Department of Physics & Astronomy
University of Pennsylvania

Experimental Particle Physics
Seminars 2020-21

>> remote only at 4pm on Wednesdays<<

Contact: Associate Professor Evelyn Thomson

See also previous years, theory seminars,
and department colloquia

Wednesday September 30 2020 at 4pm
Philip Chang (UC San Diego)
Observation of production of three massive gauge bosons
The three massive gauge boson VVV (V = W, Z) production at the LHC is interesting because measurements of such processes can probe the interactions between massive bosons including the Higgs. Up until recently, such measurements have remained elusive because of low production cross sections. This talk will discuss the recent CMS result of first observation (5.7σ) of combined VVV production at the CERN LHC and evidences for WWW (3.3σ) and WWZ (3.4σ) productions individually. Finally, I will briefly discuss the future of the physics program of the rare multi-boson processes.
Wednesday October 28 2020 at 4pm
Tova Holmes (University of Tennessee)
Off the Beaten Track: Long-Lived Particles at the LHC
The LHC has reached a new era: nearly a decade without any large jumps in energy or luminosity. For those interested in finding Beyond the Standard Model (BSM) physics, a paradigm shift is required. In my talk I’ll discuss a search program looking for long-lived particles, which often escape detection from standard BSM searches, due to the difficulty of triggering on and reconstructing their unconventional signatures. These challenges result in a long-lived particle landscape full of unexcluded territory, opening up opportunities to find TeV-scale Supersymmetry, hidden sectors, right-handed neutrinos, and more. My talk will focus on the challenge of triggering in these searches, and how we can expand our capability to explore these new signatures.
Wednesday November 18 2020 at 4pm
Stephanie Majewski (University of Oregon)
Searching for the Supersymmetric Partner to the Top Quark at ATLAS: Don't Stop Believin'
The discovery of the stop — the Supersymmetric partner of the top quark — is a key goal of the ATLAS physics program enabled by the Large Hadron Collider. I will review the status of the search for direct stop pair production, focusing on stop decays via a hadronically decaying top quark and the lightest Supersymmetric particle (a compelling dark matter candidate). I will also discuss recent developments in the natural "stealth stop" regime, where the stop is nearly degenerate with the top quark, which is characterized by decay kinematics that force the final state top quark off its mass shell. Our recast of the ATLAS top mass measurements revealed that stop decays in this regime could contaminate the measurement of the top mass by up to 2 GeV. Thus, a robust statement on the exclusion of a stealth stop requires the simultaneous consideration of the impact on the top mass.
Wednesday December 2 2020 at 4pm
Louise Skinnari (Northeastern University)
Track-triggering at CMS for the High-Luminosity LHC
The high luminosity upgrade of the Large Hadron Collider (LHC), scheduled for 2025-2027, will significantly increase the instantaneous luminosity of the LHC collisions. The resulting large proton-proton collision datasets will allow precise measurements of Higgs boson properties, searches for very rare processes, and much more. To cope with the challenging experimental environment resulting from the high luminosity, significant upgrades will be required for the LHC detectors. A key upgrade of the CMS detector is to incorporate the identification of charged particle trajectories in the hardware-based trigger system, with potential to not only solidify the CMS trigger strategy but to enable searches for completely new physics signatures. This seminar will discuss the motivation of the CMS track trigger, give an overview of the system, and discuss its expected performance based on simulation and hardware demonstration.
Wednesday March 17 2021 at 4pm
Jonathan Asaadi (University of Texas Arlington)
Q-Pix: Pixelated readout of kiloton scale noble element time projection chambers
Future long baseline neutrino experiments such as the Deep Underground Neutrino Experiment (DUNE) call for the deployment of multiple multi-kiloton scale liquid argon time projection chambers (LArTPCs). To date, two detector readout technologies are being studied in large-scale prototype detectors: the single phase (SP) and dual phase (DP) detectors using projective charge readout wire based anode planes. These projective readout technologies come with a set of challenges in the construction of the anode planes, the continuous readout of the system required to accomplish the physics goals of proton decay searches and supernova neutrino sensitivity, and the 2D projective reconstruction of complex neutrino topologies. The Q-Pix concept (arXiv: 1809.10213) is a continuously integrating low-power charge-sensitive amplifier (CSA) viewed by a Schmitt trigger. When the trigger threshold is met, the comparator initiates a ‘reset’ transition and returns the CSA circuitry to a stable baseline. This is the elementary Charge-Integrate / Reset (CIR) circuit. The instance of reset time is captured in a 32-bit clock value register, buffers the cycle and then begins again. What is exploited in this new architecture is the time difference between one clock capture and the next sequential capture, called the Reset Time Difference (RTD). The RTD measures the time to integrate a predefined integrated quantum of charge (Q). Waveforms are reconstructed without differentiation and an event is characterized by the sequence of RTDs. In quiescent mode the RTDs will be evenly spaced with time intervals of seconds between RTDs with an event signaled by the appearance of a sequence of varying $\mu$s RTDs. This technique easily distinguishes the background RTDs due to 39Ar decays (which also provide an automatic absolute charge calibration) and signal RTD sequences due to ionizing tracks. Q-Pix offers the ability to extract all track information providing very detailed track profiles and also utilizes a dynamically established network for DAQ for exceptional resilience against single point failures. A number of novel ideas could be pursued to allow the Q-Pix design to be an integrated tracking/photo-detector. One such more speculative notion is the exploration of coating the dielectric surface with a type of photo-conductor which would respond to the VUV light incident on the surface. When struck by a VUV photon, the photoconductor would have electrons elevated into the conduction band and move in the electric field toward a pixel button. Initial R&D and simulation work on the Q-Pix concept will be presented in this work.
Wednesday April 14 2021 at **4pm**
Nedaa Alexandra Asbah (Harvard)
Evidence of the four-top-quark production at the LHC
A summary of the latest results on the evidence of the four-top-quark production using proton-proton collision data at a centre of-mass energy of 13 TeV collected by the ATLAS detector at the Large Hadron Collider with an integrated luminosity of 139 fb−1. Events are selected if they contain a same-sign lepton (electron or a muon) pair or at least three leptons (2lSS/3l) or a single lepton or an opposite-sign lepton pair (1l/2lOS). A multivariate technique is used to discriminate between signal and background events in the signal rich regions. The combined four top-quark production cross section is measured to be 24 +7/−6 fb, with a corresponding observed (expected) signal significance of 4.7 (2.6) standard deviations over the background-only predictions. It is consistent within 2.0 standard deviations with the Standard Model expectation of 12.0 ± 2.4 fb.
Wednesday xxx 2021 at **4pm**
Indara Suarez (Boston University)
CMS SUSY searches for stop and electroweakinos

(Dates to avoid are in 2021 March 24, April 21, Sept 8, Oct 13, Nov 10, Dec 8, In 2022 avoid Jan 19, Feb 9, Mar 16, Apr 1 due to colloquium schedule.)