Kiyotomo Kawagoe

Detailed study of gluino decay into third generation squarks at the CERN LHC

In supersymmetric models a gluino can decay into tb\tilde{\chi}^{\pm}_1 through a stop or a sbottom. The decay chain produces an edge structure in the m_{tb} distribution. Monte Carlo simulation studies show that the end point and the edge height would be measured at the CERN LHC by using a sideband subtraction technique. The stop and sbottom masses as well as their decay branching ratios are constrained by the measurement. We study interpretations of the measurement in the minimal supergravity model. We also study the gluino decay into tb and \tilde{\chi}^{\pm}_2 as well as the influence of the stop left-right mixing on the m_{bb} distribution of the tagged

Study of the gauge mediation signal with nonpointing photons at the CERN LHC

tb

Inclusive neutral D∗ production and limits on F∗ production in e+e− annihilations at petra

events.

Irradiation and testbeam of KEK/HPK planar p-type pixel modules for HL-LHC

In this paper we study the gauge mediation signal with the ATLAS detector at the CERN LHC. We focus on the case where the NLSP is the long-lived lightest neutralino (˜ χ 0 ) which decays dominantly into a photon (γ) and a gravitino ( ˜ G). A non-pointing photon from the neutralino decay can be detected with good position and time resolutions by the electormagnetic calorimeter (ECAL), while the photon momentum would be precisely measured if the photon is converted inside the inner tracking detector before reaching the ECAL. A new technique is developed to determine the masses of the slepton ( ˜) and the neutralino from events with a lepton and a converted nonpointing photon arising from the cascade decay ˜ l → l˜ χ 0 → lγ ˜ G. A Monte Carlo simulation at a sample point shows that the masses would be measured with an error of 3% for O(100) selected lγ pairs. Once the sparticle masses are determined by this method, the decay time and momentum of the neutralino are solved using the ECAL data and the lepton momentum only, for all lγ pairs without the photon conversion. We estimate the sensitivity to the neutralino lifetime for cτ = 10 cm to O(10) m.

Performance study of SKIROC2/A ASIC for ILD Si-W ECAL

D∗0 mesons, produced in e+e− annihilations, are observed in the γD0 and π0D0 decay modes, where the D0 subsequently decays into K−π+. The production cross section and the xE distribution for D∗0 mesons are extracted from the data, and compared with corresponding measurements for D∗+ mesons. The branching ratio for the D∗0 radiative decay is measured to be 0.53 ± 0.13. An upper limit for the σ · BR of the F∗+ meson, where the associated F+ decays into φπ+, is also derived.

Physics and Detectors at Future Linear Colliders

For the ATLAS detector upgrade for the high luminosity LHC (HL-LHC), an n-in-p planar pixel sensor-module is being developed with HPK. The modules were irradiated at the Cyclotron RadioIsotope Center (CYRIC) using 70 MeV protons. For the irradiation, a novel irradiation box has been designed that carries 16 movable slots to irradiate the samples slot-by-slot independently, to reduce the time for replacing the samples by hand, thus reducing the irradiation to human body. The box can be moved horizontally and vertically to scan the samples for a maximum area of 11 cm × 11 cm. Tests were subsequently carried out with beam at CERN by using 120 GeV pions and at DESY with 4 GeV electrons. We describe the analyses of the testbeam data of the KEK/HPK sensor-modules, focussing on the comparison of the performance of old and new designs of pixel structures, together with a reference of the simplest design (no biasing structure). The novel design has shown comparably good performance as the no-structure design in detecting passing-through charged particles.

A study of silicon sensor for the ILD ECAL

The ILD Si-W ECAL is a sampling calorimeter with tungsten absorber and highly segmented silicon layers for the International Large Detector (ILD), one of the two detector concepts for the International Linear Collider. SKIROC2 is an ASIC for the ILD Si-W ECAL. To investigate the issues found in prototype detectors, we prepared dedicated ASIC evaluation boards with either BGA sockets or directly soldered SKIROC2. We report a performance study with the evaluation boards, including signal-to-noise ratio and TDC performance with comparing SKIROC2 and an updated version, SKIROC2A.

Development of a Cerenkov Trigger Detector for the COMET Experiment

Though the ATLAS and CMS experiments at the LHC have found the Higgs boson, signatures of physics beyond the standard model have not yet been observed. In this situation, precise measurements of the Higgs boson and the top quark at future \(e^+e^-\) linear colliders have become more and more important to explore new physics. The future linear colliders are complementary to the LHC and the synergy effects are striking. Physics and detectors at the linear colliders as well as the status of linear collider projects are briefly summarized.

Study of Cascade Shower Fluctuation with a Tile/Fiber Sampling Calorimeter

The International Large Detector (ILD) is a proposed detector for the International Linear Collider (ILC). It has been designed to achieve an excellent jet energy resolution by using Particle Flow Algorithms (PFA), which rely on the ability to separate nearby particles within jets. PFA requires calorimeters with high granularity. The ILD Electromagnetic Calorimeter (ECAL) is a sampling calorimeter with thirty tungsten absorber layers. The total thickness of this ECAL is about 24 X

Les Houches "Physics at TEV Colliders 2005" Beyond the Standard Model working group: summary report

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