Search for Higgs portal Dark matter

Tohoku

Ayumi Yamamoto

11/52011/11/5 1

Introduction

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Higgs portal Dark matter is assumed following things.1. No EM, weak and strong interactions2. 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

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■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

eWeqq

eeZ eeqq

Fig 1.Signal

Fig 2.Background

Comparison of Cross sections in generator with Honda-san’s

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・ 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 ECM = 250, 500GeV (350 also?) and Lint=500fb-1 for both polarization runs.

Analysis

■Model Parameters *Ecm=250GeV

DM is produced in the eeZH, Zqq, HDD 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)

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Table 2. Cross section of background

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Isolated Lepton CutTo 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

Zqq

ZZ

eWeqq

eeZeeqq

ZHZDD

Fig3 .Number of Letpons

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Forward Electron Veto

ww

ZqqZZ

eWeqq

eeZeeqq

To remove the e+e-→eW,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

ZHZDD

Fig4.Number of forward electrons

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Z mass cut (iii) Z mass cut

invariant mass of 2 Jets is consistent with Z boson mass .

83GeV<zmass<100GeV

eeZeeqq

wwZqq

ZZeWeqq

ZHZDD

Signal + BackgroundThese figures are recoil mass distribution of signal +background

No cuts Isolated lepton cut

Forward electron cut 83 < Z mass < 100

Cross Section

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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

03.0N

S 4.11 NS

Ssignificance

Summary and Plan

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■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

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Isolated lepton cut

eeZeeqq eWeqq

ZZqq

WWlqq

ZHZDD

These figures are recoil mass distribution after cut of isolated lepton.

*Efficiency due to isolated lepton cut

signal : 91.7%

background : 67.4%

Zqq

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Forward particle cut

eeZeeqq eWeqq

ZZqq

WWlqq

These figures are recoil mass distribution after cut of forward particle.

*Efficiency due to forward particle cut

signal : 99.7%

background : 94.5%

Zqq ZHZDD

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83 < Z mass <100 [GeV]

eeZeeqq

Zqq ZZqq

WWlqqeWeeqq

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%

ZHZDD