Measurement of D-meson nuclear modification factor and flow in Pb--Pb collisions with ALICE at the LHC

Heavy quarks are sensitive probes of the colour-deconfined medium formed in ultra-relativistic heavy-ion collisions, the Quark-Gluon Plasma (QGP). The ALICE Collaboration measured the production of ${\rm D}^0$, ${\rm D}^+$, ${\rm D}^{*+}$ and ${\rm D_s}^+$ mesons in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02~{\rm TeV}$. The properties of the in-medium energy loss and the possible modification of the charm-quark hadronisation mechanism are investigated via the measurement of the nuclear modification factor ($R_{\rm AA}$) of non-strange and strange D mesons. In mid-central collisions, the measurement of the D-meson elliptic flow ($v_2$) at low and intermediate transverse momentum ($p_{\rm T}$) gives insight into the participation of the charm quark in the collective motion of the system, while at high $p_{\rm T}$ it constrains the path-length dependence of the energy loss. The coupling of the charm quark to the light quarks in the underlying medium is further investigated with the application of the event-shape engineering (ESE) technique to D-meson elliptic flow. Finally, the role of the early magnetic field created in heavy-ion collisions is studied via the first measurement at the LHC energies of the charged-dependent directed flow ($v_1$) of ${\rm D}^0$ mesons as a function of pseudorapidity.Comment: 4 pages, 3 figures, Hard Probes 201

Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC

Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe

Measurement of the D-meson nuclear modification factor and elliptic flow in Pb-Pb collisions at sNN=5.02 TeV\sqrt{s_{\rm NN}}=5.02~{\rm TeV} with ALICE at the LHC

Heavy-flavour hadrons are recognised as a powerful probe for the characterisation of the deconfined medium created in heavy-ion collisions, the Quark-Gluon Plasma (QGP). The ALICE Collaboration measured the production of ${\rm D}^{0}$, ${\rm D}^{+}$, ${\rm D}^*$ and ${\rm D_s}^{+}$ mesons in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02~{\rm TeV}$. The measurement of the nuclear modification factor ($R_{\rm AA}$) provides a strong evidence of the in-medium parton energy loss. The comparison between the ${\rm D_s}^{+}$ and the non-strange D-meson $R_{\rm AA}$ can help to study the hadronisation mechanism of the charm quark in the QGP. In mid-central collisions, the measurement of the D-meson elliptic flow $v_2$ at low transverse momentum ($p_{\rm T}$) gives insight into the participation of the charm quark into the collective motion of the system, while at high $p_{\rm T}$ it constrains the path-length dependence of the energy loss. The ${\rm D_s}^{+}$ $v_2$, measured for the first time at the LHC, is found to be compatible to that of non-strange D mesons and positive with a significance of about $2.6~\sigma$. Further evidence of a strong coupling of the charm quark to the light quarks of the underlying medium is suggested by the first application of the Event-Shape Engineering (ESE) technique to D-meson elliptic flow.Heavy-flavour hadrons are recognised as a powerful probe for the characterisation of the deconfined medium created in heavy-ion collisions, the Quark-Gluon Plasma (QGP). The ALICE Collaboration measured the production of D0, D+, D*+ and mesons in Pb–Pb collisions at = 5.02 TeV. The measurement of the nuclear modification factor (RAA) provides a strong evidence of the in-medium parton energy loss. The comparison between the and the non-strange D-meson RAA can help to study the hadronisation mechanism of the charm quark in the QGP. In mid-central collisions, the measurement of the D-meson elliptic flow v2 at low transverse momentum (pT) gives insight into the participation of the charm quark into the collective motion of the system, while at high pT it constrains the path-length dependence of the energy loss. The v2, measured for the first time at the LHC, is found to be compatible to that of non-strange D mesons and positive with a significance of about 2.6 σ. The coupling of the charm quark to the light quarks in the underlying medium is further investigated for the first time with the application of the Event-Shape Engineering (ESE) technique to D-meson elliptic flow

Study of RAA\pmb{R_{\rm AA}} and v2\pmb{v_2} of non-strange D mesons and D-jet production in Pb-Pb collisions with ALICE

