First Dark Matter Search Results from the LUX-ZEPLIN (LZ) Experiment

The LUX-ZEPLIN experiment is a dark matter detector centered on a dual-phase xenon time projection chamber operating at the Sanford Underground Research Facility in Lead, South Dakota, USA. This Letter reports results from LUX-ZEPLIN's first search for weakly interacting massive particles (WIMPs) with an exposure of 60 live days using a fiducial mass of 5.5 t. A profile-likelihood ratio analysis shows the data to be consistent with a background-only hypothesis, setting new limits on spin-independent WIMP-nucleon, spin-dependent WIMP-neutron, and spin-dependent WIMP-proton cross sections for WIMP masses above 9  GeV/c^{2}. The most stringent limit is set for spin-independent scattering at 36  GeV/c^{2}, rejecting cross sections above 9.2×10^{-48}  cm at the 90% confidence level.

Comparing the cost-effectiveness of the Otago Exercise Programme among older women and men: A secondary analysis of a randomized controlled trial

Objective

Using stratified analyses, we examined the cost-effectiveness of the Otago Exercise Programme (OEP), from a health care system perspective, among older women and men who have previously fallen.

Methods

This study was a secondary stratified analysis (by women and men), of a 12-month prospective economic evaluation of a randomized clinical trial (OEP compared with usual care). Three hundred and forty four community-dwelling older adults (≥70; 172 OEP (110 women; 62 men), 172 usual care (119 women; 53 men)) who sustained a fall in the past 12 months and received a baseline assessment at the Vancouver Falls Prevention Clinic, Canada were included. A gender by OEP/usual care interaction was examined for the falls incidence rate ratio (IRR). Outcome measures stratified by gender included: falls IRR, incremental cost-per fall prevented (ICER), incremental cost per quality adjusted life year (QALY, ICUR) gained, and mean total health care resource utilization costs.

Results

Men were frailer than women at baseline. Men incurred higher mean total healthcare costs $6794 (SD: $11906)). There was no significant gender by OEP/usual care interaction on falls IRR. The efficacy of the OEP did not vary by gender. The adjusted IRR for the OEP group demonstrated a 39% (IRR: 0.61, CI: 0.40–0.93) significant reduction in falls among men but not women (32% reduction (IRR: 0.69, CI: 0.47–1.02)). The ICER showed the OEP was effective in preventing falls and less costly for men, while it was costlier for women by $42. The ICUR showed the OEP did not impact quality of life.

Conclusion

Future studies should explore gender factors (i.e., health seeking behaviours, gender related frailty) that may explain observed variation in the cost-effectiveness of the OEP as a secondary falls prevention strategy.

Trial registrations

ClinicalTrials.gov Protocol Registration System

Identifier: NCT01029171; URL: https://clinicaltrials.gov/ct2/show/NCT01029171

Identifier: NCT00323596; URL: https://clinicaltrials.gov/ct2/show/NCT00323596

Exercise, Processing Speed, and Subsequent Falls: A Secondary Analysis of a 12-Month Randomized Controlled Trial

BACKGROUND

Strength and balance retraining exercises reduce the rate of subsequent falls in community-dwelling older adults who have previously fallen. Exercise can also improve cognitive function, including processing speed. Given processing speed predicts subsequent falls, we aimed to determine whether improved processing speed mediated the effects of the Otago Exercise Program on the rate of subsequent: (i) total falls, (ii) non-injurious falls, (iii) moderate injurious falls, and (iv) serious injurious falls.

METHOD

A secondary complete case analysis of a 12-month, single-blind, randomized clinical trial among 256 of 344 adults aged at least 70 years who fell in the previous 12 months. Participants were randomized 1:1 to receive usual care plus the Otago Exercise Program (n = 123) or usual care (n = 133), consisting of fall prevention care provided by a geriatrician. The primary outcome was self-reported number of falls over 12 months (ie, rate of falls). Processing speed was assessed at baseline and at 12 months by the Digit Symbol Substitution Test (DSST). Causal mediation analyses were conducted using quasi-Bayesian estimates and 95% confidence intervals.

