2,090 research outputs found
Top-quark electroweak couplings at the FCC-ee
An optimal-observable analysis of the lepton angular and energy distributions
from top-quark pair production with semi-leptonic decays in e+e- collisions is
used to predict the potential sensitivity of the FCC-ee to the couplings of the
top quark to the photon and the Z.Comment: 18 pages, 5 figures. To be published in JHEP (accepted for
publication). Between version 2 and version 3, the suggestions of the JHEP
referee were implemented both in the text (in Sections "Results and
discussion" and "Summary and outlook") and in Figures 3 and
Direct measurement of alpha_QED(mZ) at the FCC-ee
When the measurements from the FCC-ee become available, an improved
determination of the standard-model "input" parameters will be needed to fully
exploit the new precision data towards either constraining or fitting the
parameters of beyond-the-standard-model theories. Among these input parameters
is the electromagnetic coupling constant estimated at the Z mass scale,
alpha_QED(mZ). The measurement of the muon forward-backward asymmetry at the
FCC-ee, just below and just above the Z pole, can be used to make a direct
determination of alpha_QED(mZ) with an accuracy deemed adequate for an optimal
use of the FCC-ee precision data.Comment: Version 4: Corrigendum added (2 pages). Accepted for publication in
JHE
Closing the light sbottom mass window from a compilation of e+e- -> hadron data
The e+e- -> hadron cross section data from PEP, PETRA, TRISTAN, SLC and LEP,
at centre-of-mass energies between 20 to 209 GeV, are analysed to search for
the production of a pair of light sbottoms decaying hadronically via
R-parity-violating couplings. This analysis allows the 95%C.L. exclusion of
such a particle if its mass is below 7.5 GeV/c2. The light sbottom mass window
is closed.Comment: 19 pages, 8 figures, 10 tables To be published in Physics Letters.
This new version has been reshuffled with respect to the original version to
include the suggestions from the Referees of Physics Letters. In particular,
the e+e- -> hadron data compilation and combination method are now described
in detail, to avoid references to unpublished material. A more realistic
treatment of systematic uncertainties also improved the limit slightl
The light gluino mass window revisited
The precise measurements of the ``electroweak observables'' performed at LEP and SLC are well consistent with the standard model predictions. Deviations from the standard model arising from vacuum polarization diagrams (also called ``weak loop corrections'') have been constrained in a model-independent manner with the epsilon formalism. Within the same formalism, additional deviations from new physics production processes can also be constrained, still in a model-independent way. For instance, a 95% C.L. limit of Delta Gamma_had} q qbar gluino gluino process, it allows an absolute lower limit to be set on the gluino mass, m_gluino > 6.3 GeV/c2 at 95% C.L., which definitely closes the so-called light gluino mass window. The precise measurements of the "electroweak observables" performed at LEP and SLC are well consistent with the standard model predictions. Deviations from the standard model arising from vacuum polarization diagrams (also called "weak loop corrections") have been constrained in a model-independent manner with the formalism. Within the same formalism, additional deviations from new physics production processes can also be constrained, still in a model-independent way. For instance, a 95% C.L. limit of had<3.9 MeV is set on the partial width of any purely hadronic exotic contribution to Z decays. When applied to the process, it allows an absolute lower limit to be set on the gluino mass, C.L., which definitely closes the so-called light gluino mass window
Higgs Physics
The existence of the Higgs boson was postulated more than 50 years ago, without any indication of its mass. The quest that followed, with several generations of particle physics experiments, culminated with the recent discovery of a new particle with a mass of 125 GeV. At least another half-century will be needed to map the properties of this particle with sufficient precision to understand its deepest origin.Lâexistence du boson de Higgs a Ă©tĂ© postulĂ©e il y a plus de 50 ans sans indication dâun ordre de grandeur pour sa masse. La longue recherche qui sâen suivit, impliquant plusieurs gĂ©nĂ©rations dâexpĂ©riences de physique des particules a Ă©tĂ© enfin couronnĂ©e par la dĂ©couverte rĂ©cente dâune nouvelle particule de masse de 125 GeV. Il sâen faudra sans doute de cinquante annĂ©es supplĂ©mentaires pour en dĂ©couvrir les propriĂ©tĂ©s avec une prĂ©cision suffisante pour comprendre la profonde origine physique de cette particule
Prospective Studies for LEP3 with the CMS Detector
On July 4, 2012, the discovery of a new boson, with mass around 125 GeV/c2
and with properties compatible with those of a standard-model Higgs boson, was
announced at CERN. In this context, a high-luminosity electron-positron
collider ring, operating in the LHC tunnel at a centre-of-mass energy of 240
GeV and called LEP3, becomes an attractive opportunity both from financial and
scientific point of views. The performance and the suitability of the CMS
detector are evaluated, with emphasis on an accurate measurement of the Higgs
boson properties. The precision expected for the Higgs boson couplings is found
to be significantly better than that predicted by Linear Collider studies.Comment: 25 pages, 13 figures, 3 tables, Submitted to the European Strategy
Preparatory Group (contribution 171), Companion to arXiV:1208.0504. Version 2
contains several additional Higgs decay channels studied, and numbers for
TLEP as well as for LEP
Naturalness and Higgs Decays in the MSSM with a Singlet
The simplest extension of the supersymmetric standard model - the addition of
one singlet superfield - can have a profound impact on the Higgs and its
decays. We perform a general operator analysis of this scenario, focusing on
the phenomenologically distinct scenarios that can arise, and not restricting
the scope to the narrow framework of the NMSSM. We reexamine decays to four b
quarks and four tau's, finding that they are still generally viable, but at the
edge of LEP limits. We find a broad set of Higgs decay modes, some new,
including those with four gluon final states, as well as more general six and
eight parton final states. We find the phenomenology of these scenarios is
dramatically impacted by operators typically ignored, specifically those
arising from D-terms in the hidden sector, and those arising from weak-scale
colored fields. In addition to sensitivity of m_Z, there are potential tunings
of other aspects of the spectrum. In spite of this, these models can be very
natural, with light stops and a Higgs as light as 82 GeV. These scenarios
motivate further analyses of LEP data as well as studies of the detection
capabilities of future colliders to the new decay channels presented.Comment: 3 figures, 1 appendix; version to appear in JHEP; typos fixed and
additional references and acknowledgements adde
Machine detector interface for the future circular collider
The international Future Circular Collider (FCC) study aims at a design of
, , colliders to be built in a new 100 km tunnel in the Geneva
region. The collider (FCC-ee) has a centre of mass energy range
between 90 (Z-pole) and 375 GeV (tt_bar). To reach such unprecedented energies
and luminosities, the design of the interaction region is crucial. The
crab-waist collision scheme has been chosen for the design and it will be
compatible with all beam energies. In this paper we will describe the machine
detector interface layout including the solenoid compensation scheme. We will
describe how this layout fulfills all the requirements set by the parameters
table and by the physical constraints. We will summarize the studies of the
impact of the synchrotron radiation, the analysis of trapped modes and of the
backgrounds induced by single beam and luminosity effects giving an estimate of
the losses in the interaction region and in the detector.Comment: 6 pages, 7 figures, 62th ICFA ABDW on High Luminosity Circular
Colliders, eeFACT2018, Hong Kong, Chin
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