Advances in High Energy Physics

Volume 2015 (2015), Article ID 134898, 14 pages

http://dx.doi.org/10.1155/2015/134898

## Production and Decay of Up-Type and Down-Type New Heavy Quarks through Anomalous Interactions at the LHC

^{1}Application and Research Center for Advanced Studies, Istanbul Aydin University, Sefakoy, 34295 Istanbul, Turkey^{2}Department of Physics, Ankara University, Tandogan, 06100 Ankara, Turkey

Received 23 October 2014; Revised 19 January 2015; Accepted 26 January 2015

Academic Editor: Hong-Jian He

Copyright © 2015 İ. T. Çakır et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The publication of this article was funded by SCOAP^{3}.

#### Abstract

We study the process (where and and ) through the anomalous interactions of the new heavy quarks at the LHC. Considering the present limits on the masses and mixings, the signatures of the heavy quark anomalous interactions are discussed and analysed at the LHC for the center of mass energy of 13 TeV. An important sensitivity to anomalous couplings TeV^{−1}, TeV^{−1}, TeV^{−1} and TeV^{−1}, TeV^{−1}, TeV^{−1} for the mass of 750 GeV of the new heavy quarks and can be reached for an integrated luminosity of fb^{−1}.

#### 1. Introduction

The standard model (SM) of the strong and electroweak interactions describes successfully the phenomena of particle physics. However, there are many unanswered questions suggesting the SM to be an effective theory. In order to answer some of the problems with the SM, additional new fermions can be accommodated in many models beyond the SM (see [1–9] and references therein). The new heavy quarks could also be produced in pairs at the LHC with center of mass energy of 13 TeV. However, due to the expected smallness of the mixing between the new heavy quarks and known quarks, the decay modes can be quite different from the one relevant to charged weak interactions. A new symmetry beyond the SM is expected to explain the smallness of these mixings. The arguments given in [10] for anomalous interactions of the top quark are more valid for the new heavy quarks and due to their expected larger masses than the top quark.

The ATLAS experiment [11] and CMS experiment [12] have searched for the fourth generation of quarks and set limits on the mass of GeV and GeV at TeV. The pair production of new heavy quarks has been searched by the ATLAS experiment [13, 14] and the GeV mass limits are set at TeV. The CMS experiment has excluded masses below 557 GeV [15]. The vector-like quarks have been searched by the ATLAS experiment [16, 17] and set bounds as 900 GeV for charged current channel and 760 GeV for neutral current channel at TeV. The CMS experiment [18] has set the lower bounds on the mass of 685 GeV at TeV. Some of the final states in the searches of new phenomena can also be considered in relation with the new heavy quarks.

The anomalous resonant productions of the fourth family quarks have been studied in [19, 20] at the LHC with TeV. The possible single productions of fourth generation quarks via anomalous interactions at Tevatron have also been studied in [21]. The parameter space for the mixing of the fourth generation quarks has been presented in [22]. The CP violating flavor changing neutral current processes of the fourth generation quarks have been analyzed in [23], and the large mixing between fourth generation and first three generations has been excluded under the proposed fit conditions. Investigation of the parameter space favored by the precision electroweak data has been performed for the fourth SM family fermions in [24].

In this work, we present the analysis of anomalous productions and decay of new heavy quarks and at the LHC. We have performed the fast simulation for the signal and background. Any observations of the invariant mass peak in the range of 500–1000 GeV and excess in the events with the final states originating from and can be interpreted as the signal for the new heavy quarks and via the anomalous interactions.

#### 2. New Heavy Quarks Anomalous Interactions

A general theory that includes the standard model (SM) as its low energy limit can be written as an expansion series in powers of with operators obeying the required symmetries. The dimension six gauge invariant operators can be built from the SM fields and they can induce dimension five operators after spontaneous symmetry breaking. The coefficients of the dimension five terms are related to those of dimension six operators, and they can lead to sizable effects in the heavy quark associated production in high energy collisions [25]. For our study, the effective Lagrangian with dimension five terms for the anomalous interactions among the new heavy quarks ( or ), ordinary quarks , and the gauge bosons can be written explicitly:where , , and are the field strength tensors of the gauge bosons; ; are the Gell-Mann matrices; is the electric charge of the quark (); , , and are the electromagnetic, neutral weak, and strong coupling constants, respectively. , where is the weak mixing angle. is the anomalous coupling with photon; is for the boson, and is the coupling with gluon. Finally, is the cutoff scale for the new interactions.

#### 3. Decay Widths and Branchings

For the decay channels where , , and , we use the effective Lagrangian to calculate the anomalous decay widths:with

The anomalous decay widths in different channels are proportional to , and they are assumed to be dominant for TeV^{−1} over the charged current channels. In this case, if we take all the anomalous coupling equal then the branching ratios will be nearly independent of . We have used three parametrization sets entitled PI, PII, and PIII. For the PI parametrization, we assume the constant value TeV^{−1}, and PII has the parameters TeV^{−1} with . For PIII we take the couplings TeV^{−1} with the same value of . The index is the generation number.

Tables 1 and 2 present the decay width and branching ratios of the new heavy quark through anomalous interactions for the parametrization PI, PII, and PIII, respectively. Taking the anomalous coupling TeV^{−1} we calculate the decay width GeV and 1.90 GeV for GeV and 1000 GeV, respectively. The branching into channel is the largest and branching into channel is the smallest for equal anomalous couplings with the parametrization PI. On the other hand, PII and PIII parametrization give higher branching ratios into () than () channels due to factor in the parametrization.