M_T2-assisted on-shell reconstruction of missing momenta and its application to spin measurement at the LHC

We propose a scheme to assign a 4-momentum to each WIMP in new physics event producing a pair of mother particles each of which decays to an invisible weakly interacting massive particle (WIMP) plus some visible particle(s). The transverse components are given by the value that determines the event variable M_T2, while the longitudinal component is determined by the on-shell condition on the mother particle. Although it does not give the true WIMP momentum in general, this M_T2-assisted on-shell reconstruction of missing momenta provides kinematic variables well correlated to the true WIMP momentum, and thus can be useful for an experimental determination of new particle properties. We apply this scheme to some processes to measure the mother particle spin, and find that spin determination is possible even without a good knowledge of the new particle masses.Comment: 11 pages, 10 figures, typos are corrected, figures are replace

Characteristic analysis of a photon converter in a medical LINAC using GEANT4

Medical LINACs (Linear Accelerators) use high energy photon beams to treat deeply located tumors. Generally, neutrons are produced by photonuclear reactions in the head of a medical LINAC using photon beams over 8 MV. Neutrons with high relative biological effectiveness and high permeability can cause many problems in terms of radiation protection. The threshold energy of photons producing neutrons in the head of a medical LINAC is 13.06 MV (Aluminum), 13.38 MV (Iron), 8.06 MV (Gold), and 7.41 MV (Tungsten). In this paper, we aim to analyze the characteristics of a photon converter in a medical LINAC using GEANT4 (Geometry and Tracking). For this, the photon and neutron spectrums of the optimized photon converter with tungsten were simulated with 2-24 MeV electron beams, and the ratio of photons with energies over 7.41 MV was analyzed

Spatiotemporal Stochastic Resonance in Fully Frustrated Josephson Ladders

We consider a Josephson-junction ladder in an external magnetic field with half flux quantum per plaquette. When driven by external currents, periodic in time and staggered in space, such a fully frustrated system is found to display spatiotemporal stochastic resonance under the influence of thermal noise. Such resonance behavior is investigated both numerically and analytically, which reveals significant effects of anisotropy and yields rich physics.Comment: 8 pages in two columns, 8 figures, to appear in Phys. Rev.

Matchmaker, Matchmaker, Make Me a Match: Migration of Populations via Marriages in the Past

The study of human mobility is both of fundamental importance and of great potential value. For example, it can be leveraged to facilitate efficient city planning and improve prevention strategies when faced with epidemics. The newfound wealth of rich sources of data---including banknote flows, mobile phone records, and transportation data---has led to an explosion of attempts to characterize modern human mobility. Unfortunately, the dearth of comparable historical data makes it much more difficult to study human mobility patterns from the past. In this paper, we present an analysis of long-term human migration, which is important for processes such as urbanization and the spread of ideas. We demonstrate that the data record from Korean family books (called "jokbo") can be used to estimate migration patterns via marriages from the past 750 years. We apply two generative models of long-term human mobility to quantify the relevance of geographical information to human marriage records in the data, and we find that the wide variety in the geographical distributions of the clans poses interesting challenges for the direct application of these models. Using the different geographical distributions of clans, we quantify the "ergodicity" of clans in terms of how widely and uniformly they have spread across Korea, and we compare these results to those obtained using surname data from the Czech Republic. To examine population flow in more detail, we also construct and examine a population-flow network between regions. Based on the correlation between ergodicity and migration in Korea, we identify two different types of migration patterns: diffusive and convective. We expect the analysis of diffusive versus convective effects in population flows to be widely applicable to the study of mobility and migration patterns across different cultures.Comment: 24 pages, 23 figures, 5 table

Measuring the top quark mass with m_T2 at the LHC

We investigate the possibility to measure the top quark mass using the collider variable $m_{T2}$ at the LHC experiment. Monte Carlo studies of $m_{T2}$ are performed with the events corresponding to the dilepton decays of $t\bar{t}$ produced at the LHC with 10 $fb^{-1}$ integrated luminosity. Our analysis suggests that the top quark mass can be determined by the $m_{T2}$ variable alone with a good precision at the level of 1 GeV.Comment: 10 pages, 4 figure