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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Characteristic time scales of leptonization (τ + ), deleptonization (τ – ), and fluid motion (τ a ) in a disk of hot gas accreting on to a black hole formed after a failed supernova. These time scales are set by neutrino emission, absorption, and magnetohydrodynamic turbulence, highlighting the complex interplay between the four forces of nature in these enigmatic systems.
This Snowmass 2021 contributed paper discusses a Higgs-Energy LEptoN (HELEN) e⁺e⁻ linear collider based on advances superconducting radio frequency technology. The proposed collider offers cost and AC power savings, smaller footprint (relative to the ILC), and could be built at Fermilab with an Interaction Region within the site boundaries. After the initial physics run at 250 GeV, the collider could be upgraded either to higher luminosity or to higher (up to 500 GeV) energies. If the ILC could not be realized in Japan in a timely fashion, the HELEN collider would be a viable option to build a Higgs factory in the U.S.
In this talk, I will present a search for long-lived heavy neutral leptons decaying in the CMS muon detectors.
The smallness of neutrino masses in conjunction with the observed flavor oscillations in the neutrino sector can be hinting to physics beyond the standard model. These observations can be naturally accommodated by the so-called "seesaw" mechanism, in which new Heavy Neutral Leptons (HNL) are postulated. Additionally, several HNL models provide a DM candidate or include a possible explanation for the observed baryon asymmetry. This talk presents an comprehensive overview of the CMS HNL program with a focus on the new experimental results as shown in a recently published review paper by CMS.The talk will highlight several novel and complementary approaches using both prompt and long-lived signatures using the full Run-II data-set collected at the LHC.
Neutrinoless double beta decay and Lepton Number Violation
Heavy Neutral Leptons (HNLs) are hypothetical long-lived particles that extend the Standard Model and provide a natural explanation for the origin of neutrino masses, the generation of the baryon asymmetry through leptogenesis, and the nature of dark matter. The Short-Baseline Near Detector (SBND) is a 112-ton liquid argon time projection chamber located 110 m away from the Booster Neutrino Beam (BNB) target at Fermilab (Illinois, USA). The close location to the BNB origin makes the experiment sensitive to HNLs produced from meson decays in the beam. These heavy particles arrive at the detector later than neutrinos and decay into observable final states such as 𝜈e+e- or 𝜈π0, generating isolated electromagnetic showers. Thanks to SBND’s advanced scintillation light detection system, a timing resolution at the nanosecond level further boosts the experiment capabilities. In this poster, we present ongoing reconstruction efforts towards HNLs as well as expected sensitivities factoring in the reconstruction improvements.
Mu2e will search for coherent, neutrino-less conversion of muons into electrons in the field of a nucleus with a sensitivity improvement of a factor of 10,000 over existing limits. Such a charged lepton flavor-violating reaction probes new physics at a scale unavailable with direct searches at either present or planned high energy colliders. The experiment both complements and extends the current studies at MEG and at the LHC.We present the physics motivation for Mu2e, as well as the design of the muon beamline, tracking spectrometer, and calorimeter. The Mu2e experiment is under design and construction at the Muon Campus of Fermilab. The experiment will begin near the end of 2020 with 3 years of running from 2021 to 2024.
Semileptonic $B_{(s)}$ decays are of great phenomenological interestbecause they allow to extract CKM matrix elements or test lepton flavouruniversality. Taking advantage of existing data, we explore extractingform factors for vector final states using the narrow widthapproximation. Based on RBC/UKQCD's set of 2+1 flavour gauge fieldensembles with Shamir domain-wall fermion and Iwasaki gauge fieldaction, we study semileptonic $B_{(s)}$ decays using domain-wallfermions for light, strange and charm quarks, whereas bottom quarks aresimulated with the relativistic heavy quark (RHQ) action. Exploratoryresults for $B_s \to D_s^* \ell \nu_\ell$ are presented.
The Mu2e experiment at Fermilab aims to search for Charged Lepton Flavor Violation (CLFV) through the coherent conversion of a muon into an electron in the field of an aluminum nucleus. This process, highly suppressed in the Standard Model, would clearly indicate new physics if observed. A crucial component of Mu2e is its electromagnetic calorimeter, which enhances the identification and measurement of conversion electrons. The calorimeter consists of two disks of undoped CsI crystals read out by custom-designed SiPMs and fast front-end electronics. This paper presents an overview of the calorimeter’s design, its custom SiPM technology, the readout and data acquisition system, and the results from commissioning tests.Building on the experience from Mu2e, the proposed Mu2e-II upgrade aims to enhance further the experiment’s sensitivity by an order of magnitude. This requires significant advancements in calorimeter technology, particularly in crystal materials and photodetector performance. Studies on BaF$_2$ and LYSO crystals, as well as the development of radiation-hard Silicon Photomultipliers (SiPMs), are currently underway. Test beam results demonstrate promising improvements in energy resolution and timing capabilities, ensuring the feasibility of next-generation calorimetry solutions for Mu2e-II.
