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Sökning: WFRF:(Hansen M. S.) > Breitner T.

  • Resultat 1-10 av 92
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1.
  • Abelev, B., et al. (författare)
  • Technical Design Report for the Upgrade of the ALICE Inner Tracking System
  • 2014
  • Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 41:8
  • Tidskriftsartikel (refereegranskat)abstract
    • LICE (A Large Ion Collider Experiment) is studying the physics of strongly interacting matter, and in particular the properties of the Quark–Gluon Plasma (QGP), using proton–proton, proton–nucleus and nucleus–nucleus collisions at the CERN LHC (Large Hadron Collider). The ALICE Collaboration is preparing a major upgrade of the experimental apparatus, planned for installation in the second long LHC shutdown in the years 2018–2019. A key element of the ALICE upgrade is the construction of a new, ultra-light, high-resolution Inner Tracking System (ITS) based on monolithic CMOS pixel detectors. The primary focus of the ITS upgrade is on improving the performance for detection of heavy-flavour hadrons, and of thermal photons and low-mass di-electrons emitted by the QGP. With respect to the current detector, the new Inner Tracking System will significantly enhance the determination of the distance of closest approach to the primary vertex, the tracking efficiency at low transverse momenta, and the read-out rate capabilities. This will be obtained by seven concentric detector layers based on a 50 μm thick CMOS pixel sensor with a pixel pitch of about 30×30 μm2. This document, submitted to the LHCC (LHC experiments Committee) in September 2013, presents the design goals, a summary of the R&D activities, with focus on the technical implementation of the main detector components, and the projected detector and physics performance.
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2.
  • Adam, J., et al. (författare)
  • Measurement of charm and beauty production at central rapidity versus charged-particle multiplicity in proton-proton collisions at root s=7 TeV
  • 2015
  • Ingår i: Journal of High Energy Physics. - 1029-8479. ; :9
  • Tidskriftsartikel (refereegranskat)abstract
    • Prompt D meson and non-prompt J/psi yields are studied as a function of the multiplicity of charged particles produced in inelastic proton-proton collisions at a centre-of-mass energy of root s = 7 TeV. The results are reported as a ratio between yields in a given multiplicity interval normalised to the multiplicity-integrated ones (relative yields). They are shown as a function of the multiplicity of charged particles normalised to the average value for inelastic collisions (relative charged-particle multiplicity). D-0, D+ and D*+ mesons are measured in five p(T) intervals from 1 GeV/c to 20 GeV/c and for |y| < 0.5 via their hadronic decays. The D-meson relative yield is found to increase with increasing charged-particle multiplicity. For events with multiplicity six times higher than the average multiplicity of inelastic collisions, a yield enhancement of a factor about 15 relative to the multiplicity-integrated yield in inelastic collisions is observed. The yield enhancement is independent of transverse momentum within the uncertainties of the measurement. The D-0-meson relative yield is also measured as a function of the relative multiplicity at forward pseudo-rapidity. The non-prompt J/psi, i.e. the B hadron, contribution to the inclusive J/psi production is measured in the di-electron decay channel at central rapidity. It is evaluated for p(T) > 1.3 GeV/c and |y| < 0.9, and extrapolated to p(T) > 0. The fraction of non-prompt J/psi the inclusive J/psi yields shows no dependence on the charged-particle multiplicity at central rapidity. Charm and beauty hadron relative yields exhibit a similar increase with increasing charged-particle multiplicity. The measurements are compared to PYTHIA 8, EPOS 3 and percolation calculations.
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3.
  • Adam, J, et al. (författare)
  • Measurement of pion, kaon and proton production in proton-proton collisions at [Formula: see text] TeV.
  • 2015
  • Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:5
  • Tidskriftsartikel (refereegranskat)abstract
    • The measurement of primary [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] production at mid-rapidity ([Formula: see text] 0.5) in proton-proton collisions at [Formula: see text][Formula: see text] 7 TeV performed with a large ion collider experiment at the large hadron collider (LHC) is reported. Particle identification is performed using the specific ionisation energy-loss and time-of-flight information, the ring-imaging Cherenkov technique and the kink-topology identification of weak decays of charged kaons. Transverse momentum spectra are measured from 0.1 up to 3 GeV/[Formula: see text] for pions, from 0.2 up to 6 GeV/[Formula: see text] for kaons and from 0.3 up to 6 GeV/[Formula: see text] for protons. The measured spectra and particle ratios are compared with quantum chromodynamics-inspired models, tuned to reproduce also the earlier measurements performed at the LHC. Furthermore, the integrated particle yields and ratios as well as the average transverse momenta are compared with results at lower collision energies.
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4.
