Search results for "Bottom"
showing 10 items of 450 documents
Quark and gluon form factors to four-loop order in QCD: TheNf3contributions
2017
We calculate the four-loop massless QCD corrections with three closed quark lines to quark and gluon form factors. We apply a novel integration by parts algorithm based on modular arithmetic and compute all relevant master integrals for arbitrary values of the space-time dimension. This is the first calculation of a gluon form factor at this perturbative order in QCD.
Unified QCD determination of all pseudoscalar leptonic decay constants
1992
Leptonic decay constants of all pseudoscalar mesons are determined in QCD by means of a new QCD sum-rule method. In the light meson and heavy quark limit the results are very similar and also agree with the well-known PCAC and scaling predictions respectively. The corrections to light meson pole dominance are generally small while those to the heavy quark limit are found to be sensitive to the binding energy (i.e. meson and quark mass differences). For standard values of quark masses we obtainfπ=132 MeV,fk=161 MeV,fB=128±28 MeV,fD=175±13 MeV,fBs=144±30 MeV andfDs=193±12 MeV.
Search for Pair Production of Supersymmetric Top Quarks in Dilepton Events frompp¯Collisions ats=1.96 TeV
2010
We present the results of a search for pair production of the supersymmetric partner of the top quark (the top squark (t) over tilde (1)) decaying to a b quark and a chargino (chi) over tilde (+/-)(1) with a subsequent (chi) over tilde (+/-)(1) decay into a neutralino (chi) over tilde (0)(1), lepton l, and neutrino nu Using a data sample corresponding to 2.7 fb(-1) of integrated luminosity of p (p) over bar collisions at root s = 1: 96 TeV collected by the CDF II detector, we reconstruct the mass of top squark candidate events and fit the observed mass spectrum to a combination of standard model processes and (t) over tilde (1)(t) over tilde (1). We find no evidence for (t) over tilde (1)(t…
Weak Mixing, CP Violation and the Standard Model
1990
These lectures summarize experimental information on weak couplings of quark flavours from weak decays and weak production of heavy flavours and the relation of the observed direct CP violation to a non-trivial phase in the quark mixing matrix. The interest in this field is twofold: on the one side, we can measure precisely the parameters of the standard model in its own framework; on the other side, any inconsistency amongst these measurements or evidence for any process forbidden in the standard model will lead beyond that model. The outline of these lectures is the following: 1. Weak Mixing of Quarks 1.1 Kobayashi-Maskawa-Matrix 1.2 Experimental Constraints on the KM Matrix 1.3 Allowed R…
Search for Pair Production of a Heavy Up-Type Quark Decaying to aWBoson and abQuark in thelepton+jetsChannel with the ATLAS Detector
2012
A search is presented for production of a heavy up-type quark (t') together with its antiparticle, assuming subsequent decay to a W boson and a b quark, t'(t) over bar' -> W(+)bW(-)(b) over bar. The search is based on 1.04 fb(-1) of proton-proton collisions at root s = 7 TeV collected by the ATLAS detector at the CERN Large Hadron Collider. Data are analyzed in the lepton + jets final state, characterized by a high transverse momentum isolated electron or muon, high missing transverse momentum, and at least three jets. No significant excess of events above the background expectation is observed. A 95% C.L. lower limit of 404 GeV is set for the mass of the t' quark.
Heavy Quark Symmetry and weak decays of heavy baryons
2008
I give an account of the physics ideas that go into the formulating of Heavy Quark Symmetry (HQS) and use HQS ideas to discuss various aspects of the weak semileptonic decays of heavy baryons.
Precision Measurement of the RatioB(t→Wb)/B(t→Wq)and Extraction ofVtb
2011
We present a measurement of the ratio of top quark branching fractions R = B(t -> Wb)/B(t -> Wq), where q can be a d, s or b quark, in the lepton+jets and dilepton ttbar final states. The measurement uses data from 5.4 fb-1 of ppbar collisions collected with the D0 detector at the Fermilab Tevatron Collider. We measure R = 0.90 +/- 0.04, and we extract the CKM matrix element |Vtb| as |Vtb| = 0.95 +/- 0.02, assuming unitarity of the 3x3 CKM matrix.
Hindered M1 radiative decay ofϒ(2S)from lattice NRQCD
2015
We present a calculation of the hindered M1 $\mathrm{\ensuremath{\Upsilon}}(2S)\ensuremath{\rightarrow}{\ensuremath{\eta}}_{b}(1S)\ensuremath{\gamma}$ decay rate using lattice nonrelativistic quantum chromodynamics. The calculation includes spin-dependent relativistic corrections to the NRQCD action through $\mathcal{O}({v}^{6})$ in the quark's relative velocity, relativistic corrections to the leading order current which mediates the transition through the quark's magnetic moment, radiative corrections to the leading spin-magnetic coupling and for the first time a full error budget. We also use gluon field ensembles at multiple lattice spacing values, all of which include $u$, $d$, $s$ and…
B and B-s decay constants from QCD duality at three loops
2004
Using special linear combinations of finite energy sum rules which minimize the contribution of the unknown continuum spectral function, we compute the decay constants of the pseudoscalar mesons B and B_s. In the computation, we employ the recent three loop calculation of the pseudoscalar two-point function expanded in powers of the running bottom quark mass. The sum rules show remarkable stability over a wide range of the upper limit of the finite energy integration. We obtain the following results for the pseudoscalar decay constants: f_B=178 \pm 14 MeV and f_{B_s}=200 \pm 14 MeV. The results are somewhat lower than recent predictions based on Borel transform, lattice computations or HQET…
Do the Quark Masses Run? Extractingm¯b(mZ)from CERN LEP Data
1997
We present the first results of next-to-leading order QCD corrections to three-jet heavy quark production at the CERN ${e}^{+}{e}^{\ensuremath{-}}$ collider LEP including mass effects. Among other applications, this calculation can be used to extract the bottom-quark mass from LEP data and, therefore, to test the running of masses as predicted by QCD.