Rory Miskimen
· ProfessorUniversity of Massachusetts Amherst · Physics
Active 1983–2024
About
Rory Miskimen is a Professor in the Department of Physics at the University of Massachusetts Amherst. He earned his Ph.D. from the Massachusetts Institute of Technology in 1983. His research interests include tests of fundamental symmetries and low-energy Quantum Chromodynamics (QCD), with a focus on experimental nuclear physics. He is involved in physics education, research opportunities, and interdisciplinary programs within a diverse and inclusive community of excellence. His main office is located in the Department of Physics at 1126 Lederle Graduate Research Tower, University of Massachusetts Amherst.
Research topics
- Physics
- Nuclear physics
- Optics
- Quantum mechanics
- Particle physics
- Mathematics
- Geometry
- Statistics
Selected publications
Physical Review Letters · 2024-03-19 · 3 citations
articleOpen accessWe report the measurement of the helicity asymmetry E for the pπ^{0} and nπ^{+} final states using, for the first time, an elliptically polarized photon beam in combination with a longitudinally polarized target at the Crystal Ball experiment at MAMI. The results agree very well with data that were taken with a circularly polarized photon beam, showing that it is possible to simultaneously measure polarization observables that require linearly (e.g., G) and circularly polarized photons (e.g., E) and a longitudinally polarized target. The new data cover a photon energy range 270-1400 MeV for the pπ^{0} final state (230-842 MeV for the nπ^{+} final state) and the full range of pion polar angles, θ, providing the most precise measurement of the observable E. A moment analysis gives a clear observation of the pη cusp in the pπ^{0} final state.
Physical review. C · 2024-05-06 · 3 citations
articleOpen accessThe transition from the nucleon to the $\mathrm{\ensuremath{\Delta}}(1232)$ resonance is a sensitive test for models of the nucleon structure. A magnetic dipole ($M1$) quark spin-flip transition essentially dominates photoexcitation of the $\mathrm{\ensuremath{\Delta}}$, but smaller components in the nucleon and $\mathrm{\ensuremath{\Delta}}$ wave functions allow also electric quadrupole ($E2$) contributions. The ratio $E2/M1$ then provides fundamental information on both the spatial deformation of the nucleon or $\mathrm{\ensuremath{\Delta}}$, and on the corresponding $D$ states in their quark-model wave functions. The authors measured the $E2/M1$ ratio via single ${\ensuremath{\pi}}^{0}$ production from the proton with a circularly polarized photon beam and a longitudinally polarized proton target, exploiting the presence of interference terms between the measured amplitudes that enhance the effect of smaller contributions. This most precise experimental result to date for the $E2/M1$ ratio gives deep insight into the nucleon properties and provides a precision benchmark for all nonperturbative QCD models.
arXiv (Cornell University) · 2023-08-29
preprintOpen accessPhotoproduction of $π^0π^{\pm}$-pairs from quasifree nucleons bound in the deuteron has been investigated to study the helicity dependence of this reaction. Measurements with a liquid deuterium target were used to extract the unpolarized cross sections for reactions on protons and neutrons. A deuterated, longitudinally polarized solid-butanol target, together with a circularly polarized photon beam, determined the double polarization observable $E$. From these results the spin-dependent cross sections $σ_{1/2}$ and $σ_{3/2}$, corresponding to the anti-parallel and parallel spin configurations of the beam photon and target nucleon, have been derived. The measurements were performed at the Mainz MAMI accelerator with tagged, circularly-polarized photon beams produced via bremsstrahlung from longitudinally polarized electron beams. The reaction products were detected with an almost $4π$ solid-angle covering calorimeter composed of the Crystal Ball and TAPS detectors, supplemented by plastic scintillation detectors for charged particle identification. The results are sensitive to sequential decays of nucleon resonances via intermediate states and also to the decay of nucleon resonances by emission of charged $ρ$ mesons, and are compared to recent model results.
Helicity dependent cross sections for the photoproduction of π0π± pairs from quasi-free nucleons
Physics Letters B · 2023-10-26 · 2 citations
articleOpen accessPhotoproduction of π0π±-pairs from quasifree nucleons bound in the deuteron has been investigated to study the helicity dependence of this reaction. Measurements with a liquid deuterium target were used to extract the unpolarized cross sections for reactions on protons and neutrons. A deuterated, longitudinally polarized solid-butanol target, together with a circularly polarized photon beam, determined the double polarization observable E. From these results the spin-dependent cross sections σ1/2 and σ3/2, corresponding to the anti-parallel and parallel spin configurations of the beam photon and target nucleon, have been derived. The measurements were performed at the Mainz MAMI accelerator with tagged, circularly-polarized photon beams produced via bremsstrahlung from longitudinally polarized electron beams. The reaction products were detected with an almost 4π solid-angle covering calorimeter composed of the Crystal Ball and TAPS detectors, supplemented by plastic scintillation detectors for charged particle identification. The results are sensitive to sequential decays of nucleon resonances via intermediate states and also to the decay of nucleon resonances by emission of charged ρ mesons, and are compared to recent model results.
arXiv (Cornell University) · 2023-05-15
preprintOpen accessThe GlueX experiment at Jefferson Lab studies photoproduction of mesons using linearly polarized $8.5\,\text{GeV}$ photons impinging on a hydrogen target which is contained within a detector with near-complete coverage for charged and neutral particles. We present measurements of spin-density matrix elements for the photoproduction of the vector meson $ρ$(770). The statistical precision achieved exceeds that of previous experiments for polarized photoproduction in this energy range by orders of magnitude. We confirm a high degree of $s$-channel helicity conservation at small squared four-momentum transfer $t$ and are able to extract the $t$-dependence of natural and unnatural-parity exchange contributions to the production process in detail. We confirm the dominance of natural-parity exchange over the full $t$ range. We also find that helicity amplitudes in which the helicity of the incident photon and the photoproduced $ρ(770)$ differ by two units are negligible for $-t<0.5\,\text{GeV}^{2}/c^{2}$.
