Observation of Scalar WIMP in Top Quark Decay

1
Observation of Scalar WIMP in Top Quark Decay

• hep-ph/0701156
• Tong Li
• Collaborators Xiao-Gang He, Xue-Qian Li, Ho-Chin
  Tsai
• 2007/06/26

2
Outline

• Motivation
• Scalar WIMP
• Top Decay and Two Higgs Doublet Model
• Results of h?DD and t ?cDD in SM and 2HDM
• Whats Next
• Summary

3
Motivation
4

• The evidence for cold, non-baryonic dark matter
  is one of the strongest cases for physics beyond
  the Standard Model.
• (hep-ph/0702036, V.Barger et al.)
• The most popular candidates are axions and weakly
  interacting massive particles (WIMPS).
• The simplest model which has a candidate of WIMP
  is the Standard Model with a singlet real scalar
  field D (darkon).

5
(No Transcript)
6
(No Transcript)
7

• The production of top quark pairs at LHC and ILC
  will be very high, namely for the so-called
  low-luminosity phase( ) of the
  LHC, one expects about one tt-pair will be
  produced per second, that is to say of the order
  of ten million tt-pairs per year.
• (hep-ph/0503172, A.Djouadi)
• In top decay we can probe higher range of dark
  matter masses and new physics.

8
Scalar WIMP
9
SM D

• Renormalizable Lagrangian
• Eliminating the pseudo-goldstone boson eaten by
  W and Z, we have the physical Higgs h coupling to
  D as
• where GeV is the vacuum
  expectation value of the Higgs field.

10
Relic Abundance and Constraint
11
f, V
D
D
f, V

12

• The ? in SMD model as a function of darkon
  masses where
• the areas1, 2, 3 are for 120, 200 and
  350 GeV, respectively.

13
Top decay and Two Higgs Doublet Model
14

• The decay mode t?ch?cDD is interesting and the
  signal will be a charm jet plus missing energy.
• Other processes producing similar signal, such as
  are very small.
• We can look for new physics in this flavor
  changing neutral current process.
• The mass of D up to about 80 GeV can be studied
  compared with other quark decays, such as b quark.

15
Top Decay at LHC
Signal t ?cDD among large missing energy events
of top pairs
Invisibly Higgs decay
C bar
C bar jet
16
Th. and Exp. of t?ch
FCNC in SM
hep-ph/0605003
17
2HDM
18
FCNC in 2HDM III
We used
19
2HDM D
20
2HDM D

• We obtain the mass of D and hDD, HDD, ADD
  interactions

21
The t?cDD Decay
b
a
The decay amplitude
is already averaged over initial spin and
identical particle effect. The partial decay
width where and
22

• Results of h?DD and t ?cDD in SM and 2HDM

23
Coupling of hDD
2HDM III D
SM D
The DM relic density 0.95ltOD h2lt0.112 is used.
(PDG 2006)
?, G(h?DD), BR(h?DD), BR(t?cDD) as a function of
m_D, the areas 1, 2, 3 are for m_h 120, 200,
350 GeV respectively. Here we use tana1, tanß5,
mH mA 500 GeV in 2HDM III for
illustrations. (Same for other figures.)
24
G(h?DD)
2HDM III D
SM D
25
BR(h?DD)
SM D
2HDM III D
26
BR(t?cDD)
SM D
2HDM III D
All too small in SM
Sizable when m_h lt 2m_W
27
Whats Next
28
Whats Next

• Survey Parameter Space tan alpha, tan beta
• FCNC Coefficients determined by meson mixing in
  2HDM III
• Include H (only h now)
• How to see it at LHC? Whats the Observable?
• Polluted by t?cZ?cinvisible just a little

In 2HDM III BR(t?cZ?cinvisible)BR(t?cZ)xBR(Z?inv
isible)10-6 x 0.210-7 ltlt BR(t?cDD)
29
Summary
30

• Probing Scalar WIMPs at LHC and ILC
• Effects of Darkon in Higgs Decay and FCNC Top
  Decay

31
Thank you