  • Adam, J., et al. (författare)
  • Precision measurement of the mass difference between light nuclei and anti-nuclei
  • 2015
  • Ingår i: Nature Physics. - 1745-2473. ; 11:10, s. 120-811
  • Tidskriftsartikel (refereegranskat)abstract
    • The measurement of the mass differences for systems bound by the strong force has reached a very high precision with protons and anti-protons(1,2). The extension of such measurement from (anti-)baryons to (anti-) nuclei allows one to probe any difference in the interactions between nucleons and anti-nucleons encoded in the (anti-) nuclei masses. This force is a remnant of the underlying strong interaction among quarks and gluons and can be described by effective theories(3), but cannot yet be directly derived from quantum chromodynamics. Here we report a measurement of the difference between the ratios of the mass and charge of deuterons (d) and anti-deuterons ((d) over bar), and He-3 and (3)(He) over bar nuclei carried out with the ALICE (A Large Ion Collider Experiment)(4) detector in Pb-Pb collisions at a centre-of-mass energy per nucleon pair of 2.76 TeV. Our direct measurement of the mass-over-charge differences confirms CPT invariance to an unprecedented precision in the sector of light nuclei(5,6). This fundamental symmetry of nature, which exchanges particles with anti-particles, implies that all physics laws are the same under the simultaneous reversal of charge(s) (charge conjugation C), reflection of spatial coordinates (parity transformation P) and time inversion (T).
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5.
  • Adam, J., et al. (författare)
  • Search for weakly decaying (Lambda n)over-bar and Lambda Lambda exotic bound states in central Pb-Pb collisions at root S-NN=2.76 TeV
  • 2016
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 752, s. 267-277
  • Tidskriftsartikel (refereegranskat)abstract
    • We present results of a search for two hypothetical strange dibaryon states, i.e. the H-dibaryon and the possible (Lambda n) over bar bound state. The search is performed with the ALICE detector in central (0-10%) Pb-Pb collisions at root S-NN = 2.76 TeV, by invariant mass analysis in the decay modes (Lambda n) over bar (d) over bar pi(+) and H-dibaryon -> Lambda p pi(-). No evidence for these bound states is observed. Upper limits are determined at 99% confidence level for a wide range of lifetimes and for the full range of branching ratios. The results are compared to thermal, coalescence and hybrid UrQMD model expectations, which describe correctly the production of other loosely bound states, like the deuteron and the hypertriton. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V.
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6.
  • Abelev, B., et al. (författare)
  • Charged jet cross sections and properties in proton-proton collisions at root s=7 TeV
  • 2015
  • Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 91:11
  • Tidskriftsartikel (refereegranskat)abstract
    • The differential charged jet cross sections, jet fragmentation distributions, and jet shapes are measured in minimum bias proton-proton collisions at center-of-mass energy root s = 7 TeV using the ALICE detector at the LHC. Jets are reconstructed from charged particle momenta in the midrapidity region using the sequential recombination k(T) and anti-k(T) as well as the SISCone jet finding algorithms with several resolution parameters in the range R = 0.2-0.6. Differential jet production cross sections measured with the three jet finders are in agreement in the transverse momentum (p(T)) interval 20 < p(T)(jet,ch) < 100 GeV/c. They are also consistent with prior measurements carried out at the LHC by the ATLAS Collaboration. The jet charged particle multiplicity rises monotonically with increasing jet p(T), in qualitative agreement with prior observations at lower energies. The transverse profiles of leading jets are investigated using radial momentum density distributions as well as distributions of the average radius containing 80% (< R-80 >) of the reconstructed jet p(T). The fragmentation of leading jets with R = 0.4 using scaled p(T) spectra of the jet constituents is studied. The measurements are compared to model calculations from event generators (PYTHIA, PHOJET, HERWIG). The measured radial density distributions and < R-80 > distributions are well described by the PYTHIA model (tune Perugia-2011). The fragmentation distributions are better described by HERWIG.
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7.
  • Adam, J., et al. (författare)
  • Centrality dependence of high-p(T) D meson suppression in Pb-Pb collisions at root s(NN)=2.76 TeV
  • 2015
  • Ingår i: Journal of High Energy Physics. - 1029-8479. ; :11
  • Tidskriftsartikel (refereegranskat)abstract
    • The nuclear modification factor, R-AA, of the prompt charmed mesons D-0, D+ and D*+, and their antiparticles, was measured with the ALICE detector in Pb-Pb collisions at a centre-of-mass energy root s(NN) = 2 : 76 TeV in two transverse momentum intervals, 5 < p(T) < 8 GeV/c and 8 < p(T) < 16 GeV/c, and in six collision centrality classes. The R-AA shows a maximum suppression of a factor of 5{6 in the 10% most central collisions. The suppression and its centrality dependence are compatible within uncertainties with those of charged pions. A comparison with the R-AA of non-prompt J/psi from B meson decays, measured by the CMS Collaboration, hints at a larger suppression of D mesons in the most central collisions.
