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1. Measurement of the generalized spin polarizabilities of the neutron in the low-Q2 region

   https://doi.org/10.1038/s41567-021-01245-9  

   Sulkosky, Vincent; Peng, Chao; Chen, Jian-ping; Deur, Alexandre; Abrahamyan, Sergey; Aniol, Konrad A.; Armstrong, David S.; Averett, Todd; Bailey, Stephen J.; Beck, Arie; et al (May 2021, Nature Physics)

   null (Ed.)

   Understanding the nucleon spin structure in the regime where the strong interaction becomes truly strong poses a challenge to both experiment and theory. At energy scales below the nucleon mass of about 1 GeV, the intense interaction among the quarks and gluons inside the nucleon makes them highly correlated. Their coherent behaviour causes the emergence of effective degrees of freedom, requiring the application of non-perturbative techniques such as chiral effective field theory. Here we present measurements of the neutron’s generalized spin polarizabilities that quantify the neutron’s spin precession under electromagnetic fields at very low energy-momentum transfer squared down to 0.035 GeV2. In this regime, chiral effective field theory calculations are expected to be applicable. Our data, however, show a strong discrepancy with these predictions, presenting a challenge to the current description of the neutron’s spin properties. 

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2. Light resonances and the low-q2 bin of RK*$$ {R}_{K^{*}} $$

   https://doi.org/10.1007/JHEP03(2018)188  

   Altmannshofer, Wolfgang; Baker, Michael J.; Gori, Stefania; Harnik, Roni; Pospelov, Maxim; Stamou, Emmanuel; Thamm, Andrea (March 2018, Journal of High Energy Physics)
3. Volatile Abundances, Extended Coma Sources, and Nucleus Ice Associations in Comet C/2014 Q2 (Lovejoy)

   https://doi.org/10.3847/PSJ/ac323c  

   Dello Russo, Neil; Vervack, Ronald J.; Kawakita, Hideyo; Bonev, Boncho P.; DiSanti, Michael A.; Gibb, Erika L.; McKay, Adam J.; Cochran, Anita L.; Weaver, Harold A.; Biver, Nicolas; et al (January 2022, The Planetary Science Journal)

   Abstract High-resolution infrared spectra of comet C/2014 Q2 Lovejoy were acquired with NIRSPEC at the W. M. Keck Observatory on two post-perihelion dates (UT 2015 February 2 and 3). H 2 O was measured simultaneously with CO, CH 3 OH, H 2 CO, CH 4 , C 2 H 6 , C 2 H 4 , C 2 H 2 , HCN, and NH 3 on both dates, and rotational temperatures, production rates, relative abundances, H 2 O ortho-to-para ratios, and spatial distributions in the coma were determined. The first detection of C 2 H 4 in a comet from ground-based observations is reported. Abundances relative to H 2 O for all species were found to be in the typical range compared with values for other comets in the overall population to date. There is evidence of variability in rotational temperatures and production rates on timescales that are small compared with the rotational period of the comet. Spatial distributions of volatiles in the coma suggest complex outgassing behavior. CH 3 OH, HCN, C 2 H 6 , and CH 4 spatial distributions in the coma are consistent with direct release from associated ices in the nucleus and are peaked in a more sunward direction compared with co-measured dust. H 2 O spatial profiles are clearly distinct from these other four species, likely due to a sizable coma contribution from icy grain sublimation. Spatial distributions for C 2 H 2 , H 2 CO, and NH 3 suggest substantial contributions from extended coma sources, providing further evidence for distinct origins and associations for these species in comets. CO shows a different spatial distribution compared with other volatiles, consistent with jet activity from discrete nucleus ice sources. 

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4. Ruling out Color Transparency in Quasielastic 12C(e,e'p) up to Q2 of 14.2 (GeV/c)2

   Bhetuwal, D; Matter, J; Szumila-Vance, H; Kabir, M. L; Dutta, D; Ent, R; Abrams, D; Ahmed, Z; Aljawrneh, B; Alsalmi, S; et al (February 2021, Physical review letters)

   null (Ed.)

   Quasielastic C12(e,e′p) scattering was measured at spacelike 4-momentum transfer squared Q2=8, 9.4, 11.4, and 14.2  (GeV/c)2, the highest ever achieved to date. Nuclear transparency for this reaction was extracted by comparing the measured yield to that expected from a plane-wave impulse approximation calculation without any final state interactions. The measured transparency was consistent with no Q2 dependence, up to proton momenta of 8.5  GeV/c, ruling out the quantum chromodynamics effect of color transparency at the measured Q2 scales in exclusive (e,e′p) reactions. These results impose strict constraints on models of color transparency for protons. 

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5. Layered NaBa2M3Q3(Q2) (M = Cu, Ag; Q = S, Se) Chalcogenides and Local Ordering in Their Mixed-Anion Compositions

   Tassanov, Ayat; Lee, Huiju; Xia, Yi; Hodges, James M (August 2024, Inorganic chemistry)

   Three new NaBa2M3Q3(Q2) (M = Ag, Cu; Q = S, Se) chalcogenides were prepared using solid-state methods and structurally characterized using single-crystal X-ray diffraction. NaBa2Ag3Se3(Se2) and NaBa2Cu3Se3(Se2) crystallize in the monoclinic C2/m space group and have a two-dimensional structure composed of edge-sharing MSe4/4 tetrahedra separated by Na+ and Ba2+ cations, along with (Se2)2- dimers at the center of the spacings between [M3Se3]3- slabs. NaBa2Ag3S3(S2) adopts a related structure with the C2/m space group but has additional, crystallographically distinct Ag atoms in the [Ag3S3]3- layer that are linearly coordinated. NaBa2Ag3Se3(Se2) and NaBa2Ag3S3(S2) have indirect band gaps measured to be 1.2 eV and 1.9 eV, respectively, which is supported by band structures calculated using density functional theory. Mixed- anion NaBa2Cu3Se5-xSx compositions were prepared to probe for the presence of anion ordering and heteronuclear (S-Se)2- dimers. Structural analyses of the sulfoselenides indicate selenium preferentially occupies the Q-Q dimer sites, while Raman spectroscopy reveals a mixture of (S2), (Se2), and heteronuclear (S-Se) units in the sulfur-rich products. The local ordering of the chalcogens is rationalized using simple bonding concepts and adds to a growing framework for understanding ordering phenomena in mixed-anion systems. 

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