ANTI-DID TASKFORCE ------------------ Present: K. Buesser, R. Poeschl, T. Tauchi (vidyo), Ch. Bourgeois, P. Colas, A. Besson, M. Winter, Ch. Berriaud, H. Videau, U. Schneekloth, J. List, F. Gaede, Y. Benhammou (vidyo), R. Settles (vidyo), Y. Sugimoto (vidyo), C.V. Anti-DID goals: - guide low energy e+e- from beamstrahlung into the outgoing pipe to minimize BG in beamcal - guide backscattered particles close to the beam axis to minimize beamstrahlung BG in central trackers. Technical feasibility: - an alternative design with helicoidal windings on top of the main solenoid has recently been proposed by Brett Parker to ease the construction. Expected cost is O(5 ME). It is proposed to invite B. Parker at DESY in first half of 2017 to further investigate this design. - The field map for this design has been computed by Uwe Schneekloth as input to BG simulations. - A small anti-DID option with dipole coils along the beampipe cones is proposed by Ch. Berriaud. The layout will be investigated more precisely to address the dead material implications compared to expected cables and services in this region. Background computations: - Yan Benhammou is currently compiling the past studies on the effect of the anti-DID on the backgrounds. - New simulations have to be based on an updated VFS layout adapted to the new L*, which is under definition in the VFS group. CAD drawings will be needed. - The effect of dead materials along the beampipe (cables et al.) on the backgrounds in the vertex detector should also be better understood. - Strasbourg offers the part-time contribution of an experienced postdoc in 2017 to contribute to the BG simulations. It is proposed to invite this postdoc in DESY for a few days in December to initiate his work. Effect on physics: - The anti-DID effect on polarimetry is expected to be small. - The dominant BG to some BSM signals complementary to LHC is made of acoplanar photon-photon events or radiative bhabha interactions, which can be both tagged through a high energy electron in the beamcal. Minimizing the BG in this detector increases the tagging efficiency. Other BSM signals for which LHC is blind involve very low momentum central tracks, for which beamstrahlung pair background should be minimized. Tracker requirements: - From past studies the antiDID is expected to reduce the Vertex occupancies by a factor ~2, which is well within the technological and physics uncertainties on the final occupancies of this detector. The vertex detector is therefore not a driving factor in the anti-DID issue. - The TPC can accommodate field non-uniformities provided the field maps are measured to O(1 G) precision. The anti-DID would introduce small additional inhomogeneities compared to the ~10% inhomogeneities of the main coil latest design. Controlling the effect of field inhomogeneities on tracking may be related to the question of Z0 running. Simulation options: - A too high computing power would be required to simulate beam-beam BG together with the benchmark high statistics physics samples. - The simulation of the physics samples themselves can be done with a homogeneous main field, provided effects of inhomogeneities can be corrected efficiently in real life. The physics simulation still requires the updated VFS layout for new L*, under definition. - The reconstruction of the physics samples requires adequate overlay of beam-beam BG patterns. These BG patterns must be simulated with the highest possible precision with dedicated studies, including fine-tuned field maps taking into account all magnets, since the occupancies in various parts of the detector are very sensitive to the details of the layout. - An open point is the scheduling of the physics benchmark simulations versus a detailed understanding of the beam-beam BG patterns, which are needed at the reconstruction level. VT TASKFORCE ------------ Present: K. Buesser, R. Poeschl, T. Tauchi (vidyo), Ch. Bourgeois, P. Colas, J-C Brient, I. Laktineh, F. Sefkow, K. Krueger, K. Gadow, H. Videau, M. Anduze, J-Ch Ianigro, D. Grondin, F. Gaede, R. Settles (vidyo), Y. Sugimoto (vidyo), C.V. Mechanical stability: - Detailed static and dynamic stability studies have been performed for the T(esla)-structure. They show localized displacements of up to ~10mm in the static case. They will be redone with an updated orientation of the barrel (22.5 rotation to match the endcap shape) and correspondingly updated support structures. - Static calculations have been done for the V(ideau)-structure. They show a more rigid behaviour (displacements of a fraction of mm) thanks to the vertical plates welded on both flanges of the modules. Dynamic computations (eigen modes) have been done but still have to be confronted with earthquake scenarii. - It is agreed to define common earthquake parameters within ILD to allow all subdetectors to perform comparable seismic stability studies. These parameters should in principle be common to all ILC design studies, and T. Tauchi will review what has been recommended at the ILC level along its past presentation at Cracow. Impact on ECAL design: - Both HCAL geometrical options can accommodate the ECAL geometry. - Critical points are the deformations of the first HCAL plates to which the ECAL modules are fixed, and the deformations and stresses at the boundaries of the ECAL modules. - It is agreed to exchange de detailed CAD models of all components (V-HCAL, T-HCAL, ECAL) to perform comprehensive computations of the full ECAL+HCAL wheel mechanical behaviour and allow mutual crosschecks. Effects of cracks: - Studies of the T-structure response to individual particles shows small effects of the phi cracks, but a larger effect of the z crack. The latter is proposed to be mitigated with a "staircase" structure of the modules in z. Preliminary studies of multijet events show small effects of the cracks on e.g. PTmiss but need to be completed with a higher statistics. - Studies of the V-structure z cracks also show significant effects on the response to individual hadrons. They could be mitigated by having longer modules (3 wheels instead of 5) but this may be prohibitive as regards the ECAL (deformation of the 1st plate). Studies of the non-projective phi cracks of the V-structure are also ongoing. Signal paths: - In the T-structure, HCAL signals are transported towards a concentrator board located at the barrel-endcap boundary and requiring 10cm longitudinal space. It is not clear whether access here can be granted in the collision position. Within the present push pull scheme, board exchange could be made within a few days. - In the V-structure, local data concentrators are located on the outside of the modules (inaccessible within the coil) and their signals sent to a patch panel at the end of the end-cap. It is claimed that such a configuration would allow to reduce the z-gap between the barrel and endcap to o(5 cm). The effect of this gap on physics must be studied. - The proposed signal paths are adapted to the specificities of each mechanical structure but are also specific to each technology (RPC for V-struct and Sci for T-struct). - The ECAL signal path is independent of the hadronic mechanical structure. Transport and assembly: - Both options have module sizes and weights compatible with standard containers and japenese trucks. - The different assembly schemes proposed by the teams (wheel assembly close to the coil for T-structure and in separate hall for V-structure) are motivated by arguments independent of the mechanical options. Simulation options: - 2 options have been migrated from MOKKA to the DD4HEP new framework: T-structure with AHCAL and V-structure with SDHCAL. - The crossed options (T-struct with SDHCAL and V-struct with AHCAL) also exist within MOKKA. It is agreed to also migrate them into DD4HEP to allow all kinds of comparisons. - In order to decouple the HCAL technology choice from the mechanical structure choice in simulation mass production, it is proposed to implement a combined simulation of AHCAL and SDHCAL with sensitive gaps filled with a RPC followed by Sci. This would allow the same physics events to be compared with different technology measurements, and would reduce the number of options for the simulation of physics benchmarks. This approach would work only if it does not alter the response of each technology option by more than ~1-2%. IPNL-Lyon offers to start studying this possibility and a cross-study could be done at DESY once higher priority tasks are completed. - For the reconstruction, attention will be brought to make the Pandora and arbor implementations independent of the mechanical structure options.