Search For Invisible Higgs Boson Decays In Events With Vector Boson Fusion Signatures Using 139 Fb 1 Of Proton Proton Data Recorded By The Atlas Experiment PDF Download

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Search for Invisible Higgs-boson Decays in Events with Vector-boson Fusion Signatures Using 139 Fb−1 of Proton-proton Data Recorded by the ATLAS Experiment

Search for Invisible Higgs-boson Decays in Events with Vector-boson Fusion Signatures Using 139 Fb−1 of Proton-proton Data Recorded by the ATLAS Experiment
Author: [Study Group] ATLAS Collaboration CERN
Publisher:
Total Pages: 0
Release: 2022
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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

Future Of The Large Hadron Collider, The: A Super-accelerator With Multiple Possible Lives

Future Of The Large Hadron Collider, The: A Super-accelerator With Multiple Possible Lives
Author: Oliver Bruning
Publisher: World Scientific
Total Pages: 455
Release: 2023-08-08
Genre: Science
ISBN: 9811280193
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The Large Hadron Collider (LHC) is the highest energy collider ever built. It resides near Geneva in a tunnel 3.8m wide, with a circumference of 26.7km, which was excavated in 1983-1988 to initially house the electron-positron collider LEP. The LHC was approved in 1995, and it took until 2010 for reliable operation. By now, a larger set of larger integrated luminosities have been accumulated for physics analyses in the four collider experiments: ATLAS, CMS, LHCb and ALICE.The LHC operates with an extended cryogenic plant, using a multi-stage injection system comprising the PS and SPS accelerators (still in use for particle physics experiments at lower energies). The beams are guided by 1232 superconducting high field dipole magnets.Intense works are underway in preparation of the High Luminosity LHC, aimed at upgrading the LHC and detectors for collecting ten times more luminosity, and extending the collider life to the early 2040's. So far, the (HL-)LHC project represents a cumulation of around one hundred thousand person-years of innovative work by technicians, engineers, and physicists from all over the world; probably the largest scientific effort ever in the history of humanity. The book is driven by the realisation of the unique value of this accelerator complex and by the recognition of the status of high energy physics, described by a Standard Model — which still leaves too many questions unanswered to be the appropriate theory of elementary particles and their interactions.Following the Introduction are: three chapters which focus on the initial decade of operation, leading to the celebrated discovery of the Higgs Boson, on the techniques and physics of the luminosity upgrade, and finally on major options - of using the LHC in a concurrent, power economic, electron-hadron scattering mode, when upgraded to higher energies or eventually as an injector for the next big machine. The various technical and physics chapters, provided by 61 authors, characterise the fascinating opportunities the LHC offers for the next two decades ahead (possibly longer), with the goal to substantially advance our understanding of nature.

A Search for Nothing

A Search for Nothing
Author: William Balunas
Publisher:
Total Pages: 0
Release: 2018
Genre:
ISBN:
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This thesis presents a search for invisible decays of the Higgs boson using the vector boson fusion channel. This uses 36 fb-1 of proton-proton collision data at [square root] s = 13 TeV using the ATLAS detector at the Large Hadron Collider. The experimental methods for understanding the signal and background processes as well as detector effects are described in detail. The search is carried out in several regions defined by kinematic requirements on the final-state objects, and the observed event yields are used in a profile-likelihood fit in order to constrain the backgrounds. The results are interpreted using a modified frequentist method and are found to be consistent with the Standard Model expectations. An upper limit of 34% (28% expected) at 95% C.L. is placed on the invisible branching ratio of the Higgs boson. Re-interpretation of these results in terms of dark matter is also discussed, in the context of the Higgs portal and other simplified models.

Estimating Deceiving Signatures and Their Role in the Observation of the VBF Production Mode in the Higgs-Boson Decay Into Two W Bosons

Estimating Deceiving Signatures and Their Role in the Observation of the VBF Production Mode in the Higgs-Boson Decay Into Two W Bosons
Author: Konstantin Lehmann
Publisher:
Total Pages: 0
Release: 2022
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ISBN:
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The Higgs boson is the most recently discovered fundamental particle and its precise characterization is an important test of the Standard Model. For these measurements, the decay into two W bosons is crucial because of the large branching ratio, the sensitivity to vector-boson couplings and the theoretical implications on WW scattering. The proton-proton collisions at the LHC with a centre-of-mass energy of √s = 13 TeV provide an excellent environment to study the Higgs boson. The data recorded by the ATLAS experiment between 2015 and 2018 is analyzed. With an integrated luminosity of 139/fb, it allows to measure precisely the two dominant production modes, gluon fusion (ggF) and vector-boson fusion (VBF). Only collisions with one electron and one muon in the final state are considered and cuts are applied to select signal-like events. For the VBF process, the selection is further refined with the help of a deep neural network. Then, the purified dataset is analyzed with a statistical model constructed from MC simulation and a data-driven background estimate of misidentified leptons. The cross sections times branching ratio are measured to be 12.4 ± 1.5 pb for the ggF and 0.79 +0.19 −0.16 pb for the VBF processes. For the first time, the VBF process is observed in this decay channel with a significance of 6.6 standard deviations. Also measurements of eleven Simplified Template Cross Sections are performed and found to be consistent with the Standard Model. This precise measurement could only be achieved because the treatment of events with misidentified leptons was improved significantly. These deceiving signatures are estimated with the data-driven Fake Factor Method. An auxiliary measurement is performed to extract fake factors in a phase space with a Z boson recoiling against a jet that is misidentified as lepton. This measurement is presented together with the relevant experimental improvements. As a result of this work, the uncertainties could be reduced to an extent that they do not significantly affect the measurement of the Higgs-boson cross section. Even though the Fake Factor Method is experimentally well-established, a consistent derivation for a phase space with many leptons does not exist. In this thesis, it is shown for the first time that the Fake Factor Method can be derived exactly from the Matrix Method for an arbitrary number of misidentified leptons. In addition, the uncertainty estimate is considered and cases are derived in which the fake estimate does not exhibit Gaussian uncertainties.

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]
Author:
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Release: 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

Constraints on New Phenomena Via Higgs Boson Couplings and Invisible Decays with the ATLAS Detector

Constraints on New Phenomena Via Higgs Boson Couplings and Invisible Decays with the ATLAS Detector
Author:
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Total Pages: 52
Release: 2015
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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.