RESULTS

Exercise significantly reduced the rate of subsequent moderate injurious falls (IRR = 0.49; 95% CI: 0.31, 0.77; p = .002) and improved processing speed (estimated mean difference: 1.16 points; 95% CI: 0.11, 2.21). Improved DSST mediated the effect of exercise on the rate of subsequent moderate injurious falls (estimate: -0.06; 95% CI: -0.15, -0.001; p = .036).

CONCLUSION

Improved processing speed may be a mechanism by which exercise reduces subsequent moderate injurious falls in older adults who fell previously.

CLINICAL TRIALS REGISTRATION NUMBER

ClinicalTrials.gov Protocol Registration System:NCT01029171: https://clinicaltrials.gov/ct2/show/NCT01029171NCT00323596: https://clinicaltrials.gov/ct2/show/NCT00323596.

Sex Differences in Subsequent Falls and Falls Risk: A Prospective Cohort Study in Older Adults

BACKGROUND

Sex differences for subsequent falls and falls risk factors in community-dwelling older adults who have fallen are unknown. Our aim was to: (1) compare the number of falls between sexes, (2) identify modifiable falls risk factors, and (3) explore the interaction of sex on falls risk factors in older adults who fall.

METHODS

Four hundred sixty-two community dwellers seeking medical attention after an index fall were recruited from the Vancouver Falls Prevention Clinic and participated in this 12-month prospective cohort study. Ninety-six participants were part of a randomized controlled trial of exercise. Falls were tracked with monthly falls calendars. Demographics, falls risk measures, and the number of subsequent falls were compared between sexes. A principal component analysis (PCA) was employed to reduce the falls risk measures to a smaller set of factors. The PCA factors were used in negative binomial regression models to predict the number of subsequent falls. Age, exposure time (i.e., number of falls monitoring days), and prescribed exercise (yes/no) were used as covariates, and sex (male/female) and PCA factors were used as main effects. The interaction of sex by PCA factor was then included.

RESULTS

Males fell more over 12 months (males: 2.80 ± 6.86 falls; females: 1.25 ± 2.63 falls) than females, and poorer executive function predicted falls in males. Four PCA factors were defined - impaired cognition and mobility, low mood and self-efficacy, mobility resilience, and perceived poor health - each predicted the number of falls. The sex by mobility resilience interaction suggested that mobility resilience was less protective of falls in males.

CONCLUSION

Modifiable risk factors related to cognition, physical function, psychological wellbeing, and health status predicted subsequent falls. In males, better mobility was not as protective of falls compared with females. This may be due to males' poorer executive function, contributing to decreased judgement or slowed decision-making during mobility. These results may inform efficacious sex-specific falls prevention strategies.

The Effects of Computerized Cognitive Training With and Without Physical Exercise on Cognitive Function in Older Adults: An 8-Week Randomized Controlled Trial

BACKGROUND

Aging is characterized by cognitive changes in specific domains, such as declines in memory and executive functions. Given the world's aging population, it is important to identify and evaluate strategies that promote healthy cognitive aging. Besides exercise, computerized cognitive training (CCT) is a promising approach to promote cognitive function. Moreover, a single bout of exercise immediately prior to CCT may provide additional cognitive benefits.

METHODS

An 8-week proof-of-concept randomized controlled trial to investigate the effect of a commercial CCT intervention, alone and when preceded by exercise, on cognitive function. Participants (124; aged 65-85 years) performed 8 weeks of: (i) Group-based CCT (Fit Brains) 3×/week for 1 hour plus 3×/week home-based training; (ii) Group-based CCT preceded by exercise (Ex-CCT) 3×/week for 1 hour plus 3×/week home-based training (exercise+CCT); or (iii) Group-based balanced and toned (BAT) classes 3×/week for 1 hour (control). Memory was assessed by the Rey Auditory Verbal Learning Test. Executive functions were assessed using the: (i) Stroop Test, (ii) Trail Making Tests (TMT), (iii) Flanker Test, and (iv) Dimensional Change Card Sort Test (DCCS).

