Heavy-flavour production at forward rapidity as a function of charged-particle multiplicity with ALICE at the LHC

Heavy-flavour hadrons are hadrons made up of at least a charm or beauty heavy quark. They are produced in the early stages of ultra-relativistic collisions via hard scatterings and are important tools for studying different aspects of Quantum Chromodynamics (QCD) in hadronic collisions. Charged-particle multiplicity gives information on the global characteristics of the event and could be used to characterize particle production mechanisms. In hadronic collisions at Large Hadron Collider (LHC) energies, there is a significant contribution of Multiple Parton Interactions (MPI), i.e. several hard partonic interactions occurring in a single collision between nucleons. Therefore, the measurement of heavy-flavour hadrons as a function of charged-particle multiplicity gives insight into the mechanisms influencing their production in hadronic collisions at these energies and is a tool to test the influence of MPIs. Furthermore, charged-particle multiplicity dependence of heavy-flavour hadron production is used to test the ability of QCD theoretical models to reproduce data. In this thesis we investigate the production of heavy flavours via the single muon decay channel at forward rapidity as a function of the charged-particle multiplicity measured at central rapidity in proton-lead (p–Pb) collisions at √ sNN = 8.16 TeV using ALICE (A Large Ion Collider Experiment) at the LHC. ALICE is a dedicated detector optimized to study ultra-relativistic heavy-ion collisions in which the Quark-Gluon Plasma (QGP - the state of matter which prevailed in the Early Universe shortly after the Big Bang) is created. ALICE also studies proton-proton (pp) and p–Pb collisions. In pp collisions, production cross sections obtained from data provide information used to test pQCD theories while in p–Pb collisions, where the energy density is believed to be too low to produce the QGP, the presence of additional nuclear matter can alter the wavefunction of the nucleus leading to modified observables - the so-called cold nuclear matter (CNM) effects. The study of the multiplicity dependence of heavy-flavour production in p-Pb collisions may give important information regarding initial-state effects in CNM. Both pp and p– Pb collisions provide reference for comparison with heavy-ion (Pb–Pb) collisions. ALICE measures hadrons, leptons, and photons up to very high transverse momentum (pT) ≈100 GeV/c. The detector consists of a central barrel, which covers a rapidity of |y| < 1 and a Muon Spectrometer which covers the forward rapidity, -4 < y < -2.5. In this thesis, the production of heavy flavours via the contribution of their muonic decays to the inclusive pT-differential muon yield at forward (2.03 < ycms < 3.53) and backward (-4.46 < ycms < -2.96) rapidity reconstructed with the Muon Spectrometer and charged-particle multiplicity using the Silicon Pixel Detector located in the central barrel (|y| <1) in p-Pb collisions at √ sNN = 8.16 TeV in the forward and backward rapidity are studied. The aim of the study is to probe the role of MPIs in the production of heavy flavours focusing on the contribution of hard and soft processes as well as to investigate effects of the presence of multiple binary nucleon-nucleon interactions and the initial state effects modified by CNM in particle production

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

The study of the production of heavy flavour muons as a function of charged-particle multiplicity in proton-proton collisions at 8TeV with ALICE at the LHC

ALICE (A Large Ion Collider Experiment) is a detector designed and optimized to study ultra relativistic heavy-ion collisions in which a hot, dense and strongly interacting Quantum Chromodynamics (QCD) medium called the Quark Gluon Plasma (QGP) is created. ALICE also studies proton-proton collisions both to test for pertubative QCD (pQCD) theories and as reference for comparison with heavy-ion collisions. ALICE measures hadrons, leptons, and photons up to very high transverse momentum (pT), up to ∼100 GeV/c. It consists of a central barrel which covers a rapidity of | η | < 0.9 and a Muon Spectrometer which covers the forward rapidity, -4 < η < -2.5. The Muon Spectrometer measures dimuons from the decay of quarkonia (charm-anti-charm (c c ) e.g. J/Ψ), as well as single muons from heavy flavours (e.g. charm (c) and bottom (b) hadrons) and electroweak bosons (W ± , Z 0 ), which are tools for studying QGP as well as the initial conditions of the collision. In this thesis the production of heavy flavours is measured via the contribution of their muonic decays to the inclusive pT -differential muon yield, reconstructed with the Muon Spectrometer and studied as a function of charged-particle multiplicity in proton-proton collisions at 8 TeV centre-of-mass energy. The charged-particle multi- plicity is measured in the central barrel. The aim of the study is to investigate the role of multi-parton interactions in the production of heavy quarks, particularly heavy flavour

