High Energy Physics Seminars

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Meeting ID: 922 8790 9487
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Wednesday, January 6, 2021
4:00 PM
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ABSTRACT:

Direct decays of proposed heavy force mediator particles to standard model leptons
have been largely excluded by past LHC searches, challenging theorists to explore more complex
decay chains. We begin our search with a framework model of a Leptophobic Z' cascading to a
pair anomalons, new Beyond the Standard Model fermions. These heavy intermediate particles decay in turn to neutral standard model bosons and a stable anomalon, which appears in the Compact Muon Solenoid (CMS) detector as missing transverse momentum (pT-miss). From a model independent point of view, this topology creates an interesting structure with a resonantly produced particle cascading to a final state with 2 missing particles, with each level of the cascade including new particles with unknown masses. To turn this into a bump hunt for the resonant particle, we employ Recursive Jigsaw Reconstruction (RJR), a rule-based methodology to systematically reduce degrees of freedom, allowing for the calculation of mass estimators at each level of our decay chain. RJR is an example of how analysis tools are evolving to be sensitive to the most well-hidden of new physics, and the detectors are doing the same. I will also give an overview of the Phase I upgrade to the CMS Hadronic Calorimeter.

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Wednesday, December 2, 2020
4:00 PM
Physics Building, Room 204

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"New physics searches in ATLAS"


Boping Chen , Iowa State University
[Host: Chris Neu]
ABSTRACT:

Standard Model(SM) is a very successful theory in particle physics, which can explain most of the high energy experiment. However, still there are many open questions for the SM, such as dark matter, dark energy and gravity interaction. One of the main goal for both ATLAS and CMS detector in LHC is to search for the new physics beyond the Standard model, to give us some hint for those open questions. This talk presents two analyses for the new physics search: 1: Search for the heavy resonance Z' decaying into a Higgs boson and a photon; 2: Search for lepton flavor violation Z->emu decay. Both of these two analyses use proton proton collision data set collected by ATLAS detector from 2015 to 2018. This talk also covers some upgrade study for the ATLAS inner tracker.

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Monday, November 23, 2020
4:00 PM
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ABSTRACT:

The most abundant objects produced in high-energy proton-proton collisions at the LHC are jets which are reconstructed from topologically associated energy depositions in calorimeter cells, charged-particle tracks, or simulated particles. Ideally, jets are corrected due to the intrinsic limitations of the detector system. In CMS, reconstructed jets are calibrated by using a factorized approach. This seminar will present two analyses related to jet energy scale corrections focus on the low pT region. The first part of the talk is dedicated to the Monte Carlo (MC) truth jet energy corrections for no pileup QCD PYTHIA8 sample. The study is performed using the anti-kT clustering algorithm with a distance parameter R = 0.4 in the pseudorapidity range |η| < 5.191 for jet transverse momentum 10 < pT < 905 GeV. The second part presents the calibration of the jet energy scale with respect to residual differences between data and simulation after simulation-based pre-calibrations are applied. In this analysis, low pile-up data collected by the CMS experiment in 2015 at a center-of-mass energy of 13 TeV are used. The correction factors depending on jet pT and η are derived by using two different methods based on the dijet final states in the region of |η| < 5.191 pseudorapidity and 20 < pT < 114 GeV. This will make an important contribution to the physics analysis to be performed using the low pT jets. In addition, previous physics analysis, and activities at the Phase-1 Upgrade of the CMS Hadron Calorimeter will be also presented.

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Wednesday, November 18, 2020
4:00 PM
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ABSTRACT:

The production cross-section of top quark pairs in association with a photon is measured in lepton + jets final state events during proton-proton collisions at LHC 13TeV energy using the full Run II data collected by CMS with the total integrated luminosity of  137 fb-1. The study of top quark pair production in association with a photon provides us with important information on top quark electroweak coupling. It is also sensitive to beyond the Standard Model. The analysis is done in a semi leptonic decay channel with a well isolated high Pt lepton, at least four jets from the hadronization of quarks, and an isolated photon. The photons may be emitted from initial state radiation, top quarks, and decay products of top quarks. The simultaneous maximum likelihood fitting of several control regions and kinematic observables is done extensively and carefully to distinguish the ttγ signal process from various backgrounds. The inclusive cross section of ttγ process is measured for a photon with the transverse momentum Pt ≥ 20 GeV.

