Constraining Higgs effective couplings at electron-positron colliders Hamzeh Khanpour 1,2∗ and Mojtaba Mohammadi Najafabadi 2† (1) Department of Physics, University of Science and Technology of Mazandaran, P.O.Box 48518-78195, Behshahr, Iran (2) School of Particles and Accelerators, Institute for Research in Fundamental Sciences (IPM), P.O.Box 19395-5531, Tehran, Iran (Dated: January 31, 2017) We probe the dimension-six operators contributing to Higgs production in association with a Z boson at the future high luminosity electron-positron colliders. Potential constraints on dimension- six operators in the Higgs sector are determined by performing a shape analysis on the differential angular distribution of the Higgs and Z bosons decay products. The analysis is performed at the center-of-mass energies of 350 GeV and 500 GeV including a realistic detector simulation and the main sources of background processes. The 68% and 95% confidence level upper limits are obtained on the contributing anomalous couplings considering only the decay of Higgs boson into a pair of b-quarks and leptonic Z boson decay. Our results show that angular observables provide a great sensitivity to the anomalous couplings, in particular at high luminosity regime. CONTENTS I. Introduction 1 II. Theoretical framework and assumptions 2 III. Simulation Details and Analysis 3 IV. Statistical method 6 V. Analysis results 6 VI. Summary and conclusions 8 Acknowledgments 10 A. Cut flow table for the center-of-mass energy of 350 GeV 10 References 10 I. INTRODUCTION After the Higgs boson discovery at the Large Hadron Collider (LHC) run-I in 2012 [1, 2], the main task is to provide precise measurement of its couplings to the Stan- dard Model (SM) particles as well as its other properties. This opens a way to look for potential new physics effects and provides the possibility for revealing effects which may show up at high energy scales. The recent results of the ATLAS and CMS experiments in probing the cou- plings of Higgs boson shows no signs of new physics [3]. The Higgs couplings to the SM particles also have been studied extensively in several analyses using available data from the LHC and previous experiments [4–15]. * Hamzeh.Khanpour@mail.ipm.ir † Mojtaba@cern.ch The compatibility of the current measurements with the SM predictions in the Higgs sector causes the new physics scale to be different from the electroweak scale. This suggests to search for new physics effects beyond the SM by adopting the effective field theory approach without going through the details of any specific scenar- ios. In this approach, the effective operators consist of only the SM fields and are obtained by integrating out heavy degrees of freedom. These effective interactions are suppressed by inverse powers of the new physics scale. Such an effective Lagrangian is required to respect to the Lorentz symmetry and the SU(3) C × SU(2) L × U(1) Y SM gauge symmetries. Assuming baryon and lepton number conservation, operators of dimension six are the first cor- rections which are added to the SM action. The effective Lagrangian can be written as follows: L eff = L SM +  i c i O i Λ 2 , (1) where the effects of possible new physics is assumed to appear at an energy scale of Λ , c i coefficients are di- mensionless Wilson coefficients, and O i are dimension six operators obtained by integrating out the heavy degrees of freedom in the underlying theory. So far, there are many studies to constrain these Wil- son coefficients in the Higgs boson sector from the LHC run I data and from the electroweak precision tests at large electron-positron (LEP) and future colliders [5– 7, 16–36]. If the LHC at run II does not observe any significant deviation from the SM expectations, stronger bounds on the coefficients of the effective operators would be set. Realistic estimations of constraints on the effec- tive coefficients of Higgs related operators after the LHC run II with high integrated luminosity have been pro- vided in [37]. Electron-positron colliders such as Compact Lin- ear Collider (CLIC) [38–40], International Linear Col- lider (ILC) [41–45], Circular Electron-Positron Collider (CEPC) [46, 47] or high-luminosity high-precision FC-