Seminars and Colloquia

Title Speaker Location Material
Cosmic Rays from 10^15 to 10^20 eV Gordon Thomson, PhD (University of Utah) Presentation at 3:45 PM, NPL 178 Coffee and cookies starting at 3:30 PM

The energy range covered by the Telescope Array
experiment, from 2x1015 eV to 2x1020 eV, contains the
end of the galactic cosmic ray spectrum, the
galactic-extragalactic transition, important information
about the nature of cosmic rays throughout this energy
region, and what probably are the highest energy
particles in the universe. As time permits, I will discuss
measurements of the spectrum and composition of
cosmic rays, and searches for anisotropy (and hence the
sources of these particles).

Searches for supersymmetry in final states with photons in CMS Menglei Sun (Carnegie Mellon University) Presentation at 3:45 PM, NPL 178 Coffee and cookies starting at 3:30 PM

The Standard Model (SM) is very successful at explaining a wide
range of phenomena. With the discovery of the Higgs boson,
the SM is complete. Yet there are still many questions left
unanswered: Why is the Higgs mass so light when it receives
radiative corrections up to the Planck scale? What is dark
matter? The supersymmetric extension to the SM would
provide solutions to these problems. Models of supersymmetry
with general gauge-mediated supersymmetry breaking often
lead to final states containing photons and large missing
transverse momentum. In this talk, I will discuss the searches
for supersymmetry in events with photons in proton-proton
collisions at √S = 13 TeV at the CMS experiment.

First Search for Neutrinoless Double Beta Decay in 76Ge with the Majorana Demonstrator Walter Pettus, PhD (University of Washington) Presentation at 3:45 PM, NPL 178 Coffee and cookies starting at 3:30 PM

Neutrinoless double-beta decay (0νββ) is a hypothetical
lepton-number violating process that would establish the Majorana
nature of neutrinos and serve as an indirect probe of the absolute
neutrino mass. The Majorana Demonstrator is an array of high purity
Ge detectors at the 4850’ level of the Sanford Underground Research
Facility in South Dakota searching for 0νββ in 76 Ge. The experiment
consists of two modules totaling 44 kg of p-type point contact
detectors; the first module began data taking in June 2015, with the
entire array operational since August 2016. I will report the analysis
of the first 9.95 kg*yr of exposure from the MAJORANA
DEMONSTRATOR, achieving a half-life limit of >1.9×10 25 yr for 0νββ
decay of 76 Ge. The experiment has also demonstrated the best
energy resolution and a background consistent with the best
achieved of any 0νββ experiment. These results strongly position
76 Ge for a future tonne-scale 0νββ experiment.

First Results from ADMX G2 Prof. Gray Rybka, PhD (University of Washington) Presentation at 3:45 PM, NPL 178 Coffee and cookies starting at 3:30 PM

The axion is a well-motivated dark matter candidate inspired by
the Peccei-Quinn solution to the Strong-CP problem. After
decades of work, the US DOE flagship axion dark matter search,
ADMX G2, is the first experiment to be sensitive to dark matter
axions from the plausible DFSZ coupling model, and has begun
to search the theoretically-favored axion mass region 2-40
micro-eV. ADMX G2 could now discover dark matter at any
time. I will report the first results from exploring the range
around 2.7 micro-eV last year, discuss this year's operations
and review the ADMX G2 plans to continue the search to cover
the entire mass range.

Key Technology Research of Liquid Argon Veto Detector in CDEX Qinghao Chen (Tsinghua University, Beijing, China) Remote seminar presentation starting at 3:45 PM in NPL 178 Coffee and cookies starting at 3:30 PM

The China Dark Matter Experiment (CDEX) Collaboration has been aiming to search for low mass
WIMPs with a ton-scale highly pure germanium (HPGe) detector. In order to suppress the
background, an anti-coincidence veto detector is employed in CDEX, acting as the active shielding.
However, active shielding system with solid scintillators has to be abandoned as the Ge detector get
larger in the following phases of CDEX experiments. The Liquid Argon (LAr) veto is proposed in the
second phase CDEX-10 which is the first dark matter direct detection experiment using LAr detector
as an anti-coincidence veto detector. My research work is focused on the R&D of CDEX-10 LAr veto
detector, which contains:
(1) Designing and building a prototype of the liquid argon detector. The principle of the LAr detector
experiment and the operating processes have been mastered. The methods of data analysis have
been developed. All of these will help to the operation of the CDEX-10 LAr veto detector.
(2) Measurement and the Monte Carlo simulation of the photoelectron yield of the prototype LAr
detector. The photoelectron yields of the prototype LAr detector have been measured to be
0.051-0.079 p.e./keV for 662 keV γ lines at different positions. The Monte Carlo simulation provided
a better understanding of the spectra we obtained.
(3) Research of pulse shape of the LAr scintillation lights. The pulse shape discrimination of γ
particles and α particles has been studied. The prompt fraction Fprompt was found to be different
between the γ particles and α particles, which provides the possibility to develop the pulse shape
discrimination method of the LAr detector which is unpurified. In addition, the relationship between
the slow component lifetime of Ar scintillation lights and the Ar purity has also been studied. The
purity of LAr can be monitored through this method.
(4) The performance of the CDEX-10 LAr veto detector has been estimated by Monte Carlo
simulation. The energy threshold and the veto efficiency of the LAr veto detector was got through
simulation. The background of CDEX-10 was simulated to be < 0.1 cpkkd after the active shielding
of the LAr veto detector.

