Measurement of the Charged-hadron Multiplicity in Proton-proton Collisions at LHC with the CMS Detector
Measurement of the Charged-hadron Multiplicity in Proton-proton Collisions at LHC with the CMS Detector

Author: Yen-Jie Lee

Publisher:

Published: 2011

Total Pages: 222

ISBN-13:

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Charged-hadron pseudorapidity densities and multiplicity distributions in protonproton collisions at [the square root of sigma] = 0.9, 2.36, 7.0 TeV were measured with the inner tracking system of the CMS detector at the LHC. The charged-hadron yield was obtained by counting the number of hit-pairs (tracklets). The charged-particle multiplicity per unit of pseudorapidity dNch/d[eta] [eta]

Measurement of the D0 Meson Production in Pb–Pb and p–Pb Collisions
Measurement of the D0 Meson Production in Pb–Pb and p–Pb Collisions

Author: Andrea Festanti

Publisher: Springer

Published: 2016-09-07

Total Pages: 184

ISBN-13: 3319434551

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This thesis presents the first measurement of charmed D0 meson production relative to the reaction plane in Pb–Pb collisions at the center-of-mass energy per nucleon-nucleon collision of √sNN = 2.76 TeV. It also showcases the measurement of the D0 production in p–Pb collisions at √sNN = 5.02 TeV with the ALICE detector at the CERN Large Hadron Collider. The measurement of the D0 azimuthal anisotropy with respect to the reaction plane indicates that low- momentum charm quarks participate in the collective expansion of the high-density, strongly interacting medium formed in ultra-relativistic heavy-ion collisions, despite their large mass. This behavior can be explained by charm hadronization via recombination with light quarks from the medium and collisional energy loss. The measurement of the D0 production in p–Pb collisions is crucial to separate the effect induced by cold nuclear matter from the final- state effects induced by the hot medium formed in Pb–Pb collisions. The D0 production in p–Pb collisions is consistent with the binary collision scaling of the production in pp collisions, demonstrating that the modification of the momentum distribution observed in Pb–Pb collisions with respect to pp is predominantly induced by final-state effects such as the charm energy loss.

Jet physics in ALICE
Jet physics in ALICE

Author: Constantin Loizides

Publisher: ibidem-Verlag / ibidem Press

Published: 2012-02-03

Total Pages: 180

ISBN-13: 3838255577

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The ALICE experiment is one of the experiments currently prepared for the Large Hadron Collider (LHC) at CERN, Geneva, starting operation end of 2007. ALICE is dedicated to the research on nucleus-nucleus collisions at ultra-relativistic energies, which addresses the properties of strongly interacting matter under varying conditions of high density and temperature. The conditions provided at the LHC allow significant qualitative improvement with respect to previous studies. In particular, energetic probes, light quarks and gluons, will be abundantly produced. These probes might be identified by their fragmentation into correlated particles, so called jets, of high enough energy to allow full reconstruction of jet properties; even in the underlying heavy-ion environment.Understanding the dependence of high-energy jet production and fragmentation influenced by the dense medium created in the collision region is an open field of active research. Generally, one expects energy loss of the probes due to medium-induced gluon radiation. It is suggested that hadronization products of these, rather soft gluons may be contained within the jet emission cone, resulting in a modification of the characteristic jet fragmentation, as observed via longitudinal and transverse momentum distributions with respect to the direction of the initial parton, as well as of the multiplicity distributions arising from the jet fragmentation. Particle momenta parallel to the jet axis are softened (jet quenching), while transverse to it increased (transverse heating). The present thesis studies the capabilities of the ALICE detectors to measure these jets and quantifies obtainable rates and the quality of jet reconstruction, in both proton-proton and lead-lead collisions at the LHC. In particular, it is addressed whether modification of the jet fragmentation can be detected within the high-particle-multiplicity environment of central lead-lead collisions.

Event-by-event Mean PT Fluctuations in Pp and Pb-Pb Collisions at the LHC
Event-by-event Mean PT Fluctuations in Pp and Pb-Pb Collisions at the LHC

Author: Stefan Thomas Heckel

Publisher:

Published: 2015

Total Pages: 0

ISBN-13:

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The ALICE detector at the LHC is used to study the properties of the Quark-Gluon Plasma produced in heavy-ion collisions. As a reference measurement, also the analysis of proton-proton (pp) collisions is very important. In the study presented here, event-by-event fluctuations of the mean transverse momentum are analysed in pp collisions at √s = 0.9, 2.76 and 7 TeV, and Pb-Pb collisions at √sNN = 2.76 TeV as a function of the charged-particle multiplicity. In both systems, dynamical fluctuations beyond the statistical expectation are observed. In pp collisions, no significant dependence on collision energy is found, even in comparison to inclusive results at much lower collision energies. Likewise, central A-A collisions show only little dependence on collision energy. The multiplicity dependence observed in peripheral Pb-Pb data is in agreement with that in pp collisions. Going to more central Pb-Pb collisions, a clear deviation from this trend is found, reaching a significant reduction of the fluctuations in most central collisions. Comparisons toMonte Carlo event generators show good agreement in pp, but rather large differences in Pb-Pb collisions.

Measurement of Charged Particle Multiplicities in Gluon and Quark Jets in Proton Anti-proton Collisions at S**ư
Measurement of Charged Particle Multiplicities in Gluon and Quark Jets in Proton Anti-proton Collisions at S**ư

Author:

Publisher:

Published: 2004

Total Pages: 7

ISBN-13:

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The authors report the first model independent measurement of charged particle multiplicities in quark and gluon jets, N{sub q} and N{sub g}, produced at the Tevatron in p{bar p} collisions with center-of-mass energy 1.8 TeV and recorded by the Collider Detector at Fermilab. The measurements are made for jets with average energies 41 and 53 GeV by counting charged particle tracks in cones with opening angle of?{sub c} = 0.28, 0.36, and 0.47 rad around the jet axis. The corresponding jet hardness Q = E{sub jet}?{sub c} varies in the range from 12 GeV to 25 GeV. At Q = 19 GeV, the ratio of multiplicities r = N{sub g}/N{sub q} is found to be 1.64 ± 0.17, where statistical and systematic uncertainties are added in quadrature. The results are in agreement with re-summed perturbative QCD calculations.