Particle Physics

The DEAP-3600 single-phase liquid-argon dark matter detector is under construction at SNOLAB. The fundamental goal of the design is to increase the volume of the detector while having the liquid argon contact the smallest possible surface comprising only clean acrylic and wavelength shifter. Specifically DEAP-3600 is a spherical detector with a 1000 kg fiducial mass and a design background rate less than 0.1 events in the WIMP region of interest in three years of data taking. Design sensitivity to WIMP dark matter at 100 GeV is 10-46 cm2. In order to achieve this ambitious goal an extensive program of background reduction and control is underway for all detector components including the acrylic vessel, process system, photomultiplier tubes and TPB wavelength shifter. Efforts to obtain acrylic with bulk Uranium and Thorium contamination below 0.3 and 1.3 ppt respectively and Pb-210 contamination below 1.1x10-8 ppt will be described. A resurfacer is under development to ensure that the surface contamination of acrylic is removed. Even with these stringent controls fiducialization will be required to reduce surface backgrounds by a factor of 1000. Preliminary studies are promising. We have operated the DEAP-1 prototype detector underground at SNOLAB; results from the DEAP-1 runs will be discussed and the impact of those runs on DEAP-3600 will be discussed. SNOLAB has recently made the “phase 2” expansion (including the cryopit and two drifts) part of the clean space. A photo essay showing recent progress in the facility and the experimental program will be presented.

I discuss how the results of dark matter experiments can be used to draw conclusions about the nature of WIMP dark matter that are to a large extent model-independent. Specifically, I show that combining the results of direct detection experiments with data from neutrino telescopes can help establish whether the dark matter particle is its own anti-particle. I go on to discuss how limits on the diffuse and line spectra obtained from gamma ray telescopes can be used to constrain the annihilation modes of dark matter.

There are good reasons to think that our understanding of particle physics is incomplete. The effective field theory describing the particles that we know about breaks down at the TeV scale, and new effective degrees of freedom must enter. In this talk I will discuss the role that strong dynamics might play in this new physics, focusing on the ways in which approximately scale-invariant dynamics could explain puzzling features of our low-energy Lagrangian. I will also describe recent theoretical and numerical results aimed at constraining the range of behavior that can occur in 4D conformal field theories.

What lies beyond the Standard Model of particle physics? Are there very weakly interacting forms of matter and forces waiting to be discovered? In this talk I will describe some of the efforts underway to detect very weakly interacting particles, from dark matter to new forces. I will discuss recent observations and their theoretical significance as well as the connection to other experimental results. I will conclude with a short summary of the different frontiers and their interrelations.

We show that ordinary and radiative muon capture impose stringent constraints on sterile neutrino properties. In particular, we consider a sterile neutrino with a mass between $40$ and $80~{\rm MeV}$ that has a large mixing with the muon neutrino and decays predominantly into a photon and light neutrinos due to a large transition magnetic moment. Such a model was suggested as a possible resolution to the puzzle presented by the results of the LSND, KARMEN, and MiniBooNE experiments. We find that the scenario with the radiative decay to massless neutrinos is ruled out by measurements of the radiative muon capture rates at TRIUMF in the relevant mass range by a factor of a few in the squared mixing angle. These constraints are complementary to those imposed by the process of electromagnetic upscattering and de-excitation of beam neutrinos inside the neutrino detectors induced by a large transition magnetic moment. The latter provide stringent constraints on the size of the transitional magnetic moment between muon, electron neutrinos and $N$. We also show that further extension of the model with another massive neutrino in the final state of the radiative decay may be used to bypass the constraints derived in this work.

Although the fact that a large fraction of the matter in the universe is non-baryonic is beyond doubt, the exact composition of the dark matter is still shrouded in mystery. Using ultra-sensitive detectors in the deep underground laboratories, physicists are attempting to directly detect dark matter particles streaming from space. At colliders, physicists hope to manufacture large numbers of dark matter particles and study their properties. I will first use an effective field theory approach to demonstrate the power of colliders by comparing these two approaches. I will then describe the recent efforts on measuring dark matter properties at colliders and how imminent discoveries may change our fundamental understanding of physics and the universe.

A new force mediated by a new vector boson with mass in the MeV to GeV range and with very weak coupling to ordinary matter appears naturally in many theoretical models and could also explain a variety of observed anomalies. Such anomalies include the discrepancy between the predicted and the experimentally observed value for the muon anomalous magnetic moment, and recent cosmic-ray data that can be explained by dark matter interacting through this force with ordinary matter. This talk will review the motivation for such a force and present a broad array of probes of this physics. These probes include high-luminosity e+e- colliders, such as BaBar and BELLE, whose existing data sets may contain thousands of spectacular events; new high-intensity fixed-target experiments at electron accelerators such as Jefferson Laboratory; and indirect astrophysical probes such as gamma-ray observations of Milky-Way dwarf satellite galaxies, which constitute some of the least luminous and most dark matter dominated galaxies known.

Gamma-ray production by dark matter annihilation is one of the most universal indirect dark matter signals. In order to avoid intensive astrophysical background, one can study the gamma-rays away from the Galactic plane. The problems is that the dark matter annihilation signal at high latitudes is smooth and most probably subdominant to Galactic and extragalactic fluxes. I will discuss the use of spherical harmonics decomposition as a tool to distinguish a large scale small amplitude dark matter signal from astrophysical fluxes. The sensitivity of this method for currently available Fermi data is similar to the signal from thermal WIMP dark matter annihilation into W+W- or b-bbar.

I discuss a new scenario called Hylogenesis (hylo=matter) that explains the baryon and dark matter densities of Universe in a unified way. Early universe dynamics generate the baryon asymmetry and an equal antibaryon asymmetry in a GeV-scale hidden sector. The hidden antibaryons are dark matter. Our model has a striking signature that dark matter can annihilate baryons, mimicking nucleon decay. I discuss the effective nucleon decay rates and implications for existing nucleon decay searches.

Recent observations first made in string theory led to the realization that introducing various ``deformations" (finite volume, appropriate double-trace operators...) allows for an analytic study of many nonperturbative aspects of arbitrary four-dimensional gauge theories. Notably, the confinement mechanism, the generation of mass gap, and, in some cases, chiral symmetry breaking can be studied in a theoretically controlled manner. In this talk, I will review: i.) the ideas and tools involved, ii.) the main results obtained so far in this approach (and its limitations), iii.) our understanding of its relation to other approaches to (non-)supersymmetric gauge dynamics, iv.) ongoing and possible future work.

The D0 Collaboration recently reported a 3.2sigma deviation from the standard model prediction in the like-sign dimuon asymmetry. I will discuss the implications of this anomaly assuming that new physics contributes only to B_{d,s} mixing. The data allow universal new physics with similar contributions relative to the SM in the B_d and B_s systems, but favors a larger deviation in B_s than in B_d mixing. The general minimal flavor violation framework with flavor diagonal CP violating phases can account for the former and remarkably even for the latter case. This observation makes it simpler to speculate about which extensions with general flavor structure may also fit the data.