E6 GUT model & the Higgs boson search Gökhan Ünel / UC Irvine & CERN Saleh Sultansoy / Ankara 11 October 2006 Flavour at the LHC workshop

1. E6 GUT model & the
Higgs boson search
Gökhan Ünel / UC Irvine & CERN
Saleh Sultansoy / Ankara
11 October 2006
Flavour at the LHC workshop

2. Recall the model
2
uL cL tL
, uR, dR, DL, DR , cR, sR, SL, SR ,tR, bR, BL, BR
dL sL bL
D, S, B: New iso-singlet quarks (Q=−⅓)
√
4παem
LD = √ uθ γα (1 − γ5 ) d cos φ + uθ γα (1 − γ5 ) D sin φ W α
¯ ¯ (1)
2 2 sin θW
√
4παem sin φ cos φ ¯
− dγα (1 − γ5 ) D Z α
4 sin θW cos θW
√
4παem ¯ ¯
− Dγα 4 sin2 θW − 3 sin2 φ(1 − γ5 ) D + dγα 4 sin2 θW − 3 cos2 φ(1 − γ5 ) d Z α + h.c.
12 cos θW sin θW
θ : CKM mixing angle
The measured values of CKM elements & unitarity ϕ : d - D mixing angle
of the 3x4 CKM rows constrains ϕ : sin ϕ < 0.07 .
Assumptions:
1. In-family mixing bigger than between family mixing
2. D quark is the lightest, like SM: most accessible in LHC
3. E6 gauge bosons heavy & don’t interact w/ SM bosons

3. Higgs Interaction
3
• The D-d mixing, before the SSB,will introduce D-h interaction.
• A straightforward calculation gives:
mD ¯
LM
h = sin2 φL DM DM h
ν
sin φL cos φL ¯ M
− D (1 − γ 5 ) mD + (1 + γ 5 ) md dM h
2ν
• New width calculation
sin φL cos φL ¯M
− d (1 + γ 5 ) mD + (1 − γ 5 ) md DM h
2ν
isosinglet D quark width md ¯
10 + cos2 φL dM dM h
! (GeV)
ν
1
-1
10
Illustrative case: mH=120 GeV, sinϕ=0.045,
-2 blue=w/ Higgs IA,
10
black=w/o Higgs IA
-3
10
200 400 600 800 1000 1200 1400 1600
MD(GeV)

4. New cross sections & BRs
4
100
DD pair production at LHC
BR
6
10 90
! (fb)
5 80
10
Total cross section
70
g-g contribution
10 4
_
q-q contribution 60
3
50
10
40
10 2 30
20
10
10
1 0
200 300 400 500 600 700 800 900 1000 200 300 400 500 600 700 800
MD(GeV) MD(GeV)
• if mD ~250 GeV, then pair production σ~105 fb.
• D decay BRs for a light Higgs (120..135GeV), depend on mD. For high
mD (>700GeV) 50, 25 & 25% for W, Z & h modes.

5. Impact on Higgs searches
5
PHYSICS PERFORMA
Signal significance
H !!! "!"! !"! WH, ttH (H !!! "!"!)
WH, ttH (H !!! bb)
(*)
H !!! ZZ !!! 4 l
H !!! WW
(*)
!!! l#l# source: ATLAS TDR
10 2
H !!! ZZ !!! ll##
H !!! WW !!! l#jj
Total significance
• Could we use the D quarks
to improve the Higgs search
potential of ATLAS?
10
• Consider: 5$
• D quark pair production
• a light Higgs -1
100 fb
(no K-factors)
1 2 3
10 10
mH (GeV)
BR(H→γγ )=0.2% at mH=120 GeV, best significance is from
H→γγ channel, 8σ at 100fb-1

