Muon Research Articles

Muon accelerators—muon lifetime measurements as window to Planck scale physics

A prominent effective description of particles interacting with the quantum properties of gravity is through modifications of the general relativistic dispersion relation. Such modified dispersion relations lead to modifications in the relativistic time dilation. A perfect probe for this effect, which goes with the particle energy cubed E 3 over the quantum gravity scale E QG and the square of the particle mass M 2 would be a very light unstable particle for which one can detect the lifetime in the laboratory (lab) as a function of its energy measured in the lab to very high precision. In this article we conjecture that a muon collider or accelerator would be a perfect tool to investigate the existence of an anomalous time dilation, and with it the fundamental structure of spacetime at the Planck scale.

QED calculations of the nuclear recoil effect in muonic atoms

QED calculations of the nuclear recoil effect in muonic atoms

Note on the electromagnetic radius of proton

In this paper, we have analyzed the proton form factor data by using a number of phenomenological parametrizations (models) and extracting the proton electric and magnetic radii. To this end, we performed a global fit to all available form factor data, with the virtual photon momentum squared [Formula: see text] from [Formula: see text] to nearly 10[Formula: see text]GeV2 for electric form factor and from [Formula: see text] to 31[Formula: see text]GeV2 for magnetic one. Special attention was given to the small structure shown by the form factor data near [Formula: see text][Formula: see text]GeV2. It was found that different models yield different structures with different numbers of minimum at this kinematics. Since the slope of form factor in the limit of [Formula: see text] is influenced by this structure, the extracted proton radii are consequently different for different models. Our finding recommends that future experiments should focus on this kinematics instead of low [Formula: see text]. Experimental data with accuracies comparable to those of the latest data at low [Formula: see text] would clearly help to clarify the effect of this structure on the proton charge radius. Interestingly, most of the extracted proton charge radii were found to be closer to the value obtained from the muonic hydrogen atom spectroscopy.

The Implementation of MuDirac in Geant4: A Preliminary Approach to the Improvement of the Simulation of the Muonic Atom Cascade Process

Muonic Atom X-ray Emission spectroscopy (µ-XES) is a novel elemental technique that exploits the high-energy X-rays emitted from the muonic atom cascade process to characterize materials. At the ISIS Neutron and Muon Source, the technique is performed at Port4 of the RIKEN-RAL facility, with a user demand that is increasing every year. To cope with this demand, it is necessary to continue to improve the method, either for the hardware (detectors, acquisition, etc.) or software (data analysis and interpretation). In both cases, Monte Carlo codes play an important role: with a simulation, it is possible to reproduce the experimental setup and provide a reliable quantitative analysis. In this work, we investigate the capabilities of GEANT4 for such applications. From the results, we observed that the generation of X-rays, especially the kα and kβ transition for high Z atoms, are not in agreement with the experimental ones. A solution to this issue, other than an attempt with a small modification of the GEANT4 cascade class, could be provided by a database of transition energy calculated by a Dirac equation software called MuDirac. The software, developed by the UKRI scientific computing department and the ISIS muon group, can compute all the transition energy for a given nuclide. Here, preliminary results of the implementation of the MuDirac database in GEANT4 are reported.

Background studies and normalization of signal events in the Mu2e experiment

The Mu2e experiment is currently being constructed at Fermilab to search for the neutrino-less conversion of negative muons into electrons in the field of an aluminum nucleus. The experiment aims at a sensitivity of four orders of magnitude higher than previous related experiments, which implies highly demanding accuracy requirements both in the design and during the operation. To achieve such a goal, two important tasks should be accomplished. First, it is essential to estimate precisely the particle yields and all the backgrounds that could mimic the monoenergetic conversion electron signal. Second, it is necessary to normalize the signal events accurately. The normalization of the signal events is planned to be done using a detector system made of an HPGe detector and a Lanthanum Bromide detector, which will measure the rate of muons stopped on the aluminum target by looking at the emitted characteristic X-and γ-rays of energies up to 1809 keV. Therefore, it is essential to evaluate the detector system's performance before the start of the actual experiment. In this study, the first task was addressed by an extensive campaign of Monte Carlo simulations to investigate the relevant parameters and their impact on the experiment's sensitivity. The second task was handled by taking advantage of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) pulsed Bremsstrahlung photon beam at the ELBE facility. The detector system was tested at the ELBE facility under timing and background conditions similar to the ones expected at the Mu2e experiment. The study presents and discusses the simulation results and the detector system testing campaign.

