Search for new physics in top events with the D0 detector

This review is focused on the search for new processes, performed with top quark events in D{\O}. It presents four updated or new D{\O} results. The two first analyses deal with top production properties: they search for a new heavy resonance decaying to top-antitop. The two last results concern top decay properties: the measurement of the $W$ helicity as a probe of the $tWb$ coupling structure, and the top quark branching ratio to $Wb$. Neither of these measurements reveal any deviation with respect to the standard model predictions.Comment: Submitted for the SUSY07 conference proceeding. 4 pages, LateX, 6 eps figures, 2 LateX style file

Transverse-momentum and pseudorapidity distributions of charged hadrons in pp collisions at √s=0.9 and 2.36 TeV

Measurements of inclusive charged-hadron transverse-momentum and pseudorapidity distributions are presented for proton-proton collisions at root s = 0.9 and 2.36 TeV. The data were collected with the CMS detector during the LHC commissioning in December 2009. For non-single-diffractive interactions, the average charged-hadron transverse momentum is measured to be 0.46 +/- 0.01 (stat.) +/- 0.01 (syst.) GeV/c at 0.9 TeV and 0.50 +/- 0.01 (stat.) +/- 0.01 (syst.) GeV/c at 2.36 TeV, for pseudorapidities between -2.4 and +2.4. At these energies, the measured pseudorapidity densities in the central region, dN(ch)/d eta vertical bar(vertical bar eta vertical bar and pp collisions. The results at 2.36 TeV represent the highest-energy measurements at a particle collider to date

First look at CKM parameters from early Belle II data

International audienceAfter its commissioning in 2018, the Belle II experiment has started registering first physics data delivered by SuperKEKB in 2019. The Belle II physics program focuses on the search for physics beyond the standard model with precise measurements in the flavour sector. The huge targeted dataset and the B-factory particular collision scheme will help to significantly improve the experimental precision on the three angles of the bd CKM unitarity triangle. These measurements are based on time-dependent CP asymmetry analyses for the angles phi1 and phi2, and on the reconstruction of many B and D hadronic decay modes for phi3. In this proceeding article are reported the first look at these ingredients reconstructed with early Belle II data, and the expected Belle II sensitivity on phi1, phi2 and phi3 with more data

Etude de détecteurs gazeux à micropistes pour le trajectographe de CMS et mesure de la masse du boson W dans l'expérience DELPHI

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Recherche du boson de Higgs standard léger dans le canal WH avec la statistique finale de l'expérience DØ au Tevatron

Le mécanisme de Higgs, introduit en 1964, propose une solution à un problème majeur du modèle standard de la physique des particules : l'origine de la masse. Ce mécanisme prédit l'existence d'un boson scalaire, de masse non prédite par la théorie et qui n'a encore jamais été observé expérimentalement (Juin 2012). Le Tevatron, un accélérateur hadronique basé à Fermi National Accelerator Laboratory près de Chicago, a permis la prise de données à l'aide des deux détecteurs CDF et DØ depuis 1983 jusqu'en septembre 2011. Accumulant une statistique de près de 10fb-1 à analyser. La production associée du Higgs et d'un boson vecteur est le canal principal de recherche pour un Higgs standard léger. A l'aide des données collectées par DØ, nous recherchons ce mode de production. La production du boson de Higgs étant très rare, nous avons développé des techniques sophistiquées de manière à améliorer la sensibilité au signal, telles que l'identification des jets de quarks beaux ou encore des méthodes basées sur des discriminants multivariés. Au final, une approche statistique nous permet de poser une limite supérieure sur le taux de production du Higgs observé (resp. attendu) rapporté aux prédictions du modèle standard. Les résultats obtenus dans le canal WH avec la statistique finale de l'expérience DØ au Tevatron sont de 3.15 (resp. 3.97) pour un boson de Higgs de 115 GeV/C2.Higgs mechanism, introduced in 1964, gives a satisfactory solution to a major problem of the standard model of elementary particles: the origin of the mass. It predicts the existence of the Higgs scalar boson, which mass is not defined by the theory and which has not been discovered experimentally yet (June 2012). The Tevatron, a hadron accelerator based at Fermi National Accelerator Laboratory near Chicago, took data with its two multi-purpose detectors CDF and DØ since 1983 up to september 2011. Leaving about 10 fb-1 of statistics to analyze. Associated production of Higgs and vector gauge boson is the main search channel for a light standard Higgs boson. Using data collected by DØ, we are looking for this production mode taking advantage of sophisticated techniques to improve the signal sensitivity like b-jet identification and multivariate discriminants. In the end, a statistical approach allows us to set an upper limit on the ratio between the observed (resp. expected) Higgs production and its theoretical cross section. The results obtained in the WH channel using 9.7 fb-1 at DØ is 3;15 (resp. 3.96) for a 115 GeV/c2 Higgs boson.STRASBOURG-Bib.electronique 063 (674829902) / SudocSudocFranceF

Etude du couplage top-W-b par la mesure de l'hélicité du boson W dans l'expérience Dø

STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

A new expected upper limit on the rare decay B(s) ---> mu+ mu- with the D0 experiment

We present a new expected upper limit of the rare decay branching ratio B{sub s} {yields} {mu}{sup +}{mu}{sup -} using about 5 fb{sup -1} of Run II data collected with the D0 detector at the Tevatron. When setting limits on the branching ratio, selected events are normalized to reconstructed B{sup {+-}} {yields} J/{Psi}K{sup {+-}} events in order to decrease the systematic uncertainty. The resulting expected upper limit is {Beta}(B{sub s} {yields} {mu}{sup +}{mu}{sup -}) = 4.3(5.3) x 10{sup -8} at the 90% (95%) C.L

Measurements of Beam Backgrounds in SuperKEKB Phase 2

The high design luminosity of the SuperKEKB electron-positron collider will result in challenging levels of beam-induced backgro unds in the interaction region. Understanding and mitigating these backgrounds is critical to the success of the Belle~II experi ment. We report on the first background measurements performed after roll-in of the Belle II detector, a period known as SuperKE KB Phase 2, utilizing both the BEAST II system of dedicated background detectors and the Belle II detector itself. We also repor t on first revisions to the background simulation made in response to our findings. Backgrounds measured include contributions f rom synchrotron radiation, beam-gas, Touschek, and injection backgrounds. At the end of Phase 2, single-beam backgrounds origina ting from the 4 GeV positron Low Energy Ring (LER) agree reasonably well with simulation, while backgrounds from the 7 GeV elect ron High Energy Ring (HER) are approximately one order of magnitude higher than simulation. We extrapolate these backgrounds for ward and conclude it is safe to install the Belle II vertex detector