Top Quark Research Papers - Academia.edu (original) (raw)

2025, Physical Review Letters

Evidence is presented for the associated production of a single top quark and W boson in pp collisions at ffiffi ffi s p ¼ 7 TeV with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 4:9 fb À1 . The measurement is performed using events with two leptons and a jet originated from a b quark. A multivariate analysis based on kinematic properties is utilized to separate the t t background from the signal. The observed signal has a significance of 4:0 and corresponds to a cross section of 16 þ5 À4 pb, in agreement with the standard model expectation of 15:6 AE 0:4 þ1:0 À1:2 pb.

2025, Physical Review D

The combination of searches performed by the CDF and D0 collaborations at the Fermilab Tevatron Collider for neutral Higgs bosons produced in association with b quarks is reported. The data, corresponding to 2.6 fb -1 of integrated luminosity at CDF and 5.2 fb -1 at D0, have been collected in final states containing three or more b jets. Upper limits are set on the cross section multiplied by the branching ratio varying between 44 pb and 0.7 pb in the Higgs boson mass range 90 to 300 GeV, assuming production of a narrow scalar boson. Significant enhancements to the production of Higgs bosons can be found in theories beyond the standard model, for example in supersymmetry. The results are interpreted as upper limits in the parameter space of the minimal supersymmetric standard model in a benchmark scenario favoring this decay mode.

2025, The European Physical Journal C

The top-quark mass is measured in proton-proton collisions at √ s = 7 TeV using a data sample corresponding to an integrated luminosity of 5.0 fb -1 collected by the CMS experiment at the LHC. The measurement is performed in the dilepton decay channel tt → ( + ν b) ( -ν b), where = e, μ. Candidate top-quark decays are selected by requiring two leptons, at least two jets, and imbalance in transverse momentum. The mass is reconstructed with an analytical matrix weighting technique using distributions derived from simulated samples. Using a maximum-likelihood fit, the top-quark mass is determined to be 172.5 ± 0.4 (stat.) ± 1.5 (syst.) GeV.

2025, Physical Review Letters

Results are presented from a search for the pair production of third-generation scalar and vector leptoquarks, as well as for top squarks in R-parity-violating supersymmetric models. In either scenario, the new, heavy particle decays into a lepton and a b quark. The search is based on a data sample of pp collisions at ffiffi ffi s p ¼ 7 TeV, which is collected by the CMS detector at the LHC and corresponds to an integrated luminosity of 4:8 fb À1 . The number of observed events is found to be in agreement with the standard model prediction, and exclusion limits on mass parameters are obtained at the 95% confidence level. Vector leptoquarks with masses below 760 GeV are excluded and, if the branching fraction of the scalar leptoquark decay to a lepton and a b quark is assumed to be unity, third-generation scalar leptoquarks with masses below 525 GeV are ruled out. Top squarks with masses below 453 GeV are excluded for a typical benchmark scenario, and limits on the coupling between the top squark, lepton, and b quark, 0 333 are obtained. These results are the most stringent for these scenarios to date.

2025, Physical Review Letters

2025, The European Physical Journal C

2025

Radiative corrections to the process of the top quark decay t --> bl + nul (gamma) are revisited. Complete one-loop electroweak corrections are calculated within the SANC system. Various distributions are produced by means of Monte Carlo integrator and events generator. Comparison with the re- sults of CompHEP and PYTHIA packages are presented for Born and hard photon contributions.

2025, Physics Letters B

A search for events with one jet and at most one isolated lepton used data taken at LEP-2 by the DELPHI detector. These data were accumulated at a center-of-mass energy of 183 GeV and correspond to an integrated luminosity of 47.7 pb -1 . Production of single scalar and vector leptoquarks was searched for. Limits at 95% confidence level were derived on the masses (ranging from 134 GeV/c 2 to 171 GeV/c 2 for electromagnetic type couplings) and couplings of the leptoquark states. A search for top-charm flavour changing neutral currents (e + e -→ tc or charge conjugate) used the semileptonic decay channel. A limit on the flavour changing cross-section via neutral currents was set at 0.55pb (95% confidence level).

