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Proton charge radius extraction from muon scattering at MUSE using dispersively improved chiral effective field theory
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High precision measurements of the proton charge radius with PRad-II / Considerations & issues in the radius extraction
Showing the PRad results and making comparisons to various fits of the full Mainz data set.
Proton Electric Charge Radius from Lepton Scattering
A proton is a bound state of a strong interaction, governed by Quantum Chromodynamics (QCD). The electric charge radius of a proton, denoted by $r^{p}_{E}$, characterizes the spatial distribution of its electric charge carried by the quarks. It is an important input for bound-state Quantum Electrodynamic (QED) calculations of the hydrogen atomic energy levels. However, physicists have been puzzled by the large discrepancy between $r^{p}_{E}$ measurements from muonic hydrogen spectroscopy and those from ep elastic scattering and ordinary hydrogen spectroscopy for over a decade. Tremendous efforts, both theoretical and experimental, have been dedicated to providing various insights into this puzzle, but certain issues still remain unresolved, particularly in the field of lepton scatterings. This review will focus on lepton-scattering measurements of $r^{p}_{E}$, recent theoretical and experimental developments in this field, as well as future experiments using this technique.
Lowest-order QED radiative corrections in unpolarized elastic electron–deuteron scattering beyond the ultra-relativistic limit for the proposed deuteron charge radius measurement at Jefferson laboratory
Analogous to the well-known proton charge radius puzzle, a similar puzzle exists for the deuteron charge radius, r d . There are discrepancies observed in the results of r d , measured from electron-deuteron (e - d) scattering experiments, as well as from atomic spectroscopy. In order to help resolve the charge radius puzzle of the deuteron, the PRad collaboration at Jefferson Lab has proposed an experiment for measuring r d , named DRad. This experiment is designed to measure the unpolarized elastic e - d scattering cross section in a low-Q 2 region. To extract the cross section with a high precision, having reliable knowledge of QED radiative corrections is important. Here, in this paper, we present complete numerical calculations of the lowest-order radiative corrections in e - d scattering for the DRad kinematics. The calculations have been performed within a covariant formalism and beyond the ultra-relativistic approximation ($m^2_e$ $\ll$ Q 2 ). Besides, we present a systematic uncertainty on r d arising from higher-order radiative corrections, estimated based on our cross-section results.
Absorptive corrections to the electromagnetic form factor in high-energy elastic proton-proton scattering
Recently, it was noted that absorptive corrections to the electromagnetic form factor in high-energy proton-proton scattering are important for the theoretical interpretation of the p ↑ p and p ↑ A analyzing power A N ( t ) measurements with the Hydrogen Jet Target polarimeter (HJET) at RHIC. Here, a concise expression for the absorptive correction was derived within the eikonal approach. The resulting analysis reveals a systematic bias, nearly independent of the beam energy, in the experimental determination of the real-to-imaginary ratio ρ when absorption effects are overlooked in the data analysis. Quantification of this bias, as ρ meas = ρ + ( 0.036 ± 0.016 ) bias , was achieved using a Regge fit applied to available proton-proton measurements of ρ meas ( s ) and σ tot meas ( s ) . Considering the potential impact of such an effect on the experimentally determined A N ( t ) , one may enhance consistency between the HJET and STAR measurements of the hadronic spin-flip amplitude. While the sign of the bias in the value of ρ aligns with the anticipated effective increase in the proton charge radius in p p scattering due to absorption, it amplifies the observed discrepancy between σ tot meas and ρ meas values at s = 13 TeV as measured in the TOTEM experiment. Evaluation (using published TOTEM data) of the measured proton-proton d σ / d t dependence on the absorptive corrections indicated that possible soft photon corrections to the hadronic amplitude slope may be essential for such data analysis. Published by the American Physical Society 2024
Direct comparison of using a Z -transformation instead of the traditional $Q^2$ for extraction of the proton radius from $e-p$ scattering data
A discrepancy in the determination of the proton’s charge radius, r p , between muonic hydrogen spectroscopy versus classic atomic spectroscopy and electron scattering data has become known as the proton radius puzzle. Extractions of r p from electron scattering data require determination of the slope of the proton’s charge form factor, $G$$^{p}_{E}$, in the limit of Q 2 → 0 through fitting and extrapolation. Some works have presented the Z-transformation fitting technique as the best choice for this type of extraction due to the true functional form of $G$$^{p}_{E}$ being mathematically guaranteed to exist within the parameter-space of the fit function. In this work, we test this claim by examining the mathematical bias and variances introduced by this technique as compared to the more traditional Q 2 fits using statistically sampled $G$$^{p}_{E}$ parameterizations with known input radii. Furthermore, our tests conclude that the quality of the Z-transformation technique depends on the range of data used. In the case of new experiments, the fit function and technique should be selected in advance by generating realistic pseudodata and assessing the power of different techniques.
