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DOE OSTI2021

Capturing a New State of Matter: Relativistic Electron-Positron Plasma (LDRD Final Report)

Relativistic electron-positron (pair) plasmas were a main component of the universe shortly after the Big Bang and are produced around many astrophysical objects, but laboratory pair plasmas have remained elusive. High-intensity lasers can drive dense relativistic positron jets; over the last ten years, we have optimized high-energy ultra-short-pulse laser-matter interaction experiments to make a large number (10 10 – 10 12 ) of positrons in a small volume (< 3 mm 3 ). However, these jets are transient (10 ps), making observations of collective effects difficult. The goal of 20-LW-021 was to trap laser-driven electron-positron jets using pulsed-power-driven high-magnetic-field solenoids, allowing longer confinement times and ultimately an observable laboratory relativistic pair plasma. The project has been remarkably successful: we have found that pulsed-power magnetic fields can effectively trap laser-driven charged particles and produce charge-neutral pair beams. The project thus far has resulted in six published journal articles. The success of these components has put a laboratory pair plasma almost within reach.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Particle physics at accelerators in the United States and Asia

Particle physics experiments in the United States and Asia have greatly contributed to the understanding of elementary particles and their interactions. With the recent discovery of the Higgs boson at CERN, interest in the development of next-generation colliders has been rekindled. A linear electron–positron collider in Japan and a circular collider in China have been proposed for precision studies of the Higgs boson. In addition to the Higgs programme, new accelerator-based long-baseline neutrino mega-facilities are being built in the United States and Japan. Here, we outline the present status of key particle physics programmes at accelerators, and future plans in the United States and Asia that largely complement approaches being explored in the European Strategy for Particle Physics Update. Furthermore, we encourage the pursuit of this global approach, reaching beyond regional boundaries for optimized development and operations of major accelerator facilities worldwide, to ensure an active and productive future of the field.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Detector and Physics Performance at a Muon Collider

A muon collider represents the ideal machine to reach very high center-of-mass energies and luminosities by colliding elementary particles. This is the result of the low level of beamstrahlung and synchrotron radiation compared to linear or circular electron-positron colliders. In contrast with other lepton machines, the design of a detector for a multi-TeV muon collider requires detailed knowledge of the interaction region due to the significant backgrounds created by muon beam decays in the collider ring. The physics reach can be properly evaluated only when the detector performance in such an environment is determined. In this work, the backgrounds generated by muon beams of 750 GeV are characterized and the performance of the tracking system and the calorimeter detector is illustrated. Solutions to minimize the effect of the beam-induced backgrounds are discussed and applied to obtain track and jet reconstruction performance. The μ + μ – → $Hν\bar{ν} → b\bar{b} ν\bar{ν}$ process is fully simulated and reconstructed to demonstrate that physics measurements are possible in this harsh environment. The measurement precision for the Higgs boson coupling to $b\bar{b}$ is evaluated for $\sqrt{s}$=1.5, 3, and 10 TeV and compared to other proposed machines.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS1992

X-ray flares from runaway pair production in active galactic nuclei

The hard X-ray spectrum of AGNs is nonthermal, probably arising from an electron-positron pair cascade, with some emission reflected off relatively cold matter. There has been interest in models on which protons are accelerated and create relativistic electrons on interaction with a local radiation field. It is shown here that a sufficient column density of protons can lead to runaway pair production: photons generated by the relativistic pairs are the targets for the protons to produce more pairs. This can produce X-ray fluxes with the characteristics observed in AGN. The model predicts the maximum ratio of luminosity to source size as well as their spectrum in the early phases. The same mechanism may also be able to create the knots of synchrotron-radiating pair plasma seen in sources such as 3C273.

Kirk, J. G.↗

DOE OSTI2025

First Evidence of Solar Neutrino Interactions on 13 C

The SNO+ Collaboration reports the first evidence of 8 B solar neutrinos interacting on 13 C nuclei. The charged current interaction proceeds through 13 C +𝜈 𝑒 → 13 N+𝑒 − which is followed, with a 10 minute half life, by 13 N → 13 C +𝑒 + +𝜈 𝑒 . The detection strategy is based on the delayed coincidence between the electron and the positron. Evidence for the charged current signal is presented with a significance of 4.2⁢𝜎. Using the natural abundance of 13 C present in the scintillator, 5.7 metric tons of 13 C over 231 days of data were used in this analysis. The 5.6$^{+3.0}_{−2.3}$ observed events in the data set are consistent with the expectation of 4.7$^{+0.6}_{−1.3}$ events. This result is the second real-time measurement of CC interactions of 8 B neutrinos with nuclei and constitutes the lowest energy observation of neutrino interactions on 13 C generally. This enables the first direct measurement of the CC 𝜈 𝑒 reaction to the ground state of 13 N , yielding an average cross section of (16.1$^{+8.5}_{−6.7}$⁢(stat.)$^{+1.6}_{−2.7}$⁢(syst.))×10 −43 cm 2 over the relevant 8 B solar neutrino energies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

