Extreme alpha-clustering in the 18O nucleus

The structure of the 18O nucleus at excitation energies above the alpha decay threshold was studied using 14C+alpha resonance elastic scattering. A number of states with large alpha reduced widths have been observed, indicating that the alpha-cluster degree of freedom plays an important role in this N not equal Z nucleus. However, the alpha-cluster structure of this nucleus is very different from the relatively simple pattern of strong alpha-cluster quasi-rotational bands in the neighboring 16O and 20Ne nuclei. A 0+ state with an alpha reduced width exceeding the single particle limit was identified at an excitation energy of 9.9+/-0.3 MeV. We discuss evidence that states of this kind are common in light nuclei and give possible explanations of this feature.Comment: 4 pages, 2 figures, 1 table. Resubmission with minor changes for clarity, including removal of one figur

Population of bound excited states in intermediate-energy fragmentation reactions

Fragmentation reactions with intermediate-energy heavy-ion beams exhibit a wide range of reaction mechanisms, ranging from direct reactions to statistical processes. We examine this transition by measuring the relative population of excited states in several sd-shell nuclei produced by fragmentation with the number of removed nucleons ranging from two to sixteen. The two-nucleon removal is consistent with a non-dissipative process whereas the removal of more than five nucleons appears to be mainly statistical.Comment: 5 pages, 6 figure

Shell structure at N=28 near the dripline: spectroscopy of 42^{42}Si, 43^{43}P and 44^{44}S

Measurements of the N=28 isotones 42Si, 43P and 44S using one- and two-proton knockout reactions from the radioactive beam nuclei 44S and 46Ar are reported. The knockout reaction cross sections for populating 42Si and 43P and a 184 keV gamma-ray observed in 43P establish that the d_{3/2} and s_{1/2} proton orbits are nearly degenerate in these nuclei and that there is a substantial Z=14 subshell closure separating these two orbits from the d_{5/2} orbit. The increase in the inclusive two-proton knockout cross section from 42Si to 44S demonstrates the importance of the availability of valence protons for determining the cross section. New calculations of the two-proton knockout reactions that include diffractive effects are presented. In addition, it is proposed that a search for the d_{5/2} proton strength in 43P via a higher statistics one-proton knockout experiment could help determine the size of the Z=14 closure.Comment: Phys. Rev. C, in pres

Fermi's golden rule and exponential decay as a RG fixed point

We discuss the decay of unstable states into a quasicontinuum using models of the effective Hamiltonian type. The goal is to show that exponential decay and the golden rule are exact in a suitable scaling limit, and that there is an associated renormalization group (RG) with these properties as a fixed point. The method is inspired by a limit theorem for infinitely divisible distributions in probability theory, where there is a RG with a Cauchy distribution, i.e. a Lorentz line shape, as a fixed point. Our method of solving for the spectrum is well known; it does not involve a perturbation expansion in the interaction, and needs no assumption of a weak interaction. We use random matrices for the interaction, and show that the ensemble fluctuations vanish in the scaling limit. Thus the limit is the same for every model in the ensemble with probability one.Comment: 20 pages, 1 figur

g9/2g_{9/2} neutron strength in the N=29N=29 isotones and the 52^{52}Cr(d,pd,p)53^{53}Cr reaction

We performed a measurement of the $^{52}$Cr$(d,p)^{53}$Cr reaction at 16 MeV using the Florida State University Super-Enge Split-Pole Spectrograph (SE-SPS) and observed 26 states. While all of the states observed here had been seen in previous $(d,p)$ experiments, we changed five $L$ assignments from those reported previously and determined $L$ values for nine states that had not had such assignments made previously. The $g_{9/2}$ neutron strength observed in $^{53}$Cr in the present work and in the $N=29$ isotones $^{49}$Ca, $^{51}$Ti, and $^{55}$Fe via $(d,p)$ reactions is much smaller than the sum rule for this strength. Most of the observed $L=4$ strength in these nuclei is located in states near 4 MeV excitation energy. The remaining $g_{9/2}$ strength may be located in the continuum or may be fragmented among many bound states. A covariant density functional theory calculation provides support for the hypothesis that the $g_{9/2}$ neutron orbit is unbound in $^{53}$Cr. The ($\alpha,^3$He) reaction may provide a more sensitive probe for the missing $g_{9/2}$ neutron strength. In addition, particle-$\gamma$ coincidence experiments may help resolve some remaining questions in this nucleus.Comment: 15 pages, 5 figures. arXiv admin note: text overlap with arXiv:2212.0438

