33 research outputs found
Non-invasive prenatal assessment of trisomy 21 by multiplexed maternal plasma DNA sequencing: large scale validity study.
To validate the clinical efficacy and practical feasibility of massively parallel maternal plasma DNA sequencing to screen for fetal trisomy 21 among high risk pregnancies clinically indicated for amniocentesis or chorionic villus sampling. Diagnostic accuracy validated against full karyotyping, using prospectively collected or archived maternal plasma samples. Prenatal diagnostic units in Hong Kong, United Kingdom, and the Netherlands. 753 pregnant women at high risk for fetal trisomy 21 who underwent definitive diagnosis by full karyotyping, of whom 86 had a fetus with trisomy 21. Intervention Multiplexed massively parallel sequencing of DNA molecules in maternal plasma according to two protocols with different levels of sample throughput: 2-plex and 8-plex sequencing. Proportion of DNA molecules that originated from chromosome 21. A trisomy 21 fetus was diagnosed when the z score for the proportion of chromosome 21 DNA molecules was >3. Diagnostic sensitivity, specificity, positive predictive value, and negative predictive value were calculated for trisomy 21 detection. Results were available from 753 pregnancies with the 8-plex sequencing protocol and from 314 pregnancies with the 2-plex protocol. The performance of the 2-plex protocol was superior to that of the 8-plex protocol. With the 2-plex protocol, trisomy 21 fetuses were detected at 100% sensitivity and 97.9% specificity, which resulted in a positive predictive value of 96.6% and negative predictive value of 100%. The 8-plex protocol detected 79.1% of the trisomy 21 fetuses and 98.9% specificity, giving a positive predictive value of 91.9% and negative predictive value of 96.9%. Multiplexed maternal plasma DNA sequencing analysis could be used to rule out fetal trisomy 21 among high risk pregnancies. If referrals for amniocentesis or chorionic villus sampling were based on the sequencing test results, about 98% of the invasive diagnostic procedures could be avoided.published_or_final_versio
Search for extraterrestrial antineutrino sources with the KamLAND detector
We present the results of a search for extraterrestrial electron
antineutrinos ('s) in the energy range using the KamLAND detector. In an exposure of
4.53 kton-year, we identify 25 candidate events. All of the candidate events
can be attributed to background, most importantly neutral current atmospheric
neutrino interactions, setting an upper limit on the probability of B
solar 's converting into 's at
(90% C.L.), if we assume an undistorted shape. This limit
corresponds to a solar flux of or an event
rate of above the energy threshold
. The present data also allows us to set more
stringent limits on the diffuse supernova neutrino flux and on the annihilation
rates for light dark matter particles.Comment: 22 pages, 6 figure
Production of Radioactive Isotopes through Cosmic Muon Spallation in KamLAND
Radioactive isotopes produced through cosmic muon spallation are a background
for rare-event detection in detectors, double--decay experiments,
and dark-matter searches. Understanding the nature of cosmogenic backgrounds is
particularly important for future experiments aiming to determine the pep and
CNO solar neutrino fluxes, for which the background is dominated by the
spallation production of C. Data from the Kamioka liquid-scintillator
antineutrino detector (KamLAND) provides valuable information for better
understanding these backgrounds, especially in liquid scintillators, and for
checking estimates from current simulations based upon MUSIC, FLUKA, and
GEANT4. Using the time correlation between detected muons and neutron captures,
the neutron production yield in the KamLAND liquid scintillator is measured to
be . For other isotopes,
the production yield is determined from the observed time correlation related
to known isotope lifetimes. We find some yields are inconsistent with
extrapolations based on an accelerator muon beam experiment.Comment: 16 pages, 20 figure
Measurement of the 8B Solar Neutrino Flux with the KamLAND Liquid Scintillator Detector
We report a measurement of the neutrino-electron elastic scattering rate from
8B solar neutrinos based on a 123 kton-day exposure of KamLAND. The
background-subtracted electron recoil rate, above a 5.5 MeV analysis threshold
is 1.49+/-0.14(stat)+/-0.17(syst) events per kton-day. Interpreted as due to a
pure electron flavor flux with a 8B neutrino spectrum, this corresponds to a
spectrum integrated flux of 2.77+/-0.26(stat)+/-0.32(syst) x 10^6 cm^-2s^-1.
