Determination Of Top Quark Mass Research Articles

Top-quark mass determination in the optimised threshold scan

One of the important goals at the future e^++e^-− colliders is to measure the top-quark mass and width in a scan of the pair production threshold. Presented in this work is the most general approach to the top-quark mass determination from the threshold scan at CLIC, with all relevant model parameters and selected systematic uncertainties included in the fit procedure. In the baseline scan scenario the top-quark mass can be extracted with precision of the order of 30 to 40,MeV, already for 100 fb^{-1}−1 of data collected at the threshold. We present the optimisation procedure based on the genetic algorithm with which the statistical uncertainty of the mass measurement can be reduced by about 20%.

Optimising top-quark threshold scan at CLIC using genetic algorithm

One of the important goals at the future e+e− colliders is to measure the top-quark mass and width in a scan of the pair production threshold. However, the shape of the pair-production cross section at the threshold depends also on other model parameters, as the top Yukawa coupling, and the measurement is a subject to many systematic uncertainties. Presented in this work is the study of the top-quark mass determination from the threshold scan at CLIC. The most general approach is used with all relevant model parameters and selected systematic uncertainties included in the fit procedure. Expected constraints from other measurements are also taken into account. It is demonstrated that the top-quark mass can be extracted with precision of the order of 30 to 40 MeV, including considered systematic uncertainties, already for 100 fb−1 of data collected at the threshold. Additional improvement is possible, if the running scenario is optimised. With the optimisation procedure based on the genetic algorithm the statistical uncertainty of the mass measurement can be reduced by about 20%. Influence of the collider luminosity spectra on the expected precision of the measurement is also studied.

Top-quark mass determination from t-channel single top production at the LHC

We study the determination of the top-quark mass using leptonic observables in t-channel single top-quark production at the LHC. We demonstrate sensitivity of transverse momentum of the charged lepton on the input top-quark mass. We present predictions at next-to-next-to-leading order (NNLO) in QCD with narrow width approximation and structure function approach. Further corrections due to parton shower and hadronization, non-resonant and non-factorized contributions are discussed. To reduce impact of SM backgrounds we propose to use the charge weighted distribution for the measurement, i.e., differences between distributions of charged lepton with positive and negative charges. By modeling both signal and background processes, we found the projections for (HL-)LHC to be promising, with a total theoretical uncertainty on the extracted top-quark mass of about 1 ∼ 2 GeV.

Invariant-mass distribution of top-quark pairs and top-quark mass determination * * Supported in part by the National Natural Science Foundation of China (11975030, 11635001, 11575004). W.-L. Ju was Supported in part by the China Postdoctoral Science Foundation (2017M610685)

In this study, we investigate the invariant-mass distribution of top-quark pairs near the 2mt threshold, which strongly influences the determination of the top-quark mass mt. Higher-order non-relativistic corrections lead to large contributions, which are not included in the state-of-the-art theoretical predictions. A factorization formula is derived to resum such corrections to all orders in the strong-coupling, and necessary ingredients are calculated to perform the resummation at next-to-leading power. We combine the resummation with fixed-order results and present phenomenologically relevant numerical results. The resummation effect significantly increases the differential cross-section in the threshold region and makes the theoretical prediction more compatible with experimental data. We estimate that using our prediction in the determination of mt will lead to a value closer to the direct measurement result.

Top quark pair production near threshold: single/double distributions and mass determination

We investigate top quark pair production near the threshold where the pair invariant mass {M}_{toverline{t}} approaches 2mt, which provides sensitive observables to extract the top quark mass mt. Using the effective field theory methods, we derive a factorization and resummation formula for kinematic distributions in the threshold limit up to the next-to- leading power, which resums higher order Coulomb corrections to all orders in the strong coupling constant. Our formula is similar to those in the literature but differs in several important aspects. We apply our formula to the {M}_{toverline{t}} distribution, as well as to the double differential cross section with respect to {M}_{toverline{t}} and the rapidity of the toverline{t} pair. We find that the resummation effects significantly increase the cross sections near the threshold, and lead to predictions better compatible with experimental data than the fixed-order ones. We demonstrate that incorporating resummation effects in the top quark mass determination can shift the extracted value of mt by as large as 1.4 GeV. The shift is much larger than the estimated uncertainties in previous experimental studies, and leads to a value of the top quark pole mass more consistent with the current world average.