2025, Nuclear Physics B

During the 1992 running period of the LEP e + e ; collider, the DELPHI experiment accumulated approximately 24 pb ;1 of data at the Z 0 peak. The decays into hadrons and charged leptons have been analysed to give v alues for the cross sections and leptonic forward-backward asymmetries which are sig-ni cantly improved with respect to those previously published by the DELPHI collaboration. Incorporating these new data, more precise values for the Z 0 res-onance parameters are obtained from model{independent ts. The results are interpreted within the framework of the Standard Model, yielding for the top quark mass m t = 1 5 7 +36 ;48 (expt:) +19 ;20 (Higgs) GeV, and for the e ective mixing angle sin 2 lept eff = 0 :2328 0:0013(expt:) +0:0001 ;0:0003 (Higgs), where (Higgs) repre- sents the variation due to Higgs boson mass in the range 60 to 1000 GeV, with central value 300 GeV.

2025, Zeitschrift für Physik C Particles and Fields

A measurement of the strange quark forward{backward asymmetry at the Z 0 peak was performed using 718,000 multihadronic Z 0 decays collected by the DELPHI detector at LEP in 1992. The s quark was tagged by the presence of high momentum charged kaons identied by the Ring Imaging Cherenkov detector and by 0 's decaying into p . The s quark purity obtained was estimated for the two hadrons to be 43%. The average s quark asymmetry was found to be 0:131 0:035 (stat:) 0:013 (syst:). The forward{backward asymmetry was measured for unresolved d and s quarks, tagged by the detection of a high energy neutron or neutral kaon in the Hadron Calorimeter. The combined d and s quark purity w as 69% and their asymmetry was found to be 0:112 0:031 (stat:) 0:054 (syst:).

2025, Physical Review D

We argue that a relatively light massive gluon with mass 1 TeV, small purely axial couplings to light quarks and sizable vector and axial couplings to the top quark can reproduce the large forward-backward asymmetry observed at the Tevatron without conflicting with the t t and the dijet invariant mass distributions measured at the Tevatron and the LHC. We show that realistic Higgsless models with warped extra dimensions naturally fulfil all the necessary ingredients to realize this scenario. While current data is unable to discover or exclude these heavy gluons with masses ≈ 850 GeV, they should be observed at the (7 TeV) LHC with a luminosity 300 pb -1 .

2025, Physical Review Letters

R. M. Keup,(') H. Keutelian,(4) D. Kim,c4) S. Kim,(19) L. Kirsch,(l) K. Kondo,(19) J. KoGgsberg,(e) E. Kovac~,(~) S. E. Kuhlmann,(') E. KuIx,('~) A. T. Laa~anen,('~) J. I. Lmoureux,(2l)

2025, The European Physical Journal C

A measurement of the production cross-section for top quark pairs (t t) in pp collisions at √ s = 7 TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in two different topologies: single lepton (electron e or muon μ) with large missing transverse energy and at least four jets, and dilepton (ee, μμ or eμ) with large missing transverse energy and at least two jets. In a data sample of 2.9 pb -1 , 37 candidate events are observed in the single-lepton topology and 9 events in the dilepton topology. The corresponding expected backgrounds from non-t t Standard Model processes are estimated using data-driven methods and determined to be 12.2 ± 3.9 events and 2.5 ± 0.6 events, respectively. The kinematic properties of the selected events are consistent with SM t t production. The inclusive top quark pair production cross-section is measured to be σ t t = 145 ± 31(stat.) +42 -27 (syst.) pb. The measurement agrees with perturbative QCD calculations.

2025, Physics Letters B

Many extensions of the Standard Model involve two Higgs doublet fields to break the electroweak symmetry, leading to the existence of three neutral and two charged Higgs particles. In particular, this is the case of the Minimal Supersymmetric extension of the Standard Model, the MSSM. A very important parameter is tan β defined as the ratio of the vacuum expectation value of the two Higgs doublets. In this paper we focus on the leftright asymmetry in the production of polarised top quarks in association with charged Higgs bosons at the LHC. This quantity allows for a theoretically clean determination of tan β. In the MSSM, the asymmetry remains sensitive to the strong and electroweak radiative corrections and, thus, to the superparticle spectrum. Some possible implications of these results are discussed.

