A Novel Generic Framework for Track Fitting in Complex Detector Systems

This paper presents a novel framework for track fitting which is usable in a wide range of experiments, independent of the specific event topology, detector setup, or magnetic field arrangement. This goal is achieved through a completely modular design. Fitting algorithms are implemented as interchangeable modules. At present, the framework contains a validated Kalman filter. Track parameterizations and the routines required to extrapolate the track parameters and their covariance matrices through the experiment are also implemented as interchangeable modules. Different track parameterizations and extrapolation routines can be used simultaneously for fitting of the same physical track. Representations of detector hits are the third modular ingredient to the framework. The hit dimensionality and orientation of planar tracking detectors are not restricted. Tracking information from detectors which do not measure the passage of particles in a fixed physical detector plane, e.g. drift chambers or TPCs, is used without any simplifications. The concept is implemented in a light-weight C++ library called GENFIT, which is available as free software

Evaluation of evapotranspiration methods for model validation in a semi-arid watershed in northern China

International audienceThis study evaluates the performance of four evapotranspiration methods (Priestley-Taylor, Penman-Monteith, Hargreaves and Makkink) of differing complexity in a semi-arid environment in north China. The results are compared to observed water vapour fluxes derived from eddy flux measurements. The analysis became necessary after discharge simulations using an automatically calibrated version of the Soil and Water Assessment Tool (SWAT) failed to reproduce runoff measurements. Although the study area receives most of the annual rainfall during the vegetation period, high temperatures can cause water scarcity. We investigate which evapotranspiration method is most suitable for this environment and whether the model performance of SWAT can be improved with the most adequate evapotranspiration method. The evapotranspiration models were tested in two consecutive years with different rainfall amounts. In general, the simple Hargreaves and Makkink equations outmatch the more complex Priestley-Taylor and Penman-Monteith methods, although their performance depended on water availability. Effects on the quality of SWAT runoff simulations, however, remained minor. Although evapotranspiration is an important process in the hydrology of this steppe environment, our analysis indicates that other driving factors still need to be identified to improve SWAT simulations

Charge carrier transfer in the gas electron multiplier at low gas gains

Connected to the Linear Collider project TESLA at DESY, studies on the readout of TPCs based on the GEM-technology are ongoing. For particle identication via dE/dx - measurement, a good energy resolution is indispensable, and therefore losses of primary electrons have to be avoided. It turned out, that in the GEM transverse diffusion inside or close to the holes is a not negligible reason for these losses. For Ar-CH4 90:10 and TPC-like field configurations it was found, that when operated in normal amplification mode, the Standard Geometry GEM should not lose primaries, whereas for low gains, also when operated in magnetic fields up to 5T, a GEM with larger pitch and hole diameter would be necessary

Determination of the pole position of the lightest hybrid meson candidate

Mapping states with explicit gluonic degrees of freedom in the light sector is a challenge, and has led to controversies in the past. In particular, the experiments have reported two different hybrid candidates with spin-exotic signature, pi1(1400) and pi1(1600), which couple separately to eta pi and eta' pi. This picture is not compatible with recent Lattice QCD estimates for hybrid states, nor with most phenomenological models. We consider the recent partial wave analysis of the eta(') pi system by the COMPASS collaboration. We fit the extracted intensities and phases with a coupled-channel amplitude that enforces the unitarity and analyticity of the S-matrix. We provide a robust extraction of a single exotic pi1 resonant pole, with mass and width 1564 +- 24 +- 86 MeV and 492 +- 54 +- 102 MeV, which couples to both eta(') pi channels. We find no evidence for a second exotic state. We also provide the resonance parameters of the a2(1320) and a2'(1700).Comment: 6 pages + 3 pages of supplemental material. Version to appear on Phys.Rev.Let

Information on antiprotonic atoms and the nuclear periphery from the PS209 experiment

In the PS209 experiments at CERN two kinds of measurements were performed: the in-beam measurement of X-rays from antiprotonic atoms and the radiochemical, off-line determination of the yield of annihilation products with mass number A_t -1 (less by 1 than the target mass). Both methods give observables which allows to study the peripheral matter density composition and distribution.Comment: LaTeX (espcrc1 style), 6 pages, 3 EPS figures, 1 table, Proceedings of the Sixth Biennal Conference on Low-Energy Antiproton Physics LEAP 2000, Venice, Ital

A digital calorimetric trigger for the COMPASS experiment at CERN

In order to provide a trigger for the Primakoff reaction, in 2009, the trigger system of the COMPASS experiment at CERN will be extend by an electromagnetic calorimeter trigger. Since it was decided to gain from various benefits of digital data processing, an FPGA based implementation of the trigger is foreseen, running on the front-end electronics, which are used for data acquisition at the same time. This, however, includes further modification of the existing trigger system to combine the digital calorimeter trigger, with its higher latency, and the analogue trigger signals, which will also make use of digital data processing

Beam Performance of Tracking Detectors with Industrially Produced GEM Foils

Three Gas-Electron-Multiplier tracking detectors with an active area of 10 cm x 10 cm and a two-dimensional, laser-etched orthogonal strip readout have been tested extensively in particle beams at the Meson Test Beam Facility at Fermilab. These detectors used GEM foils produced by Tech-Etch, Inc. They showed an efficiency in excess of 95% and spatial resolution better than 70 um. The influence of the angle of incidence of particles on efficiency and spatial resolution was studied in detail.Comment: 8 pages, 9 figures, accepted by Nuclear Instruments and Methods in Physics Research

New pixelized Micromegas detector for the COMPASS experiment

New Micromegas (Micro-mesh gaseous detectors) are being developed in view of the future physics projects planned by the COMPASS collaboration at CERN. Several major upgrades compared to present detectors are being studied: detectors standing five times higher luminosity with hadron beams, detection of beam particles (flux up to a few hundred of kHz/mm^2, 10 times larger than for the present detectors) with pixelized read-out in the central part, light and integrated electronics, and improved robustness. Studies were done with the present detectors moved in the beam, and two first pixelized prototypes are being tested with muon and hadron beams in real conditions at COMPASS. We present here this new project and report on two series of tests, with old detectors moved into the beam and with pixelized prototypes operated in real data taking condition with both muon and hadron beams.Comment: 11 pages, 5 figures, proceedings to the Micro-Pattern Gaseous Detectors conference (MPGD2009), 12-15 June 2009, Kolympari, Crete, Greece Minor details added and language corrections don

Neutron density distributions from antiprotonic 208Pb and 209Bi atoms

The X-ray cascade from antiprotonic atoms was studied for 208Pb and 209Bi. Widths and shifts of the levels due to the strong interaction were determined. Using modern antiproton-nucleus optical potentials the neutron densities in the nuclear periphery were deduced. Assuming two parameter Fermi distributions (2pF) describing the proton and neutron densities the neutron rms radii were deduced for both nuclei. The difference of neutron and proton rms radii /\r_np equal to 0.16 +-(0.02)_{stat} +- (0.04)_{syst} fm for 208Pb and 0.14 +- (0.04)_{stat} +- (0.04)_{syst} fm for 209Bi were determined and the assigned systematic errors are discussed. The /\r_np values and the deduced shapes of the neutron distributions are compared with mean field model calculations.Comment: 22 pages, 8 tables, 15 figure