NPAC (Nuclear/Particle/Astro/Cosmo) Forum

The particle nature of dark matter remains one of the biggest challenges in Astroparticle physics today. The use of liquid noble elements as scintillators for direct detection of dark matter insingle and dual phase configurations are one of the most promising techniques to reach sensitivities beyond 10$^{-44}$cm$^2$ in spin-independent WIMP-nucleon cross section. MiniCLEAN (CLEAN- Cryogenic Low Energy Astrophysics with Noble Gases) is an approximately spherical ~500~kg liquid argon or neon vessel that encloses 92 optical cassettes (modular photo-detectors) pointing at the center of the sphere through a TPB (Tetraphenyl Butadine) evaporated window that converts VUV light from the argon or neon scintillation into the visible. The modular spherical design allows both for a viable radon-mitigated assembly and for position reconstruction. Furthermore, the use of Pulse-Shape discrimination techniques between nuclear and electronic recoils that are particularly good for these two condensed noble gases will test the single-phase approach as a viable instrument for direct detection of dark matter at the multi-tonne scale with a projected sensitivity of 10$^{-46}$~cm$^2$ for a $sim$100~GeV/c$^2$ WIMP mass in terms of spin-independent WIMP-nucleon cross section. I will be presenting a review and status of the MiniCLEAN research program as well as new developments in the mitigation of depth-dependent and radiogenic neutron backgrounds.

Host: 
Reina Maruyama
Speaker: Raul Hennings-Yeomans Los Alamos National Laboratory

 

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Room and Building: 
4274 Chamberlin Hall

We investigate the possibility of new fermion multiplets charged under the Standard Model gauge group, with the aim of obtaining a possible dark matter candidate. These new fermions are charged under SU(2)xU(1); their quantum numbers are determined by requiring anomaly cancellation and insisting that all new particles become massive via Yukawa couplings with the SM Higgs boson. Constraints from colliders, electroweak precision measurements, and DM direct detection are considered; we find that this model can accommodate a viable DM candidate.

Host: 
Michael Ramsey-Musolf
Speaker: Jennifer Kile Northwestern University

 

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Room and Building: 
4274 Chamberlin
Despite many efforts, the extragalactic magnetic field (EGMF), presumed to exist in the voids of the large scale structure, remains undetected. Since the EGMF may be generated either by processes in the early universe or by outflows from galaxies, and it could supply the seed fields required by many models of galactic and cluster field formation, its properties are of interest from both cosmological and astrophysical viewpoints. I will review a recently developed technique for measuring the EGMF strength using combined gamma-ray observations from the Fermi Gamma-Ray Space Telescope and ground-based instruments such as VERITAS. The technique relies on modeling the electromagnetic cascade that develops in extragalactic space due to gamma-ray interactions with the extragalactic background light and CMB and for the first time permits the placement of a lower limit on the EGMF strength. I will describe two approaches to characterizing the cascade and discuss the interpretation of gamma-ray observations of the blazar RGB J0710+591 as limits on the existence of an EGMF-induced "halo."
Host: 
Stefan Westerhoff
Speaker: Tom Weisgarber University of Chicago

 

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Room and Building: 
4274 Chamberlin Hall
Precision timepieces are marvels of human ingenuity. Over the past half-a-century, precision time-keeping has been carried out with atomic clocks. I will review a novel and rapidly developing class of atomic clocks, optical lattice clocks. At their projected accuracy level, these would neither lose nor gain a fraction of a second over estimated age of the Universe. In other words, if someone were to build such a clock at the Big Bang and if such a timepiece were to survive the 14 billion years, the clock would be off by no more than a mere second. I will also talk about the next frontier: nuclear clock.

In the second part I will overview atomic searches for new physics beyond the Standard Model of elementary particles. I will report on a refined analysis of table-top experiments on violation of mirror symmetry in atoms that sets powerful constraints on a hypothesized particle, the extra Z-boson. Our raised bound on the Z' masses improves upon the Tevatron results and carves out a lower-energy part of the discovery reach of the Large Hadron Collider.
Host: 
Mark Saffman
Speaker: Andrei Derevianko University of Nevada-Reno

 

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Room and Building: 
4274 Chamberlin Hall

Bubble chambers have emerged as promising detectors for Weakly Interacting Massive dark matter Particles (WIMPs). A very high degree of background discrimination can be achieved by tuning the thermodynamic parameters to avoid nucleation by electron recoils, while maintaining low nuclear-recoil thresholds. Nuclear recoils from WIMPs can be discriminated from alpha particle induced events by analysis of the acoustic pulses produced by the expanding bubbles. The COUPP collaboration operated a 4-kg CF3I bubble chamber at SNOLAB in 2010-2011 and is in the process of commissioning a 60-kg chamber. Initial data from SNOLAB demonstrate reduced alpha backgrounds and greatly improved sensitivity to WIMPs.

