TRIUMF Speaker: Oliver Stelzer-Chilton

Fri. Mar. 1 12:30 PM - Fri. Mar. 1 01:20 PM
Location: 3M69 & via Zoom

TRIUMF Senior Scientist on ATLAS, Adjunct Professor of Physics at UBC, & Former ATLAS Exotics group convenor

Searching in (the) Dark and New Directions

News from the ATLAS experiment at the Large Hadron Collider

It is an interesting time in particle physics. On the one hand the discovery of the Higgs boson at the LHC has been a tremendous success for consolidating the Standard Model. On the other hand, many questions remain unanswered. Why is the Higgs boson mass so light and where is the “new physics” we expect at the TeV scale? Can we produce dark matter at colliders and is the Higgs boson somehow connected to the dark sector?

During Run 2 of the LHC, the ATLAS experiment has collected an unprecedented sensitive dataset to answer many of these questions. In this talk, I will discuss some of the highlights of the new results released by ATLAS so far in the areas listed above, including searches using long-lived and challenging unconventional signatures. I will also give an update on what’s in store for Run 3 and beyond.

BIO: My primary interest is the study of elementary particle physics. My current physics emphasis are searches for new particles beyond the Standard Model and studying the newly discovered Higgs boson. With its discovery at the LHC by ATLAS and CMS, there are many questions we are trying to answer with more measurements. Have we observed the Higgs that is predicted in the Standard Model, or are the results pointing towards new physics that goes beyond the Standard Model? We have studied the Higgs boson in various ways, including the consistency with the spin-0 and even parity characteristics following the discovery. We continued our studies by finding evidence for the order of magnitude suppressed vector boson fusion production mode in Higgs decays to WW decays which allows the most precise determination of the Higgs to vector boson coupling. More recently in Run 2, we contributed to the observation of the third Higgs boson production mode in association with top quarks that is suppressed by another order of magnitude. This allowed for the first time a direct measurement of the Higgs-top Yukawa coupling. We are also intensly searching for other new particles which appear in many theories that go beyond the Standard Model. We just recently completed a search for new gauge bosons Z' in the leptonic final state. I am currently one of the two ATLAS Exotics Group conveners.

I am a member of the ATLAS Muon group and am active in the phase-1 upgrades of the ATLAS detector. A Canadian consortium around clusters at TRIUMF, Carleton University and McGill University will build 25% of novel high precision thin gap chambers for the ATLAS New Small Wheel (NSW) to be installed in 2019-2020. We have setup laboratory space at TRIUMF to produce detector half gaps for these chambers with a dedicated team. The basic sTGC structure consists of a grid of gold-plated tungsten wires sandwiched between two resistive cathode planes at a small distance from the wire plane. The precision cathode plane has strips with a 3.2mm pitch for precision readout and the cathode plane on the other side has pads for triggering. The pads are used to produce a 3-out-of-4 coincidence to identify muon tracks in an sTGC quadruplet. A full size sTGC quadruplet has been constructed and equipped with the first prototype of dedicated front end electronics. The performance of an sTGC quadruplet has been studied at various testbeams, including at Fermilab, where we measured spacial resolutions of 45 microns. NSW performance plots can be found here. We are currently producing sTGC detectors at TRIUMF and across Canada and detector integration at CERN is ongoing.

Past involvements: I worked on the ATLAS Level-1 Calorimeter Trigger for my Diplom in Germany and for my PhD I became a member of CDF and made major contributions to the world's most precise measurement of the W boson mass, which improved the indirect constraint on the Higgs boson mass and was consistent with the discovery in 2012.

For a zoom invitation to this talk, please email: an.wiebe@uwinnipeg.ca