AliPDU Upgrade

A power distribution unit (PDU) is a device used in data centres to distribute AC power to multiple servers and other equipment. Power distribution units (PDUs) can be managed remotely via the Web browser or other management console, causing outlets to be turned on and off at prescribed times and in a proper sequence for shutting down and powering up equipment. The task in this project was to create as many PDUs on one click and customize them

Measurement of open heavy-flavour production as a function of charged-particle multiplicity with ALICE at the LHC

Heavy quarks are produced in the early stages of ultra-relativistic hadron collisions via hard scatterings and are an important tool for studying different aspects of Quantum Chromodynamics (QCD) in hadronic collisions. Charged-particle multiplicity gives information on the global characteristics of the event and could be used to characterize particle production mechanisms. In hadronic collisions at Large Hadron Collider (LHC) energies, there is a significant contribution of multi-parton interactions. The measurement of heavy-flavour yields as a function of charged-particle multiplicity gives insight into the mechanisms influencing their production in hadronic collisions at these energies and it is a tool to test the possible influence of multi-parton interactions. Furthermore, the charged-particle multiplicity dependence of open heavy flavours is used to test the ability of QCD theoretical models to describe the data. In ALICE, heavy-flavour production is measured via the hadronic and semi-leptonic decay channels (electrons at central rapidity and muons at forward rapidity). Charged-particle multiplicity is measured at central and forward rapidity. We will present the results on open heavy-flavour production as a function of the charged-particle multiplicity in pp and p–Pb collisions. Results will be compared to quarkonia measurements as well as theoretical model calculations.Heavy quarks are produced in the early stages of ultra-relativistic hadron collisions via hard scatterings and are an important tool for studying different aspects of Quantum Chromodynamics (QCD) in hadronic collisions. Charged-particle multiplicity gives information on the global characteristics of the event and could be used to characterize particle production mechanisms. In hadronic collisions at Large Hadron Collider (LHC) energies, there is a significant contribution of multi-parton interactions. The measurement of heavy-flavour yields as a function of charged-particle multiplicity gives insight into the mechanisms influencing their production in hadronic collisions at these energies and it is a tool to test the possible influence of multi-parton interactions. Furthermore, the charged-particle multiplicity dependence of open heavy flavours is used to test the ability of QCD theoretical models to describe the data. In ALICE, heavy-flavour production is measured via the hadronic and semi-leptonic decay channels (electrons at central rapidity and muons at forward rapidity). Charged-particle multiplicity is measured at central and forward rapidity. We will present the results on open heavy-flavour production as a function of the charged-particle multiplicity in pp and pPb collisions. Results will be compared to quarkonia measurements as well as theoretical model calculations

Multiplicity dependence of light (anti-)nuclei production in p–Pb collisions at sNN=5.02 TeV

The measurement of the deuteron and anti-deuteron production in the rapidity range −1 < y < 0 as a function of transverse momentum and event multiplicity in p–Pb collisions at √sNN = 5.02 TeV is presented. (Anti-)deuterons are identified via their specific energy loss dE/dx and via their time-of- flight. Their production in p–Pb collisions is compared to pp and Pb–Pb collisions and is discussed within the context of thermal and coalescence models. The ratio of integrated yields of deuterons to protons (d/p) shows a significant increase as a function of the charged-particle multiplicity of the event starting from values similar to those observed in pp collisions at low multiplicities and approaching those observed in Pb–Pb collisions at high multiplicities. The mean transverse particle momenta are extracted from the deuteron spectra and the values are similar to those obtained for p and particles. Thus, deuteron spectra do not follow mass ordering. This behaviour is in contrast to the trend observed for non-composite particles in p–Pb collisions. In addition, the production of the rare 3He and 3He nuclei has been studied. The spectrum corresponding to all non-single diffractive p-Pb collisions is obtained in the rapidity window −1 < y < 0 and the pT-integrated yield dN/dy is extracted. It is found that the yields of protons, deuterons, and 3He, normalised by the spin degeneracy factor, follow an exponential decrease with mass number

