{"id":14108,"date":"2021-08-17T13:40:51","date_gmt":"2021-08-17T12:40:51","guid":{"rendered":"https:\/\/www.innovationnewsnetwork.com\/?p=14108"},"modified":"2021-08-17T13:40:51","modified_gmt":"2021-08-17T12:40:51","slug":"discussing-the-future-circular-collider-feasibility-study","status":"publish","type":"post","link":"https:\/\/www.innovationnewsnetwork.com\/discussing-the-future-circular-collider-feasibility-study\/14108\/","title":{"rendered":"Discussing the Future Circular Collider feasibility study"},"content":{"rendered":"

Following the recommendations of the European Strategy for Particle Physics, CERN and its international partners are now studying the technical and financial feasibility of a 100km circular collider, the Future Circular Collider integrated project.<\/h2>\n

The Future Circular Collider (FCC) will host a Higgs and Electroweak Factory, followed by the highest energy frontier machine ever made, which will offer a rich physics programme until the end of the century.<\/p>\n

The Higgs boson broke the news worldwide on 4 July 2012, when the ATLAS and CMS collaborations at CERN announced its discovery. This boson completed the Standard Model (SM) of elementary particles, which successfully describes all High Energy Physics (HEP) observations. With this discovery, the community of particle physicists also knew that an exciting era was opening. The Higgs boson is indeed unique among elementary particles, both by its nature (it is the only elementary particle to have no spin) and because of its novel interactions with elementary particles of matter. Shedding light on the Higgs\u2019 properties will help us understand how it is related to other open questions in modern particle physics and its role in the evolution of the Universe. Indeed, there are well known \u2018unknowns\u2019 in our understanding of the Universe as shown by the few examples given below.<\/p>\n

For instance, we know that dark matter and dark energy amount together to 95% of the energy density of the Universe, but their nature still needs to be understood. A dark matter elementary particle in the TeV1 mass range is a good candidate to be searched for at accelerators, as is being done at the CERN\u2019s Large Hadron Collider (LHC) and its HL-LHC upgrade programme, which will extend until the late 2030s. But future, more precise or more sensitive investigations will be crucial to unravel its mysteries if it has been discovered, or simply to search for it if it was not in the sensitivity domain of the LHC or other presently running experiments.<\/p>\n

The fact that we live in a Universe composed of matter, the antimatter having disappeared by matter-antimatter annihilation just after the Big Bang, contradicts the predictions of the Standard Model and requires additional sources of violation of the matter-antimatter symmetry as well as matter-antimatter transition; this might (or might not) be related to the unexplained origin and values of the masses of neutrinos, which differ strongly from their associated charged leptons. Finally, the origin of the existence of three similar families of particles, while only one is sufficient to compose our visible Universe, remains mysterious.<\/p>\n

Many of these questions, and others, as further detailed in References one and three, may be solved by the existence of new particle physics phenomena \u2013 all of which require an extension of the SM, but within a very large range of energies and interaction strengths. Evidence for this new physics \u2018beyond the SM\u2019 can be obtained by high precision measurements of SM particles properties, searches for tiny violations of the SM conservation laws and for rare phenomena, or by searching for new particles at high energies. This variety of cases shows that the future of particle physics necessitates a multi-pronged approach and that the accelerator branch must rely on a versatile infrastructure\/programme like that offered at CERN by the LEP\/LHC complex, and the one foreseen with the FCC-int project (FCC-ee followed by FCC-hh), which will provide the highest precision, sensitivity and energy, to explore the known and unknown unknowns as thoroughly as possible.<\/p>\n

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Fig. 1: A possible placement of the FCC 100km ring which will be about 300m underground. The placement needs extensive studies on many aspects, related among others to the geology, the existing infrastructures, and the sociological impact. As can be seen in this placement, the FCC and the LHC meet underground in the Geneva airport area<\/figcaption><\/figure>\n

The Future Circular Collider and its competitors<\/h3>\n

Different machines have been proposed to study these fundamental topics and these studies have reached a good level of maturity as they have been taking place for a decade or more. Broadly speaking, there are two approaches, one with a circular machine, which reuses its bunches of particles over many turns making them collide again and again, thus offering very high collision rates in the interaction regions where are located the detectors (two or four for the FCC), and the other, with a linear machine in which the particle bunches coming from two linear branches collide head-on only once in a single interaction region but in an extremely focused mode to also increase the collision rate.<\/p>\n

