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All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Diagnosing Ghost Bunches with the Upstream Extinction Monitor in the Mu2e Experiment

The Mu2e experiment has a stringent requirement for extinction of the pulsed proton beam, referring to the elimination of particles between proton bunches to a relative level of 10$^-10$, which means a single out-of-time particle in the inter-pulse gaps for every 250 complete proton pulses. As the construction of the Mu2e experiment nears completion, it is crucially important to make an early measurement of the beam extinction in its current condition. Hence the upstream extinction monitor was constructed and operated to probe for problems in the proton pulse structure or a higher than expected incidence rate of out-of-time particles. The analysis in this work comes from data taken in March 2026. The long data run showed a significant presence of out-of-time particles from ghost bunches in the Delivery Ring approximately 388 ns after the centers of the main proton pulses. These are hypothesized to be the result of a combination of a RF frequency mismatch, particle space charge, and machine impedance during the rebunching sequence in the Recycler Ring, which can lead to particles leaking into adjacent buckets, but further studies and simulations are needed to confirm this

Hensley, R. [UC, Davis] (ORCID:0000000216064485)↗
DOE OSTI2026

Mu2e Production Target Thermal Test Project

The Mu2e experiment requires a production target that is capable of operating under extreme thermal conditions caused by an 8 GeV proton beam. This project’s objective supports the development of the Mu2e Pro- duction Target by testing the Stickman model’s thermal behavior. Angel Flores Luviano has assisted Jonathan Williams in progressing this project by contributing to the development of a Radiative Cooling Test Fixture (RCTF) that will be used to evaluate the thermal behavior of the new production target model. Engineering calculations were performed to an- alyze thermal performance and pressure drop within the cold well and wa- ter cooling circuit. These calculations also determined the optimal sizing for key components of the water system. An engineering note was made to document these calculations. CAD models of the water circuit piping, thermocouple mounting bars, and radiator chimney were developed, and prototype test rig components were fabricated using 3D printing. Future work will focus on continued RCTF development which includes control system integration, heater hardware design, and interfaces that can be scaled up to increase thermal capacity.

Flores Luviano, Angel Augusto [Unlisted, US]↗
DOE OSTI2026

Analysis of Slow Spill Data for the Mu2e Experiment

The execution of the Mu2e experiment requires a stable, low-intensity proton beam from the Delivery Ring to produce clean data and protect equipment. This is done by performing a “slow extraction,” which is the gradual contraction of the stable region within the accelerator’s beam pipe. The Delivery Ring is currently unable to perform slow extraction with the stability required by Mu2e. To resolve this, the FAN-C team is training machine learning models with the purpose of replacing the Delivery Ring’s current PID controllers with AI-powered controllers. Training these models requires clean, processed data from slow spills. Over the course of this project, data from previous slow spills were processed and analyzed, and the clean data, graphs, and insights gained from the process were provided to the FAN-C team to assist them in their efforts.

Osborn, Thomas [Purdue U., West Lafayette]↗
DOE OSTI2026

Mu2e straw tube tracker gas flow quality control

Here, we present a tracker gas flow quality control method developed for the Mu2e straw tube tracker. Using time-dependent current measurements, we quantify the onset time of ionization gain induced by an 55 F source during gas exchange, which is correlated to the gas conductance in the straw. This allows for the identification of channels with inadequate flow. This approach is broadly applicable to other gaseous detectors that require high-channel-count screening.

