High Energy Physics Seminars

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.

The axion is a hypothetical particle that may solve two problems in particle physics & cosmology, the Strong-CP problem and the nature of dark matter. The Axion Dark Matter Experiment (ADMX) is the DOE Flagship search for these particles as part of the “Generation-2” direct dark matter search program in High Energy Physics. The experiment uses a tunable resonant cavity in a large static magnetic field to enhance the conversion of axions to detectable microwaves. Quantum-limited amplifiers based on superconducting Josephson Junction circuits are critical to allow the search to be sensitive enough to rapidly scan the frequencies where the axion may exist.  Here I will describe the status of the search along with an update on the planning and prototyping for the next phase of ADMX.”

Despite the successes of the Standard Model of particle physics, it remains a challenge to understand the dynamics of the strong interaction among the building blocks of hadronic matter, namely quarks and gluons. At small distance scales or at high energies, the underlying theory, the Quantum Chromodynamics (QCD), is well tested and understood. Our understanding of the strong interaction deteriorates dramatically at larger distances scales such as the size of the nucleon. This so-called "strong QCD regime” exhibits spectacular effects such as the generation of hadron masses and color confinement. Moreover, the nature of QCD implies the existence of gluon-rich hadrons, such as glueballs and hybrids, multi-quark states, and molecules. This presentation will highlight a future research program that aims to provide precision data exploiting collisions of an intense beam of cooled anti-protons with protons or nuclei. This experiment, called PANDA at FAIR, has the ambition to carry out comprehensive spectroscopy studies of hadrons in the strange, charm, and gluon-rich regimes, covering topics in the field of nuclear, hadron, and particle physics.

The Standard Model of particle physics has been a crowning achievement of fundamental physics, culminating in the discovery of the Higgs boson in 2012. As a quantum theory of the building blocks of matter and forces, it has been one of the most successful theories in science. The recent measurement of the mass of the W boson disagrees with the theory prediction. This upset to the Standard Model may point towards exciting new discoveries in particle physics in the coming years. We will discuss the Standard Model, the crucial role of the W boson, and how it has become the harbinger of new laws of nature.

The discovery of coherent elastic neutrino-nucleus scattering (CEvNS) was made by the COHERENT Collaboration in 2017 using a CsI[Na] scintillating crystal at Oak Ridge National Laboratory's Spallation Neutron Source (SNS). This observation was made over 40 years after the theoretical prediction by Freedman et al. and consists of a neutral-current neutrino-nucleus interaction on an entire nucleus as a whole. The CEvNS process is the dominant scattering mode below 100 MeV and serves as a fertile testbed for precisely examining the Standard Model and has applications in nuclear reactor monitoring and stellar astrophysics. COHERENT built out the CEvNS physics program to include detector systems using liquid argon (CENNS-10), germanium (GeMini) and NaI[Tl] crystals (NaIvEte)--of which liquid argon successfully yielded an additional CEvNS measurement. The variety of media studied within the COHERENT detector suite works towards establishing the predicted N^2 dependence of the CEvNS cross section. Additionally, the COHERENT Collaboration houses several detector systems aimed at elucidating inelastic neutrino-nucleus interactions in support of CEvNS searches and as standalone investigates of neutrino-induced nuclear reactions. This presentation will consist of both the published results and the ongoing work being done on new detectors to further advance the physics goals of the collaboration. 

The nature of dark matter poses one of the most pressing questions in fundamental physics today. Thermal freeze-out of a weakly interacting massive particle (WIMP) has proved to be a successful framework for explaining the measured dark matter abundance in the Universe. However, the sizeable couplings of dark matter to the Standard Model particles required in its simplest realizations have been put under severe pressure by experimental null-results at colliders, direct and indirect detection experiments. Hence, fulfilling the relic density constraint often requires the exploration of ‘exceptional’ regions, e.g. the region where coannihilation effects increase the effective annihilation rate. In this talk, we revisit the assumptions commonly made within the coannihilation scenario and discuss a new variant of dark matter freeze-out, dubbed conversion-driven freeze-out (or coscattering). In this scenario, the relic abundance is set by the freeze-out of conversion processes requiring significantly smaller couplings of dark matter to the standard model. While this parameter region is largely immune to direct detection constraints, it predicts an interesting signature of disappearing tracks or displaced vertices at the LHC. We will also discuss the effect of bound state formation of the coannihilating particle which considerably enhanced the valid parameter space into the multi-TeV region, making it a prime target for upcoming long-lived particle searches at the LHC.