Measurements in the final states with taus or with no-leptons are among the most challenging as they are those with the smallest signal-to-background ratio. However, these final states are of particular interest as they can be important probes of new physics. Tau identification techniques and cross section measurements in top quark decays in these final states are discussed. The results, limited by systematical uncertainties, are consistent with standard model predictions, and are used to setstringent limits on new physics searches. The large data samples available at the Fermilab and at the Large Hadron Collider may help further improving the measurements.
In this paper, we elaborate on the new understanding of the cosmological constant and the gauge hierarchy problems in the context of string theory in its metastring formulation, based on the concepts of modular spacetime and Born geometry. The interplay of phase space (and Born geometry), the Bekenstein bound, the mixing between ultraviolet (UV) and infrared (IR) physics and modular invariance in string theory is emphasized. This new viewpoint is fundamentally rooted in quantum contextuality and not in statistical observer bias (anthropic principle). We also discuss the extension of this point of view to the problem of masses of quarks and leptons and their respective mixing matrices.
We investigate the electrostatic acceleration of electrons and positrons in the vicinity of the event horizon, applying the pulsar outer-gap model to black hole (BH) magnetospheres. During a low accretion phase, the radiatively inefficient accretion flow (RIAF) cannot emit enough MeV photons that are needed to sustain the force-free magnetosphere via two-photon collisions. In such a charge-starved region (or a gap), an electric field arises along the magnetic field lines to accelerate electrons and positrons into ultra-relativistic energies. These relativistic leptons emit copious gamma rays via curvature and inverse-Compton (IC) processes. Some of such gamma rays collide with the submillimeter-IR photons emitted from the RIAF to materialize as pairs, which polarize to partially screen the original acceleration electric field. It is found that the gap gamma-ray luminosity increases with decreasing accretion rate. However, if the accretion rate decreases too much, the diminished RIAF soft photon field can no longer sustain a stationary pair production within the gap. As long as a stationary gap is formed, the magnetosphere becomes force-free outside the gap by the cascaded pairs, irrespective of the BH mass. If a nearby stellar-mass BH is in quiescence, or if a galactic intermediate-mass BH is in a very low accretion state, its curvature and IC emissions are found to be detectable with Fermi /LAT and imaging atmospheric Cherenkov telescopes (IACT). If a low-luminosity active galactic nucleus is located within about 30 Mpc, the IC emission from its supermassive BH is marginally detectable with IACT.
The forward-backward asymmetry in Drell-Yan production and the effective leptonic electroweak mixing angle are measured in proton-proton collisions at $\sqrt{s}$ = 13 TeV, collected by the CMS experiment and corresponding to an integrated luminosity of 138 fb$^{-1}$. The measurement uses both dimuon and dielectron events, and is performed as a function of the dilepton mass and rapidity. The unfolded angular coefficient $A_4$ is also extracted, as a function of the dilepton mass and rapidity. Using the CT18Z set of parton distribution functions, we obtain $\sinθ^\ell_\text{eff}$ = 0.23152 $\pm$ 0.00031, where the uncertainty includes the experimental and theoretical contributions. The measured value agrees with the standard model fit result to global experimental data. This is the most precise $\sinθ^\ell_\text{eff}$ measurement at a hadron collider, with a precision comparable to the results obtained at LEP and SLD.
We report on the status of charged lepton flavor violating (CLFV) experiments with muons. We focus on the three "golden channels": $\mu^{+} \rightarrow e^{+} \gamma$, $\mu^{+} \rightarrow e^{+} e^{-} e^{+}$ and $\mu^{-} N \rightarrow e^{-} N$. The collection of upcoming experiments aim for sensitivity improvements up to $10^{4}$ with respect to previous searches. The MEG II experiment, searching for $\mu^{+} \rightarrow e^{+} \gamma$, is currently in its 4th year of physics data-taking with a published result from its first year of data. The Mu3e experiment is an upcoming experiment searching for $\mu^{+} \rightarrow e^{+} e^{-} e^{+}$ with plans of physics data-taking as soon as 2025. The Mu2e and COMET experiments are upcoming searches for $\mu^{-} N \rightarrow e^{-} N$ with the goal of physics data-taking starting in 2027 and 2026 respectively. This proceeding summarizes the signal signature, expected background, resolutions, and timelines for the mentioned searches.
Neutrino-lepton scattering contribution to total neutrino opacity of matter, noting astrophysical relevance
Deep inelastic lepton-hadron scattering cross sections universality properties based on Wilson theory