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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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At least 253 records · Page 14
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DOE OSTI2015

Sterile Neutrino Search with MINOS

MINOS, Main Injector Neutrino Oscillation Search, is a long-baseline neutrino oscillation experiment in the NuMI muon neutrino beam at the Fermi National Accelerator Laboratory in Batavia, IL. It consists of two detectors, a near detector positioned 1 km from the source of the beam and a far detector 734 km away in Minnesota. MINOS is primarily designed to observe muon neutrino disappearance resulting from three flavor oscillations. The Standard Model of Particle Physics predicts that neutrinos oscillate between three active flavors as they propagate through space. This means that a muon-type neutrino has a certain probability to later interact as a different type of neutrino. In the standard picture, the neutrino oscillation probabilities depend only on three neutrino flavors and two mass splittings, Δm 2 . An anomaly was observed by the LSND and MiniBooNE experiments that suggests the existence of a fourth, sterile neutrino flavor that does not interact through any of the known Standard Model interactions. Oscillations into a theoretical sterile flavor may be observed by a deficit in neutral current interactions in the MINOS detectors. A distortion in the charged current energy spectrum might also be visible if oscillations into the sterile flavor are driven by a large mass-squared difference, m s 2 ~ 1 eV 2 . The results of the 2013 sterile neutrino search are presented here.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Once-in-a-lifetime encounter models for neutrino media: From coherent oscillations to flavor equilibration

Collective neutrino oscillations are typically studied using the lowest-order quantum kinetic equation, also known as the mean-field approximation. However, some recent quantum many-body simulations suggest that quantum entanglement among neutrinos may be important and may result in flavor equilibration of the neutrino gas. In this work, we develop new quantum models for neutrino gases in which any pair of neutrinos can interact at most once in their lifetimes. A key parameter of our models is γ = μ Δ z , where μ is the neutrino coupling strength, which is proportional to the neutrino density, and Δ z is the duration over which a pair of neutrinos can interact each time. Our models reduce to the mean-field approach in the limit γ → 0 and achieve flavor equilibration in time t ≫ ( γ μ ) − 1 . These models demonstrate the emergence of coherent flavor oscillations from the particle perspective and may help elucidate the role of quantum entanglement in collective neutrino oscillations. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

A polarized Drell-Yan experiment to probe the dynamics of the nucleon sea

In QCD, nucleon spin comes from the sum of the quark spin, gluon spin, and the quark and gluon orbital angular momentum, but how these different components contribute and the interplay among them is not yet understood. For instance, sea quark orbital contribution remains largely unexplored. Measurements of the Sivers function for the sea quarks will provide a probe of the sea quark orbital contribution. The upcoming E1039 experiment at Fermilab will measure the Sivers asymmetry of the sea quarks via the Drell-Yan process using a 120 GeV unpolarized proton beam directed a transversely polarized ammonia target. We report on the status and plans of the E1039 polarized Drell-Yan experiment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Once-in-a-lifetime encounter models for neutrino media. II. Quasisteady states and miscidynamic flavor evolution

We extended the once-in-a-lifetime encounter (OILE) model to stochastic interactions among neutrinos. As in the original OILE model, the new model reproduces the mean-field behavior of a dense neutrino gas for time 𝑡 ≲ (𝜇⁢𝛾) −1 , where 𝜇 measures the strength of the mean-field neutrino self-interaction potential and is proportional to the neutrino density, and the dimensionless “impact parameter” 𝛾 is a measure of the change in the flavor quantum state of a neutrino during interaction with another neutrino when the wave packets of the two neutrinos overlap. As in the mean-field case, the OILE model with random neutrino velocities experiences kinetic flavor decoherence as the flavor quantum states of the neutrinos diverge from each other. Unlike the mean-field case, however, the OILE model has a “collision term” due to the quantum entanglement among neutrinos. For 𝛾 ≪ 1, this incoherent effect can drive the neutrinos into a quasisteady state that is similar to the collective precession mode in a homogeneous and isotropic neutrino gas in the mean-field approximation. Subsequently, the collision term drives the neutrino gas adiabatically through different quasisteady states and eventually to flavor equilibration. This process is an example of miscidynamic flavor evolution, with the mixing equilibria being the quasisteady precession states.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Heavy quarkonia description from a generalized screened potential model

The spectral effect of open flavor meson-meson thresholds in heavy quarkonia is analyzed by using a Non Relativistic Quark Model. The proposed form of the effective quark-antiquark potential, based on lattice indications, incorporates implicitly screening effects from meson-meson configurations. The application of the model to heavy quarkonia provides a resonable description of unconventional J{sup ++} charmonium states and a definite prediction for unconventional J{sup ++} states in bottomonium.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Testing lepton flavor universality at future Z factories

