18410762
DEVELOPMENT OF A POSITRON PRODUCTION TARGET FOR THE ILC POSITRON SOURCE
The future International Linear Collider (ILC) will require of order 10 14 positrons per second to fulfil its luminosity requirements. The current baseline design produces this unprecedented flux of positrons using an undulatorbased source. In this concept, a collimated beam of photons produced from the action of an undulator on the main electron beam of the ILC is incident on a conversiontarget. Positrons producedin the resulting electromagneticshower can then be captured, accelerated and injected into a damping ring. The positron source community is pursuing several alternative technologies to develop a target capable of long-term operation in the intense photon beam. In the design being developed jointly by Lawrence Livermore National Laboratory (LLNL), Stanford Linear Accelerator Center (SLAC), the University of Liverpool and the Cockcroft Institute a thin (0.4 radiation length) watercooled titanium alloy target wheel of diameter 2 m is rotated at approximately 1000 rpm to spread the incident power of each pulse over a wide area. We review the role of the target in the positron source and present the latest target design.
53410002
A double-sided silicon micro-strip Super-Module for the ATLAS Inner Detector upgrade in the High-Luminosity LHC
The ATLAS experiment is a general purpose detector aiming to fully exploit the discovery potential of the Large Hadron Collider (LHC) at CERN. It is foreseen that after several years of successful data-taking, the LHC physics programme will be extended in the so-called High-Luminosity LHC, where the instantaneous luminosity will be increased up to 5 × 1034 cm−2 s−1. For ATLAS, an upgrade scenario will imply the complete replacement of its internal tracker, as the existing detector will not provide the required performance due to the cumulated radiation damage and the increase in the detector occupancy. The current baseline layout for the new ATLAS tracker is an all-silicon-based detector, with pixel sensors in the inner layers and silicon micro-strip detectors at intermediate and outer radii. The super-module is an integration concept proposed for the strip region of the future ATLAS tracker, where double-sided stereo silicon micro-strip modules are assembled into a low-mass local support structure. An electrical super-module prototype for eight double-sided strip modules has been constructed. The aim is to exercise the multi-module readout chain and to investigate the noise performance of such a system. In this paper, the main components of the current super-module prototype are described and its electrical performance is presented in detail.
53461882
A double-sided, shield-less stave prototype for the ATLAS Upgrade strip tracker for the High Luminosity LHC
A detailed description of the integration structures for the barrel region of the silicon strips tracker of the ATLAS Phase-II upgrade for the upgrade of the Large Hadron Collider, the so-called High Luminosity LHC (HL-LHC), is presented. This paper focuses on one of the latest demonstrator prototypes recently assembled, with numerous unique features. It consists of a shortened, shield-less, and double sided stave, with two candidate power distributions implemented. Thermal and electrical performances of the prototype are presented, as well as a description of the assembly procedures and tools.
17710231
Monopole scattering with a twist
Abstract By imposing certain combined inversion and rotation symmetries on the rational maps for SU(2) BPS monopoles we construct geodesics in the monopole moduli space. In the moduli space approximation these geodesics describe a novel kind of monopole scattering. During these scattering processes axial symmetry is instantaneously attained and, in some, monopoles with the symmetries of the regular solids are formed. The simplest example corresponds to a charge three monopole invariant under a combined inversion and 90° rotation symmetry. In this example three well-separated collinear unit charge monopoles coalesce to form first a tetrahedron, then a torus, then the dual tetrahedron and finally separate again along the same axis of motion. We explicitly construct the spectral curves in this case and use a numerical ADHMN construction to compute the energy density at various times during the motion. We find that the dynamics of the zeros of the Higgs field is extremely rich and we discover a new phenomenon; there exist charge k SU(2) BPS monopoles with more than k zeros of the Higgs field.
16513554
Skyrmed Monopoles
We investigate multi-monopole solutions of a modified version of the BPS YangMills-Higgs model in which a term quartic in the covariant derivatives of the Higgs field (a Skyrme term) is included in the Lagrangian. Using numerical methods we find that this modification leads to multi-monopole bound states. We compute axially symmetric monopoles up to charge five and also monopoles with Platonic symmetry for charges three, four and five. The numerical evidence suggests that, in contrast to Skyrmions, the minimal energy Skyrmed monopoles are axially symmetric. ∗On leave of absence from Institute for Nuclear Research of Russian Academy of Sciences
121875444
Nontrivial soliton scattering in an integrable chiral model in (2+1)-dimensions
Soliton solutions of an integrable chiral model in (2+1)‐dimensions are studied. Through the solution of a ‘‘Riemann problem with zeros’’ solitons of this model have already been found [R. S. Ward, J. Math. Phys. 29, 386 (1988)] which scatter in a trivial manner. By exploiting a connection with the O(3) σ model, it is shown that the model also has solitons that are not contained in the above construction, and whose scattering properties are highly nontrivial. Soliton scattering is also discussed for a σ model which interpolates between this integrable model and the SU(2) chiral σ model.