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We describe a laser–plasma platform for photon–photon collision experiments to measure fundamental quantum electrodynamic processes. As an example we describe using this platform to attempt to observe the linear Breit–Wheeler process. The platform has been developed using the Gemini laser facility at the Rutherford Appleton Laboratory. A laser Wakefield accelerator and a bremsstrahlung convertor are used to generate a collimated beam of photons with energies of hundreds of MeV, that collide with keV x-ray photons generated by a laser heated plasma target. To detect the pairs generated by the photon–photon collisions, a magnetic transport system has been developed which directs the pairs onto scintillation-based and hybrid silicon pixel single particle detectors (SPDs). We present commissioning results from an experimental campaign using this laser–plasma platform for photon–photon physics, demonstrating successful generation of both photon sources, characterisation of the magnetic transport system and calibration of the SPDs, and discuss the feasibility of this platform for the observation of the Breit–Wheeler process. The design of the platform will also serve as the basis for the investigation of strong-field quantum electrodynamic processes such as the nonlinear Breit–Wheeler and the Trident process, or eventually, photon–photon scattering.

We describe a laser-plasma platform for photon-photon collision experiments to measure fundamental quantum electrodynamic processes such as the linear Breit-Wheeler process with real photons. The platform has been developed using the Gemini laser facility at the Rutherford Appleton Laboratory. A laser wakefield accelerator and a bremsstrahlung convertor are used to generate a collimated beam of photons with energies of hundreds of MeV, that collide with keV x-ray photons generated by a laser heated plasma target. To detect the pairs generated by the photon-photon collisions, a magnetic transport system has been developed which directs the pairs onto scintillation-based and hybrid silicon pixel single particle detectors. We present commissioning results from an experimental campaign using this laser-plasma platform for photon-photon physics, demonstrating successful generation of both photon sources, characterisation of the magnetic transport system and calibration of the single particle detectors, and discuss the feasibility of this platform for the observation of the Breit-Wheeler process. The design of the platform will also serve as the basis for the investigation of strong-field quantum electrodynamic processes such as the nonlinear Breit-Wheeler and the Trident process, or eventually, photon-photon scattering.

We describe a laser-plasma platform for photon-photon collision experiments to measure fundamental quantum electrodynamic processes such as the linear Breit-Wheeler process with real photons. The platform has been developed using the Gemini laser facility at the Rutherford Appleton Laboratory. A laser wakefield accelerator and a bremsstrahlung convertor are used to generate a collimated beam of photons with energies of hundreds of MeV, that collide with keV x-ray photons generated by a laser heated plasma target. To detect the pairs generated by the photon-photon collisions, a magnetic transport system has been developed which directs the pairs onto scintillation-based and hybrid silicon pixel single particle detectors. We present commissioning results from an experimental campaign using this laser-plasma platform for photon-photon physics, demonstrating successful generation of both photon sources, characterisation of the magnetic transport system and calibration of the single particle detectors, and discuss the feasibility of this platform for the observation of the Breit-Wheeler process. The design of the platform will also serve as the basis for the investigation of strong-field quantum electrodynamic processes such as the nonlinear Breit-Wheeler and the Trident process, or eventually, photon-photon scattering.

We report on a direct search for elastic photon-photon scattering using x-ray and \\(\\gamma\\) photons from a laser-plasma based experiment. A gamma photon beam produced by a laser wakefield accelerator provided a broadband gamma spectrum extending to above \\(E_\\gamma = 200\\) MeV. These were collided with a dense x-ray field produced by the emission from a laser heated germanium foil at \\(E_x \\approx 1.4\\) keV, corresponding to an invariant mass of \\(\\sqrt{s} = 1.22 \\pm 0.22\\) MeV. In these asymmetric collisions elastic scattering removes one x-ray and one high-energy \\(\\gamma\\) photon and outputs two lower energy \\(\\gamma\\) photons. No changes in the \\(\\gamma\\) photon spectrum were observed as a result of the collisions allowing us to place a 95% upper bound on the cross section of \\(1.5 \\times 10^{15}\\,\\mu\\)b. Although far from the QED prediction, this represents the lowest upper limit obtained so far for \\(\\sqrt{s} \\lesssim 1\\) MeV.

EUDAQ is a generic data acquisition software developed for use in conjunction with common beam telescopes at charged particle beam lines. Providing high-precision reference tracks for performance studies of new sensors, beam telescopes are essential for the research and development towards future detectors for high-energy physics. As beam time is a highly limited resource, EUDAQ has been designed with reliability and ease-of-use in mind. It enables flexible integration of different independent devices under test via their specific data acquisition systems into a top-level framework. EUDAQ controls all components globally, handles the data flow centrally and synchronises and records the data streams. Over the past decade, EUDAQ has been deployed as part of a wide range of successful test beam campaigns and detector development applications.

