LBNL Physics Division Research Progress Meetings

Roger O’Brient (JPL) “The Search for Inflationary Gravitational Waves: Current Status of the BICEP Program and Next Generation Instrumentation.”
2017-03-21 16:00 - 17:00 (America/Los_Angeles) | Zoom Talk, 50A-5132, Berkeley, ca, 94720
Abstract:
For over a decade, the BICEP collaboration has been deploying small aperture telescopes to the South Pole Station to map B-mode polarization in the Cosmic Microwave Background and
search for evidence of primordial gravitational waves. If detected, they would allow physicists
to constrain physics at energy scales of ~10 16 GeV levels. To date, this program places the
tightest constrains on the tensor-scalar ratio of r<0.07 (95% confidence). We are at an
important point in our program as we transition into “Stage-3” instruments with the BICEP-
array, which will search to a level of r>0.01. This rapid progress is fueled by the antenna-
coupled superconducting bolometers that we have developed at NASA’s Jet Propulsion
Laboratory. In my talk, I’ll summarize the science case for these experiments, describe the
instruments themselves with a focus on the detectors, discuss the recently collected data, and
comment on the future of our program. In particular, Thermal KIDs, an emerging bolometer
technology, will be critical for this next phase. Finally, I’ll comment on how LBL and DOE can
and will play a future role in this exciting frontier of fundamental physics.

Prof. Stacy McGaugh (Case Western) "The Radial Acceleration Relation in Rotationally Supported Galaxies"
2017-03-16 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
ABSTRACT:
We report a correlation between the radial acceleration traced by rotation curves and that predicted by the observed distribution of baryons. The same relation is followed by 2693 points in 153 galaxies with very different morphologies, masses, sizes, and gas fractions. The correlation persists even when dark matter dominates. Consequently, the dark matter contribution is fully specified by that of the baryons. The observed scatter is small and largely dominated by observational uncertainties. This radial acceleration relation is tantamount to a natural law for rotating galaxies.

Timon Heim (LBNL) “Challenges of the ATLAS Phase 2 Tracker Upgrade”
2017-03-09 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
For the phase 2 upgrade of the ATLAS experiment at the LHC, its inner detector will be replaced by a new all-silicon tracker, the Inner Tracker (ITk). This upgrade is necessary both because the inner detector will have reached its intended lifetime and to maintain tracking performance of the ATLAS detector under the demands of a 5 to 7 times higher collision rate after the high luminosity upgrade of the LHC. This presentation will give an overview and status of the ITk Strip and Pixel detector. It will highlight one major challenge for each of the detectors: the on-module DC-DC powering circuit of the ITk Strip detector and the 65nm readout chip of the ITk Pixel detector. Furthermore I will present a readout concept which could be used as a base for a common ITk readout software core. This core can operate with multiple hardware platforms and user interfaces, an essential feature for the successful transition from prototyping and production to detector commissioning and operation.

Elisabetta Pianori (CERN) "Unveiliing the Origin of Particles' Mass: Higgs Boson Coupling Measurements at the LHC"
2017-03-07 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
Abstract:
Although the Standard Model (SM) of particle physics is a very successful theory, it fails to explain the origin of particles’ mass. If the Higgs mechanism, developed in the 60s as a solution to this puzzle, is the correct theory of Nature, a new fundamental particle, the Higgs boson, must exist. In 2012, at the LHC, a particle consistent with the Higgs boson was discovered. The theory prescribes the strength of the Higgs boson interaction with SM particles, but physics beyond the Standard Model could modify it. In this talk I will present the evidence of direct couplings of the Higgs boson to fermions and compare them with the predictions. I will also discuss the ATLAS+CMS combined measurement of the Higgs boson production and decay rates, and how they constrains the Higgs boson’s couplings to SM particles and the existence of new physics.