2025, Physics Letters …

Laboratoire de Physique Nucléaire et de Hautes Energies.

2025

We propose that the nontrivial zeros of the Riemann zeta function represent fundamental modes of the quantum vacuum, capable of inducing curvature in spacetime. This hypothesis is formulated through a Lagrangian extension incorporating a discrete spectral dependence, wherein the oscillations associated with these zeros couple to the metric and generate observable gravitational effects. Furthermore, we construct a spectral formulation based on operators whose spectrum reproduces the zeros, linking spacetime geometry to spectral invariants. This proposal is validated through two complementary approaches: (i) a direct numerical evaluation of the discrete action functional over tabulated Riemann zeros, and (ii) an empirical comparison with the angular spectrum of the Cosmic Microwave Background (CMB). Both lines of analysis exhibit nontrivial correlations in shape, structure, and spectral peaks, suggesting a deep connection between number theory and the quantum geometry of the universe.

2025, Physics Letters B

Results are presented from a search for a W boson using a dataset corresponding to 5.0 fb -1 of integrated luminosity collected during 2011 by the CMS experiment at the LHC in pp collisions at √ s = 7 TeV. The W boson is modeled as a heavy W boson, but different scenarios for the couplings to fermions are considered, involving both lefthanded and right-handed chiral projections of the fermions, as well as an arbitrary mixture of the two. The search is performed in the decay channel W → tb, leading to a final state signature with a single electron or muon, missing transverse energy, and jets, at least one of which is identified as a b-jet. A W boson that couples to the right-handed (left-handed) chiral projections of the fermions with the same coupling constants as the W is excluded for masses below 1.85 (1.51) TeV at the 95% confidence level. For the first time using LHC data, constraints on the W gauge couplings for a set of left-and right-handed coupling combinations have been placed. These results represent a significant improvement over previously published limits.

2025

We present a search for tt production in events having dielectron final states in 120.2 ± 6.5 pb -1 of pp collisions at s = 1.8 TeV using the DØ detector. This analysis has been optimized to search for a heavy top quark (ie. m top > 140 GeV/c 2 ). One candidate event is seen with a background estimated to be 0.82 ± 0.08 events, giving a cross section of 0.9 ± 5.0 pb if m top = 170 GeV/c 2 . Therefore, no conclusive evidence for top production is seen in this channel. Assuming the candidate is not top, we obtain an upper limit to the dielectron branching ratio for tt events to be < 3.8 % at the 95% confidence level if m top = 170 GeV/c 2 . In the process of this analysis we have studied the reponse of the DØ U/LAr calorimeter to jets using direct photon candidate events. A number of systematics have been studied which result in a cumulative systematic error which varies from 5% at low and high energy ( GeV and 500 GeV, respectively) to 2% at 80 GeV. The response to jets relative to the electromagnetic scale is found to behave as 0.77 + 0.024 * ln(E jet ) as expected from test beam and Monte Carlo studies. ii This dissertation is dedicated to my parents, Cassandra, Albert and Robert, and to my brother Anthony. iii The Road goes ever on and on Down from the door where it began. Now far ahead the Road has gone, And I must follow, if I can, Pursuing it with weary feet, Until it joins some other way, Where many paths and errands meet. And whither then? I cannot say. Fellowship of the Ring, J. R. R. Tolkien When I heard the learn'd astronomer, When the proofs, the figures, were ranged in columns before me, When I was shown the charts and diagrams, to add, divide, and measure t h e m , When I sitting heard the astronomer where he lectured with much applause in the lecture-room. How soon unaccountable I became tired and sick, Till rising and gliding out I wander'd off by myself, In the mystical moist night-air, and from time to time, Look'd up in perfect silence at the stars. Leaves of Grass, Walt Whitman i v TABLE OF CONTENTS 1 INTRODUCTION .

