Advances in High Energy Physics

Volume 2018, Article ID 1627051, 8 pages

https://doi.org/10.1155/2018/1627051

## Constraints on Higgs Effective Couplings in Production of CLIC at 380 GeV

Department of Physics, Abant Izzet Baysal University, 14280 Bolu, Turkey

Correspondence should be addressed to A. Senol; moc.liamg@lonesridakludba

Received 14 December 2017; Revised 8 March 2018; Accepted 29 March 2018; Published 13 May 2018

Academic Editor: Enrico Lunghi

Copyright © 2018 H. Denizli and A. Senol. 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

The potential of the process in the first stage of CLIC considering center-of-mass energy of 380 GeV and assuming the baseline integrated luminosity of 500 is examined to probe CP-conserving dimension-six operators in a model-independent Standard Model effective field theory framework. In the analysis, a detailed fast simulation on signal processes and dominant backgrounds is performed including parton showering with PYTHIA and detector simulation based on ILD type detector with DELPHES in MadGraph. The obtained best limits on , , and are , , and , respectively.

#### 1. Introduction

The recent Large Hadron Collider (LHC) discovery of a scalar particle with 125 GeV which is compatible with Standard Model (SM) Higgs boson predicted by Brout-Englert-Higgs symmetry breaking mechanism opens up a gateway to search for physics beyond the SM [1, 2]. But evidence for new physics beyond the SM using analysis of combined ATLAS and CMS data for probing the couplings of Higgs boson has not been observed yet. Possible deviation from the SM predictions of Higgs boson couplings would imply the presence of new physics involving massive particles that are decoupled at energy scales much larger than the Higgs sector energies being probed [3]. The SM Effective Field Theory (EFT) is a well-known model-independent method for investigation of any deviation from SM [4, 5]. The origin of this method is based on all new physics contributions to the SM described by a systematic expansion in a series of high dimensional operators beyond the SM fields. All high dimensional operators conform to SM gauge symmetry. The dimension-6 operators play an important role in the framework since they match ultraviolet (UV) models which are simplified by the universal one-loop effective action. There have been many analyses for constraints on SM EFT operators with available data from LHC-Run 1 [6–13] and with electroweak precision measurements provided from a previous accelerator, namely, Large Electron Positron (LEP) [14–17]. In particular, the prediction on dimension-6 operators has been examined in many rewarding studies at High Luminosity LHC (HL-LHC) [18–20] and future colliders [21–29].

The precision measurements of Higgs boson couplings with the other SM particles at the LHC and planned future colliders will give us detailed information about its true nature. The future multi-TeV colliders with extremely high luminosity and clean environment due to the absence of hadronic initial state would grant access to precise measurement, especially for the Higgs couplings. The Compact Linear Collider (CLIC) is one of the mature proposed linear colliders with center-of-mass energies from a few hundred GeV up to 3 TeV [30]. The first energy stage of CLIC operation was chosen to be = 380 GeV, with the predicted integrated luminosity of 500 . The primary motivation of this stage is the precision measurements of SM Higgs properties and also the model-independent Higgs couplings to both fermions and bosons [30, 31].

In this study, we focus on the analysis of production process in order to assess the projection of the first energy stage of the CLIC on the CP-conserving dimension-6 operators involving the Higgs and gauge bosons (, , ) defined by an SM EFT Lagrangian in the next section.

#### 2. Effective Operators

The well-known SM Lagrangian () involving renormalizable interactions is suppressed by higher dimensional operators in SM EFT approach. All these operators are parametrized by an energy scale of nonobserved states assumed larger than vacuum expectation value of Higgs field (). A few different operator bases are presented in the literature; we consider SM EFT operators as the strongly interacting light Higgs Lagrangian () in bar convention [18, 33, 34]. Assuming the baryon and lepton number conservation, the most general form of dimension-6 effective Lagrangian including Higgs boson couplings that keep SM gauge symmetry is given as follows:where are normalized Wilson coefficients that are free parameters. In this work, we consider the dimension-6 CP-conserving interactions of the Higgs boson and electroweak gauge boson in SILH basis as [34]where represents the Higgs quartic coupling; , , and are the Yukawa coupling matrices in flavor space; , , and denote coupling constant of , , and gauge fields, respectively; the generators of in the fundamental representation are given by , being the Pauli matrices; is Higgs field that contains a single doublet of fields; and are the electroweak field strength tensors; is the strong field strength tensors; and the Hermitian derivative operators are defined as . The SM EFT Lagrangian (see (2)) containing the Wilson coefficients in the SILH bases of dimension-6 CP-conserving operators can be defined in terms of the mass eigenstates after electroweak symmetry breaking (Higgs boson, , , photon, etc.) as follows:where , , and are the field strength tensors of -boson, -boson, and photon, respectively; represents the mass of the Higgs boson; the effective couplings in gauge basis defined as dimension-6 operators are given in Table 1 in which () coupling is the SM contribution to the Higgs boson to two photons’ (gluons) vertex at loop level.