Exploring Neutrino and Axion Physics with the Majorana Demonstrator Clint Wiseman (University of South Carolina) Presentation at 3:45 PM, NPL 178 Coffee and cookies starting at 3:30 PM

The MAJORANA DEMONSTRATOR is an array of P-type point contact
germanium detectors enclosed in a low-background shield, operating at
the Sanford Underground Research Facility. The first results from its
search for neutrinoless double beta decay with a 10 kg-y data set show
world-leading energy resolution at the Q-value (2039 keV) and extremely
low background levels in its optimal configuration. This is an important
milestone in the development of a next-generation, ton-scale experiment.
Complementary to its neutrino program, the DEMONSTRATOR is also
capable of low energy rare event searches, routinely operating with
sub-keV thresholds. This is enabling a search for dark matter and solar
axions. The lowest energy regions of the data set present a challenge to
reliably discriminate physics from electronics noise.
In addition to a discussion of the recent double-beta decay result, I will
discuss new noise rejection methods for the DEMONSTRATOR and
prospects for an upcoming solar axion result.

Alpha-Related Backgrounds in the DarkSide-50 Detector Alissa Monte (University of Massachusetts, Amherst) Presentation at 3:45 PM, NPL 178 Coffee and cookies starting at 3:30 PM

DarkSide-50 is the current phase of the DarkSide direct dark matter
search program, operating underground at the Laboratori Nazionali
del Gran Sasso in Italy. The detector is a dual-phase argon Time
Projection Chamber (TPC), designed for direct detection of Weakly
Interacting Massive Particles (WIMPs), and housed within a veto
system of liquid scintillator and water Cherenkov detectors. Since
switching to a target of low radioactivity argon extracted from
underground sources in April 2015, the background is no longer
dominated by naturally occurring Ar-39. However, alpha backgrounds
from radon and its daughters remain, both from the liquid argon bulk
and internal detector surfaces. This talk will focus on the analysis of
alpha events in DarkSide-50. In some cases, the alpha events are a
dangerous background in need of mitigation. In others, the alpha
events can be used as a tool to deepen our understanding of our

Recent High Mass WIMP search results from DarkSide-50 Xin Xiang (Princeton University) Presentation at 3:45 PM, NPL 178 Coffee and cookies starting at 3:30 PM

Located at the LNGS, Italy, DarkSide (DS) is a dark matter search
project, which features a dual-phase Time Projection Chamber
as the WIMP detector, surrounded by an organic
liquid-scintillator neutron veto and a water-Cherenkov muon
veto. The current DS-50 has been taking data with Ar extracted
from underground sources (UAr) since April 2015. As of October
2017, the experiment accumulated 532.4 live-days exposure of
blinded data with the UAr target. In this talk, I will present the
recent blind analysis and the spin-independent dark
matter-nucleon coupling results. Various background studies will
be discussed, with an emphasis on a novel concept of
Cherenkov coincidence background. The Monte Carlo modeling
of the background predictions will be presented .

Towards reliable nuclear matrix elements for neutrinoless double-beta decay Prof. Javier Menéndez (The University of Tokyo, Japan) Presentation at 3:45 PM, NPL 178 Coffee and cookies starting at 3:30 PM

Observing neutrinoless double-beta (0nbb) decay is the most promising
way to detect lepton number violation in the laboratory, and it would imply
that neutrinos are its own antiparticle. The decay half-life naturally
depends on a nuclear matrix element that needs to be calculated
theoretically. A good knowledge of this matrix element is key for the
planning of 0nbb decay experiments, and also to extract information on
the neutrino mass once 0nbb decay is observed.
At the moment, predicted matrix-element values depend on the
many-body method used to calculate them and, in addition, they may
need to be ”quenched”, as the matrix elements of other beta decays that,
however, have a very different momentum-transfer regime. I will discuss
recent efforts towards obtaining reliable nuclear matrix elements, ranging
from improved calculations with standard many-body approaches, to the
first application of "ab initio" many-body methods to 0nbb decay, finalizing
with possible measurements that could be very useful to test calculations
and to constrain the value of the 0nbb matrix elements.

What Stubs and Sparkles In Vast Vats of Liquid Will Tell Us About Exploding Stars Kate Scholberg (Duke University) PAA A-102

When a massive star collapses at the end of its life, nearly all of the gravitational binding energy of the resulting remnant is released in the form of neutrinos. I will discuss the nature of the core-collapse neutrino burst and what we can learn about particle physics and about astrophysics from the detection of these neutrinos. I will cover supernova neutrino detection techniques in general, current supernova neutrino detectors, and prospects for specific future experiments. ​