Seminars and Colloquia

Title Speaker Location Abstract Material
Lepton flavors: high-intensity probes of new physics Dr. Ana Teixeira (Laboratoire de Physique de Clermont, France) Presentation at 3:45 PM, NPL 178 Coffee and cookies starting at 3:30 PM

Massive neutrinos and leptonic mixings have provided the first evidence of flavor violation in the lepton sector, opening a unique gateway to many new phenomena, with an impact ranging from low-energy observables to colliders, as well as cosmology and astroparticle physics. If observed, charged lepton flavor violation (cLFV) is a clear sign of New Physics - beyond the Standard Mode (SM) minimally extended to accommodate neutrino oscillation data. We begin by a brief overview of the experimental status of cLFV (and other high-intensity observables) searches and the prospects for upcoming years. We then consider extensions of the SM which could potentially give rise to observable cLFV signals: following a model-independent discussion, we comment on the prospects of several New Physics models regarding cLFV, with a particular emphasis on low-energy seesaw mechanisms.

Microscopic uncertainties in the standard solar model Prof. Doron Gazit - Racah Institute of Physics (Hebrew University of Jerusalem, Isreal) Presentation at 3:45 PM, NPL 178 Coffee and cookies starting at 3:30 PM

Over the past decade, an outstanding open problem in solar physics has emerged, as solar photospheric abundances of metallic elements have been significantly revised downward. Standard solar models cannot reproduce helioseismic measurements, such as the convection zone radius, the surface helium abundance and the sound speed profile, when using these revised abundances. This gave rise to the solar composition problem, motivating a rapid growth of research efforts in the field. With this problem of in mind, I study two main microscopic phenomena occurring in the Solar interior, and discuss their theoretical uncertainties and ways to reduce them. Firstly, the fusion rate of two protons into a deuteron, which is too rare to measure terrestrially in the solar conditions, is studied using a novel application of pion-less effective field theory.
Secondly, I use a new atomic code “STAR" to study two major plasma effects on the solar profile, namely ionic correlations and line broadening. These effects are untested in the relevant thermodynamic conditions, and use crude approximations, whose applicability at this regime is unclear. Both microscopic phenomena have a significant effect on the solar problem. Moreover, we argue that the solar opacity problem is hindered due to the large uncertainties. In the case of the atomic effects, we propose a method to measure opacities at solar temperatures and densities that were never reached in the past via laboratory radiation flow experiments.

The Quest for a Background-Free Detector Daniel Baxter (Northwestern University) CENPA Conference Room NPL-178

Dark matter represents one of the most sought after discoveries in physics. Leading theories predict that extremely sensitive detectors could probe nuclear recoils from dark matter interactions. The PICO collaboration uses bubble chambers to look for the energy deposition from such an interaction. The biggest challenge in searching for dark matter is the mitigation and understanding of the numerous other sources of events that could look like dark matter, namely radioactive backgrounds. I will discuss how a long effort to understand backgrounds in the PICO bubble chambers led to the recent background-free result of PICO-60 and how discoveries made along the way might affect other rare event searches.

First observation of coherent elastic neutrino-nuclear scattering with COHERENT Prof. Jason Detwiler, PhD (University of Washington) Presentation at 3:45 PM, NPL 178 Coffee and cookies starting at 3:30 PM

Coherent elastic neutrino-nuclear scattering (CEνNS), the most frequent of all low-energy neutrino interactions, was predicted over forty years ago, but had eluded observation due to itsultra-faint experimental signature. At last, the first observation of CEνNS was recently made by the COHERENT Collaboration using the world's smallest neutrino detector: a 14 kg CsI scintillating crystal. The measurement made use of the pulsed, stopped-pion neutrinos emitted by the Spallation Neutron Source in Oak Ridge, TN. The result confirms the Standard Model prediction and places new constraints on non-standard interactions of neutrinos with nuclei. The collaboration is now deploying additional nuclear targets employing different technologies to further explore this interaction. I will discuss this experimental effort and the first evidence for the CEνNS signal. I will also give an update on the status and prospects for the additional deployments, and summarize the potential scientific impact of this measurement program.

Bounds on new physics from electric dipole moments Dr. Martin Jung - Technical University of Munich, Germany Presentation at 3:45 PM, NPL 178 Coffee and cookies starting at 3:30 PM

Electric dipole moments are extremely sensitive probes for
additional sources of CP violation in new physics models. The
multi-scale problem of relating the high precision measurements
with neutrons, atoms and molecules to fundamental parameters
can be approached model-independently to a large extent;
however, care must be taken to include the uncertainties from
especially nuclear and QCD calculations properly. The resulting
bounds on fundamental parameters are illustrated in the context
of Two-Higgs-Doublet models.