Javier Tiffenberg (Fermilab) "Things to do with less than one electron: the dawn of the ultimate ionization detector"
2017-03-02 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
Abstract:

Silicon charged coupled devices (CCDs) have proven to be exceptional for the detection and measurement of photons and other ionizing radiation. Their low energy threshold of 50eV (~14 e-) have made them ideal for astronomical aplications and for detectors exploring Neutrino interactions (CONNIE) and searching for Dark Matter particles (DAMIC). However, the counting of individual photons and energy depositions below 50 eV has proven difficult due to an inability to reduce electronic noise below the level of a single charge carrier. Here I’ll present the results of a collaboration between Fermilab and LBL to build a Sub-Electron Noise Skipper Experimental Instrument (SENSEI) which uses a non-destructive readout technique to achieve stable readout for a thick fully depleted silicon CCD in the far sub-electron regime (∼ 0.05 e − rms/pix). This is the first time that discrete sub-electron counting has been achieved reproducibly over millions of pixels on a stable, large-area detector (7 cm^2 ) with large dynamic range. This innovative technology has nearly immediate implications for a wide range of scientific disciplines including astronomy and fundamental particle physics.

slides: pdf

Yun-Tse Tsai (SLAC/Stanford) "Exploring ν Territory: Using LArTPC Technology ("ν“ here is a Greek alphabet accounting for neutrinos)"
2017-02-28 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
Abstract:

The discovery of neutrino oscillation, which implies neutrinos have non-zero masses, is the first instance of a conflict with the Standard Model of particle physics. The fruitful results from neutrino experiments in the past two decades have opened a window into a new territory, where the unanswered questions in the current theory, such as the observed matter-antimatter asymmetry, may be addressed by the upcoming precision measurements.
In this talk, I will introduce the core topics of neutrino physics and the requirements of neutrino experiments, focusing on the technology of liquid argon time projection chamber (LArTPC). The outstanding spatial and energy resolution of LArTPC provides us with a promising apparatus for the required precision. In particular, I will discuss detection of neutrinos from supernova explosions, and searches for other weakly interacting particles as well as rare physics processes. I will talk about the MicroBooNE experiment, the first large LArTPC in the U.S., its recent results, and the future LArTPC experiments.

Alvaro Chavarria (U. Chicago) “Solid-State Imaging Detectors for Low-Energy Particle Physics”
2017-02-23 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
Abstract:
The low noise, high spatial resolution and reliable performance of charge-coupled devices (CCDs) and complementary metal-oxide-semiconductor (CMOS) active-pixel sensors have made them detectors of choice for digital imaging. Although the slow time response of these devices has limited their application in high-energy particle physics, for the case of rare-event searches, where the particle interaction rate is extremely low, their properties can be fully exploited to build detectors that outperform in many aspects the traditional technologies of the field. I will present recent results from the DAMIC experiment, a low-mass dark matter search consisting of low-noise CCDs deployed in the SNOLAB laboratory. I will show how the exquisite spatial resolution of the detector allows for particle identification, and provides the unique capability to reject sequences of radioactive decay with utmost efficiency. These techniques can be extended to the search for neutrinoless double beta decay. I will present a recent proposal where we argue that a large array of amorphous Se-82 imagers based on CMOS technology could achieve the background levels necessary to test if neutrinos are Majorana fermions even in the case of a normal hierarchy of neutrino masses.

Stefano Camarda (CERN) "Electroweak precision physics at the LHC"
2017-02-21 16:00 - 17:00
Abstract:
Precision measurements of electroweak observables offer a viable
option for finding indications of new physics and also guidance for
the next big discovery. In this talk, I will focus on the latest
electroweak precision measurements at the LHC, with an emphasis on the
W-boson mass measurement recently published by ATLAS. The evaluation
of the experimental systematic uncertainties, as well as the
uncertainties due to the modeling of the vector boson production and
decay of the ATLAS W-boson mass measurement will be discussed.
In addition, the LHC results will be put in context to previous
measurements at the Tevatron and LEP colliders.

