Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session X18: Electroweak and Standard Model Physics IILive
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Sponsoring Units: DPF Chair: Lindsey Gray, Fermilab |
Tuesday, April 20, 2021 10:45AM - 10:57AM Live |
X18.00001: Search for vector boson scattering in semi-leptonic final states Jay Lawhorn A search for electroweak production of WW, WZ, and ZZ boson pairs in association with two jets in proton-proton collisions at $\sqrt{s} = 13$ TeV at the LHC is presented. The data sample corresponds to an integrated luminosity of 137 fb$^{-1}$ collected with the CMS detector. Events are selected by requiring two jets with large rapidity separation and invariant mass, one or two leptons, and a W or Z boson decaying hadronically. Limits on the Standard Model electroweak production cross section and parameters of quartic vector boson interactions in the framework of dimension-8 effective field theory operators are reported. [Preview Abstract] |
Tuesday, April 20, 2021 10:57AM - 11:09AM Live |
X18.00002: Study of Longitudinally Polarized Vector Boson Scattering Fractions in Semileptonic VBS Decays at the HL-LHC Jennifer Roloff, Marc-Andre Pleier, Lailin Xu, Viviana Cavaliere Longitudinal vector boson scattering (VBS) provides an important probe of electroweak symmetry breaking, bringing sensitivity to physics beyond the Standard Model as well as constraining properties of the Higgs boson. Despite its importance, it is challenging to study, due to the low cross section and difficulties in distinguishing between the different polarization states. While there have been some studies of the prospects for measuring VBS of longitudinally polarized W bosons ($W_{L}W_{L}$) production in the fully leptonic final state, little has been said about the semi-leptonic final state. While the backgrounds are larger in the semi-leptonic case, the signal cross section is also higher due to the enhanced branching fraction. It also provides different handles for determining the polarization through full reconstruction of the event kinematics using the W boson mass constraint and through the use of jet substructure. This talk will discuss the prospects for the search of semi-leptonic VBS production of $W_{L}W_{L}$ at the HL-LHC. [Preview Abstract] |
Tuesday, April 20, 2021 11:09AM - 11:21AM Live |
X18.00003: NNLO single-top-quark production and decay: Discrepancies resolved, PDFs challenged Zack Sullivan, John Campbell, Tobias Neumann We present our recent NNLO calculation of t-channel single-top-quark production and decay that resolves a disagreement between two previous calculations whose size at the inclusive level was comparable to the NNLO correction itself, and was even larger differentially. Moving beyond those comparisons, we have included b-quark tagging to allow for comparison with experiment, and added the ability to use double deep inelastic scattering (DDIS) scales ($\mu^2=Q^2$ for the light-quark line and $\mu^2=Q^2+m_t^2$ for the heavy-quark line) that allow for direct testing of parton distribution function (PDF) stability. All code will be made publicly available in MCFM. We demonstrate that several characteristic fiducial and differential standard model observables, and observables sensitive to new physics, are stable between NLO and NNLO, but point out there is a sizable difference in the prediction of some exclusive t+n-jet cross sections. Finally, we use this calculation to present preliminary results which indicate that some commonly used PDF sets are in significant disagreement, both with each other and with themselves between perturbative orders when evaluated at Tevatron energies. [Preview Abstract] |
Tuesday, April 20, 2021 11:21AM - 11:33AM Live |
X18.00004: Search for single-top quark production in association with a photon in pp collisions with the ATLAS detector at the LHC Harish Potti Associated production of a single top quark and a photon ($tq\gamma$) is one of the rare processes predicted in the Standard Model. However, this process has not been observed yet. Cross-section of this process is sensitive to the top quark charge and its electric and magnetic dipole moments. In this talk, I will outline the first-ever ATLAS search for the $tq\gamma$ production performed with 139 fb$^{-1}$ of $pp$ collision data collected by the ATLAS detector at the LHC at $\sqrt{s}$ = 13 TeV. Expected results from this search will be presented. [Preview Abstract] |