2025, Physical Review Letters

A search for new phenomena in t " t events with large missing transverse momentum in proton-proton collisions at a center-of-mass energy of 7 TeV is presented. The measurement is based on 1:04 fb À1 of data collected with the ATLAS detector at the LHC. Contributions to this final state may arise from a number of standard model extensions. The results are interpreted in terms of a model where new top-quark partners are pair produced and each decay to an on-shell top (or antitop) quark and a long-lived undetected neutral particle. The data are found to be consistent with standard model expectations. A limit at 95% confidence level is set excluding a cross section times branching ratio of 1.1 pb for a top-partner mass of 420 GeV and a neutral particle mass less than 10 GeV. In a model of exotic fourth generation quarks, toppartner masses are excluded up to 420 GeV and neutral particle masses up to 140 GeV.

2025, Physical Review Letters

A search for direct pair production of supersymmetric top squarks ( t1 ) is presented, assuming the t1 decays into a top quark and the lightest supersymmetric particle, 0 1 , and that both top quarks decay to purely hadronic final states. A total of 16 (4) events are observed compared to a predicted standard model background of 13:5 þ3:7 À3:6 ð4:4 þ1:7 À1:3 Þ events in two signal regions based on R Ldt ¼ 4:7 fb À1 of pp collision data taken at ffiffi ffi s p ¼ 7 TeV with the ATLAS detector at the LHC. An exclusion region in the t1 versus 0 1 mass plane is evaluated: 370 < m t1 < 465 GeV is excluded for m 0 1 $ 0 GeV while m t1 ¼ 445 GeV is excluded for m 0 1 50 GeV.

2025, Physical Review D

We present a measurement of the elastic differential cross section dσ(pp → pp)/dt as a function of the four-momentum-transfer squared t. The data sample corresponds to an integrated luminosity of ≈ 31 nb -1 collected with the D0 detector using dedicated Tevatron pp Collider operating conditions at √ s = 1.96 TeV and covers the range 0.26 < |t| < 1.2 GeV 2 . For |t| < 0.6 GeV 2 , dσ/dt is described by an exponential function of the form Ae -b|t| with a slope parameter b = 16.86 ± 0.10 (stat) ± 0.20 (syst) GeV -2 . A change in slope is observed at |t| ≈ 0.6 GeV 2 , followed by a more gradual |t| dependence with increasing values of |t|.

2025, Physical Review D

We determine the top quark mass mt using tt pairs produced in the DØ detector by √ s = 1.8 TeV pp collisions in a 125 pb -1 exposure at the Fermilab Tevatron. We make a two constraint fit to mt in tt → bW + bW -final states with one W boson decaying to qq and the other to eν or µν. Likelihood fits to the data yield mt(l + jets) = 173.3 ± 5.6 (stat) ± 5.5 (syst) GeV/c 2 . When this result is combined with an analysis of events in which both W bosons decay into leptons, we obtain mt = 172.1 ± 5.2 (stat) ± 4.9 (syst) GeV/c 2 . An alternate analysis, using three constraint fits to fixed top quark masses, gives mt(l + jets) = 176.0 ± 7.9 (stat) ± 4.8 (syst) GeV/c 2 , consistent with the above result. Studies of kinematic distributions of the top quark candidates are also presented.

2025, arXiv (Cornell University)

The ratio of the vacuum expectation value of the two Higgs doublets, tan β, is an important parameter of the general 2-Higgs-Doublet Model (2HDM) and the Minimal Supersymmetric extension of the Standard Model (MSSM). The expected uncertainty on the determination of tan β at a Linear Collider (LC) of at least 500 GeV center-of-mass energy and high luminosity is reviewed based on studies of neutral and charged Higgs boson production.

2025, Modern Physics Letters A

We review the present status of the QCD corrected cross-sections and kinematic distributions for the production of a Higgs boson in association with bottom quarks at the Fermilab Tevatron and CERN Large Hadron Collider. Results are presented for the Minimal Supersymmetric Standard Model where, for large tan β, these production modes can be greatly enhanced compared to the Standard Model case. The next-to-leading order QCD results are much less sensitive to the renormalization and factorization scales than the lowest order results, but have a significant dependence on the choice of the renormalization scheme for the bottom quark Yukawa coupling. We also investigate the uncertainties coming from the Parton Distribution Functions and find that these uncertainties can be comparable to the uncertainties from the remaining scale dependence of the next-to-leading order results. We present results separately for the different final states depending on the number of bottom quarks identified.

