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French Linear Collider community meets to reinforce links with world-wide partners

Marc Besancon (CEA/Irfu), Maxim Titov (CEA/Irfu), Marc Winter (CNRS/IN2P3, IPHC) | 9 January 2014

French Linear Collider Days participants

CEA/Irfu and CNRS/IN2P3 organised a special event called “Irfu Linear Collider Days” from 27 to 29 November 2013. It served as an opportunity to discuss the French Linear Collider landscape in the areas of physics, theory and phenomenology, as well as accelerator and detector technologies. This was the second “Journées Collisionneur Linéaire (JCL)” of the French community, following the first event that had taken place in Lyon on 13 and 14 May 2013.

Held in CEA Saclay, the Irfu LC days brought together more than 80 attendees. The first two days of the meeting concentrated on the French activities and plans, providing a possibility to discuss future technological and engineering efforts needed to realise the ILC with the French accelerator and instrumentation communitiesat large. The last day was open to the rest of the world and was devoted to “country reports”, where experts from European countries, Japan and the US provided feedback on the status of the ILC efforts in their countries. All presentations can be found at the event webpage. Here are some meeting highlights.

Physics, theory and phenomenology

The opening session of the Irfu LC days was devoted to the review of recent theory, phenomenology and physics simulation activities; it was expertly organised by Marc Besancon of Irfu/SPP and Dirk Zerwas of LAL in Orsay. The power of the ILC lies in its flexibility. It can be tuned to well-defined initial state energies, allowing model-independent measurements from the Higgs threshold to 1 TeV. In his opening talk, Abdelhak Djouadi of LPT, Orsay summarised “the Higgs Boson profile” and the implication of the discovery on phenomenology, e.g. supersymmetric theories. He discussed areas where input from the linear collider, complementary to the LHC, will serve as “part of the therapy” to reveal the mechanism of electroweak symmetry breaking. Continuing with the Higgs sector, Yacin Haddad of LLR in Palaiseau presented recent studies of associated production of Z and Higgs bosons, with the Z-boson decaying into a di-jet final state. A highlight was a talk of Dirk Zerwas on the recent results from SFitter collaboration which combines results from electroweak precision measurements into a combined picture . He addressed the importance of separate measurements of Higgs couplings to top and charm quarks. These remove the assumption on a link between second- and third-generation fermions and avoid deterioration in precision due to theoretical uncertainties for all Higgs couplings.

Sensitivity to new physics effects (tree-level or higher-order) at a higher energy scale from different models beyond the Standard Model drastically improves with ILC precision measurements of electroweak precision observables (EWPO) and the top mass. Lisa Zeune of DESY in Hamburg reviewed the status of experimental results and predictions for W and top masses and electroweak precision observables, which provide constraints on undetected particles. In particular, a precise measurement of the W boson mass restricts light supersymmetric bottom (sbottom) and heavy supersymmetric top (stop) mass ranges to small intervals. The ILC will be the first machine to produce top pairs in electroweak production, allowing qualitative and quantitative improvement of top mass measurement. Roman Poeschl (for Amjad Sohail) and Jérémy Rouëne, both of LAL, presented results on the precise determination of top quark electroweak couplings, reconstruction of top quark production angle in fully hadronic states and measurements of top quark polarisation. Open questions, in particular higher order corrections, the role of single top production and reliable generators, demonstrate the need of close contact with theory groups in the future.

Searches for weakly interacting massive particles (WIMPs) constitute one of the major priorities of the ILC physics programme. Yann Mambrini of LPT Orsay reviewed the current status of direct and indirect dark matter (DM) searches. The ILC will have better sensitivity than any DM experiment for a WIMP mass below 10 GeV. Mikael Berggren of DESY in Hamburg presented recent results of model-independent DM searches in monophoton final state. Beam polarisation offers unique access to the chirality of couplings, the structure of interactions, and provides a major opportunity for WIMP property determination (mass, the helicity structure, or the spin of the mediator) and allows for model discrimination. Studies are ongoing to extend previous analyses to different vector and axial operators, a joint effort of DESY and CEA Saclay. Finally, Ana M. Teixeira of LPC Clermont-Ferrand presented a comprehensive review of the ILC potential for new physics searches and its complementarity to the LHC results.