Studies of e+e- Pair Photo-Production on Proton Target at 8 GeV in the GlueX Experiment
Lepton pair production has played an important role in both nuclear and particle physics, being among the earliest calculations utilizing QED, and seen most famously in the discovery of the J= at BNL. A technique is presented for measuring the linear polarization of GeV scale photon beams through the detection of e+e? pairs photo-produced in the target. This technique is applied to the analysis of GlueX data on proton target. Simulation predicts the analyzing power for pair production to be :5725 ? 0:0025 for the GlueX data, and the analysis of experimental data gives a linear polarization of approximately 35%, in good agreement with other measurements of beam polarization. The pair production technique is complementary to other electromagnetic and hadronic measurements of beam polarization, and is generally applicable in experiments that allow for forward angle electron and positron identi?fication and tracking. To facilitate this study, a neural net was trained for e=? separation to eliminate the pion background. Further, it is demonstrated that these e+e? pairs are sensitive to the proton charge form factor, which opens up the possibility for a new method to measure the proton RMS charge radius.
Construction and Commissioning of Gas Electron Multiplier (GEM) Detectors in Advanced Assembly Design for Low-Energy Applications at High Rates and Analysis of GEM Data From the Muse Experiment at PSI
The search beyond the Standard Model explores dark matter and a potential fifth force. DarkLight@ARIEL investigates the dark photon as a mediator between ordinary and dark matter. The experiment aims to measure the process e?Ta ? e?TaX ? e?Ta(e?e+), by detecting a charged lepton pair in the final state. The spectrometers will be instrumented with Gas Electron Multiplier (GEM) detectors with minimal material budget for tracking. A novel GEM construction technique is employed for fabricating 25 cm x 40 cm GEM detectors, where all layers are mechanically stretched and assembled within a double frame. The dissertation outlines physics motivation, methods, experimental setup, and the role of GEM detectors in DarkLight. A comprehensive discussion on GEM detectors, focusing on the "NS2" technique, including design, parts, assembly, testing, and performance evaluation will be discussed. The proton has garnered attention due to discrepancies in measuring its charge radius using muonic hydrogen and electron-based methods. The 2010 muonic hydrogen measurement of the proton charge radius Rp = 0.84184(67) fm, showed a significant 7? discrepancy compared to the previously known value of Rp = 0.8775(51) fm, giving rise to the proton radius puzzle. Through simultaneous measurements of e ? p and ? ? p elastic scattering, MUSE facilitates a precise and direct comparison of the proton radius. The physics background of the proton radius puzzle, measurement techniques, the approach adopted by the MUSE experiment, its significance and the experimental setup will be discussed. Furthermore, the role of GEM detectors, along with an in-depth analysis of their data and efficiency will be discussed and evaluated.
