Welcome

• Umberto Dosselli (LNF Director)

SAPPHIRE, a cost-effective photon-photon collider to study the Higgs boson

• Marco Zanetti (MIT)

The option of a photon collider as a Higgs factory will be discussed. The relatively low mass of the Higgs boson candidate stimulated the studies of a dedicated facility, decoupled from a high energy Linear Collider: the s-channel production requires indeed much smaller center of mass energy than for the e+e- case and consequently a relatively compact machine design and reduced cost. SAPPHiRE is an example of a photon collider based on a pair of 10 GeV recirculating Linacs similar in design to those proposed for the LHeC; we will present parameters for the e- beams and the laser back-scattering system that will allow a peak luminosity of 0.36x10^34/cm2/s at E_CM (gamma-gamma) ~125 GeV. Such luminosity will lead to a total number of signal events per year (O(10^4)) comparable to the one expected at the ILC. The physics program is complementary to the e+e- one and includes the analysis of several decay modes, the measurement of the mass, the CP quantum numbers and total width (relying on branching ratios determined somewhere else). We will also stress the importance of the possible synergy with other fields such as laser physics or nuclear physics that can profit from a very intense and brilliant photon beam, e.g. extending/complementing the programme of facilities like ELI-NP.

Perspectives on Higgs Physics at LHC

• Aleandro Nisati (INFN-ROMA1)

The discovery of a new boson with mass around 125 GeV by ATLAS and CMS at the Large Hadron Collider (LHC) opens a new fundamental chapter in high-energy physics. The measurement of the physics properties of this particle are crucial to establish whether this is the elementary scalar, the Higgs boson, predicted by the Standard Model. Deviations from Standard Model expectations would represent the first direct evidence of new physics beyond this theory. The perspectives on the coupling measurements of this new particlewith elementary bosons and fermions at the LHC and at the luminosity upgrade of LHC (HL-LHC) are presented and discussed. This talk will include also preliminary simulation results on the HL-LHC physics potential on Higgs selfcoupling and CP studies.

TLEP/LEP3 Accelerator

• FRANK ZIMMERMANN (CERN)

We will present tentative design parameters, novel concepts and accelerator-physics challenges for these two circular e+e− Higgs-factory colliders. They both require – in addition to the collider ring – a fast cycling accelerator ring for quasi-continuous top-up injection to compensate for the short beam lifetime due to radiative Bhabha scattering. In addition, a large momentum aperture and flat beams are needed to ensure an adequate beam lifetime with regard to beamstrahlung. Both TLEP and LEP3 become Tera-Z factories when operated around the Z pole. The 80-km tunnel of TLEP would also provide a path towards much higher energies, e.g. it could later accommodate a very high energy LHC (“VHE-LHC”), with a centre-of-mass energy approaching 100 TeV in pp collisions.

TLEP/LEP3 Physics

• Patrick Janot (CERN)

The physics potential of these circular colliders at all energies will be presented and compared to that of other options, in particular to the International Linear Collider (ILC) and the Large Hadron Collider (LHC) prospects. With its unique instantaneous luminosity and the possibility of four interaction points operating simultaneously, the TLEP option will be able to reach the sub-percent precision for most Higgs boson couplings to gauge bosons and to fermions. This accuracy, needed for these measurements to become sensitive to new physics at and beyond the TeV scale, can be achieved with detector performance similar to those of the present LHC detectors. It will also allow unprecedented accuracies to be reached for all precision electroweak measurements, and will determine with great precision the top quark properties. The cost-effective LEP3 option, which would re-use the existing tunnel and detectors, would be a very interesting back-up, should the world financial situation stay at a critical level.

European HEP Stategy

• Roy Aleksan (CEA)

We will briefly present the various scientific challenges that Particle Physics is facing up and review the status of the process aiming at an update of the European Strategy for addressing these issues. Various accelerator options for precise electroweak and Higgs property measurements will then be presented and we will discuss how large circular colliders can be part of a general European long-term vision aiming at keeping the forefront science in Europe. Finally, we will conclude by discussing a possible plan of work, which needs to be set up for allowing the community to decide on the next large Particle Physics project in Europe in a timely and educated manner.