Aritoki Suzuki (UCB) "Next Generation Cosmic Microwave Background Polarimetry Experiment - Enabling Technologies for an Order of Magnitude Increase in Detector Count"
2017-02-16 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
Precision measurements of Cosmic Microwave Background (CMB) temperature anisotropies over the last two decades have been a spectacular success, constraining all six parameters of the LambdaCDM cosmological model to the percent level. However, while CMB temperature is well explored, current experiments are just now becoming sensitive enough to explore the rich physics of CMB polarization.
“Stage-II” CMB experiments started to deploy in early 2010’s, contain ~1,000 millimeter-wave, polarization-sensitive detectors, and have discovered B-mode polarization due to weak gravitational lensing and set limits on B-modes due to inflationary gravitational waves. “Stage-III” experiments have begun to deploy this year and contain ~10,000 detectors for an order-of-magnitude improvement in sensitivity.
Looking to the future, the CMB community has begun studying “CMB-S4”, a “Stage-IV” experiment that will contain ~500,000 detectors, a factor ~100 increase over experiments currently in the field. The goal of CMB-S4 is to make a definitive measurement of CMB polarization from the ground in order to explore inflationary scenarios, constrain the sum of the neutrino masses, and search for new physics within the early universe.
During this presentation, I will discuss the exciting science objectives of modern CMB experiments, the tremendous technological challenge of fielding large numbers of highly-sensitive detector arrays, and the advancement in technologies we are developing to overcome these challenges to conduct the ultimate CMB polarization measurement.

Manuel Franco Sevilla (UCSB) "Strategies for Searches of Physics Beyond the Standard Model in the XXI Century"
2017-02-14 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
ABSTRACT:

At the end of the XIX century, Lord Kelvin summarized a widespread feeling among physicists by saying that “physics is essentially complete, save for two little clouds”. The “clouds” he was referring to were the puzzling results from two measurements, the Michelson-Morley experiment and the Black-body spectrum, whose explanations ushered in an unprecedented era of discoveries that stretched throughout most of the XX century. After the culmination of the Standard Model in the 70’s, the field of particle physics has found itself in a similar situation. Today, the “clouds” guiding the searches for physics beyond the Standard Model are issues like dark matter or the hierarchy problem. Using SUSY searches at CMS and the measurement of B->D(*)TauNu decays at BaBar as models, I will give an overview of some of the main strategies that are being followed in the quest to find new physics in the XXI century.

Peter Sorensen (LBNL) "How to See Dark Photons: A Status Report on a New Avenue in Direct Detection"
2017-02-09 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
Abstract:
I will discuss the new (old) idea that dark matter may reside in a hidden sector whose interactions with the standard model are mediated by a dark photon. Possibilities for direct detection of such particles will be discussed. This is particularly timely given the recent DOE call for a small scale direct detection experiment that can search new parameter space.
20170209_RPM slides

Reserved
2017-02-07 16:00 - 17:00, 2017-02-02 16:00 - 17:00, 2017-01-31 16:00 - 17:00, 2017-01-26 16:00 - 17:00, 2017-01-24 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720

Kirit Karkare (Harvard) "B-Mode Polarization Results from BICEP/Keck Array and Beam Systematics in Current and Next-Generation CMB Experiments"
2017-01-19 16:00 - 17:00
Abstract:
The BICEP/Keck Array cosmic microwave background (CMB) polarization experiments located at the South Pole are a series of small-aperture refracting telescopes focused on the degree-scale B-mode signature of inflationary gravitational waves. I will present our latest results which have produced the most stringent constraints on the tensor-to-scalar ratio to date: sigma(r) = 0.024 and r < 0.09 from B-modes alone (r < 0.07 in combination with other datasets). These constraints will rapidly improve with upcoming measurements at the multiple frequencies needed to separate Galactic foregrounds from the CMB, and in combination with higher-resolution experiments to remove B-modes induced by gravitational lensing. I will provide an update on our expanded frequency coverage and plans for future receivers.
Next-generation CMB experiments with hundreds of thousands of detectors will require exquisite control of instrumental systematics. I will review key aspects of the BICEP/Keck instrument design which maximize polarization sensitivity and reduce systematics at large angular scales, including the ability to measure beams in the far field with high precision. Finally, I will discuss the prospects for dealing with temperature-to-polarization leakage in future experiments, and how the beams systematics levels we achieve with current instrument and analysis technology will scale with detector count.

