Stringent constraint on the scalar-neutrino coupling constant from quintessential cosmology

An extremely light ($m_{\phi} \ll 10^{-33} {\rm eV}$), slowly-varying scalar field $\phi$ (quintessence) with a potential energy density as large as 60% of the critical density has been proposed as the origin of the accelerated expansion of the Universe at present. The interaction of this smoothly distributed component with another predominately smooth component, the cosmic neutrino background, is studied. The slow-roll approximation for generic $\phi$ potentials may then be used to obtain a limit on the scalar-neutrino coupling constant, found to be many orders of magnitude more stringent than the limits set by observations of neutrinos from SN 1987A. In addition, if quintessential theory allows for a violation of the equivalence principle in the sector of neutrinos, the current solar neutrino data can probe such a violation at the 10^{-10} level.Comment: 7 pages, MPLA in press, some parts disregarded and a footnote adde

Precision Drift Chambers for the Atlas Muon Spectrometer

ATLAS is a detector under construction to explore the physics at the Large Hadron Collider at CERN. It has a muon spectrometer with an excellent momentum resolution of 3-10%, provided by three layers of precision monitored-drift-tube chambers in a toroidal magnetic field. A single drift tube measures a track point with a mean resolution close to 100 micron, even at the expected high neutron and gamma background rates. The tubes are positioned within the chamber with an accuracy of 20 microns, achieved by elaborate construction and assembly monitoring procedures.Comment: 3 pages, 2 eps figures, Proceedings for poster at Physics in Collisions Conference (PIC03), Zeuthen, Germany, June 2003. FRAP1

Large-Scale Production of Monitored Drift Tube Chambers for the ATLAS Muon Spectrometer

Precision drift tube chambers with a sense wire positioning accuracy of better than 20 microns are under construction for the ATLAS muon spectrometer. 70% of the 88 large chambers for the outermost layer of the central part of the spectrometer have been assembled. Measurements during chamber construction of the positions of the sense wires and of the sensors for the optical alignment monitoring system demonstrate that the requirements for the mechanical precision of the chambers are fulfilled

Upgrade of the ATLAS Muon Trigger for the SLHC

The outer shell of the ATLAS experiment at the LHC consists of a system of toroidal air-core magnets in order to allow for the precise measurement of the transverse momentum p$_T$ of muons, which in many physics channels are a signature of interesting physics processes. For the precise determination of the muon momentum Monitored Drift Tube chambers (MDT) with high position accuracy are used, while for the fast identification of muon tracks chambers with high time resolution are used, able to select muons above a predefined p$_T$ threshold for use in the first Level of the ATLAS triggering system (Level-1 trigger). When the luminosity of the LHC will be upgraded to 4-5 times the present nominal value (SLHC) in about a decade from now, an improvement of the selectivity of the ATLAS Level-1 triggering system will be mandatory in order to cope with the maximum allowed trigger rate of 100 kHz. For the Level-1 trigger of the ATLAS muon spectrometer this means an increase of the p$_T$ threshold for single muons. Due to the limited spatial resolution of the trigger chambers, however, the selectivity for tracks above ~20 GeV/c is insufficient for an effective reduction of the Level-1 rate. We describe how the track coordinates measured in the MDT precision chambers can be used to decisively improve the selectivity for high momentum tracks. The resulting increase in latency will also be discussed.Comment: These are the proceedings of a presentation given at the Topical Workshop of Electronics for Particle Physics 2010 in Aachen, Germany (sept., 20-24, 2010

Performance of the ATLAS Muon Drift-Tube Chambers at High Background Rates and in Magnetic Fields

The ATLAS muon spectrometer uses drift-tube chambers for precision tracking. The performance of these chambers in the presence of magnetic field and high radiation fluxes is studied in this article using test-beam data recorded in the Gamma Irradiation Facility at CERN. The measurements are compared to detailed predictions provided by the Garfield drift-chamber simulation programme

Dynamical approach to chains of scatterers

Linear chains of quantum scatterers are studied in the process of lengthening, which is treated and analysed as a discrete dynamical system defined over the manifold of scattering matrices. Elementary properties of such dynamics relate the transport through the chain to the spectral properties of individual scatterers. For a single-scattering channel case some new light is shed on known transport properties of disordered and noisy chains, whereas translationally invariant case can be studied analytically in terms of a simple deterministic dynamical map. The many-channel case was studied numerically by examining the statistical properties of scatterers that correspond to a certain type of transport of the chain i.e. ballistic or (partially) localised.Comment: 16 pages, 7 figure

Performance of the ATLAS Precision Muon Chambers under LHC Operating Conditions

For the muon spectrometer of the ATLAS detector at the large hadron collider (LHC), large drift chambers consisting of 6 to 8 layers of pressurized drift tubes are used for precision tracking covering an active area of 5000 m2 in the toroidal field of superconducting air core magnets. The chambers have to provide a spatial resolution of 41 microns with Ar:CO2 (93:7) gas mixture at an absolute pressure of 3 bar and gas gain of 2?104. The environment in which the chambers will be operated is characterized by high neutron and background with counting rates of up to 100 per square cm and second. The resolution and efficiency of a chamber from the serial production for ATLAS has been investigated in a 100 GeV muon beam at photon irradiation rates as expected during LHC operation. A silicon strip detector telescope was used as external reference in the beam. The spatial resolution of a chamber is degraded by 4 ?m at the highest background rate. The detection efficiency of the drift tubes is unchanged under irradiation. A tracking efficiency of 98% at the highest rates has been demonstrated

Resolution and Efficiency of the ATLAS Muon Drift-Tube Chambers at High Background Rates

The resolution and efficiency of a precision drift-tube chamber for the ATLAS muon spectrometer with final read-out electronics was tested at the Gamma Irradiation Facility at CERN in a 100 GeV muon beam and at photon irradiation rates of up to 990 Hz/square cm which corresponds to twice the highest background rate expected in ATLAS. A silicon strip detector telescope was used as external reference in the beam. The pulse-height measurement of the read-out electronics was used to perform time-slewing corrections which lead to an improvement of the average drift-tube resolution from 104 microns to 82 microns without irradiation and from 128 microns to 108 microns at the maximum expected rate. The measured drift-tube efficiency agrees with the expectation from the dead time of the read-out electronics up to the maximum expected rate

Magnetic field processing to enhance critical current densities of MgB2 superconductors

Magnetic field of up to 12 T was applied during the sintering process of pure MgB2 and carbon nanotube (CNT) doped MgB2 wires. We have demonstrated that magnetic field processing results in grain refinement, homogeneity and significant enhancement in Jc(H) and Hirr. The Jc of pure MgB2 wire increased by up to a factor of 3 to 4 and CNT doped MgB2 by up to an order of magnitude in high field region respectively, compared to that of the non-field processed samples. Hirr for CNT doped sample reached 7.7 T at 20 K. Magnetic field processing reduces the resistivity in CNT doped MgB2, straightens the entangled CNT and improves the adherence between CNTs and MgB2 matrix. No crystalline alignment of MgB2 was observed. This method can be easily scalable for a continuous production and represents a new milestone in the development of MgB2 superconductors and related systems