As one of the hypothetical principles in the Standard Model (SM), lepton flavor universality (LFU) should be tested with a precision as high as possible such that the physics violating this principle can be fully examined. The run of a Z factory at a future e + e − collider, such as the Circular Electron-Positron Collider or Future Circular Collider (electron/positron), provides a great opportunity to perform this task because of the large statistics and high reconstruction efficiencies for b hadrons at the Z pole. In this paper, we present a systematic study on the LFU test in future Z factories. The goal is threefold. First, we study the sensitivities of measuring the LFU-violating observables of b → c τ ν , i.e., R J / ψ , R D s , R D s * , and R Λ c , where τ decays muonically. For this purpose, we develop the strategies for event reconstruction, based on the track information significantly. Second, we explore the sensitivity robustness against detector performance and its potential improvement with the message of event shape or beyond the b -hadron decays. A picture is drawn on the variation of analysis sensitivities with the detector tracking resolution and soft photon detectability, and the impact of Fox-Wolfram moments is studied on the measurement of relevant flavor events. Finally, we interpret the projected sensitivities in the SM effective field theory, by combining the LFU tests of b → c τ ν and the measurements of b → s τ + τ − and b → s ν ¯ ν . We show that the limits on the LFU-violating energy scale can be pushed up to ∼ O ( 10 ) TeV for ≲ O ( 1 ) Wilson coefficients at Tera- Z . Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2012

HYBRID STARS IN THE LIGHT OF THE MASSIVE PULSAR PSR J1614-2230

We perform a systematic study of hybrid star configurations using several parameterizations of a relativistic mean-field hadronic equation of state (EoS) and the Nambu-Jona-Lasinio (NJL) model for three-flavor quark matter. For the hadronic phase we use the stiff GM1 and TM1 parameterizations, as well as the very stiff NL3 model. In the NJL Lagrangian we include scalar, vector, and 't Hooft interactions. The vector coupling constant g{sub v} is treated as a free parameter. We also consider that there is a split between the deconfinement and the chiral phase transitions which is controlled by changing the conventional value of the vacuum pressure -{Omega}{sub 0} in the NJL thermodynamic potential by -({Omega}{sub 0} + {delta}{Omega}{sub 0}), with {delta}{Omega}{sub 0} a free parameter. We find that, as we increase the value of {delta}{Omega}{sub 0}, hybrid stars have a larger maximum mass but are less stable, i.e., hybrid configurations are stable within a smaller range of central densities. For large enough {delta}{Omega}{sub 0}, stable hybrid configurations are not possible at all. The effect of increasing the coupling constant g{sub v} is very similar. We show that stable hybrid configurations with a maximum mass larger than the observed mass of the pulsar PSR J1614-2230 are possible for a large region of the parameter space of g{sub v} and {delta}{Omega}{sub 0} provided the hadronic EoS contains nucleons only. When the baryon octet is included in the hadronic phase, only a very small region of the parameter space allows an explanation of the mass of PSR J1614-2230. We compare our results with previous calculations of hybrid stars within the NJL model. We show that it is possible to obtain stable hybrid configurations also in the case {delta}{Omega}{sub 0} = 0 that corresponds to the conventional NJL model for which the pressure and density vanish at zero temperature and chemical potential.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The spectrum and flavor composition of the astrophysical neutrinos in IceCube

We fit the energy distribution of the IceCube starting events by a model which involves four parameters in the neutrino spectrum, namely three normalizations n{sub e},n{sub μ},n{sub τ} and a common power-law index γ, with a fixed background simulated by IceCube. It is found that the best fit index is γ = 2.7 with χ{sup 2}{sub min} = 32.3/24 dof. As for the two parameter model involving a democratic normalization and an index, the best fit is at γ = 2.8 with χ{sup 2}{sub min} = 33.9/26 dof. The flavored model and the democratic model do not have much difference in the quality of the (energy-spectrum) fit. The standard 1 : 1 : 1 composition is not disfavored by the current data.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Three-dimensional core-collapse supernova models with phenomenological treatment of neutrino flavor conversions

Abstract We perform three-dimensional supernova simulations with a phenomenological treatment of neutrino flavor conversions. We show that the explosion energy can increase to as high as $\sim 10^{51}$ erg depending on the critical density for the onset of flavor conversions, due to a significant enhancement of the mean energy of electron antineutrinos. Our results confirm previous studies showing such energetic explosions, but for the first time in three-dimensional configurations. In addition, we predict neutrino and gravitational wave (GW) signals from a nearby supernova explosion aided by flavor conversions. We find that the neutrino event number decreases because of the reduced flux of heavy-lepton neutrinos. In order to detect GWs, next-generation GW telescopes such as Cosmic Explorer and the Einstein Telescope are needed even if the supernova event is located at the Galactic Center. These findings show that the neutrino flavor conversions can significantly change supernova dynamics and highlight the importance of further studies on the quantum kinetic equations to determine the conditions of the conversions and their asymptotic states.

