The first evidence for X(3872) production in relativistic heavy ion collisions is reported. The X(3872) production is studied in lead-lead (PbPb) collisions at a center-of-mass energy of $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV per nucleon pair, using the decay chain X(3872) $\to$ J$/\psi\, \pi^+\pi^- \to$ $\mu^+\mu^-\pi^+\pi^-$. The data were recorded with the CMS detector in 2018 and correspond to an integrated luminosity of 1.7 nb$^{-1}$. The measurement is performed in the rapidity and transverse momentum ranges $|y|$ $\lt$ 1.6 and 15 $\lt$ $p_\mathrm{T}$ $\lt$ 50 GeV$/c$. The significance of the inclusive X(3872) signal is 4.2 standard deviations. The prompt X(3872) to $\psi$(2S) yield ratio is found to be $\rho^\mathrm{PbPb} = $ 1.08 $\pm$ 0.49 (stat) $\pm$ 0.52 (syst), to be compared with typical values of 0.1 for pp collisions. This result provides a unique experimental input to theoretical models of the X(3872) production mechanism, and of the nature of this exotic state.
The yield ratio $\rho^{\mathrm{PbPb}}$ of prompt X(3872) over $\psi(\mathrm{2S})$ production in PbPb collisions at 5.02 TeV
Jet production in lead-lead (PbPb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV is studied with the CMS detector at the LHC, using PbPb and pp data samples corresponding to integrated luminosities of 404 $\mu$b$^{-1}$ and 27.4 pb$^{-1}$, respectively. Jets with different areas are reconstructed using the anti-$k_\mathrm{T}$ algorithm by varying the distance parameter $R$. The measurements are performed using jets with transverse momenta ($p_\mathrm{T}$) greater than 200 GeV and in a pseudorapidity range of $|\eta|$$\lt$ 2. To reveal the medium modification of the jet spectra in PbPb collisions, the properly normalized ratio of spectra from PbPb and pp data is used to extract jet nuclear modification factors as functions of the PbPb collision centrality, $p_\mathrm{T}$ and, for the first time, as a function of $R$ up to 1.0. For the most central collisions, a strong suppression is observed for high-$p_\mathrm{T}$ jets reconstructed with all distance parameters, implying that a significant amount of jet energy is scattered to large angles. The dependence of jet suppression on $R$ is expected to be sensitive to both the jet energy loss mechanism and the medium response, and so the data are compared to several modern event generators and analytic calculations. The models considered do not fully reproduce the data.
Spectra of jets with |eta jet| < 2.0 for R = 0.2, for pp collisions and different centrality classes of PbPb collisions.
Spectra of jets with |eta jet| < 2.0 for R = 0.3, for pp collisions and different centrality classes of PbPb collisions.
Spectra of jets with |eta jet| < 2.0 for R = 0.4, for pp collisions and different centrality classes of PbPb collisions.
The $p_\mathrm{T}$-differential production cross sections of prompt and non-prompt (produced in beauty-hadron decays) D mesons were measured by the ALICE experiment at midrapidity ($|y|<0.5$) in proton--proton collisions at $\sqrt{s}=5.02~\mathrm{TeV}$. The data sample used in the analysis corresponds to an integrated luminosity of $(19.3\pm0.4)~\mathrm{nb^{-1}}$. D mesons were reconstructed from their decays $\mathrm{D^0 \to K^-\pi^+}$, $\mathrm{D^+\to K^-\pi^+\pi^+}$, and $\mathrm{D_s^+\to \phi\pi^+\to K^-K^+\pi^+}$ and their charge conjugates. Compared to previous measurements in the same rapidity region, the cross sections of prompt $\mathrm{D^+}$ and $\mathrm{D_s^+}$ mesons have an extended $p_\mathrm{T}$ coverage and total uncertainties reduced by a factor ranging from 1.05 to 1.6, depending on $p_\mathrm{T}$, allowing for a more precise determination of their $p_\mathrm{T}$-integrated cross sections. The results are well described by perturbative QCD calculations. The fragmentation fraction of heavy quarks to strange mesons divided by the one to non-strange mesons, $f_\mathrm{s}/(f_\mathrm{u}+f_\mathrm{d})$, is compatible for charm and beauty quarks and with previous measurements at different centre-of-mass energies and collision systems. The $\mathrm{b\overline{b}}$ production cross section per rapidity unit at midrapidity, estimated from non-prompt D-meson measurements, is $\mathrm{d}\sigma_\mathrm{b\overline{b}}/\mathrm{d} y|_\mathrm{|y|<0.5} = 34.5 \pm 2.4 (\mathrm{stat.}) ^{+4.7}_{-2.9} (\mathrm{tot. syst.})~\mu\mathrm{b}$. It is compatible with previous measurements at the same centre-of-mass energy and with the cross section predicted by perturbative QCD calculations.
