PhysicsEstimated reading time: 3 minutes
The CEPC is a circular electron positron collider with total circumference of 100 km. It could be operated at center of mass energy of the Z pole (91.2 GeV), the WW threshold (161 GeV), the Higgs factory (240 GeV), and is upgradable to the top threshold (350 GeV). The typical physics cross sections at the non-polarized electron positron collision is shown in Fig AAA.
Using Nano-beam technology and the cutting edge accelerator design, the CEPC could deliver very high luminosity in its operation range. Table B gives the baseline luminosity at different center of mass energy.
The CEPC itself is a powerful factory of Z, W and Higgs bosons. As a Higgs factory, the CEPC can produce 1 Million Higgs boson together with 100 Million W bosons, and almost 1 Billion Z bosons in a time scale of 10 years. Operating at center of mass energy of the Z pole, the CEPC could deliver 10-100 Billion of Z boson in 1 year. The CEPC could also be operating at the WW thresholds, where, combined with precise beam energy calibration, could measure the W boson mass to an unprecedented level.
There are a few key points we would like to emphasize on the CEPC physics potential.
In general, comparing to the proton collider, the theoretical uncertainty and the event rate at the electron positron collider is much limited. In fact, most of the physics event could be recorded at detector of the electron positron collider.
As a Higgs factory, the inclusive cross section of all the physics channels is only 2-3 orders of magnitude higher than the Higgs signal. Dedicated detector design ensures a high-efficient classification of the Higgs event from the SM background. In addition, different kinds of the SM processes, such as the bhabha process, the WW, ZZ, single W, Single Z process, and the ISR return process, could be efficiently distinguished. These SM processes can be used not only for the Calibration and systematic control for the Higgs measurement, themselves provides good access to EW observations. Meanwhile, different generation and decay mode of the Higgs boson could also be identified. As a result, the CEPC allows precise reconstruction of the Higgs boson properties. Comparing to the anticipated physics performance of the HL-LHC, the Higgs boson properties, characterized by the Higgs coupling strengths* to its decay final states, could be measured to an accuracy that is one order of magnitude superior than the HL-LHC. Meanwhile, CEPC could measure lots of the key quantity that the proton collider has limited access, for instance the Higgs exotic decay modes, the Higgs total width, and the absolute Higgs couplings.
As a Z factory, the productivity of Z boson is 3-4 orders of magnitudes higher than that at LEP. In fact, most of the physics event at Z pole will be the decay from Z boson resonance. As a result, the precision of EW measurement could also be boosted by at least one order of magnitude with respect to Nowadays’ access. In fact, the uncertainties of most of these measurements are essentially dominated by systematic. Therefore, the stability of the experimental devices, and the systematical control, would be the key challenge for the EW measurements. In addition, huge Z boson yield is certainly highly appreciated for any exotic decay mode search (such as FCNC, invisible mode search, etc).