Search for Higgs portal Dark matter

1. Search for Higgs portal Dark matter Tohoku Ayumi Yamamoto 11/5

2. Introduction Higgs portal Dark matter is assumed following things. • No EM, weak and strong interactions • 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.

3. Signal and Background ■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 nnZ  nnqq WW enWenqq eeZ eeqq Fig 1.Signal Fig 2.Background

4. Comparison of Cross sections in generator with Honda-san’s ・Parameters ・Ecm :300[GeV] ・ electron polarization: 80% ・ positron polarization: -30% ・Spin of DM:1/2 ・DM mass :50GeV ・Cf :6.86 ・Λ :1000 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 ECM= 250, 500GeV (350 also?) and Lint=500fb-1 for both polarization runs. Table 1. Cross section of background

5. 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 *L : 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) Table 2. Cross section of background

6. Isolated Lepton Cut To remove the e+e-→WW background. • 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. ZZ eeZeeqq ww nnZnnqq enWenqq ZHZDD Fig3 .Number of Letpons

7. Forward Electron Veto To remove the e+e-→enW,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 Ee > 10GeV and 0.98<|cosθe|<0.9999875 eeZeeqq ww ZZ enWenqq nnZnnqq 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 enWenqq ZZ ZHZDD nnZnnqq ww

9. Signal + Background These figures are recoil mass distribution of signal +background No cuts Isolated lepton cut Forward electron cut 83 < Z mass < 100

10. Cross Section After the all selection, σ of WW is the largest. →I should add other cuts to reduce σof 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

11. Summary and Plan ■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

12. backup

13. Isolated lepton cut These figures are recoil mass distribution after cut of isolated lepton. *Efficiency due to isolated lepton cut signal : 91.7% background : 67.4% eeZeeqq WWlnqq enWenqq ZZnnqq ZHZDD nnZnnqq

14. Forward particle cut These figures are recoil mass distribution after cut of forward particle. *Efficiency due to forward particle cut signal : 99.7% background : 94.5% eeZeeqq WWlnqq enWenqq nnZnnqq ZZnnqq ZHZDD

15. 83 < Z mass <100 [GeV] 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% ZZnnqq eeZeeqq enWeeqq WWlnqq nnZnnqq ZHZDD