Samarium addition-mediated simultaneous achievement of excellent resistance drift and superior thermal stability in phase-change compound antimony-selenium thin film

The Sm-doped Sb7Se3 thin films were systematically investigated, including phase change behavior, phase structure, microstructure, and electrical properties. The in-situ resistance test displays that the addition of Sm element leads to a significant increase in the crystallization temperature, decadal data retention and crystallization activation energy, implying better thermal stability. Crystallization kinetic analysis indicates a one-dimensional growth crystallization pattern, exhibiting an ultra-fast crystallization speed. The change in optical bandgap reflects that the exotic Sm atoms enhance the bandgap energy, which facilitates the reduction of the threshold current. Resistance drift test highlights the suppression of structural relaxation by Sm atoms, which would greatly improve the reliability of the information readout. X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectra, and transmission electron microscopy demonstrate that the addition of Sm retards the crystallization process and refines the grain size. Energy dispersive spectroscopy shows that the Sm dopant has incorporated into Sb7Se3 thin film. The phase change memory cell based on Sm-doped Sb7Se3 film exhibits faster running speed (100 ns) and lower power consumption (3.0 × 10−11 J) than the conventional Ge2Sb2Te5 material. All the results prove that incorporating appropriate amounts of Sm into Sb7Se3 material is an ideal technique for optimizing resistance drift and thermal stability of Sb7Se3 thin films.

Revisiting the extraction of charge radii of 40Ca and 208Pb with muonic atom spectroscopy

The extractions of nuclear charge radii from muonic atom spectroscopy for 40Ca and 208Pb are revisited to analyze the model dependencies induced by employing a Fermi-type charge distribution. For that, the charge densities, together with the corresponding muonic transition energies, calculated by the covariant density functional theory are used as a benchmark. The root-mean-square deviation of transition energies is calculated to quantitatively investigate the sensitivities of transition energies to the details of the two-parameter Fermi distribution. It is found that the second and fourth moments of the charge distribution can be extracted accurately from the muonic atom spectroscopy without much model dependencies, whereas the obtained two-parameter Fermi distributions cannot reproduce the details of the benchmarking charge densities and, in particular, its surface-diffuseness parameter cannot be determined accurately with the present experimental uncertainties on the muonic transition energies.

Flavor Symmetry of Hydrogen Atoms Potentially Affecting the Proton Radius Deduced from the Electron-Hydrogen Scattering

Precise knowledge of such fundamental quantity as the proton charge radius rp is extremely important both for the quantum chromodynamics (for quark-gluon structure) and for atomic physics (for atomic hydrogen spectroscopy). Yet the ambiguity in measuring rp persists for over a dozen of years by now—from the time when in 2010 the muonic hydrogen spectroscopy experiment yielded rp ≈ 0.84 fm in contrast to the form factor experiment by the Mainz group that produced rp ≈ 0.88 fm. Important was that this difference corresponded to about seven standard deviations and therefore was inexplicable. In the intervening dozen of years, more experiments of various kinds were performed in this regard. Nevertheless, the controversy remains, which is why several different types of new experiments are being prepared for measuring rp. In one of our previous papers, we pointed out the factor that was never taken into account by the corresponding research community: the flavor symmetry of electronic hydrogen atoms, whose existence was confirmed by four kinds of atomic or molecular experiments and also evidenced by two kinds of astrophysical observations. Specifically, in that paper there was discussed the possible presence of the second flavor of muonic hydrogen atoms (in the corresponding experimental gas) and its effect on the shift of the ground state of muonic hydrogen atoms due to the proton finite size. In the present paper we analyze the effect of the flavor symmetry of electronic hydrogen atoms on the corresponding elastic scattering cross-section and on the proton charge radius rp deduced from the cross-section. As an example, we use our analytical results for reconciling two distinct values of rp obtained in different elastic scattering experiments: 0.88 fm and 0.84 fm (which is by about 4.5% smaller than 0.88 fm). We show that if the ratio of the second flavor of hydrogen atoms to the usual hydrogen atoms in the experimental gas would be about 0.3, then the extraction of rp from the corresponding cross-section would yield by about 4.5% smaller value of rp compared to its true value. We also derive the corresponding general formulas that can be used for interpreting the future electronic and muonic experiments.

