A search for invisible decays of Higgs bosons is performed using the vector boson fusion and associated ZH production modes. In the ZH mode, the Z boson is required to decay to a pair of charged leptons or a b b-bar quark pair. The searches use the 8 TeV pp collision dataset collected by the CMS detector at the LHC, corresponding to an integrated luminosity of up to 19.7 inverse femtobarns. Certain channels include data from 7 TeV collisions corresponding to an integrated luminosity of 4.9 inverse femtobarns. The searches are sensitive to non-standard-model invisible decays of the recently observed Higgs boson, as well as additional Higgs bosons with similar production modes and large invisible branching fractions. In all channels, the observed data are consistent with the expected standard model backgrounds. Limits are set on the production cross section times invisible branching fraction, as a function of the Higgs boson mass, for the vector boson fusion and ZH production modes. By combining all channels, and assuming standard model Higgs boson cross sections and acceptances, the observed (expected) upper limit on the invisible branching fraction at m[H] = 125 GeV is found to be 0.58 (0.44) at 95% confidence level. We interpret this limit in terms of a Higgs-portal model of dark matter interactions.

A search for invisibly decaying Higgs bosons is performed using the vector boson fusion production (VBF) mode. This search was conducted using Run 2 data, collected by the CMS detector at the LHC in 2016 at a center of mass energy of 13 TeV, corresponding to an integrated luminosity of 5.9 fb-1. The control regions for the signal, invisibly decaying VBF Higgs bosons, are estimated using a cut-based selection strategy adapted from prior analyses. Selection criteria for the signal is applied as well. Assuming standard model Higgs boson cross sections and acceptances, the observed (expected) upper limit on the signal strength of VBF Higgs bosons invisibly decaying at mH = 125 GeV is found to be r

Abstract: A direct search for Higgs bosons produced via vector-boson fusion and subsequently decaying into invisible particles is reported. The analysis uses 139 fb−1 of pp collision data at a centre-of-mass energy of s√ = 13 TeV recorded by the ATLAS detector at the LHC. The observed numbers of events are found to be in agreement with the background expectation from Standard Model processes. For a scalar Higgs boson with a mass of 125 GeV and a Standard Model production cross section, an observed upper limit of 0.145 is placed on the branching fraction of its decay into invisible particles at 95% confidence level, with an expected limit of 0.103. These results are interpreted in the context of models where the Higgs boson acts as a portal to dark matter, and limits are set on the scattering cross section of weakly interacting massive particles and nucleons. Invisible decays of additional scalar bosons with masses from 50 GeV to 2 TeV are also studied, and the derived upper limits on the cross section times branching fraction decrease with increasing mass from 1.0 pb for a scalar boson mass of 50 GeV to 0.1 pb at a mass of 2 TeV

The ATLAS experiment at the LHC has measured the Higgs boson couplings and mass, and searched for invisible Higgs boson decays, using multiple production and decay channels with up to 4.7 fb-1 of pp collision data at √s=7 TeV and 20.3 fb-1 at √s=8 TeV. In the current study, the measured production and decay rates of the observed Higgs boson in the [gamma][gamma], ZZ, W W , Z[gamma], bb, [tau] [tau] , and [mu][mu] decay channels, along with results from the associated production of a Higgs boson with a top-quark pair, are used to probe the scaling of the couplings with mass. The limits are set on parameters in extensions of the Standard Model including a composite Higgs boson, an additional electroweak singlet, and two-Higgs-doublet models. Together with the measured mass of the scalar Higgs boson in the [gamma][gamma] and ZZ decay modes, a lower limit is set on the pseudoscalar Higgs boson mass of mA > 370 GeV in the "hMSSM" simplified Minimal Supersymmetric Standard Model. Results from direct searches for heavy Higgs bosons are also interpreted in the hMSSM. Finally, direct searches for invisible Higgs boson decays in the vector-boson fusion and associated production of a Higgs boson with W/Z (Z → ll, W/Z → jj) modes are statistically combined to set an upper limit on the Higgs boson invisible branching ratio of 0.25. As a result, the use of the measured visible decay rates in a more general coupling fit improves the upper limit to 0.23, constraining a Higgs portal model of dark matter.

This book provides a comprehensive overview of the field of Higgs boson physics. It offers the first in-depth review of the complete results in connection with the discovery of the Higgs boson at CERN’s Large Hadron Collider and based on the full dataset for the years 2011 to 2012. The fundamental concepts and principles of Higgs physics are introduced and the important searches prior to the advent of the Large Hadron Collider are briefly summarized. Lastly, the discovery and first mensuration of the observed particle in the course of the CMS experiment are discussed in detail and compared to the results obtained in the ATLAS experiment.

These proceedings gather invited and contributed talks presented at the XXI DAE-BRNS High Energy Physics Symposium, which was held at the Indian Institute of Technology Guwahati in December 2014. The contributions cover many of the most active research areas in particle physics, namely (i) Electroweak Physics; (ii) QCD and Heavy Ion Physics; (iii) Heavy Flavour Physics and CP Violation; (iv) Neutrino Physics; (v) Astro-particle Physics and Cosmology; (vi) Formal Theory; (vii) Future Colliders and New Machines; and (viii) BSM Physics: SUSY, Extra Dimensions, Composites etc. The DAE-BRNS High Energy Physics Symposium, widely considered to be one of the premiere symposiums organised in India in the field of elementary particle physics, is held every other year and supported by the Board of Research in Nuclear Sciences, Department of Atomic Energy, India. Roughly 250 physicists and researchers participated in the 21st Symposium, discussing the latest advancements in the field in 18 plenary review talks, 15 invited mini-review talks and approximately 130 contributed presentations. Bringing together the essential content, the book offers a valuable resource for both beginning and advanced researchers in the field.