Colour Reconnection in WW Events and the Models with It

The colour reconnection effects were intensively studied with LEP2 data and are a dominant sources of systematic uncertainty in the W boson mass in e+e− annihilation at LEP2 and one of a dominant sources of systematic uncertainty in the top quark mass determination at hadronic colliders. With the discovery of Higgs boson, a new arena for the effects studies opened up. The effects are discussed within the existent different models and what future tests may come with a future FCC-ee.

Top quark mass determination from the energy peaks of b-jets and B-hadrons at NLO QCD

We analyze the energy spectra of $single$ b-jets and B-hadrons resulting from the production and decay of top quarks within the SM at the LHC at the NLO QCD. For both hadrons and jets, we calculate the correlation of the peak of the spectrum with the top quark mass, considering the "energy-peak" as an observable to determine the top quark mass. Such a method is motivated by our previous work where we argued that this approach can have reduced sensitivity to the details of the production mechanism of the top quark, whether it is higher-order QCD effects or new physics contributions. As part of the NLO improvement over the original proposal, we assess the residual sensitivity of the extracted top quark mass to perturbative effects both in top quark production and decay. For a 1% jet energy scale uncertainty (and assuming negligible statistical error), the top quark mass can then be extracted using the energy-peak of b-jets with an error +- (1.2 (exp) + 0.6(th)) GeV. We note that recently the CMS collaboration reported a top quark mass measurement based on the original proposal (with b-jets) so that our result contributes to a precise evaluation of the associated theory uncertainty. In view of the dominant jet energy scale uncertainty in the measurement using b-jets, we also investigate the extraction of the top quark mass from the energy-peak of the corresponding B-hadrons which, in principle, can be measured without this uncertainty. The calculation of the B-hadron energy spectrum is carried out using fragmentation functions at NLO. The dependence on the fragmentation scale turns out to be the largest theoretical uncertainty in this extraction of top quark mass. Future improvement of the treatment of bottom quark hadronization can reduce this uncertainty, rendering methods based on the B-hadron energy-peak competitive for the top quark mass measurement.

New method for precise determination of top quark mass at LHC

A new method to measure the mass of the top quark at the LHC is presented [S. Kawabata, Y. Shimizu, Y. Sumino and H. Yokoya, arXiv:1405.2395 [hep-ph]]. This method uses lepton energy distribution and ideally does not depend on the velocity distribution of the top quark. We perform a simulation analysis of the top quark mass reconstruction using this method at the leading order, taking account of experimental circumstances. We estimate the sensitivity of the mass determination. The results show that this method is viable in realistic experimental conditions and has a possibility to achieve a good accuracy in determining a theoretically well-defined top quark mass by including higher-order corrections.

High-Precision Differential Predictions for Top-Quark Pairs at the LHC.

We present the first complete next-to-next-to-leading order (NNLO) QCD predictions for differential distributions in the top-quark pair production process at the LHC. Our results are derived from a fully differential partonic MonteCarlo calculation with stable top quarks which involves no approximations beyond the fixed-order truncation of the perturbation series. The NNLO corrections improve the agreement between existing LHC measurements [V. Khachatryan etal. (CMS Collaboration), Eur. Phys. J. C 75, 542 (2015)] and standard model predictions for the top-quark transverse momentum distribution, thus helping alleviate one long-standing discrepancy. The shape of the top-quark pair invariant mass distribution turns out to be stable with respect to radiative corrections beyond NLO which increases the value of this observable as a place to search for physics beyond the standard model. The results presented here provide essential input for parton distribution function fits, implementation of higher-order effects in MonteCarlo generators, as well as top-quark mass and strong coupling determination.