The nature and origin of dark matter are among the most compelling mysteries of contemporary science. LUX-ZEPLIN (LZ) is a dark matter direct detection experiment located at the Sanford Underground Research Facility in Lead, South Dakota. The experiment consists of a dual-phase xenon Time Projection Chamber with an active volume of 7 tonnes, surrounded by an active liquid xenon skin region and a gadolinium-loaded liquid scintillator neutron detector. With an exposure of 60 live days using a fiducial mass of 5.5 tonnes, LZ has achieved world-leading sensitivity to Weakly Interacting Massive Particles (WIMPs). This talk will give an overview of the LZ experiment and present results from LZ's first dark matter search.

In quantum many-body systems, measurement tends to kill quantum entanglement and correlations between different degrees of freedom. Nonetheless, recent developments have explored how measurement can be used to engineer new non-equilibrium phases of matter, but mostly in the context of quantum entanglement in random quantum circuits. In this talk, I will first take a different perspective and first examine how a protocol of repeated, periodic measurements can be used to generate chiral transport in a system of free fermions [1], mimicking the anomalous Floquet topological insulators [2]. We will then examine the effects of different types of realistic disorder, namely site blockade, lattice distortions, and random onsite potential on this measurement induced chiral transport. Most notably, one observes a percolation phase transition in the flow of measurement induced chirality with percolation threshold matching previous result on the percolation cluster in a Lieb lattice [3]. Our work demonstrates how measurements can be used to engineer new states of matter, and I will point out future directions on the fundamental role of measurements in the dynamics of quantum many-body systems.

References:

[1] "Stirring by staring: Measurement induced Chirality", arXiv:2108.05906

[2] "Anomalous Edge States and the Bulk-Edge Correspondence for Periodically Driven Two-Dimensional Systems", PRX 3, 031005 (2013).

[3] "Percolation on Lieb Lattices", PRE 104, 064122 (2021).

Tests of Lorentz invariance continue to inform and challenge our modern understanding of spacetime symmetries. Using a model-independent framework based on effective field theory, generic deviations from exact Lorentz and CPT invariance can be studied in a wide class of physical systems. Despite the large number of constraints extracted over the past two decades, stringent limits on many quark-sector effects remain relatively scarce. I discuss the sensitivity of dedicated searches at electron-proton and proton-proton colliders.

The MoEDAL experiment deployed at IP8 on the LHC ring was the first dedicated search experiment to take data at the LHC in 2010.  It was designed to search for Highly Ionizing Particle (HIP) avatars of new physics such as magnetic monopoles, dyons, Q-balls, multiply charged particles, massive slowly moving charged particles and long-lived massive charge SUSY particles. We shall report on our search at LHC’s Run-2 for Magnetic monopoles and dyons produced in p-p and photon-fusion. We will report in a little more detail our most recent result in this arena:  the search for magnetic monopoles via the Schwinger Mechanism in Pb-Pb collisions, that was recently published in Nature.

            The MoEDAL detector will be reinstalled for LHC’s Run-3 to continue the search for electrically and magnetically charged HIPs. As part of this effort we will initiate the search for massive long-very lived SUSY particles to which MoEDAL has a competitive sensitivity.   An upgrade to MoEDAL, the MoEDAL Apparatus for Penetrating Particles (MAPP), approved by CERN’s Research Board is now the LHC’s newest detector. The MAPP detector, positioned in UA83, expands the physics reach of MoEDAL to include sensitivity to feebly-charged particles with charge, or effective charge, as low as 10^-3 e (where e is the electron charge). Also, the MAPP detector In conjunction with MoEDAL’s trapping detector gives us a unique sensitivity to extremely long-lived charged particles. MAPP also has some sensitivity to long-lived neutral particles.

            Additionally, we will briefly report on the plans for the MAPP-2 upgrade to the MoEDAL-MAPP experiment for the High Luminosity LHC (HL-LHC). We envisage that this detector will be deployed in the UGC1 gallery near to IP8. This phase of the experiment is designed to maximize  MoEDAL-MAPP’s sensitivity to very long-lived neutral messengers of physics beyond the Standard Model.

NOvA is a long-baseline neutrino oscillation experiment, designed to make measurements using muon neutrino disappearance and electron neutrino appearance. It consists of two functionally equivalent detectors and utilizes the Fermilab NuMI beam. NOvA uses a convolutional neural network for particle identification of electron neutrino events with a validation process that includes several data-driven techniques. In particular, a suite of studies called the Muon Removed studies checks for bias in our particle identifier between simulation and data arising from potential mismodelling in our simulation by modifying samples of muonic events to create samples of pure electron neutrino like events. This talk will discuss the implementation and results of these techniques being applied to our most recent analysis as well as how these cross checks could be extended to corrections to our predicted electron neutrino signal.