Heavy quarks are sensitive probes of the colour-deconfined medium formed in ultra-relativistic heavy-ion collisions, the Quark-Gluon Plasma (QGP). The ALICE Collaboration measured the production of $\rm D^0$, $\rm D^+$, and $\rm D^{*+}$ mesons in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. The properties of the in-medium energy loss are investigated via the measurement of the nuclear modification factor ($R_{\rm AA}$) of non-strange D mesons. The modification of the D-meson transverse momentum ($p_{\rm T}$) distributions inside the jet is studied via the measurement of the D-meson tagged jet $R_{\rm AA}$ in central Pb-Pb collisions. In mid-central collisions, the measurement of the D-meson elliptic flow ($v_2$) at low and intermediate $p_{\rm T}$ gives insight into the participation of the charm quark in the collective motion of the system, while at high $p_{\rm T}$ it constrains the path-length dependence of the energy loss. The coupling of the charm quark to the light quarks in the underlying medium is further investigated with the application of the event-shape engineering (ESE) technique to D-meson elliptic flow.Heavy quarks are sensitive probes of the colour-deconfined medium formed in ultra-relativistic heavy-ion collisions, the Quark--Gluon Plasma (QGP). The ALICE Collaboration measured the production of $\rm D^0$, $\rm D^+$, and $\rm D^{*+}$ mesons in $\rm Pb-Pb$ collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV. The properties of the in-medium energy loss are investigated via the measurement of the nuclear modification factor ($R_{\rm AA}$) of non-strange D mesons. The modification of the D-meson transverse momentum ($p_{\rm T}$) distributions inside the jet is studied via the measurement of the D-meson tagged jet $R_{\rm AA}$ in central $\rm Pb-Pb$ collisions. In mid-central collisions, the measurement of the D-meson elliptic flow ($v_2$) at low and intermediate $p_{\rm T}$ gives insight into the participation of the charm quark in the collective motion of the system, while at high $p_{\rm T}$ it constrains the path-length dependence of the energy loss. The coupling of the charm quark to the light quarks in the underlying medium is further investigated with the application of the event-shape engineering (ESE) technique to D-meson elliptic flow

Strange and non-strange D-meson production in pp, p-Pb, and Pb-Pb collisions with ALICE at the LHC

L'abstract è presente nell'allegato / the abstract is in the attachmen

Strange and non-strange D-meson production in pp, p-Pb, and Pb-Pb collisions with ALICE at the LHC

The ALICE experiment at the CERN LHC was designed to study the colour-deconfined state of the nuclear matter created in heavy-ion collisions, called Quark-Gluon Plasma (QGP). Heavy flavours (i.e. charm and beauty quarks) represent an ideal probe of the QGP, since they are produced via hard-scattering processes in short time scales and hence experience the full system evolution, loosing energy via elastic and inelastic scatterings with the medium constituents. The measurement of open-heavy flavour hadrons represents also an important test for the understanding of the hadronisation mechanism in the hot environment created in heavy-ion collisions. In fact, if a fraction of heavy quarks hadronises via recombination with the medium constituents, the relative abundance of open heavy-flavour hadrons containing strange quarks with respect to those without strange-quark content is expected to be larger in heavy-ion collisions compared to proton-proton (pp) collisions, due to the enhanced production of strange quarks in the QGP. The aim of the studies presented in this Thesis is the precise measurement of charmed mesons with and without strange-quark content, reconstructed in the three-body decay channels $\mathrm{D}_\mathrm{s}^+\rightarrow\phi\pi^+\rightarrow\mathrm{K^+K^-}\pi^+$ and $\mathrm{D}^+\rightarrow\mathrm{K^-}\pi^+\pi^+$. The measurement of the $\mathrm{D}_\mathrm{s}^+$-meson production in pp collisions at a centre-of-mass energy of $\sqrt{s}=5.02~$TeV is described by perturbative QCD calculations. The abundance of $\mathrm{D}_\mathrm{s}^+$ mesons relative to that of non-strange D mesons is found to be compatible with that measured in $e^+e^-$ collisions, indicating that the charm-quark hadronisation mechanism is not significantly modified in pp collisions. The multiplicity-dependent nuclear modification factor of $\mathrm{D}^+$ mesons $Q_\mathrm{pA}$ measured in p-Pb collisions at a centre-of-mass-energy per nucleon pair of $\sqrt{s_\mathrm{NN}}=5.02~$TeV was found compatible with unity, with a hint of enhancement for the transverse-momentum interval $2 < p_\mathrm{T} < 10~\mathrm{GeV}/c$. A strong suppression of the $p_\mathrm{T}$-differential yields of $\mathrm{D}^+$ and $\mathrm{D}_\mathrm{s}^+$ mesons, increasing with the collision centrality, is observed in Pb-Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02~$TeV. The nuclear modification factor $R_\mathrm{AA}$ of $\mathrm{D}^+$ mesons is found to be higher than that of charged particles for $p_\mathrm{T}<8~\mathrm{GeV}/c$. The central values of the $\mathrm{D}_\mathrm{s}^+$-meson $R_\mathrm{AA}$ are found to be higher than those of non-strange D mesons, as expected in case of hadronisation via recombination in a strangeness-rich medium, but still compatible within uncertainties. The measurement of the azimuthal anisotropies in the momentum distribution of $\mathrm{D}^+$ mesons in Pb-Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02~$TeV, quantified by the second-harmonic coefficient of the Fourier decomposition, denoted elliptic flow $v_2$, indicates that the charm quarks participate in the collective motions of the system. The comparison with the $v_2$ of charged pions and $\mathrm{J}/\psi$ mesons suggests a contribution to the $\mathrm{D}^+$-meson $v_2$ originated by the hadronisation of the charm quark via recombination with flowing light-quarks in the medium. A positive correlation between the $v_2$ of $\mathrm{D}^+$ mesons and that of light-flavour hadrons is observed thanks to the first application of the event-shape engineering (ESE) technique to the measurement of the D-meson azimuthal anisotropies. The perspectives of improved measurements with the application of machine-learning techniques for the selection of the D-meson signal and with the upgrade of the ALICE Inner Tracking System (ITS), planned for the LHC Run3 in 2020, are discussed

