846 research outputs found

    Measurement of non-prompt D -meson elliptic flow in Pb–Pb collisions at √sNN=5.02 TeV

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    The elliptic flow (v2) of D mesons from beauty-hadron decays (non-prompt D) was measured in midcentral (30–50%) Pb–Pb collisions at a centre-of-mass energy per nucleon pair sNN=5.02 TeV with the ALICE detector at the LHC. The D mesons were reconstructed at midrapidity (| y| < 0.8) from their hadronic decay D → K -π + , in the transverse momentum interval 2 < pT< 12 GeV/c. The result indicates a positive v2 for non-prompt D mesons with a significance of 2.7 σ . The non-prompt D -meson v2 is lower than that of prompt non-strange D mesons with 3.2 σ significance in 2<8GeV/c , and compatible with the v2 of beauty-decay electrons. Theoretical calculations of beauty-quark transport in a hydrodynamically expanding medium describe the measurement within uncertainties

    Study of flavor dependence of the baryon-to-meson ratio in proton-proton collisions at √s=13 TeV

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    The production cross sections of D0{\rm D^0} and Λc+\Lambda^+_{\rm c} hadrons originating from beauty-hadron decays (i.e. non-prompt) were measured for the first time at midrapidity (y<0.5|y|<0.5) by the ALICE Collaboration in proton-proton collisions at a center-of-mass energy s=13\sqrt{s}=13 TeV. They are described within uncertainties by perturbative QCD calculations employing the fragmentation fractions of beauty quarks to baryons measured at forward rapidity by the LHCb Collaboration. The bb{\rm b\overline{b}} production cross section per unit of rapidity at midrapidity, estimated from these measurements, is dσbb/dyy<0.5=83.1±3.5(stat.)±5.4(syst.)3.2+12.3(extrap.)μ{\rm d}\sigma_{\rm b\overline{b}}/{\rm d}y|_{|y|<0.5} = 83.1 \pm 3.5 (\mathrm{stat.}) \pm 5.4(\mathrm{syst.}) ^{+12.3}_{-3.2} (\mathrm{extrap.})\,\mub. The baryon-to-meson ratios are computed to investigate the hadronization mechanism of beauty quarks. The non-prompt Λc+/D0\Lambda^+_{\rm c}/{\rm D^0} production ratio has a similar trend to the one measured for the promptly produced charmed particles and to the p/π+/\pi^+ and Λ/KS0\Lambda/{\rm K^0_S} ratios, suggesting a similar baryon-formation mechanism among light, strange, charm, and beauty hadrons. The pTp_{\rm T}-integrated non-prompt Λc/D0\Lambda_{\rm c}/{\rm D^0} ratio is found to be significantly higher than the one measured in e+^+e^- collisions

    Prompt D0, D+, and D*+ production in Pb–Pb collisions at √sNN = 5.02 TeV

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    The production of prompt D0, D+, and D*+ mesons was measured at midrapidity (|y| &lt; 0.5) in Pb–Pb collisions at the centre-of-mass energy per nucleon–nucleon pair sNN = 5.02 TeV with the ALICE detector at the LHC. The D mesons were reconstructed via their hadronic decay channels and their production yields were measured in central (0–10%) and semicentral (30–50%) collisions. The measurement was performed up to a transverse momentum (pT) of 36 or 50 GeV/c depending on the D meson species and the centrality interval. For the first time in Pb–Pb collisions at the LHC, the yield of D0 mesons was measured down to pT = 0, which allowed a model-independent determination of the pT-integrated yield per unit of rapidity (dN/dy). A maximum suppression by a factor 5 and 2.5 was observed with the nuclear modification factor (RAA) of prompt D mesons at pT = 6–8 GeV/c for the 0–10% and 30–50% centrality classes, respectively. The D-meson RAA is compared with that of charged pions, charged hadrons, and J/ψ mesons as well as with theoretical predictions. The analysis of the agreement between the measured RAA, elliptic (v2) and triangular (v3) flow, and the model predictions allowed us to constrain the charm spatial diffusion coefficient Ds. Furthermore the comparison of RAA and v2 with different implementations of the same models provides an important insight into the role of radiative energy loss as well as charm quark recombination in the hadronisation mechanisms. [Figure not available: see fulltext.