$p_\mathrm{T}$-differential production cross section of non-prompt $\mathrm{D^0}$ mesons in pp collision at $\sqrt{s}=5.02~\mathrm{TeV}$ in the rapidity interval $|y|<0.5$. Branching ratio of $\mathrm{D^0 \to K^-\pi^+}$: 0.0395
$p_\mathrm{T}$-differential production cross section of non-prompt $\mathrm{D^+}$ mesons in pp collision at $\sqrt{s}=5.02~\mathrm{TeV}$ in the rapidity interval $|y|<0.5$. Branching ratio of $\mathrm{D^+\to K^-\pi^+\pi^+}$: 0.0938
$p_\mathrm{T}$-differential production cross section of non-prompt $\mathrm{D_{s}^{+}}$ mesons in pp collision at $\sqrt{s}=5.02~\mathrm{TeV}$ in the rapidity interval $|y|<0.5$. Branching ratio of $\mathrm{D_s^+\to \phi\pi^+\to K^-K^+\pi^+}$: 0.0224
The spectra measurements of charged hadrons produced in the shower of a parton originating in the same hard scattering with a leptonically decaying Z boson, are reported in lead-lead (PbPb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Both PbPb and pp data sets are recorded by the CMS experiment at the LHC, and correspond to an integrated luminosity of 1.7 nb$^{-1}$ and 320 pb$^{-1}$, respectively. Hadronic collision data with one reconstructed Z boson candidate with the transverse momentum $p_\mathrm{T}$$\gt$ 30 GeV/$c$ are analyzed. The Z boson constrains the initial energy and direction of the associated parton. In heavy ion events, azimuthal angular distributions of charged hadrons with respect to the direction of a Z boson are sensitive to modifications of the in-medium parton shower and medium response. Compared to reference data from pp interactions, the results for central PbPb collisions indicate a modification of the angular correlations. The measurements of the fragmentation functions and $p_\mathrm{T}$ spectra of charged particles in Z boson events, which are sensitive to medium modifications of the parton shower longitudinal structure, are also reported. Significant modifications in central PbPb events compared to pp reference data are also found for these observables.
Distributions of $\Delta\phi_{\mathrm{trk,Z}}$ in pp collisions at 5.02 TeV.
Distributions of $\Delta\phi_{\mathrm{trk,Z}}$ in 70-90% centrality PbPb collisions at 5.02 TeV.
Distributions of $\Delta\phi_{\mathrm{trk,Z}}$ in 50-70% centrality PbPb collisions at 5.02 TeV.
The CMS experiment at the LHC has measured the differential cross sections of Z bosons decaying to pairs of leptons, as functions of transverse momentum and rapidity, in lead-lead collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The measured Z boson elliptic azimuthal anisotropy coefficient is compatible with zero, showing that Z bosons do not experience significant final-state interactions in the medium produced in the collision. Yields of Z bosons are compared to Glauber model predictions and are found to deviate from these expectations in peripheral collisions, indicating the presence of initial collision geometry and centrality selection effects. The precision of the measurement allows, for the first time, for a data-driven determination of the nucleon-nucleon integrated luminosity as a function of lead-lead centrality, thereby eliminating the need for its estimation based on a Glauber model.
The v2 of Z bosons in PbPb collisions for various centrality bins.
The v2 of Z bosons in PbPb collisions for various centrality bins.
The v2 of Z bosons in PbPb collisions for various centrality bins.
The production of $\phi$ mesons has been studied in pp collisions at LHC energies with the ALICE detector via the dimuon decay channel in the rapidity region $2.5 < y < 4$. Measurements of the differential cross section ${\rm d}^2\sigma/{\rm d}y {\rm d}p_{\rm T}$ are presented as a function of the transverse momentum ($p_{\rm T}$) at the center-of-mass energies $\sqrt{s}=5.02$, 8 and 13 TeV and compared with the ALICE results at midrapidity. The differential cross sections at $\sqrt{s}=5.02$ and 13 TeV are also studied in several rapidity intervals as a function of $p_{\rm T}$, and as a function of rapidity in three $p_{\rm T}$ intervals. A hardening of the $p_{\rm T}$-differential cross section with the collision energy is observed, while, for a given energy, $p_{\rm T}$ spectra soften with increasing rapidity and, conversely, rapidity distributions get slightly narrower at increasing $p_{\rm T}$. The new results, complementing the published measurements at $\sqrt{s}=2.76$ and 7 TeV, allow one to establish the energy dependence of $\phi$ meson production and to compare the measured cross sections with phenomenological models. None of the considered models manages to describe the evolution of the cross section with $p_{\rm T}$ and rapidity at all the energies.
