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| CMS-HIN-16-016 ; CERN-EP-2018-264 | ||
| Studies of beauty suppression via nonprompt ${\mathrm{D^0}}$ mesons in PbPb collisions a ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV | ||
| CMS Collaboration | ||
| 25 October 2018 | ||
| Phys. Rev. Lett. 123 (2019) 022001 | ||
| Abstract: The transverse momentum spectra of $ {\mathrm{D^0}} $ mesons from b hadron decays are measured at midrapidity ($| y | < $ 1) 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 $ {\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}\to{\mathrm{D^0}}} $ yield is found to be suppressed in the measured $ {p_{\mathrm{T}}} $ range from 2 to 100 GeV/$c$ as compared to pp collisions. The suppression is weaker than that of prompt $ {\mathrm{D^0}} $ mesons and charged hadrons for $ {p_{\mathrm{T}}} $ around 10 GeV/$c$. While theoretical calculations incorporating partonic energy loss in the quark-gluon plasma can successfully describe the measured ${\mathrm{B}\to{\mathrm{D^0}}}$ suppression at higher $ {p_{\mathrm{T}}} $, the data show an indication of larger suppression than the model predictions in the range of 2 $ < {p_{\mathrm{T}}} < $ 5 GeV/$c$. | ||
| Links: e-print arXiv:1810.11102 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
a) Example of a three-component invariant mass fit of a $ {{\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 the mass range ratio of 0.5) for $ {{\mathrm {D^0}}} $ $ {p_{\mathrm {T}}} $ of 6-7 GeV/$c$ in pp collisions; c) Signal DCA distribution obtained with the invariant mass fit for each 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 DCA distribution obtained with the 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. |
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Figure 2:
Upper panel: $ {{{\mathrm {B}}}\to {\mathrm {D^0}}} $ $ {p_{\mathrm {T}}} $ -differential cross section in pp collisions and invariant yield in PbPb collisions normalized with $ {T_{\mathrm {AA}}} $, at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV. The vertical bands around the data points represent the bin-by-bin systematic uncertainties. Uncertainties are smaller than the symbols in most cases. The cross section in pp collisions is compared to FONLL calculations [33]. Lower panel: The $\text {data}/\mathrm {FONLL}$ ratio for the $ {{{\mathrm {B}}}\to {\mathrm {D^0}}} $ $ {p_{\mathrm {T}}} $ spectra in pp collisions. |
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Figure 3:
The $ {{{\mathrm {B}}}\to {\mathrm {D^0}}} $ nuclear modification factor $ {R_{\mathrm {AA}}} $ for PbPb collisions at ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} = $ 5.02 TeV (red circles) compared to other particles [18,19,16,24] (upper panel), and to various theoretical predictions [34,35,36,37,38,39,40,41] (lower panel). The vertical bands around the data points and at unity represent the bin-by-bin and global systematic uncertainties, respectively. |
| Summary |
| In summary, this letter presents the transverse momentum spectra of $ {\mathrm{D^0}} $ mesons from b hadron decays measured in pp and PbPb collisions at a center-of-mass energy ${\sqrt {\smash [b]{s_{_{\mathrm {NN}}}}}} =$ 5.02 TeV per nucleon pair with the CMS detector at the LHC. The $ {\mathrm{D^0}} $ mesons from b hadron decays are distinguished from the prompt $ {\mathrm{D^0}} $ mesons by the distance of closest approach of the $ {\mathrm{D^0}} $ path relative to the primary vertex. The measured spectrum in pp collisions is close to the upper limit of a Fixed-Order Next-to-Leading Logarithm perturbative quantum chromodynamics calculation. In PbPb collisions, the ${\mathrm{B}\to{\mathrm{D^0}}}$ yield is suppressed in the measured transverse momentum ($ {p_{\mathrm{T}}} $) range from 2 to 100 GeV/$c$. The ${\mathrm{B}\to{\mathrm{D^0}}}$ nuclear modification factor $ R_{\mathrm{AA}} $ is higher than for prompt $ {\mathrm{D^0}} $ mesons and charged hadrons around 10 GeV/$c$, which is in line with a quark mass ordering of suppression. Compared 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 all of the available models at low $ {p_{\mathrm{T}}} $. This could indicate a stronger energy loss of b quarks in the quark-gluon plasma than predicted at low $ {p_{\mathrm{T}}} $, or could reflect an enhanced b baryon production due to quark coalescence in PbPb collisions. |
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