205 research outputs found
After LUX: The LZ Program
The LZ program consists of two stages of direct dark matter searches using
liquid Xe detectors. The first stage will be a 1.5-3 tonne detector, while the
last stage will be a 20 tonne detector. Both devices will benefit tremendously
from research and development performed for the LUX experiment, a 350 kg liquid
Xe dark matter detector currently operating at the Sanford Underground
Laboratory. In particular, the technology used for cryogenics and electrical
feedthroughs, circulation and purification, low-background materials and
shielding techniques, electronics, calibrations, and automated control and
recovery systems are all directly scalable from LUX to the LZ detectors.
Extensive searches for potential background sources have been performed, with
an emphasis on previously undiscovered background sources that may have a
significant impact on tonne-scale detectors. The LZ detectors will probe
spin-independent interaction cross sections as low as 5E-49 cm2 for 100 GeV
WIMPs, which represents the ultimate limit for dark matter detection with
liquid xenon technology.Comment: Conference proceedings from APS DPF 2011. 9 pages, 6 figure
Multijet production in neutral current deep inelastic scattering at HERA and determination of α_{s}
Multijet production rates in neutral current deep inelastic scattering have been measured in the range of exchanged boson virtualities 10 5 GeV and â1 < η_{LAB}^{jet} < 2.5. Next-to-leading-order QCD calculations describe the data well. The value of the strong coupling constant α_{s} (M_{z}), determined from the ratio of the trijet to dijet cross sections, is α_{s} (M_{z}) = 0.1179 ± 0.0013 (stat.)_{-0.0046}^{+0.0028}(exp.)_{-0.0046}^{+0.0028}(th.)
An NLO QCD analysis of inclusive cross-section and jet-production data from the ZEUS experiment
The ZEUS inclusive differential cross-section data from HERA, for charged and
neutral current processes taken with e+ and e- beams, together with
differential cross-section data on inclusive jet production in e+ p scattering
and dijet production in \gamma p scattering, have been used in a new NLO QCD
analysis to extract the parton distribution functions of the proton. The input
of jet data constrains the gluon and allows an accurate extraction of
\alpha_s(M_Z) at NLO;
\alpha_s(M_Z) = 0.1183 \pm 0.0028(exp.) \pm 0.0008(model)
An additional uncertainty from the choice of scales is estimated as \pm
0.005. This is the first extraction of \alpha_s(M_Z) from HERA data alone.Comment: 37 pages, 14 figures, to be submitted to EPJC. PDFs available at
http://durpdg.dur.ac.uk/hepdata in LHAPDFv
High-E_T dijet photoproduction at HERA
The cross section for high-E_T dijet production in photoproduction has been
measured with the ZEUS detector at HERA using an integrated luminosity of 81.8
pb-1. The events were required to have a virtuality of the incoming photon,
Q^2, of less than 1 GeV^2 and a photon-proton centre-of-mass energy in the
range 142 < W < 293 GeV. Events were selected if at least two jets satisfied
the transverse-energy requirements of E_T(jet1) > 20 GeV and E_T(jet2) > 15 GeV
and pseudorapidity requirements of -1 < eta(jet1,2) < 3, with at least one of
the jets satisfying -1 < eta(jet) < 2.5. The measurements show sensitivity to
the parton distributions in the photon and proton and effects beyond
next-to-leading order in QCD. Hence these data can be used to constrain further
the parton densities in the proton and photon.Comment: 36 pages, 13 figures, 20 tables, including minor revisions from
referees. Accepted by Phys. Rev.