Determining the gluonic gravitational form factors of the proton
The proton is one of the main building blocks of all visible matter in the Universe. Among its intrinsic properties are its electric charge, mass and spin. These properties emerge from the complex dynamics of its fundamental constituents—quarks and gluons—described by the theory of quantum chromodynamics. The electric charge and spin of protons, which are shared among the quarks, have been investigated previously using electron scattering. An example is the highly precise measurement of the electric charge radius of the proton. By contrast, little is known about the inner mass density of the proton, which is dominated by the energy carried by gluons. Gluons are hard to access using electron scattering because they do not carry an electromagnetic charge. Here we investigated the gravitational density of gluons using a small colour dipole, through the threshold photoproduction of the J/ψ particle. We determined the gluonic gravitational form factors of the proton from our measurement. Here we used a variety of models and determined, in all cases, a mass radius that is notably smaller than the electric charge radius. In some, but not all cases, depending on the model, the determined radius agrees well with first-principle predictions from lattice quantum chromodynamics. This work paves the way for a deeper understanding of the salient role of gluons in providing gravitational mass to visible matter.
A potential model study of the nucleon's charge and mass radius
We study the charge and mass distributions within a nucleon and compute the associated squared radii based on a potential model approach. Different constituent quark configurations such as Δ, Y, and quark-diquark are considered and compared, with model parameters calibrated by experimental measurements of the proton and neutron charge radius. The results suggest that while the charge radius is dictated by quark dynamics, the mass radius is strongly influenced by nonperturbative QCD contributions to a nucleon's mass that are not sensitive to the constituent quarks. As a result, the mass radius could become substantially different from the charge radius. The obtained nucleon mass distributions of different configurations are further used for simulations of the initial conditions in heavy ion collisions. Furthermore, the computed eccentricities ε 2 and ε 3 are found to demonstrate a considerable sensitivity to the input nucleon profiles, especially to the mass radius in the peripheral region as well as for systems with fewer participants.
The MUSE beamline calorimeter
The MUon Scattering Experiment (MUSE) was motivated by the proton radius puzzle arising from the discrepancy between muonic hydrogen spectroscopy and electron–proton measurements. The MUSE physics goals also include testing lepton universality, precisely measuring two-photon exchange contribution, and testing radiative corrections. MUSE addresses these physics goals through simultaneous measurement of high precision cross sections for electron–proton and muon–proton scattering using a mixed-species beam. The experiment will run at both positive and negative beam polarities. Measuring precise cross sections requires understanding both the incident beam energy and the radiative corrections. For this purpose, a lead-glass calorimeter was installed at the end of the beam line in the MUSE detector system. Here, in this article, we discuss the detector specifications, calibration and performance. We demonstrate that the detector performance is well reproduced by simulation, and meets experimental requirements.
Reduction in Nuclear Size and Quadrupole Deformation of High-Spin Isomers of 127,129 In
We employed laser spectroscopy of atomic transitions to measure the nuclear charge radii and electromagnetic properties of the high-spin isomeric states in neutron-rich indium isotopes (𝑍 =49) near the closed proton and neutron shells at 𝑍 = 50 and 𝑁 = 82. Our data reveal a reduction in the nuclear charge radius and intrinsic quadrupole moment when protons and neutrons are fully aligned in 129 In (𝑁 = 80), to form the high spin isomer. Such a reduction is not observed in 127 In (𝑁 = 78), where more complex configurations can be formed by the existence of four neutron holes. These observations are not consistently described by nuclear theory.
Nuclear Radii of Proton-Unbound Systems
Nuclear radius is a fundamental structural observable that informs many properties of atomic nuclei and nuclear matter. Experimental studies of radii in drip line nuclei are in the forefront of research with radioactive ion beams. Of particular interest are charge radii of proton-unbound nuclei that will soon be approached in laser spectroscopy. In this Letter, using the complex-energy approach and direct time propagation, we investigate the radius of the proton resonance whose size is ill defined in the standard stationary quantum-mechanical description. An early-time plateau is identified during which the radius of the Gamow resonance coincides with the real-energy radius accessible experimentally. We demonstrate a nonmonotonic dependence of the complex radius on decay energy and a local increase of the charge radius across the threshold (a halolike enhancement).
Energetic ion and electron phase space densities in the magnetosphere of Uranus
Proton and electron phase space density profiles are constructed from an analysis of Voyager 2 low-energy charged particle data from the magnetosphere of Uranus. The Uranus proton profiles reveal an approximately exponential decline with decreasing radius for L less than about 9 in a relatively dense thermal plasma region with intense plasma wave activity. Among the distributed loss mechanisms at Uranus are satellite sweeping, wave-particle interactions, and charge exchange of protons with an extended hydrogen corona.
