Applying Machine Learning to Vertex Recognition for Neutrino Interactions
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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Results for “Elementary Particle Interactions”
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Enhancement of Exciton–Phonon Scattering from Monolayer to Bilayer WS 2
Layered transition metal dichalcogenides exhibit the emergence of a direct bandgap at the monolayer limit along with pronounced excitonic effects. In these materials, interaction with phonons is the dominant mechanism that limits the exciton coherence lifetime. Exciton-phonon interaction also facilitates energy and momentum relaxation, and influences exciton diffusion under most experimental conditions. However, the fundamental changes in the exciton–phonon interaction are not well understood as the material undergoes the transition from a direct to an indirect bandgap semiconductor. Here, we address this question through optical spectroscopy and microscopic theory. In the experiment, we study room-temperature statistics of the exciton line width for a large number of mono- and bilayer WS 2 samples. We observe a systematic increase in the room-temperature line width of the bilayer compared to the monolayer of 50 meV, corresponding to an additional scattering rate of ~0.1 fs –1 . We further address both phonon emission and absorption processes by examining the temperature dependence of the width of the exciton resonances. Using a theoretical approach based on many-body formalism, we are able to explain the experimental results and establish a microscopic framework for exciton–phonon interactions that can be applied to naturally occurring and artificially prepared multilayer structures.
2D materials↗
Infrared Constraint on Ultraviolet Theories
While our current paradigm of particle physics, the Standard Model (SM), has been extremely successful at explaining experiments, it is theoretically incomplete and must be embedded into a larger framework. In this thesis, we review the main motivations for theories beyond the SM (BSM) and the ways such theories can be constrained using low energy physics. The hierarchy problem, neutrino mass and the existence of dark matter (DM) are the main reasons why the SM is incomplete . Two of the most plausible theories that may solve the hierarchy problem are the Randall-Sundrum (RS) models and supersymmetry (SUSY). RS models usually suffer from strong flavor constraints, while SUSY models produce extra degrees of freedom that need to be hidden from current experiments. To show the importance of infrared (IR) physics constraints, we discuss the flavor bounds on the anarchic RS model in both the lepton and quark sectors. For SUSY models, we discuss the difficulties in obtaining a phenomenologically allowed gaugino mass, its relation to R-symmetry breaking, and how to build a model that avoids this problem. For the neutrino mass problem, we discuss the idea of generating small neutrino masses using compositeness. By requiring successful leptogenesis and the existence of warm dark matter (WDM), we can set various constraints on the hidden composite sector. Finally, to give an example of model independent bounds from collider experiments, we show how to constrain the DM–SM particle interactions using collider results with an effective coupling description.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
On Baryon-Antibaryon Cross Sections from Initial State Radiation Processes at BABAR and their Surprising Threshold Behavior
BABAR has measured with unprecedented accuracy the e + e - → pp-bar and e + e - → ΛΛ-bar cross sections by means of the initial state radiation technique, which has the advantages of good efficiency and energy resolution, and full angular acceptance in the threshold region. A striking feature of these cross sections is their non-vanishing values at threshold. In the case of charged baryons, the phenomenon is well understood in terms of the Coulomb interaction between the outgoing baryon and antibaryon. However, such an effect is not expected for neutral baryons. We suggest a simple explanation for both charged and neutral baryon pairs based on Coulomb interactions at the valence quark level.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
From dynamical systems to renormalization
In this paper we study logarithmic derivatives associated to derivations on completed graded Lie algebra, as well as the existence of inverses. These logarithmic derivatives, when invertible, generalize the exp-log correspondence between a Lie algebra and its Lie group. Such correspondences occur naturally in the study of dynamical systems when dealing with the linearization of vector fields and the non linearizability of a resonant vector fields corresponds to the non invertibility of a logarithmic derivative and to the existence of normal forms. These concepts, stemming from the theory of dynamical systems, can be rephrased in the abstract setting of Lie algebra and the same difficulties as in perturbative quantum field theory (pQFT) arise here. Surprisingly, one can adopt the same ideas as in pQFT with fruitful results such as new constructions of normal forms with the help of the Birkhoff decomposition. The analogy goes even further (locality of counter terms, choice of a renormalization scheme) and shall lead to more interactions between dynamical systems and quantum field theory.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Assessing compatibility of direct detection data: halo-independent global likelihood analyses