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Wednesday, November 11, 2020
4:00 PM
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"Search for Displaced Leptons & Beam Tests for the CMS Pixel Detector Upgrade"


Bryan Cardwell , Ohio State University
[Host: Chris Neu]
ABSTRACT:

I present the two foci of my graduate research: a search for long-lived beyond-the-Standard-Model particles and R&D for the high-luminosity upgrade of the CMS pixel detector. First, I discuss the search for long-lived particles, which is performed in over 100 fb-1 of 13 TeV proton-proton collision data collected by the CMS experiment and uses electron and muon transverse impact parameter to identify displaced leptons, an exotic signature that is not covered by traditional analyses. In the second portion of the talk, I discuss the upcoming CMS silicon pixel detector upgrade, which will result in significant improvements in both functionality and radiation tolerance to stand up to the unprecedented particle flux and radiation dose of the High-Luminosity LHC. The discussion will focus on beam tests of prototype sensors and readout chips performed at the Fermilab Test Beam Facility.

VIDEO:
Special HEP seminar

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Thursday, November 5, 2020
4:00 PM
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"Gravitational wave memory effects in Brans-Dicke theory"


Shammi Tahura , University of Virginia - Department of Physics
[Host: Kent Yagi]
ABSTRACT:

When gravitational waves pass through observers located far away from the source, they cause oscillatory distortions of the separations among the observers. There is one more interesting phenomenon that the gravitational waves can create lasting relative displacements of the observers, which is called the gravitational wave memory effect. Such effects are closely related to infrared properties of gravity and other massless field theories, including their asymptotic symmetries and conserved quantities. In this talk, I will present the Brans-Dicke theory in Bondi-Sachs form, discussing asymptotic symmetries, conserved charges, and the gravitational wave memory effects.

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Wednesday, November 4, 2020
3:30 PM
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"Latest Oscillation Results Combining Neutrino and Antineutrino Data from the NOvA Experiment"


Michael Baird , University of Virginia - Department of Physics
[Host: Craig Dukes]
ABSTRACT:

The NOvA experiment is a long-baseline neutrino oscillation experiment that uses the NuMI beam from Fermilab to detect both electron and muon flavored neutrinos in a Near Detector, located at Fermilab, and a Far Detector, located at Ash River, Minnesota. NOvA’s primary physics goals include precision measurements of neutrino oscillation parameters, such as θ23 and the atmospheric mass- squared splitting, along with probes of the mass hierarchy and the CP violating phase. This talk will present the latest NOvA results using a combined neutrino and anti-neutrino dataset based on a beam exposure of approximately 13 × 1020 protons-on-target in each dataset.

VIDEO:
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Wednesday, October 28, 2020
4:00 PM
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"Heavy or dark photon searches at Jefferson Lab"


Stepan Stepanyan , JLAB
[Host: Craig Dukes]
ABSTRACT:
The overwhelming evidence for dark matter (DM) in cosmological observations, manifested by its gravitational interactions, has inspired a major experimental effort to uncover its particle nature. The LHC, as well as direct and indirect detection experiments, have significantly constrained one of the best-motivated weak-scale DM models (WIMPs as dark matter candidates). In contrast, scenarios involving a light hidden sector dark matter with mediators in the MeV-GeV range has garnered a good deal of attention. Models with a hidden U(1) gauge symmetry, with a "dark" or "hidden sector" photons, are particularly attractive as they can be tested experimentally. If they exist, dark or heavy photons mix with ordinary photons through kinetic mixing, which induces their weak coupling to electrons, ∈e. Since they couple to electrons, heavy photons are radiated in electron scattering and can subsequently decay into e+e-. Experiments at Jefferson Lab use these features to search for heavy photons in the mass range of 20 MeV/c2 to 500 MeV/c2 and couplings of ∈2 > 10 -10 .
In this talk, I will summarize the experimental program for dark photon searches at Jefferson Lab. Results from the experiments that already took data, APEX and HPS, will be discussed together with plans for future measurements.