$\phi$ meson production cross section $\mathrm{d}^2\sigma/(\mathrm{d}y\mathrm{d}p_\mathrm{T})$ as a function of $p_\mathrm{T}$ at $\sqrt{s}=5.02$ TeV at forward rapidity in pp collisions.
$\phi$ meson production cross section $\mathrm{d}^2\sigma/(\mathrm{d}y\mathrm{d}p_\mathrm{T})$ as a function of $p_\mathrm{T}$ at $\sqrt{s}=8$ TeV at forward rapidity in pp collisions.
$\phi$ meson production cross section $\mathrm{d}^2\sigma/(\mathrm{d}y\mathrm{d}p_\mathrm{T})$ as a function of $p_\mathrm{T}$ at $\sqrt{s}=13$ TeV at forward rapidity in pp collisions.
A measurement of inclusive, prompt, and non-prompt ${\rm J}/\psi$ production in p$-$Pb collisions at a nucleon$-$nucleon centre-of-mass energy $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV is presented. The inclusive ${\rm J}/\psi$ mesons are reconstructed in the dielectron decay channel at midrapidity down to a transverse momentum $p_{\rm T} = 0$. The inclusive ${\rm J}/\psi$ nuclear modification factor $R_{\rm pPb}$ is calculated by comparing the new results in p$-$Pb collisions to a recently measured proton$-$proton reference at the same centre-of-mass energy. Non-prompt ${\rm J}/\psi$ mesons, which originate from the decay of beauty hadrons, are separated from promptly produced ${\rm J}/\psi$ on a statistical basis for $p_{\rm T}$ larger than 1.0 GeV/$c$. These results are based on the data sample collected by the ALICE detector during the 2016 LHC p$-$Pb run, corresponding to an integrated luminosity ${\cal L}_{\rm int} = 292 \pm 11 \; {\rm \mu b}^{-1}$, which is six times larger than the previous publications. The total uncertainty on the $p_{\rm T}$-integrated inclusive ${\rm J}/\psi$ and non-prompt ${\rm J}/\psi$ cross section are reduced by a factor 1.7 and 2.2, respectively. The measured cross sections and $R_{\rm pPb}$ are compared with theoretical models that include various combinations of cold nuclear matter effects. From the non-prompt ${\rm J}/\psi$ production cross section, the ${\rm b\overline{b}}$ production cross section at midrapidity, $\mathrm{d}\sigma_{\rm b\overline{b}}/\mathrm{d}y$, and the total cross section extrapolated over full phase space, $\sigma_{\rm b\overline{b}}$, are derived.
Fraction of non-prompt $\rm{J}/\psi$ in pp collisions at $\sqrt{s}$ = 5.02 TeV for different $p_\mathrm{T}$ ranges, as determined with a procedure of interpolation from measurments at other energies. It is not a direct measurment.
Inclusive d$^2\sigma$/d$y$d$p_{\rm T}$ in bins of $p_{\mathrm{T}}^{J/\psi}$ for prompt J/$\psi$ in p--Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV.
Fraction of non-prompt J/$\psi$ in p--Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV for different $p_\mathrm{T}$ ranges.
The production of $\Lambda$ baryons and ${\rm K}^{0}_{\rm S}$ mesons (${\rm V}^{0}$ particles) was measured in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV and pp collisions at $\sqrt{s} = 7$ TeV with ALICE at the LHC. The production of these strange particles is studied separately for particles associated with hard scatterings and the underlying event to shed light on the baryon-to-meson ratio enhancement observed at intermediate transverse momentum ($p_{\rm T}$) in high multiplicity pp and p-Pb collisions. Hard scatterings are selected on an event-by-event basis with jets reconstructed with the anti-$k_{\rm T}$ algorithm using charged particles. The production of strange particles associated with jets $p_{\rm T,\;jet}^{\rm ch}>10$ and $p_{\rm T,\;jet}^{\rm ch}>20$ GeV/$c$ in p-Pb collisions, and with jet $p_{\rm T,\;jet}^{\rm ch}>10$ GeV/$c$ in pp collisions is reported as a function of $p_{\rm T}$. Its dependence on angular distance from the jet axis, $R({\rm V}^{0},\;{\rm jet})$, for jets with $p_{\rm T,\;jet}^{\rm ch}>10$ GeV/$c$ in p-Pb collisions is reported as well. The $p_{\rm T}$-differential production spectra of strange particles associated with jets are found to be harder compared to that in the underlying event and both differ from the inclusive measurements. In events containing a jet, the density of the ${\rm V}^{0}$ particles in the underlying event is found to be larger than the density in the minimum bias events. The $\Lambda/{\rm K}^{0}_{\rm S}$ ratio associated with jets in p-Pb collisions is consistent with the ratio in pp collisions and follows the expectation of jets fragmenting in vacuum. On the other hand, this ratio within jets is consistently lower than the one obtained in the underlying event and it does not show the characteristic enhancement of baryons at intermediate $p_{\rm T}$ often referred to as "baryon anomaly" in the inclusive measurements.