Physics searches and measurements at high-energy collider experiments traditionally focus on the high-pT region. However, if particles are light and weakly-coupled, this focus may be completely misguided: light particles are typically highly collimated around the beam line, allowing sensitive searches with small detectors, and even extremely weakly-coupled particles may be produced in large numbers there. The FASER experiment will use the opportunity and extend the LHC’s physic potential by searching for long-lived particles and study-

ing neutrino interactions at TeV energies. In this talk, I will present the physics potential of FASER for new physics searches, neutrino physics and QCD and astro-particle physics.

Abstract attached. 

In this talk I will review work on `decomposition,' a property of 2d theories with 1-form symmetries and, more generally, d-dim'l theories with (d-1)-form symmetries.  Decomposition is the observation that such quantum field theories are equivalent to ('decompose into’) disjoint unions of other QFTs, known in this context as "universes.” Examples include two-dimensional gauge theories and orbifolds with matter invariant under a subgroup of the gauge group. 

Decomposition explains and relates several physical properties of these theories -- for example, restrictions on allowed instantons arise as a "multiverse interference effect" between contributions from constituent universes. First worked out in 2006 as part of efforts to understand string propagation on generalizations of spaces,  decomposition has been the driver of a number of developments since. 

In the first half of this talk, I will review decomposition; in the second half, I will focus on the recent application to anomaly resolution of Wang-Wen-Witten in two-dimensional finite gauge theories known as orbifolds.

I will present the first oscillation-related results from the MicroBooNE neutrino experiment at Fermilab. These measurements, featuring extensive searches for anomalous rates of both electron neutrinos and neutrino-induced gammas from the Booster Neutrino Beamline with multiple final-state topologies, directly address the 4.8sigma excess of electron-like events seen by the MiniBooNE experiment.
 

The Cryogenic Underground Observatory for Rare Events (CUORE), hosted at the Laboratori Nazionali del Gran Sasso in Italy, is the first one-tonne scale cryogenic experiment searching for neutrinoless double-beta (0νββ) decay of 130Te. The discovery of this process would demonstrate that lepton number is not a symmetry of nature and that neutrinos are massive Majorana particles. The CUORE experiment has also the potential for the search for rare events and/or for physics beyond the Standard Model other than the 0νββ decay. CUORE is currently in stable operating mode, an exposure of more than 1 tonne∙yr has been achieved and the data taking is currently underway to collect 5 years of run time. In this talk, the current results of CUORE's main analyses will be presented, as well as a review of the detector performance and the analysis techniques. The seminar conclusion will provide an insight on the future perspectives of 0vββ decay searches utilising cryogenic calorimeters, mainly the CUPID experiment.

Since the discovery of the SM Higgs boson in 2012, the investigation of the apparent difference between the electroweak and Planck scales has led to more interest in collisions with energies above the electroweak scale. One consequence of this new regime is expanded interest in hadronic final states resulting in collimated sprays of particles called jets. Understanding jets and jet substructure has therefore become of vital interest to particle physicists. In this seminar, I present recent measurements of jet substructure quantities, which can help us better understand multijet systems and to improve machine learning taggers by reducing systematic uncertainties. I also detail my work on jet reconstruction and plans to understand jet substructure at future colliders.

Experimental particle physics is an intensely computational field of science. In fact, particle physicists were arguably the first non-secret (non-cryptography) users of digital computers, and have been pushing the boundaries of pattern recognition and throughput ever since. For decades, our unique needs justified custom software at all levels of the stack, maintained "in-house" by physicists, but the situation changed in the 21st century. Machine learning and analysis of web-scale datasets (i.e. "Big Data") has become an industry on its own, under the catch-all name "data science." Physicists are responding by adopting data science toolsets and methodologies, integrating them with traditional physics software, though the process is ongoing and differs in degree across physics groups. 

This talk will present a big picture of how experimental particle physicists have used data analysis software in the past 75 years, how our needs have dictated a choice of programming languages and toolkits, and how those choices are changing. We'll see how pattern recognition evolved from semi-automated to algorithmic to machine learning, how programming languages transitioned from Fortran to C++ to include a significant mix of Python, and how software was organized from site-custom solutions to standard packages like CERNLIB and ROOT to also include a mix of data science tools. Finally, these choices are not purely technical: communities form around software tools, and integrating toolsets integrates physicists with the larger world.