    Prompt D0, D+, and D*+ production in Pb–Pb collisions at √sNN = 5.02 TeV

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    The production of prompt D0, D+, and D*+ mesons was measured at midrapidity (|y| T) of 36 or 50 GeV/c depending on the D meson species and the centrality interval. For the first time in Pb–Pb collisions at the LHC, the yield of D0 mesons was measured down to pT = 0, which allowed a model-independent determination of the pT-integrated yield per unit of rapidity (dN/dy). A maximum suppression by a factor 5 and 2.5 was observed with the nuclear modification factor (RAA) of prompt D mesons at pT = 6–8 GeV/c for the 0–10% and 30–50% centrality classes, respectively. The D-meson RAA is compared with that of charged pions, charged hadrons, and J/ψ mesons as well as with theoretical predictions. The analysis of the agreement between the measured RAA, elliptic (v2) and triangular (v3) flow, and the model predictions allowed us to constrain the charm spatial diffusion coefficient Ds. Furthermore the comparison of RAA and v2 with different implementations of the same models provides an important insight into the role of radiative energy loss as well as charm quark recombination in the hadronisation mechanisms. [Figure not available: see fulltext.

    Investigating charm production and fragmentation via azimuthal correlations of prompt D mesons with charged particles in pp collisions at √s = 13 TeV

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    Angular correlations of heavy-flavour and charged particles in high-energy proton–proton collisions are sensitive to the production mechanisms of heavy quarks and to their fragmentation as well as hadronisation processes. The measurement of the azimuthal-correlation function of prompt D mesons with charged particles in proton–proton collisions at a centre-of-mass energy of √s = 13 TeV with the ALICE detector is reported, considering D0, D+, and D∗+ mesons in the transverse-momentum interval 3 0.3 GeV/c and pseudorapidity |η| < 0.8. This measurement has an improved precision and provides an extended transverse-momentum coverage compared to previous ALICE measurements at lower energies. The study is also performed as a function of the charged-particle multiplicity, showing no modifications of the correlation function with multiplicity within uncertainties. The properties and the transverse-momentum evolution of the near- and awayside correlation peaks are studied and compared with predictions from various Monte Carlo event generators. Among those considered, PYTHIA8 and POWHEG+PYTHIA8 provide the best description of the measured observables. The obtained results can provide guidance on tuning the generators

    Investigating charm production and fragmentation via azimuthal correlations of prompt D mesons with charged particles in pp collisions at √s=13 TeV

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    Angular correlations of heavy-flavour and charged particles in high-energy proton–proton collisions are sensitive to the production mechanisms of heavy quarks and to their fragmentation as well as hadronisation processes. The measurement of the azimuthal-correlation function of prompt D mesons with charged particles in proton–proton collisions at a centre-of-mass energy of s=13&nbsp;TeV with the ALICE detector is reported, considering D , D +, and D ∗ + mesons in the transverse-momentum interval 3 &lt; pT&lt; 36 GeV/c at midrapidity (| y| &lt; 0.5), and charged particles with pT&gt; 0.3 GeV/c and pseudorapidity | η| &lt; 0.8. This measurement has an improved precision and provides an extended transverse-momentum coverage compared to previous ALICE measurements at lower energies. The study is also performed as a function of the charged-particle multiplicity, showing no modifications of the correlation function with multiplicity within uncertainties. The properties and the transverse-momentum evolution of the near- and away-side correlation peaks are studied and compared with predictions from various Monte Carlo event generators. Among those considered, PYTHIA8 and POWHEG+PYTHIA8 provide the best description of the measured observables. The obtained results can provide guidance on tuning the generators

    Charm fragmentation fractions and c-cbar cross section in p–Pb collisions at sqrt(sNN)=5.02 TeV

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    The total charm-quark production cross section per unit of rapidity dσ (cc)/dy, and the fragmentation fractions of charm quarks to different charm-hadron species f (c → hc), are measured for the first time in p–Pb collisions at √sNN = 5.02 TeV at midrapidity (−0.96 < y < 0.04 in the centre-of-mass frame) using data collected by ALICE at the CERN LHC. The results are obtained based on all the available measurements of prompt production of ground-state charm-hadron species: D0 , D+, D+s , and J/ψ mesons, and Lambda+c and Csi0c baryons. The resulting cross section is dσ (cc)/dy = 219.6 ± 6.3 (stat.) +10.5−11.8 (syst.) +8.3−2.9 (extr.) ± 5.4 (BR) ±4.6 (lumi.)±19.5 (rapidity shape)+15.0 (Omega0c ) mb, which is consistent with a binary scaling of pQCD calculations from pp collisions. The measured fragmentation fractions are compatible with those measured in pp collisions at √s = 5.02 and 13 TeV, showing an increase in the relative production rates of charm baryons with respect to charm mesons in pp and p–Pb collisions compared with e+e− and e−p collisions. The pT -integrated nuclear modification factor of charm quarks, RpPb(cc) = 0.91 ± 0.04 (stat.)+0.08−0.09 (syst.)+0.05−0.03 (extr.) ±0.03 (lumi.), is found to be consistent with unity and with theoretical predictions including nuclear modifications of the parton distribution functions

