While the standard model of particle physics does not include free particles with fractional charge, experimental searches have not ruled out their existence. We report results from the Cryogenic Dark Matter Search (CDMS II) experiment that give the first direct-detection limits for cosmogenically produced relativistic particles with electric charge lower than e/6. A search for tracks in the six stacked detectors of each of two of the CDMS II towers finds no candidates, thereby excluding new parameter space for particles with electric charges between e/6 and e/200.
Reproducing the in vivo physiologic conditions and biomechanical environment to stimulate natural growth and behavior of lymphatic endothelial cells (LECs) is critical in studying the lymphatic system and its response to stimuli. In vitro studies that deconstruct the biomechanical environment, e.g. independently incorporate flow-induced shear stress or membrane strain have demonstrated the significance of mechanotransduction in LECs (and vascular endothelial cells). Such studies have facilitated the investigation of intracellular signaling pathways stimulated by a particular mechanical cue but do not accurately reproduce natural physiologic behavior of in vivo LECs given the absence of other natural mechanical cues. In this study, we present a novel experimental device designed to reconstruct the in vivo biomechanical environment, i.e. a device that enables the simultaneous application of flow-induced shear stress and cyclic stretching of LECs in vitro. The device is uniquely capable of simulating physiologically-relevant conditions for lymphatic endothelial cells, such as low-flow, high-strain scenarios. Using this device, we observed that, like vascular ECs, LECs aligned in the direction of fluid shear stress when steady flow was applied. In our case the behavior was observed under conditions closer to the physiological mean flow in the lymphatic vessels than vascular levels of shear stress. When concurrent cyclic stretching was applied, the alignment in the direction of flow and perpendicular to the uniaxial stretch was detected in a substantially shortened timeframe. Additionally, the distribution of alignment angles was more closely clustered around 90 degrees under the flow/stretch scenario after 6 hours than the 24 hour flow only scenario, perhaps indicating a greater sensitivity to cyclic stretching than to fluid shear stress in the morphological alignment response of LECs. We also observed alignment of cell nuclei and F-actin filaments in HDLECs after only 6 hours of combined flow and stretch. These observations underscore the importance of including both sources of mechanical stress when studying the growth and behavior of LECs.
The CDMS low ionization threshold experiment (CDMSlite) uses cryogenic germanium detectors operated at a relatively high bias voltage to amplify the phonon signal in the search for weakly interacting massive particles (WIMPs). Results are presented from the second CDMSlite run with an exposure of 70 kg day, which reached an energy threshold for electron recoils as low as 56 eV. A fiducialization cut reduces backgrounds below those previously reported by CDMSlite. New parameter space for the WIMP-nucleon spin-independent cross section is excluded for WIMP masses between 1.6 and 5.5 GeV/c^{2}.
We report results of a search for weakly interacting massive particles (WIMPS) with the silicon detectors of the CDMS II experiment. This blind analysis of 140.2 kg day of data taken between July 2007 and September 2008 revealed three WIMP-candidate events with a surface-event background estimate of 0.41(-0.08)(+0.20)(stat)(-0.24)(+0.28)(syst). Other known backgrounds from neutrons and 206Pb are limited to <0.13 and <0.08 events at the 90% confidence level, respectively. The exposure of this analysis is equivalent to 23.4 kg day for a recoil energy range of 7-100 keV for a WIMP of mass 10 GeV/c2. The probability that the known backgrounds would produce three or more events in the signal region is 5.4%. A profile likelihood ratio test of the three events that includes the measured recoil energies gives a 0.19% probability for the known-background-only hypothesis when tested against the alternative WIMP+background hypothesis. The highest likelihood occurs for a WIMP mass of 8.6 GeV/c2 and WIMP-nucleon cross section of 1.9×10(-41) cm2.
We present limits on spin-independent dark matter-nucleon interactions using a 10.6 g Si athermal phonon detector with a baseline energy resolution of ${\ensuremath{\sigma}}_{E}=3.86\ifmmode\pm\else\textpm\fi{}0.04(\mathrm{stat}{)}_{\ensuremath{-}0.00}^{+0.19}(\mathrm{syst})\text{ }\text{ }\mathrm{eV}$. This exclusion analysis sets the most stringent dark matter-nucleon scattering cross-section limits achieved by a cryogenic detector for dark matter particle masses from 93 to $140\text{ }\text{ }\mathrm{MeV}/{c}^{2}$, with a raw exposure of 9.9 g d acquired at an above-ground facility. This work illustrates the scientific potential of detectors with athermal phonon sensors with eV-scale energy resolution for future dark matter searches.
