UC Davis Particle Physics Seminars John Terning

Events with three or more prompt leptons are rare at hadron colliders. At the LHC, where high interaction energies and rates create extremely busy final states, such multilepton events are well suited as a probe for new physics beyond the Standard Model (BSM). Mike Hance describes some recent analyses from ATLAS based on multilepton signatures. In particular, focusing on new model-independent limits for anomalous production of multilepton events that can be used to test a variety of BSM scenarios.

The July 4th announcement of the discovery of a Higgs-like particle at CERN LHC is only the beginning of a challenging program of "Higgs Identification" to establish the quantum numbers and couplings of the new particle, and to reveal its relationship, if any, to electroweak symmetry-breaking and fermion mass generation. Ian Low discusses preliminary efforts in this direction and explore implications of current measurements on future searches at the LHC and beyond.

Jet substructure is typically studied using clustering algorithms, such as kT, which arrange the jets' constituents into trees. Instead of considering a single tree per jet, Tuhin Roy proposes that multiple trees should be considered, weighted by an appropriate metric. Then each jet in each event produces a distribution for an observable, rather than a single value. Advantages of this approach include: 1) observables have significantly increased statistical stability; and, 2) new observables, such as the variance of the distribution, provide new handles for signal and background discrimination. For example, we find that employing a set of trees substantially reduces the observed fluctuations in the pruned mass distribution, enhancing the likelihood of new particle discovery for a given integrated luminosity. Furthermore, we introduce a new quantity 'volatility', a cut on which reduces the luminosity needed for a given significance requirement by a factor of two.

Nonlinear realizations describe the low-energy degrees of freedom of strongly coupled theories with spontaneously broken symmetry. When combined with SUSY, the Goldstone bosons of these theories are complex fields with "Goldstone fermion" super-partners. These, in turn, offer novel weakly interacting massive particle (WIMP) dark matter candidates. Flip Tanedo discusses how these can be used in realistic models of dark matter.

Guido D'Amico describes a new model of inflation using branes unwrapping from extra dimensions.

Weak scale SUSY with R-symmetry is a plausible solution to the SUSY flavor problem. In this talk, Yuhsin Tsai discusses two interesting aspects of R-symmetric SUSY models: electroweak baryogenesis and superpartner oscillations. Regarding baryogenesis, the new superpotential couplings between the adjoints and the Higgs can increase the strength of the electroweak phase transition, and large CP-violating phases consistent with electric dipole moments can generate large baryon asymmetry. R-symmetric models can also give spectacular signals at the LHC. If a tiny Majorana mass splits the degenerate mass eigenstates of gauginos and higgsinos, states produced at the LHC can oscillate between the spraticles and their Dirac mass partners. With displaced decays, the oscillation can be visible in the distribution of displaced vertex lengths at the LHC.