arXiv (Cornell University) · 2023-12-13
preprintOpen accessA new data set for the helicity-dependent differential cross section of the single-meson photoproduction reaction $γp \to p π^{0}$ was obtained for the photon energy interval 150-400 MeV. The experiment was performed at the A2 tagged photon facility of the Mainz Microtron MAMI using a circularly polarized photon beam and a longitudinally polarized proton target. The reaction products were detected with the large acceptance Crystal Ball/TAPS calorimeter covering 97\% of the full solid angle. These new results, obtained with a fine energy and polar angle binning, greatly increase both the existing quantity and quality of the data available for this observable. A moment analysis, based on a finite expansion in Legendre polynomials, was applied to these data by using a bootstrap-based fitting method to correctly account for their systematic uncertainties. From the resulting decomposition of the differential cross sections, the $E2/M1$ ratio for the $N\to Δ(1232)$ transition was determined to be $[-2.38 \pm 0.16{\hbox{ (stat.+sys.)}} \pm 0.10 {\hbox{ (model)}}] \%$. Combining this value with previous results also allowed us to evaluate the most precise available estimate of the $E2/M1$ ratio to be used for all further reference and model comparisons.
Neutron polarisation transfer, Cx′, in π+ photoproduction off the proton, d(γ⊙,n→π+)nspec
Physics Letters B · 2023-10-27
articleOpen accessWe report a first measurement of the double-polarisation observable, Cx′, in π+ photoproduction off the proton. The Cx′ double-polarisation observable represents the transfer of polarisation from a circularly polarised photon beam to the recoiling neutron. The MAMI circularly polarised photon beam impinged on a liquid deuterium target cell, with reaction products detected in the Crystal Ball calorimeter. Ancillary apparatus surrounding the target provided tracking, particle identification and determination of recoil nucleon polarisation. The Cx′ observable is determined for photon energies 800-1400 MeV, providing new constraints on models aiming to elucidate the spectrum and properties of nucleon resonances. This is the first determination of any polarisation observable from the beam-recoil group of observables for this reaction. Inclusion of the new data in the database of the SAID partial wave analysis shifted the solution to a new global minima which, not only gives better agreement with the current data, but also improves the description of a range of other single and double polarisation observables for charged pion photoproduction.
Physical Review Letters · 2022-04-01 · 16 citations
articleOpen accessA precise measurement of the differential cross sections $d\ensuremath{\sigma}/d\mathrm{\ensuremath{\Omega}}$ and the linearly polarized photon beam asymmetry ${\mathrm{\ensuremath{\Sigma}}}_{3}$ for Compton scattering on the proton below pion threshold has been performed with a tagged photon beam and almost $4\ensuremath{\pi}$ detector at the Mainz Microtron. The incident photons were produced by the recently upgraded Glasgow-Mainz photon tagging facility and impinged on a cryogenic liquid hydrogen target, with the scattered photons detected in the Crystal Ball/TAPS setup. Using the highest statistics Compton scattering data ever measured on the proton along with two effective field theories (both covariant baryon and heavy-baryon) and one fixed-$t$ dispersion relation model, constraining the fits with the Baldin sum rule, we have obtained the proton electric and magnetic polarizabilities with unprecedented precision: ${\ensuremath{\alpha}}_{E1}=10.99\ifmmode\pm\else\textpm\fi{}0.16\ifmmode\pm\else\textpm\fi{}0.47\ifmmode\pm\else\textpm\fi{}0.17\ifmmode\pm\else\textpm\fi{}0.34$, ${\ensuremath{\beta}}_{M1}=3.14\ifmmode\pm\else\textpm\fi{}0.21\ifmmode\pm\else\textpm\fi{}0.24\ifmmode\pm\else\textpm\fi{}0.20\ifmmode\pm\else\textpm\fi{}0.35$; in units of ${10}^{\ensuremath{-}4}\text{ }\text{ }{\mathrm{fm}}^{3}$ where the errors are statistical, systematic, spin polarizability dependent, and model dependent.
Physical review. C · 2022-03-03 · 7 citations
articleOpen accessWe report on the measurement of spin density matrix elements of the Λ(1520) in the photoproduction reaction γp→Λ(1520)K+, via its subsequent decay to K-p. The measurement was performed as part of the GlueX experimental program in Hall D at Jefferson Laboratory using a linearly polarized photon beam with Eγ=8.2GeV–8.8GeV. These are the first such measurements in this photon energy range. Results are presented in bins of momentum transfer squared, -(t-t0). We compare the results with a Reggeon exchange model and determine that natural exchange amplitudes are dominant in Λ(1520) photoproduction.
Measurement of the helicity dependence for single $$\pi ^{0}$$ photoproduction from the deuteron
The European Physical Journal A · 2022-06-01 · 5 citations
article
Frequent coauthors
- 254 shared
S. Stepanyan
Thomas Jefferson National Accelerator Facility
- 246 shared
S. A. Morrow
Institut de Physique
- 246 shared
F. Sabatié
CEA Paris-Saclay
- 235 shared
B. A. Raue
- 228 shared
H. O. Funsten
New Mexico Consortium
- 224 shared
D. I. Sober
Catholic University of America
- 218 shared
M. Taiuti
University of Genoa
- 217 shared
H. Egiyan
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