Correction: Oks, E. A Possible Explanation of the Proton Radius Puzzle Based on the Second Flavor of Muonic Hydrogen Atoms. Foundations 2022, 2, 912–917

There was an error/misprint in the original publication [...]

Measurement of the muon lifetime and the Michel spectrum in the LAGO water Cherenkov detectors as a tool to enhance the signal-to-noise ratio

The Latin American Giant Observatory (LAGO) consists of a network of water Cherenkov detectors (WCDs) installed in the Latin American region at various latitudes, from Sierra Negra in Mexico, 18°59′ N 97°18′ W to the Antarctic Peninsula, 64°14′ S 56°38′ W and altitudes from Lima, Peru at 20m a.s.l. to Chacaltaya, Bolivia at 5500m a.s.l.The detectors of the network are built from commercial water tanks, so they have several geometries (cylindrical in general) and different water purification methods. All these features generate different profiles in the response to air shower particles measured by our detectors and produce pulse-shaped electronic signals. Common sources of noise in a WCD come from light leakage, electronic noise, and noise associated with the operation of photomultiplier tubes (PMTs) such as thermionic emission and after-pulses; they all could produce detectable pulses recorded by the LAGO data acquisition (DAQ) system. In LAGO WCDs, these noise signals are expected to present a short pulse width (of a few nanoseconds), while secondary radiation typically produces pulses of several tens of nanoseconds.We used data from the LAGO DAQ system, which digitises pulses at 40MHz sampling rate on windows of 300ns (12 temporal bins) and with a 10-bit resolution. The LAGO DAQ configuration uses a single threshold-based trigger in the third temporal bin. We proposed a secondary trigger threshold at the fourth bin to improve the noise rejection. In this work, we show how the optimal values for these triggers are now obtained from the measurement of the muon lifetime within the water volume and the resulting Michel spectrum. Our results were also simulated using the LAGO ARTI simulation framework to estimate the expected flux of secondary particles at the detector site; and the Meiga framework, a Geant4-based simulator used to estimate the WCDs response to the atmospheric radiation flux.

Non‐destructive elemental analysis of lunar meteorites using a negative muon beam

AbstractWe report the result of a non‐destructive elemental analysis of lunar meteorites using a negative muon beam at J‐PARC. An experimental system of six Ge semiconductor detectors and a newly designed He analysis chamber (to enable quantitative analysis of Al) was used to provide a high signal‐to‐noise ratio for the detection of major elements from lunar rocks (Mg, Si, Fe, O, Ca, and Al). We performed a Monte Carlo simulation to determine the chemical compositions at two sides and the center of a sample (at depths of 0.33 and 0.96 mm below the sample surface, respectively) of the lunar meteorite DEW 12007. These results indicate that the three interior regions of DEW 12007 are likely to be 55.8:44.2, 51.4:48.6, and 54.4:45.6 wt% mixtures of anorthositic and basaltic clasts, respectively. This study is the first quantitative analysis of a heterogeneous meteorite interior using a negative muon beam. As elemental analysis using a muon beam is non‐destructive and highly sensitive to light elements, including C, N, and O, the protocols established in this study are applicable to initial characterization of returned samples from the South Pole of the Moon.