RESULTS

At trial completion, there were no significant between-group differences in memory (p > .05). However, compared with BAT, CCT, and Ex-CCT significantly improved Stroop performance (-10.72, 95% confidence interval [CI]: -16.53, -4.91; -7.95, 95% CI: -13.77, -2.13, respectively). Moreover, Ex-CCT significantly improved the performance on TMT (-13.65, 95% CI: -26.09, -1.22), the Flanker Test (6.72, 95% CI: 2.55, 10.88), and the DCCS Test (6.75, 95% CI: 0.99, 12.50).

CONCLUSION

An 8-week CCT program may promote executive functions in older adults and combining it with a bout of exercise may provide broader benefits.

COMPUTERIZED COGNITIVE TRAINING, WITH OR WITHOUT EXERCISE, TO PROMOTE COGNITIVE FUNCTION: A RANDOMIZED TRIAL

Given the world’s aging population, it is important to identify strategies that promote healthy cognitive aging. Computerized cognitive training (CCT) may be a promising method to combat cognitive decline in older adults. Moreover, physical exercise immediately prior to CCT might provide additional cognitive benefits. We conducted a randomized controlled trial to examine the effect of a CCT intervention, alone or preceded by physical exercise, on memory and executive functions in older adults. 124 community-dwelling older adults aged 65-85 years were randomly assigned to either 8-weeks of: 1) 3x/week group-based CCT plus 3x/week CCT sessions at home; 2) 3x/week group-based CCT combined with a 15-minute brisk walk (Ex-CCT) plus 3x/week Ex-CCT sessions at home; or 3)3x/week group-based sham exercise and education sessions (CON). At baseline and 8-weeks standard neuropsychological tests of verbal memory and learning and executive functions were administered, including the Rey Auditory Verbal Learning Test (RAVLT), Stroop test, Flanker test, Trail Making Tests (TMT B-A), and Dimensional Change Card Sort (DCCS) Test. At trial completion, there were no differences in RAVLT performance. Compared with CON, FBT and Ex-FBT participants significantly improved performance on the Stroop test (p = .001 and p = .023, respectively). Additionally, those randomized to Ex-CCT improved performance on the Flanker test (p = .002), TMT B-A (p = .047), and the DCCS Test (p = .023) compared with BAT. These findings suggest that an 8-week CCT program could benefit executive functions, and that implementing exercise immediately prior to CCT could provide broader benefits.

Results of a Search for Sub-GeV Dark Matter Using 2013 LUX Data

The scattering of dark matter (DM) particles with sub-GeV masses off nuclei is difficult to detect using liquid xenon-based DM search instruments because the energy transfer during nuclear recoils is smaller than the typical detector threshold. However, the tree-level DM-nucleus scattering diagram can be accompanied by simultaneous emission of a bremsstrahlung photon or a so-called "Migdal" electron. These provide an electron recoil component to the experimental signature at higher energies than the corresponding nuclear recoil. The presence of this signature allows liquid xenon detectors to use both the scintillation and the ionization signals in the analysis where the nuclear recoil signal would not be otherwise visible. We report constraints on spin-independent DM-nucleon scattering for DM particles with masses of 0.4-5  GeV/c^{2} using 1.4×10^{4}  kg day of search exposure from the 2013 data from the Large Underground Xenon (LUX) experiment for four different classes of mediators. This analysis extends the reach of liquid xenon-based DM search instruments to lower DM masses than has been achieved previously.

