20,455 research outputs found

    Jet quenching measurements with ATLAS at LHC

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    A broad program of measurements is planned for heavy ion collisions in ATLAS. With up to a factor of 30 increase in collision energy compared to existing data, significant new insights are anticipated to be obtained with the first data measured. Global features of the LHC collisions will be accessible with the early data and will set the stage for the precision measurements to follow. ATLAS is particularly well suited for exploration of "jet quenching," the extinction of energetic jets in the hot dense medium. Observations of heavy quark jet suppression will be possible with unprecedented energy reach and statistical precision, potentially yielding new insights into the basic mechanisms involved.Comment: 5 pages, 3 figure

    J/{\Psi} and {\Psi}(2S) Production in p-Pb Collisions at 5.02 TeV with ATLAS

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    The production rates of heavy quarkonia in ion-ion collisions provide sensitive probes in the studies of the hot and dense matter formed in these collisions at high energies. However, a reference for understanding the behavior in the hot medium is necessary; p-A collisions open the possibility to study heavy quarkonia states in a smaller system of much lower average temperature. This is an important step in forming a baseline for understanding A-A collisions, as well as an investigation into the nature of modifications of the parton distributions in the nucleus. Using data collected at the LHC in 2013, we show results on the prompt J/{\Psi} and {\Psi}(2S) nuclear modification factors and the double ratio, {\Psi}(2S) divided by J/{\Psi} in p-Pb divided by the same in p-p, in p-Pb collisions at 5.02 TeV. The charmonia states were reconstructed via the dimuon decay channel and the yield is analyzed differentially in bins of transverse momentum, rapidity, and event activity.Comment: Proceedings contribution for the HARD PROBES 2015 Conference at McGill University in Montreal, June 29 - July 3, 2015. Four pages. To be published in Nuclear Physics B Proceedings Supplemen

    Medium Modifications of Hadron Properties and Partonic Processes

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    Chiral symmetry is one of the most fundamental symmetries in QCD. It is closely connected to hadron properties in the nuclear medium via the reduction of the quark condensate , manifesting the partial restoration of chiral symmetry. To better understand this important issue, a number of Jefferson Lab experiments over the past decade have focused on understanding properties of mesons and nucleons in the nuclear medium, often benefiting from the high polarization and luminosity of the CEBAF accelerator. In particular, a novel, accurate, polarization transfer measurement technique revealed for the first time a strong indication that the bound proton electromagnetic form factors in 4He may be modified compared to those in the vacuum. Second, the photoproduction of vector mesons on various nuclei has been measured via their decay to e+e- to study possible in-medium effects on the properties of the rho meson. In this experiment, no significant mass shift and some broadening consistent with expected collisional broadening for the rho meson has been observed, providing tight constraints on model calculations. Finally, processes involving in-medium parton propagation have been studied. The medium modifications of the quark fragmentation functions have been extracted with much higher statistical accuracy than previously possible.Comment: to appear in J. Phys.: Conf. Proc. "New Insights into the Structure of Matter: The First Decade of Science at Jefferson Lab", eds. D. Higinbotham, W. Melnitchouk, A. Thomas; added reference

    Prostorno-vremenske značajke hadronizacije u duboko neelastičnom rasprŔenju

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    Hadronization, the process by which energetic quarks evolve into hadrons, has been studied phenomenologically for decades. However, little experimental insight has been gained into the space-time features of this fundamentally non-perturbative process. New experiments at Jefferson Lab, in combination with HERMES data, will provide significant new insights into the phenomena connected with hadron formation in deep inelastic scattering, such as quark energy loss in-medium, gluon emission, and color field restoration.Proučavanje hadronizacije, procesa kojim kvarkovi tvore hadrone, proučava se fenomenoloÅ”ki desetljećima. Međutim, prostorno-vremenske značajke tog u osnovi neperturbativnog procesa slabo su eksperimentalno istražene. Novi podaci u JLabu zajedno s podacima HERMES pružiti će važna nova saznanja o pojavama nastajanja hadrona u duboko neelastičnom rasprÅ”enju: gubitak energije kvarkova u jezgrama, tvorba gluona i obnavljanje polja boje

    Prostorno-vremenske značajke hadronizacije u duboko neelastičnom rasprŔenju

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    Hadronization, the process by which energetic quarks evolve into hadrons, has been studied phenomenologically for decades. However, little experimental insight has been gained into the space-time features of this fundamentally non-perturbative process. New experiments at Jefferson Lab, in combination with HERMES data, will provide significant new insights into the phenomena connected with hadron formation in deep inelastic scattering, such as quark energy loss in-medium, gluon emission, and color field restoration.Proučavanje hadronizacije, procesa kojim kvarkovi tvore hadrone, proučava se fenomenoloÅ”ki desetljećima. Međutim, prostorno-vremenske značajke tog u osnovi neperturbativnog procesa slabo su eksperimentalno istražene. Novi podaci u JLabu zajedno s podacima HERMES pružiti će važna nova saznanja o pojavama nastajanja hadrona u duboko neelastičnom rasprÅ”enju: gubitak energije kvarkova u jezgrama, tvorba gluona i obnavljanje polja boje

    Logic and the Retinal Image

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    Spinā€Waves in Dilute Antiferromagnets

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    The effect of dilution on spin waves in isotropic Heisenberg antiferromagnets is studied. The model includes only nearestā€neighbor interactions for a bcc lattice and spinā€wave interactions are neglected, i.e. the results are correct in the limit sā†’āˆž. The dynamical susceptibility X (?,Ļ‰) and inelastic neutron cross section are obtained for arrays 8192 sites randomly occupied by a concentration c of magnetic ions. For a given array the calculation is done by inverting the dynamical matrix and thus is essentially exact. Our results are as follows. For large k we find that Isingā€like resonances corresponding to different numbers of occupied neighboring sites become increasingly prominent as c is decreased. The envelope of these resonances agrees with previous results using the coherent potential approximation where fluctuations in environment are suppressed. For small k we find a single spinwave resonance broadened by the random dilution. The application of these results to Mnc Zn 1āˆ’cF2 is discussed
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