Aleksandra Dimitrievska (U. Belgrade) "Measurement of the W-boson mass with the ATLAS detector "
2017-01-17 16:00 - 17:00
Abstract:
The precise measurements of the W boson, the Higgs boson and the top quark masses enables to test the consistency of the Standard Model. Constraints on physics beyond the Standard Model are currently limited by the precision of the W-boson mass measurement. In this talk a measurement of the W-boson mass is presented with the data collected in 2011 at centre-of-mass energy of 7 TeV with the ALTAS detector corresponding to an integrated luminosity of 4.6 fb⁻¹. The measurement is based on about 8 and 6 million W candidates in the muon and electron channels, respectively. The W-boson mass is extracted from the template fits to the transverse momentum of the charged lepton and to the transverse mass of the W boson distributions. This measurement yields a W-boson mass:
mW = 80370 ± 7 (stat.) ± 11 (exp. syst.) ± 14 (mod. syst.) MeV = 80370 ± 19 MeV,
where the first uncertainty is statistical, the second corresponds to the experimental systematic uncertainty, and the third to the physics-modelling systematic uncertainty.

Siyuan Sun (Harvard) "Gaining Sensitivity to New Physics with a Compressed Mass Spectra at the ATLAS Experiment"
2017-01-12 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
ABSTRACT
The ATLAS experiment at Large Hadron Collider (LHC) searches for experimental ev-
idence of many new beyond the standard model physics at the TeV scale. As we collect
more data at the LHC we continue to extend our sensitivity to these new phenomenon,
particularly probing increasingly more massive new particles. Despite this progress there
are still regions of parameter space where constraints remain weak. One common cause of
this lack of sensitivity is because the new particle has a very small mass splitting between it
and its decay products. The particle then has little energy left over to give momenta to its
decay products and the low momenta decay products are difficult to experimentally detect.
These regions of small mass splitting are called compressed regions. We are able to gain
sensitivity to these difficult regions by searching for new particles produced in conjunction
with strong initial state radiation (ISR). The strong initial state radiation boosts the new
particle’s decay products and gives them momentum.
In this seminar, I will cover in detail the search for the supersymmetric partner to the
top quark (stop) in the region when the stop and its decay products are nearly degenerate in
mass. No searches prior to 2016 was sensitive to this region. We were able to exclude stops
up to a mass of 425 GeV in this region with the 2015 and summer 2016 ATLAS dataset. I will
demonstrate a new and more accurate technique for identifying whole initial state radiation
systems instead of a single ISR jet. As the LHC provides more data and traditional search
methods rule out parameter space at higher masses, it becomes more important that we also
gain sensitivity to these compressed regions that are still unconstrained at low masses. I will
show that this initial state radiation identification technique is completely generalizable and
useful for many other searches that target small mass splittings.

Michael James Wilson (Institute of Astronomy, U. Edinburgh) "Extracting precision tests of gravity from the intricate pattern of galaxies"
2017-01-10 16:00 - 17:00 | 50A-4133 (Director's Conference Room)
ABSTRACT:
Galaxy redshift surveys deliver increasingly precise tests of gravity on cosmological scales and shed light on the uncertain nature of Dark Energy. I will present the VIPERS (http://vipers.inaf.it) census of the galaxy distribution at redshift 0.8 and describe its consistency with the expansion history and rate of gravitational collapse predicted by General Relativity and a Planck (2015) cosmology. This is facilitated by the anisotropy of the observed clustering, which is sensitive to both the coherent infall of galaxies towards clusters and the assumption of an expansion history differing from the true one.
I will then present the results of including a simple density transform prior to this conventional analysis, which suppresses the most massive structures and extends the validity of the simplest models. Moreover, this has been shown to amplify signatures of modified gravity in ‘shielded’ theories and contains information beyond that available to the power spectrum. To do so requires correcting for many systematics that are characteristic of high-redshift surveys. I will describe the properties common to VIPERS, eBOSS and DESI and the potential of a density-weighted analysis with these next-generation surveys.
Finally, tests of gravity have predominantly focused on the large-scale velocities of galaxies to date, but that of clusters is imprinted on the Cosmic Microwave Background by the kinetic Sunyaev-Zel’dovich effect. The Simons Observatory and CMB-S4 experiments represent ideal test-beds for exploring the latter. I will discuss this and other future avenues for revealing the properties of Dark Energy with large-scale structure.

