16924180
The anomaly in the cosmic-ray positron spectrum
A recent analysis of cosmic-ray data from a space borne experiment by the AMS collaboration supports the observation of an excess in the cosmic-ray positron spectrum by previous balloon experiments. The combination of the various experimental data establishes a deviation from the expected background with a significance of more than four standard deviations. The observed change in the spectral index cannot be explained without introducing a new source of positrons. When interpreted within the MSSM a consistent description of the antiproton spectrum, the diffuse gamma-ray flux and the positron fraction is obtained which is compatible with all other experimental data, including recent WMAP data.
120282214
A transition radiation detector for AMS
Abstract For cosmic particle spectroscopy on the International Space Station the AMS experiment will be equipped with a Transition Radiation Detector to improve proton background supression up to 300 GeV. The TRD has 20 layers of fleece radiator with Xe/CO2 proportional-mode straw-tube chambers. They are supported in a conically shaped octagon structure made of CFC-Al-honeycomb. For low power consumption VA analog multiplexers are used as front-end readout. A 20 layer prototype has achieved proton rejections above 100 at 90% electron efficiency for beam energies up to 250 GeV. The detector is under construction at RWTH Aachen, the gas system will be built at MIT, slow-control and DAQ at TH Karlsruhe.
18512144
A Scintillating Fiber Tracker With SiPM Readout
We present a prototype for the first tracking detector consisting of 250 mu m thin scintillating fibers and silicon photomultiplier (SiPM) arrays. The detector has a modular design, each module consists of a mechanical support structure of 10 mm Rohacell foam between two 100 mu m thin carbon fiber skins. Five layers of scintillating fibers are glued to both top and bottom of the support structure. SiPM arrays with a channel pitch of 250 mu m are placed in front of the fibers.
37596742
The AMS-02 TRD for the international space station
The Alpha Magnetic Spectrometer (AMS-02) is an experiment which will be mounted on the international space station (ISS) to measure primary cosmic ray spectra in space. A key element is the transition radiation detector (TRD) to extract an e/sup +/ or p/sup -/ signal reducing the p/sup +/ or e/sup -/ background by a rejection factor 10/sup 2/--10/sup 3/ in an energy range from 10 to 300 GeV. This will be used in combination with an electromagnetic calorimeter to provide overall p/sup +/ rejection of 10/sup 6/ at 90% e/sup +/ efficiency. The detector consists of 20 layers of 6 mm diameter straw tubes alternating with 20 mm layers of polyethylene/polypropylene fleece radiator. The tubes are filled with a 4:1 mixture of Xe:CO/sub 2/ at 1 bar absolute pressure from a recirculating gas system designed to operate >3 years in space. There are in total 5248 straw tubes which are read out by a custom-made DAQ system in less than 80 /spl mu/s. The electronics must be low in power consumption and sustain the stringent requirements of operation in space. The construction of the detector and its electronics is presented in this paper.
119184369
Nagy-Soper subtraction scheme for multiparton final states
In this work, we present the extension of an alternative subtraction scheme for nextto-leading order QCD calculations to the case of an arbitrary number of massless final-state partons. The scheme is based on the splitting kernels of an improved parton shower and comes with a reduced number of final state momentum mappings. While a previous publication including the setup of the scheme has been restricted to cases with maximally two massless partons in the final state, we here provide the final state real emission and integrated subtraction terms for processes with any number of massless partons. We apply our scheme to three jet production at lepton colliders at next-toleading order and present results for the differential C parameter distribution.
118584363
An Alternative Subtraction Scheme For NLO Calculations
We discuss an alternative subtraction scheme for NLO QCD calculations, which is based on the splitting kernels of an improved parton shower. As an example, we show results for the C parameter of the process e + e ! 3 jets at NLO used for the verification of this scheme.
118573871
An alternative subtraction scheme using Nagy-Soper dipoles
In this thesis we address an alternative subtraction scheme in high energy colliders at Nextto-Leading Order (NLO) QCD calculations. In particular, we focus on the treatment of real radiation contributions in the soft and collinear limits. After UV-renormalization, the remaining infrared singularities appearing both in the real radiation and in the virtual contributions can be regularized using dipole subtraction method. In this scheme, dipoles are based on the momentum mapping and on the splitting functions derived from an improved parton shower formulation with quantum interference effects. In our new scheme, we employ a slightly altered momentum mapping such that the number of subtraction terms is greatly reduced in comparison with the standard Catani-Seymour scheme. In addition, the new scheme also facilitates the matching of NLO calculations with parton showers using the same splitting functions. We also achieve the complete integrations of the splitting functions over an unresolved one parton phase space, obtaining the correct soft and collinear singularity structures that are necessary to cancel the soft divergences in the virtual contributions. We discuss the general framework setup of the scheme as well as some scattering processes at colliders; we find complete agreement with the results in the widely used Catani-Seymour dipole subtraction scheme.