Search for the electric dipole moment of the neutron Dr. Guillaume Pignol Presentation at 3:45 PM, NPL 178 Coffee and cookies starting at 3:30 PM

Why is there so little antimatter in the Universe? How the matter/antimatter asymmetry
was generated? New physics, beyond the Standard Model, was certainly at play in a
hypothetical phase of the early Universe called baryogenesis. Since this new physics
must induce a violation of CP symmetry, it could be revealed in the laboratory by
measuring a nonzero electric dipole moment of a spin 1/2 particle such as the neutron.
A collaboration of 15 institutions is searching for the neutron electric dipole moment
(nEDM) using the ultracold neutron source at the Paul Scherrer Institute (PSI) in
Switzerland. The most precise measurement of the nEDM has been produced by the
Sussex/RAL/ILL spectrometer at the ILL research reactor in Grenoble, it is compatible
with zero, with the upper limit 𝑑" < 3×10()* 𝑒 cm @ 90% C. L. [J.M. Pendlebury et al. PRD
92, 092003 (2015)]. We have operated an upgraded version of this apparatus to take data
at PSI in the period 2015-2017 and we are now building the next generation spectrometer,
n2EDM.
In my talk I will present the current status of the measurement and discuss the statistical
and systematical uncertainties. Also, I will present a search for an oscillating nEDM in our
data. Such an oscillation could be induced in a scenario where Dark Matter is formed by
an oscillating Axion-like field.

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The neutron lifetime: a haiku Daniel Salvat, Ph.D. CENPA Conference Room NPL-178

Precise knowledge of the free neutron lifetime is required for the prediction of
primordial light element abundances, and is a probe of the charged-current weak
interaction at low energies. The lifetime is primarily measured by either counting
the decay products in a neutron beam of absolutely-known flux, or by trapping
ultracold neutrons (UCN) in material bottles and counting the survivors after
varying time intervals. There is currently a 3.9 standard deviation discrepancy
between these two methods, and new techniques are needed to address this
discrepancy and resolve the neutron lifetime with high precision. The UCNtau
experiment at the Los Alamos Neutron Science Center (LANSCE) consists of a
magnetic UCN trap to eliminate systematic effects related to the absorption and
scattering of neutrons from the walls of previously-used material traps. In addition,
we have developed a novel UCN detector to count the UCN in situ, providing a
powerful check of potential systematic effects. Using the UCNtau apparatus, we
have measured the neutron lifetime to be 877.7 ± 0.7 (stat) +0.3/-0.1 (sys)
seconds, with systematic corrections smaller than their associated uncertainties.
In this talk, I will provide the motivation and context for the measurement, describe
the novel characteristics of the UCNtau experiment, present the results of the
blinded analysis, and discuss potential improvements to the apparatus.

Developing Cyclotron Radiation Emission Spectroscopy, a novel technique for nuclear physics Ben LaRoque (University of California at Santa Barbara) CENPA Conference Room NPL-178

Cyclotron Radiation Emission Spectroscopy is a new approach to measuring electron energies being actively developed by the Project 8 collaboration. The technique determines the energy of individual electrons by observing the changes in their cyclotron frequency resulting from their relativistic mass shifts. Our first demonstration of the methodology was made in 2014 and we have been working since then to evaluate and enhance the performance. Here I will review the principles of CRES and the experimental milestones achieved thus far. I will also briefly discuss progress towards using CRES for nuclear physics applications and specifically direct neutrino mass measurement in Project 8.

Development of low background detectors for high sensitivity measurements. Elena Sala CENPA Conference Room NPL-178

In the field of rare physics events experiments the background reduction plays an important role to distinguish the feeble signal under study above the background. Low level counting techniques are continuously under development to improve the measurement sensitivity. In my presentation I will summarise my contribution in the development and optimisation of both detectors and methods for high sensitivity measurements. I will focus on three main projects I have finalised during my career up to now using germanium detectors. The projects have different purposes spacing from material screening and selection for rare events experiments, to the investigation on natural and artificial radioactivity until the rare decay searches. They are a gamma-gamma coincidence spectrometer, the optimisation of a BEGe detector and the development of a HPGe Array. I will then present the duties and the achievements I reached during my current researcher position.

Measuring g-2 of the electron and positron to test the Standard Model’s most precise prediction. Elise Novitski (Harvard University) CENPA Conference Room NPL-178