More Like this

1. Measurement of the H3∆₁ Radiative Lifetime in ThO

   Ang, D.G.; Meisenhelder, C.; Panda, C.D.; Wu, X; DeMille, D.; Doyle, J.M.; Gabrielse, G. (April 2022, ArXivorg)

   The best limit on the electron electric dipole moment (eEDM) comes from the ACME II experiment [Nature \textbf{562} (2018), 355-360] which probes physics beyond the Standard Model at energy scales well above 1 TeV. ACME II measured the eEDM by monitoring electron spin precession in a cold beam of the metastable H3Δ1 state of thorium monoxide (ThO) molecules, with an observation time τ≈1 ms for each molecule. We report here a new measurement of the lifetime of the ThO (H3Δ1) state, τH=4.2±0.5 ms. Using an apparatus within which τ≈τH will enable a substantial reduction in uncertainty of an eEDM measurement. 

   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)

   Abstract 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. Bimetallic, Silylene‐Mediated Multielectron Reductions of Carbon Dioxide and Ethylene

   https://doi.org/10.1002/anie.202011489  

   Whited, Matthew T.; Zhang, Jia; Conley, Anna M.; Ma, Senjie; Janzen, Daron E.; Kohen, Daniela (November 2020, Angewandte Chemie International Edition)

   Abstract A metal/ligand cooperative approach to the reduction of small molecules by metal silylene complexes (R₂Si=M) is demonstrated, whereby silicon activates the incoming substrate and mediates net two‐electron transformations by one‐electron redox processes at two metal centers. An appropriately tuned cationic pincer cobalt(I) complex, featuring a central silylene donor, reacts with CO₂to afford a bimetallic siloxane, featuring two Co^IIcenters, with liberation of CO; reaction of the silylene complex with ethylene yields a similar bimetallic product with an ethylene bridge. Experimental and computational studies suggest a plausible mechanism proceeding by [2+2] cycloaddition to the silylene complex, which is quite sensitive to the steric environment. The Co^II/Co^IIproducts are reactive to oxidation and reduction. Taken together, these findings demonstrate a strategy for metal/ligand cooperative small‐molecule activation that is well‐suited to 3dmetals. 

   more » « less
4. Bridging High-density Electron Beam Coronal Transport and Deep Chromospheric Heating in Stellar Flares

   https://doi.org/10.3847/2041-8213/acb144  

   Kowalski, Adam F. (February 2023, The Astrophysical Journal Letters)

   Abstract The optical and near-ultraviolet (NUV) continuum radiation in M-dwarf flares is thought to be the impulsive response of the lower stellar atmosphere to magnetic energy release and electron acceleration at coronal altitudes. This radiation is sometimes interpreted as evidence of a thermal photospheric spectrum withT≈ 10⁴K. However, calculations show that standard solar flare coronal electron beams lose their energy in a thick target of gas in the upper and middle chromosphere (log₁₀column mass/[g cm⁻²] ≲ −3). At larger beam injection fluxes, electric fields and instabilities are expected to further inhibit propagation to low altitudes. We show that recent numerical solutions of the time-dependent equations governing the power-law electrons and background coronal plasma (Langmuir and ion-acoustic) waves from Kontar et al. produce order-of-magnitude larger heating rates than those that occur in the deep chromosphere through standard solar flare electron beam power-law distributions. We demonstrate that the redistribution of beam energy aboveE≳ 100 keV in this theory results in a local heating maximum that is similar to a radiative-hydrodynamic model with a large, low-energy cutoff and a hard power-law index. We use this semiempirical forward-modeling approach to produce opaque NUV and optical continua at gas temperaturesT≳ 12,000 K over the deep chromosphere with log₁₀column mass/[g cm⁻²] of −1.2 to −2.3. These models explain the color temperatures and Balmer jump strengths in high-cadence M-dwarf flare observations, and they clarify the relation among atmospheric, radiation, and optical color temperatures in stellar flares. 

   more » « less
5. Dark photon and dark Z mediated B meson decays

   https://doi.org/10.1007/JHEP03(2023)108  

   Datta, Alakabha; Hammad, A.; Marfatia, Danny; Mukherjee, Lopamudra; Rashed, Ahmed (March 2023, Journal of High Energy Physics)

   A<sc>bstract</sc> We study flavor changing neutral current decays ofBandKmesons in the dark U(1)_Dmodel, with the dark photon/darkZmass between 10 MeV and 2 GeV. Although the model provides an improved fit (compared to the standard model) to the differential decay distributions ofB → K^(∗)ℓ⁺ℓ⁻, withℓ=μ,e, andB_s→ ϕμ⁺μ⁻, the allowed parameter space is ruled out by measurements of atomic parity violation,K⁺→ μ⁺+invisibledecay, and$$ {B}_s-{\overline{B}}_s $$ $B_s-{\overline{B}}_s$mixing, among others. To evade constraints from low energy data, we extend the model to allow for (1) additional invisibleZ_Ddecay, (2) a direct vector coupling ofZ_Dto muons, and (3) a direct coupling ofZ_Dto both muons and electrons, with the electron coupling fine-tuned to cancel theZ_Dcoupling to electrons via mixing. We find that only the latter case survives all constraints. 

   more » « less