Quark Spin Correlations Research Articles

Global tensor polarization of spin 3/2 hadrons and quark spin correlations in relativistic heavy ion collisions

We study the global polarization of spin-3/2 hadrons in relativistic heavy ion collisions. We show in particular that the global tensor polarizations of rank two or three for spin-3/2 hadrons are sensitive to the local two or three quark spin correlations respectively in the quark gluon plasma produced in the collision processes. We present the relationships between these measurable tensor polarizations and quark spin correlations in the quark matter system. Published by the American Physical Society 2024

Binned top quark spin correlation and polarization observables for the LHC at 13.6 TeV

We consider top-antitop quark (tt¯) production at the Large Hadron Collider (LHC) with subsequent decays into dileptonic final states. We use and investigate a set of leptonic angular correlations and distributions with which all the independent coefficient functions of the top-spin-dependent parts of the tt¯ production spin density matrices can be experimentally probed. We compute these observables for the LHC center-of-mass energy 13.6 TeV within the Standard Model at next-to-leading order in the QCD coupling including the mixed QCD weak corrections. We determine also the tt¯ charge asymmetry where we take in addition also the mixed QCD-QED corrections into account. In addition we analyze and compute possible new physics (NP) effects on these observables within effective field theory in terms of a gauge-invariant effective Lagrangian that contains the operators up to mass dimension six that are relevant for hadronic tt¯ production. First, we compute our observables inclusive in phase space. Then, in order to investigate which region in phase space has, for a specific observable, a high NP sensitivity, we determine our observables also in two-dimensional (Mtt¯,cosθt*) bins, where Mtt¯ denotes the tt¯-invariant mass and θt* is the top quark scattering angle in the tt¯ zero-momentum frame. Published by the American Physical Society 2024

Global quark spin correlations in relativistic heavy ion collisions

The observation of the vector meson’s global spin alignment by the STAR Collaboration reveals that strong spin correlations may exist for quarks and antiquarks in relativistic heavy-ion collisions in the normal direction of the reaction plane. We propose a systematic method to describe such correlations in the quark matter. We classify them as local and long range quark spin correlations in the system. We show in particular that the effective quark spin correlations contain the genuine spin correlations originated directly from the dynamical process as well as those induced by averaging over other degrees of freedom. We also show that such correlations can be studied by measuring the vector meson’s spin density matrix and hyperon-hyperon and hyperon-anti-hyperon spin correlations. We present the relationships between these measurable quantities and spin correlations of quarks and antiquarks. Published by the American Physical Society 2024

Properties of the Top Quark

Recent measurements of the properties of the top quark at the CERN Large Hadron Collider are discussed. The results were measured for single and top quark pair production in their final states, including jets with either one or two leptons or only in hadronic final states. Top quark properties include angular correlations, top quark spin correlations, mass, and width. When looking towards the future, top quark properties open new and even interdisciplinary avenues for probing quantum information science.

Top quark properties and mass measurements with the ATLAS detector

Highlights on recent measurements of top quark properties in ATLAS, using pp collision data at s = 8 TeV and 13 TeV, are presented. The measurements of the top quark polarization and spin correlation coefficients, the W boson helicity fractions, the structure of the Wtb vertex, the associated production of a tt‾ pair with a vector boson or a photon, and the top quark mass are all in agreement with the Standard Model expectations.

Associated production of Higgs boson and tt̄ at LHC**Supported by National Natural Science Foundation of China(11275114, 11325525 and 11305075) and Natural Science Foundation of Shandong Province (ZR2013AQ006)

One of the future goals of the LHC is to precisely measure the properties of the Higgs boson. The associated production of a Higgs boson and top quark pair is a promising process to investigate the related Yukawa interaction and the properties of the Higgs. Compared with the pure scalar sector in the Standard Model, the Higgs sector contains both scalars and pseudoscalars in many new physics models, which makes the tt̄H interaction more complex and provides a variety of phenomena. To investigate the tt̄H interaction and the properties of the Higgs, we study the top quark spin correlation observables at the LHC.