The analysis threshold is driven by 208Tl present in the liquid scintillator,
and the main source of systematic uncertainty is due to background from
cosmogenic 11Be. The measured rate is consistent with existing measurements and
with Standard Solar Model predictions which include matter enhanced neutrino
oscillation.Comment: 6 pages, 3 figure
Noninvasive Prenatal Diagnosis of Fetal Trisomy 18 and Trisomy 13 by Maternal Plasma DNA Sequencing
Massively parallel sequencing of DNA molecules in the plasma of pregnant women has been shown to allow accurate and noninvasive prenatal detection of fetal trisomy 21. However, whether the sequencing approach is as accurate for the noninvasive prenatal diagnosis of trisomy 13 and 18 is unclear due to the lack of data from a large sample set. We studied 392 pregnancies, among which 25 involved a trisomy 13 fetus and 37 involved a trisomy 18 fetus, by massively parallel sequencing. By using our previously reported standard z-score approach, we demonstrated that this approach could identify 36.0% and 73.0% of trisomy 13 and 18 at specificities of 92.4% and 97.2%, respectively. We aimed to improve the detection of trisomy 13 and 18 by using a non-repeat-masked reference human genome instead of a repeat-masked one to increase the number of aligned sequence reads for each sample. We then applied a bioinformatics approach to correct GC content bias in the sequencing data. With these measures, we detected all (25 out of 25) trisomy 13 fetuses at a specificity of 98.9% (261 out of 264 non-trisomy 13 cases), and 91.9% (34 out of 37) of the trisomy 18 fetuses at 98.0% specificity (247 out of 252 non-trisomy 18 cases). These data indicate that with appropriate bioinformatics analysis, noninvasive prenatal diagnosis of trisomy 13 and trisomy 18 by maternal plasma DNA sequencing is achievable
Constraints on from A Three-Flavor Oscillation Analysis of Reactor Antineutrinos at KamLAND
We present new constraints on the neutrino oscillation parameters , , and from a
three-flavor analysis of solar and KamLAND data. The KamLAND data set includes
data acquired following a radiopurity upgrade and amounts to a total exposure
of 3.49 \textyen times 10^{32} target-proton-year. Under the assumption of
{\textyen it CPT} invariance, a two-flavor analysis (/textyen mbox{\textyen
theta_{13} = 0}) of the KamLAND and solar data yields the best-fit values
\textyen tan^{2} \textyen theta_{12} = 0.444^{+0.036}_{-0.030} and \textyen
Delta m^{2}_{21} = 7.50^{+0.19}_{-0.20} \textyen times 10^{-5} ~ {\textyen rm
eV}^{2}; a three-flavor analysis with \textyen theta_{13} as a free
parameter yields the best-fit values \textyen tan^{2} \textyen theta_{12} =
0.452^{+0.035}_{-0.033}, \textyen Delta m^{2}_{21} = 7.50^{+0.19}_{-0.20}
\textyen times 10^{-5} ~ {\textyen rm eV}^{2}, and \textyen sin^{2} \textyen
theta_{13} = 0.020^{+0.016}_{-0.016}. This \textyen theta_{13} interval is
consistent with other recent work combining the CHOOZ, atmospheric and
long-baseline accelerator experiments. We also present a new global \textyen
theta_{13} analysis, incorporating the CHOOZ, atmospheric and accelerator
data, which indicates \textyen sin^{2} \textyen theta_{13} =
0.009^{+0.013}_{-0.007}. A nonzero value is suggested, but only at the
79\textyen% C.L.Comment: 10 pages, 7 figures. Version as published in PRD. The dChi2-map and
prompt energy spectrum for this analysis are available at
http://www.awa.tohoku.ac.jp/KamLAND/4th_result_data_release/4th_result_data_release.htm
The KamLAND Full-Volume Calibration System
We have successfully built and operated a source deployment system for the
KamLAND detector. This system was used to position radioactive sources
