Search for Higgs portal Dark matter Tohoku Ayumi Yamamoto 11/5 2011/11/51

Introduction 2011/11/5 2 Higgs portal Dark matter is assumed following things. 1.No EM, weak and strong interactions 2.Interact only with Higgs I study Higgs portal Dark matter to estimate the sensitivities of coupling, spin and mass. ■What I have done so far i) Generation of signal and background. ii) Try to reproduce the analysis done by Honda-san.

Signal and Background 2011/11/5 3 ■ Signal event e + e -  ZH  qq DM DM. →2 Jets and 2 missing particles Recoil mass against Z boson reconstructed from di-jet should be Higgs mass. ■ background events ZZ Z  qq WW e W  e qq eeZ  eeqq Fig 1.Signal Fig 2.Background

Comparison of Cross sections in generator with Honda-san’s 2011/11/54 ・ Parameters ・ Ecm :300[GeV] ・ electron polarization: 80% ・ positron polarization: - 30% ・ Spin of DM:1/2 ・ DM mass :50GeV ・ Cf :6.86 ・ Λ :1000 Table 1. Cross section of background There is an inconsistency of cross section btw Honda-san’s and mine, even the same parameters are used. Cannot compare the anlyses. → So I gave up to reproduce Honda-san’s analysis. I will study more realistic situation at ILC, I mean E CM = 250, 500GeV (350 also?) and Lint=500fb -1 for both polarization runs.

Analysis ■ Model Parameters *Ecm=250GeV DM is produced in the ee  ZH, Z  qq, H  DD process * luminosity : 500[fb -1 ] *Spin of DM : 1/2 *DM mass : 50GeV *Cf : 6.86 *  : 1000 *electron polarization :-0.8 *positron polarization : 0.3 ■ Event Generation * 100k events are generated for both signal and backgrounds. * signal cross section is assumed 15fb. (We will use the cross section calculated by thoerists) 5 Table 2. Cross section of background

6 Isolated Lepton Cut To remove the e + e - →WW background. (i)Isolated lepton cut The events which have tracks with more than 10GeV energy and energy flow in the cosθ=0.94 cone along the tracks less than 1GeV are rejected. ww Z  qq ZZ e W  e qq eeZ  eeqqZH  ZDD Fig3.Number of Letpons

7 Forward Electron Veto ww Z  qq ZZ e W  e qq eeZ  eeqq To remove the e + e - →e W,eeZ background. (ii) Forward electron veto T-channel event contains forward electron Since fast simulator does not have forward detector, looking at generator information and events with following electron are rejected E e > 10GeV and 0.98<|cosθ e |< ZH  ZDD Fig4.Number of forward electrons

8 Z mass cut (iii) Z mass cut invariant mass of 2 Jets is consistent with Z boson mass. 83GeV<zmass<100GeV eeZ  eeqq ww Z  qq ZZ e W  e qq ZH  ZDD

Signal + Background These figures are recoil mass distribution of signal +background No cutsIsolated lepton cut Forward electron cut83 < Z mass < 100

Cross Section 2011/9/910 After the all selection, σ of WW is the largest. →I should add other cuts to reduce σ of WW try to use likelihood for kinetic variables of Z boson Right handed electron pol. should give smaller cross section for WW. Table 2. Changes in signal and background due to cut significance

Summary and Plan 2011/9/911 ■Summary Cross section at 300GeV is inconsistent with Honda-san’s. Analysis at 250GeV are started. backgrounds are still high so additional cuts are needed. ■Plan 1. use liklihood of kinetic variables for Z boson to reduce backgrounds. 2. analyze right handed electron pol, Scalar and Vector DM, and off-shell Higgs production for heavier DM. 3. do the same analysis at 500GeV and write the first paper 4. T-channel Higgs production at 1TeV and write the second paper

backup 2011/9/912

13 Isolated lepton cut eeZ  eeqq e W  e qq ZZ  qq WW  l qq ZH  ZDD These figures are recoil mass distribution after cut of isolated lepton. *Efficiency due to isolated lepton cut signal : 91.7% background : 67.4% Z  qq

14 Forward particle cut eeZ  eeqq e W  e qq ZZ  qq WW  l qq These figures are recoil mass distribution after cut of forward particle. *Efficiency due to forward particle cut signal : 99.7% background : 94.5% Z  qq ZH  ZDD

15 83 < Z mass <100 [GeV] eeZ  eeqq Z  qq ZZ  qq WW  l qqe W  eeqq These figures are recoil mass distribution after cut of 83 < z mass < 100 *Efficiency due to 83 < Z mass < 100 signal : 75.6% background : 40.1% ZH  ZDD