Luminosity and beam-induced background studies for the Cool Copper Collider

A high-energy electron-positron collider has been widely recognized by the particle physics community to be the next crucial step for detailed studies of the Higgs boson and other fundamental particles and processes. Several proposals for such colliders, either linear or circular, are currently under evaluation. Any such collider will be required to reach high lumimosities, in order to collect enough data at a reasonable time scale, while at the same time coping with high rates of background particles produced from beam-beam interactions during the collisions. In this paper, we analyze the luminosity and beam-beam interaction characteristics of the Cool Copper Collider ( C 3 ) and perform a comparison with other linear collider proposals. We conclude that C 3 can reach the same or higher collision rates as the other proposals, without having to cope with higher beam-induced background fluxes. Thus, C 3 emerges as an attractive option for a future electron-positron collider, benefiting from the collective advancements in beam delivery and final focus system technologies developed by other linear collider initiatives. Published by the American Physical Society 2024

43 PARTICLE ACCELERATORS↗

NASA NTRS1982

Processes in relativistic plasmas

The establishment and maintenance of a Boltzmann distribution in particle kinetic energies is investigated for a plasma with theta = KTe/mc-squared much greater than unity, where m is the electron mass. It is shown that thermalization of the electron gas by binary collisions is not sufficiently effective to maintain the equilibrium distribution when other processes that perturb the equilibrium are taken into account. Electron-positron pair production in electron-electron and electron-ion collisions, and perturbations of a Boltzmann distribution by nonthermal processes are evaluated. Thermalization by means of other mechanisms, such as interaction with plasma waves is discussed, and the opacity of a relativistic plasma is computed for Compton scattering, pair production in the fields of electrons and ions, inverse bremsstrahlung, and synchrotron self-absorption.

Gould, R. J.↗

NASA NTRS1983

Simultaneous acceleration of electrons and ions in solar flares

Data from the observations of two gamma ray and electron bremsstrahlung X-ray emitting solar flares, on June 7 and 21, 1980, were used to examine the relative starting times of the energetic ion and electron interactions. The data were gathered by the SMM, which was viewing the 2.223 MeV line from H-1(n, gamma)H-2, the 0.511 MeV line from electron-positron annihilation, the prompt nuclear lines at 4.44 and 6.13 MeV from excited C-12 and excited O-16, and the energetic solar neutrons at 1 AMU. Excess gamma ray and X-ray emissions were detected at relatively the same times during both flares in all energy bands, and were attributed to ion-induced emissions. The timing of the peaks of electron and ion activity indicate that both electrons and ions are accelerated to their peak activity in under 5 sec.

Forrest, D. J.↗

DOE OSTI2023

Two-particle azimuthal correlations in γp interactions using pPb collisions at s NN = 8.16 TeV

The first measurements of the Fourier coefficients ( V n Δ ) of the azimuthal distributions of charged hadrons emitted from photon-proton (γp) interactions are presented. The data are extracted from 68.8 nb −1 of ultra-peripheral proton-lead (pPb) collisions at s NN = 8.16 TeV using the CMS detector. The high energy lead ions produce a flux of photons that can interact with the oncoming proton. This γp system provides a set of unique initial conditions with multiplicity lower than in photon-lead collisions but comparable to recent electron-positron and electron-proton data. The V n Δ coefficients are presented in ranges of event multiplicity and transverse momentum ( p T ) and are compared to corresponding hadronic minimum bias pPb results. For a given multiplicity range, the mean p T of charged particles is smaller in γp than in pPb collisions. For both the γp and pPb samples, V 1 Δ is negative, V 2 Δ is positive, and V 3 Δ consistent with 0. For each multiplicity and p T range, V 2 Δ is larger for γp events. The γp data are consistent with model predictions that have no collective effects.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Plasma-based particle sources