Measurement of spin correlation between top and antitop quarks produced in pp¯ collisions at s=1.96 TeV

We present a measurement of the correlation between the spins of t and t¯ quarks produced in proton–antiproton collisions at the Tevatron Collider at a center-of-mass energy of 1.96 TeV. We apply a matrix element technique to dilepton and single-lepton+jets final states in data accumulated with the D0 detector that correspond to an integrated luminosity of 9.7fb−1. The measured value of the correlation coefficient in the off-diagonal basis, Ooff=0.89±0.22(stat+syst), is in agreement with the standard model prediction, and represents evidence for a top–antitop quark spin correlation difference from zero at a level of 4.2 standard deviations.

Top quark spin correlations and polarization at the LHC: Standard model predictions and effects of anomalous top chromo moments

A number of top-spin observables are computed within the Standard Model (SM), at next-to-leading order in the strong and weak gauge couplings for hadronic top-quark anti-quark (tt¯) production and decay at the LHC for center-of-mass energies 7 and 8 TeV. For dileptonic final states we consider the azimuthal angle correlation, the helicity correlation, and the opening angle distribution; for lepton plus jets final states we determine distributions and asymmetries that trace a longitudinal and transverse polarization, respectively, of the t and t¯ samples. The QCD-induced transverse polarization of the top quarks leads to an asymmetry of about 8% that should be detectable with existing data. In addition, we investigate the effects of a non-zero chromo-magnetic and chromo-electric dipole moment of the top quark on these and other top-spin observables and associated asymmetries. These observables allow to disentangle the contributions from the real and imaginary parts of these moments.

A new twist on top quark spin correlations

Top-antitop pairs produced at hadron colliders are largely unpolarized, but their spins are highly correlated. The structure of these correlations varies significantly over top production phase space, allowing very detailed tests of the Standard Model. Here, we explore top quark spin correlation measurement from a general perspective, highlighting the role of azimuthal decay angles. By taking differences and sums of these angles about the top-antitop production axis, the presence of spin correlations can be seen as sinusoidal modulations resulting from the interference of different helicity channels. At the LHC, these modulations exhibit nontrivial evolution from near-threshold production into the boosted regime, where they become sensitive to almost the entire QCD correlation effect for centrally produced tops. We demonstrate that this form of spin correlation measurement is very robust under full kinematic reconstruction, and should already be observable with high significance using the current LHC data set. We also illustrate some novel ways that new physics can alter the azimuthal distributions. In particular, we estimate the power of our proposed measurements in probing for anomalous color-dipole operators, as well as for broad resonances with parity-violating couplings. Using these methods, the 2012 run of the LHC may be capable of setting simultaneous limits on the top quark’s anomalous chromomagnetic and chromoelectric dipole moments at the level of 3 × 10−18 cm (0.03/m t ).

Top Quark Polarization and Spin Correlation in the Littlest Higgs Model with T-Parity at the ILC

In the framework of the littlest Higgs model with T-parity (LHT), we study the top quark spin correlation and polarization at the International Linear Collider (ILC). We find that the top quark polarization asymmetry δPt and the left-right asymmetry δALR can respectively reach −35% and −37.5% for √s = 500 GeV and √s = 1000 GeV via e+e− collision, which can reach the observable level at the ILC. By contrast, the spin correlation δC is smaller. The correlation behaviors of these observables at the e+e− collision and the γγ collision will be helpful to distinguish different models and test the LHT model at the ILC.

W helicity, top quark spin and charge

An overview of the recent measurements of top quark charge, spin correlations, and top quark and W boson polarisation in tevents is presented. The measurements were performed at the Fermilab Tevatron collider in p ¯ p collision data at p s = 1:96 TeV by the CDF and D0 experiments and in pp collision data at p s = 7 TeV by the ATLAS and CMS experiments

Top quark spin correlations at the Tevatron and the LHC

Spin correlations of top quarks produced in hadron collisions have not been observed experimentally with large significance. In this Letter, we propose a new variable that may enable demonstration of the existence of spin correlations with 3–4 σ significance using just a few hundred dilepton events both at the Tevatron and the LHC. Such number of dilepton events has been observed at the Tevatron. At the LHC, it will become available once integrated luminosity of a few hundred inverse picobarns is collected.

