UC Davis Particle Physics Seminars

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.

Jason Gallicchio explains how distinguishing light-quark jets from gluon jets on an event-by-event basis could significantly enhance the reach for many new physics searches at the Large Hadron Collider. Through an exhaustive search of existing and novel jet substructure observables, we find that a combination of two simple variables, the charge track multiplicity and the p_T-weighted linear radial moment (width), can filter out over 85-95% of the gluon jets while keeping more than half of the light-quark jets. I will discuss applications, address theoretical issues in the definitions of quark and gluon jets, and show progress that ATLAS has made in measuring these observables.

Recent signs of a Standard Model-like Higgs at 125 GeV point towards large A-terms in the MSSM. This presents special challenges for gauge mediation, which by itself predicts vanishing A-terms at the messenger scale. In this paper, we review the general problems that arise when extending gauge mediation to achieve large A-terms, and the mechanisms that exist to overcome them. Using these mechanisms, we construct weakly-coupled models of low-scale gauge mediation with extended Higgs-messenger couplings that generate large A-terms at the messenger scale and viable mu/Bmu-terms. Our models are simple, economical, and complete realizations of supersymmetry at the weak scale.

The W boson mass is a crucial parameter in the standard model of particle physics, providing constraints on the mass of the Higgs boson as well as on new physics models via quantum loop corrections. Bo Jayatilaka describes the measurement of the W boson mass using data corresponding to 2.2/fb of integrated luminosity collected with the CDF II detector. The measurement, performed using electron and muon decays of W bosons, yields a mass of 80387±19 MeV. This represents the single most precise measurement of the W boson mass ever performed, significantly surpassing the precision of all prior measurements combined. An updated world average of the W boson mass, including all recent Tevatron measurements, as well as the resulting standard model implications, is presented.

Both the ATLAS and CMS detectors have operated with high efficiency in the first two years of LHC operation and produced an impressive number of physics results. In this talk I will discuss some of the differences between the detectors and describe some unique features of the ATLAS detector and how these features have been exploited in our physics analyses. I will describe some selected recent results and conclude with an overview of the planned, near term ATLAS detector upgrades.

The bulk matter Randall-Sundrum (RS) model is a setup where Standard Model (SM) matter and gauge fields reside in the bulk of 5D warped spacetime while the Higgs field is confined on the IR brane. The wavefunctions of the 1st and 2nd generation matter particles are localized towards the UV brane and those of the 3rd generation towards the IR brane, so that the hierarchical structure of the Yukawa couplings arises geometrically without hierarchy in fundamental parameters. This paper discusses an experimental test of this model in the case where the Kaluza-Klein scale is far above the collider scale, but the model is combined with 5D Minimal SUSY Standard Model (MSSM) and SUSY particles are in the reach of collider experiments. A general SUSY breaking mass spectrum consistent with the bulk matter RS model is considered: SUSY breaking sector locates on the IR brane and its effects are mediated to 5D MSSM through a hybrid of gravity mediation, gaugino mediation and gauge mediation.

I look for a golden region in the parameter space of the NMSSM with a low cut-off where a SM-like Higgs with a mass m_h ~ 125 GeV can be obtained in a minimal bottom-up approach of field content.

The experimental signature of two leptons with the same electric charge is a great way to search for new physics as the backgrounds from Standard Model processes are quite low and a large variety of new physics models can produce this signature, e.g models with extended Higgs sectors, Supersymmetry, additional quark generations, and many more. Beate Heinemann reviews the ATLAS analyses in this signature based on the 2011 LHC data.

It is widely believed that the emergent magnetic gauge symmetry of SQCD is analogous to a hidden local symmetry (HLS). James Barnard explores this idea in detail, deriving the entire (spontaneously broken) magnetic theory by applying the HLS formalism to spontaneously broken SU(N) SQCD. We deduce the Kahler potential in the HLS description, and show that gauge and flavour symmetry are smoothly restored along certain scaling directions in moduli space. We propose that it is these symmetry restoring directions, associated with the R-symmetry of the theory, that allow full Seiberg duality. Reconsidering the origin of the magnetic gauge bosons as the rho-mesons of the electric theory, colour-flavour locking allows a simple determination of the parameter "a". Its value continuously interpolates between a=2 on the baryonic branch of moduli space - corresponding to "vector meson dominance" - and a=1 on the mesonic branch.