2025

The recent CDF-II measurement of the W boson mass reports M CDF W = 80.4335 ± 0.0094 GeV, significantly higher than the Standard Model (SM) prediction M SM W = 80.357 ± 0.004 GeV. We show that within the Helix-Light-Vortex (HLV) framework, a natural geometric rescaling of the electroweak sector arises: a spiral-time correction A = 1 + ε and a stationary U 3 -mode induce effective shifts of the Higgs vacuum expectation value v eff . This yields ) , which accounts for the observed anomaly without introducing new particles. We present quantitative estimates, discuss renormalization-group effects, and propose collider observables that distinguish this geometric origin from conventional beyond-SM scenarios.

2025

2025, Physical Review Letters

2025, Physical Review D

2025, Physical Review A

Evaluations of parity-violating and charge-parityviolating effects in heavy one-valence-electron atoms, employing the Hartree-Fock potential and several model potentials, are extended to include first-order electron-electron Coulomb corrections using many-body perturbation theory. Parity- conserving quantities, including valence energies, hyperfine splittings, and oscillator strengths, are also calculated and compared with experiment to determine the reliability of the weak-interaction calculations. It is found that the spread between calculations carried out in first-order perturbation theory starting from different potentials is of the same order of magnitude as the spread between the corresponding lowest-order evaluations. It is concluded that second-order many-body perturbation theory must give significant contributions. Some technical problems associated with going to second order are discussed. Presumably, this spread will vanish as higher-and-higher- order perturbations are included. For this purpose we em- ploy three model potentials (described in the Appendix) together with the Hartree-Fock potential. The principal result of our first-order calculations is that there is a great deal of sensitivity to core polarization, so that the spread in values between quantities calculated in first order start- ing from different potentials ranges up to 20%, compar- able to the spread found in lowest order. While somewhat better results were obtained for excited-state properties, due to the diminished effect of core polarization, it is clear that predictions of ground-state atomic properties at a level well under 10% will require the use of second- order perturbation theory and perhaps some form of in- finite summation. During the past decade, various many-body calculations of parity violation in heavy atoms have appeared, several of which go beyond the present calculations and include second-order correlation corrections. Closest to the present approach is the calculation of Martensson- Pendrill, which is a complete first-order calculation of the parity violation in Cs starting from a Hartree-Fock potential. The first-order parity-violating matrix element in Cs based on the Hartree-Pock potential in the present paper agrees very well with the result of Ref. 7. Indeed, such agreement is expected since the principal difference between the present calculation and that of Martensson- Pendrill concerns the way in which perturbation theory is implemented. %e also mention the elegant work of Dzu- ba et aI. on Cs which also starts with a Hartree-Fock po- tential and includes both firstand second-order correla- 34 1043 Qc1986 The American Physical Society -0.162 99 -0.095 57 -0.00644 -0.10200 -O.Q93 98 -0.007 12 -0.101 11 -0.06140 -0.002 29 -0.063 70 -0.04505 -0.002 12 -0.047 16 -0.044 56 -0.002 30 -0.046 86 -0.033 45 -0.00092 -0.034 37 -0.143 43 0.003 16 -0.14027 -0.09247 0.001 71 -0.09077 -0.088 92 -0.000 13 -0.08905 -0.058 27 O.OQ046 -0.057 81 -0.043 79 0.00026 -0.043 53 -0.042 70 -0.000 19 -0.042 89 -0.032 13 0.000 16 -0.031 97 -0.15348 0.022 58 -0.13090 -0.096 15 0.009 70 -0.08645 -0.094 80 0.008 98 -0.085 82 -0.062 15 0.005 31 -0.056 84 -0,045 70 0.003 20 -0.042 51 -0.045 26 0.003 00 -0.042 26 -0.033 82 0.002 11 -0.031 72 -0.14309 0.02608 -0.11701 -0.092 23 0.012 14 -0.08009 -0.089 15 0.01025 -0.07890 -0.05901 0.00607 -0.052 95 -0.04424 0,003 91 -0.040 33 -0.043 23 0,003 43 -0.039 80 -0.032 51 0.00243 -0.03007 Norcross -0.15345 0.011 96 -0.141 49 -0.096 31 0.005 27 -0.091 04 -0.09494 0.004 64 -0.090 31 -0.061 97 0.002 79 -0.059 18 -0.045 56 0.001 58 -0.043 98 -0.045 12 0.001 42 -0.043 70 -0.033 72 0.001 09 -0.032 63 -0.143 01 0.017 63 -0.125 38 -0.092 50 0.00924 -0.083 26 -0.089 28 0.007 42 -0.081 86 -0.058 83 0.004 19 -0.054 63 -0.044 10 0.002 78 -0.041 32 -0.043 07 0.002 33 -0.040 74 -0.032 40 0.001 67 -0.030 73 HF -0.13929 -0.090 82 -0.089 99 -0.58 70 -0.043 89 -0.043 60 -0.03244 -0.127 37 -0.085 62 -0.083 79 -0.055 19 -0.04202 -0.041 37 -0.03095 Expt. ' -0.153 51 -0.096 19 -0.095 11 -0.061 77 -0.045 45 -0.045 10 -O.Q33 62 -0.143 10 -0.092 17 -0.089 64 -0.058 65 -0.043 93 -0.043 10 -0.032 30 0th 1st Sum 0th 1st Sum 0th 1st Sum 0th 1st Sum 0th 1st Sum -0.370 79 -0.01442 -0.385 20 -0.18707 0.001 22 -0.185 86 -0.15907 0.00024 -0.158 83 -0.093 83 0.001 98 -0.091 85 -0.06441 0.000 67 -0.063 74 -0.369 75 0.088 79 -0.28096 -0.171 33 0.040 32 -0.13100 -0.144 23 0.023 20 -0.121 03 -0.092 67 0.007 54 -0.085 13 -0.063 13 0.005 76 -0.057 37 -0.377 98 0.10506 -0.272 92 -0.17626 0.049 22 -0.12704 -0.148 52 0.030 32 -0.11820 -0.095 24 0.01122 -0.08402 -0.06426 0.007 77 -0.05649 -0.274 61 -0.13379 -0.121 62 -0.083 22 -0.05644 -0.33904 -0.16882 -0.15143 -0.09079 -0.065 51 'M. A.

