High Energy Physics Seminars

TBA

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TBA

The existence of dark matter has been long established through astrophysical and cosmological observations, yet we still do not know what it is made of. Direct detection experiments have extensively searched for dark matter particles above the proton mass for decades. However, recent technological developments have made it possible to look for lighter (sub-GeV) dark matter candidates with single-electron cameras. These “skipper” charged-coupled devices (CCDs) are used as both the target material and detector in the DAMIC-M experiment underneath the French Alps. We will discuss the status of the experiment and first results from the prototype Low Background Chamber installed at the Laboratories Souterrain de Modane.

Sterile Neutrinos occur in a wide variety of scenarios Beyond the Standard Model. In this talk, I'll go over some of the novel search strategies being employed to search for their existence. This will include terrestrial searches such as DUNE and IceCube, as well as satellite, and supernova data

The MEG experiment, conducted at the Paul Scherrer Institut in Zurich, Switzerland, achieved a significant milestone in 2016 by establishing the best current upper limit of 4.2 × 10⁻¹³ for the branching ratio of the µ− > eγ decay process. The search for this decay holds tremendous potential for uncovering extensions to the Standard Model, as its existence would unequivocally signify the presence of new physics. To further amplify our sensitivity by an order of magnitude, we embarked on the development and construction of an upgraded apparatus known as MEG II in subsequent years. After conducting an engineering run in 2020 with a reduced set of electronic channels, MEG II officially commenced physics data collection in the summer of 2021 and is currently opertional. In this presentation, I will offer an overview of the subdetectors' performances and share our analysis results from the initial data set gathered in 2021. MEG II is commited to maintaining data acquisition until 2026 as we strive to atain our ultimate goal. This seminar will also shed light on the current status and future prospects of MEG II, including our investigations into other exotic phenomena, such as the exploration of a potential 17.6 MeV/c² particle originating from the 7Li(p,e+e-)7Be reaction.

LHC still holds the promise for beyond standard model (BSM) physics hiding in the Higgs potential, which to date has no direct experimental evidence. The primary mechanism for experimentally determining the shape of the Higgs potential is to search for Higgs boson pair production, whose kinematics and cross section would be impacted by BSM strength tri-linear Higgs boson self-coupling from the Higgs potential. In this seminar I will describe the recent CMS search for VHH in the HH4b channel, which has been spearheaded by our group. The expected (observed) 95% confidence level bounds on the Higgs boson self-coupling are approximately ±30 (±37) times the SM expected coupling strength.  Bounds on the strength of the coupling of two Higgs bosons with two vector bosons will also be shown.

This presentation highlights the latest technology advancement on 3-dimensional position-sensitive room-temperature CdZnTe (CZT) semiconductor gamma-ray imaging spectrometers. Sustained advancement on CZT detector technology, including larger detection volume, digital application specific integrated circuits (H3DD-UM ASIC) and integrated electronic data acquisition systems will be described, as well as research and development on alternative semiconductor gamma-ray spectrometers. The applications of 3D CZT detectors will be summarized in national security, nuclear power industry, international nuclear safeguard and non-proliferation, space exploration, and medical imaging. The operational principle and unique capabilities will be introduced to explore potential applications in high-energy, particle and nuclear physics.

Low-energy searches for rare processes and fundamental symmetry violations provide one of the most promising avenues for discovering hints of new physics. The planning and interpretation of experiments which utilize nuclei as laboratories require input from non-perturbative QCD calculations, namely, lattice QCD. In this talk, I will present several ways in which lattice QCD can interplay with experimental low-energy searches for new physics, focusing on neutrino and dark matter physics. In particular, I will discuss results for nucleon charges, form factors, and sigma terms of relevance for neutrino scattering experiments and direct dark matter detection, as well as matrix elements relevant for neutrinoless double beta decay experiments. 

In this talk, I will briefly review the global effort in searching for axions, a hypothetical particle that can potentially address the strong CP problem, explain the nature of dark matter, and has deep connections with string theories. I will focus on a new resonance in the axion-photon system, axion magnetic resonance (AMR), that can greatly enhance the conversion rate between axions and photons. A series of axion search experiments rely on converting axions into photons inside a constant magnetic field background. A common bottleneck of such experiments is the conversion amplitude being suppressed by the axion mass when ma≳10−4 eV. I will show that a spatial or temporal variation in the magnetic field can cancel the difference between the photon dispersion relation and that of the axion, hence greatly enhancing the conversion probability. I will demonstrate that the enhancement can be achieved by both a helical magnetic field profile and a harmonic oscillation of the magnitude. Our approach can extend the projected ALPS II reach in the axion-photon coupling (gaγ) by two orders of magnitude at ma=10−3eV with moderate assumptions.

The Cryogenic Underground Observatory for Rare Events (CUORE) is a world leading cryogenic experiment searching for neutrinoless double beta decay (0vBB). CUORE is a one-tonne mass scale experiment, has been running since 2017, and has achieved statistics of one tonne-year worth of data taking. While no evidence of double beta decay has yet been found (with limit: T1/2 > 3.6 × 10^24 yr), CUORE can also be used to search for more exotic decay processes such as a triple proton decay. This talk will show how a data analysis framework built around machine learning can be used to classify different kinds of energy depositing events for counting experiments. A methodology which combines Poisson counting statistics with supervised classification machine learning tools is presented. Additionally, a sensitivity calculation is provided which uses the classification counting likelihood. Using the new analysis framework, we can achieve a preliminary lower 2σ half-life bound of 7.4×10^24yr for triple-proton decay of 130Te.