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8.
  • Adam, J., et al. (författare)
  • Centrality dependence of particle production in p-Pb collisions at root s(NN)=5.02 TeV
  • 2015
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 91:6
  • Tidskriftsartikel (refereegranskat)abstract
    • We report measurements of the primary charged-particle pseudorapidity density and transverse momentum distributions in p-Pb collisions at root s(NN) = 5.02 TeV and investigate their correlation with experimental observables sensitive to the centrality of the collision. Centrality classes are defined by using different event-activity estimators, i.e., charged-particle multiplicities measured in three different pseudorapidity regions as well as the energy measured at beam rapidity (zero degree). The procedures to determine the centrality, quantified by the number of participants (N-part) or the number of nucleon-nucleon binary collisions (N-coll) are described. We show that, in contrast to Pb-Pb collisions, in p-Pb collisions large multiplicity fluctuations together with the small range of participants available generate a dynamical bias in centrality classes based on particle multiplicity. We propose to use the zero-degree energy, which we expect not to introduce a dynamical bias, as an alternative event-centrality estimator. Based on zero-degree energy-centrality classes, the N-part dependence of particle production is studied. Under the assumption that the multiplicity measured in the Pb-going rapidity region scales with the number of Pb participants, an approximate independence of the multiplicity per participating nucleon measured at mid-rapidity of the number of participating nucleons is observed. Furthermore, at high-pT the p-Pb spectra are found to be consistent with the pp spectra scaled by N-coll for all centrality classes. Our results represent valuable input for the study of the event-activity dependence of hard probes in p-Pb collisions and, hence, help to establish baselines for the interpretation of the Pb-Pb data.
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9.
  • Adam, J., et al. (författare)
  • Forward-backward multiplicity correlations in pp collisions at root s=0.9, 2.76 and 7 TeV
  • 2015
  • Ingår i: Journal of High Energy Physics. - 1029-8479. ; :5
  • Tidskriftsartikel (refereegranskat)abstract
    • The strength of forward-backward (FB) multiplicity correlations is measured by the ALICE detector in proton-proton (pp) collisions at = 0.9, 2.76 and 7 TeV. The measurement is performed in the central pseudorapidity region (|eta| < 0.8) for the transverse momentum p (T) > 0.3 GeV/c. Two separate pseudorapidity windows of width (delta eta) ranging from 0.2 to 0.8 are chosen symmetrically around eta = 0. The multiplicity correlation strength (b (corr)) is studied as a function of the pseudorapidity gap (eta (gap)) between the two windows as well as the width of these windows. The correlation strength is found to decrease with increasing eta (gap) and shows a non-linear increase with delta eta. A sizable increase of the correlation strength with the collision energy, which cannot be explained exclusively by the increase of the mean multiplicity inside the windows, is observed. The correlation coefficient is also measured for multiplicities in different configurations of two azimuthal sectors selected within the symmetric FB eta-windows. Two different contributions, the short-range (SR) and the long-range (LR), are observed. The energy dependence of b (corr) is found to be weak for the SR component while it is strong for the LR component. Moreover, the correlation coefficient is studied for particles belonging to various transverse momentum intervals chosen to have the same mean multiplicity. Both SR and LR contributions to b (corr) are found to increase with p (T) in this case. Results are compared to PYTHIA and PHOJET event generators and to a string-based phenomenological model. The observed dependencies of b (corr) add new constraints on phenomenological models.
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10.
  • Adam, J., et al. (författare)
  • Inclusive, prompt and non-prompt J/psi production at mid-rapidity in Pb-Pb collisions at root S-NN=2.76 TeV
  • 2015
  • Ingår i: Journal of High Energy Physics. - 1029-8479. ; :7
  • Tidskriftsartikel (refereegranskat)abstract
    • The transverse momentum (p(T)) dependence of the nuclear modification factor R-AA and the centrality dependence of the average transverse momentum for inclusive J/psi have been measured with ALICE for Pb-Pb collisions at root S-NN = 2.76TeV in the e(+)e(-) decay channel at mid-rapidity (vertical bar y vertical bar < 0.8). The is significantly smaller than the one observed for pp collisions at the same centre-of-mass energy. Consistently, an increase of RAA is observed towards low p(T). These observations might be indicative of a sizable contribution of charm quark coalescence to the J/psi production. Additionally, the fraction of non-prompt J/psi from beauty hadron decays, f(B), has been determined in the region 1.5 < p(T) < 10 GeV/c in three centrality intervals. No significant centrality dependence of fB is observed. Finally, the RAA of non-prompt J/psi is discussed and compared with model predictions. The nuclear modification in the region 4.5 < p(T) < 10 GeV/c is found to be stronger than predicted by most models.
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  • Resultat 1-10 av 92

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