Recent results on open heavy flavour with ALICE (by F.G.) - Recent results on jets and high-pT hadrons with ALICE (by L.B.H.)

First talk (30'): Heavy flavours are recognised as excellent probes of the colour-deconfined state of the hadronic matter called quark-gluon plasma (QGP) created in heavy-ion collisions. Due to the very short time scale characterising their production, they experience the whole evolution of the system serving as Brownian-motion markers of the QGP. Measurements of open heavy-flavour hadron production in heavy-ion collisions give insight in the mechanisms of heavy-quark transport and energy loss in the hot and dense QCD matter, and the abundances of different hadron species are fundamental to investigate the hadronisation processes. Measurements of the production of heavy-flavour hadrons in proton-proton collisions provide the baseline for observations of hot-medium effects in heavy-ion collisions, as well as tests of perturbative QCD calculations. In recent years, they gained additional interest due to the observation of unexpected features typical of the heavy-ion phenomenology. In this seminar, the most recent results of the ALICE collaboration on the production of Λc, Ξc, and Σc baryons in pp collisions, D mesons from beauty-hadron decays in pp and Pb-Pb collisions, the charm production cross section in pp and p-Pb collisions from low-mass dielectron measurements, and the azimuthal anisotropy in the production of open charm and beauty hadrons in Pb-Pb collision are presented. Second talk (30'): Jets and high transverse momentum (pT) hadrons are excellent probes of the QGP produced in heavy-ion (HI) collisions because the partons inside jets interact with the medium, leading to jet energy loss and substructure modification - a phenomenon called jet quenching. New measurements that probe several aspects of jet quenching in Pb-Pb collisions with the ALICE detector will be shown in new regions of phase space for HI jet measurements at the LHC. These include measurements of jet suppression using machine learning techniques, measurements of jet acoplanarity using hadron-jet correlations, and the first unfolded groomed jet substructure measurements. This talk will discuss these new results, including comparisons to jet quenching models, and how they further our knowledge of the microscopic composition of the QGP. Additionally, measurements in pp collisions of groomed inclusive and heavy-flavour tagged jet substructure that are calculable with pQCD will be shown. Jets and high-pT&nbsp;hadron measurements in small systems (pp, p-Pb) help elucidate initial and final state effects and constrain nuclear PDFs. ALICE has set limits on the magnitude of jet quenching in small systems, which complement observations of flow-like signatures in these systems. This talk will also discuss new results in small systems with ALICE and how they fit into our understanding of QCD matter. &nbsp; Password: 247811</p

Flow Dominance and Factorization of Transverse Momentum Correlations in Pb-Pb Collisions at the LHC

We present the first measurement of the two-particle transverse momentum differential correlation function, P-2 = <Delta pT Delta p(T)>/ < p(T)>(2), in Pb-Pb collisions at root s(NN) = 2.76 TeV. Results for P-2 are reported as a function of the relative pseudorapidity (Delta eta) and azimuthal angle (Delta phi) between two particles for different collision centralities. The Delta phi dependence is found to be largely independent of Delta eta for broken vertical bar Delta eta broken vertical bar >= 0.9. In the 5% most central Pb-Pb collisions, the two-particle transverse momentum correlation function exhibits a clear double-hump structure around Delta phi=pi (i. e., on the away side), which is not observed in number correlations in the same centrality range, and thus provides an indication of the dominance of triangular flow in this collision centrality. Fourier decompositions of P-2, studied as a function of the collision centrality, show that correlations at broken vertical bar Delta eta broken vertical bar >= 0.9 can be well reproduced by a flow ansatz based on the notion that measured transverse momentum correlations are strictly determined by the collective motion of the system