For the International Large Detector concept at the planned International Linear Collider, the use of time projection chambers (TPC) with micro-pattern gas detector readout as the main tracking detector is investigated. In this paper, results from a prototype TPC, placed in a 1 T solenoidal field and read out with three independent GEM-based readout modules, are reported. The TPC was exposed to a 6 GeV electron beam at the DESY II synchrotron. The efficiency for reconstructing hits, the measurement of the drift velocity, the space point resolution and the control of field inhomogeneities are presented.

Unprecedented charged particle momentum resolution is required for precision Higgs studies at the International Linear Collider (ILC), which in turn demands as many as 200 sampling points with a high spatial resolution of 100 microns or better if we are to adopt a TPC for the central tracker. We discuss a novel theoretical resolution formula for a GEM-readout TPC, which is applicable to inclined tracks as opposed to the previous formula which is valid only for normal incidence. The formula identifies key factors that determine the spatial resolution and helps optimize the readout pad geometry and High Voltage settings for a given gas mixture. The formula is compared to the latest beam test results for a LC TPC Large prototype.

We have developed a novel technique for the measurement of the avalanche fluctuation of gaseous detectors using a UV laser. The technique is simple and requires a short data-taking time of about ten minutes. Furthermore, it is applicable for relatively low gas gains. Our experimental setup as well as the measurement principle, and the results obtained with a stack of Gas Electron Multipliers (GEMs) operated in several gas mixtures are presented.Gas amplification of the electrons created by X-rays, UV photons, or charged particles plays an essential role in their detection with gaseous detectors. It acts as "preamplifier" with a sufficient gain. However, its gain fluctuates because of avalanche statistics, thereby degrading the energy resolution for monochromatic X-rays. For large Time Projection Chambers (TPCs) the azimuthal spatial resolution at long drift distances is partly limited by the relative variance of the gas gain for single drift electrons [1,2]. Historically many analytical models have been proposed to understand the fluctuation (see, for example, Ref.[3] and reference cited therein). A Monte-Carlo simulation approach is also available these days [4].Conventionally, avalanche fluctuations are estimated from the gas-amplified charge spectrum for single electrons created by a UV lamp or a laser. This method is, however, not easy because of electronic noise interference, especially for low gas gains. We have developed a novel technique for the measurement of the relative variance of avalanche fluctuation (f ) using laser-induced tracks, exploiting the fixed cluster size of unity for each ionization act along the tracks. The primary electrons are multiplied by a gas amplification device, and then collected by readout pad rows arranged along the laser beam.The signal charges on adjacent pad rows are compared for each laser shot. The value of f is estimated from the width of the distribution of their differences using a straightforward relation. The technique is relatively simple and the typical data-taking time is ten minutes.

We evaluate the measurement precision of the production cross section times the branching ratio of the Higgs boson decaying into tau lepton pairs at the International Linear Collider (ILC). We analyze various final states associated with the main production mechanisms of the Higgs boson, the Higgs-strahlung and W W -fusion processes. The statistical precision of the production cross section times the branching ratio is estimated to be 2.6 and 6.9 % for the Higgs-strahlung and W W -fusion processes, respectively, with the nominal integrated luminosities assumed in the ILC Technical Design Report; the precision improves to 1.0 and 3.4 % with the running scenario including possible luminosity upgrades. The study provides a reference performance of the ILC for future phenomenological analyses.

We studied the feasibility of the measurement of Higgs pair creation at a Photon Linear Collider (PLC). From the sensitivity to the anomalous self-coupling of the Higgs boson, the optimum γγ collision energy was found to be around 270 GeV for a Higgs mass of 120 GeV/c 2 . We found that large backgrounds such as γγ → W + W − , ZZ, and b bb b, can be suppressed if correct assignment of tracks to parent partons is achieved and Higgs pair events can be observed with a statistical significance of ∼ 5σ by operating the PLC for 5 years.