Detector instrumentation

For at least a decade, nine CNRS/IN2P3 laboratories and CEA/Irfu institutes have been actively involved in detector (or accelerator) R&D activities, meaning that a substantial fraction of the French particle physics community is interested in the ILC. Moreover, France has been historically involved in many subsystems, often with major contributions: high-precision vertex detector based on CMOS pixel sensor technology (MIMOSA), main tracking systems using a gaseous TPC with Micromegas-based readout, and a highly granular calorimeter, both electromagnetic (with silicon sensors) and hadronic (with glass RPCs and/or Micromegas). The session conveners – Paul Colas of Irfu/SPP and Vincent Bourdry of LLR have arranged a well-balanced programme of the Irfu Days, building on the successful outcome of and minimising the overlap with the first JLC meeting in Lyon, where comprehensive summaries of detector R&D efforts were presented.

This time, the focus was set on very short reports of the future French activities in different sub detectors. Marc Winter of IPHC in Strasbourg, Paul Colas and Maxim Titov of Irfu/SPP, Vladislav Balagura of LLR, Imad Laktineh of INPL in Lyon and Max Chefdeville of LAPP in Annecy reviewed the vertex detector, TPC, SiW-ECAL and DHCAL subsystem plans for the next few years. Common developments were discussed, taking into account the difference in the time constrains for the various systems: for example, the technology choice will have to be made much earlier for the calorimeters than for the vertex detector. At LCWS 2013 in Tokyo, it became clear that a phase transition is ongoing for ILD and SiD concepts moving towards optimisation, integration and questions at system level. A cost-performance re-optimisation of the ILD concept was presented by Trong Hieu Tran of LLR, who studied the effect of reducing the size of the of ILD both in terms of radius and length, and several ECAL and HCAL geometries on the physics performance. The efforts on particle flow reconstruction in France were summarised by Naomi van der Kolk of LAL and LLR who emphasised the importance of the future coordinated effort. As Christian Bourgeois of LAL reported, another very important area are the overall mechanical and engineering integration studies of a real ILD detector. Aspects of mechanical monitoring, cooling and power pulsing of the electronics were reviewed globally. Jérémy Rouëne of LAL presented recent successful testbeam results with SiW-ECAL and DHCAL electronics using power pulsing. The possibility of the two-phase CO2 cooling of the Micromegas-TPC module was discussed by David Attié of Irfu/SEDI; first tests in the large TPC prototype at DESY are being planned for February 2014. A possibility of SiW-ECAL cooling with a leak-less water system, including integration aspects, were addressed by Denis Grondin of LPSC in Grenoble. Finally, carbon-aluminum composite structures for the TPC and the use of fiber Bragg grating sensors for the characterisation of deformation of composites structures were presented by Pierre Manil of Irfu/SIS and Marc Anduze of LLR, respectively. The session ended with an open discussion aimed at identifying transverse detector instrumentation activities and to make it easier to organise French detector R&D. This has been particularly important in a view of a special Horizon 2020 (H2020) meeting at LAL, organised by Brian Foster and Juan Fuster on Friday, 29 November, where possibilities to obtain funding for ILC-related activities from the new European scientific framework were discussed.