First Searches for Axions and Axionlike Particles with the LUX Experiment

The first searches for axions and axionlike particles with the Large Underground Xenon experiment are presented. Under the assumption of an axioelectric interaction in xenon, the coupling constant between axions and electrons g_{Ae} is tested using data collected in 2013 with an exposure totaling 95 live days ×118  kg. A double-sided, profile likelihood ratio statistic test excludes g_{Ae} larger than 3.5×10^{-12} (90% C.L.) for solar axions. Assuming the Dine-Fischler-Srednicki-Zhitnitsky theoretical description, the upper limit in coupling corresponds to an upper limit on axion mass of 0.12  eV/c^{2}, while for the Kim-Shifman-Vainshtein-Zhakharov description masses above 36.6  eV/c^{2} are excluded. For galactic axionlike particles, values of g_{Ae} larger than 4.2×10^{-13} are excluded for particle masses in the range 1-16  keV/c^{2}. These are the most stringent constraints to date for these interactions.

Limits on Spin-Dependent WIMP-Nucleon Cross Section Obtained from the Complete LUX Exposure

We present experimental constraints on the spin-dependent WIMP-nucleon elastic cross sections from the total 129.5  kg yr exposure acquired by the Large Underground Xenon experiment (LUX), operating at the Sanford Underground Research Facility in Lead, South Dakota (USA). A profile likelihood ratio analysis allows 90% C.L. upper limits to be set on the WIMP-neutron (WIMP-proton) cross section of σ_{n}=1.6×10^{-41}  cm^{2} (σ_{p}=5×10^{-40}  cm^{2}) at 35  GeV c^{-2}, almost a sixfold improvement over the previous LUX spin-dependent results. The spin-dependent WIMP-neutron limit is the most sensitive constraint to date.

Results from a Search for Dark Matter in the Complete LUX Exposure

We report constraints on spin-independent weakly interacting massive particle (WIMP)-nucleon scattering using a 3.35×10^{4}  kg day exposure of the Large Underground Xenon (LUX) experiment. A dual-phase xenon time projection chamber with 250 kg of active mass is operated at the Sanford Underground Research Facility under Lead, South Dakota (USA). With roughly fourfold improvement in sensitivity for high WIMP masses relative to our previous results, this search yields no evidence of WIMP nuclear recoils. At a WIMP mass of 50  GeV c^{-2}, WIMP-nucleon spin-independent cross sections above 2.2×10^{-46}  cm^{2} are excluded at the 90% confidence level. When combined with the previously reported LUX exposure, this exclusion strengthens to 1.1×10^{-46}  cm^{2} at 50  GeV c^{-2}.

Results on the Spin-Dependent Scattering of Weakly Interacting Massive Particles on Nucleons from the Run 3 Data of the LUX Experiment

We present experimental constraints on the spin-dependent WIMP (weakly interacting massive particle)-nucleon elastic cross sections from LUX data acquired in 2013. LUX is a dual-phase xenon time projection chamber operating at the Sanford Underground Research Facility (Lead, South Dakota), which is designed to observe the recoil signature of galactic WIMPs scattering from xenon nuclei. A profile likelihood ratio analysis of 1.4×10^{4}  kg day of fiducial exposure allows 90% C.L. upper limits to be set on the WIMP-neutron (WIMP-proton) cross section of σ_{n}=9.4×10^{-41}  cm^{2} (σ_{p}=2.9×10^{-39}  cm^{2}) at 33  GeV/c^{2}. The spin-dependent WIMP-neutron limit is the most sensitive constraint to date.

Improved Limits on Scattering of Weakly Interacting Massive Particles from Reanalysis of 2013 LUX Data

We present constraints on weakly interacting massive particles (WIMP)-nucleus scattering from the 2013 data of the Large Underground Xenon dark matter experiment, including 1.4×10^{4}  kg day of search exposure. This new analysis incorporates several advances: single-photon calibration at the scintillation wavelength, improved event-reconstruction algorithms, a revised background model including events originating on the detector walls in an enlarged fiducial volume, and new calibrations from decays of an injected tritium β source and from kinematically constrained nuclear recoils down to 1.1 keV. Sensitivity, especially to low-mass WIMPs, is enhanced compared to our previous results which modeled the signal only above a 3 keV minimum energy. Under standard dark matter halo assumptions and in the mass range above 4  GeV c^{-2}, these new results give the most stringent direct limits on the spin-independent WIMP-nucleon cross section. The 90% C.L. upper limit has a minimum of 0.6 zb at 33  GeV c^{-2} WIMP mass.