Host: 
Karsten Heeger
Speaker: Andrew Sonnenschein Fermilab

 

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Room and Building: 
4274 Chamberlin Hall
The Non-Perturbative Gluon Propagator is a principal tool in investigating strongly coupled QCD. It may be obtained from Lattice QCD or its Schwinger-Dyson equation, which shall be discussed here. The transition from perturbative behaviour at large momenta to non-perturbative behaviour at small momenta is accompanied by characteristic phenomena such as dynamical chiral symmetry breaking and confinement. The gluon is expected to play a key role in this through the behaviour of the propagator dressing and its coupling to quarks. Solutions in the Landau gauge working in Euclidean space will be presented and compared to those obtained via other methods.

Secondly, results from a recently completed project will also be presented where the Nucleon, Roper and transition electromagnetic form factors are obtained in a symmetry preserving treatment of the bound state equations of QCD. Using a simplified interaction, the form factors are presented as part of a framework capable of simultaneously describing nucleon and meson physics. The aim of the present study is to address the structure of the Roper resonance which has been a puzzle for several decades and is a key target of the JLab N* program.
Host: 
Michael J. Ramsey-Musolf & Mario Pitschmann
Speaker: David Wilson Argonne National Laboratory

 

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Room and Building: 
4274 Chamberlin Hall
The Background Imager of Cosmic Extragalactic Polarization (BICEP) experiment is the first cosmic microwave background (CMB) polarimeter designed to measure the "B-mode" polarization of the CMB, hypothesized to originate during the Inflationary epoch. Beginning in 2006 BICEP observed 3% of the sky from our observatory at the Amundsen-Scott South Pole Research Station in Antarctica. In this colloquium I will present our initial results and discuss the unique design features of BICEP which led to the first meaningful limits on the energy scale of Inflation to come from CMB polarization. Soon after BICEP's initial results were released, a publication (Xia, Li & Zhang, 2009), claimed a first-detection of parity-violating "cosmic birefringence" effects using publicly available BICEP data. I will discuss the challenges of polarimetry at the few parts per billion level and explain why systematic effects are particularly pernicious for probes of cosmic parity violation. I will conclude by discussing how BICEP and its successor, BICEP2, currently in its second observing season at the South Pole will constrain Inflationary cosmology and future measurements of cosmic birefringence.
Host: 
Peter Timbie
Speaker: Brian Keating UCSD Department of Physics

 

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Room and Building: 
4274 Chamberlin Hall
I will focus on two topics in top physics - the anomalously large forward backward asymmetry (A_FB) in t-tbar production and the newly suggested signal of dark matter production - single top with missing E_T. Large A_FB may be a sign of new physics, with new flavor symmetric sectors representing an attractive possibility. I will show which representations of SM global flavor group can lead to acceptable phenomenology. As for the second topic, I will show that a monotop signal may be the dominant signal of DM at LHC for a large set of models.
Host: 
Michael Ramsey-Musolf
Speaker: Jure Zupan University of Cincinnati

 

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Room and Building: 
4274 Chamberlin
Recent measurements of front-back asymmetry in t-quark productions at the Tevatron hint at new flavor structure beyond the Standard Model. There is also a tension in the determination of |V_ub| from inclusive and exclusive semileptonic B-meson decays and B--> au u. We examine whether the models proposed to explain the first anomaly can or cannot alleviate the latter tension.
Host: 
Michael Ramsey-Musolf
Speaker: John Ng TRIUMF

 

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Room and Building: 
4274 Chamberlin
I will briefly present the latest results of MEG experiment for searching the violation of Flavor conservation law for the muon as it has been found in neutrino sector. Further a proposal for a sensitive experiment for calorimetric neutrino absolute mass scale determination will be outlined. Both experimental searches should give valuable informations about the nature and the origin of the neutrino mass.
Host: 
Dan McCammon
Speaker: Prof. Flavio Gatti Genoa University

 

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Room and Building: 
5310 Chamberlin (coffee and cookies at 2:15 in 5310)

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