Higgs measurement at e+e- circular colliders

Now that the mass of the Higgs boson is known, circular electron positron colliders, able to measure the properties of these particles with high accuracy, are receiving considerable attention. Design studies have been launched (i) at CERN with the Future Circular Colliders (FCC), of which an e+e- collider is a potential first step (FCC-ee, formerly caller TLEP) and (ii) in China with the Circular Electron Positron Collider (CEPC). Hosted in a tunnel of at least 50 km (CEPC) or 80-100 km (FCC), both projects can deliver very high luminosity from the Z peak to HZ threshold (CEPC) and even to the top pair threshold and above (FCC-ee). At the ZH production optimum, around 240 GeV, the FCC-ee (CEPC) will be able to deliver 10 (5) ab-1 integrated luminosity in 5 (10) years with 4 (2) interaction points: hence to produce millions of Higgs bosons through the Higgsstrahlung process and vector boson fusion processes. This sample opens the possibility of subper- cent precision absolute measurements of the Higgs boson couplings to fermions and to gauge-bosons, and of the Higgs boson width. These precision measurements are potentially sensitive to multi-TeV range new physics interacting with the scalar sector. The ZH production mechanism also gives access to the invisible or exotic branching ratios down to the per mil level, and with a more limited precision to the triple Higgs coupling. For the FCC-ee, the luminosity expected at the top pair production threshold (sqrt(s) ~ 340-350 GeV) further improves some of these accuracies significantly, and is sensitive to the Higgs boson coupling to the top quark.Comment: 6 pages. Report at ICHEP 201

Semi-DHCAL software developments: Digitization and Display

GRPC Semi-Digital HCAL is a solid option for the PFA oriented calorimetry of the International Linear Collider. Together with the hardware, the software developments is progressing steadily. The stauts and plans for the GRPC SDHCAL software development are presented, as well the first order digitization module for the GRPC and the display program DRUID (Display Root module Used for ILD) have been introduced.Comment: Proceeding of LCWS 2010, Beijin

Fractal Dimension of Particle Showers Measured in a Highly Granular Calorimeter

We explore the fractal nature of particle showers using Monte-Carlo simulation. We define the fractal dimension of showers measured in a high granularity calorimeter designed for a future lepton collider. The shower fractal dimension reveals detailed information of the spatial configuration of the shower. %the information hidden in the details of shower spatial configuration, It is found to be characteristic of the type of interaction and highly sensitive to the nature of the incident particle. Using the shower fractal dimension, we demonstrate a particle identification algorithm that can efficiently separate electromagnetic showers, hadronic showers and non-showering tracks. We also find a logarithmic dependence of the shower fractal dimension on the particle energy.Comment: 4 pages, 5 figure

Requirement analysis for dE/dx measurement and PID performance at the CEPC baseline detector

The Circular Electron-Positron Collider (CEPC) can be operated not only as a Higgs factory but also as a Z-boson factory, offering great opportunities for flavor physics studies where Particle Identification (PID) is critical. The baseline detector of the CEPC could record TOF and dE/dx information that can be used to distinguish particles of different species. We quantify the physics requirements and detector performance using physics benchmark analyzes with full simulation. We conclude that at the benchmark TOF performance of $50\,$ps, the dE/dx resolution should be better than 3% for incident particles in the barrel region with a relevant energy larger than $2\,$GeV/c. This performance leads to an efficiency/purity of $K^{\pm}$ identification 97%/96%, $D^0\to \pi^+K^-$ reconstruction 68.19%/89.05%, and $\phi\to K^+K^-$ reconstruction 82.26%/77.70%, providing solid support for relevant CEPC flavor physics measurements

Fast simulation of the CEPC detector with Delphes

Fast simulation tools are highly appreciated in particle physics phenomenology studies, especially in the exploration of the physics potential of future experimental facilities. The Circular Electron Positron Collider is a proposed Higgs and Z factory that can precisely measure the Higgs boson properties and the electroweak precision observables. A fast-simulation toolkit dedicated to the CEPC detector has been developed using Delphes. The comparison shows that this fast simulation tool is highly consistent with the full simulation, on a set of benchmark distributions. Therefore, we recommend this fast simulation toolkit for CEPC phenomenological investigations