The Standard Model

Results of direct searches for neutral, supersymmetric Higgs bosons at the LEP, in the case of maximum CP symmetry violation in the Higgs sector. The area of tested parameters is shown according to the mass of the lightest neutral boson, mH1, and tan(beta), parameter of the model.

Experiments using accelerators at the highest accessible energy can be used to perform precise tests on the Standard Model. At CERN, the LEP has obtained many results leading to more precise knowledge in this field. The degree of precision attained in measuring the mass of the W boson has been exploited to obtain an indirect upper bound for the mass of the Higgs boson through quantum corrections. The Tevatron accelerator at Fermilab (near Chicago) has yielded results on the physics and mass of the top quark. The HERA collider at the DESY research centre in Hamburg has obtained more precise measurements of inclusive cross sections, related to parton (i.e. quark and gluon) densities in the proton, offering vital physics data for the LHC. All these experiments have also included an extensive search for possible deviations from the Standard Model.


Last update : 10/18 2005 (598)


Les collaborations ATLAS et CMS ont présenté pour la première fois leur mesure combinée de la masse du boson de Higgs, parvenant à une mesure précise à 0,2% près. Présentée lors de la 50e  édition des «Rencontres de Moriond» en Italie le 17 mars 2015, cette mesure est l’une des plus précises obtenues au LHC à ce jour. Les physiciens du CEA-Irfu ont joué un rôle majeur pour obtenir ce ... More »
The CDF and D0 experiments announce their new results in the search for the Higgs Boson
Physicist working on the CDF and D0 experiments using Fermilab's Tevatron accelerator in Chicago, including scientists from IN2P3/CNRS and IRFU/CEA, announced their latest results on 26 July at the International Conference on High-Energy Physics (ICHEP 2010) in Paris. Their measurement further constrain the Higgs boson mass domain still open within the standard model of particle physics. This means that CDF and D0 have ruled out a Higgs Boson with a mass between 158 and 175 GeV/c2.       An ... More »

The D0 experiment at the Tevatron accelerator at Fermilab (Chicago), in which physicists from CEA/IRFU and CNRS/IN2P3 are involved, has measured a significant matter-antimatter _asymmetry_ in the behaviour of particles containing b quarks, known as B mesons (or beauty mesons) beyond the predictions of the standard model (the current theory of particle physics). This result has been submitted for publication in the Journal Physical Review D.

Since researchers have been confronting the standard model of particle physics with experimentation, nothing has been able to shake it. Of all particles it describes, only the Higgs Boson has not yet been discovered. But the standard model is probably not the ultimate theory: it does not cover gravitation and numerous experimental observations remain unexplained. A new invariance, called supersymmetry, was suggested during the 1970s. It associates particles with different spins (integer spin bosons and ... More »
    Until the advent of the LHC, the Tevatron at the Fermi National Accelerator Laboratory, Fermilab (close to Chicago, USA), will remain the world's most powerful collider and the only location where the top1 quark can be produced. The DØ experiment recently published2 results on the measurement of the rate of production of top-antitop quark pairs. This quantity, which is dependent on the value taken for the mass of the top quark, enables a prediction to be made for that mass using the standard ... More »
The ground state of bottomonium.
  η b is the name of the particle recently discovered by the physicists working on the BaBar experiment.This ground state of ‘bottomonium’, a collection of particles formed from a bottom quark and an anti-bottom quark, has been sought for over thirty years. It has now been identified in the disintegration products of the Y(3S) particle, an excited state of bottomonium, using the latest data taken in 2008 by the BaBar experiment.An accurate measurement of the characteristics of this new particle ... More »
Scientists from the CDF and DZero collaborations at the U.S. Department of Energy's Fermilab have combined Tevatron data from the two experiments to advance the quest for the long-sought Higgs boson. They have presented their results on August 3rd at the International Conference on High Energy  Physics in Philadelphia indicating that they have for the first time excluded, with 95 percent probability, a mass for the Higgs  of 170 GeV (about 170 proton masses). This value lies near the middle of the possible ... More »
This program covers the experiments at accelerators with the top beam energy in the world. At Cern close to Geneva , the LEP was a large electron-positron collider, in operation from 1989 to 2000. It allowed a very detailed exploration of the Standard Model, with outstanding results, such as the measurement of the number of neutrino species -3-, or the indirect measurement of the top quark mass, and a large range of precision measurements. The last phase of operation has set important limits on the possibilities ... More »




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