Eleonora Di Valentino (Institut d'Astrophysique de Paris) "New Constraints on Extensions of the Standard Cosmological Model"
2017-01-05 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
Abstract:
The Cosmic Microwave Background (CMB) temperature and polarization anisotropy measurements from the Planck mission have significantly improved previous constraints on the neutrino masses, as well as the bounds on extended models with massive sterile neutrino states or extra particles, as for example thermal axions. In this talk firstly I will show the recent constraints from cosmology for the thermal axion mass and the neutrino sector, by considering several combination of datasets and scenarios. In particular, I will show how the inclusion of additional low redshift priors is mandatory in order to sharpen the CMB neutrino bounds, and that we are close to test the neutrino mass hierarchy with existing cosmological probes. Secondly, I will discuss how these constraints can change by taking into account the possibility that the primordial power spectrum could assume a more general shape than the usual power law description. Finally, I will present cosmological constraints in a significantly extended scenario, varying up to 12 cosmological parameters simultaneously, by looking for a new concordance model that should solve at the same time all the current tensions between the Planck data and the new direct measurements of the Hubble constant by Riess et al. 2016 and the parameters from weak lensing surveys, such as CFHTLenS and KiDS-450.

Zackay Barak (Weizmann Institute of Science) Algorithms for searching Fast radio bursts, pulsars in tight binary systems and "Planet 9"
2017-01-03 16:00 - 17:00
Abstract:
Fast radio bursts (FRB’s) are an exciting, recently discovered, astrophysical transients which their origins are unknown.
Currently, these bursts are believed to be coming from cosmological distances, potentially allowing us to probe the electron content on cosmological length scales. Even though their precise localization is crucial for the determination of their origin, radio interferometers were not extensively employed in searching for them due to computational limitations.
I will briefly present the Fast Dispersion Measure Transform (FDMT) algorithm, allowing to reduce the operation count in blind incoherent dedispersion by 2-3 orders of magnitude.
In addition, FDMT enables to probe the unexplored domain of sub-microsecond astrophysical pulses.Pulsars in tight binary systems are among the most important astrophysical objects as they provide us our best tests of general relativity in the strong field regime.
I will provide a preview to a novel algorithm that enables the detection of pulsars in short binary systems using observation times longer than an orbital period.
Current pulsar search programs limit their searches for integration times shorter than a few percents of the orbital period.
Until now, searching for pulsars in binary systems using observation times longer than an orbital period was considered impossible as one has to blindly enumerate all options for the Keplerian parameters, the pulsar rotation period, and the unknown DM.
Using the current state of the art pulsar search techniques and all computers on the earth, such an enumeration would take longer than a Hubble time. I will demonstrate that using the new algorithm, (called Pruning) it is possible to conduct such an enumeration on a laptop using real data of the double pulsar, PSR J0737-3039.
Among the other (astronomical) applications of the Pruning technique are:
1) Searching for all pulsars on all sky positions in gamma ray observations of the Fermi LAT satellite.
2) Blind searching for continuous gravitational wave sources emitted by pulsars with non-axis-symmetric matter distribution.

3) Blind searching for planets in the outskirts of the solar system (AKA “Planet 9”), both in imaging data and on GAIA data (through astrometric deflection of background stars).

4) Blind searching for asteroids and Kuiper belt objects in imaging data.

