Looking for BSM physics using top-quark polarization and decay-lepton kinematic asymmetries

Godbole, Rohini M.; Mendiratta, Gaurav; Rindani, Saurabh D.

doi:10.1103/physrevd.92.094013

Cited by 16 publications

(14 citation statements)

References 86 publications

(128 reference statements)

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“…To a very good approximation the top quark decays as a free quark, because of the top quark lifetime of about 4.7 × 10 −25 s (corresponding to the width of 1.41 GeV) is too short for the top quark to bind with light quarks before it decays [61]. Furthermore, the maximally parity-violating two-body top-quark decay t → W + b enables us to analyze the top-quark polarization efficiently, which is in general non-zero if its production proceeds through some parity-violating interactions [38,39,[62][63][64][65][66][67][68][69][70][71][72][73][74].…”

Section: 2mentioning

confidence: 99%

General spin analysis from angular correlations in two-body decays

2020

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Determining the spin of any new particle and measuring its couplings to other particles and/or itself are crucial in reconstructing the structure of any quantum field theory containing the particle. A general helicity formalism is employed to describe the polarization of the particle Y in a two-body decay X2 → Y X1 with polarized X2 for the purpose of diagnosing the dynamical properties of three involved particles and for determining their spins altogether. We perform a general and comprehensive analytic analysis with our special focus on grasping fully how to connect the decay helicity amplitudes and decay distributions in the X2 rest frame and those in a laboratory frame with X2 moving with a non-zero velocity through Wick helicity rotation on helicity states and amplitudes. This theoretical framework is demonstrated in a detailed illustrative manner with the Standard Model (SM) processes, the sequential process e − e + → Z → τ − τ + followed by τ − → ρ − ντ → (π − π 0 )ντ and the sequential process e − e + → tt followed by t → W + b → (ℓ + ν ℓ )b-, and one non-standard decay process of a new vectorlike heavy top quark, T → Zt, followed by Z → ℓ − ℓ + . All the useful formulas directly applicable to any combinations of spins and any types of couplings in the two-body decay X2 → Y X1 followed by suitable Y two-body decays processes are collected and described in detail.On the high energy frontier, equipped with the Large Hadron Collider (LHC) [5], we are now probing the electroweak (EW) scale (v = 246 GeV) and beyond intensively and extensively after having established the SM by the decisive discovery of a Higgs boson [6,7] followed by very precise measurements of its mass and couplings [8,9] and model-independent determinations of its spinless nature [10][11][12][13][14][15]. The true theory for the origin and stability of the EW scale [16][17][18][19] beyond the SM is highly expected to be revealed with a huge amount of accumulated data.One generic prediction in most of new models is the presence of new particles partnered with some or all of the SM particles. For instance, every SM particle in low-energy supersymmetry (SUSY) [20-25] has a * choisy7@gmail.com † jeong229@jbnu.ac.kr ‡ sonjiho0@nate.com 1 Generally, azimuthal-angle correlations can be included in the analysis as well, but they involve quantum interference among the states with different helicities and require by far more complicated kinematic reconstructions [28]. For the sake of simple and straightforward kinematical analyses, we do not consider them here, postponing the analysis involving azimuthal-angle correlations as our later project.2 In principle any multi-body decay modes of the particle Y can be considered for extracting the information on Y polarization.As a consequence, the decay helicity amplitudes in the LAB for the two-body decay are related to those in the X 2 RF through two Wick helicity rotations on the Y and X 1 states as

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Section: 2mentioning

confidence: 99%

General spin analysis from angular correlations in two-body decays

2020

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“…5. The reference point for the corresponding asymmetry, A x 0 is chosen to be x 0 ,c = 0.5, i.e the value x 0 at the peak position in the SM [72].…”

Section: Charged Lepton Energymentioning

confidence: 99%

“…We use observables suggested in [68], but many of them were proposed long time ago in [65,69] and were used for several studies (see [67,[70][71][72][73]). In addition, we separate the study into two different categories; parton and particle level.…”

Section: Introductionmentioning

confidence: 99%

Probing anomalous Wtb couplings at the LHC in single t -channel top quark production

Jueid

2018

Phys. Rev. D

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We study the sensitivity of certain observables to the anomalous right tensorial coupling in single top production at the LHC at √ s = 13 TeV. The observables consist of asymmetries constructed from the energy and angles of the decay products of the top quark produced in single top production through t-channel. The computation is done at Leading Order (LO) and Next-to-Leading Order (NLO) in the strong coupling in the 5 flavor scheme. We have estimated projected limits on the anomalous coupling, both at the parton level without cuts and at the particle level with cuts. We find that the asymmetries are robust with respect to the higher order QCD corrections and are indeed a very good probe of this anomalous coupling of the top. Hence they can be be used as experimental probes of the same.

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“…For reviews see [6,7]. Some recent papers in the context of hadron colliders are [8][9][10][11][12][13][14][15][16][17][18][19][20][21]. For example, in Ref.…”

Section: Introductionmentioning

confidence: 99%

“…Refs. [18][19][20][21] suggest utilizing top polarization as a probe of models for the top forward-backward asymmetry observed at the Tevatron.…”

Section: Introductionmentioning

confidence: 99%

Polarization of top quark as a probe of its chromomagnetic and chromoelectric couplings in tW production at the Large Hadron Collider

Rindani

Sharma

Thomas

2015

J. High Energ. Phys.

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Abstract:We study the sensitivity of the Large Hadron Collider (LHC) to top quark chromomagnetic (CMDM) and chromoelectric (CEDM) dipole moments and W tb effective couplings in single-top production in association with a W − boson, followed by semileptonic decay of the top. The W t single-top production mode helps to isolate the anomalous ttg and W tb couplings, in contrast to top-pair production and other single-top production modes, where other new-physics effects can also contribute. We calculate the top polarization and the effects of these anomalous couplings on it at two centre-of-mass (cm) energies, 8 TeV and 14 TeV. As a measure of top polarization, we look at decay-lepton angular distributions in the laboratory frame, without requiring reconstruction of the rest frame of the top, and study the effect of the anomalous couplings on these distributions. We construct certain asymmetries to study the sensitivity of these distributions to top-quark couplings. We determine individual limits on the dominant couplings, viz., the real part of the CMDM Reρ 2 , the imaginary part of the CEDM Imρ 3 , and the real part of the tensor W tb coupling Ref 2R , which may be obtained by utilizing these asymmetries at the LHC. We also obtain simultaneous limits on pairs of these couplings taking two couplings to be non-zero at a time.

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Looking for BSM physics using top-quark polarization and decay-lepton kinematic asymmetries

Cited by 16 publications

References 86 publications

General spin analysis from angular correlations in two-body decays

General spin analysis from angular correlations in two-body decays

Probing anomalous Wtb couplings at the LHC in single t -channel top quark production

Polarization of top quark as a probe of its chromomagnetic and chromoelectric couplings in tW production at the Large Hadron Collider

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