A DAQ System for Linear Collider TPC Prototypes based on the ALEPH TPC Electronics

Within the international studies of a high energy linear electron positron collider, several groups are developing and testing prototypes for a Linear Collider TPC. This detector is planned to be used as a central part in the tracking system of a detector at such a machine. In this note we describe a DAQ system, which has been developed for the use in tests of TPC prototypes. It is based on electronics used at the ALEPH experiment at CERN.Comment: 15 pages, 4 figure

The race for supersymmetry: using mT2 for discovery

We describe how one may employ a very simple event selection, using only the kinematic variable mT2, to search for new particles at the LHC. The method is useful when searching for evidence of models (such as R-parity conserving supersymmetry) which have a Z2 parity and a weakly-interacting lightest parity-odd particle. We discuss the kinematic properties which make this variable an excellent discriminant against the great majority of Standard Model backgrounds. Monte Carlo simulations suggest that this approach could be used to discover supersymmetry with somewhat smaller integrated luminosities (or perhaps lower center-of-mass energies) than would be required for other comparable analyses.Comment: 8 page

Charge Transfer and Charge Broadening of GEM Structures in High Magnetic Fields

We report on measurements of charge transfer in GEM structures in high magnetic fields. These were performed in the framework of the R&D work for a Time Projection Chamber at a future Linear Collider. A small test chamber has been installed into the aperture of a superconducting magnet with the GEM structures mounted perpendicular to the B field direction. The charge transfer is derived from the electrical currents monitored during irradiation with an ${}^{55}$Fe source. No severe loss of primary ionisation charge is observed, but an improved ion feedback suppression is achieved for high magnetic fields. Additionally, the width of the charge cloud released by individual ${}^{55}$Fe photons is measured using a finely segmented strip readout after the triple GEM structure. Charge widths between 0.3 and 0.5 mm RMS are observed, which originate from the charge broadening inside the GEM readout. This charge broadening is only partly suppressed at high magnetic fields.Comment: 11 pages, 9 figure

Measuring a Light Neutralino Mass at the ILC: Testing the MSSM Neutralino Cold Dark Matter Model

The LEP experiments give a lower bound on the neutralino mass of about 46 GeV which, however, relies on a supersymmetric grand unification relation. Dropping this assumption, the experimental lower bound on the neutralino mass vanishes completely. Recent analyses suggest, however, that in the minimal supersymmetric standard model (MSSM), a light neutralino dark matter candidate has a lower bound on its mass of about 7 GeV. In light of this, we investigate the mass sensitivity at the ILC for very light neutralinos. We study slepton pair production, followed by the decay of the sleptons to a lepton and the lightest neutralino. We find that the mass measurement accuracy for a few-GeV neutralino is around 2 GeV, or even less if the relevant slepton is sufficiently light. We thus conclude that the ILC can help verify or falsify the MSSM neutralino cold dark matter model even for very light neutralinos.Comment: 7 pages, 1 figure; references adde

Readout of GEM Detectors Using the Medipix2 CMOS Pixel Chip

We have operated a Medipix2 CMOS readout chip, with amplifying, shaping and charge discriminating front-end electronics integrated on the pixel-level, as a highly segmented direct charge collecting anode in a three-stage gas electron multiplier (Triple-GEM) to detect the ionization from $^{55}$Fe X-rays and electrons from $^{106}$Ru. The device allows to perform moderate energy spectroscopy measurements (20 % FWHM at 5.9 keV $X$-rays) using only digital readout and two discriminator thresholds. Being a truly 2D-detector, it allows to observe individual clusters of minimum ionizing charged particles in $Ar/CO_2$ (70:30) and $He/CO_2$ (70:30) mixtures and to achieve excellent spatial resolution for position reconstruction of primary clusters down to $\sim 50 \mu m$, based on the binary centroid determination method.Comment: 18 pages, 14 pictures. submitted to Nuclear Instruments and Methods in Physics Research

Probing CP Violation with and without Momentum Reconstruction at the LHC

We study the potential to observe CP-violating effects in SUSY cascade decay chains at the LHC. We consider squark and gluino production followed by subsequent decays into neutralinos with a three-body leptonic decay in the final step. Asymmetries composed by triple products of momenta of the final state particles are sensitive to CP-violating effects. Due to large boosts these asymmetries can be difficult to observe at a hadron collider. We show that using all available kinematic information one can reconstruct the decay chains on an event-by-event basis even in the case of 3-body decays, neutrinos and LSPs in the final state. We also discuss the most important experimental effects like major backgrounds and momentum smearing due to finite detector resolution. We show that with 300 fb$^{-1}$ of collected data, CP violation may be discovered at the LHC for a wide range of the phase of the bino mass parameter $M_1$.Comment: Version accepted for publication in JHEP. Clarifications added on the assumptions used for plots. New references adde

Measuring tau-polarisation in Neutralino2 decays at the LHC

We show how the sum of the two average tau polarisations in the decay chain chi20 -> stau1 tau -> tau tau chi10 in minimal supersymmetry with conserved R-parity can be measured at the LHC. This is accomplished by exploiting the polarisation dependence of the visible di-tau mass spectrum. Such a measurement provides information on the couplings of the involved SUSY particles and allows a more precise determination of the di-tau mass endpoint. If different tau decay modes can be distinguished, the polarisation and endpoint measurement can be improved even further.Comment: 16 pages, 9 figures, minor change

Infrastructure for Detector Research and Development towards the International Linear Collider

The EUDET-project was launched to create an infrastructure for developing and testing new and advanced detector technologies to be used at a future linear collider. The aim was to make possible experimentation and analysis of data for institutes, which otherwise could not be realized due to lack of resources. The infrastructure comprised an analysis and software network, and instrumentation infrastructures for tracking detectors as well as for calorimetry.Comment: 54 pages, 48 picture

Measurement of Exclusive rho^0 rho^0 Production in Two-Photon Collisions at High Q^2 at LEP

Exclusive rho rho production in two-photon collisions involving a single highly virtual photon is studied with data collected at LEP at centre-of-mass energies 89GeV < \sqrt{s} < 209GeV with a total integrated luminosity of 854.7pb^-1 The cross section of the process gamma gamma^* -> rho rho is determined as a function of the photon virtuality, Q^2 and the two-photon centre-of-mass energy, Wgg, in the kinematic region: 1.2GeV^2 < Q^2 < 30GeV^2 and 1.1GeV < Wgg < 3GeV