Weight function method for precise determination of top quark mass at Large Hadron Collider

We propose a new method to measure a theoretically well-defined top quark mass at the LHC. This method is based on the “weight function method,” which we proposed in our preceding paper. It requires only lepton energy distribution and is basically independent of the production process of the top quark. We perform a simulation analysis of the top quark mass reconstruction with tt¯ pair production and lepton + jets decay channel at the leading order. The estimated statistical error of the top quark mass is about 0.4 GeV with an integrated luminosity of 100 fb−1 at s=14 TeV. We also estimate some of the major systematic uncertainties and find that they are under good control.

Determination of the top quark mass circa 2013: methods, subtleties, perspectives

We present an up-to-date overview of the problem of top quark mass determination. We assess the need for precision in the top mass extraction in the LHC era together with the main theoretical and experimental issues arising in precision top mass determination. We collect and document existing results on top mass determination at hadron colliders and map the prospects for future precision top mass determination at e+e- colliders. We present a collection of estimates for the ultimate precision of various methods for top quark mass extraction at the LHC.

Top quark mass measurements at and above threshold at CLIC

We present a study of the expected precision of the top quark mass determination, measured at a linear e+ e- collider based on CLIC technology. GEANT4-based detector simulation and full event reconstruction including realistic physics and beam-induced background levels are used. Two different techniques to measure the top mass are studied: The direct reconstruction of the invariant mass of the top quark decay products and the measurement of the mass together with the strong coupling constant in a threshold scan, in both cases including first studies of expected systematic uncertainties. For the direct reconstruction, experimental uncertainties around 100 MeV are achieved, which are at present not matched by a theoretical understanding on a similar level. With a threshold scan, total uncertainties of around 100 MeV are achieved, including theoretical uncertainties in a well-defined top mass scheme. For the threshold scan, the precision at ILC is also studied to provide a comparison of the two linear collider technologies.

The short-term strategy and plan for t anti-t and single-top at the LHC

This paper is intended to give an overview of first t¯t and single-top physics results that the CMS and ATLAS Collaborations are going to provide with the early data. Particular attention is given to the determination of the t¯t crosssection and to the observation of the single top process at LHC. Early results on top quark mass determination are also discussed.

Top quark production near threshold and the top quark mass

We consider top-anti-top production near threshold in e + e − collisions, resumming Coulomb-enhanced corrections at next-to-next-to-leading order (NNLO). We also sum potentially large logarithms of the small top quark velocity at the next-to-leading logarithmic level using the renormalization group. The NNLO correction to the cross section is large, and it leads to a significant modification of the peak position and normalization. We demonstrate that an accurate top quark mass determination is feasible if one abandons the conventional pole mass scheme and if one uses a subtracted potential and the corresponding mass definition. Significant uncertainties in the normalization of the t t ̄ cross section, however, remain.

Heavy quark results at DØ

Recent results on heavy quark physics from the DØ experiment at the Fermilab Tevatron Collider are reported. Topics included are top quark production and mass determination, bottom production and correlations, and charmonium production.

Top quark production in the reaction $e^+e^- \longrightarrow e\nu tb$ at linear collider energies

The complete tree-level cross sections for the reaction e +e− →e?tb are computed for top masses of 160 to 200 GeV at center-of-mass energies between 0.2 and 2.0 TeV using the packages CompHEP and GRACE. It is demonstrated that tt -pair production dominates around $sqrt s=0.5$ TeV, whereas soft photon t-channel exchange contributions grow with increasing energy such that above 1.5 TeV it dominates. Detailed cross section considerations close to the tt threshold reveals some peculiar properties. It is shown that a precise top quark mass determination is not significantly hampered by the existence of non-tt diagrams. With desirable assumptions on linear collider luminosities the CKM matrix element | V tb | might be measured best at or close to $sqrt s=2$ TeV.

Hard gluon radiation and the top mass value from CDF

The effect of hard gluon radiation on the top quark mass determination at Tevatron energies is studied. An expectation value 〈 Δm 〉 for the correction implied on m top is defined, and it is shown that the hard gluon effect is of the order of GeV. Quantitative numerical results are obtained on the basis of the complete higher order matrix elements for production and decay of the top quark.