More Like this

1. Electrostatic focusing of cold and heavy molecules for the ACME electron EDM search

   https://doi.org/10.1088/1367-2630/ac8014  

   Wu, X. ; Hu, P. ; Han, Z. ; Ang, D. G. ; Meisenhelder, C. ; Gabrielse, G. ; Doyle, J. M. ; DeMille, D. ( August 2022 , New Journal of Physics)

   The current best upper limit for electron electric dipole moment (EDM), |d_e| < 1.1 × 10⁻²⁹e cm (90% confidence), was set by the ACME Collaboration in 2018. The ACME experiment uses a spin-precession measurement in a cold beam of thorium monoxide (ThO) molecules to detectd_e. An improvement in statistical uncertainty would be possible with more efficient use of molecules from the cryogenic buffer gas beam source. Here, we demonstrate electrostatic focusing of the ThO beam with a hexapole lens. This results in a factor of 16 enhancement in the molecular flux detectable downstream, in a beamline similar to that built for the next generation of ACME. We also demonstrate an upgraded rotational cooling scheme that increases the ground state population by 3.5 times compared to no cooling, consistent with expectations and a factor of 1.4 larger than previously in ACME. When combined with other demonstrated improvements, we project over an order of magnitude improvement in statistical sensitivity for the next generation ACME electron EDM search.

    

   more » « less
2. The metastable Q 3 Δ 2 state of ThO: a new resource for the ACME electron EDM search

   https://doi.org/10.1088/1367-2630/ab6a3a  

   Wu, X. ; Han, Z. ; Chow, J. ; Ang, D. G. ; Meisenhelder, C. ; Panda, C. D. ; West, E. P. ; Gabrielse, G. ; Doyle, J. M. ; DeMille, D. ( February 2020 , New Journal of Physics)

   The best upper limit for the electron electric dipole moment was recently set by the ACME collaboration. This experiment measures an electron spin-precession in a cold beam of ThO molecules in their metastable$H{(}^3{\mathrm{\Delta }}_1)$state. Improvement in the statistical and systematic uncertainties is possible with more efficient use of molecules from the source and better magnetometry in the experiment, respectively. Here, we report measurements of several relevant properties of the long-lived$Q{(}^3{\mathrm{\Delta }}_2)$state of ThO, and show that this state is a very useful resource for both these purposes. TheQstate lifetime is long enough that its decay during the time of flight in the ACME beam experiment is negligible. The large electric dipole moment measured for theQstate, giving rise to a large linear Stark shift, is ideal for an electrostatic lens that increases the fraction of molecules detected downstream. The measured magnetic moment of theQstate is also large enough to be used as a sensitive co-magnetometer in ACME. Finally, we show that theQstate has a large transition dipole moment to the$C{(}^1{\mathrm{\Pi }}_1)$state, which allows for efficient population transfer between the ground state$X{(}^1{\mathrm{\Sigma }}^{+})$and theQstate via$X-C-Q$Stimulated Raman Adiabatic Passage (STIRAP). We demonstrate 90 % STIRAP transfer efficiency. In the course of these measurements, we also determine the magnetic moment ofCstate, the$X\to C$transition dipole moment, and branching ratios of decays from theCstate.

    

   more » « less
3. Radio Scattering Horizons for Galactic and Extragalactic Transients

   https://doi.org/10.3847/1538-4357/ac75ba  

   Ocker, Stella Koch ; Cordes, James M. ; Chatterjee, Shami ; Gorsuch, Miranda R. ( July 2022 , The Astrophysical Journal)

   Radio wave scattering can cause severe reductions in detection sensitivity for surveys of Galactic and extragalactic fast (∼ms duration) transients. While Galactic sources like pulsars undergo scattering in the Milky Way interstellar medium (ISM), extragalactic fast radio bursts (FRBs) can also experience scattering in their host galaxies and other galaxies intervening in their lines of sight. We assess Galactic and extragalactic scattering horizons for fast radio transients using a combination of NE2001 to model the dispersion measure and scattering time (τ) contributed by the Galactic disk, and independently constructed electron density models for the Galactic halo and other galaxies’ ISMs and halos that account for different galaxy morphologies, masses, densities, and strengths of turbulence. For source redshifts 0.5 ≤z_s≤ 1, an all-sky, isotropic FRB population has simulated values ofτ(1 GHz) ranging from ∼1μs to ∼2 ms (90% confidence, observer frame) that are dominated by host galaxies, althoughτcan be ≫2 ms at low Galactic latitudes. A population atz_s= 5 has 0.01 ≲τ≲ 300 ms at 1 GHz (90% confidence), dominated by intervening galaxies. About 20% of these high-redshift FRBs are predicted to haveτ> 5 ms at 1 GHz (observer frame), and ≳40% of FRBs betweenz_s∼ 0.5–5 haveτ≳ 1 ms forν≤ 800 MHz. Our scattering predictions may be conservative if scattering from circumsource environments is significant, which is possible under specific conditions. The percentage of FRBs selected against from scattering could also be substantially larger than we predict if circumgalactic turbulence causes more small-scale (≪1 au) density fluctuations than observed from nearby halos.

