General ILL seminar
organised by College 3
Friday, 3 October 2025 at 13h30
Seminar room 110-111, ILL 50, 1st floor
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Zoom link: https://ill.zoom.us/j/98964195699?pwd=vPhNT17CAeoDUr7QX4PjfyPnWsHuMU.1
Password : SeminarC3
Kent Leung
Montclair State University, Dept. of Physics & Astronomy, Montclair, NJ, USA
Neutrons and photons can penetrate deep into atomic nuclei or bulk materials and avoid unwanted effects from stray electric fields or Coulomb scattering. This makes them exceptionally clean probes of nuclear structure and fundamental symmetries. Neutral beams can be used with delicate cryogenic systems without overwhelming heating from charged particles and have reduced backgrounds, allowing them to probe sensitive effects in precision nuclear physics. Searches for the permanent neutron electric dipole moment (nEDM) offer deep insights into the time-reversal violation and the origin of the observed matter-antimatter asymmetry in the Universe. In the nEDMSF (nEDM with SuperFluid) scheme [1], a cold neutron beam impinges on a 0.4-K measurement cell. Leveraging on a unique combination of polarized 3He, superfluid 4He, and ultracold neutron (UCN) properties, live and in-situ neutron spin analysis and fine control of co-magnetometry systematics can be implemented. To reach the ~ 10⁻²⁸ e·cm design sensitivity, an experimental challenge is to construct 3-L-volume cells that can provide UCN wall loss times of ~ 2000 s, long 3He transverse spin-coherence times (~ 3 hours), and sufficiently low cold-neutron-beam-related backgrounds [2].
round-state properties of protons and neutrons provide critical tests of Quantum Chromodynamics (QCD) in the non-perturbative low-energy regime. In the Compton@HIGS (nuclear Compton scattering at the High Intensity Gamma-ray Source) series of experiments, a beam of mono-energetic photons in the 50 to 100 MeV range impinges on a 0.3-L target cell made from 0.1-mm-thick Kapton sheets filled with liquid H2 [3], D2, 3He, or 4He [4,5]. The photons undergo Compton scattering from the target nucleus, inducing electric and magnetic dipole moments, and are detected by an array of large NaI detectors—featuring single-crystal cores up to ~ 90 L in size. The photons come from the HIGS facility of Triangle Universities Nuclear Laboratory (TUNL), which are produced via Compton backscattering of free-electron laser photons from relativistic electrons in a storage ring. Using a Chiral Effective Field Theory framework [6], the proton and neutron electric and magnetic polarizabilities can be extracted from our absolute (angular) differential cross-sections that are ~10 nano-barn (per steradians) in size. Polarizabilities can also be compared with lattice-QCD calculations now possible at physical pion mass [7], offering a unique bridge between our two best descriptions of the strong force in everyday nuclear matter. Despite the significance of these fundamental quantities, the polarizabilities remain relatively poorly constrained; for example, the neutron’s electric and magnetic polarizabilities (
n and 
n) are known to approximately ±10% and ±30%, respectively. Our latest data, currently under analysis, should reduce our uncertainties in n and n by roughly a factor of two. In parallel, we have initiated R&D efforts for a new scintillating polarized proton target, which is essential for our future intent to measure proton spin polarizabilities.
[1] Golub and Lamoreaux. Physics Reports, 237,1–62 (1994)
[2] Ahmed et al., Journal of Instrumentation, 14, P11017 (2019).
[3] Li et al. (Compton@HIGS), Phys. Rev. Lett. 128, 132502 (2022)
[4] Sikora et al. (Compton@HIGS), Phys. Rev. C 96, 055209 (2017)
[5] Li et al. (Compton@HIGS), Phys. Rev. C 101, 034618 (2020)
[6] Griesshammer et al., Prog. Part. Nucl. Phys. 67, 841 (2012)
[7] Wang et al., Phys. Rev. Lett. 133, 141901 (2024).
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Hanno Filter (College 3 Secretary)