throughout the delicate 1-kton liquid scintillator volume, while meeting
stringent material cleanliness, material compatibility, and safety
requirements. The calibration data obtained with this device were used to fully
characterize detector position and energy reconstruction biases. As a result,
the uncertainty in the size of the detector fiducial volume was reduced by a
factor of two. Prior to calibration with this system, the fiducial volume was
the largest source of systematic uncertainty in measuring the number of
anti-neutrinos detected by KamLAND. This paper describes the design, operation
and performance of this unique calibration system.Comment: 30 pages, 22 figures, to be submitted to JINS
Precision Measurement of Neutrino Oscillation Parameters with KamLAND
The KamLAND experiment has determined a precise value for the neutrino
oscillation parameter and stringent constraints on
. The exposure to nuclear reactor anti-neutrinos is increased
almost fourfold over previous results to 2.44 proton-yr due to
longer livetime and an enlarged fiducial volume. An undistorted reactor
energy spectrum is now rejected at >5. Extending the
analysis down to the inverse beta decay energy threshold, and incorporating
geo-neutrinos, gives a best-fit at =
eV and
=. Local
-minima at higher and lower are disfavored
at >4. Combining with solar neutrino data, we obtain = eV and =.Comment: Version as published in PRL. Revised Fig. 2 (allowed contours) due to
an error in the figure generating code (numbers or conclusions did not
change). The full dChi2-map for this analysis is available at
http://www.awa.tohoku.ac.jp/KamLAND/chi2map_3rdresult/chi2map.html . Fig. 3
(low E spectrum) was dropped due to space limitation
Constraints on theta 13 from a three-flavor oscillation analysis of reactor antineutrinos at KamLAND
We present new constraints on the neutrino oscillation parameters Δm212, θ12, and θ13 from a three-flavor analysis of solar and KamLAND data. The KamLAND data set includes data acquired following a radiopurity upgrade and amounts to a total exposure of 3.49×1032 target-proton-year. Under the assumption of CPT invariance, a two-flavor analysis (θ13=0) of the KamLAND and solar data yields the best-fit values tan2θ12=0.444-0.030+0.036 and Δm212=7.50-0.20+0.19×10-5 eV2; a three-flavor analysis with θ13 as a free parameter yields the best-fit values tan2θ12=0.452-0.033+0.035, Δm212=7.50-0.20+0.19×10-5 eV2, and sin2θ13=0.020-0.016+0.016. This θ13 interval is consistent with other recent work combining the CHOOZ, atmospheric and long-baseline accelerator experiments. We also present a new global θ13 analysis, incorporating the CHOOZ, atmospheric, and accelerator data, which indicates sin2θ13=0.009-0.007+0.013. A nonzero value is suggested, but only at the 79% C.L
SEARCH FOR EXTRATERRESTRIAL ANTINEUTRINO SOURCES WITH THE KamLAND DETECTOR
We present the results of a search for extraterrestrial electron antineutrinos ( 's) in the energy range 8.3 MeV < Eve < 31.8 MeV using the KamLAND detector. In an exposure of 4.53 kton-year, we identify 25 candidate events. All of the candidate events can be attributed to background, most importantly neutral current atmospheric neutrino interactions, setting an upper limit on the probability of 8B solar ν e 's converting into Ve 's at 5.3 × 10-5 (90% CL), if we assume an undistorted Ve shape. This limit corresponds to a solar Ve flux of 93 cm-2 s-1 or an event rate of 1.6 events (kton - year)-1 above the energy threshold (Eve ≥8.3 MeV) . The present data also allows us to set more stringent limits on the diffuse supernova neutrino flux and on the annihilation rates for light dark matter particles