2025, Brazilian Journal of Physics

By using the Cheng, Sher and Yuan's anzats, we study the light Higgs Boson production associated with b quark production at TEVATRON using the 2HDM type III. We compare the simulations with experimental results coming from TEVATRON, finding valid ranges for the bb coupling. By using these results, we calculate the cross section for the process pp → b bh(b b) for the LHC collider.

2025, Physical Review Letters

A search is performed in pp collisions at ffiffi ffi s p ¼ 7 TeV for exotic particles decaying via WZ to final states with electrons and muons. The data sample corresponds to an integrated luminosity of approximately 5 fb À1 . No significant excess is observed in the data above the expected standard model background. Upper bounds at 95% confidence level are set on the production cross section of the W 0 boson described by the sequential standard model and on the W 0 WZ coupling. W 0 bosons with masses below 1143 GeV are excluded. Limits are also set in the context of low-scale technicolor models, under a range of assumptions concerning the model parameters.

2025, Journal of High Energy Physics

In this note we analyse the prospects of a future electron-positron collider in testing a particular realisation of a composite Higgs model encompassing partial compositeness, namely, the 4-Dimensional Composite Higgs Model. We study the main Higgs production channels for three possible energy stages and different luminosity options of such a machine and confront our results to the expected experimental accuracies in the various Higgs decay channels accessible herein and, for comparison, also at the Large Hadron Collider.

2025, Journal of High Energy Physics

We propose a four dimensional description of Composite Higgs Models which represents a complete framework for the physics of the Higgs as a pseudo-Nambu-Goldstone boson. Our setup captures all the relevant features of 5D models and more in general of composite Higgs models with partial compositeness. We focus on the minimal scenario where we include a single multiplet of resonances of the composite sector, as these will be the only degrees of freedom which might be accessible at the LHC. This turns out to be sufficient to compute the effective potential and derive phenomenological consequences of the theory. Moreover our simplified approach is well adapted to simulate these models at the LHC. We also consider the impact of non-minimal terms in the effective lagrangian which do not descend from a 5D theory and could be of phenomenological relevance, for example contributing to the S − parameter.

