NPAC (Nuclear/Particle/Astro/Cosmo) Forum

The first run of the Large Hadron Collider (LHC) has been a great success, most notably with the discovery of the Higgs boson. Despite the continued triumph of the Standard Model, critical questions remain unanswered about how nature works on small scales. As the most massive of all known elementary particles, the top quark plays a central role in many proposed extensions to the Standard Model that address some of these questions. A precise understanding of top quarks and their production and properties is therefore critical. In this talk, I will discuss the motivation and status of top quark physics at the LHC, presenting recent results from the CMS experiment. Additionally, I will give an outlook to the future upgrade of the LHC to higher luminosities (HL-LHC), and its resulting potential and challenges for the CMS experiment.

Host: 
Sridhara Dasu
Speaker: Louise Skinnari Cornell

 

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Room and Building: 
4274 Chamberlin Hall

The top quark is the heaviest known elementary particle: with a mass as large as an entire gold atom and the only fermion with a natural Yukawa coupling. Millions of top quarks have been produced at the LHC allowing precise measurements of its properties that have been compared with Standard Model predictions. The high center-of-mass energy of the LHC can also be exploited for dedicated searches for new heavy particles decaying preferentially to top quarks. I will review the latest ATLAS results searching for evidence of new physics in the production and decay of top quarks at the LHC with the ATLAS detector.

Host: 
Sridhara Dasu
Speaker: Kevin Black Boston University

 

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Room and Building: 
4274 Chamberlin Hall

A search for the standard model (SM) Higgs boson (H) decaying to bb when produced in association with an electroweak vector boson is reported for the following processes: Z(νν)H, W(μν)H, W(eν)H, Z(μμ)H, and Z(ee)H. The search is performed in data samples corresponding to an integrated luminosity of 35.9 fb−1 at √s = 13 TeV recorded by the CMS experiment at the LHC during Run 2 in 2016. An excess of events is observed in data compared to the expectation in the absence of a H → bb signal. The significance of this excess is 3.3 standard deviations, where the expectation from SM Higgs boson production is 2.8. The signal strength corresponding to this excess, relative to that of the SM Higgs boson production, is 1.2 ± 0.4. When combined with the Run 1 measurement of the same processes, the signal significance is 3.8 standard deviations with 3.8 expected. The corresponding signal strength, relative to that of the SM Higgs boson, is 1.06+0.31. −0.29

Host: 
Sridhara Dasu
Speaker: Stephane Cooperstein Princeton

 

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Room and Building: 
4274 Chamberlin Hall
Recent HAWC observations have found extended TeV emission coincident<br><br>
with the Geminga and Monogem pulsars. In this talk, I will show that<br><br>
these detections have significant implications for our understanding<br><br>
of pulsar emission. First, the spectrum and intensity of these TeV<br><br>
Halos indicates that a large fraction of the pulsar spindown energy is<br><br>
efficiently converted into electron-positron pairs. This provides<br><br>
observational evidence supporting pulsar interpretations of the rising<br><br>
positron fraction observed by PAMELA and AMS-02. Second, the isotropic<br><br>
nature of this emission provides a new avenue for detecting nearby<br><br>
pulsars with radio beams that are not oriented towards Earth. Lastly,<br><br>
I will show that the total emission from all unresolved pulsars<br><br>
produces the majority of the TeV gamma-ray flux observed from the<br><br>
Milky Way.
Host: 
Francis Halzen
Speaker: Tim Linden CCAP, Ohio State University

 

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Room and Building: 
4274 Chamberlin
Host: 
Halzen
Speaker: Ryan Bay UC Berkeley

 

Available Downloads:

Room and Building: 
4274 Chamberlin Hall

The laboratory of the early universe provides a setting for testing Beyond Standard Model (BSM) physics in the particle and cosmological sectors. Any BSM physics in operation at early times may produce slight deviations on the primordial element abundances and cosmic microwave background observables predicted within the standard cosmology. The identification and characterization of such BSM signatures require a precise treatment of the neutrino energy and flavor wave functions during the time of Big Bang Nucleosynthesis (BBN) using the Quantum Kinetic Equations (QKEs). I will review some of the work done on characterizing BBN with a Boltzmann-energy-transport approach, as well as ongoing work towards a full QKE treatment with neutrino oscillations and collisions. A QKE treatment of early-universe neutrino physics will greatly assist observers and theorists as the next generation cosmological experiments come on line in the near future.

