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Here, an analysis of the distribution of the elementary particles that make up the proton provides evidence that it contains a type of quark known as an intrinsic charm quark — verifying a proposal made four decades ago.
In this report, we summarize the research in physics of elementary particles conducted by the Florida Tech DOE supported group at the CMS experiment at CERN, during the last 3-year cycle under this grant.
Over the past three decades, it has been shown that discrete and continuous media can support topologically nontrivial waves. Recently, it was shown that the same is true of the vacuum, in particular, right (R) and left (L) circularly polarized photons are topologically nontrivial. Here, we study the topology of another class of massless particles, namely gravitons. We show that the collection of all gravitons forms a topologically trivial vector bundle over the lightcone, allowing us to construct a globally smooth basis for gravitons. The graviton bundle also has a natural geometric splitting into two topologically nontrivial subbundles, consisting of the R and L gravitons. The R and L gravitons are unitary irreducible bundle representations of the Poincaré group, and are thus elementary particles; their topology is characterized by the Chern numbers ∓4. This nontrivial topology obstructs the splitting of graviton angular momentum into spin and orbital angular momentum.
The University of Pennsylvania elementary particle physics/particle cosmology group, funded by the Department of Energy Office of Science, participates in research in high energy physics and particle cosmology that addresses some of the most important unanswered questions in science. The research is divided into five areas. Energy Frontier - We participate in the study of proton-proton collisions at the Large Hadron Collider in Geneva, Switzerland using the ATLAS detector. The University of Pennsylvania group was responsible for the design, installation, and commissioning of the front-end electronics for the Transition Radiation Tracker (TRT) and plays the primary role in its maintenance and operation. We play an important role in the triggering of ATLAS, and we have made large contributions to the TRT performance and to the study and identification of electrons, photons, and taus. We have been actively involved in searches for the Higgs boson and for SUSY and other exotic particles. We have made significant contributions to measurement of Standard Model processes such as inclusive photon production and WW pair production. We also have participated significantly in R&D for upgrades to the ATLAS detector. Cosmic Frontier - The Dark Energy Survey (DES) telescope will be used to elucidate the nature of dark energy and the distribution of dark matter. Penn has played a leading role both in the use of weak gravitational lensing of distant galaxies and the discovery of large numbers of distant supernovae. The techniques and forecasts developed at Penn are also guiding the development of the proposed Large Synoptic Survey Telescope (LSST).We are also developing a new detector, MiniClean, to search for direct detection of dark matter particles. Intensity Frontier - We are participating in the design and R&D of detectors for the Long Baseline Neutrino Experiment (now DUNE), a new experiment to study the properties of neutrinos. Advanced Techology R&D - We have an extensive involvement in electronics required for sophisticated new detectors at the LHC and are developing electronics for the LSST camera. Theoretical Physics - We are carrying out a broad program studying the fundamental forces of nature and early universe cosmology and mathematical physics. Our activities span the range from model building, formal field theory, and string theory to new paradigms for cosmology and the interface of string theory with mathematics. Our effort combines extensive development of the formal aspects of string theory with a focus on real phenomena in particle physics, cosmology and gravity.
Only one-sixth of the matter in our Universe is made of the fundamental particles we understand. Understanding what the remaining “dark” matter is made of is one of the most important fundamental goals in modern science. It connects such disparate scientific areas as the formation of stars and galaxies, the earliest moments of our Universe, and the constituents of matter at the smallest length scales. Astronomical evidence for dark matter has built steadily for eight decades, though the elementary particles or waves that constitute dark matter remain a mystery. Recent theoretical developments have highlighted the importance of searching for dark matter particles in the range from as heavy as a single hydrogen atom to the lightest mass consistent with galactic structure (30 orders of magnitude lighter). Remarkably, small projects at the $5M–15M scale can explore key milestones throughout this range. By seizing these opportunities, we are now in a position to finally discover the nature of dark matter.