5) Searching for stars in close orbits around the super massive black hole in the galactic center.

Previous attempts to conduct all of the above searches (if even considered) contained substantial sensitivity compromises.

Karol Krizka (U. Chicago) "Dark Matter Mediators and Dijet Resonance Searches by the ATLAS Experiment"
2016-12-20 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
Abstract:Using 13 TeV pp collisions, the ATLAS experiment has used a collection of dijet resonance searches (high-mass dijet, trigger-level dijet and dijet+ISR) to search for new particles with masses ranging from 200 GeV to 7 TeV. This talk summarizes the searches, with a focus on new the “dijet+ISR” channel. The dijet+ISR analysis is an LHC-first and reaches mediator masses below 500 GeV by utilizing an ISR jet or photon to trigger the event. This region was previously accessible only by the LEP and Tevatron experiments. This is an important improvement for Dark Matter simplified models, based on a mediator between a Dark Matter particle and the Standard Model. Cosmological measurements of the Dark Matter relic density prefer the mediator mass to be sub-TeV. By searching for a dijet resonance produced by the mediator decaying back into quarks, powerful new limits are set on the simplified Dark Matter models.

Nan Lu (U. Michigan - Ann Arbor) ""Higgs Boson Property Measurements with ATLAS at the LHC""
2016-12-15 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
Abstract:
“After the discovery of Higgs boson by the ATLAS and CMS experiments at the LHC in 2012, a new era of studying the properties of this new particle has begun. In this talk, I will give a brief overview of Higgs boson property measurements using LHC Run 1 data, and then focus on the measurements of Higgs boson production in the four-lepton decay channel and in combination with the diphoton decay channel using 13.3 fb-1 to 14.8 fb-1 of Run 2 data collected at √s=13 TeV by the ATLAS detector.”

ChangHoon Hahn (NYU) "Fundamental Physics with Galaxy Clustering"
2016-12-13 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
Abstract:

Galaxies’ connection to the cosmic web allows us to use them to trace the matter distribution in the Universe and make precise measurements of large scale structure. The next galaxy surveys (eBOSS and DESI) will expand the cosmic volumes probed with galaxies by an order of magnitude and provide unprecedented statistical power. The main challenges for realizing their full potential are methodological.

I will present how the main challenges can be solved with robust treatment of systematics (e.g. fiber collisions), accurate probabilistic inference, and higher order statistics. By overcoming these challenges and unlocking the full potential of eBOSS and DESI, I will present how we can measure the growth of structure and total neutrino mass with unprecedented precision.

Johanna Nagy (Case Western) "Probing Inflation with SPIDER, a Balloon-Borne CMB Polarimeter"
2016-12-08 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
Abstract:

The generation of a stochastic gravitational wave background is a key prediction of cosmological theories of inflation. At large angular scales, these gravitational waves imprint a “B-mode” polarization pattern in the Cosmic Microwave Background, providing a new window into the physics of the early universe and helping to constrain and distinguish between inflationary models. SPIDER is a balloon-borne telescope that has been uniquely optimized to search for the inflationary B-mode signature in the CMB. Over the course of two Antarctic flights, SPIDER will make polarization maps over 10% of the sky in three frequency bands with degree-scale angular resolution. After an overview of the instrument and science goals, preliminary results from SPIDER’s 2015 flight will be presented along with a summary of progress towards the second flight.

Cristián H. Peña (Caltech) "Searches for New Physics at CMS and Precision Timing Detectors"
2016-12-06 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
ABSTRACT:

Searches for dark matter and supersymmetry are part of an ambitious and well motivated quest to discover new physics at the LHC. In the first part of this seminar I will be presenting two novel searches for new physics using the data collected by the CMS experiment. The first is a search for dark matter in multijet events using the razor variables to discriminate signal from background events. The second is a search for anomalous production of Higgs bosons in association with jets, where the Higgs is reconstructed through its diphoton decay channel. The second part of my seminar will cover cutting edge detector R&D towards a device with ~10 ps time resolution. Such detectors will have a positively disruptive impact in future experiments such as the High Luminosity upgrade of the LHC by maintaining the current event reconstruction performance, which is expected to otherwise significantly deteriorate due to the high pileup environment.