Forbidden dark matter annihilation into leptons with full collision terms

The standard approach of calculating the relic density of thermally produced dark matter based on the assumption of kinetic equilibrium is known to fail for forbidden dark matter models since only the high momentum tail of the dark matter phase space distribution function contributes significantly to dark matter annihilations. Furthermore, it is known that the computationally less expensive Fokker-Planck approximation for the collision term describing elastic scattering processes between non-relativistic dark matter particles and the Standard Model thermal bath breaks down if both scattering partners are close in mass. This, however, is the defining feature of the forbidden dark matter paradigm. In this paper, we therefore include the full elastic collision term in the full momentum-dependent Boltzmann equation as well as in a set of fluid equations that couple the evolution of the number density and dark matter temperature for a simplified model featuring forbidden dark matter annihilations into muon or tau leptons through a scalar mediator. On the technical side, we perform all angular integrals in the full collision term analytically and take into account the effect of dark matter self-interactions on the relic density. The overall phenomenological outcome is that the updated relic density calculation results in a significant reduction of the experimentally allowed parameter space compared to the traditional approach, which solves only for the abundance. In addition, almost the entire currently viable parameter space can be probed with CMB-S4, next-generation beam-dump experiments or at a future high-luminosity electron-position collider, except for the resonant region where the mediator corresponds to approximately twice the muon or tau mass.

Proposal and Analysis of an Experiment for Accurate Measurement of the Muon Lifetime and the Fermi Constant

Proposal and Analysis of an Experiment for Accurate Measurement of the Muon Lifetime and the Fermi Constant

Construction and Commissioning Status of the Superconducting Magnets for COMET Phase-I Experiment at J-PARC

A new muon beamline is under construction for the COMET Phase-I experiment at J-PARC. The experiment requires a negative muon beam with the world-highest intensity to search for muon-electron conversion processes. The muon beamline consists of a series of superconducting solenoid magnets to generate muons by 8 GeV pulsed proton beam from MR of J-PARC, to transport muons to the detectors. A radiation-tolerant superconducting solenoid, the Pion Capture Solenoid, is developed to generate a high magnetic field on a production target to trap pions and muons efficiently. A long curved solenoid, the Muon Transport Solenoid, with correction dipole coils is utilized not only to transport muons but also to select low-momentum muons against unnecessary particles. A large detector solenoid is planned to connect to the muon beamline with a gradually reduced solenoidal field tuned by additional small solenoids. This paper reports the status of the construction and commissioning of the superconducting magnet system.

Are claims of cheap muon production correct?

Abstract Background Muon catalyzed fusion is a process, whereby isotopes of hydrogen undergo nuclear fusion thanks to a muon replacing an electron bringing the nuclei within fusion distance. The muon is then ejected and can facilitate a next fusion process. ‘Break even’ has not been achieved yet in spite of the optimization of isotope mixtures and initial muon energy. A main limiting factor is the muon lifetime and the cost in energy of accelerator-based muon production. The possibilities would receive an immense boost toward practical applications if a cheap muon source could be constructed. We challenge a recent publication claiming to have constructed a very intense, yet very ‘cheap’ muon source. Main text A recent publication in this journal (Holmlid in Energ Sustain 12:14, 2022, 10.1186/s13705-022-00338-4) promotes the idea that such a source has been constructed and demonstrated. The suggestion is based on a long series of articles by the same author as main investigator. They all center around a spectacular new aggregation state of hydrogen, so called ultra-dense hydrogen (UDH). The claims in the article (Holmlid in Energ Sustain 12:14, 2022, 10.1186/s13705-022-00338-4), as well as in the previous articles, are based on speculations going far beyond the experiments they purport to explain, and on a striking disregard of very well-established facts, both concerning conservation laws, elementary quantum mechanics and the phase diagrams of hydrogen. There are strong arguments why the claimed muon production does not occur and that the suggested evidence for it is a collection of instrumental artefacts. Conclusion The muon source suggested by Holmlid (Energ Sustain 12:14, 2022, 10.1186/s13705-022-00338-4) does not produce any muons.

