52 research outputs found
A simple high-sensitivity technique for purity analysis of xenon gas
We report on the development and performance of a high-sensitivity
purity-analysis technique for gaseous xenon. The gas is sampled at macroscopic
pressure from the system of interest using a UHV leak valve. The xenon present
in the sample is removed with a liquid-nitrogen cold trap, and the remaining
impurities are observed with a standard vacuum mass-spectroscopy device. Using
calibrated samples of xenon gas spiked with known levels of impurities, we find
that the minimum detectable levels of N2, O2, and methane are 1 ppb, 160 ppt,
and 60 ppt respectively. This represents an improvement of about a factor of
10,000 compared to measurements performed without a coldtrap.Comment: 20 pages, 5 figure
A Xenon Condenser with a Remote Liquid Storage Vessel
We describe the design and operation of a system for xenon liquefaction in
which the condenser is separated from the liquid storage vessel. The condenser
is cooled by a pulse tube cryocooler, while the vessel is cooled only by the
liquid xenon itself. This arrangement facilitates liquid particle detector
research by allowing easy access to the upper and lower flanges of the vessel.
We find that an external xenon gas pump is useful for increasing the rate at
which cooling power is delivered to the vessel, and we present measurements of
the power and efficiency of the apparatus.Comment: 22 pages, 7 figures Corrected typos in authors lis
Study of a zirconium getter for purification of xenon gas
Oxygen, nitrogen and methane purification efficiencies for a common zirconium
getter are measured in 1050 Torr of xenon gas. Starting with impurity
concentrations near 10^{-6} g/g, the outlet impurity level is found to be less
than 120*10^{-12} g/g for O2 and less than 950*10^{-12} g/g for N2. For methane
we find residual contamination of the purified gas at concentrations varying
over three orders of magnitude, depending on the purifier temperature and the
gas flow rate. A slight reduction in the purifier's methane efficiency is
observed after 13 mg of this impurity has been absorbed, which we attribute to
partial exhaustion of the purifier's capacity for this species. We also find
that the purifier's ability to absorb N2 and methane can be extinguished long
before any decrease in O2 performance is observed, and slower flow rates should
be employed for xenon purification due to the cooling effect that the heavy gas
has on the getter.Comment: 14 pages, 5 figure
Characterization of large area APDs for the EXO-200 detector
EXO-200 uses 468 large area avalanche photodiodes (LAAPDs) for detection of
scintillation light in an ultra-low-background liquid xenon (LXe) detector. We
describe initial measurements of dark noise, gain and response to xenon
scintillation light of LAAPDs at temperatures from room temperature to 169K -
the temperature of liquid xenon. We also describe the individual
characterization of more than 800 LAAPDs for selective installation in the
EXO-200 detector.Comment: 10 pages, 17 figure
A xenon gas purity monitor for EXO
We discuss the design, operation, and calibration of two versions of a xenon
gas purity monitor (GPM) developed for the EXO double beta decay program. The
devices are sensitive to concentrations of oxygen well below 1 ppb at an
ambient gas pressure of one atmosphere or more. The theory of operation of the
GPM is discussed along with the interactions of oxygen and other impurities
with the GPM's tungsten filament. Lab tests and experiences in commissioning
the EXO-200 double beta decay experiment are described. These devices can also
be used on other noble gases.Comment: 41 pages, 26 figure
Search for Neutrinoless Double- β Decay with the Complete EXO-200 Dataset
A search for neutrinoless double-β decay (0νββ) in Xe136 is performed with the full EXO-200 dataset using a deep neural network to discriminate between 0νββ and background events. Relative to previous analyses, the signal detection efficiency has been raised from 80.8% to 96.4±3.0%, and the energy resolution of the detector at the Q value of Xe136 0νββ has been improved from σ/E=1.23% to 1.15±0.02% with the upgraded detector. Accounting for the new data, the median 90% confidence level 0νββ half-life sensitivity for this analysis is 5.0×1025 yr with a total Xe136 exposure of 234.1 kg yr. No statistically significant evidence for 0νββ is observed, leading to a lower limit on the 0νββ half-life of 3.5×1025 yr at the 90% confidence level