Aged-senescent cells contribute to impaired heart regeneration

Aging leads to increased cellular senescence and is associated with decreased potency of tissue-specific stem/progenitor cells. Here, we have done an extensive analysis of cardiac progenitor cells (CPCs) isolated from human subjects with cardiovascular disease, aged 32-86 years. In aged subjects (>70 years old), over half of CPCs are senescent (p16INK4A , SA-β-gal, DNA damage γH2AX, telomere length, senescence-associated secretory phenotype [SASP]), unable to replicate, differentiate, regenerate or restore cardiac function following transplantation into the infarcted heart. SASP factors secreted by senescent CPCs renders otherwise healthy CPCs to senescence. Elimination of senescent CPCs using senolytics abrogates the SASP and its debilitative effect in vitro. Global elimination of senescent cells in aged mice (INK-ATTAC or wild-type mice treated with D + Q senolytics) in vivo activates resident CPCs and increased the number of small Ki67-, EdU-positive cardiomyocytes. Therapeutic approaches that eliminate senescent cells may alleviate cardiac deterioration with aging and restore the regenerative capacity of the heart

Identification of Radiopure Titanium for the LZ Dark Matter Experiment and Future Rare Event Searches

The LUX-ZEPLIN (LZ) experiment will search for dark matter particle interactions with a detector containing a total of 10 tonnes of liquid xenon within a double-vessel cryostat. The large mass and proximity of the cryostat to the active detector volume demand the use of material with extremely low intrinsic radioactivity. We report on the radioassay campaign conducted to identify suitable metals, the determination of factors limiting radiopure production, and the selection of titanium for construction of the LZ cryostat and other detector components. This titanium has been measured with activities of $^{238}$U$_{e}$~$<$1.6~mBq/kg, $^{238}$U$_{l}$~$<$0.09~mBq/kg, $^{232}$Th$_{e}$~$=0.28\pm 0.03$~mBq/kg, $^{232}$Th$_{l}$~$=0.25\pm 0.02$~mBq/kg, $^{40}$K~$<$0.54~mBq/kg, and $^{60}$Co~$<$0.02~mBq/kg (68\% CL). Such low intrinsic activities, which are some of the lowest ever reported for titanium, enable its use for future dark matter and other rare event searches. Monte Carlo simulations have been performed to assess the expected background contribution from the LZ cryostat with this radioactivity. In 1,000 days of WIMP search exposure of a 5.6-tonne fiducial mass, the cryostat will contribute only a mean background of $0.160\pm0.001$(stat)$\pm0.030$(sys) counts.Comment: 13 pages, 3 figures, accepted for publication in Astroparticle Physic

Projected WIMP sensitivity of the LUX-ZEPLIN dark matter experiment

LUX-ZEPLIN (LZ) is a next-generation dark matter direct detection experiment that will operate 4850 feet underground at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, USA. Using a two-phase xenon detector with an active mass of 7 tonnes, LZ will search primarily for low-energy interactions with weakly interacting massive particles (WIMPs), which are hypothesized to make up the dark matter in our galactic halo. In this paper, the projected WIMP sensitivity of LZ is presented based on the latest background estimates and simulations of the detector. For a 1000 live day run using a 5.6-tonne fiducial mass, LZ is projected to exclude at 90% confidence level spin-independent WIMP-nucleon cross sections above 1.4×10-48 cm2 for a 40 GeV/c2 mass WIMP. Additionally, a 5σ discovery potential is projected, reaching cross sections below the exclusion limits of recent experiments. For spin-dependent WIMP-neutron(-proton) scattering, a sensitivity of 2.3×10-43 cm2 (7.1×10-42 cm2) for a 40 GeV/c2 mass WIMP is expected. With underground installation well underway, LZ is on track for commissioning at SURF in 2020