New physics effects on top quark spin correlation and polarization at the LHC: A comparative study in different models

Extensions of the standard model often predict new chiral interactions for top quarks, which will contribute to top quark spin correlation and polarization in $t\overline{t}$ production at the LHC. In this work, under the constraints from the current Tevatron measurements, a comparative study of the spin correlation and polarization is performed in three new physics models: the minimal supersymmetric model without R-parity, the third-generation enhanced left-right model, and the axigluon model. We find that the polarization asymmetry may be enhanced to the accessible level in all these models, while the correction to the spin correlation may be detectable in the axigluon model and the minimal supersymmetric model without R-parity with ${\ensuremath{\lambda}}^{\ensuremath{'}\ensuremath{'}}$ couplings.

Color Sextet Scalars in Early LHC Experiments

We explore the potential for discovery of an exotic color sextet scalar in same-sign top quark pair production in early running at the LHC. We present the first phenomenological analysis at colliders of color sextet scalars with full top quark spin correlations included. We demonstrate that one can measure the scalar mass, the top quark polarization, and confirm the scalar resonance with 1 fb⁻¹ of integrated luminosity. The top quark polarization can distinguish gauge triplet and singlet scalars.

Influence of graviton on top-antitop production at the LHC

We examine the top quark production in the brane world scenario. We study two typical models - the model proposed by Arkani-Hamed, Dimopoulos and Dvali (ADD) and the model of Randall and Sundrum (RS). In addition to the Standard Model processes, there is a new contribution to the top-antitop pair production process mediated by graviton Kaluza-Klein modes in the s-channel. We calculated the density matrix for the top-antitop pair production including the new contribution. With a reasonable parameter choice, we find a sizable deviation of the top-antitop quark spin correlations from those in the Standard Model.

Top quark spin correlations in the Randall-Sundrum model at the CERN Large Hadron Collider

In the Randall-Sundrum model, we study top-antitop pair production and top spin correlations at the Large Hadron Collider. In addition to the standard model processes, there is a new contribution to the top-antitop pair production process mediated by graviton Kaluza-Klein modes in the $s$-channel. We calculate the density matrix for the top-antitop pair production including the new contribution. With a reasonable parameter choice in the Randall-Sundrum model, we find a sizable deviation of the top-antitop pair production cross section and the top spin correlations from those in the standard model. In particular, resonant productions of the graviton Kaluza-Klein modes give rise to a remarkable enhancement of such a deviation.

Top quark pair production and decay at a polarized photon collider

Top quark pair production by (polarized) γγ collisions offers an interesting testing ground of the Standard Model and its extensions. In this Letter we present results for differential cross sections of top quark pair production and decay including QCD radiative corrections. We take into account the full dependence on the top quark spins. We give analytic and numerical results for single and double differential angular distributions of tt¯ decay products which are due to top quark polarizations and spin correlations in the intermediate state.

Maximizing the spin correlation of top quark pairs produced at the large hadron collider

The measurement of top quark spin correlation is an important tool for precise studies of top quark interactions. In this Letter I construct a quantization axis maximizing the spin correlation at the LHC within the Standard Model. Using this axis a spin correlation of 48% or even more, on applying additional cuts, can be reached. This represents a significant improvement compared to the helicity bases studied thus far.

Top quark spin correlations in theories with large extra dimensions at the CERN Large Hadron Collider

In theories with large extra dimensions, we study the top-spin correlations at the Large Hadron Collider. The $s$-channel process mediated by graviton Kaluza-Klein modes contributes to the top-antitop pair production in addition to the standard model processes, and affects the resultant top-spin correlations. We calculated the full density matrix for the top-antitop pair production. With the fundamental scale of the extra dimensional theory below 2 TeV, we find a sizable deviation of the top-spin correlations from the standard model one.

Top quark pair production and decay at hadron colliders

In ongoing and upcoming hadron collider experiments, top quark physics will play an important role in testing the Standard Model and its possible extensions. In this work we present analytic results for the differential cross sections of top quark pair production in hadronic collisions at next-to-leading order in the QCD coupling, keeping the full dependence on the spins of the top quarks. These results are combined with the corresponding next-to-leading order results for the decay of polarized top quarks into dilepton, lepton plus jets, and all jets final states. As an application we predict double differential angular distributions which are due to the QCD-induced top quark spin correlations in the intermediate state. In addition to the analytic results, we give numerical results in terms of fit functions that can easily be used in an experimental analysis.