The standard model of particle physics
describes the known fundamental particles and forces that make up our Universe, with the exception of gravity. One of the central features of the standard model ...is a field that permeates all of space and interacts with fundamental particles
. The quantum excitation of this field, known as the Higgs field, manifests itself as the Higgs boson, the only fundamental particle with no spin. In 2012, a particle with properties consistent with the Higgs boson of the standard model was observed by the ATLAS and CMS experiments at the Large Hadron Collider at CERN
. Since then, more than 30 times as many Higgs bosons have been recorded by the ATLAS experiment, enabling much more precise measurements and new tests of the theory. Here, on the basis of this larger dataset, we combine an unprecedented number of production and decay processes of the Higgs boson to scrutinize its interactions with elementary particles. Interactions with gluons, photons, and W and Z bosons-the carriers of the strong, electromagnetic and weak forces-are studied in detail. Interactions with three third-generation matter particles (bottom (b) and top (t) quarks, and tau leptons (τ)) are well measured and indications of interactions with a second-generation particle (muons, μ) are emerging. These tests reveal that the Higgs boson discovered ten years ago is remarkably consistent with the predictions of the theory and provide stringent constraints on many models of new phenomena beyond the standard model.
Search for neutral MSSM Higgs bosons at LEP Casado, M.P.; Ouyang, Q.; Xu, R. ...
The European physical journal. C, Particles and fields,
09/2006, Letnik:
47, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by the Minimal Supersymmetric standard model (MSSM). The data of the four ...collaborations are statistically combined and examined for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number of “benchmark” models, including CP-conserving and CP-violating scenarios. These interpretations lead in all cases to large exclusions in the MSSM parameter space. Absolute limits are set on the parameter cosβ and, in some scenarios, on the masses of neutral Higgs bosons.
Ageing studies for the ATLAS-monitored drift tubes Kollefrath, M.; Paschhoff, V.; Spegel, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/1998, Letnik:
419, Številka:
2-3
Journal Article
Recenzirano
The lifetime of drift tubes operated with Ar–CH4–N2 91–5–4, Ar–CH4–N2–CO2 94–3–2–1, Ar–CF4–N2–CO2 94.5–0.5–2–3 and Ar–CO2 80–20 is studied under various conditions. H2O and ethanol were successfully ...tested as a remedy against ageing.
The method of glow discharge in argon is used to clean the cathode and inefficient wires and first results of this treatment are presented.
High rate performance of drift tubes Scherberger, G.; Paschhoff, V.; Waldmann, V. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/1999, Letnik:
424, Številka:
2
Journal Article
Recenzirano
Odprti dostop
This article describes calculations and measurements of space charge effects due to high rate irradiation in high resolution drift tubes. Two main items are studied: the reduction of the gas gain and ...changes of the drift time. Whereas the gain reduction is similar for all gases and unavoidable, the drift time changes depend on the kind of gas that is used. The loss in resolution due to high particle rate can be minimized with a suitable gas. This behaviour is calculable, allowing predictions for new gas mixtures.
Drift chamber ageing is a serious concern for the operation of the Monitored Drift Tube chambers (MDT) in the ATLAS muon system. Therefore systematic studies of ageing effects have been carried out ...at the University of Freiburg. It has been shown that tiny contaminations with volatile silicon compounds, which are found in many components supplied by industry, cause a severe degradation of the drift tube performance. Since the ATLAS MDT system contains many thousands of commercial components the cleanliness of all parts cannot be guaranteed. Therefore gas filters with zeolites have been developed in Freiburg, which remove these impurities efficiently. They will be employed in the gas system for the MDT chambers.
The differential cross section for the process $Z/\gamma^*\rightarrow ll$ ($l=e,\mu$) as a function of dilepton invariant mass is measured in pp collisions at $\sqrt{s}=$7 TeV at the LHC using the ...ATLAS detector. The measurement is performed in the $e$ and $\mu$ channels for invariant masses between 26 GeV and 66 GeV using an integrated luminosity of 1.6 fb$^{-1}$ collected in 2011 and these measurements are combined. The analysis is extended to invariant masses as low as 12 GeV in the muon channel using 35 pb$^{-1}$ of data collected in 2010. The cross sections are determined within fiducial acceptance regions and corrections to extrapolate the measurements to the full kinematic range are provided. Next-to-next-to-leading-order QCD predictions provide a significantly better description of the results than next-to-leading-order QCD calculations, unless the latter are matched to a parton shower calculation.
This paper describes topological searches for neutral scalar bosons S0 produced in association with a Z0 boson via the Bjorken process \(e^+e^- \to{\rm S}^0{}{\rm Z}^0\) at centre-of-mass energies of ...91 GeV and 183-209 GeV. These searches are based on studies of the recoil mass spectrum of \({\rm Z}^0 \to e^+e^-\) and \(\mu^+ \mu^-\) events and on a search for \({\rm S}^0{\rm Z}^0\) with \({\rm Z}^0 \to \nu\bar{\nu}\) and S\(^0 \to e^+ e^-\) or photons. They cover the decays of the S0 into an arbitrary combination of hadrons, leptons, photons and invisible particles as well as the possibility that it might be stable. No indication for a signal is found in the data and upper limits on the cross section of the Bjorken process are calculated. Cross-section limits are given in terms of a scale factor k with respect to the Standart Model cross section for the Higgs-strahlung process \(e^+ e^-\to{\rm H}_{\rm SM}{\rm Z}^0\). These results can be interpreted in general scenarios independently of the decay modes of the S0. The examples considered here are the production of a single new scalar particle with a decay width smaller than the detector mass resolution, and for the first time, two scenarios with continuous mass distributions, due to a single very broad state or several states close in mass.
This Letter presents the first search for supersymmetry in final states containing one isolated electron or muon, jets, and missing transverse momentum from {radical}(s)=7 TeV proton-proton ...collisions at the LHC. The data were recorded by the ATLAS experiment during 2010 and correspond to a total integrated luminosity of 35 pb{sup -1}. No excess above the standard model background expectation is observed. Limits are set on the parameters of the minimal supergravity framework, extending previous limits. Within this framework, for A{sub 0}=0 GeV, tan{beta}=3, and {mu}>0 and for equal squark and gluino masses, gluino masses below 700 GeV are excluded at 95% confidence level.
A search for diphoton events with large missing transverse energy is presented. The data were collected with the ATLAS detector in proton-proton collisions at {radical}(s)=7 TeV at the CERN Large ...Hadron Collider and correspond to an integrated luminosity of 3.1 pb{sup -1}. No excess of such events is observed above the standard model background prediction. In the context of a specific model with one universal extra dimension with compactification radius R and gravity-induced decays, values of 1/R<729 GeV are excluded at 95% C. L., providing the most sensitive limit on this model to date.
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