Search for Invisible Decays of the Higgs Boson Produced in Association with a Hadronically Decaying Vector Boson in Pp Collisions at [arrow]"
Search for Invisible Decays of the Higgs Boson Produced in Association with a Hadronically Decaying Vector Boson in Pp Collisions at [arrow]

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Published: 2015

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A search for Higgs boson decays to invisible particles is performed using 20.3 fb−1 of pp collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the Large Hadron Collider. The process considered is Higgs boson production in association with a vector boson (V = W or Z) that decays hadronically, resulting in events with two or more jets and large missing transverse momentum. No excess of candidates is observed in the data over the background expectation. The results are used to constrain V H production followed by H decaying to invisible particles for the Higgs boson mass range 115

Search for Exotic Decays of a Higgs Boson Into Undetectable Particles and One Or More Photons
Search for Exotic Decays of a Higgs Boson Into Undetectable Particles and One Or More Photons

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Published: 2015

Total Pages: 26

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A search is presented for exotic decays of a Higgs boson into undetectable particles and one or two isolated photons in pp collisions at a center-of-mass energy of 8 TeV. The data correspond to an integrated luminosity of up to 19.4 inverse femtobarns collected with the CMS detector at the LHC. Higgs bosons produced in gluon-gluon fusion and in association with a Z boson are investigated, using models in which the Higgs boson decays into a gravitino and a neutralino or a pair of neutralinos, followed by the decay of the neutralino to a gravitino and a photon. The selected events are consistent with the background-only hypothesis, and limits are placed on the product of cross sections and branching fractions. Assuming a standard model Higgs boson production cross section, a 95% confidence level upper limit is set on the branching fraction of a 125 GeV Higgs boson decaying into undetectable particles and one or two isolated photons as a function of the neutralino mass. For this class of models and neutralino masses from 1 to 120 GeV an upper limit in the range of 7 to 13% is obtained. Further results are given as a function of the neutralino lifetime, and also for a range of Higgs boson masses.

Searches for Invisible Decays of the Higgs Boson in Pp Collisions at $\sqrt{s}$
Searches for Invisible Decays of the Higgs Boson in Pp Collisions at $\sqrt{s}$

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Published: 2016

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Searches for invisible decays of the Higgs boson are presented. The data collected with the CMS detector at the LHC correspond to integrated luminosities of 5.1, 19.7, and 2.3 inverse femtobarns at centre-of-mass energies of 7, 8, and 13 TeV, respectively. The search channels target Higgs boson production via gluon fusion, vector boson fusion, and in association with a vector boson. Upper limits are placed on the branching fraction of the Higgs boson decay to invisible particles, as a function of the assumed production cross sections. The combination of all channels, assuming standard model production, yields an observed (expected) upper limit on the invisible branching fraction of 0.24 (0.23) at the 95% confidence level. The results are also interpreted in the context of Higgs-portal dark matter models.

Search for a Higgs Boson Decaying Into $\gamma*̂\gamma\to\ell\ell\gamma$ with Low Dilepton Mass in Pp Collisions at $\sqrt{s}
Search for a Higgs Boson Decaying Into $\gamma*̂\gamma\to\ell\ell\gamma$ with Low Dilepton Mass in Pp Collisions at $\sqrt{s}

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Published: 2015

Total Pages: 22

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Our search is described for a Higgs boson decaying into two photons, one of which has an internal conversion to a muon or an electron pair (ll?). The analysis is performed using proton–proton collision data recorded with the CMS detector at the LHC at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7 fb-1. The events selected have an opposite-sign muon or electron pair and a high transverse momentum photon. No excess above background has been found in the three-body invariant mass range 120 mll? 150 GeV, and limits have been derived for the Higgs boson production cross section times branching fraction for the decay H → ?*? → ll?, where the dilepton invariant mass is less than 20 GeV. A Higgs boson with mH=125 GeV has a 95% confidence level (CL) exclusion observed (expected) limit is 6.7 (5.9sup+2.8/supsub-1.8/sub ) times the standard model prediction. Additionally, an upper limit at 95% CL on the branching fraction of H → (J/?)? for the 125 GeV Higgs boson is set at 1.5 × 10

A Search for Exotic Higgs Decays
A Search for Exotic Higgs Decays

Author: Jackson Burzynski

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Published: 2023

Total Pages: 0

ISBN-13: 9783031304675

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This work describes a search for exotic decays of the Higgs boson to two long-lived, neutral, spin-0 particles which subsequently decay to pairs of b quarks, giving the striking signature of displaced hadronic jets in the ATLAS inner detector. Several other ATLAS searches have probed this decay topology previously, excluding branching ratios of the Higgs boson to long-lived particles (LLPs) of more than 10% for proper lifetimes greater than 100mm. These searches relied on dedicated triggers designed to select events with LLPs decaying in the ATLAS calorimeter or muon spectrometer. The lack of an equivalent trigger for LLP decays in the ATLAS inner detector has been a limiting factor in probing LLP lifetimes less than 100mm. To circumvent the difficulty of triggering on LLP decays, the search presented in this thesis exploits the ZH associated production mode, relying on leptonic trigger signatures to select interesting events. This is the first search for Higgs boson decays into LLPs to exploit this analysis methodology and additionally makes use of several novel methods for both background rejection and background estimation. No excess over Standard Model predictions is observed, and upper limits are set on the branching ratio of the Higgs boson to LLPs . Depending on the mass of the LLP, branching ratios greater than 10% are excluded for lifetimes as small as 4mm and as large as 100mm, probing an important gap in the ATLAS exotic Higgs decay programme. In comparison to the previous searches for Higgs decays to LLPs, these are among the most stringent limits placed on this scenario, and for LLPs with masses below 40 GeV these results represent the strongest existing constraints on the branching ratio of the Higgs boson to LLPs in this lifetime regime.