Mori, Kanji↗
DOE OSTI2025

The role of chromatin state in intron retention: A case study in leveraging large scale deep learning models

Complex deep learning models trained on very large datasets have become key enabling tools for current research in natural language processing and computer vision. By providing pre-trained models that can be fine-tuned for specific applications, they enable researchers to create accurate models with minimal effort and computational resources. Large scale genomics deep learning models come in two flavors: the first are large language models of DNA sequences trained in a self-supervised fashion, similar to the corresponding natural language models; the second are supervised learning models that leverage large scale genomics datasets from ENCODE and other sources. We argue that these models are the equivalent of foundation models in natural language processing in their utility, as they encode within them chromatin state in its different aspects, providing useful representations that allow quick deployment of accurate models of gene regulation. We demonstrate this premise by leveraging the recently created Sei model to develop simple, interpretable models of intron retention, and demonstrate their advantage over models based on the DNA language model DNABERT-2. Our work also demonstrates the impact of chromatin state on the regulation of intron retention. Using representations learned by Sei, our model is able to discover the involvement of transcription factors and chromatin marks in regulating intron retention, providing better accuracy than a recently published custom model developed for this purpose.

Biochemistry & Molecular Biology↗
DOE OSTI2024

Interplay of freeze-in and freeze-out: Lepton-flavored dark matter and muon colliders

We study a lepton-flavored dark matter model and its signatures at a future muon collider. We focus on the less-explored regime of feeble dark matter interactions, which suppresses the dangerous lepton-flavor-violating processes, gives rise to dark matter freeze-in production, and leads to long-lived particle signatures at colliders. We find that the interplay of dark matter freeze-in and its mediator freeze-out gives rise to an upper bound of around TeV scales on the dark matter mass. The signatures of this model depend on the lifetime of the mediator and can range from generic prompt decays to more exotic long-lived particle signals. In the prompt region, we calculate the signal yield, study useful kinematics cuts, and report tolerable systematics that would allow for a 5 σ discovery. In the long-lived region, we calculate the number of charged tracks and displaced lepton signals of our model in different parts of the detector and uncover kinematic features that can be used for background rejection. We show that, unlike in hadron colliders, multiple production channels contribute significantly, which leads to sharply distinct kinematics for electroweakly charged long-lived particle signals. Ultimately, the collider signatures of this lepton-flavored dark matter model are common among models of electroweak-charged new physics, rendering this model a useful and broadly applicable benchmark model for future muon collider studies that can help inform work on detector design and studies of systematics. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2018

Matter-neutrino resonance in a multiangle neutrino bulb model

Simulations of neutrino flavor evolution in compact merger environments have shown that neutrino flavor, and hence nucleosynthesis, can be strongly affected by the presence of matter-neutrino resonances (MNRs), where there is a cancelation between the matter and the neutrino potential. Simulations performed thus far follow flavor evolution along a single neutrino trajectory, but self-consistency requires all trajectories to be treated simultaneously, and it has not been known whether MNR phenomena would still occur in multiangle models. In this paper, we present the first fully multi-angle calculations of MNR. We find that familiar MNR phenomena, where neutrinos transform to a greater extent than anti-neutrinos and a feedback mechanism maintains the cancellation between the matter and neutrino potential, still occurs for a subset of angular bins, although the flavor transformation is not as efficient as in the single-angle case. In addition, we find other types of flavor transformation that are not seen in single-angle simulations. These flavor transformation phenomena appear to be robust and are present for a wide range of model parameters, as long as an MNR is present. Although computational constraints currently limit us to models with spherical symmetry, our results suggest that the presence of an MNR generally leads to large-scale neutrino flavor evolution in multiangle systems.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Unification of gauge, family, and flavor symmetries illustrated in gauged SU(12) models

In this study, to explain quark and lepton masses and mixing angles, one has to extend the standard model, and the usual practice is to put the quarks and leptons into irreducible representations of discrete groups. We argue that discrete flavor symmetries (and their concomitant problems) can be avoided if we extend the gauge group. In the framework of SU(12) we give explicit examples of models having varying degrees of predictability obtained by scanning over groups and representations and identifying cases with operators contributing to mass and mixing matrices that need little fine- tuning of prefactors. Fitting with quark and lepton masses run to the GUT scale and known mixing angles allows us to make predictions for the neutrino masses and hierarchy, the octant of the atmospheric mixing angle, leptonic CP violation, Majorana phases, and the effective mass observed in neutrinoless double beta decay.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