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 Q19: Flavor and BSM New PhysicsLive
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Sponsoring Units: DPF Chair: Linda Carpenter, Ohio State |
Monday, April 19, 2021 10:45AM - 10:57AM Live |
Q19.00001: Search for Charmed Baryons Oscillations at Belle Tianping Gu, Vladimir Savinov We search for baryon number violation in $B$ decays to pairs of charmed baryons and report the results based on the full Belle data sample. We interpret our measurement in terms of charmed baryons-antibaryons oscillations, which is a promising pathway to explain the missing piece in Sakharov's three conditions for baryogenesis. We outline the analysis procedure, background suppression optimization, data-based calibration approach, and present preliminary results for oscillation frequency and, alternatively, for baryon number violating branching fraction. [Preview Abstract] |
Monday, April 19, 2021 10:57AM - 11:09AM Live |
Q19.00002: Testing Lepton Flavor Universality With High Mass Dilepton Events Using the CMS Run 2 Dataset Minxi Yang Searches for new physics beyond standard model in high-mass dilepton final states is an important part of the CMS physics program. Recently, hints of lepton flavor universality (LFU) violation were observed in the measurements of the branching fractions of B meson decays to Kaons and dilepton pairs. This created interest in performing complementary studies in high-mass dilepton events. In our analysis, LFU is tested by calculating the dimuon to dielectron invariant mass ratio at high dilepton invariant mass with 137 fb-1 of data at sqrt(s) $=$ 13 TeV. The ratio is corrected for the difference in acceptance and efficiency of two muons and electrons and are unfolded to particle level. This is the first direct measurement of this flavor ratio at the LHC. The result is in agreement with the expectation from the SM. [Preview Abstract] |
Monday, April 19, 2021 11:09AM - 11:21AM Live |
Q19.00003: Density Matrix Evaluation of nn' Oscillations and the Neutron Lifetime Anomaly James Ternullo The neutron () lifetime ``anomaly'' is an unexplained difference in measurements of the neutron lifetime between two precision measurements. The cold neutron (CN) beam experiment, from NIST in 2013, measured a 888.7 s. This value is higher than the lifetime measured using ultracold neutrons (UCN) by the UCNA$\tau $ experiment in Los Alamos, 879.4 s. As an explanation for this difference, Z. Berezhiani proposed that in the beam experiment could oscillate into \textit{sterile} (mirror) neutrons which belong to a parallel, hidden, dark, mirror sector. The would then decay through an invisible mirror channel within the dark sector, artificially increasing the apparent , thus providing an explanation for the apparently missing decays in the NIST experiment. Berezhiani has shown that transformations in magnetic field can be amplified due to Landau-Zener transitions, where a small mass splitting between and is compensated by the applied magnetic field. To explain the anomalous 1{\%} difference in , Berezhiani predicted a range of possible mixing angles of the system, and plotted them vs in the range . In this study we reproduce the results of these previously published calculations and extend them to the region of using the density matrix evolution technique. This produces an extended limit for transformation in terms of and parameters that can be challenged by a new search being performed with a cold neutron beam at ORNL. [Preview Abstract] |
Monday, April 19, 2021 11:21AM - 11:33AM Live |
Q19.00004: Sensitivities to neutrino non-standard interactions at the NOvA experiment Luiz Ricardo Prais Investigations of the existence of the so called Physics Beyond the Standard Model is a subject of growing interest and effort in the field of particle physics. Interactions of neutrinos with matter are well described by the Standard Model, however in the presence of new physics, additional phenomena regarding neutrino properties would be possible, including non-standard interactions (NSI) of neutrinos with matter. The NOvA experiment, at Fermilab, has been investigating neutrino oscillations through studies of $\nu_{\mu}$ and $\bar{\nu}_{\mu}$ produced at the Fermilab accelerator facilities, and we present the status of the sensitivities to Neutral Current-like NSI (NC-NSI) through analysis of the disappearance of muon (anti)neutrinos during their evolution in the NOvA 810 km baseline. We assess the effects of the NC-NSI flavor-changing parameters $\left|\varepsilon_{\mu\tau}\right|$ and $\delta_{\mu\tau}$ on the determination of the standard oscillation parameters $\sin^{2}\left(\theta_{23}\right)$ and $\Delta m_{32}^{2}$, as well as the relation between each parameter, for both neutrino mass hierarchies, using a combined exposure of $9.48\times10^{20}$ POT for a simulated neutrino beam, and $12.33\times10^{20}$ POT for a simulated antineutrino beam. [Preview Abstract] |
Monday, April 19, 2021 11:33AM - 11:45AM Live |
Q19.00005: Searching for Non-Standard Interactions Through IceCube Neutrino Fluxes Grant Parker The IceCube neutrino observatory is a kiloton-scale Cherenkov detector located several kilometers beneath the surface of the South Pole. Sensitive to atmospheric and astrophysical neutrino signals of energies on the order of GeV to PeV, IceCube has the capacity to investigate theorized neutrino-nucleus interactions not described by the Standard Model (non-standard interactions, or NSI). This is possible through analysis of deviations from predicted neutrino fluxes in patterns that can be derived from a generalized NSI model. One such analysis uses 8 years of data within the energy range of ~500 GeV to ~10 TeV, and we report here the methods and progress of the project. [Preview Abstract] |
