon center of mass energy of 5.02 TeV with the CMS detector at the LHC. The measurement is performed in the $\mathrm{D^0}$ $p_{\rm{T}}$ range of 2-100 GeV/$c$ and in the rapidity range of $\|y\| < $ 1. The $\mathrm{D^0}$ mesons from b hadron decays are distinguished from prompt $\mathrm{D^0}$ mesons by their decay topologies. In PbPb collisions, the $\mathrm{B\rightarrow{D^0}}$ yield is found to be suppressed in most of the measured $p_{\rm{T}}$ range compared to pp collisions. The suppression is weaker than that of prompt $\mathrm{D^0}$ mesons and charged hadrons for $p_{\rm{T}}$ around 10 GeV/$c$. While theoretical calculations incorporating partonic energy loss in the quark gluon plasma can successfully describe the measured $\mathrm{B\rightarrow{D^0}}$ suppression at higher $p_{\rm{T}}$, the data show an indication of larger suppression than the model predictions in the range of 2 $ < p_{T} < $ 5 GeV/$c$.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, PRL 123 (2019) 022001. The superseded preliminary plots can be found here.

Figures	Summary	Additional Figures	References	CMS Publications

Figures
png pdf	Figure 1: a): three-component invariant mass fit for an example ${\mathrm {D}^{0}}$ DCA bin for ${p_{\mathrm {T}}}$ of 6-7 GeV/$c$ in PbPb collisions; b): DCA distributions for ${\mathrm {D}^{0}}$ candidates in the signal invariant mass region and in the sidebands (scaled by 0.5) for ${\mathrm {D}^{0}}$ ${p_{\mathrm {T}}}$ of 6-7 GeV/$c$ in pp collisions; c): Signal ${\mathrm {D}^{0}}$ DCA distribution obtained with the invariant mass fit for each ${\mathrm {D}^{0}}$ DCA bin, and a prompt + nonprompt two-component fit to it, for ${\mathrm {D}^{0}}$ ${p_{\mathrm {T}}}$ of 6-7 GeV/$c$ in PbPb collisions; d): Signal ${\mathrm {D}^{0}}$ DCA distribution obtained with sideband subtraction, and a prompt + nonprompt two-component fit to it, for ${\mathrm {D}^{0}}$ ${p_{\mathrm {T}}}$ of 6-7 GeV/$c$ in pp collisions.
png pdf	Figure 2: Upper panel: ${\mathrm {{B}\rightarrow {D}^{0}}}$ ${p_{\mathrm {T}}} $-differential cross section in pp collisions and invariant yield in PbPb collisions normalized with the nuclear overlap function $T_{\rm {AA}}$, at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV. The cross section in pp is compared to calculations using FONLL [28]. Lower panel: The $\rm {FONLL}/data$ ratio for the ${\mathrm {{B}\rightarrow {D}^{0}}}$ ${p_{\mathrm {T}}}$ spectra in pp collisions.
png pdf	Figure 3: ${\mathrm {{B}\rightarrow {D}^{0}}}$ nuclear modification factor ${R_{\mathrm {AA}}}$ for PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV compared to B mesons [15], $ \mathrm{J}/\psi $ from b hadron decays [16], prompt ${\mathrm {D}^{0}}$ [13] and charged hadrons [21] (upper panel), and to various theoretical predictions [29,30,31,32,33,34,35,36] (lower panel).

Summary

To conclude, this note presents the transverse momentum spectra of $\mathrm{D^0}$ mesons from B decay measured in pp and PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}}= $ 5.02 TeV with the CMS detector at the LHC. The $\mathrm{D^0}$ from B decay are distinguished from prompt $\mathrm{D^0}$ by the DCA of their flight path relative to the primary vertex. The measured spectrum in pp collisions is close to the upper limit of the pQCD FONLL calculation. In PbPb collisions, the $\mathrm{ B \to D }$ is suppressed in most of the measured $ p_\mathrm{T} $ range from 2 to 100 GeV/$c$. The $\mathrm{ B \to D }$ nuclear modification factor $R_{\mathrm{AA}}$ is higher than prompt $\mathrm{D^0}$ and charged hadrons around 10 GeV/$c$, which is in line with the predicted mass ordering of suppression. Comparing to theoretical predictions, the measured $R_{\mathrm{AA}}$ is consistent with some models at higher $ p_\mathrm{T} $, but shows a hint of stronger suppression than the models available at low $ p_\mathrm{T} $.

Additional Figures
png pdf	Additional Figure 1: ${\mathrm {{B}\rightarrow {D}^{0}}}$ nuclear modification factor ${R_{\mathrm {AA}}}$ for PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV compared to B mesons [15], $ \mathrm{J}/\psi $ from b hadron decays [16], prompt ${\mathrm {D}^{0}} $ [13] and charged hadrons [21].
png pdf	Additional Figure 2: ${\mathrm {{B}\rightarrow {D}^{0}}}$ nuclear modification factor ${R_{\mathrm {AA}}}$ for PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV compared to various theoretical predictions [29, 30, 31, 32, 33, 34, 35, 36].

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