CEPC Technical Design Report

The Circular Electron Positron Collider(CEPC)is a large scientific project initiated and hosted by China,fostered through extensive collaboration with international partners.The complex comprises four accelerators:a 30 GeV Linac,a 1.1 GeV Damping Ring,a Booster capable of achieving energies up to 180 GeV,and a Collider operating at varying energy modes(Z,W,H,and tt).The Linac and Damping Ring are situated on the surface,while the subterranean Booster and Collider are housed in a 100 km circumference underground tunnel,strategically accommodating future expansion with provisions for a potential Super Proton Proton Collider(SPPC).The CEPC primarily serves as a Higgs factory.In its baseline design with synchrotron radiation(SR)power of 30 MW per beam,it can achieve a luminosity of 5×10^(34)cm^(-2)s^(-1)per interaction point(IP),resulting in an integrated luminosity of 13 ab^(-1)for two IPs over a decade,producing 2.6 million Higgs bosons.Increasing the SR power to 50 MW per beam expands the CEPC's capability to generate 4.3 million Higgs bosons,facilitating precise measurements of Higgs coupling at sub-percent levels,exceeding the precision expected from the HL-LHC by an order of magnitude.This Technical Design Report(TDR)follows the Preliminary Conceptual Design Report(Pre-CDR,2015)and the Conceptual Design Report(CDR,2018),comprehensively detailing the machine's layout,performance metrics,physical design and analysis,technical systems design,R&D and prototyping efforts,and associated civil engineering aspects.Additionally,it includes a cost estimate and a preliminary construction timeline,establishing a framework for forthcoming engineering design phase and site selection procedures.Construction is anticipated to begin around 2027-2028,pending government approval,with an estimated duration of 8 years.The commencement of experiments and data collection could potentially be initiated in the mid-2030s.

Probing anomalous top-Higgs couplings at the HL-LHC via H→WW~* decay channels

We study the prospects of probing the anomalous tHq(q=u,c)couplings via SS2L or 3L signatures at the High Luminosity(HL-LHC)run of the 14 Te V CERN collider.We focus on signals of the tH associated production followed by the decay modes t→b?^+ν_?and H→W W~*,and ■ production followed by the decay modes t→b?^+ν_?and■where?=e,μ.Based on two types of H→W W~*decay topologies,one assuming the semileptonic decay mode H→W W~*→?^+νjj and the other the fully leptonic decay mode■,we perform a full simulation for signals and backgrounds.It is shown that,at the future HL-LHC,the branching ratio Br(t→uh)(Br(t→ch))can be probed to 1.17(1.56)×10^(-3)for the same-sign di-lepton channel,and to7.1×10^(-4)(1.39×10^(-3))for the 3L channel at 3σsensitivity.

Search for single production of vectorlike B-quarks at the LHC

New vectorlike quarks have been proposed in many scenarios of new physics beyond the Standard Model,which address the hierarchy problem and may be potentially discovered at the Large Hadron Collider(LHC).Based on a model-independent framework,we propose to search for the vectorlike B-quark(VLQ-B)and focus on resonant production via b-gluon fusion through chromomagnetic interactions.We then explore the possible signals of the VLQ-B through the B→tW decay mode at the 14 TeV LHC.After a rapid simulation of signal and background events,the 2σ excluded regions and the 5σdiscovery reach in the parameter plane of k_(B)-M_(B)are obtained at the LHC with an integrated luminosity of 300(3000)fb^(-1)in the dilepton final states.

Probing tq Z anomalous couplings in the trilepton signal at the HL-LHC,HE-LHC,and FCC-hh

We investigate the prospect of discovering the Flavour Changing Neutral Current(FCNC)tqZ couplings via two production processes yielding trilepton signals:top quark pair production pp→tt with one top quark decaying to the Z boson and one light jet and the anomalous single top quark plus Z boson production process pp→tZ.We study these channels at various successors of the Large Hadron Collider(LHC),i.e,the approved High-Luminosity LHC(HL-LHC)as well as the proposed High-Energy LHC(HE-LHC)and Future Circular Collider in hadron-hadron mode(FCC-hh).We perform a full simulation for the signals and the relevant Standard Model(SM)backgrounds and obtain limits on the Branching Ratios(BRs)of t→qZ(q=u,c),eventually yielding a trilepton final state through the decay modes t→bW+→bl^(+)V_(l)and Z→l^(+)l^(-).The upper limits on these FCNC BRs at 95%Confidence Level(CL)are obtained at the HL-LHC with√s=14 TeV and 3 ab^(-1),at the HE-LHC with√s=27TeV and 15 ab^(-1),and at the FCC-hh with√s=100 TeV and 30ab^(-1).