First results from the LUX dark matter experiment at the Sanford underground research facility

The Large Underground Xenon (LUX) experiment is a dual-phase xenon time-projection chamber operating at the Sanford Underground Research Facility (Lead, South Dakota). The LUX cryostat was filled for the first time in the underground laboratory in February 2013. We report results of the first WIMP search data set, taken during the period from April to August 2013, presenting the analysis of 85.3 live days of data with a fiducial volume of 118 kg. A profile-likelihood analysis technique shows our data to be consistent with the background-only hypothesis, allowing 90% confidence limits to be set on spin-independent WIMP-nucleon elastic scattering with a minimum upper limit on the cross section of 7.6 × 10(-46) cm(2) at a WIMP mass of 33 GeV/c(2). We find that the LUX data are in disagreement with low-mass WIMP signal interpretations of the results from several recent direct detection experiments.

Limits on spin-dependent WIMP-nucleon cross sections from 225 live days of XENON100 data

We present new experimental constraints on the elastic, spin-dependent WIMP-nucleon cross section using recent data from the XENON100 experiment, operated in the Laboratori Nazionali del Gran Sasso in Italy. An analysis of 224.6 live days×34 kg of exposure acquired during 2011 and 2012 revealed no excess signal due to axial-vector WIMP interactions with 129Xe and 131Xe nuclei. This leads to the most stringent upper limits on WIMP-neutron cross sections for WIMP masses above 6 GeV/c², with a minimum cross section of 3.5×10(-40) cm² at a WIMP mass of 45 GeV/c², at 90% confidence level.

Dark matter results from 225 live days of XENON100 data

We report on a search for particle dark matter with the XENON100 experiment, operated at the Laboratori Nazionali del Gran Sasso for 13 months during 2011 and 2012. XENON100 features an ultralow electromagnetic background of (5.3 ± 0.6) × 10(-3) events/(keV(ee) × kg × day) in the energy region of interest. A blind analysis of 224.6 live days × 34 kg exposure has yielded no evidence for dark matter interactions. The two candidate events observed in the predefined nuclear recoil energy range of 6.6-30.5 keV(nr) are consistent with the background expectation of (1.0 ± 0.2) events. A profile likelihood analysis using a 6.6-43.3 keV(nr) energy range sets the most stringent limit on the spin-independent elastic weakly interacting massive particle-nucleon scattering cross section for weakly interacting massive particle masses above 8 GeV/c(2), with a minimum of 2 × 10(-45) cm(2) at 55 GeV/c(2) and 90% confidence level.

Limits on the spin-dependent WIMP-nucleon cross sections from the first science run of the ZEPLIN-III experiment

We present new experimental constraints on the WIMP-nucleon spin-dependent elastic cross sections using data from the first science run of ZEPLIN-III, a two-phase xenon experiment searching for galactic dark matter weakly interacting massive particles based at the Boulby mine. Analysis of approximately 450 kg x days fiducial exposure allow us to place a 90%-confidence upper limit on the pure WIMP-neutron cross section of sigma(n)=1.9x10(-2) pb at 55 GeV/c(2) WIMP mass. Recent calculations of the nuclear spin structure based on the Bonn charge-dependent nucleon-nucleon potential were used for the odd-neutron isotopes 129Xe and 131Xe. These indicate that the sensitivity of xenon targets to the spin-dependent WIMP-proton interaction could be much lower than implied by previous calculations, whereas the WIMP-neutron sensitivity is impaired only by a factor of approximately 2.