Harald Fritzsch discusses a model of composite weak bosons.

Jamison Galloway reviews recent Higgs data from the LHC and discuss ways in which model-independent conclusions can be drawn. The bottom-up thinking that goes into this can help to determine what other new physics we might anticipate finding at accessible scales, while allowing us to assess emerging proposals for the origins of the hinted Higgs-like state at 125 GeV. Using composite Higgs and the MSSM as two case studies, Galloway discusses the benefits of constructing these generalized exclusions and describe some very general conclusions that they will help to illuminate with current and future data.

Louie Strigari reviews astrophysical constraints on dark matter.

Ian Shoemaker discusses other missing energy signatures at particles colliders.

Tim Tait examines uncertainties in dark matter production at particle colliders.

Bernard Sadoulet discusses the future of dark matter searches.

JP Chou reviews limits on dark matter from CDF and CMS.

Roni Harnik reviews the theory of dark matter detection at the LHC.

Yu-Hsin Tsai reviews dark matter to Higgs coupling constraints from LEP.

Maxim Pospelov reviews how single effective operator approximation can break down.

Spencer Klein reviews results from the IceCube experiment.

Dave Mason gives a summary of the dark matter workshop at Fermilab.

Matthew Szydagis reviews different searches for dark matter.

Sergey Dubovsky discusses the effective field theory of long relativistic strings such as confining flux tubes in QCD. We derive the Polchinski-Strominger interaction by a calculation in static gauge. This interaction implies that a non-critical string which initially oscillates in one direction gets excited in orthogonal directions as well. In static gauge no additional term in the effective action is needed to obtain this effect. It results from a one-loop calculation using the Nambu-Goto action. Non-linearly realized Lorentz symmetry is manifest at all stages in dimensional regularization. We also explain that independent of the number of dimensions non-covariant counterterms have to be added to the action in the commonly used zeta-function regularization.

Yuri Shirman describes a simple recipe for obtaining local supersymmetry-breaking vacua in s-confining theories coupled to gauge singlets. This recipe gives rise to effective O'Raifeartaigh models in the IR, with calculable supersymmetry-breaking minima near the origin and can be applied to both vector-like and chiral theories. Since the properties of the vacuum are largely determined by superpotential terms that are non-renormalizable in the UV, it is calculable even when all dimensionless couplings are taken to be of order one. By construction, the models preserve a large subgroup of the original global symmetry. While we only study here s-confining theories, we expect our tools to be useful for inducing dynamical supersymmetry breaking in many gauge theories.

Matt Wettstein gives a brief overview of the Large Area Picosecond Photodetector (LAPPD) project, an effort to develop compact, microchannel plate (MCP) photomultiplier tubes capable of sub-millimeter, sub nanosecond spatial resolutions and with potential for scalability to large experiments. Wettstein will also discuss steps taken towards the construction of experimental LAPPD-based neutrino detectors and the potential applications for such detector systems in answering the important questions of neutrino physics.

Henrique Gomes discusses new ways to build effective theories that are Poincare invariant but the symmetry is not manifest.

Sung Park discusses the development of Resistive Plate Chamber (RPC), multi-gap RPC and Resistive Micropattern Detectors, in particle physics.

Sho Maruyama reviews Supersymmetric particle and Standard Model Higgs boson searches in high energy physics. Maruyama continues on to describe how trigger and Data Quality Monitoring system are used at the Compact Muon Solenoid experiment at CERN. The trend in trigger menu development will be discussed in detail. One of main focuses of this talk is the work that can be done by graduate students.

