Cross-section-constrained top-quark mass measurement from dilepton events at the Tevatron

We report the first top-quark mass measurement that uses a cross-section constraint to improve the mass determination. This measurement is made with a dilepton tt event candidate sample collected with the Collider Detector II at Fermilab. From a data sample corresponding to an integrated luminosity of 1.2 fb(-1), we measure a top-quark mass of 170.7(-3.9)(+4.2)(stat)+/-2.6(syst)+/-2.4(theory) GeV/c(2). The measurement without the cross-section constraint is 169.7(-4.9)(+5.2)(stat)+/-3.1(syst) GeV/c(2).     

Top-quark mass measurement from dilepton events at CDF II

We report a measurement of the top-quark mass using events collected by the CDF II detector from pp collisions at square root of s = 1.96 TeV at the Fermilab Tevatron. We calculate a likelihood function for the top-quark mass in events that are consistent with tt --> bl(-)nu(l)bl'+ nu'(l) decays. The likelihood is formed as the convolution of the leading-order matrix element and detector resolution functions. The joint likelihood is the product of likelihoods for each of 33 events collected in 340 pb(-1) of integrated luminosity, yielding a top-quark mass M(t) = 165.2 +/- 6.1(stat) +/- 3.4(syst) GeV/c2. This first application of a matrix-element technique to tt --> bl+ nu(l)bl'- nu(l') decays gives the most precise single measurement of M(t) in dilepton events. Combined with other CDF run II measurements using dilepton events, we measure M(t) = 167.9 +/- 5.2(stat) +/- 3.7(syst) GeV/c2.     

Independent measurement of the top quark mass and the light- and bottom-jet energy scales at hadron colliders

A method for the simultaneous determination of the energy scales for bottom-quark jets and light jets, the jet energy resolution, and the top quark mass at hadron colliders is presented. The method exploits the unique kinematics of events with top-antitop pair production, where one of the top quarks involves a leptonic and one a hadronic boson decay. The paper shows a feasibility study of how this simultaneous measurement can be performed at the upcoming LHC experiments ATLAS and CMS.     

Model-independent measurement of the top quark polarisation

We introduce a new asymmetry in the decay t→Wb→?νb$t\to Wb\to ?\nu b$, which is shown to be directly proportional to the polarisation of the top quark along a chosen axis, times a sum of W helicity fractions. The latter have already been precisely measured at the Tevatron and the Large Hadron Collider. Therefore, this new asymmetry can be used to obtain a model-independent measurement of the polarisation of top quarks produced in any process at hadron or lepton colliders.     

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.     

Review of the top quark mass measurement at the CDF in p \bar p collisions at \sqrt s = 1.96 TeV

Upgraded Tevatron RUN-II luminosity has opened a new chapter in a modern heavy quark studies—a top physics: a dozen level of a Tevatron Run-I top events statistic now is being replaced by hundreds events. This work reviews a mass measurement of the top quark produced at $\sqrt s $ = 1.96 TeV in p $\bar p$ collisions at the Collider Detector at Fermilab (CDF) with the integrated luminosity samples up to 359 pb^?1. The review covers the M(top) measurement using mainly the so-called template methods both in the “lepton + jets” and “dilepton” channels of top quark decay. The CDF top quark mass obtained in the lepton + jets mode is currently the world’s most precise single measurement of this important physical parameter. This work summarizes the essential results of the CDF top quark mass measurement achieved and published for the recent 2003–2005 period.     

Some thoughts on the mass of the top quark

We propose a new mechanism for up-down symmetry breaking within the context of a technicolor scenario. The experimentally determined ratio $\text{M}{}_{\mathrm{<mtext>W</mtext>}}\text{M}{}_{\mathrm{<mtext>Z</mtext>}}\text{cos}\text{θ}{}_{\mathrm{<mtext>W</mtext>}}\text{? 1}$ is in addition preserved at the technicolor scale. If we assume that the mechanism works at the level of the heaviest generation we find $\text{m}{}_{\mathrm{<mtext>t</mtext>}}\text{= (?}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{)38}\text{GeV}$. The parameter ? depends on strong technicolor dynamics and can in principle be determined. Via a crude estimate we find ? to be a number of order 1.     