The Compact Linear Collider (CLIC) is an option for a future ${\\mathrm{e}^{+}}{\\mathrm{e}^{-}} $ collider operating at centre-of-mass energies up to $3\\,\\text {TeV} $ , providing sensitivity to a wide range of new physics phenomena and precision physics measurements at the energy frontier. This paper is the first comprehensive presentation of the Higgs physics reach of CLIC operating at three energy stages: $\\sqrt{s} = 350\\,\\text {GeV} $ , 1.4 and $3\\,\\text {TeV} $ . The initial stage of operation allows the study of Higgs boson production in Higgsstrahlung ( ${\\mathrm{e}^{+}}{\\mathrm{e}^{-}} \\rightarrow {\\mathrm{Z}} {\\mathrm{H}} $ ) and ${\\mathrm{W}} {\\mathrm{W}} $ -fusion ( ${\\mathrm{e}^{+}}{\\mathrm{e}^{-}} \\rightarrow {\\mathrm{H}} {{\\nu }}_{\\!\\mathrm{e}} {\\bar{{\\nu }}}_{\\!\\mathrm{e}} $ ), resulting in precise measurements of the production cross sections, the Higgs total decay width $\\varGamma _{{\\mathrm{H}}}$ , and model-independent determinations of the Higgs couplings. Operation at $\\sqrt{s} > 1\\,\\text {TeV} $ provides high-statistics samples of Higgs bosons produced through ${\\mathrm{W}} {\\mathrm{W}} $ -fusion, enabling tight constraints on the Higgs boson couplings. Studies of the rarer processes ${\\mathrm{e}^{+}}{\\mathrm{e}^{-}} \\rightarrow \\mathrm{t} {\\bar{\\mathrm{t}}} {\\mathrm{H}} $ and ${\\mathrm{e}^{+}}{\\mathrm{e}^{-}} \\rightarrow {\\mathrm{H}} {\\mathrm{H}} {{\\nu }}_{\\!\\mathrm{e}} {\\bar{{\\nu }}}_{\\!\\mathrm{e}} $ allow measurements of the top Yukawa coupling and the Higgs boson self-coupling. This paper presents detailed studies of the precision achievable with Higgs measurements at CLIC and describes the interpretation of these measurements in a global fit.

The CLIC Tracker Detector (CLICTD) is a monolithic pixel sensor. It is fabricated in a 180 nm CMOS imaging process, modified with an additional deep low-dose n-type implant to obtain full lateral depletion. The sensor features a small collection diode, which is essential for achieving a low input capacitance. The CLICTD sensor was designed as a technology demonstrator in the context of the tracking detector studies for the Compact Linear Collider (CLIC). Its design characteristics are of broad interest beyond CLIC, for HL-LHC tracking detector upgrades. It is produced in two different pixel flavours: one with a continuous deep n-type implant, and one with a segmented n-type implant to ensure fast charge collection. The pixel matrix consists of \\(16\\times128\\) detection channels measuring \\(300 \\times 30\\) microns. Each detection channel is segmented into eight sub-pixels to reduce the amount of digital circuity while maintaining a small collection electrode pitch. This paper presents the characterisation results of the CLICTD sendor in a particle beam. The different pixel flavours are compared in detail by using the simultaneous time-over-threshold and time-of-arrival measurement functionalities. Most notably, a time resolution down to \\((5.8 \\pm 0.1)\\) ns and a spatial resolution down to \\((4.6 \\pm 0.2)\\) microns are measured. The hit detection efficiency is found to be well above 99.7% for thresholds of the order of several hundred electrons.

In order to achieve the challenging requirements on the CLIC vertex detector, a range of technology options have been considered in recent years. One prominent idea is the use of active sensors implemented in a commercial high-voltage CMOS process, capacitively coupled to hybrid pixel readout chips. Recent results have shown the approach to be feasible, though more detailed studies of the performance of such devices, including simulation, are required. The CLICdp collaboration has developed a number of ASICs as part of its vertex detector R&D programme, and here we present results on the performance of a CCPDv3 active sensor glued to a CLICpix readout chip. Charge collection characteristics and tracking performance have been measured over the full expected angular range of incident particles using 120 GeV/c secondary hadron beams from the CERN SPS. Single hit efficiencies have been observed above 99% in the full range of track incidence angles, down to shallow angles. The single hit resolution has also been observed to be stable over this range, with a resolution around 6 \\(\\mu\\)m. The measured charge collection characterstics have been compared to simulations carried out using the Sentaurus TCAD finite-element simulation package combined with circuit simulations and parametrisations of the readout chip response. The simulations have also been successfully used to reproduce electric fields, depletion depths and the current-voltage characteristics of the device, and have been further used to make predictions about future device designs.

The Compact Linear Collider (CLIC) is a proposed future high-luminosity linear electron-positron collider operating at three energy stages, with nominal centre-of-mass energies: 380 GeV, 1.5 TeV, and 3 TeV. Its aim is to explore the energy frontier, providing sensitivity to physics beyond the Standard Model (BSM) and precision measurements of Standard Model processes with an emphasis on Higgs boson and top-quark physics. The opportunities for top-quark physics at CLIC are discussed in this paper. The initial stage of operation focuses on top-quark pair production measurements, as well as the search for rare flavour-changing neutral current (FCNC) top-quark decays. It also includes a top-quark pair production threshold scan around 350 GeV which provides a precise measurement of the top-quark mass in a well-defined theoretical framework. At the higher-energy stages, studies are made of top-quark pairs produced in association with other particles. A study of ttH production including the extraction of the top Yukawa coupling is presented as well as a study of vector boson fusion (VBF) production, which gives direct access to high-energy electroweak interactions. Operation above 1 TeV leads to more highly collimated jet environments where dedicated methods are used to analyse the jet constituents. These techniques enable studies of the top-quark pair production, and hence the sensitivity to BSM physics, to be extended to higher energies. This paper also includes phenomenological interpretations that may be performed using the results from the extensive top-quark physics programme at CLIC.