Evan Pease (Yale) "Searching for WIMPs and More: Results from 3 Years of Underground Science with the LUX Experiment"
2016-12-01 16:00 - 17:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
ABSTRACT:
The Large Underground Xenon (LUX) experiment recently concluded underground operationat the Sanford Underground Research Facility. This talk will cover the full LUX search for dark matter in the form of Weakly Interacting Massive Particles (WIMPs) and will describe new measurements of xenon’s properties and new analysis techniques developed for further LUX science.

SPECIAL SEMINAR: Wai Ling Kimmy Wu (Stanford) "Constraining Inflation with BICEP/Keck and SPT"
2016-11-30 12:00 - 13:00 | Zoom Talk, 50A-5132, Berkeley, ca, 94720
Abstract:

Inflation generically predicts a background of stochastic gravitational waves. In the standard cosmological model LCDM, these primordial gravitational waves (PGW) are the only source to the odd-parity (curl) B-mode polarization on the Cosmic Microwave Background (CMB) at the epoch of recombination. Therefore, we can learn much about inflation by constraining or potentially detecting primordial gravitational waves. In this talk, I will present two frontiers that advance the search for primordial gravitational waves: instrumentation of BICEP3 and delensing with SPTpol. I will conclude with the future outlook of such search with CMB-S4.

In the first part of the talk, I will discuss the design and performance of BICEP3 — the path-finder of BICEP/Keck program’s Stage-3 effort. The BICEP/Keck telescopes are small aperture (~0.5m) cryogenic refractors that focus on measuring the degree-angular scale feature of the PGW-generated B modes. BICEP3 has ~10x optical throughput compared to BICEP2 due to a larger field-of-view and aperture size. As a result, we adopt new designs in BICEP3 for thermal filtering, optical elements selection, and detector modules packing. We deployed BICEP3 in the Austral summer of 2014-2015 and upgraded the instrument after the first season of testing and observations. I will present the improvements of the noise levels due to this upgrade.

The second part of my talk will focus on delensing SPTpol data. Gravitational lensing of primordial (curl-free) E modes generates B modes. These lensing B modes are a source of foreground contamination to detecting the PGW-generated B modes. We can characterize and reduce the lensing B-mode contribution through a technique called “delensing.” I will present results of a first demonstration of delensing on polarization data. In this work, we delens B-mode maps from multi-frequency SPTpol observations of a 100 deg^2 patch of sky by subtracting a lensing B template constructed from two components: SPTpol E-mode maps and a lensing potential map formed from a Herschel 500 μm map of the CIB. In addition, we build and use a suite of realistic simulations to study the current limitations and expected future improvements in delensing with implications for future experiments.

Scott Kravitz (Stanford) "Identification of Single Barium Atoms for the nEXO Neutrinoless Double Beta Decay Experiment"
2016-11-29 16:00 - 17:00
Abstract:
nEXO is a next-generation experiment designed to search for neutrinoless double beta decay of xenon-136 in a liquid xenon time projection chamber. Positive observation of this decay would determine the neutrino to be a Majorana particle, as well as measure the absolute neutrino mass scale. In order to greatly reduce background contributions to this search, the collaboration is developing several “barium tagging” techniques to recover and identify the decay daughter, barium-136. Barium tagging may be available for a second phase of nEXO operation, allowing for neutrino mass sensitivity beyond the inverted mass hierarchy. Tagging methods for this phase include barium-ion capture on a probe with identification by resonance ionization laser spectroscopy (RIS). An apparatus has been built to deposit barium atoms onto a surface and recover them using infrared laser desorption followed by RIS, with the resulting ions passing through a time-of-flight mass spectrometer for further identification. Recent results from this system will be presented, including those from incorporating an argon ion gun which allows for improved cleaning and preparation of the barium deposition substrate.