Flow↗
DOE OSTI2025

Temperature-dependent calibration procedures for the silicon photomultiplier readout of the cosmic ray veto detector for the Mu2e experiment

The cosmic ray veto detector for the Mu2e experiment consists of scintillation bars embedded with wavelength-shifting fibers and read out by silicon photomultipliers (SiPMs). Here, in this manuscript, the calibration procedures of the SiPMs are described including corrections for the temperature dependence of their light yield. These corrections are needed as the SiPMs are not kept at a constant temperature due to the complexity and cost of implementing a cooling system on such a large detector. Rather, it was decided to monitor the temperature to allow the appropriate corrections to be made. The SiPM temperature dependence has been measured in a dedicated experiment and the calibration procedures were validated with data from production detectors awaiting installation at Fermilab.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Performance studies of the Mu2e cosmic ray veto detector

The cosmic ray veto (CRV) detector of the Mu2e experiment consists of four layers of plastic scintillation counters that surround the detector solenoid. These counters are embedded with wavelength-shifting fibers and are read out by silicon photomultipliers (SiPMs). The performance of a subset of the CRV counters was studied in a cosmic-ray test stand. Here, using data taken over a two-year period, we report the single-layer muon detection efficiency and the rate at which the light yield degrades due to the aging of the plastic scintillation counters.

Aging↗
DOE OSTI2025

Closeout Report for: Experimental High Energy Physics at the University of South Alabama: Mu2e

The researcher worked on the Fermilab Mu2e Experiment. This experiment is in the construction phase. This experiment will look at a large number of stopped muon decays to search for the stopped muon converting directly into an electron with no other particles (i.e. neutrinos). The signature will be a nearly mono-energetic electron with the momentum of just below the rest mass energy of the muon. The researcher worked with in the Cosmic Ray Veto group (cosmic rays are a major source of background) and he also worked on the global alarms system.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Multi-track reconstruction algorithms in the Mu2e experiment

The Mu2e experiment, under construction at Fermilab, will search for the neutrino-less coherent µ−N → e−N conversion in the field of a 27 Al nucleus, a CLFV process. While the main goal of the experiment is to reconstruct the conversion electron, i.e., an event with a single track, there are motivations to develop an efficient tracking algorithm for reconstructing more simultaneous tracks. This could better constrain the background generated by p¯-annihilation in the Al target and search for Beyond the Standard Model processes. In this paper, we present the algorithms designed to reconstruct multi-particle events.

Ricci, Alessandro Maria [Pisa U.; INFN, Pisa] (ORC↗
DOE OSTI2025

Searches for Sub-GeV Dark Matter with NOvA and LDMX and Performance Studies of the Cosmic-Ray Veto for Mu2e

The constituents of dark matter are still unknown, and the viable possibilities span a very large mass range. Specific scenarios for the origin of dark matter sharpen the focus to within about an MeV to 100 TeV. Most of the stable constituents of known matter have masses in the lower range, and a thermal origin for dark matter works in a simple and predictive manner in this mass range as well. Non-gravitational couplings of dark matter to Standard Model particles would make it possible to produce dark matter at accelerators. Through 120 GeV proton-nucleus collisions, NOvA is effectively a beam dump experiment for producing and detecting dark matter. This thesis presents a search for dark matter – electron scattering in the NOvA near detector from sub-GeV dark matter produced at the target. A future search for sub-GeV dark matter with the Light Dark Matter eXperiment (LDMX) is discussed, along with a study of LDMX's expected sensitivity to visibly decaying dark photons. Additionally, performance studies of the Mu2e cosmic ray veto (CRV) are presented. A calibration procedure for the CRV counters is discussed, along with tests of the efficiency, position resolution, and light yield decline of the CRV counters.

Horoho, Tyler Gregory [Virginia U.] (ORCID:0000000↗
DOE OSTI2026

Slow Extraction Beam Commissioning for the Mu2e Experiment at Fermilab

Following the successful completion of the Muon g-2 experiment run at Fermilab, the Muon Campus facility has been reconfigured from delivering 3 GeV muon beams to the g-2 storage ring to providing slow-extracted 8 GeV proton beam spills for the Mu2e experiment. The first full-scale commissioning run with slow extraction was conducted during the 2025 run, followed by the second run in early 2026. We present the results and current status of this commissioning campaign.