High-brightness particle beams generated by advanced accelerator concepts have the potential to become an essential part of future accelerator technology. In particular, high-gradient accelerators can generate and rapidly accelerate particle beams to relativistic energies. The rapid acceleration and strong confining fields can minimize irreversible detrimental effects to the beam brightness that occur at low beam energies, such as emittance growth or pulse elongation caused by space charge forces. Due to the high accelerating gradients, these novel accelerators are also significantly more compact than conventional technology. Advanced accelerators can be extremely variable and are capable of generating particle beams with vastly different properties using the same driver and setup with only modest changes to the interaction parameters. So far, efforts have mainly been focused on the generation of electron beams, but there are concepts to extend the sources to generate spin-polarized electron beams or positron beams. The beam parameters of these particle sources are largely determined by the injection and subsequent acceleration processes. Although, over the last decade there has been significant progress, the sources are still lacking a sufficiently high 6-dimensional (D) phase-space density that includes small transverse emittance, small energy spread and high charge, and operation at high repetition rate. This is required for future particle colliders with a sufficiently high luminosity or for more near-term applications, such as enabling the operation of free-electron lasers (FELs) in the X-ray regime. Major research and development efforts are required to address these limitations in order to realize these approaches for a front-end injector for a future collider or next-generation light sources. In particular, this includes methods to control and manipulate the phase-space and spin degrees-of-freedom of ultrashort plasma-based electron bunches with high accuracy, and methods that increase efficiency and repetition rate. These efforts also include the development of high-resolution diagnostics, such as full 6D phase-space measurements, beam polarimetry and high-fidelity simulation tools. A further increase in beam luminosity can be achieve through emittance damping. Emittance cooling via the emission of synchrotron radiation using current technology requires kilometer-scale damping rings. For future colliders, the damping rings might be replaced by a substantially more compact plasma-based approach. Here, plasma wigglers with significantly stronger magnetic fields are used instead of permanent-magnet based wigglers to achieve similar damping performance but over a two orders of magnitude reduced length.

43 PARTICLE ACCELERATORS↗

DOE OSTI2022

Dynamical Pair Production at Sub-Barrier Energies for Light Nuclei

In the collision of two heavy ions, the strong repulsion coming from the Coulomb field is enough to produce e+e− pair(s) from vacuum fluctuations. The energy is provided by the kinetic energy of the ions and the Coulomb interaction at the production point. If, for instance, the electron is located at the center of mass (C.M.) of the two ions moving along the z-axis, and the positron is at a distance x from the electron, the ions can be accelerated towards each other since the Coulomb barrier is lowered by the presence of the electron. This screening results in an increase in the kinetic energy of the colliding ions and may result in an increase in the fusion probability of light ions above the adiabatic limit.

Settlemyre, Thomas (ORCID:0000000276824773)↗

NASA NTRS1991

Preferential positron heating and acceleration by synchrotron maser instabilities in relativistic positron-electron-proton plasmas

A new process of the preferential strong heating of positrons through the ion synchrotron maser instability in positron-electron-proton magnetized plasmas is investigated using particle-in-cell simulations. It is shown that the positrons form a nonthermal power-law-like energy distribution via their gyroresonant interaction with the extraordinary modes emitted by the ions. It is noted that this process may be of significance in connection with the shock excitation of nonthermal synchrotron radiation from astrophysical systems powered by relativistic outflows from compact central objects, e.g., supernova remnants powered by pulsars and jets from active galactic nuclei.

Hoshino, Masahiro↗

DOE OSTI2024

Ab initio investigation of the Li 7 ( p , e + e - ) Be 8 process and the X17 boson

Observations of anomalies in the electron-positron angular correlations in high-energy decays in 4 He, 8 Be, and 12 C have been reported recently by the ATOMKI collaboration. These could be explained by the creation and subsequent decay of a new boson with a mass of ≈ 17MeV. Theoretical understanding of pair creation in the proton capture reactions used in these experiments is important for the interpretation of the anomalies. We apply the ab initio no-core shell model with continuum (NCSMC) to the proton capture on 7 Li. The NCSMC describes both bound and unbound states in light nuclei in a unified way with chiral two- and three-nucleon interactions as the only input. We investigate the structure of 8 Be, the p+ 7 Li elastic scattering, the 7 Li(p,y)⁢ 8 Be cross section, and the internal pair creation 7 Li ⁢(p,e + ⁢e - ) 8 Be. Here we discuss the impact of a proper treatment of the initial scattering state on the electron-positron angular correlation spectrum and compare our results to available ATOMKI data sets. Finally, we calculate 7 Li ⁢(p,X)⁢ 8 Be cross sections for several proposed models of the hypothetical X17 particle.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2021