We present two different halo-independent methods to assess the compatibility of several direct dark matter detection data sets for a given dark matter model using a global likelihood consisting of at least one extended likelihood and an arbitrary number of Gaussian or Poisson likelihoods. In the first method we find the global best fit halo function (we prove that it is a unique piecewise constant function with a number of down steps smaller than or equal to a maximum number that we compute) and construct a two-sided pointwise confidence band at any desired confidence level, which can then be compared with those derived from the extended likelihood alone to assess the joint compatibility of the data. In the second method we define a “constrained parameter goodness-of-fit” test statistic, whose p-value we then use to define a “plausibility region” (e.g. where p≥10%). For any halo function not entirely contained within the plausibility region, the level of compatibility of the data is very low (e.g. p<10%). We illustrate these methods by applying them to CDMS-II-Si and SuperCDMS data, assuming dark matter particles with elastic spin-independent isospin-conserving interactions or exothermic spin-independent isospin-violating interactions.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Probing QCD with jets, photons and weak bosons at the LHC with ATLAS
A summary of ATLAS measurements that probe 'hard' QCD interactions in the protonproton collisions of the LHC are presented.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Nonperturbative quark-antiquark interactions in mesonic form factors
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Wakefields generated by collisional neutrinos in neutral-electron-positron plasma
A classical fluid description is adopted to investigate nonlinear interaction between an electron-type neutrino beam and a relativistic collisionless unmagnetized neutral-electron-positron plasma. In this work, we consider the collisions of the neutrinos with neutrals in the plasma and study their effect on the generation of wakefields in this plasma.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Reflection of light beams from a chirped dielectric plane-layered structure
The reflection of light beams with various widths of the angular spectrum from a chirped plane-layered dielectric structure is numerically studied. For wide beams, the total lateral shift of the reflected beam depends on the position of the photonic barrier inside the structure and the value of the Goos – Hänchen shift. For narrow beams, the region of the interaction with the structure increases, the profile broadens and the reflected beam wavefront becomes phase modulated. It is shown that the light reflected from a quasi-periodic structure with negative spatial dispersion undergoes focusing. (light beams)
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Quantum corrections for the cubic Galileon in the covariant language
We present for the first time an explicit exposition of quantum corrections within the cubic Galileon theory including the effect of quantum gravity, in a background- and gauge-invariant manner, employing the field-reparametrisation approach of the covariant effective action at 1-loop. We show that the consideration of gravitational effects in combination with the non-linear derivative structure of the theory reveals new interactions at the perturbative level, which manifest themselves as higher-operators in the associated effective action, which' relevance is controlled by appropriate ratios of the cosmological vacuum and the Galileon mass scale. The significance and concept of the covariant approach in this context is discussed, while all calculations are explicitly presented.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
A portalino to the dark sector
“Portal” models that connect the Standard Model to a Dark Sector allow for a wide variety of scenarios beyond the simplest WIMP models. Kinetic mixing of gauge fields in particular has allowed a broad range of new ideas. However, the models that evade CMB constraints are often non-generic, with new mass scales and operators to split states and suppress indirect detection signals. Models with a “portalino”, a neutral fermion that marries a linear combination of a standard model neutrino and dark sector fermion and carries a conserved quantum number, can be simpler. This is especially interesting for interacting dark sectors; then the unmarried linear combination which we identify as the standard model neutrino inherits these interactions too, and provides a new, effective interaction between the dark sector and the standard model. These interactions can be simple Z' type interactions or lepton-flavor changing. Dark matter freezes out into neutrinos, thereby evading CMB constraints, and conventional direct detection signals are largely absent. The model offers different signals, however. The “portalino” mechanism itself predicts small corrections to the standard model neutrino couplings as well as the possibility of discovering the portalino particle in collider experiments. Possible cosmological and astroparticle signatures include monochromatic neutrino signals from annihilation, spectral features in high energy CR neutrinos as well as conventional signals of additional light species and dark matter interactions.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