Searching for Ultralight Scalar Dark Matter with Muonium and Muonic Atoms.

Ultralight scalar dark matter may induce apparent oscillations of the muon mass, which may be directly probed via temporal shifts in the spectra of muonium and muonic atoms. Existing datasets and ongoing spectroscopy measurements with muonium are capable of probing scalar-muon interactions that are up to 12 orders of magnitude more stringent than astrophysical bounds. Ongoing free-fall experiments with muonium can probe forces associated with the exchange of virtual ultralight scalar bosons between muons and standard-model particles, offering up to 5 orders of magnitude improvement in sensitivity over complementary laboratory and astrophysical bounds.

Exploring muonphilic ALPs at muon colliders

Axion-like particles (ALPs) are new particles that extend beyond the standard model (SM) and are extensively investigated. When considering ALPs within an effective field theory framework, their couplings with SM particles can be studied independently. It is a daunting task to search for GeV-scale ALPs coupled to muons in collider experiments because their coupling is proportional to the muon mass. However, a recent study by Altmannshofer, Dror, and Gori (2022) highlighted the importance of a four-point interaction, W-μ--a, as well as interactions from the chiral anomaly, whose couplings are not dependent on the muon mass. These interactions provide a new opportunity to explore muonphilic ALPs (μALPs) at the GeV scale. We explore various μALP production channels at muon colliders with μALPs decaying into a pair of muons. In particular, we find that a pair of neutrinos accompanied by a μALP is the most effective channel to search for μALPs in the electrowek violating (EWV) scenario. In contrast, a photon plus a μALP becomes a better channel to search for μALPs in the electroweak preserving (EWP) scenario because there is no W-μ--a interaction in this situation. Most importantly, we find that the future bounds for μALPs in the EWV scenario are considerably stronger than those in the EWP scenario and the existing bounds for exploring μALPs with GeV .

Proposal and Analysis of an Experiment for Accurate Measurement of the Muon Lifetime and the Fermi Constant

An experiment is proposed for a record-breaking measurement of the world Fermi constant GF during the decay of a positive muon. All systematic errors were analyzed. The Fast Program (FP) was developed and tested using the GEANT data and running ≈1500 times faster. 1014 events were collected with two options for selecting events. An accuracy of 0.46 ps for the muon lifetime and 0.1 ppm for the GF value was obtained taking into account all systematic errors. The accuracy of the theoretical calculations of GF is 0.14 ppm within the framework of the Standard Model interactions of elementary particles

The Mu2e Crystal and SiPM Calorimeter: Construction Status

The Mu2e experiment at Fermilab searches for the neutrino-less conversion of a negative muon into an electron, with a distinctive signature of a mono-energetic electron with energy of 104.967 MeV. The calorimeter is made of two disks of pure CsI crystals, each read out by two custom large area UV-extended SiPMs. It plays a fundamental role in providing excellent particle identification capabilities and an online trigger filter while improving the track reconstruction, requiring better than 10% energy and 500 ps timing resolutions for 100 MeV electrons. In this paper, we present the status of construction and the Quality Control (QC) performed on the produced crystals and photosensors, the development of the rad-hard electronics and the most important results of the irradiation tests. Construction of the mechanics is also reported. Status and plans for the calorimeter assembly and its first commissioning are described.

Investigation of the muonic atoms distribution in materials through muonic x-rays momentum simulation using Geant4

Determining the distribution of muonic atoms is essential for μ-X ray imaging. In this study, the generation and de-excitation of muonic atoms in multi-elemental targets were simulated using the Monte Carlo software toolkit Geant4. An approach that reconstructs the production sites of muonic atoms from the μ-X ray momentum is proposed. The imaging results indicated a high simulated spatial resolution of 0.1 mm and a significant increase in the detection efficiency compared to that achieved by the 3-mm pinhole imaging technique. In addition, an analysis of the image quality index (Q) revealed that a superior image quality can be achieved for elements with high and medium atomic numbers. The proposed method has the potential to be further developed into an accurate and efficient technique for positioning the distribution of elements.