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DOE OSTI2024

Taking aim at the wino-Higgsino plane with the LHC

In this work we explore multiple search strategies for Higgsinos and mixed Higgsino-wino states in the minimal supersymmetric Standard Model (MSSM) and project the results onto the ( μ , M 2 ) plane. Assuming associated production of Higgsino-like pairs with a W / Z boson, we develop a search in a channel characterized by a hadronically tagged vector boson accompanied by missing energy. We use as our template an ATLAS search for dark matter produced in association with a hadronically decaying vector boson, but upgrade the search by implementing a joint-likelihood analysis, binning the missing transverse energy distribution, which greatly improves the search sensitivity. For Higgsino-like states (more than 96% admixture) we find sensitivity to masses up to 550 GeV. For well-mixed Higgsino-wino states (70–30% Higgsino) we still find sensitivities above 300 GeV. Using this newly proposed search, we draw a phenomenological map of the wino-Higgsino parameter space, recasting several complementary searches for disappearing tracks, soft leptons, trileptons, and hadronic diboson events in order to predict LHC coverage of the ( μ , M 2 ) mass plane at integrated luminosities of up to 3 ab − 1 . Altogether, the full run of the HL-LHC can exclude much of the “natural” ( μ , M 2 < 500 GeV ) wino-Higgsino parameter space. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2024

Stau pairs from natural SUSY at high luminosity LHC

Natural supersymmetry (SUSY) with light Higgsinos is perhaps the most plausible of all weak scale SUSY models while a variety of motivations point to (right) tau sleptons as the lightest of all the sleptons. We examine a SUSY model line with rather light right staus embedded within natural SUSY. For light τ ˜ 1 of a few hundred GeV, the decays τ ˜ 1 → τ χ ˜ 1 , 2 0 and ν τ χ ˜ 1 − occur at comparable rates where the (Higgsino-like) χ ˜ 1 ± and χ ˜ 2 0 release only small visible energy: in this case, the expected τ + τ − + E T signature is diminished from the usual expectations due to the presence of the nearly invisible decay mode τ ˜ 1 → ν τ χ ˜ 1 − . However, once m τ ˜ 1 ≳ m ( b i n o ) , decays to binos such as τ ˜ 1 → τ χ ˜ 3 0 open up where χ ˜ 3 0 decays to Higgsinos plus W ± , Z 0 , and h at comparable rates. For these heavier staus, the stau pair production gives rise to diboson + E T events, which may contain 0, 1, or 2 additional hard τ leptons. From these considerations, we examine the potential for future discovery of tau-slepton pair production at a high-luminosity LHC. While we do not find a 5 σ HL-LHC discovery reach for 3000 fb − 1 , we do find a 95% CL exclusion reach, ranging between m τ ˜ 1 : 100 – 450 GeV for m χ ˜ 1 0 ∼ 100 GeV . This latter reach disappears for m χ ˜ 1 0 ≳ 200 GeV . Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2023

Search for new heavy resonances decaying to WW, WZ, ZZ, WH, or ZH boson pairs in the all-jets final state in proton-proton collisions at √s = 13 TeV

A search for new heavy resonances decaying to WW, WZ, ZZ, WH, or ZH boson pairs in the all-jets final state is presented. The analysis is based on proton-proton collision data recorded by the CMS detector in 2016–2018 at a centre-of-mass energy of 13 TeV at the CERN LHC, corresponding to an integrated luminosity of 138 fb –1 . The search is sensitive to resonances with masses between 1.3 and 6 TeV, decaying to bosons that are highly Lorentz-boosted such that each of the bosons forms a single large-radius jet. Machine learning techniques are employed to identify such jets. No significant excess over the estimated standard model background is observed. A maximum local significance of 3.6 standard deviations, corresponding to a global significance of 2.3 standard deviations, is observed at masses of 2.1 and 2.9 TeV. In a heavy vector triplet model, spin-1 Z' and W' resonances with masses below 4.8 TeV are excluded at the 95% confidence level (CL). These limits are the most stringent to date. In a bulk graviton model, spin-2 gravitons and spin-0 radions with masses below 1.4 and 2.7 TeV, respectively, are excluded at 95% CL. Production of heavy resonances through vector boson fusion is constrained with upper cross section limits at 95% CL as low as 0.1 fb.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Boson–Boson Interactions at the LHC

Vector boson scattering is a key production process to probe the electroweak symmetry breaking of the Standard Model and is one of the most important topics of the physics program for the HL-LHC since it involves both self-couplings of vector bosons and their coupling with the Higgs boson. If the Higgs mechanism is not the sole source of electroweak symmetry breaking, the scattering amplitude deviates from the Standard Model prediction at high scattering energy. Moreover, deviations may be detectable even if a New Physics scale is higher than the reach of direct searches. In this review, the most recent experimental measurements of the production cross sections of vector boson pairs in association with two jets in proton–proton collisions at $\sqrt{s}$ = 13 TeV at the LHC are reported, using data sets recorded by the ATLAS and CMS detectors. Applications to searches for New Physics, as well as prospects for measuring the electroweak vector boson scattering processes with larger data samples, are also summarized.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

"Experimental Research at the Energy Frontier in High Energy Physics" (Final Technical Report)

Recent developments in particle physics and cosmology raise the exciting prospect that we are on the threshold of a major step forward in our understanding of the universe. This proposal describes a research program at the University of Illinois in experimental high-energy physics on the ATLAS experiment at CERN’s Large Hadron Collider (LHC). Our group actively collaborates with the Theory Group and other experimental efforts within the Office of Science frontiers (energy, intensity, and cosmic) to search broadly in the ATLAS data to maximize our potential for scientifc discovery. The thrust of this proposal is to search for new physics using ATLAS data. Emphasis is placed on novel use of the Higgs boson as a tool to search for new particles and interactions and development of fast particle tracking systems for use in triggering. We propose to continue our strong role in FTK commissioning and operations. To maximize the impact and vitality of the proposed physics program through the HL-LHC running, we will lead firmware efforts in the HWTT Phase-II TDAQ upgrade, leveraging our expertise acquired through development of fast tracking hardware and firmware for the FTK system.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