Genome-Wide Association Study in BRCA1 Mutation Carriers Identifies Novel Loci Associated with Breast and Ovarian Cancer Risk
BRCA1-associated breast and ovarian cancer risks can be modified by common genetic variants. To identify further cancer risk-modifying loci, we performed a multi-stage GWAS of 11,705 BRCA1 carriers (of whom 5,920 were diagnosed with breast and 1,839 were diagnosed with ovarian cancer), with a further replication in an additional sample of 2,646 BRCA1 carriers. We identified a novel breast cancer risk modifier locus at 1q32 for BRCA1 carriers (rs2290854, P = 2.7×10-8, HR = 1.14, 95% CI: 1.09-1.20). In addition, we identified two novel ovarian cancer risk modifier loci: 17q21.31 (rs17631303, P = 1.4×10-8, HR = 1.27, 95% CI: 1.17-1.38) and 4q32.3 (rs4691139, P = 3.4×10-8, HR = 1.20, 95% CI: 1.17-1.38). The 4q32.3 locus was not associated with ovarian cancer risk in the general population or BRCA2 carriers, suggesting a BRCA1-specific associat
Measurement of the charge ratio of atmospheric muons with the CMS detector
This is the pre-print version of this Article. The official published version can be accessed from the link below - Copyright @ 2010 ElsevierWe present a measurement of the ratio of positive to negative muon fluxes from cosmic ray interactions in the atmosphere, using data collected by the CMS detector both at ground level and in the underground experimental cavern at the CERN LHC. Muons were detected in the momentum range from 5 GeV/c to 1 TeV/c. The surface flux ratio is measured to be 1.2766 \pm 0.0032(stat.) \pm 0.0032 (syst.), independent of the muon momentum, below 100 GeV/c. This is the most precise measurement to date. At higher momenta the data are consistent with an increase of the charge ratio, in agreement with cosmic ray shower models and compatible with previous measurements by deep-underground experiments
Search for microscopic black hole signatures at the Large Hadron Collider
This is the Pre-Print version of the Article. The official published paper can be accessed from the link below - Copyright @ 2011 ElsevierA search for microscopic black hole production and decay in pp collisions at a center-of-mass energy of 7 TeV has been conducted by the CMS Collaboration at the LHC, using a data sample corresponding to an integrated luminosity of 35 inverse picobarns. Events with large total transverse energy are analyzed for the presence of multiple high-energy jets, leptons, and photons, typical of a signal expected from a microscopic black hole. Good agreement with the expected standard model backgrounds, dominated by QCD multijet production, is observed for various final-state multiplicities. Limits on the minimum black hole mass are set, in the range 3.5 -- 4.5 TeV, for a variety of parameters in a model with large extra dimensions, along with model-independent limits on new physics in these final states. These are the first direct limits on black hole production at a particle accelerator.This work is supported by the FMSR (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES (Croatia); RPF (Cyprus); Academy of
Sciences and NICPB (Estonia); Academy of Finland, ME, and HIP (Finland); CEA and
CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NKTH
(Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF and WCU
(Korea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and UASLP-FAI (Mexico); PAEC
(Pakistan); SCSR (Poland); FCT (Portugal); JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan); MST and MAE (Russia); MSTD (Serbia); MICINN and CPAN (Spain); Swiss
Funding Agencies (Switzerland); NSC (Taipei); TUBITAK and TAEK (Turkey); STFC (United Kingdom); DOE and NSF (USA)
Observation of a new Xi(b) baryon
The first observation of a new b baryon via its strong decay into Xi(b)^-
pi^+ (plus charge conjugates) is reported. The measurement uses a data sample
of pp collisions at sqrt(s) = 7 TeV collected by the CMS experiment at the LHC,
corresponding to an integrated luminosity of 5.3 inverse femtobarns. The known
Xi(b)^- baryon is reconstructed via the decay chain Xi(b)^- to J/psi Xi^- to
mu^+ mu^- Lambda^0 pi^-, with Lambda^0 to p pi^-. A peak is observed in the
distribution of the difference between the mass of the Xi(b)^- pi^+ system and
the sum of the masses of the Xi(b)^- and pi^+, with a significance exceeding
five standard deviations. The mass difference of the peak is 14.84 +/- 0.74
(stat.) +/- 0.28 (syst.) MeV. The new state most likely corresponds to the
J^P=3/2^+ companion of the Xi(b).Comment: Submitted to Physical Review Letter
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