Search results for "Standard Model"
showing 10 items of 1206 documents
Search for the Standard Model Higgs Boson in AssociatedWHProduction in9.7 fb−1ofpp¯Collisions with the D0 Detector
2012
We present a search for the standard model Higgs boson in final states with a charged lepton (electron or muon), missing transverse energy, and two or three jets, at least one of which is identified as a b-quark jet. The search is primarily sensitive to WH→lνbb production and uses data corresponding to 9.7 fb(-1) of integrated luminosity collected with the D0 detector at the Fermilab Tevatron pp Collider at √s = 1.96 TeV. We observe agreement between the data and the expected background. For a Higgs boson mass of 125 GeV, we set a 95% C.L. upper limit on the production of a standard model Higgs boson of 5.2 × σ(SM), where σ(SM) is the standard model Higgs boson production cross section, whi…
Testing the Standard Model at the precision frontier: the anomalous magnetic moment of the muon
2014
The anomalous magnetic moment of the muon (g − 2)μ is one of the most precisely measured quantities in particle physics (0.54 ppm). There is a long-standing discrepancy of 3-4 standard deviations between the direct measurement of (g − 2)μ and its theoretical evaluation. This theoretical prediction is subdivided into three contributions: QED, weak and hadronic. The QED and weak parts can be determined in perturbative approaches with very high precision. Thus, the hadronic uncertainty dominates the total theoretical uncer- tainty. Within the hadronic uncertainty, the largest contribution stems from the vacuum polarization term, which can be evaluated with the measurement of the inclusive hadr…
Minimal Leptoquark Explanation for theRD(*),RK, and(g−2)μAnomalies
2016
We show that by adding a single new scalar particle to the standard model, a TeV-scale leptoquark with the quantum numbers of a right-handed down quark, one can explain in a natural way three of the most striking anomalies of particle physics: the violation of lepton universality in B[over ¯]→K[over ¯]l^{+}l^{-} decays, the enhanced B[over ¯]→D^{(*)}τν[over ¯] decay rates, and the anomalous magnetic moment of the muon. Constraints from other precision measurements in the flavor sector can be satisfied without fine-tuning. Our model predicts enhanced B[over ¯]→K[over ¯]^{(*)}νν[over ¯] decay rates and a new-physics contribution to B_{s}-B[over ¯]_{s} mixing close to the current central fit v…
Hadronic inputs to the (g– 2)μpuzzle
2016
There is a long standing discrepancy of 3 – 4 standard deviations between the direct measurement and the Standard Model prediction of the anomalous magnetic moment of the muon (g – 2) μ . While new direct measurements have been proposed to clarify the situation, theory calculations are completely limited by the accuracy of the hadronic contributions to (g – 2) μ . In order to increase their precision, experimental information can be used as input. In this presentation we will discuss recent and future measurements of relevant hadronic cross sections and transition form factors.
Measurement of the Time-like Pion Transition Form Factor at BESIII
2019
The pion transition form factor is an important input to the dispersive approaches of the Standard Model calculations for the anomalous magnetic moment of the muon. We report the prospects of a first measurement at high momentum transfer in the time-like region performed at BESIII. The aim is to improve the uncertainty of the hadronic light-by-light calculations and to shed light on the BaBar-Belle puzzle in the space-like region.
Search for the Production of Single Sleptons throughR-Parity Violation inpp¯Collisions ats=1.8 TeV
2002
We report the first search for supersymmetric particles via s-channel production and decay of smuons or muon sneutrinos at hadronic colliders. The data for the two-muon and two-jets final states were collected by the D0 experiment and correspond to an integrated luminosity of 94+/-5 pb(-1). Assuming that R parity is violated via the single coupling lambda(211)('), the number of candidate events is in agreement with expectation from the standard model. Exclusion contours are given in the (m(0),m(1/2)) and (m((χ) over bar),m((ν) over bar)) planes for lambda(211)(')=0.09, 0.08, and 0.07.
Evidence for Spin correlation in tt̄ production
2012
Made available in DSpace on 2022-04-29T03:09:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-01-19 We present a measurement of the ratio of events with correlated t and t̄ spins to the total number of tt̄ events. This ratio f is evaluated using a matrix-element-based approach in 729 tt̄ candidate events with a single lepton (electron or muon) and at least four jets. The analyzed pp̄ collisions data correspond to an integrated luminosity of 5.3fb -1 and were collected with the D0 detector at the Fermilab Tevatron collider operating at a center-of-mass energy √s=1.96TeV. Combining this result with a recent measurement of f in dileptonic final states, we find f in agreement with the …
Measurement of transition form factors in two-photon collisions at BESIII
2019
The two-photon physics program of the BESIII Collaboration is mainly motivated by the need of new measurements of transition form factors as input for the Standard Model calculations of $ \mathop a\nolimits_\mu ^{HLbL} $, the hadronic light-by-light scattering contribution to the anomalous magentic moment of the muon. The large data sets acquired at BESIII allow to study the transition form factors of pseudoscalar mesons in the relevant region of momentum transfer for $ \mathop a\nolimits_\mu ^{HLbL} $. In this presentation the status of the respective measurements for π0,η and η’ mesons are discussed, and prospects for studies of multi-meson systems as well as of doubly-virtual transition …
Search for a Dark Photon ine+e−Collisions atBaBar
2014
Dark sectors charged under a new Abelian interaction have recently received much attention in the context of dark matter models. These models introduce a light new mediator, the so-called dark photon (A^{'}), connecting the dark sector to the standard model. We present a search for a dark photon in the reaction e^{+}e^{-}→γA^{'}, A^{'}→e^{+}e^{-}, μ^{+}μ^{-} using 514 fb^{-1} of data collected with the BABAR detector. We observe no statistically significant deviations from the standard model predictions, and we set 90% confidence level upper limits on the mixing strength between the photon and dark photon at the level of 10^{-4}-10^{-3} for dark photon masses in the range 0.02-10.2 GeV. W…