Our research focuses on the “Cosmic Frontier”, one of the three principle thrusts of the DoE Office of Science High Energy Physics research program. The 2013 community summer study “Snowmass on the Mississippi” catalyzed joint work to describe the status and future prospects of this research thrust. Over its history, the field of cosmic ray studies has provided many discoveries of central importance to the the progress of high energy physics, including the identification of new elementary particles, measurements of particle interactions far above accelerator energies, and the confirmation of neutrino oscillations. In our research we continued this tradition, employing 2 instruments (the Auger Observatory and the HAWC Observatory) to study high energy physics questions using cosmic rays. One approach to addressing particle physics questions at the cosmic frontier is to study the very highest energy cosmic rays. This has been the major thrust of our research effort. The two largest currently operating ultra-high energy cosmic ray (UHECR) observatories are the Pierre Auger Observatory in the Southern hemisphere, covering an area of 3000 km 2 and the Telescope Array (TA) in the Northern hemisphere, covering about 700 km 2 . The observatories sample the cosmic ray air showers at ground level (with 1660 water Cerenkov stations in the Auger surface detector), and also measure the longitudinal development of air showers on clear moonless nights (approx. 10% of the events) using atmospheric fluorescence detectors. The observatories have recently installed low energy extensions, which provide an overlap with the LHC energy regime. The Auger and TA teams have established joint working groups to discuss experimental methods, compare data analyses and modeling, and perform cross calibrations. Another approach is to study high energy gamma rays. The High Altitude Water Cerenkov (HAWC) gamma-ray observatory is located at 4100 m above sea level near Pico de Orizaba in central Mexico. HAWC is the most sensitive, wide field of view, TeV gamma-ray observatory in operation. After 4 years of construction, operation of the full detector began in March 2015. The HAWC detector contains 300 tanks each 7.3 m in diameter and 4.5 m deep containing pure water. Each water tank is instrumented with 4 upward-viewing photomultiplier tubes mounted at their bottom. The water tanks record the energy deposited by and arrival times of the constituent components of impinging extensive air showers (EAS). The tanks are close-packed to optimize the spatial sampling of the shower front. The distribution of deposited energy across the shower is used for gamma-hadron rejection. Showers with large energy deposit away from the core are rejected as being hadron-initiated. The detector operates at full efficiency above 3 TeV. The angular resolution above that energy approaches 0.1 degree. As the detector operates both day and night, the wide field of view of ~2 sr, allows ~2/3 of the sky to be observed each day.
As it is known, the principal research interest of V.G. Kadyshevsky was the development of a geometric approach to quantum field theory with a constraint imposed on the mass spectrum of elementary particles. Non-Hermitian operators arising in this case seemed to be a major obstacle to the development of a consistent theory. These issues have been resolved recently, and the introduction of the pseudo-Hermitian algebraic approach to the construction of quantum theory was a major advance in this physical research. The central point of such theories is the construction of PT -symmetric non-Hermitian Hamiltonians with real eigenvalues. It is important to note that both purely theoretical and experimental studies (e.g., in non-Hermitian optics) are found among the many published papers on this subject. Therefore, we believe that the development of pseudo-Hermitian relativistic quantum theory with a maximal mass may provide favorable opportunities to discuss the possible experimental verification of theoretical results obtained in this field. Kadyshevsky himself regarded the hypothesis of existence of new particles, which he called exotic fermions, as an important prediction of his theory. The possibility of discovery of exotic neutrinos in precision experiments on the determination of the neutrino mass is discussed in the present study.
Only one-sixth of the matter in our universe is made of the fundamental particles we understand. Understanding what the remaining “dark” matter is made of is one of the most important fundamental goals in modern science. It connects such disparate scientific areas as the formation of stars and galaxies, the earliest moments of our universe, and the constituents of matter at the smallest length scales. Astronomical evidence for dark matter has built steadily for eight decades, though the elementary particles or waves that constitute dark matter remain a mystery. Recent theoretical developments have highlighted the importance of searching for dark matter particles in the range from as heavy as a single hydrogen atom to the lightest mass consistent with galactic structure (30 orders of magnitude lighter). Remarkably, small projects at the $5M–$15M scale can explore key milestones throughout this range. By seizing these opportunities, we are now in a position to finally discover the nature of dark matter. The Particle Physics Project Prioritization Panel (P5) identified the search for dark matter as one of the five priority science drivers for the High-Energy Physics Program. The 2014 P5 report further recommended a portfolio of small projects to enable an uninterrupted flow of high-priority results. This Basic Research Needs (BRN) Report presents a program of small projects to lead to the discovery of the nature of dark matter. The program makes use of Department of Energy (DOE) facilities and infrastructure and is complementary to the ongoing Generation-2 (G2) dark matter program.