Measurement of electrons from semileptonic heavy-flavour hadron decays at midrapidity in pp and Pb–Pb collisions at √sNN = 5.02 TeV

The differential invariant yield as a function of transverse momentum (pT) of electrons from semileptonic heavy-flavour hadron decays was measured at midrapidity in central (0–10%), semi-central (30–50%) and peripheral (60–80%) lead–lead (Pb–Pb) collisions at √sNN = 5.02 TeV in the pT intervals 0.5–26 GeV/c (0–10% and 30–50%) and 0.5–10 GeV/c (60–80%). The production cross section in proton–proton (pp) collisions at √s = 5.02 TeV was measured as well in 0.5 < pT < 10 GeV/c and it lies close to the upper band of perturbative QCD calculation uncertainties up to pT = 5 GeV/c and close to the mean value for larger pT. The modification of the electron yield with respect to what is expected for an incoherent superposition of nucleon–nucleon collisions is evaluated by measuring the nuclear modification factor RAA. The measurement of the RAA in different centrality classes allows in-medium energy loss of charm and beauty quarks to be investigated. The RAA shows a suppression with respect to unity at intermediate pT, which increases while moving towards more central collisions. Moreover, the measured RAA is sensitive to the modification of the parton distribution functions (PDF) in nuclei, like nuclear shadowing, which causes a suppression of the heavy-quark production at low pT in heavy-ion collisions at LHC

Nuclear modification factor of light neutral-meson spectra up to high transverse momentum in p–Pb collisions at sNN=8.16 TeV

International audienceNeutral pion (π0) and η meson production cross sections were measured up to unprecedentedly high transverse momenta (pT) in p–Pb collisions at sNN=8.16TeV. The mesons were reconstructed via their two-photon decay channel in the rapidity interval −1.3&lt;y&lt;0.3 in the ranges of 0.4&lt;pT&lt;200 GeV/c and 1.0&lt;pT&lt;50 GeV/c, respectively. The respective nuclear modification factor (RpPb) is presented for pT up to of 200 and 30 GeV/c, where the former was achieved by extending the π0 measurement in pp collisions at s=8TeV using the merged cluster technique. The values of RpPb are below unity for pT&lt;10 GeV/c, while they are consistent with unity for pT&gt;10 GeV/c, leaving essentially no room for final state energy loss. The new data provide strong constraints for nuclear parton distribution and fragmentation functions over a broad kinematic range and are compared to model predictions as well as previous results at sNN=5.02TeV

Relative particle yield fluctuations in Pb-Pb \text{ Pb-Pb } collisions at sNN=2.76 TeV\sqrt{s_\mathrm{{NN}}} =2.76\hbox { TeV}

First results on $\hbox {K}/\pi$ , $\hbox {p}/\pi$ and K/p fluctuations are obtained with the ALICE detector at the CERN LHC as a function of centrality in $\text{ Pb-Pb }$ collisions at $\sqrt{s_\mathrm{{NN}}} =2.76\hbox { TeV}$ . The observable $\nu _{\mathrm{dyn}}$ , which is defined in terms of the moments of particle multiplicity distributions, is used to quantify the magnitude of dynamical fluctuations of relative particle yields and also provides insight into the correlation between particle pairs. This study is based on a novel experimental technique, called the Identity Method, which allows one to measure the moments of multiplicity distributions in case of incomplete particle identification. The results for $\hbox {p}/\pi$ show a change of sign in $\nu _{\mathrm{dyn}}$ from positive to negative towards more peripheral collisions. For central collisions, the results follow the smooth trend of the data at lower energies and $\nu _{\mathrm{dyn}}$ exhibits a change in sign for $\hbox {p}/\pi$ and K/p