Nagaslaev, V. [Fermilab]↗
DOE OSTI2026

Mu2e resonant extraction regulation system simulation in delivery ring

Mu2e is an upcoming experiment at Fermilab that relies on the slowly extracted 8 GeV proton beam from the Delivery Ring. The experiment imposes strong requirements on the spill uniformity. To address these requirements, the fast spill regulations system is being developed and commissioned. To inform this development and optimize the system performance we are carrying out the detailed simulations of the regulation process. The simulation includes the effect of six harmonic sextupoles that excite the third-integer resonance and three fast ramping quadrupoles that drive the horizontal tune to 29/3. The components of spill regulation system are designed to mitigate long-term drifts in the beam, ensuring stable operation over extended timescales, as well as addresses rapid variations within single spill. In this study, we review the regulation system design, simulation of the slow regulation, and the fast regulation PID regulation to curtail random variations in the extraction rate that could occur within a single spill.

Narayanan, Aakaash [Fermilab]↗
DOE OSTI2024

Mu2e: Modeling Drift of Ionized Particles with ML

The Mu2e experiment searches for charged lepton flavor violation through muon-to-electron conversion in the field of a nucleus. The signal is a monoenergetic electron with an energy of 104.97 MeV. Its momentum is reconstructed using information from drifting ionized particles in a straw tracker detector. This project analyzes the drift of ionized particles with a deep neural network to help improve the momentum reconstruction process. The model yields a 20% improvement in resolution from a reference linear model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Reinforcement Learning for In-Spill Optimization of the Mu2e Resonant Extraction: Compensating Non-Stationarity

We present design considerations and challenges for the fast machine learning component of a third-order resonant beam extraction regulation system being commissioned to deliver steady beam rates to the mu2e experiment at Fermilab. Dedicated quadrupoles drive the tune toward the 29/3 resonance each spill, extracting beam at kV multiwire septa. The overall Spill Regulation System consists of (1) a “slow” process using ~100-spill averages to adjust the base quad ramp infrequently, (2) a feedforward harmonic content compensator, and (3) the “fast” ML agent reacting during each ongoing spill with on-the-fly additive corrections to the sum of (1) and (2). We have demonstrated improved beam-rate steadying for a fast ML agent compared to a PID controller using a quasi-physical spill simulation, and demonstrated distillation of that simulation into a predictive surrogate model. Current work includes a data-and-training pipeline to generate data-aware surrogates with real-world dynamics, even as the dynamics shift unpredictably. The surrogates are to act as RL environments against which to train our fast ML control agents before deploying them on FPGA in the live system. Further current efforts focus on modeling and controlling beam loss around the storage ring, understanding additional available hardware inputs to the model, and the interplay of these with beam-steadying performance.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

LLRF System for the Fermilab Mu2e Project – AC Dipole Extinction

The Mu2e experiment measures the conversion rate of muons into electrons. The experiments requires 53 MHz batches of 8 GeV protons to be re-bunched into 150 ns, 2.5 MHz pulses for extraction to a single RF cavity running at 2.36 MHz. To meet stringent limits on the amount of beam between pulses, an Extinction System is used comprising of 2 AC dipole magnets (4.4MHz, 296Khz) and a collimator.

Guran, M. [Fermilab] (ORCID:0009000235538559)↗
DOE OSTI2026

Inconel 718 Oxide Coating Process for Mu2e Target Redesign

A method of growing an oxide coating on Inconel 718 samples was investigated to increase the emissivity of the redesigned Inconel Mu2e production target. Microscopy and emissivity measurements of a range of samples indicate excellent performance.

Williams, J. [Fermilab]↗
DOE OSTI2026

Slow Extraction Beam Commissioning for the Mu2e Experiment at Fermilab

Following the successful completion of the Muon g-2 experiment run at Fermilab, the Muon Campus facility has been reconfigured from delivering 3 GeV muon beams to the g-2 storage ring to providing slow-extracted 8 GeV proton beam spills for the Mu2e experiment. The first full-scale commissioning run with slow extraction was conducted during the 2025 run, followed by the second run in early 2026. We present the results and current status of this commissioning campaign.

Nagaslaev, V. [Fermilab] (ORCID:0000000235719205)↗