 

 

 

VIDEO:
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Wednesday, October 14, 2020
4:00 PM
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ABSTRACT:

In 1970 L.  Alvarez et al. reported on the first experiment to use cosmic-ray muons to investigate the interior of a very large structure. That structure was Khafre's Pyramid at Giza.  In 2017, the Scan Pyramids team reported on the discovery of a new large void in the Great Pyramid (Khufu).  Although they used modern equipment, their system was not much larger than the one used by Alvarez's team. In order for the technique of cosmic-ray muon tomography to be able to answer detailed questions regarding the core structure of these enormous creations, a new approach must be taken.  The Exploring the Great Pyramid (EGP) Mission will use detector technology currently deployed in high-energy physics experiments to field very large muon telescopes outside of the Great Pyramid.  This will allow for a high-resolution study of almost all of its internal structure. It will go beyond simply looking for voids, but will potentially yield new information on the building techniques used to construct the Great Pyramid.  In this talk, I will review previous experiments, describe in detail the techniques the EGP Mission proposes to use and present preliminary simulation results.

 

VIDEO:
High Energy
Wednesday, March 4, 2020
4:00 PM
Physics Building, Room 204

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ABSTRACT:

The Muon-to-Electron-Conversion (Mu2e) Experiment is a high-precision, intensity-frontier experiment being developed at Fermilab which will search for coherent, neutrino-less muon to electron conversion in the presence of an atomic nucleus. Such a process would exhibit charged lepton flavor violation (CLFV), which has not yet been observed. Continuing the search for CLFV, Mu2e will improve the sensitivity by four orders of magnitude over the present limits. In the search for beyond the standard model (BSM) physics, Mu2e is uniquely sensitive to a wide range of models by indirectly probing mass scales up to the energy scale of 104 TeV. While muon-to-electron-conversion is permissible through neutrino oscillations in an extension of the standard model, the rate is extremely low at about one event in 1054. By design, the background for the experiment will be well-understood and kept at a sub-event level, which results in the observation of muon-to-electron conversion as direct confirmation of BSM physics. The largest background comes from processes initiated by cosmic-ray muons, which will produce approximately one CLFV-like event per day. In order to reduce this rate to less than one event over the lifetime of the experiment a large and highly efficient cosmic ray veto (CRV) detector is needed. The CRV will cover the experimental apparatus with an area of approximately 330 m2. The overall efficiency must be no les than 99.99%, a requirement that must be maintained in the presence of intense backgrounds produced by proton and muon beams. The detector employs long scintillator strips with embedded wavelength shifting fibers, read out using silicon photomultipliers. Key features of the talk involve the design, fabrication, and performance of the CRV, along with an overview of the Mu2e experiment.

Special Seminar


Monday, January 27, 2020
3:30 PM
Physics Building, Room 204
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"Precision timing with the CMS MIP timing detector and search for new particle production at the LHC "


Matt Joyce , University of Virginia - Department of Physics
[Host: Brad Cox]
ABSTRACT:

The Compact Muon Solenoid (CMS) detector at the CERN Large Hadron Collider (LHC) is undergoing an extensive Phase II upgrade program to prepare for the challenging conditions of the High-Luminosity LHC (HL-LHC). In particular, a new timing layer will measure minimum ionizing particles (MIPs) with a time resolution of ~30ps and hermetic coverage up to a pseudo-rapidity of |η|=3. This MIP Timing Detector (MTD) will consist of a central barrel region based on LYSO:Ce crystals read out with SiPMs and two end-caps instrumented with radiation-tolerant Low Gain Avalanche Diodes. The precision time information from the MTD will reduce the effects of the high levels of pile-up expected at the HL-LHC and will bring new and unique capabilities to the CMS detector. The time information assigned to each track will enable the use of 4D reconstruction algorithms and will further discriminate interaction vertices within the same bunch crossing to recover the track purity of vertices in current LHC conditions.  We present motivations for precision timing at the HL-LHC and the ongoing MTD R&D targeting enhanced timing performance and radiation tolerance for the barrel layer components.  We will also describe the progress of our search for new physics in final states with two photons and missing transverse energy using the full Run2 dataset.  

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