H. Wellenstein

First dark matter search results from a surface run of the 10-L DMTPC directional dark matter detector

Abstract The Dark Matter Time Projection Chamber (DMTPC) is a low pressure (75 Torr CF4) 10 liter detector capable of measuring the vector direction of nuclear recoils with the goal of directional dark matter detection. In this Letter we present the first dark matter limit from DMTPC from a surface run at MIT. In an analysis window of 80–200 keV recoil energy, based on a 35.7 g-day exposure, we set a 90% C.L. upper limit on the spin-dependent WIMP-proton cross section of 2.0 × 10 − 33 cm 2 for 115 GeV/c2 dark matter particle mass.

A high energy (keV), large angular range, precision electron spectrometer for atomic and molecular targets

An electron impact spectrometer for operation in the keV incident−electron energy range is described. The spectrometer operates between 20 and 60 keV incident−electron energy, utilizing both a low−resolution silicon surface barrier detector (5 keV FWHM), and a high−resolution (0.7 eV FWHM) Mollenstedt energy analyzer over a 1.7 keV energy loss range. It features a large angular scan range (0⩽ϑ<120°), high target gas throughput (i.e., 19000 l/sec for He and 13000 l/sec for N2 through a tube of 0.15 mm diam), and a wide range of incident−electron beam currents (0.1−400 μA) with a focused electron beam size of less than 200 μ FWHM over most of the current range. Careful measurements of the gas density profile of the target gas emanating from the nozzle are also reported. Results are presented for the Bethe surface of He and N2. The latter example is reported here for the first time. In addition, the observation of the angular dependence of the Lyman−Birge−Hopfield band in N2 (dipole forbidden) is compared wi...

A background-free direction-sensitive neutron detector

The detection and measurements of properties of neutrons are of great importance in many fields of research, including neutron scattering and radiography, measurements of solar and cosmic ray neutron flux, measurements of neutron interaction cross sections, monitoring of neutrons at nuclear facilities, oil exploration, and searches for fissile weapons of mass destruction. Many neutron detectors are plagued by large backgrounds from x-rays and gamma rays, and most current neutron detectors lack single-event energy sensitivity or any information on neutron directionality. Even the best detectors are limited by cosmic ray neutron backgrounds. All applications would benefit from improved neutron detection sensitivity and improved measurements of neutron properties. Here we show data from a new type of detector that can be used to determine neutron flux, energy distribution, and direction of neutron motion. The detector is free of backgrounds from x-rays, gamma rays, beta particles, and relativistic singly charged particles. It is relatively insensitive to cosmic ray neutrons because of their distinctive angular and energy distributions. It is sensitive to thermal neutrons, fission spectrum neutrons, and high energy neutrons, with detection features distinctive for each energy range. It is capable of determining the location of a source of fission neutrons based on characteristics of elastic scattering of neutrons by helium nuclei. A portable detector could identify one gram of reactor grade plutonium, one meter away, with less than one minute of observation time.

The Optical Alignment System of the ATLAS Muon Spectrometer Endcaps

The muon spectrometer of the ATLAS detector at the Large Hadron Collider (LHC) at CERN consists of 1182 muon chambers for precision track measurements, arranged in three concentric cylinders in the barrel region, and in four wheels in each of the two endcaps. The endcap wheels are located between 7 m and 22 m from the interaction point, and have diameters between 13 m and 24 m. Muon chambers are equipped with a complex optical alignment system to monitor their positions and deformations during ATLAS data-taking. We describe the layout of the endcap part of the alignment system and the design and calibration of the optical sensors, as well as the various software components. About 1% of the system has been subjected to performance tests in the H8 beam line at CERN, and results of these tests are discussed. The installation and commissioning of the full system in the ATLAS cavern has been completed, and the analysis of the first data indicates that it performs already now at a level close to the goal of a 40 μm alignment accuracy, ultimately required for reconstructing high-momentum final-state muons with the desired momentum resolution of 10% at 1 TeV.

Construction of monitored drift tube chambers for ATLAS end-cap muon spectrometer at IHEP (Protvino)

Abstract Trapezoidal-shaped Monitored Drift Tube (MDT) chambers will be used in end-caps of ATLAS muon spectrometer. Design and construction technology of such chambers in IHEP (Protvino) is presented. X-ray tomography results confirm desirable 20 μm precision of wire location in the chamber.

A specialized torsion balance designed to measure the absolute flux density of hyperthermal molecular beams containing reactive species

A torsion balance is described that has been used to measure the absolute flux density of seeded hyperthermal molecular beams containing reactive and/or condensable species with uncertainties of approximately ±5%. The balance is ultrahigh‐vacuum compatible and can be used in corrosive environments. A specially designed beam stop mounted on the torsion balance lever arm, traps the incoming beam and allows only completely thermalized molecules to exit. The thermalized molecules exit the beam stop in equal numbers per unit time in opposite directions, ensuring that the force exerted on the beam stop by the exiting molecules is zero. The balance was suspended from a 25‐μm‐diam gold‐coated tungsten wire that had a torsion constant of 6.04×10−8 N m/rad and a period of slightly larger than 400 s. Absolute molecular beam flux density measurements were made using both the torsion balance and the effusive method for a variety of pure and seeded molecular beams. The beams were composed of gases that could easily be ...

Results from DMTPC 10-liter detector

The known direction of motion of dark matter particles relative to the Earth may be a key for their unambiguous identification even in the presence of backgrounds. A direction-sensitive detector prototype using a low-density CF4 gas with a 10 liter fiducial volume is operated for several weeks in a basement laboratory. We present initial results that confirm good detector performance and set preliminary limits on spin-dependent dark matter interactions.

The DMTPC detector

Directional Dark Matter detectors have the potential of yielding an unambiguous observation of WIMPs even in presence of insidious background. In addition, by measuring the direction of the Dark Matter particles such detectors can discriminate between the various models that describe Dark Matter in our galaxy. The DMTPC detector is a novel directional DM detector consisting of a low-pressure CF4 time projection chamber with optical readout. Recent measurements proved that this technology is able to reconstruct the energy, direction, and sense of the lowenergy nuclear recoils produced by neutrons from a 252Cf source, as well as efficiently reject electromagnetic backgrounds. A 10-liter DMTPC detector is ready for underground operation. A 1 m3 detector, now in the design phase, will soon allow us to improve the existing limits of SD-interactions of WIMPs on protons by over one order of magnitude.

Observation and removal of higher‐order (ghost) energy‐loss lines present in Möllenstedt electron velocity analyzers

Mollenstedt electron velocity analyzers, used in high-energy electron impact spectroscopy, have been found to be limited by higher-order (ghost) energy-loss lines superimposed upon the real energy-loss spectrum. The origin of these ghost lines, as well as a method of removing them experimentally, is discussed.

Dark Matter Time Projection Chamber: Recent R&D Results

The Dark Matter Time Projection Chamber collaboration recently reported a dark matter limit obtained with a 10 liter time projection chamber lled with CF 4 gas. The 10 liter detector was capable of 2D tracking (perpendicular to the drift direction) and 2D ducialization, and only used information from two CCD cameras when identifying tracks and rejecting backgrounds. Since that time, the col- laboration has explored the potential benets of photomultiplier tube and electronic charge readout to achieve 3D tracking, and particle iden- tication for background rejection. The latest results of this eort is described here.