Transverse momentum spectra of charged particles are measured by the CMS experiment at the CERN LHC in pPb collisions at [arrow]"NN = 5.02 TeV, in the range 0.4

Transverse momentum spectra of charged particles are measured by the CMS experiment at the CERN LHC in pPb collisions at [arrow]"NN = 5.02 TeV in the range 0.4

The production of identified charged particles in pp collisions at .sqrt.s = 63 GeV with an identified high p/sub T/ trigger particle emitted in the central region is studied. The measurements were performed at the CERN ISR using the Axial Field Spectrometer. Trigger particle ratios, sigma(.pi./sup + -/)/ sigma(all/sup + -/), sigma(K/sup + -/) and sigma(p/sup + -/)/sigma(all/sup + -/) are presented for p/sub T/ from 5 GeV/c to 8 GeV/c. In addition sigma(.pi./sup + -/)/sigma(all/sup + -/) is presented in the p/sub T/ region from 2.5 GeV/c to 4.5 GeV/c. The charge compensation in the hemisphere containing the trigger particle is shown to depend strongly on the identity of the trigger particle and on the identity of the associated particles. 13 references.

The phenomenology of the strong nuclear force is still not well understood at low momentum transfers and requires experimental input to constrain. Collisions of heavy ions at the Large Hadron Collider provide a unique opportunity to explore this kinematic region because they create a novel form of matter: the quark-gluon plasma (QGP). Using the CMS detector, spectra of charged particles originating from protonproton (pp), proton-lead (pPb), and lead-lead (PbPb) collisions at a center of mass energy per nucleon pair ( [square root of SNN) of 5.02 TeV are examined as a function of transverse momentum and centrality. Nuclear modification factors and fragmentation functions are constructed from these spectra. By comparing to pp collision reference spectra, a puzzle concerning previous measurements in pPb collisions is clarified. A strong suppression of particle production observed in PbPb collisions is also quantified. Finally, collisions of xenon nuclei are also studied to constrain the path length dependence of parton energy loss. The strength of energy loss is found to increase with both [square root of SNN and the average path length through the QGP. Comparisons to theoretical models and previous measurements indicate that the path length dependence is between linear and quadratic, as expected from a combination of collisional and radiative energy loss mechanisms.

The charged particle transverse momentum (pT) spectra are presented for pp collisions at sqrt(s)=0.9 and 7 TeV. The data samples were collected with the CMS detector at the LHC and correspond to integrated luminosities of 231 inverse microbarns and 2.96 inverse picobarns, respectively. Calorimeter-based high-transverse-energy triggers are employed to enhance the statistical reach of the high-pT measurements. The results are compared with both leading-order QCD and with an empirical scaling of measurements at different collision energies using the scaling variable xT = 2 pT/sqrt(s) over the pT range up to 200 GeV/c. Using a combination of xT scaling and direct interpolation at fixed pT, a reference transverse momentum spectrum at sqrt(s)=2.76 TeV is constructed, which can be used for studying high-pT particle suppression in the dense QCD medium produced in heavy-ion collisions at that centre-of-mass energy.

This thesis offers an excellent, comprehensive introduction to the physics of the quark–gluon plasma. It clearly explains the connection between theory and experiment, making the topic accessible to non-specialists in this field. The experimental work, which contributes significantly to our understanding of the quark–gluon plasma, is described in great detail. The results described in the final chapters of the thesis provide interesting new ideas about the connection between proton-proton and Pb-Pb collisions. Simone Schuchmann received the 'ALICE Thesis Award 2016' for this excellent work.

In the Standard Model of particle physics,the theory of the strong interaction, Quantum Chromodynamics (QCD), is a gauge theory of symmetry group SU (Nc) with respect to the color quantum number. QCD obeys the property of asymptotic freedom, allowing the computation of high-energy physical observables using perturbative QCD (pQCD). This thesis deals with the pQCD description of hadron production rates in high-energy hadronic collisions, in view of applications to the phenomenology of proton-nucleus and nucleus-nucleus collisions at hadron colliders (RHIC,LHC), where so-called nuclear effects (shadowing, parton energy loss, transverse momentum broadening) come into play. In a first part, I study the transverse broadening of an energetic parton system crossing a nucleus, putting emphasis on the color structure of the process. A theoretical setup based on the dipole formalism is used,and a kinetic equation is derived for the parton pair transverse momentum distribution, requiring the parton pair to be in a given color state (SU (Nc) irreducible representation) both in the initial and final state. The color structure is encoded in a color evolution operator, which is obtained for any type of parton pair. For a small-size compact pair, the derivation yields a transparent physical interpretation of the pair transverse broadening process. In a second part, I discuss the soft anomalous dimension matrix Q, which is formally analogous to the previous evolution operator, and which appears when studying soft gluon radiation associated to 2 -> 2 hard parton scattering. It has been noticed that the Q-matrix associated to gg -> gg has a surprising symmetry (relating external and internal degrees of freedom). I developed tools to derive the Q-matrices associated to2 -> 2 scatterings involving generalized partons, in order to explore if the symmetry observed for gg -> gg is fortuitous or not.

Dijet production has been measured in pPb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV. A data sample corresponding to an integrated luminosity of 35 inverse-nanobarns was collected using the Compact Muon Solenoid detector at the Large Hadron Collider. The dijet transverse momentum balance, azimuthal angle correlations, and pseudorapidity distributions are studied as a function of the transverse energy in the forward calorimeters ($E_T^{4\lt.