Host: 
Baha Balantekin
Speaker: Evan Grohs University of Michigan

 

Available Downloads:

Room and Building: 
5280 Chamberlin Hall

Cosmic-ray anti-deuterium and anti-helium have long been suggested as probes of dark matter, as their secondary astrophysical production was thought extremely scarce. But how does one actually predict the secondary flux? Anti-nuclei are dominantly produced in pp collisions, where laboratory cross section data is lacking. We make a new attempt at tackling this problem by appealing to a scaling law of nuclear coalescence with the physical volume of the hadronic emission region. The same volume is probed by Hanbury Brown-Twiss (HBT) two-particle correlations. We demonstrate the consistency of the scaling law with systems ranging from central and off-axis AA collisions to pA collisions, spanning 3 orders of magnitude in coalescence yield. Extending the volume scaling to the pp system, HBT data allows us to make a new estimate of coalescence, that we test against preliminary ALICE pp data. For anti-helium the resulting cross section is 1-2 orders of magnitude higher than earlier estimates. The astrophysical secondary flux of anti-helium could be within reach of a five-year exposure of AMS02.

Host: 
Albrecht Karle
Speaker: Kfir Blum Weizmann Institute of Sciences

 

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Room and Building: 
5280 Chamberlin Hall
Host: 
Francis Halzen
Speaker: Jordi Salvado Serra IFIC, Valencia

 

Available Downloads:

Room and Building: 
4274 Chamberlin hall
Cosmic rays, high energy particles originating from outside of the solar system, are believed to be dominated by particles from our Galaxy at least up to the energy of 1015 eV. Recent results from direct measurements of cosmic rays, including the rise of the positron flux, the hardening of the light nuclei, and the different spectral indexes of the proton and helium spectra, challenge the classical models of the Galactic cosmic rays. Meanwhile, the development of gamma-ray experiments has opened a new window to study the acceleration and propagation of high-energy particles in the vicinity of the source sites, such as supernova remnants.

I will introduce HELIX (High Energy Light Isotope eXperiment), a near-future balloon-borne experiment designed to improve our understanding of the propagation of Galactic cosmic rays by measuring the key clock isotope 10Be up to 10 GeV/n. I will also present the Galactic gamma-ray measurements from the VERITAS experiment, an imaging atmospheric Cherenkov telescope measuring gamma rays with energies higher than 85 GeV and up to ~ 30 TeV. Focusing on the supernova remnants, I will discuss what we have learned about the acceleration of high-energy particles and what we expect to learn in the near future. Finally, I will highlight how neutrino observations with IceCube, in coordination with gamma-ray and cosmic-ray direct measurements, will broaden our perspective on the production and propagation of high-energy particles and advance us toward a new paradigm of Galactic cosmic rays.
Host: 
Westerhoff
Speaker: Nahee Park University of Chicago

 

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Room and Building: 
WIPAC (222 W Washington, 5th floor, Supernova Conference Room)

The Micro-X sounding rocket uses a Transition Edge Sensor (TES) array to make X-ray observations. The improved energy resolution of TESs compared to traditional space-based X-ray detectors brings new precision to both supernova observations and the X-ray search for sterile neutrino dark matter. Current X-ray observations disagree over the potential presence of a 3.5 keV X-ray line consistent with a sterile neutrino interaction, and Micro-X is in a unique position to establish or refute the presence of this line. We present the construction status of the instrument and expectations for flight observations, with special emphasis given to the prospects of sterile neutrino studies.

Host: 
Kim Palladino
Speaker: Antonia Hubbard Northwestern

 

Available Downloads:

Room and Building: 
5280 Chamberlin Hall

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