$p_{\rm T}$-differential density of inclusive ${\rm V}^{0}$ particles in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV.
$p_{\rm T}$-differential density of ${\rm V}^{0}$ particles in underlying events (perp. cone) in p-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV.
$p_{\rm T}$-differential densities of ${\rm V}^{0}$ particles selected with $R({\rm V}^{0},{\rm jet}) < 0.4$ and that produced in jets in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV.
The transverse momentum ($p_{\rm T}$) differential cross section of the charm-strange baryon $\Xi^0_{\rm c}$ is measured at midrapidity ($|y|<$ 0.5) via its semileptonic decay into ${\rm e^{+}}\Xi^{-}\nu_{\rm e}$ in pp collisions at $\sqrt{s}$ = 5.02 TeV with the ALICE detector at the LHC. The ratio of the $p_{\rm T}$-differential $\Xi^0_{\rm c}$-baryon and ${\rm D^0}$-meson production cross sections is also reported. The measurements are compared with simulations with different tunes of the PYTHIA 8 event generator, with predictions from a statistical hadronisation model (SHM) with a largely augmented set of charm-baryon states beyond the current lists of the Particle Data Group, and with models including hadronisation via quark coalescence. The $p_{\rm T}$-integrated cross section of prompt $\Xi^0_{\rm c}$-baryon production at midrapidity is also reported, which is used to calculate the baryon-to-meson ratio $\Xi^0_{\rm c}/{\rm D^0} = 0.20 \pm 0.04~{\rm (stat.)} ^{+0.08}_{-0.07}~{\rm (syst.)}$. These results provide an additional indication of a modification of the charm fragmentation from $\rm e^+e^-$ and $\rm e^{-}p$ collisions to pp collisions.
$p_{\rm T}-$differential production cross section of prompt $\Xi^{0}_{\rm c}$ baryons in pp collisions at $\sqrt{s} =$ 5.02 TeV for $|y| < 0.5$.
$p_{\rm T}-$differential production cross section of inclusive $\Xi^{0}_{\rm c}$ baryons in pp collisions at $\sqrt{s} =$ 7 TeV for $|y| < 0.5$. The cross section result now is divided by the BR, which was not applied in the previous paper and HEPData.
$\Xi^0_{\rm c}$/${\rm D^0}$ ratio measured in pp collisions at $\sqrt{s}$ = 5.02 TeV for $|y| < 0.5$. The uncertainty of the BR of ${\rm D^0}$ and $\Xi^0_{\rm c}$ are written separately
In quantum scattering processes between two particles, aspects characterizing the strong and Coulomb forces can be observed in kinematic distributions of the particle pairs. The sensitivity to the interaction potential reaches a maximum at low relative momentum and vanishing distance between the two particles. Ultrarelativistic heavy-ion collisions at the LHC provide an abundant source of many hadron species and can be employed as a measurement method of scattering parameters that is complementary to scattering experiments. This study confirms that momentum correlations of particles produced in Pb-Pb collisions at the LHC provide an accurate measurement of kaon-proton scattering parameters at low relative momentum, allowing precise access to the $ {K}^{-} p\rightarrow {K}^{-} p$ process. This work also validates the femtoscopic measurement in ultrarelativistic heavy-ion collisions as an alternative to scattering experiments and a complementary tool to the study of exotic atoms with comparable precision. In this work, the first femtoscopic measurement of momentum correlations of ${K}^{-} p\ ({K}^{+}\overline{p})$ and ${K}^{+}p ({K}^{-}\overline{p})$ pairs in Pb-Pb collisions at centre-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}} = 5.02$ TeV registered by the ALICE experiment is reported. The components of the ${K}^{-} p$ complex scattering length are extracted and found to be $\Re f_0=-0.91\pm~{0.03}$(stat)$^{+0.17}_{-0.03}$(syst) and $\Im f_0 = 0.92\pm~{0.05}$(stat)$^{+0.12}_{-0.33}$(syst). The results are compared with chiral effective field theory predictions as well as with existing data from dedicated scattering and exotic kaonic atom experiments.
K p (opposite charge) correlation function for centrality 0-5% from Pb-Pb collisions at 5020 GeV
K p (same charge) correlation function for centrality 0-5% from Pb-Pb collisions at 5020 GeV
K p (opposite charge) correlation function for centrality 5-10% from Pb-Pb collisions at 5020 GeV
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