Results are presented from searches for the standard model Higgs boson in proton-proton collisions at root s = 7 and 8 TeV in the Compact Muon Solenoid experiment at the LHC, using data samples corresponding to integrated luminosities of up to 5.1 fb(-1) at 7 TeV and 5.3 fb(-1) at 8 TeV. The search is performed in five decay modes: gamma gamma, ZZ, W+W-, tau(+)tau(-), and b (b) over bar. An excess of events is observed above the expected background, with a local significance of 5.0 standard deviations, at a mass near 125 GeV, signalling the production of a new particle. The expected significance for a standard model Higgs boson of that mass is 5.8 standard deviations. The excess is most significant in the two decay modes with the best mass resolution, gamma gamma and ZZ; a fit to these signals gives a mass of 125.3 +/- 0.4(stat.) +/- 0.5(syst.) GeV. The decay to two photons indicates that the new particle is a boson with spin different from one. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved

The Higgs boson was postulated nearly five decades ago within the framework of the standard model of particle physics and has been the subject of numerous searches at accelerators around the world. Its discovery would verify the existence of a complex scalar field thought to give mass to three of the carriers of the electroweak force—the W+, W–, and Z0 bosons—as well as to the fundamental quarks and leptons. The CMS Collaboration has observed, with a statistical significance of five standard deviations, a new particle produced in proton-proton collisions at the Large Hadron Collider at CERN. The evidence is strongest in the diphoton and four-lepton (electrons and/or muons) final states, which provide the best mass resolution in the CMS detector. The probability of the observed signal being due to a random fluctuation of the background is about 1 in 3 × 106. The new particle is a boson with spin not equal to 1 and has a mass of about 125 giga–electron volts. Although its measured properties are, within the uncertainties of the present data, consistent with those expected of the Higgs boson, more data are needed to elucidate the precise nature of the new particle

One of the interesting portals linking a dark sector and the standard model (SM) is the kinetic mixing between the SM U (1) Y field with a new dark photon A from a U (1) A gauge interaction. Stringent limits have been obtained for the kinetic mixing parameter through various processes. In this work, we study the possibility of searching for a dark photon interaction at a circular e + e − collider through the process e + e − → γA * → γµ + µ − . We find that the constraint on 2 for dark photon mass in the few tens of GeV range, assuming that the µ + µ − invariant mass can be measured to an accuracy of 0.5%m A , can be better than 3 × 10 −6 for the proposed CEPC with a ten-year running at 3σ (statistic) level, and better than 2 × 10 −6 for FCC-ee with even just one-year running at √ s = 240 GeV, better than the LHC and other facilities can do in a similar dark photon mass range. For FCC-ee, running at √ s = 160 GeV, the constraint can be even better. * Electronic address: hemin sjtu@163.com

A coupling of a dark photon A from a U(1) A with the standard model (SM) particles can be generated through kinetic mixing represented by a parameter . A non-zero also induces a mixing between A and Z if dark photon mass m A is not zero. This mixing can be large when m A is close to m Z even if the parameter is small. Many efforts have been made to constrain the parameter for a low dark photon mass m A compared with the Z boson mass m Z . We study the search for dark photon in e + e − → γA → γµ + µ − for a dark photon mass m A as large as kinematically allowed at future e + e − colliders. For large m A , care should be taken to properly treat possible large mixing between A and Z. We obtain sensitivities to the parameter for a wide range of dark photon mass at planed e + e − colliders, such as Circular Electron Positron Collider (CEPC), International Linear Collider (ILC) and Future Circular Collider (FCC-ee). For the dark photon mass 20 GeV m A 330 GeV, the 2σ exclusion limits on the mixing parameter are 10 −3 -10 −2 . The CEPC with √ s = 240 GeV and FCC-ee with √ s = 160 GeV are more sensitive than the constraint from current LHCb measurement once the dark photon mass m A 50 GeV. For m A 220 GeV, the sensitivity at the FCC-ee with √ s = 350 GeV and 1.5 ab −1 is better than that at the 13 TeV LHC with 300 fb −1 , while the sensitivity at the CEPC with √ s = 240 GeV and 5 ab −1 can be even better than that at 13 TeV LHC with 3 ab −1 for m A 180 GeV. We also comment on sensitivities of e + e − → γA with dark photon decay into several other channels at future e + e − colliders.

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