We recently introduced in [9] a boundary-to-bound dictionary between gravitational scattering data and observables for bound states of non-spinning bodies. In this paper, we elaborate further on this holographic map. We start by deriving the following — remarkably simple — formula relating the periastron advance to the scattering angle: $ΔΦ(J,ε)=χ(J,ε)+χ(-J,ε)$, via analytic continuation in angular momentum and binding energy. Using explicit expressions from [9], we confirm its validity to all orders in the Post-Minkowskian (PM) expansion. Furthermore, we reconstruct the radial action for the bound state directly from the knowledge of the scattering angle. The radial action enables us to write compact expressions for dynamical invariants in terms of the deflection angle to all PM orders, which can also be written as a function of the PM-expanded amplitude. As an example, we reproduce our result in [9] for the periastron advance, and compute the radial and azimuthal frequencies and redshift variable to two-loops. Agreement is found in the overlap between PM and Post-Newtonian (PN) schemes. Last but not least, we initiate the study of our dictionary including spin. We demonstrate that the same relation between deflection angle and periastron advance applies for aligned-spin contributions, with J the (canonical) total angular momentum. Explicit checks are performed to display perfect agreement using state-of-the-art PN results in the literature. Using the map between test- and two-body dynamics, we also compute the periastron advance up to quadratic order in spin, to one-loop and to all orders in velocity. We conclude with a discussion on the generalized ‘impetus formula’ for spinning bodies and black holes as ‘elementary particles’. Our findings here and in [9] imply that the deflection angle already encodes vast amount of physical information for bound orbits, encouraging independent derivations using numerical and/or self-force methodologies.
The standard model of particle physics describes the known fundamental particles and forces that make up our Universe, with the exception of gravity. One of the central features of the standard model is a field that permeates all of space and interacts with fundamental particles. The quantum excitation of this field, known as the Higgs field, manifests itself as the Higgs boson, the only fundamental particle with no spin. In 2012, a particle with properties consistent with the Higgs boson of the standard model was observed by the ATLAS and CMS experiments at the Large Hadron Collider at CERN. Since then, more than 30 times as many Higgs bosons have been recorded by the ATLAS experiment, enabling much more precise measurements and new tests of the theory. Here, on the basis of this larger dataset, we combine an unprecedented number of production and decay processes of the Higgs boson to scrutinize its interactions with elementary particles. Interactions with gluons, photons, and W and Z bosons—the carriers of the strong, electromagnetic and weak forces—are studied in detail. Interactions with three third-generation matter particles (bottom (b) and top (t) quarks, and tau leptons (τ)) are well measured and indications of interactions with a second-generation particle (muons, μ) are emerging. These tests reveal that the Higgs boson discovered ten years ago is remarkably consistent with the predictions of the theory and provide stringent constraints on many models of new phenomena beyond the standard model.
When the heaviest elementary particle known today, the top quark, was discovered in 1995 by the CDF and D0 collaborations at the Fermilab Tevatron collider, a large program to study this particle in details has started. In this article, an overview of the status of top quark physics at the Tevatron is presented. In particular, recent results on top quark production, properties and searches using top quarks are discussed.
Here I discuss a possibility to connect quantum numbers of elementary particles with their structure on the base of four connected components of Lorentz group. The complete and closed (with respect to homogenous Lorentz group) series of equations for description of lepton sector forms the pattern and ground for the present project.
The charge-conjugation and parity-reversal (CP) symmetry of fundamental particles is a symmetry between matter and antimatter. Violation of this CP symmetry was first observed in 1964, and CP violation in the weak interactions of quarks was soon established. Sakharov proposed that CP violation is necessary to explain the observed imbalance of matter and antimatter abundance in the Universe. Yet, CP violation in quarks is too small to support this explanation. So far, CP violation has not been observed in non-quark elementary particle systems. It has been shown that CP violation in leptons could generate the matter–antimatter disparity through a process called leptogenesis. Leptonic mixing, which appears in the standard model’s charged current interactions, provides a potential source of CP violation through a complex phase δ CP , which is required by some theoretical models of leptogenesis. This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible using accelerator-produced beams as established by the Tokai-to-Kamioka (T2K) and NOvA experiments. Until now, the value of δ CP has not been substantially constrained by neutrino oscillation experiments. Here we report a measurement using long-baseline neutrino and antineutrino oscillations observed by the T2K experiment that shows a large increase in the neutrino oscillation probability, excluding values of δ CP that result in a large increase in the observed antineutrino oscillation probability at three standard deviations (3σ). The 3σ confidence interval for δ CP , which is cyclic and repeats every 2π, is [-3.41, -0.03] for the so-called normal mass ordering and [-2.54, -0.32] for the inverted mass ordering. Our findings indicate CP violation in leptons and our method enables sensitive searches for matter–antimatter asymmetry in neutrino oscillations using accelerator-produced neutrino beams. Future measurements with larger datasets will test whether leptonic CP violation is larger than the CP violation in quarks.