    Measurement of non-prompt D0{{\textrm{D}}^{0}}-meson elliptic flow in Pb–Pb collisions at sNN=5.02\sqrt{s_{\textrm{NN}}} = 5.02 TeV

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    The elliptic flow (v2) of D0 mesons from beautyhadron decays (non-prompt D0) was measured in midcentral (30–50%) Pb–Pb collisions at a centre-of-mass energy per nucleon pair √sNN = 5.02 TeV with the ALICE detector at the LHC. The D0 mesons were reconstructed at midrapidity (|y| &lt; 0.8) from their hadronic decay D0 → K−π+, in the transverse momentum interval 2 &lt; pT &lt; 12 GeV/c. The result indicates a positive v2 for non-prompt D0 mesons with a significance of 2.7σ. The non-prompt D0-meson v2 is lower than that of prompt non-strange D mesons with 3.2σ significance in 2 &lt; pT &lt; 8 GeV/c, and compatible with the v2 of beauty-decay electrons. Theoretical calculations of beautyquark transport in a hydrodynamically expanding medium describe the measurement within uncertainties

    Measurement of beauty-quark production in pp collisions at s s \sqrt{s} = 13 TeV via non-prompt D mesons

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    Abstract The p T-differential production cross sections of non-prompt D0, D+, and D s + Ds+ {\textrm{D}}_{\textrm{s}}^{+} mesons originating from beauty-hadron decays are measured in proton–proton collisions at a centre-of-mass energy s s \sqrt{s} = 13 TeV. The measurements are performed at midrapidity, |y| < 0.5, with the data sample collected by ALICE from 2016 to 2018. The results are in agreement with predictions from several perturbative QCD calculations. The fragmentation fraction of beauty quarks to strange mesons divided by the one to non-strange mesons, f s /(f u + f d), is found to be 0.114 ± 0.016 (stat.) ± 0.006 (syst.) ± 0.003 (BR) ± 0.003 (extrap.). This value is compatible with previous measurements at lower centre-of-mass energies and in different collision systems in agreement with the assumption of universality of fragmentation functions. In addition, the dependence of the non-prompt D meson production on the centre-of-mass energy is investigated by comparing the results obtained at s s \sqrt{s} = 5.02 and 13 TeV, showing a hardening of the non-prompt D-meson p T-differential production cross section at higher s s \sqrt{s} . Finally, the b b ¯ bb \textrm{b}\overline{\textrm{b}} production cross section per unit of rapidity at midrapidity is calculated from the non-prompt D0, D+, D s + Ds+ {\textrm{D}}_{\textrm{s}}^{+} , and Λ c + Λc+ {\Lambda}_{\textrm{c}}^{+} hadron measurements, obtaining d σ / d y = 75.2 ± 3.2 stat . ± 5.2 syst . − 3.2 + 12.3 extrap . dσ/dy=75.2±3.2(stat.)±5.2(syst.)3.2+12.3(extrap.) \textrm{d}\sigma /\textrm{d}y=75.2\pm 3.2\left(\textrm{stat}.\right)\pm 5.2{\left(\textrm{syst}.\right)}_{-3.2}^{+12.3}\left(\textrm{extrap}.\right) μb

    Azimuthal correlations of prompt D mesons with charged particles in pp and p–Pb collisions at

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    The measurement of the azimuthal-correlation function of prompt D mesons with charged particles in pp collisions at s=5.02 TeV\sqrt{s} =5.02\ \hbox {TeV} and p–Pb collisions at sNN=5.02 TeV\sqrt{s_{\mathrm{NN}}} = 5.02\ \hbox {TeV} with the ALICE detector at the LHC is reported. The D0\mathrm{D}^{0}, D+\mathrm{D}^{+} , and D+\mathrm{D}^{*+} mesons, together with their charge conjugates, were reconstructed at midrapidity in the transverse momentum interval 30.3 GeV/c3 0.3\ \hbox {GeV}/c and pseudorapidity η<0.8|\eta | < 0.8. The properties of the correlation peaks appearing in the near- and away-side regions (for Δφ0\Delta \varphi \approx 0 and Δφπ\Delta \varphi \approx \pi , respectively) were extracted via a fit to the azimuthal correlation functions. The shape of the correlation functions and the near- and away-side peak features are found to be consistent in pp and p–Pb collisions, showing no modifications due to nuclear effects within uncertainties. The results are compared with predictions from Monte Carlo simulations performed with the PYTHIA, POWHEG+PYTHIA, HERWIG, and EPOS 3 event generators
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