Monday, April 19, 2021 11:45AM - 11:57AM Live |
Q19.00006: CP violation in Standard Model Effective Field Theory: C vs P violation Jun Shi, Susan Gardner It has long been thought that the observed size of the cosmic baryon asymmetry suggests that mechanisms of CP violation beyond the Standard Model should exist. Standard Model Effective Field Theory (SMEFT) is a useful way of classifying new CP-violating sources at low energy from underlying new physics effects. We present the results of our study of leading-mass-dimension CP-violating operators from SMEFT, carefully separating operators that are P-odd from those that are C-odd just below the electroweak scale. The P-odd and CP-odd effective operators that generate permanent electric dipole moments (EDM) have been much investigated; we now consider C-odd and CP-odd operators systematically as well. We emphasize that for flavor-conserving interactions, the lowest-mass-dimension CP-odd operators from SMEFT which are also C-odd, such as those contributing to mirror-symmetry breaking in the Dalitz plot in $\eta\to \pi^+\pi^-\pi^0$ decay, and those which are P-odd, such as those constrained by permanent EDM searches, are completely different, and we analyze the consequences explicitly. [Preview Abstract] |
Monday, April 19, 2021 11:57AM - 12:09PM Live |
Q19.00007: Graph Neural Network to Measure Four-top Production with the ATLAS Detector Ryan Roberts The ATLAS collaboration recently published evidence for the production of four top quarks at the $4.3\sigma$ level in $pp$ collisions at $\sqrt{s}=$ 13 TeV with the ATLAS detector. This rare high energy process is sensitive to a number of scenarios for physics beyond the Standard Model, including modifications to the coupling of the Higgs boson to the top quark. A major challenge to improving the sensitivity of this analysis is that the signal and main backgrounds both involve the production of multiple top quarks and therefore have very similar event topology. We present a novel application of a Graph Neural Network (GNN) for the measurement of four top quark production. The GNN-based event classification leverages deep learning and graph representation of collision data to provide significant performance improvement over other classifiers, including Boosted Decision Trees. The use of this GNN in the ATLAS four-top measurement will significantly improve the experimental sensitivity to both the Standard Model signal and possible effects from beyond the Standard Model. [Preview Abstract] |
Monday, April 19, 2021 12:09PM - 12:21PM Live |
Q19.00008: Search for Charged Lepton Flavor Violation at the Electron-Ion Collider Jinlong Zhang, Abhay Deshpande, Ciprian Gal, Jin Huang, Krishna Kumar, Yuxiang Zhao In the Standard Model of Physics (SM) associated with every conservation law there exists a symmetry. While no such symmetry associated with conservation of charge lepton flavors (CLF) has been identified, we still have not observed its experimental violation.Evidence for CLF violation (CLFV) would hence mean existence of physics Beyond the SM (BSM) and is of high interest. The recently approved Electron-Ion Collider (EIC) at BNL with 100-1000 times higher high luminosity than HERA (at DESY, German) will provide a unique new opportunity for such a search. In contrast with the CLFV transition between the $e$ and $\mu$ for which very stringent limits exist, there is still relatively large discovery space for the CLFV transition between the $e$ and $\tau$ within EIC’s reach. With the modern detector designed for the EIC, $\tau$s created in e-p scattering at the EIC are expected to be identified with high efficiency. In this talk, we will present results from an ongoing study of sensitivity possible for $e \rightarrow \tau$ conversion in e-p scattering at the EIC. [Preview Abstract] |
Monday, April 19, 2021 12:21PM - 12:33PM Live |
Q19.00009: Search for paired diphoton resonances using Machine Learning techniques Steven Clark, Marc Osherson, Eva Halkiadakis, Scott Thomas We describe a general search for the production of new Beyond Standard Model resonances in a multiphoton final state. The analysis uses data collected with the CMS detector at the CERN LHC from proton-proton collisions at a center-of-mass energy of 13 TeV. The benchmark signal model considered is in an extended higgs sector which has an approximate global symmetry and spontaneous symmetry breaking, resulting in two new scalar particles. The heavier of these ($X$) has a large branching fraction to the lighter ($a$), which has Higgs-like couplings. This search focuses on the process $X\to aa\to (\gamma\gamma)(\gamma\gamma)$ and on the region where the relative mass of the new particles results in final-state photons that have little separation and cannot be reconstructed with standard reconstruction algorithms. Thus, we develop novel Machine Learning methods in the form of Convolutional Neural Networks (CNN) to identify these merged multiphoton objects. The CNNs are used to identify merged pairs of photons and reconstruct the invariant mass of the pair. The network inputs are images created from energy deposits in the electromagnetic calorimeter. Initial results show the CNNs have strong discriminating power and we are able to well reconstruct the mass spectra of both resonances. [Preview Abstract] |
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