Top quark spin and interaction in charged Higgs and top quark associated production at LHC

Xue Gong

2013.01.04In collaboration with Z. Si , S. Yang & Y. Zheng arXiv: 1210.7822

Htb

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Outline• Motivation

• Charged Higgs production from process and its signatures at LHC

• Observables to identify the Htb interaction

• Summary

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tHgb

Motivation

• Electroweak spontaneous symmetry breaking mechanism

(EWSM) weak gauge bosons and fermions masses & the existence of Higgs bosons in SM

EWSM has not been confirmed experimentally

• One Higgs-like particle around 126 GeV has been discovered at LHC by ATLAS and CMS

Whether it is indeed the SM Higgs boson is still open

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Motivation

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has been predicted by many non-mininal Higgs scenarios , eg. 2HDM,MSSM, LRSM

The observation of would :

Be an unambiguous evidence for an extended Higgs vector

Help to unveil the mysteries of EWSB

Further to confirm the identification of Higgs-like boson (126GeV) & distinguish models

H

H

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Motivation

Kunszt et.al(1992)

identify Htb couplings

Charged Higgs production channel

Gunion et.al(1987), Barnett et.al(1988),Barger et.al(1994), Miller et.al(2000)

2HDM particle content

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Higgs Potential:

Two Higgs doublet fields:

After SSB: 5 physical Higgs scalar left:

2 CP-even 1 CP-odd 2 Charged

h0, H0 A0 H±

One of the most important feature of all 2HDMs: the existence of charged scalar

Theoretical framework7

2HDM Lagrangian:

with

Coupling:

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Signal:

Process at LHC

Background:

• Charged Higgs and top quark associated production at LHC

• Observables to identify the Htb interaction

Cross section at LHC9

Invariant mass distribution

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To determine charged Higgs mass

Cross section of signal and background

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20 fb-1@ 8 TeV

MadEvent

tanβ=30 @ 8 TeV

Cross section of signal and background

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300 fb-1@ 14 TeV

MadEvent

tanβ=30 @ 14 TeV

: of lepton in anti-top quark rest frame : of anti-top quark in H- frame

Angular distribution13

Top quark spin effect is related to the product of ga and gb

p.st gagb

Angular distribution of charged lepton

:unit 3-momentum of lepton in top quark rest frame : unit 3-momentum of top quark in tH c.m. frame

2HDM

Angular distribution14

>0

=0

<0

Before cuts

Before cuts

After cuts

After cuts

TeVs 14

TeVs 14

Angular distribution15

>0

=0

<0

Before cuts After cuts

<0

=0

>0Before cuts After cuts

TeVs 14

TeVs 14

Predictions of AFB & AFB

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Summary

• Based on 2HDM, we discussed tH- associated production via at LHC and find that the signal can be distinguished from the background for charged Higgs mass up to 1 TeV or even larger with 14Tev.

• Identify Htb interaction from charged lepton angular

distribution cosθ and Forward-Backward asymmetry AFB

induced by top quark spin which are sensitive to ga gb

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Coupling vs. top spin

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Process at LHC20