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Meetings & Workshops

  1. OCT

    19

    Today

    NSLS-II Friday Lunchtime Seminar

    "RIXS study of the charge and magnetic evolution in La2-xCexCuO4 combi-film"

    Presented by Xuerong Liu, Shanghai Tech University, China

    12 pm, NSLS-II Bldg. 743 Rm 156

    Friday, October 19, 2018, 12:00 pm

    Hosted by: Ignace Jarrige

    Different from the simple one-band Hubbard model prediction, it has been recognized that the cuprate superconductors are electron-hole asymmetric. Recent RIXS work on the electron-doped Nd2-xCexCuO4 by K. Ishii et al. [1] and W. S. Lee et al. [2] reported a hardening of the spin excitations and the emergence of a charge excitation mode. Both these observations are in distinct contrast to that reported on the hole doped side, and brought attention again to the profound electron-hole asymmetry issue in the cuprates. Taking the advantage of a La2-xCexCuO4 combi-film, namely a film with large range doping gradient distribution, we studied the evolution of the charge and magnetic excitations from optimal- to over-doping systematically in fine steps. Our results establish the universality of the previous observation for the electron-doped cuprates. And more importantly, the doping dependent evolutions show that the magnetic and charge excitations are not the two faces of a coin. Rather, the spin-correlation roots in the short range correlation, and the charge-fluctuation stems from long range Coulomb interaction. [1] K. Ishii et al, Nat. Commun. 5, 3714 (2014). [2] W. S. Lee et al, Nat. Phys. 10, 883 (2014).

  2. DEC

    20

    Thursday

    Particle Physics Seminar (Leona Woods Distinguished Postdoctoral Lectureship Award)

    "Measurement of top quark pair production in association with a Higgs or gauge boson at the LHC with the ATLAS detector"

    Presented by María Moreno Llácer, CERN

    3 pm, Small Seminar Room, Bldg. 510

    Thursday, December 20, 2018, 3:00 pm

    Hosted by: Alessandro Tricoli

    The top quark is unique among the known quarks since it decays before it has an opportunity to form hadronic bound states. This makes measurements of its properties particularly interesting as one can access directly the properties of a bare quark. Given its large mass (the heaviest fundamental particle), the top quark may play a special role in the electroweak symmetry breaking mechanism and therefore, new physics related to this might be found first in top quark precision measurements. Possible new physics signals would cause deviations of the top quark couplings from the Standard Model (SM) prediction. It couples to the SM fields through its gauge and Yukawa interactions. The high statistics top quark sample at the LHC has allowed to access the associated production of a top quark pair with a boson: tt+photon, tt+W, tt+Z and tt+H. The latest measurements carried out by the ATLAS detector for these physics processes will be presented, highlighting the main challenges.