Session G07: Beyond the Standard Model II

A Search for Ultra-heavy Resonances Decaying to Vector-like Quark Pairs at the Run 2 CMS Experiment

Diquarks are a class of ultra-heavy resonances that can theoretically be produced at the Large Hadron Collider with relatively large cross-sections and could provide explanations for a number of curious high-mass events reconstructed at the CMS Experiment during the Run 2 data-taking period. In theories where diquarks decay to pairs of vector-like quarks (VLQs), the resulting hadronic final state kinematics are highly complex, and new analysis techniques are needed to study these in a comprehensive way. Presented is a novel technique that uses event geometry and a series of Lorentz boosts to reach the approximate center-of-mass frames of the diquark and each VLQ in order to reconstruct their respective masses.   

Search for Pair-Produced Vector-Like Quarks in the All-Hadronic Final State using the Boosted Event Shape Tagger with Full Run 2 Data Collected by CMS

We present a search for hadronically-decaying pair-produced vector-like quarks (T/B) in data collected by the CMS detector during the Run 2 data taking period. The analysis is performed using the Boosted Event Shape Tagger (BEST): a multi-class jet tagger optimized for the boosted heavy particle final state jets. We train a neural-net-based tagger to identify high momentum, large-radius jets as originating from one of six particle classes: QCD (light jets), bottom, W, Z, Higgs, and top. Data are triggered on high calorimeter activity, requiring events with a scalar sum of jet transverse momenta of at least 1600 $\GeV$. The dominant multi-jet background is estimated from a data-driven process in a QCD-rich three-jet region. The signal regions are categorized based on the classification of the four leading jets of the event. A statistical analysis is performed simultaneously across all regions and compared to the standard model only hypothesis.   

TT -> Wb+X VLQ Pair Production

The Standard Model (SM) of particle physics explains many natural phenomena yet remains incomplete. Vector-like quarks (VLQs) lie at the heart of many extensions to the SM seeking to address the hierarchy prob- lem. VLQs could be produced either singly or in pairs, and then decay to a SM boson and a third-generation quark. While single-production depends on the coupling of the VLQ to the SM particles, pair-production via the QCD interaction provides a model-independent test for VLQs. This talk presents a search for pair- produced VLQs that decay into a W boson and a bottom quark, with one W decaying leptonically while the other decays hadronically. The analysis uses b-tagging algorithms, charge asymmetry metrics, multiple on- line triggers, and data driven corrections of the ttbar and W+jets background Monte Carlo samples to improve sensitivity during the analysis of the full LHC Run 2 ATLAS dataset.   

Baryon Number Violation Involving Tauons

Baryon number violation is our most sensitive probe of physics beyond the Standard Model, especially through the study of nucleon decays. Angular momentum conservation requires a lepton in the final state of such decays, kinematically restricted to electrons, muons, or neutrinos. We show that operators involving tauons, which are at first sight too heavy to play a role in nucleon decays, still lead to clean nucleon decay channels with tau neutrinos.   

An alternative form of supersymmetry with reduced cross-sections and modified experimental signatures

There is a convincing case for some form of supersymmetry, but conventional supersymmetry (SUSY) has been plagued by many unsolved theoretical difficulties since its inception half a century ago. Even more importantly, not a single SUSY superpartner has been observed up to surprisingly high experimental limits. These failures suggest that it is appropriate to rethink the meaning of supersymmetry at the most fundamental level. Here we consider a radically different form of supersymmetry (called susy here to avoid confusion), which initially combines standard Weyl fermion fields and primitive (unphysical) boson fields. A stable vacuum then requires that the initial boson fields, whose excitations would have negative energy, be transformed into three kinds of scalar-boson fields: the usual complex fields $\phi$, auxiliary fields $F$, and real fields $\varphi$ of a new kind (with degrees of freedom and gauge invariance preserved under the transformation). The requirement of a stable vacuum thus imposes Lorentz invariance, and also immediately breaks the initial susy -- whereas the breaking of conventional SUSY has long been a formidable difficulty. Even more importantly, for future experimental success, the present formulation may explain why no superpartners have yet been identified: Embedded in an $SO(10)$ grand-unified description, most of the conventional processes for production, decay, and detection of sfermions are excluded, and the same is true for many processes involving gauginos and higgsinos. This implies that superpartners with masses $\sim 1$ TeV may exist, but with reduced cross-sections and modified experimental signatures. For example, a top squark (as redefined here) will not decay at all, but can radiate pairs of gauge bosons and will also leave straight tracks through second-order (electromagnetic, weak, strong, and Higgs) interactions with detectors. The predictions of the present theory include (1)~the dark matter candidate of our previous papers, (2)~many new fermions with masses not far above 1 TeV, and (3)~the full range of superpartners with a modified phenomenology.   

Search for R-parity violating and stealth supersymmetry in the all-hadronic final state with the CMS detector.

Typical SUSY searches look for large MET in the collisions. However, certain models of SUSY predict low-MET signatures while still providing a natural solution to the hierarchy problem, and completely evade the strong experimental bounds from high-MET searches. We consider stealth as well as R-parity violating models where the chargino-neutralino are degenerate in mass, and give boosted AK8 jets in the final state. These models generate low-MET and we will focus on fully hadronic signatures of W/Z/H bosons. We report the results of preliminary studies for the sensitivity of the CMS experiment in combined Run 2 and Run 3 dataset.   

Evaluating Flavor Tagging Systematic Uncertainties in SUSY Long Lived Particle Decays

A method is presented to evaluate systematic uncertainties pertaining to flavor tagging of b-jets originating from long lived particle decays. The method is based on extrapolation of systematic uncertainties derived for prompt b-jets from top quark decays to the non-prompt case using jet variable parameterizations. Using this method, the overall flavor tagging systematic uncertainties for ATLAS events due to hypothetical pair production of stop quarks decaying into a b-quark and hadronically decaying lightest neutralino in the R-parity violation scenario are evaluated.