Inclusive jet cross sections and dijet correlations in photoproduction at HERA
Inclusive jet cross sections in photoproduction for events containing a
meson have been measured with the ZEUS detector at HERA using an integrated
luminosity of . The events were required to have a
virtuality of the incoming photon, , of less than 1 GeV, and a
photon-proton centre-of-mass energy in the range . The measurements are compared with next-to-leading-order (NLO) QCD
calculations. Good agreement is found with the NLO calculations over most of
the measured kinematic region. Requiring a second jet in the event allowed a
more detailed comparison with QCD calculations. The measured dijet cross
sections are also compared to Monte Carlo (MC) models which incorporate
leading-order matrix elements followed by parton showers and hadronisation. The
NLO QCD predictions are in general agreement with the data although differences
have been isolated to regions where contributions from higher orders are
expected to be significant. The MC models give a better description than the
NLO predictions of the shape of the measured cross sections.Comment: 43 pages, 12 figures, charm jets ZEU
An Ultra-Low Background PMT for Liquid Xenon Detectors
Results are presented from radioactivity screening of two models of
photomultiplier tubes designed for use in current and future liquid xenon
experiments. The Hamamatsu 5.6 cm diameter R8778 PMT, used in the LUX dark
matter experiment, has yielded a positive detection of four common radioactive
isotopes: 238U, 232Th, 40K, and 60Co. Screening of LUX materials has rendered
backgrounds from other detector materials subdominant to the R8778
contribution. A prototype Hamamatsu 7.6 cm diameter R11410 MOD PMT has also
been screened, with benchmark isotope counts measured at <0.4 238U / <0.3 232Th
/ <8.3 40K / 2.0+-0.2 60Co mBq/PMT. This represents a large reduction, equal to
a change of \times 1/24 238U / \times 1/9 232Th / \times 1/8 40K per PMT,
between R8778 and R11410 MOD, concurrent with a doubling of the photocathode
surface area (4.5 cm to 6.4 cm diameter). 60Co measurements are comparable
between the PMTs, but can be significantly reduced in future R11410 MOD units
through further material selection. Assuming PMT activity equal to the measured
90% upper limits, Monte Carlo estimates indicate that replacement of R8778 PMTs
with R11410 MOD PMTs will change LUX PMT electron recoil background
contributions by a factor of \times1/25 after further material selection for
60Co reduction, and nuclear recoil backgrounds by a factor of \times 1/36. The
strong reduction in backgrounds below the measured R8778 levels makes the
R11410 MOD a very competitive technology for use in large-scale liquid xenon
detectors.Comment: v2 updated to include content after reviewer comments (Sep 2012
LUXSim: A Component-Centric Approach to Low-Background Simulations
Geant4 has been used throughout the nuclear and high-energy physics community
to simulate energy depositions in various detectors and materials. These
simulations have mostly been run with a source beam outside the detector. In
the case of low-background physics, however, a primary concern is the effect on
the detector from radioactivity inherent in the detector parts themselves. From
this standpoint, there is no single source or beam, but rather a collection of
sources with potentially complicated spatial extent. LUXSim is a simulation
framework used by the LUX collaboration that takes a component-centric approach
to event generation and recording. A new set of classes allows for multiple
radioactive sources to be set within any number of components at run time, with
the entire collection of sources handled within a single simulation run.
Various levels of information can also be recorded from the individual
components, with these record levels also being set at runtime. This
flexibility in both source generation and information recording is possible
without the need to recompile, reducing the complexity of code management and
the proliferation of versions. Within the code itself, casting geometry objects
within this new set of classes rather than as the default Geant4 classes
automatically extends this flexibility to every individual component. No
additional work is required on the part of the developer, reducing development
time and increasing confidence in the results. We describe the guiding
principles behind LUXSim, detail some of its unique classes and methods, and
give examples of usage.
* Corresponding author, [email protected]: 45 pages, 15 figure
First Results from the LUX Dark Matter Experiment at the Sanford Underground Research Facility
The Large Underground Xenon (LUX) experiment, a dual-phase xenon
time-projection chamber operating at the Sanford Underground Research Facility
(Lead, South Dakota), was cooled and filled in February 2013. We report results
of the first WIMP search dataset, taken during the period 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 cm at a WIMP mass of 33
GeV/c. We find that the LUX data are in strong disagreement with low-mass
WIMP signal interpretations of the results from several recent direct detection
experiments.Comment: Accepted by Phys. Rev. Lett. Appendix A included as supplementary
material with PRL articl
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