The Origins of Matter on Near-Exascale Supercomputing
This LDRD addressed one of the central questions in physics today: the lack of antimatter relative to matter in the universe. If antimatter and matter existed in equal amounts they would have annihilated into radiation and we would not exist today. DOE is funding experiments to investigate processes that could lead to lepton number violation and the resulting neutrino-less double beta decay (0nbb) signal that may be observed (lepton number is a property of elementary particles similar to electric charge and lepton number violation would explain the matter-antimatter imbalance). However, even if the 0nbb decay is detected in these experiments, the physics mechanism that violates lepton number would not be known, as there are several candidates. Determining the appropriate mechanism from the experimental data requires theoretical calculations. Theoretical effort in the field has focused on long-range 0nbb decay mechanisms associated with the exchange of light neutrinos between two nucleons. An equally important set of mechanisms are associated with the exchange of heavy particles and short-range physics, including the exchange of massive Majorana neutrinos. Calculating the event rate for 0nbb decays for candidate theories involving heavy particle exchange requires large-scale Lattice simulations of the underlying fundamental theory of Quantum Chromodynamics (QCD). We have performed these simulations on the LLNL supercomputers and have calculated the necessary matrix elements of short-range operators that arise from the exchange of heavy mediators that contribute to 0nbb decay via the leading pion exchange diagrams. Our published results can now be used as input to effective field theory calculations to calculate the 0nbb decay rate for the nuclei involved in the various experimental detectors. In the process of this work we entered the 2018 Gordon Bell Prize competition (the highest prize in scientific supercomputing) with our innovative and highly optimized code and methods and were selected as one of the six international finalists. During this effort we helped with the bring-up of the new LLNL Sierra and Lassen supercomputers by identifying hardware and software problems. Aiming towards the next step of this research, involving the sub-leading nucleon-nucleon direct vertex, we have developed algorithms and codes that will play a significant role in future Lattice QCD calculations involving nucleon-nucleon interactions.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Unexpected manifestation of quark condensation
A comparative analysis of some quark ensembles governed by a four-fermion interaction is performed. Arguments in support of the statement that the presence of a gas-liquid phase transition is a feature peculiar to them are adduced. The instability of small quark droplets is discussed and is attributed to the formation of a chiral soliton. The stability of baryon matter is due to a mixed phase of the vacuum and baryon matter.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Neutral Current Elastic Interactions in MiniBooNE
Neutral Current Elastic (NCE) interactions in MiniBooNE are discussed. In the neutrino mode MiniBooNE reported: the flux averaged NCE differential cross section as a function of four-momentum transferred squared, an axial mass (M{sub A}) measurement, and a measurement of the strange quark spin content of the nucleon, {Delta}s. In the antineutrino mode we present the background-subtracted data which is compared with the Monte Carlo predictions.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
2p2h or not 2p2h?
This paper summarizes the discussion about the role of two-particle-two-hole (2p2h) excitations in neutrino-nucleus interactions in the few-GeV region, held at NuInt11.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Broadening of particle distributions in electron-, neutrino-, and antineutrino-nucleus scattering from QED interactions
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
First measurement of electron neutrino scattering cross section on argon
We report the first electron neutrino cross section measurements on argon, based on data collected by the ArgoNeuT experiment running in the GeV-scale NuMI beamline at Fermilab. A flux-averaged $\nu_e + \overline{\nu}_e$ total and a lepton angle differential cross section are extracted using 13 $\nu_e$ and $\overline{\nu}_e$ events identified with fully-automated selection and reconstruction. We employ electromagnetic-induced shower characterization and analysis tools developed to identify $\nu_e/\overline{\nu}_e$-like events among complex interaction topologies present in ArgoNeuT data ($\langle E_{\bar{\nu}_e} \rangle = 4.3$ GeV and $\langle E_{\nu_e} \rangle = 10.5$ GeV). The techniques are widely applicable to searches for electron-flavor appearance at short- and long-baseline using liquid argon time projection chamber technology. Notably, the data-driven studies of GeV-scale $\nu_e/\overline{\nu}_e$ interactions presented in this Letter probe an energy regime relevant for future DUNE oscillation physics.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