Accelerator instrumentation

Accelerator research and development has a rich historical background in France, as testified by the present diversity within numerous laboratories which contribute to European programmes dedicated to accelerator R&D (CARE, EUROTRANS, EURISOL, EuCARD, HL-LHC, ILC HiGrade, …) and provide technological support to European, and international projects. Highlights of the recent ILC-related accelerator activities in France were presented in a dedicated session, organised by Olivier Napoly of Irfu/SACM and Philip Bambade of LAL. The opening talk by Philip Bambade provided a comprehensive summary of the 2013 LCWS Accelerator Working Groups. Two presentations by Walid Kaabi of LAL Orsay and Olivier Napoly reviewed the progress with coupler and cryomodule production for the European XFEL facility at DESY Hamburg. LAL is in charge of the production and conditioning of 808 radiofrequency couplers (1.3 GHz, repetition rate 10Hz, peak power 150 kW). In his talk, Olivier Napoly reviewed four main areas where the ILC could benefit from XFEL cryomodule construction: industrialisation, ILC cryomodule demonstration, XFEL large-scale system test and building-up of expertise and infrastructure for an ‘EU hub’ for ILC cryomodule assembly. Fabien Eozenou of CEA/SACM described high-gradient R&D activities at CEA/Irfu with the goal to reach 35 MV/m at 90% yield. Efforts towards improving large-scale production of superconducting cavities are also ongoing within the KEK – CEA (A_RD_9) collaboration, with industry participation; recent results from vertical electropolishing developed in CEA/Irfu were discussed. Andrea Jeremie of LAPP summarised French activities around ATF2 and the final focus/ machine-detector-interface (MDI) for ILC and CLIC, including beam instrumentation, alignment and module control with sub-nanometre stabilisation. Olivier Napoly presented an idea to build a dressed nine-cell 1.3-GHz ILC cavity with a high gradient of 40 MV/m, Q0 = 2e10 and tested in a horizontal cryostat. In terms of electricity consumption ILC is a real scale workbench to develop, maintain and manage a mix of sustainable energy sources. ILC goes beyond basic science and Denis Perret-Gallix of LAPP explained a model of a “green ILC” summarising the outcome of the workshop “Energy for sustainable science” which took place at CERN in October 2013.
All participants of the Irfu ILC days also had the opportunity to visit Saclay cryomodule construction facility, an impressive “XFEL village” on the CEA Saclay site. While not yet in production mode, when the construction of one cryomodule per week will be expected, this assembly line has already produced a module with performance reaching ILC requirement –a major breakthrough.

Building up the European ILC community

In order to realise the ILC, a well-coordinated effort between Asia, Europe and the North America is mandatory. Therefore, any European initiative (both at country and EU level) can only be viewed in a world-wide context. Representatives from Germany, Italy, Norway, Spain, UK as well as from Japan and the US joined “Irfu Linear Collider Days” on 29 November. A special session organised by Maxim Titov and Marc Winter was dedicated to so-called “country reports” where accelerator and detector activities in different continents were reviewed in the context of their possible future cooperation with France. Following a welcome address by Philippe Chomaz, head of CEA/Irfu, and a message from Jacques Martino, head of CNRS/IN2P3, represented by Marc Winter, accelerator activities in France, Germany, UK, Japan and the USA were summarised by Olivier Napoly, Eckhard Elsen of DESY in Hamburg, Philip Burrows of Oxford University, Hitoshi Yamamoto of Tohoku University (for Akira Yamamoto) and Marc Ross of SLAC. As Eckhard Elsen explained, the ILC is a vital element of the next five-year plan just submitted to Helmholtz Association. Detector activities in Germany, Italy, the UK and Japan as well as accelerator and detector summaries from Spain were presented by Klaus Desch of Bonn University, Massimo Caccia of University Milano-Bicocca, Mark Thomson of University of Cambridge, Hitoshi Yamamoto and Angeles Faus-Golfe of IFIC Valencia. There is evidence that a significant movement is going on in the Japanese government, which together with the release of the ILC Technical Design Report describing the technical feasibility of the ILC project, and selection of the northern “Kitakami” site, puts ILC much closer to reality. However, the major discussion concentrated on optimisation of limited ILC resources and somewhat more targeted R&D funding before the project gets the green light, which will hopefully happen within a few years.

Last, but not least, we would like to thank all members of the programme and local organising committee: David Attié, Marc Besancon, Paul Colas, Olivier Napoly, Martine Oger, Maxim Titov, Philip Bambade, Jean-Claude Brient of LLR, Yannis Karyotakis of LAPP and Marc Winter. We are the most thankful to our world-wide partners for taking their valuable time to join the event and to contribute to the discussions of the future French Linear Collider roadmap. This meeting also provided an opportunity to further strengthen the international links and served as a building block in constructing the European ILC community – vital for the ILC project realisation. Shared successes do wonders in bringing a group of people together as the team and setting the stage to address future endeavors. This event was a truly cooperative effort. Thanks so much to everyone who came to the Paris meeting late November!

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