The CERN community and its international partners have proposed one machine of each type for an ambitious collider project after the LHC. The Future Circular Collider (FCC), which could run first as a Higgs and Electroweak factory in e+<\/sup>e–<\/sup> collisions (FCC-ee), may also ultimately reach a centre-of-mass energy of 100 TeV in proton-proton collisions (FCC-hh), and the Compact LInear Collider (CLIC) which could reach an energy in e+<\/sup>e–<\/sup> collisions of 3 TeV.<\/p>\n

In Asia, for many years Japan has been a candidate to host the International Linear Collider (ILC), which has now a setup optimised for studying the Higgs boson, i.e. running at a lower centre-of-mass energy than initially foreseen (250 GeV in ee collisions, while 1,000 GeV could be reachable), since the Higgs mass is 125 GeV. Chinese physicists have more recently proposed to build the Circular electron-positron collider (CEPC) which is quite similar to FCC-ee, with also a possible hh extension, SppC.<\/p>\n

Between 2018 and 2020, the European Strategy Group has coordinated the process of recommendations for the future of the worldwide particle-physics landscape. It concluded that an electron-positron Higgs factory is the highest-priority next collider and, for the longer term, that the European particle physics community must have the ambition to operate a proton-proton collider at the highest achievable energy. To reach such a goal, it says, \u2018Europe, together with its international partners, should investigate the technical and financial feasibility of a future hadron collider at CERN with a centre-of-mass energy of at least 100 TeV and with an electron-positron Higgs and electroweak factory as a possible first stage. Such a feasibility study of the colliders and related infrastructure should be established as a global endeavour and be completed on the timescale of the next Strategy update.\u2019<\/p>\n

The FCC integrated programme (first ee at different energies, then in a second stage hh collisions at the highest energy) will provide the richest Higgs physics programme. It would also be the best electroweak factory by far, provide additionally Heavy flavour and Quantum Chromodynamics (QCD) physics programmes, and allow for extensive searches beyond the SM (BSM) both for high masses and small couplings.<\/p>\n

The CLIC approach is not optimal for the observed Higgs mass. It should thus rather be continued as an R&D programme and be revisited later in case the FCC could not be done. The ILC would be another option for a Higgs factory, in particular since it may be ready slightly earlier if its funding materialises rapidly. However, similar to CLIC, the breadth of its physics programme is more limited than that of the FCC, both from the point of view of precision and sensitivity and for the maximum energy it can reach.<\/p>\n

The CepC would also be an outstanding collider, but the technology and its realisation are less advanced than the CERN FCC-ee one, as its subsequent hh collider, the SppC, compared to FCC-hh. Besides, as for the ILC, a completely new laboratory and all the related infrastructure would have to be built.<\/p>\n

Finally, the importance of the realisation of the feasibility study of FCC as a global endeavour has been stressed by the European strategy, and CERN has an excellent track record in this domain, so let\u2019s have a look to what this entails.<\/p>\n

The FCC Feasibility Study<\/h3>\n

For such a large scientific project, the organisational and collaborative aspect are primordial. In order to take the decision to invest the 10 BCHF necessary to reach completion of the first stage (FCC-ee inside a new 100km tunnel), a feasibility study has been requested by the CERN Council which will be performed over the next four years. The Feasibility Study will further develop the design study which led to the Conceptual Design Report (FCC CDR)3-6<\/sup> submitted as input to the European strategy in 2019. It will again be carried out in collaboration with institutions in the Member and Associate Member States and beyond, under the overall authority and strategic guidance of the Council.<\/p>\n

Without entering into the details of the governance, the study will be organised in several ‘pillars’, covering all essential areas such as accelerators, technical infrastructure, civil engineering (tunnel and surface), administrative processes in CERN Host States (France and Switzerland), financing and operation model, communications and outreach, and, last but not least, physics, experiments, and detectors. Some high-level objectives of these pillars are as follows.<\/p>\n