    

   more » « less
4. Rapid acquisition of broadband two-dimensional electronic spectra by continuous scanning with conventional delay lines

   https://doi.org/10.1364/OL.391360  

   Spencer, Austin P. ; Chen, Lin X. ( May 2020 , Optics Letters)

   A passively phase-stable, broadband ($\sim <\#comment/>7\mathrm{f}\mathrm{s}$,$><\#comment/>2000{\mathrm{c}\mathrm{m}}^{-<\#comment/>1}$) two-dimensional (2D) electronic spectroscopy apparatus that achieves rapid acquisition rates by continuously—rather than step-wise—scanning the Fourier-transform dimension is demonstrated for the first time, to the best of our knowledge. This is made possible through use of a partially common path interferometer design in which the coherence time$\mathrm{\tau <\#comment/>}$is sampled in a “rotating frame.” Rapid, continuous scanning of$\mathrm{\tau <\#comment/>}$increases the duty cycle of signal collection, rejects the majority of excitation pulse scatter, and enables the measurement of a complete 2D spectrum in 92 ms, which minimizes the influence of pulse intensity and delay fluctuations on the 2D spectrum. In practice, these improvements make possible the acquisition of hundreds of 2D spectra in tens of minutes, which opens the door to dense sampling of ultrafast relaxation dynamics and to generating extremely broadband 3D Fourier-transform spectra.

    

   more » « less
5. Acceleration and Spectral Redistribution of Cosmic Rays in Radio-jet Shear Flows

   https://doi.org/10.3847/1538-4357/acfda9  

   Webb, G. M. ; Xu, Y. ; Biermann, P. L. ; Al-Nussirat, S. ; Mostafavi, P. ; Li, G. ; Barghouty, A. F. ; Zank, G. P. ( November 2023 , The Astrophysical Journal)

   A steady-state, semi-analytical model of energetic particle acceleration in radio-jet shear flows due to cosmic-ray viscosity obtained by Webb et al. is generalized to take into account more general cosmic-ray boundary spectra. This involves solving a mixed Dirichlet–Von Neumann boundary value problem at the edge of the jet. The energetic particle distribution functionf₀(r,p) at cylindrical radiusrfrom the jet axis (assumed to lie along thez-axis) is given by convolving the particle momentum spectrum$f_0(\infty ,p\prime )$with the Green’s function$G(r,p;p\prime )$, which describes the monoenergetic spectrum solution in which$f_0\to \delta (p-p\prime )$asr→ ∞ . Previous work by Webb et al. studied only the Green’s function solution for$G(r,p;p\prime )$. In this paper, we explore for the first time, solutions for more general and realistic forms for$f_0(\infty ,p\prime )$. The flow velocityu=u(r)e_zis along the axis of the jet (thez-axis).uis independent ofz, andu(r) is a monotonic decreasing function ofr. The scattering time$\tau {(r,p)={\tau }_0(p/p_0)}^{\alpha }$in the shear flow region 0 <r<r₂, and$\tau {(r,p)={\tau }_0(p/p_0)}^{\alpha }{(r/r_2)}^s$, wheres> 0 in the regionr>r₂is outside the jet. Other original aspects of the analysis are (i) the use of cosmic ray flow lines in (r,p) space to clarify the particle spatial transport and momentum changes and (ii) the determination of the probability distribution${\psi }_p(r,p;p\prime )$that particles observed at (r,p) originated fromr→ ∞ with momentum$p\prime$. The acceleration of ultrahigh-energy cosmic rays in active galactic nuclei jet sources is discussed. Leaky box models for electron acceleration are described.

    

   more » « less