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.     

On measurement of helicity parameters in top quark decay

To enable an evaluation of future measurements of the helicity parameters for decay in regard to violation, this paper considers the effects of an additional pure-imaginary coupling, or , associated with a specific, single additional Lorentz structure, . Sizable violation signatures can occur for low-effective mass scales (), but in most cases can be more simply excluded by precision measurement of the probabilities and . Signatures for excluding the presence of violation associated with the two dynamical phase-type ambiguities are investigated. Received: 10 July 2000 / Published online: 8 September 2000     

Unified spin gauge model and the top quark mass

Spin gauge models use a real Clifford algebraic structure R_p,q associated with a real manifold of dimension p + q to describe the fundamental interactions of elementary particles. This review provides a comparison between those models and the standard model, indicating their similarities and differences. By contrast with the standard model, the spin gauge model based on R_3,8 generates intermediate boson mass terms without the need to use the Higgs-Kibble mechanism and produces a precise prediction for the mass of the top quark. The potential of this model to account for exactly three families of fermions is considered.     

Measurement of the top quark pair production cross section in pp collisions at s=7TeV in dilepton final states with ATLAS

A measurement of the production cross section of top quark pairs ($t\overline{t}$) in proton–proton collisions at a center-of-mass energy of 7 TeV recorded with the ATLAS detector at the Large Hadron Collider is reported. Candidate events are selected in the dilepton topology with large missing transverse energy and at least two jets. Using a data sample corresponding to an integrated luminosity of $35{\mathrm{pb}}^{?1}$, a $t\overline{t}$ production cross section ${\sigma }_{t\overline{t}}=177\pm 20(\text{stat.})\pm 14(\text{syst.})\pm 7(\text{lum.})\text{pb}$ is measured for an assumed top quark mass of $m_t=172.5\text{GeV}$. A second measurement requiring at least one jet identified as coming from a b quark yields a comparable result, demonstrating that the dilepton final states are consistent with being accompanied by b-quark jets. These measurements are in good agreement with Standard Model predictions.     

Implications of the top quark mass measurement for the CKM parameters,x s and CP asymmetries

Motivated by the recent determination of the top quark mass by the CDF collaboration,m _t =174±10 _?12 ⁺¹³ GeV, we review and update the constraints on the parameters of the quark flavour mixing matrixV _CKM in the standard model. In performing our fits, we use inputs from the measurements of the following quantities: (i) |∈|, the CP-violating parameter inK decays, (ii) ΔM _d , the mass difference due to the $B_d^0 - \overline {B_d^0 }$ mixing, (iii) the matrix elements |V _cb | and |V _ub |, and (iv)B-hadron lifetimes. We find that the allowed region of the unitarity triangle is very large, mostly due to theoretical uncertainties. (This emphasizes the importance of measurements of CP-violating rate asymmetries in theB system.) Nevertheless, the present data do some-what restrict the allowed values of the coupling constant product $f_{B_d } \sqrt {\hat B_{B_d } }$ and the renormalization-scale-invariant bag constant $\hat B_K$ . With the updated CKM matrix we present the currently-allowed range of the ratio |V _td /V _ts |, as well as the standard model predictions for the $B_s^0 - \overline {B_s^0 }$ mixing parameterx _s and the quantities sin 2α, sin 2β and sin² γ, which characterize the CP-asymmetries inB-decays. The ALEPH collaboration has recently reported a significant improvement on the lower limit on the $B_s^0 - \overline {B_s^0 }$ mass difference, ΔM _s /Δx _d >11.3 (95% C.L.). This has interesting consequences for the CKM parameters which are also worked out.