Tuesday, April 20, 2021 11:33AM - 11:45AM Live |
X18.00005: Turning Light Into Matter: First Physics Results Using ATLAS Forward Proton Jesse Liu What happens when we collide light at the most extreme laboratory energies? A hallmark of LHC photon collisions is that incident protons can stay intact as light collides and turns into matter-antimatter. This remarkable phenomenon is observed with a significance exceeding $5\sigma$ in the first physics results using a novel instrument installed in 2017 called the ATLAS Forward Proton spectrometer. The analysis pioneers new data-driven calibration, background estimation and proton reconstruction techniques in $pp$ collisions at $\sqrt{s}=$ 13 TeV with the ATLAS detector. This enables the first fiducial cross-section measurements of forward proton scattering when dielectron and dimuon pairs are produced via photon fusion $(\gamma\gamma\to\ell\ell)+p$. Directly measuring the intact proton resolves a long-standing question in non-perturbative dynamics about how often protons scattered down the beam pipe survive such processes. The proton-tagging techniques introduced to ATLAS open novel tests of QED at unprecedented energies and searches for new phenomena such as dark matter using the LHC as a photon collider. Based on Phys. Rev. Lett. 125 (2020) 261801 [Preview Abstract] |
Tuesday, April 20, 2021 11:45AM - 11:57AM Live |
X18.00006: Search for four-top production in CMS using the latest collision data (2016 - 2018) Nicholas Manganelli The production of four top quarks is predicted by the Standard Model with a cross-section of 12fb, 69,000 times rarer than top-antitop production, and has not yet been observed. With the high invariant mass of the system and multiple decay channels, the process produces distinct signatures including 4 b-jets and multiple lighter-quark jets (up to 8 in the all-hadronic decay) and massive leptons (up to 4 in the all-semi-leptonic decay). The latest results from CMS for 2016 to 2018 data taking at the LHC are presented, with a focus on non Semi-Leptonic decays. [Preview Abstract] |
Tuesday, April 20, 2021 11:57AM - 12:09PM Live |
X18.00007: WZ + Heavy Flavor Production in Proton-Proton Collisions at $\sqrt{s}$ = 13 TeV with the ATLAS Detector Aaron Webb WZ + heavy flavor is a significant background for many physics processes but is difficult to accurately simulate. While WZ production has been measured extensively, the production of WZ with an associated heavy flavor jet remains poorly understood. We perform a measurement of this process in the fully leptonic channel using 140 fb$^{-1}$ of proton-proton collision data collected by the ATLAS detector at the LHC. We present an overview of the analysis techniques used to make this measurement, as well as the results of the analysis. [Preview Abstract] |
Tuesday, April 20, 2021 12:09PM - 12:21PM Live |
X18.00008: Reactor CEνNS Physics Reach with an SBC Liquid Argon Bubble Chamber Noah Lamb The large flux of ~MeV neutrinos that nuclear reactors generate offer an excellent opportunity to study Coherent Elastic neutrino-Nucleus Scattering (CEνNS), but reactors also produce significant backgrounds. The Scintillating Bubble Chamber (SBC) collaboration is currently constructing a 10-kg liquid argon scintillating bubble chamber at Fermilab. The detector’s target threshold is 100 eV in order to demonstrate sensitivities to sub-keV nuclear recoils while remaining highly insensitive to electron recoil backgrounds. This talk presents a physics reach analysis of such a detector for reactor CEνNS experiments. Specifically, for studying the sensitivities to the weak mixing angle, neutrino magnetic moment, and a light Z gauge boson mediator. Monte Carlo simulations assess the background’s contribution to the signal, and silicon photomultipliers (SiPM) can measure scintillation light to maximize background rejection. Nearly mono-energetic photoneutron sources can calibrate the detector for nuclear recoils below 8 keV and gamma sources can use Thomson scattering to probe the nucleation efficiency function near the target threshold. [Preview Abstract] |
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