The snowball chamber is analogous to the bubble and cloud chambers in that it relies on a phase transition, but it is new to high-energy particle physics. The concept of the snowball chamber relies on supercooled water, which can remain metastable for long time periods in a sufficiently clean and smooth container (on the level of the critical radius for nucleation). The results gleaned from the first prototype setup (20 grams) will be reviewed, as well as plans for the future, with an eye to future deployment of a larger (kg-scale) device underground for direct detection of dark matter WIMPs (Weakly Interacting Massive Particles), with a special focus on low-mass (GeV-scale) WIMPs, capitalizing on the presence of Hydrogen, which could potentially also lead to world-leading sensitivity to spin-dependent-proton interactions for O(1 GeV/c^2)-mass WIMPs and coherent neutrino scattering. Supercooled water also has the potential advantage of a sub-keV energy threshold for nuclear recoils, but this remains an atmospheric chemistry prediction that must be verified by careful measurements.

Searches for long-lived particles (LLPs) with macroscopic decay lengths are a rapidly expanding frontier at the LHC and other collider experiments. Still, many gaps remain in the current search program, in particular for light LLPs with masses at the GeV or sub-GeV scale and with decay lengths on the order of meters. In this talk, I will illustrate approaches to filling this gap by discussing two models of light LLPs that naturally fall into this decay length regime and their signals at the LHC and at Belle II. First, I will discuss a theory with a heavy vectorlike lepton that decays into pseudoscalar and a tau lepton, and focus on signals of long-lived pseudoscalars in the muon chambers of CMS or ATLAS. Second, I will illustrate the sensitivity of Belle II to light LLPs with meter-scale decay lengths using displaced vertex signals from strongly interacting dark sectors as an example.

Higgs bosons produced at high momentum are rare, but measurable. The tails of their kinetic spectrum can provide a unique insight on whether anomalous interactions exist at the TeV scale. The production of Higgs boson pairs is even rarer - about 1000 times less frequent- but it can be enhanced in some new physics models, particularly when the pairs are produced at high momentum. This talk reviews how final states with jets have enabled the exploration of these elusive and possibly anomalous couplings, even in a difficult collider environment that is full of quarks and gluons like the Large Hadron Collider. We examine advances on particle jet identification that have drastically improved our ability to identify boosted Higgs and increased our physics reach. Finally, I will talk about how calorimetry detectors need more spatial precision, greater radiation tolerance, and smarter readout electronics to ensure that this and other search programs can continue at the upcoming High-Luminosity LHC run.

The CMS experiment at CERN will be significantly upgraded during Long Shutdown 3 of the LHC (2026-2028) to operate with a 10-fold increase in luminosity and the associated event pileup of 140-200 proton-proton interactions per bunch crossing of the High-Luminosity LHC (HL-LHC).  The endcap calorimeter region, covering 1.5 < |η| < 3.0, will be exposed to very high radiation levels and to mitigate this, a new calorimeter, the High Granularity Calorimeter (CE), will replace the existing endcap calorimeter.  It will have higher transverse and longitudinal segmentation for both electromagnetic (CE-E) and hadronic (CE-H) sections to facilitate particle-flow reconstruction.  The fine structure of showers can be measured and used to enhance particle identification, whilst still achieving good energy resolution.  The CE-E, and a large fraction of CE-H, will use hexagonal silicon sensors produced from 8-inch wafers as active material, each with several hundreds of individual cells of 0.5-1 sq. cm cell size.  The remainder of the CE-H will use highly-segmented scintillators read out with SiPMs as active material.  An overview of the CE project, including motivation, design, timeline, and expected performance, will be presented in this talk together with a deeper look at the silicon sensor design and performance status on the eve of pre-production.

The constituents of dark matter are still unknown, and the viable possibilities span a very large mass range. Specific scenarios for a thermal origin of dark matter sharpen this mass range to within about an MeV to 100 TeV. Most of the stable constituents of known matter have masses in the MeV to GeV range, and a thermal origin for dark matter works in a simple and predictive manner in this mass range as well, yet it remains largely unexplored. The Heavy Photon Search (HPS) at Jefferson Lab is a fixed target experiment that uses an electron beam to probe models of thermal dark matter involving sub-GeV dark photons. HPS searches for visibly decaying dark photons through two distinct methods - a resonance search in the e+e- invariant mass distribution and a displaced vertex search for long-lived dark photons. This seminar will give an overview of the theoretical motivations, the main experimental challenges and how they are addressed, the results for the 2016 Engineering Run, and future data and upgrades. In addition, an introduction to the Light Dark Matter eXperiment (LDMX), a planned next generation experiment at SLAC that will search for invisibly decaying dark photons through a missing-momentum experiment, will be presented.

Monte Carlo Event Generators are essential for the analysis and interpretation of Collider data. Event generation starts at energies of several hundred GeV with the hard interaction between quarks and gluons and ends at the scale of several hundred MeV with hadrons, leptons and photons as the final products. This energy gap is bridged by parton shower algorithms, which evolve the products of the hard interaction down to the hadronization scale. In this talk I will discuss recent improvements on the formal accuracy of parton showers and the performance of phase-space integrators, both crucial ingredients for precision physics at the HL-LHC.