The European Organization for Nuclear Research (CERN) was created in 1954 as international entity for the benefit of advancing the scope of knowledge in particle physics. The designation of CERN refers simply to an organization, which hosts the world’s largest particle physics laboratory. CERN employs close to 2,400 full-time employees, 1,500 part-time employees and hosts 10,000 visiting engineers and scientists, affiliated with 608 universities and research facilities ranging from over 113 nationalities. (Wikipedia, CERN) The European Organization for Nuclear Research houses various colliders, which on a daily basis makes attempts at defining the initial anatomy of the universe. CERN utilizes the world’s largest and most sophisticated scientific tools, which aid in the analysis of clarifying the fundamental components of matter – Elementary Particles. These particles are forced into collisions that are near the speed of light or rather “relativistic”. These collisions aid scientists and engineers who work at CERN in the endeavor of illustrating the process of how the fundamental forces of nature affect the interactions of particles/matter at various energy levels.
The properties of disordered metamaterial absorbers are analyzed on the basis of numerical simulations and experimental characterizations. A broadening of the absorption spectrum is clearly evidenced. This effect is the consequence of both the coupling between nearby resonators leading to the occurrence of extended magnetic resonance modes and the interconnection of elementary particles yielding the definition of resonating clusters. The angular robustness of the absorbing structure under oblique incidence is also demonstrated for a wide domain of angles.
We report that the top quark is the heaviest known elementary particle, and it is often seen as a window to search for new physics processes in particle physics. A large program to study the top-quark properties has been performed both at the Tevatron and LHC colliders by the D0, CDF, ATLAS and CMS experiments. The most recent results are discussed here in this article.
In the International Linear Collider, two linear accelerators will accelerate bunches of positrons and electrons to over a hundred billion electron volts and collide them in a central detector. In order to obtain useful collision rates, the bunches, each containing twenty billion particles, must be compressed to a cross section of a few nanometers by a few hundred nanometers. In order to prepare these ultra high density bunches, damping rings (DRs) are employed before the linear accelerators. The DRs take the high emittance bunches that are provided by the electron and positron sources and, through the process of radiation damping, squeeze them into ultra low emittance beams that are ready for the main linear accelerators. In the damping rings, a number of effects can prevent the successful preparation of the beams. In the electron ring, an effect known as the fast ion instability can lead to beam growth and, in the positron ring, the build-up of an electron cloud (EC), which interacts with the circulating bunches, can produce the same effect. EC build-up and the subsequent interaction of the cloud with the positron beam in the DR have been identified as major risks for the successful construction of a linear collider. The CESRTA research program at the Cornell Electron Storage Ring (CESR) was developed in order to study the build-up of the EC, the details of its impact on ultra low emittance beams, as well as methods to mitigate the impact of the cloud. In the DR, the EC forms when synchrotron photons radiated from the circulating beam strike the walls of the vacuum chamber, resulting in the emission of photoelectrons. These low energy electrons can be accelerated across the vacuum chamber by the electric field of the beam, and strike the walls, causing the emission of secondary electrons. The secondary electrons are subsequently accelerated into the walls yet again via the same mechanism. The result is that the EC can rapidly begin to fill the vacuum chamber. In an electron DR, the EC build-up is limited by the Coulomb repulsion. But in a positron ring, the electrons are pulled into the potential well of the beam. The resulting interaction of the circulating bunches of positrons with the EC that ultimately limits DR performance. Typically we store long trains of closely space bunches in the damping ring. The interaction of stored beam and the EC that is generated by the long train is manifested by different mechanisms: (1) The cloud focuses the beam, which causes a tune shift that increases along the bunch train as the cloud density increases. (2) The cloud electrons couple the motion of bunches along a train. Transverse motion of a leading bunch is transferred to the cloud, and subsequently to a trailing bunch which can result in a multi-bunch instability. (3) The cloud couples the positrons in the head of the bunch to those in the tail of the same bunch, which can excite a 'head-tail' instability. (4) The nonlinear fields of the EC can lead to emittance growth before the onset of instabilities. The CESRTA collaboration, which includes researchers from Cornell University's Laboratory for Elementary-Particle Physics as well as more than 50 senior staff members from over a dozen accelerator laboratories and universities around the world, has operated CESR as a damping ring for the past three years to study these EC effects. A range of specialized instrumentation has been deployed to study the local build-up of the cloud in the vacuum chambers as well as the complicated dynamics exhibited when the beam and the EC interact. The program has significantly advanced our understanding of these issues and has helped identify the most promising methods to mitigate the impact of the EC on the DR beams. It has pointed the way towards a DR design that can meet the stringent specifications of the ILC.
Composite Higgs Models explore the possibility that the Higgs boson is an excitation of a new strongly interacting sector giving rise to electro-weak symmetry breaking. After describing how this new sector can be embedded into the Standard Model of elementary particle physics meeting experimental constraints, I will review efforts by the community to explore the physics of the new strong interaction using methods of lattice field theory. Challenges in understanding the numerical results are discussed and an outlook is given on possible future directions allowing to confirm or reject the composite Higgs hypothesis.