Plasma physics in strong-field regimes: Theories and simulations

In strong electromagnetic fields, unique plasma phenomena and applications emerge whose description requires recently developed theories and simulations [Y. Shi, Ph.D. thesis, Princeton University (2018)]. In the classical regime, to quantify effects of strong magnetic fields on three-wave interactions, a convenient formula is derived by solving the fluid model to the second order in general geometry. As an application, magnetic resonances are exploited to mediate laser pulse compression, whereby higher intensity pulses can be produced in wider frequency ranges, as confirmed by particle-in-cell simulations. In even stronger fields, relativistic-quantum effects become important, and a plasma model based on scalar quantum electrodynamics (QED) is developed which unveils observable corrections to Faraday rotation and cyclotron absorption in strongly magnetized plasmas. Beyond the perturbative regime, lattice QED is extended as a numerical tool for plasma physics, using which the transition from wakefield acceleration to electron-positron pair production is captured when laser intensity exceeds the Schwinger threshold.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2025

Final Search for Short-Baseline Neutrino Oscillations with the PROSPECT-I Detector at HFIR

The PROSPECT experiment is designed to perform precise searches for antineutrino disappearance at short distances (7–9 m) from compact nuclear reactor cores. This Letter reports results from a new neutrino oscillation analysis performed using the complete data sample from the PROSPECT-I detector operated at the High Flux Isotope Reactor in 2018. The analysis uses a multiperiod selection of inverse beta decay neutrino interactions with reduced backgrounds and enhanced statistical power to set limits on electron neutrino disappearance caused by mixing with sterile neutrinos with 0.2–20 eV 2 mass splittings. Inverse beta decay positron energy spectra from six different reactor-detector distance ranges are found to be statistically consistent with one another, as would be expected in the absence of sterile neutrino oscillations. The data excludes at 95% confidence level the existence of sterile neutrinos in regions above 3 eV 2 previously unexplored by terrestrial experiments, including all space below 10 eV 2 suggested by the recently strengthened Gallium Anomaly. The best-fit point of the Neutrino-4 reactor experiment’s claimed observation of short-baseline oscillation is ruled out at more than 5 standard deviations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS1989

The nature of the cosmic-ray electron spectrum, and supernova remnant contributions

The observed cosmic-ray (CR) electron spectrum and position fraction e+/(e- + e+) spectrum above 1 GeV are examined, and it is found that a deconvolution of the total spectrum into three components is necessary because of the increase of e+/(e- + e+) above 5 GeV: (1) secondary electrons e+ or e- from the interaction of the CR protons with the interstellar gas provide the total e+ for energies less than 3 GeV, but for energies above 3 GeV these electrons cannot account for the observed positron flux; (2) Electrons (e-) generally thought to derive from supernova remnants (SNRs), probably via shock acceleration, dominate the total spectrum for E of 10 GeV or less but definitely decline relative to total at higher energies; (3) Another (e- + e+) source dominates the total spectrum at E of 40 GeV or greater. The derived spectrum of (2) is consistent in its energy cutoff (though gradual) with that deduced from the observed synchrotron emission of some old SNRs and follows naturally from shock acceleration with synchrotron and inverse Compton scattering losses taken into account. As for (3), nearby pulsars may be important contributors.

Boulares, Ahmed↗

DOE OSTI2022

Simulation Studies of Intra-Train, Bunch-by-Bunch Feedback Systems at the International Linear Collider

The International Linear Collider (ILC) is a proposed electron-positron collider targeting collision energies from 250 GeV to 1 TeV. With design luminosities of order 10³⁴ cm²s⁻¹, a beam-based, intra-train feedback system would be required near the Interaction Point (IP) to provide nanometre-level stabilisation of the beam overlap in the collisions. Here we present results from beam-tracking simulations of the 500 GeV ILC, including the impact of beam-trajectory imperfections on the luminosity, and the capability of the IP feedback system to compensate for them. Effects investigated include the position jitter introduced by the damping ring extraction kicker, short-range and long-range wakefields, and ground motion. The feedback system was shown to be able to correct for beam-beam offsets of up to 200 nm and stabilise the collision overlap to the nanometre level, within a few bunch crossings.

Ramjiawan, R. L.↗

DOE OSTI2023

Compact Multicell SRF Crab Cavity for ILC

International Linear Collider (ILC), a proposed linear electron-positron collider, plans to utilize crab cavities to enhance its luminosity. By introducing a transverse kick to the beams, the crab cavities (CC) rotate the beam bunches, allowing for increased overlap at the interaction points. High intensity of the beam current and limited transverse space along the beam pipe near the interaction point resulted in choosing superconducting technology for the ILC/CC. We present a scalable design of a superconducting Quasi-waveguide Multicell Resonator (QMiR) seamlessly connected with a beam vacuum chamber. The cavity is completely open at both ends, which avoids complex HOM couplers, and thus simplifies the mechanical design of the cavity.

Lunin, A.↗