2025, Physics Letters B

We consider a description of propagators for particle resonances which takes into account the quantum mechanical interference due to the width of two or more nearby states that have common decay channels, by incorporating the effects arising from the imaginary parts of the one-loop self-energies. Depending on the couplings to the common decay channels, the interference effect, not taken into account in the usual Breit-Wigner approximation, can significantly modify the cross section or make the more long-lived resonance narrower. We give few examples of New Physics models for which the effect is sizable, namely a generic two and multiple Higgs model and neutral vector resonances in Higgsless models. Based on these results we suggest the implementation of a proper treatment of nearby resonances into Monte Carlo generators.

2025, Nuclear Physics B

The two{jet invariant mass spectrum as measured in the UA2 experiment is used to search for additional heavy vector bosons decaying to two{jets. The mass of an additional W boson that couples to fermions with a V + A form is constrained to be greater than 261 GeV to the 90% condence level. A limit on the production cross section of additional W and Z bosons is given as a function of the boson mass. A limit on the production of excited quarks is also given as a function of the excited quark mass.

2025, Zeitschrift für Physik C Particles and Fields

2025, Physics Reports

Dg ih qp sr tp vu xw y vg h tf Du i g g r t f Dg g w Dr u xw g g ir Uu xw w h g ed gf h ji lk nm eo p tq rk ni sm eo jt up ti v wp Dx ym h ji qp {z |i sq ¾ s¿ À ÁÀ sÂ PÃ "Ã $À ÅÄ µAE QÇ ÉÈ Â ËÊ ÍÌ ÏÎ ÑÐ ÓÒ µÀ VÔ ÉÇ ÖÕ ×Ð ØÕ ÑÌ 9Ê aÙ 9Ú QÐ «Ò "Ì ÏÎ ØÕ ÁÛ Ü sÝ À ÅÞ Ù Ïß Áß À ÁÕ «Õ ÑÙ àÐ 1á Qâ â ã Fä Óå å 9ae ae ae Ñç Øè Ïé 7ê 7ë Fç Øè Áá å 7ì 7í î í ï ï ð %

2025, Journal of High Energy Physics

A search is presented for a massive particle, generically referred to as a Z′, decaying into a $ {\mathrm{t}}\overline {\mathrm{t}} $ pair. The search focuses on Z′ resonances that are sufficiently massive to produce highly Lorentz-boosted top quarks, which yield collimated decay products that are partially or fully merged into single jets. The analysis uses new methods to analyze jet substructure, providing suppression of the non-top multijet backgrounds. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 5 fb−1. Upper limits in the range of 1 pb are set on the product of the production cross section and branching fraction for a topcolor Z′ modeled for several widths, as well as for a Randall-Sundrum Kaluza-Klein gluon. In addition, the result contrain any enhancement in $ {\mathrm{t}}\overline {\mathrm{t}} $ production beyond expectations of the standard mode for tt invariant mass lar...

2025, Physical Review Letters

This paper was published online on 17 November 2010 with typographical errors in an author name in Refs. and. Reference [4] should read as ''U. Baur, I. Hinchliffe. . .' ' and Ref. [9] should read as ''E. Eichten, I Hinchliffe,. . ..'' The references have been corrected as of 6 January 2011. The references are incorrect in the printed version of the journal.

2025, Physical Review Letters

A search for pair-produced heavy vectorlike charge-2=3 quarks, T, in pp collisions at a center-of-mass energy of 7 TeV, is performed with the CMS detector at the LHC. Events consistent with the flavorchanging-neutral-current decay of a T quark to a top quark and a Z boson are selected by requiring two leptons from the Z-boson decay, as well as an additional isolated charged lepton. In a data sample corresponding to an integrated luminosity of 1:14 fb À1 , the number of observed events is found to be consistent with the standard model background prediction. Assuming a branching fraction of 100% for the decay T ! tZ, a T quark with a mass less than 475 GeV=c 2 is excluded at the 95% confidence level.

