Determination of the b quark mass at the MZ scale with the DELPHI detector at LEP

An experimental study of the normalized three-jet rate of b quark events with respect to light quarks events (light=ℓ≡u,d,s) has been performed using the CAMBRIDGE and DURHAM jet algorithms. The data used were collected by the DELPHI experiment at LEP on the Z peak from 1994 to 2000. The results are found to agree with theoretical predictions treating mass corrections at next-to-leading order. Measurements of the b quark mass have also been performed for both the b pole mass: M_b and the b running mass: m_b(M_Z). Data are found to be better described when using the running mass. The measurement yields: for the CAMBRIDGE algorithm. This result is the most precise measurement of the b mass derived from a high energy process. When compared to other b mass determinations by experiments at lower energy scales, this value agrees with the prediction of quantum chromodynamics for the energy evolution of the running mass. The mass measurement is equivalent to a test of the flavour independence of the strong coupling constant with an accuracy of 7 ‰.     

Inclusive analysis of the b quark fragmentation function in Z decays at LEP

A study of quark hadronisation is presented using inclusively reconstructed B hadrons in about four million hadronic Z decays recorded in 1992-2000 with the OPAL detector at LEP. The data are compared to different theoretical models, and fragmentation function parameters of these models are fitted. The average scaled energy of weakly decaying B hadrons is determined to be

Determination of the top quark mass through the measurement of the\frac{{\Gamma ({\rm Z} \to b\bar b)}}{{\Gamma _{hadr} - \Gamma (Z \to b\bar b)}} ratio at high luminosity LEP

We investigate a possible role of invariant (the integral of motion) in nonstationary field theory by employing an explicit example of a scalar field interacting with a time-dependent external electromagnetic field. We show how in a unique manner the invariant operator leads to the particle concept in the Schrödinger picture. This approach gives an intermediate connection between the operator and functional-Schrödinger-equation formalisms. An application to the problem of particle creation is also discussed briefly.     

Higher order QCD and quark mass corrections to the Z widths in the standard model

We estimate, in the scheme, the strenghts of the higher order QCD (_s², _s³) and quark mass (m_f², m_f⁴, _s(m_f², m_f⁴)) corrections to the Z widths in the standard model (SM). Then, we give improved SM predictions of these widths. The observables Γ_H/Γ_e and σ_H, which can be predicted and measured accurately are almost insensitive to the changes of the Higgs ( 40 GeV M_H 1 TeV) and top quark (M_zM_t230 GeV) masses. Then, they should be useful in the high precision tests of the SM> Improved estimates of some quantities related to the width which are sensitive to the top quark mass are also given.     

Charm quark mass

We report on the result for the charm quark mass as obtained from our lattice QCD computation in the quenched approximation. Our result is $\text{m}{}_{\mathrm{c}}{}^{\mathrm{<mtext>\; </mtext><mtext>\; </mtext><mtext>MS</mtext><mtext>\; </mtext><mtext>\; </mtext>}}\text{(m}{}_{\mathrm{c}}\text{)=1.26(4)(12)}$ GeV.     

Determination of A FB b at the Z pole using inclusive charge reconstruction and lifetime tagging

A novel high precision method measures the b-quark forward-backward asymmetry at the Z pole on a sample of 3,560,890 hadronic events collected with the DELPHI detector in 1992 to 2000. An enhanced impact parameter tag provides a high purity b sample. For event hemispheres with a reconstructed secondary vertex the charge of the corresponding quark or anti-quark is determined using a neural network which combines in an optimal way the full available charge information from the vertex charge, the jet charge and from identified leptons and hadrons. The probability of correctly identifying b-quarks and anti-quarks is measured on the data themselves comparing the rates of double hemisphere tagged like-sign and unlike-sign events. The b-quark forward-backward asymmetry is determined from the differential asymmetry, taking small corrections due to hemisphere correlations and background contributions into account. The results for different centre-of-mass energies are: .Combining these results yields the b-quark pole asymmetry Received: 22 July 2004, Revised: 9 December 2004, Published online: 4 February 2005     

Is the b quark abnormal?

We compare the phenomenology of models containing b_R in an SU(2) doublet with recent data on B-decays. The only such models allowed are ones where the b decays solely through mixing with the d and s, with no new interactions near the weak scale. In particular, this rules out the SO(14) model of flavor unification proposed by Kim.     

The sixth quark mass

In six quark models with the gauge group SU (2)_L × SU (2)_R × U (1), and left-right symmetry, we investigate how weak mixing angles can be predicted in a natural way as functions of the quark masses, and find that the mass of the sixth quark can be naturally determined by the five others.     

A new observable to measure the top quark mass at hadron colliders

The $t\bar{t}+\mbox{1-jet} + X$ differential cross-section in proton?Cproton collisions at 7?TeV centre of mass energy is investigated with respect to its sensitivity to the top quark mass. The analysis includes higher order QCD corrections at NLO. The impact of the renormalization scale (?? _R), the factorization (?? _F) scale and of the choice of different proton??s PDF (parton distribution function) has been evaluated. In this study it is concluded that differential jet rates offer a promising option for alternative mass measurements of the top quark, with theoretical uncertainties below 1 GeV.     

Top quark search beyond theW mass at tevatron collider energy

The upgraded Tevatron collider, with an expected integrated luminosity of 100 pb^?1, shall push up the top quark discovery limit from 80 to 200 GeV. The distinctive signature of the signal vis-a-vis background are analysed for this mass range of top.     

Flavor changing Z0 decay and the top quark

The flavor changing neutral current decay of the Z⁰ boson into charge $\text{2}\text{3}$ quarks in the standard three generation SU(2)_L × U(1) theory of electroweak interactions has been studied. This process occurs first at one-loop order, where it has been calculated without approximation. The possibility of producing the as yet undiscovered top quark by this decay has been considered. The branching ratios are extremely small, independent of the top quark mass and plausible quark mixing matrices if there are three generations, making it unlikely that the top quark will be produced by this mechanism. However, a massive fourth bottom quark could increase the rates.