Anti-polyelectrolyte and polyelectrolyte effects on conformations of polyzwitterionic chains in dilute aqueous solutions
Abstract Polyzwitterions (PZs) are considered as model synthetic analogs of intrinsically disordered proteins. Based on this analogy, PZs in dilute aqueous solutions are expected to attain either globular (i.e. molten, compact) or random coil conformations. Addition of salt is expected to open these conformations. To the best of our knowledge, these hypotheses about conformations of PZs have never been verified. In this study, we test these hypotheses by studying effects of added salt [potassium bromide (KBr)] on gyration and hydrodynamic radii of poly(sulfobetaine methacrylate) in dilute aqueous solutions using dynamic light scattering and small-angle X-ray scattering, respectively. Effects of zwitteration are revealed by direct comparisons of the PZs with the polymers of the same backbone but containing (1) no explicit charges on side groups such as poly(2-dimethylaminoethyl methacrylate)s and (2) explicit cationic side groups with tertiary amino bromide pendants. Zeta-potential measurements, transmission electron microscopy, and ab initio molecular dynamics simulations reveal that the PZs acquire net positive charge in near salt-free conditions due to protonation but retain coiled conformations. Added KBr leads to nonmonotonic changes exhibiting an increase followed by a decrease in radius of gyration (and hydrodynamic radius), which are called antipolyelectrolyte and polyelectrolyte effects, respectively. Charge regulation and screening of charge–charge interactions are discussed in relation to the antipolyelectrolyte and polyelectrolyte effects, respectively, which highlight the importance of salt in affecting net charge and conformations of PZs.
The nuclear charge radius of 13 C
The size is a key property of a nucleus. Accurate nuclear radii are extracted from elastic electron scattering, laser spectroscopy, and muonic atom spectroscopy. The results are not always compatible, as the proton-radius puzzle has shown most dramatically. Beyond helium, precision data from muonic and electronic sources are scarce in the light-mass region. The stable isotopes of carbon are an exception. We present a laser spectroscopic measurement of the root-mean-square (rms) charge radius of 13 C and compare this with ab initio nuclear structure calculations. Measuring all hyperfine components of the 2 3 S → 2 3 P fine-structure triplet in 13 C 4+ ions referenced to a frequency comb allows us to determine its center-of-gravity with accuracy better than 2 MHz although second-order hyperfine-structure effects shift individual lines by several GHz. We improved the uncertainty of R c ( 13 C) determined with electrons by a factor of 6 and found a 3σ discrepancy with the muonic atom result of similar accuracy.
Precision Mass Measurement of the Proton Dripline Halo Candidate 22 Al
Here, we report the first mass measurement of the proton-halo candidate 22 Al performed with the low energy beam ion trap facility’s 9.4 T Penning trap mass spectrometer at facility for rare isotope beams. This measurement completes the mass information for the lightest remaining proton-dripline nucleus achievable with Penning traps. 22 Al has been the subject of recent interest regarding a possible halo structure from the observation of an exceptionally large isospin asymmetry [J. Lee et al ., Large isospin asymmetry in Si22/O22 Mirror Gamow-Teller transitions reveals the halo structure of 22 Al , Phys. Rev. Lett. 125, 192503 (2020).]. The measured mass excess value of ME=18 092.5(3) keV, corresponding to an exceptionally small proton separation energy of 𝑆𝑝=100.4(8) keV, is compatible with the suggested halo structure. Our result agrees well with predictions from 𝑠𝑑-shell USD Hamiltonians. While USD Hamiltonians predict deformation in the 22 Al ground state with minimal 1𝑠 1/2 occupation in the proton shell, a particle-plus-rotor model in the continuum suggests that a proton halo could form at large quadrupole deformation. These results emphasize the need for a charge radius measurement to conclusively determine the halo nature.