2025, Physical Review Letters

We have searched for first generation scalar leptoquark (LQ) pairs in the eν+jets channel using pp collider data ( Ldt ≈ 115 pb -1 ) collected by the DØ experiment at the Fermilab Tevatron during 1992-96. The analysis yields no candidate events. We combine the results with those from the ee+jets and νν+jets channels to obtain 95% confidence level (CL) upper limits on the LQ pair production cross section as a function of mass and of β, the branching fraction to a charged lepton. Comparing with the next-to-leading order theory, we set 95% CL lower limits on the LQ mass of 225, 204, and 79 GeV/c 2 for β = 1, 1 2 , and 0, respectively.

2025, Journal of Physics G: Nuclear and Particle Physics

We report the first measurements of inclusive W and Z boson cross sections times the corresponding leptonic branching ratios for pp collisions at √ s = 1.96 TeV based on the decays of the W and Z bosons into electrons and muons. The data were recorded with the CDF II detector at the Fermilab Tevatron and correspond to an integrated luminosity of 72.0 ± 4.3 pb -1 . We test e-µ lepton universality in W decays by measuring the ratio of the W → µν to W → eν cross sections and determine a value of 0.991 ± 0.004(stat.) ± 0.011(syst.) for the ratio of W -ℓ-ν couplings (gµ/ge). Since there is no sign of non-universality, we combine our cross section measurements in the different lepton decay modes and obtain σW ×Br(pp → W → ℓν) = 2.749 ± 0.010(stat.) ± 0.053(syst.) ± 0.165(lum.) nb and σ γ * /Z × Br(pp → γ * /Z → ℓℓ) = 254.9 ± 3.3(stat.) ± 4.6(syst.) ± 15.2(lum.) pb for dilepton pairs in the mass range between 66 GeV/c 2 and 116 GeV/c 2 . We compute the ratio R of the W → ℓν to Z → ℓℓ cross sections taking all correlations among channels into account and obtain R = 10.84 ± 0.15(stat.) ± 0.14(syst.) including a correction for the virtual photon exchange component in our measured γ * /Z → ℓℓ cross section. Based on the measured value of R, we extract values for the W leptonic branching ratio, Br(W → ℓν) = 0.1082 ± 0.0022; the total width of the W boson, Γ(W ) = 2092 ± 42 MeV; and the ratio of W and Z boson total widths, Γ(W )/Γ(Z) = 0.838 ± 0.017. In addition, we use our extracted value of Γ(W ) whose value depends on various electroweak parameters and certain CKM matrix elements to constrain the Vcs CKM matrix element, |Vcs| = 0.976± 0.030.

2025, Proceedings of The 39th International Conference on High Energy Physics — PoS(ICHEP2018)

2025, Physics Letters B

We explore the physics of a new neutral gauge boson, (Z ), coupling to only third-generation particles and with a mass near the electroweak gauge boson mass poles. A Z boson produced by top quarks and decaying to tau leptons is considered. With a simple search strategy inspired by existing analyses of the standard model gauge boson production in association with top quarks, we show that the Large Hadron Collider has good exclusionary power over the model parameter space of the Z boson even at the advent of the high-luminosity era. It is shown that the t tZ process allows one to place limits on right-handed top couplings with a Z boson that preferentially couples to third generation fermions, which are at present very weakly constrained.

2025, Physical Review Letters

Production of tt by gluon fusion followed by t bW+, t bW, and W -e -v, (v, ) is studied to extract the CP-violating chromoelectric dipole moment form factor of the top quark. The fact that the spin of the top quark, in its rest frame, is in the direction of the e+ momentum facilitates the analysis. Expressions for the diAerential cross section and decays are given. We find that at the Superconducting Super Collider or CERN Large Hadron Collider, it is possible to put a limit of 10 g, to 10 ' g, cm on these eA'ective couplings through the use of "optimal observables. " Naive observables such as simple triple product correlations are typically an order of magnitude less efrective.

2025, The European Physical Journal C

You will be contacted as soon as possible.