John Terning discusses how a SUSY model of a composite top-Higgs sector can resolved the four hierarchy problems: the gauge hierarchy, the yukawa hierarchy, the little hierarchy, and the squark mass hierarchy.

Inspired by models designed to explain the top-quark foward-backward asymmetry, Daniel Whiteson discusses studies of unexplored experimental signatures inside WWbb+jet events, which mimic the top quark signature and may be hiding inside the top quark sample. Whiteson presents the first search for top+jet resonances, the first search to use boosted hadronic W bosons, new same-sign top quark limits, new heavy quark limits, and discuss ttbar+jet resonances, as well as the possibility that Higgs cascades could be hiding inside WWbb events.

Ami Katz discusses a general model independent analysis of DM experiments.

Katherine Copic discusses ATLAS's first searches for fourth generation quarks, including a preview of new results for the winter conferences. While we search explicitly for fourth generation quarks, the final states examined are also more broadly applicable to searching for wider classes of new phenomenona.

Jared Kaplan discusses muon colliders and neutrino factories. They are aimed at achieving the highest lepton-antilepton collision energies and precision measurements of parameters of the neutrino mixing matrix. The performance and cost of these depend sensitively on how well a beam of muons can be cooled. Recent progress in muon cooling design studies and prototype tests nourish the hope that such facilities can be built during the next decade. The status of the key technologies and their various demonstration experiments will be summarized.

Jared Kaplan discusses how to derive a simple relation between the Mellin amplitude for AdS/CFT correlation functions and the bulk S-Matrix in the flat spacetime limit, proving a conjecture of Penedones. As a consequence of the Operator Product Expansion, the Mellin amplitude for any unitary CFT must be a meromorphic function with simple poles on the real axis. This provides a powerful and suggestive handle on the locality vis-a-vis analyticity properties of the S-Matrix. We begin to explore analyticity by showing how the familiar poles and branch cuts of scattering amplitudes arise from the holographic description. We use this to show how the existence of small black holes in AdS leads to a universal prediction for the conformal block decomposition of the dual CFT.

Jean-Francois Arguin discusses how ecent measurements of the top quark charge asymmetry performed at both CDF and DZero produced tantalizing deviations from the SM prediction. Given that the dataset for these analyses will not improved dramatically, decisive confirmations will be required by the LHC experiments. After reviewing the measurements performed at the Tevatron, Arguin will discuss the challenges to perform these measurements at the LHC by describing the ATLAS measurement. In particular Arguin will describe how one needs to exploit the large datasets of top quarks at the LHC to compensate for the difficulty to perform such a measurement in a symmetric proton-proton collider environment.

Csaba Csaki discusses how minimal flavor violation in supersymmetry can give a consistent phenomenology with resorting to R-party.

A generic prediction of string theory is the existence of many axion fields. It has recently been argued that many of these fields should be light and, like the well known QCD axion, lead to observable cosmological consequences. In this video, Marsh talks about in detail the effect of the so-called string axiverse on large scale structure, focusing on the morphology and evolution of density perturbations, anisotropies in the cosmic microwave background and weak gravitational lensing of distant galaxies.

Eric Zimmerman offers the experimental results from the T2K experiment on neutrino mixing.

Dmitry Bandurin talks about the D0 measurement of a sample of photon+3jet events used to determine the fraction of events with double parton (DP) scattering at sqrt{s}=1.96 TeV.

This video offers an alternative scheme to allow R-parity violation with phenomenological disasters.

Ben Heidenreich discusses constraining R-parity violation with minimal flavor violation.

Matt Reece talks about near degeneracy of superpartners enforced by the couplings of a new sector to supersymmetry breaking.

Albert De Roeck gives a summary of the Hidden SUSY workshop and the future outlook.

Stuart gives the status of searches for supersymmetry (SUSY) at the LHC.

Gordon Watts gives the status and prospects for supersymmetry searches with the ATLAS detector.

David Shih discusses the phenomenology of the stop squark as the the next to lightest superpartner.