Non-Universal Gauge Bosons Z′ and Rare Top Decays

Yue, C. X.; Zong, Hongjie; Liu, Lanjun

doi:10.1142/s0217732303011915

Cited by 19 publications

(16 citation statements)

References 17 publications

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“…Such model independent analysis are useful in probing the strength of observable FCNC couplings. Many detailed studies of the Z ′ phenomenology have been done in recent years [2,3,4,5,6,13,14,15,16,17,18].…”

Section: Introductionmentioning

confidence: 99%

Single top quark production in flavor-changingZ′models

et al. 2006

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In some models with an extra U (1) gauge boson Z ′ , the gauge couplings of the Z ′ to different generations of fermions may not be universal. Flavor mixing in general can be induced at the tree level in the up-type and/or down-type quark sector after diagonalizing their mass matrices. In this work, we concentrate on the flavor mixing in the up-type quark sector. We deduce a constraint from D 0 − D 0 mixing. We study in detail single top-quark production via flavor-changing Z ′ exchange at the LHC and the ILC. We found that for a typical value of M Z ′ = 1 TeV, the production cross section at the LHC can be of the order of 1 fb. However, the background from the Standard Model single top-quark production makes it difficult to detect the flavor-changing Z ′ signal unless with a decent charm tagging method. On the other hand, at the ILC, the production cross section at the resonance energy of √ s ≈ M Z ′ can reach a size of more than 100 fb. Even away from the resonance, the cross section at ILC is shown to be larger than the threshold of observability of 0.01 fb.

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Section: Introductionmentioning

confidence: 99%

Single top quark production in flavor-changingZ′models

et al. 2006

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“…Since our previous findings seems to be in contradiction with that result, it is convenient to reevaluate B(t → cγ) in the scenario discussed in [12]. The flavor diagonal and flavor changing couplings of the Z ′ boson relevant for our calculation are…”

Section: Fig 1: Generic Feynman Diagrams Depicting the Contribution mentioning

confidence: 82%

“…The inequality stems from the fact that the mixing matrix elements V 3c and V 3t are smaller than the unity and so is the coefficient |V 3c V 3t | 2 . The Z ′ contribution to t → cγ was previously calculated in the context of topcolor-assisted technicolor (TC2) models [12]. Those authors claim that, in that class of models, B(t → cγ) ranges between 1.3 × 10 −6 and 1.7 × 10…”

Section: Fig 1: Generic Feynman Diagrams Depicting the Contribution mentioning

confidence: 99%

“…In this brief report we will consider the contribution of the Z ′ gauge boson to the t → cγ decay. It has been claimed recently [12] that B(t → cγ) is at the 10 −6 level in topcolor assisted technicolor models for m Z ′ = 1 TeV, which would allow the detection of this decay channel at future particle colliders. Prompted by this assertion, we will evaluate this decay in the context of some other models.…”

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confidence: 99%

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Effects of an extraZ′gauge boson on the top quark decayt→cγgamma

2005

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The effects of an extra Z ′ gauge boson with family nonuniversal fermion couplings on the rare top quark decay t → cγ are first examined in a model independent way and then in the minimal 331 model. It is found that the respective branching fraction is at most of the order of 10 −8 for m Z ′ = 500 GeV and dramatically decreases for a heavier Z ′ boson. This results is in sharp contrast with a previous evaluation of this decay in the context of topcolor assisted technicolor models, which found that B(t → cγ) ≃ 10 −6 for m Z ′ = 1 TeV. [6]. Quite recently, the CDF collaboration used the Fermilab Tevatron data to search for new massive neutral particles decaying into lepton pairs [7]. As far as new gauge bosons are concerned, they considered a new SM-like) and the one from the littlest Higgs model (Z H ) . The following lower bounds were obtained [7] for the masses of Z ′ SM , Z χ , Z ψ , Z η and Z I : 825, 690, 675, 720 and 615 GeV, whereas m ZH was found to be larger than 885, 860 ,805 and 725 GeV for the following values of the mixing parameter cotθ H : 1.0, 0.9, 0.7 and 0.5, respectively.If the couplings of the Z ′ to the fermions are assumed to be family universal, there is no flavor changing neutral current (FCNC) effects mediated by this particle even if there is fermion flavor mixing via the GIM mechanism. Nevertheless, it is possible that the Z ′ couples nonuniversally to the fermions, thereby giving rise to FCNCs. For instance, some theories require that the Z ′ couplings to the third family fermions are different than the ones to the fermions of the first two families. This is the case of the Z ′ predicted by the 331 model [8], which is based on the SU (3) L × U (1) X symmetry and has attracted considerably attention recently [9]. This model is particularly appealing due to its unique mechanism of anomaly cancelation: instead of the usual cancelation between each fermion family, it is necessary that all the three fermion families are summed over, which automatically requires the existence of a number of families that is multiple of 3. It has been conjectured that this may provide a hint to the solution of the family number problem. There are thus good motivations for an extra Z ′ boson, with a mass in the range 500 GeV-1 TeV, which couples nondiagonally to the fermions.Although the phenomenology of a Z ′ gauge boson is interesting by itself, so is the study of FCNC effects as they would be a hint of new physics because of their large suppression in the SM. This class of effects has been considerably studied in the literature via some rare decay modes of the top quark. The interest in the top quark phenomenology stems from its large mass, which has led to some belief that new physics effects are more likely to show through processes involving this particle. Even more, the copious production of top quark pairs at the CERN large hadron collider (LHC) will allow us to examine several top quark properties and some of its rare decays. It is thus very interesting to consider the virtual effects of a Z ′ gauge ...

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“…The FCNC effects from the Z ′ mediation have been studied for the down-type sector and implications in flavor physics [7][8][9][10][11][12][13][14][15][16][17] and up-type sector in top quark production [4,[18][19][20][21][22].…”

Section: Modelmentioning

confidence: 99%

Search for top quark FCNC couplings in Z′ models at the LHC and CLIC

et al. 2010

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The top quark is the heaviest particle to date discovered, with a mass close to the electroweak symmetry breaking scale. It is expected that the top quark would be sensitive to the new physics at the TeV scale. One of the most important aspects of the top quark physics can be the investigation of the possible anomalous couplings. Here, we study the top quark flavor changing neutral current (CLIC) energies, including the initial state radiation and beamstrahlung effects, we find the cross section 27.96(0.91) fb at √ s e + e − = 1(3) TeV, respectively. We make the analysis to investigate the parameter space (mixing-mass) through various Z ′ models. It is shown that the results benefit from the flavor tagging.

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Non-Universal Gauge Bosons Z′ and Rare Top Decays

Cited by 19 publications

References 17 publications

Single top quark production in flavor-changingZ′models

Single top quark production in flavor-changingZ′models

Effects of an extraZ′gauge boson on the top quark decayt→cγgamma

Search for top quark FCNC couplings in Z′ models at the LHC and CLIC

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