6. MC study on h discovery
6
D1 D2 BR #expected Higgs/100fb−1 expected final state
D → hj D → hj 0.029 (0.053) 0.58×106 (2.65×104 ) 2j 4jb
D → hj D→Zj 0.092 (0.120) 0.92×106 (3.0×104 ) 2j 2jb 2l
D → hj D→Wj 0.190 (0.235) 1.9×106 ( 5.88×104 ) 2j 2jb l ET,miss
• >3x106 (>1x105) additional Higgs bosons at LHC, if mD=250 (500) GeV
‣enough to motivate a study for 250, 500, 750 & 1000 GeV quarks using
the 2j 2jb l ET
miss signal
• SM background: W jb jb j j events, 80% from t-t background
• Signal implemented in CompHEP, bg from MadGraph, simulation in
athena 11.0.41 using ATLfast
• Final analysis done with physics objects in Root
• Generator level cuts are: |ηp | ≤ 3.2 ,
PT p ≥ 20 GeV ,
Rp > 0.4

7. Event Kinematics
7
• Example for mD = 500 GeV
t
G b-je t igna
l
B
ha rd je s
pdf
pdf
pdf
0.1
BG
0.09 0.07
a l
sign
0.08
0.06
0.08
0.07
0.05
0.06
0.06
BG
jet
0.04
rd
0.05
a
n al h
Sig
0.04 0.03
0.04
BG
0.03
0.02
0.02 0.02
0.01
0.01
00 50 100 150 200 250 300 350 400 450 500 0 -0.8 -0.6 -0.4 -0.2 0
-1 0.2 0.4 0.6 0.8 1 00 200 400 600 800 1000 1200 1400
PT GeV cos ! jb jb HT GeV
PT jet
jb
HT = ∑ |PT |
particles
θ
jb

8. D and H Reconstruction 1/2
8
cut value % si % bg
• Only e & μ are considered for W decays #lep = 1 82.6 79.1
• Missing ET is assumed to come from ν #jet = 4
#bjet =2
98.7
33.7
99.4
36.2
• Analysis cuts (example at mD = 750 GeV) are : PT lep>20 GeV 96.0 93.5
• only HT & PTjet optimized PT jet>140 GeV
cosθjet > -0.8
86.3
97.8
36.2
90.4
Mjet−jet > 90 GeV 99.9 83.1
HT > 1300 GeV 77.0 20.2
#events/20GeV/10fb^-1
#events/20GeV/10fb^-1 ∆mD < 100 GeV 55.7 32.9
2500 3500
V
0 Ge GeV combined 9.54 0.48
2000 25 GeV 3000
2 50 GeV
= 20 = 20
m =1
D 2500
mD = 1 --- SM background
1500
mH 2000 mH ++ Signal
1000 1500
10fb-1
1000 ✓ With these parameters,
500
using 10fb-1 integrated
500
0
luminosity, both the Higgs
0 100 200 300 400 500 600 700 800 9001000
0
0 50 100 150 200 250 300 350 400
Mbj - bj (GeV)
boson and the D quark can
be discovered.
GeV
Reconstructed Reconstructed
invariant mass of D invariant mass of h

9. D and H Reconstruction 2/2
9
Figure 6: The reconstructed masses for the Higgs particles for different D quark mass values of 250
fb−1 integrated luminosities.
•For higher D quark masses lets concentrate only on Higgs searches:
8000
#events/16GeV/100fb^-1
#events/16GeV/3000fb^-1
#events/20GeV/30fb^-1
70
mD = 500 GeV
7000
mD = 750 GeV 300
#events/16GeV/300fb^-1
60
#events/20GeV/30fb^-1
180 6000 250 250
160 50
5000
200
140 40 200
4000
120 150
100
3000
30fb-1 30 150
300fb-1 100
80 2000 20
100
60 1000 50
10
40 0 50 0
0 100 200 300 400 500 600 700 800 900 1000 00 50 100 150 200 250 300 350 400 0
20
MD (GeV) Mbj - bj (GeV)
00 50 100 150 200 250 300 350 400
00 50 100 150 200 250 300 350 400 GeV
GeV
Table III: The expected number of signal (S) and background (B) events for D quark and Higgs
• 30fb ∫Luminosity yields:
-1
luminosity. The counted events are in a range of ±50 GeV (±20 GeV) from the generator level valu
MD (GeV) 250 500 750 1000
S 8802 5303 336 222 27 19 1.9 1.4
B 29379 31717 313 321 32 56 3.1 10.6
√
S/ B + S 45.1 27.6 13.2 9.5 3.5 2.1 0.84 0.42

10. Higgs and D signal reach
10
L ( fb-1)
• 5σ Higgs discovery 10 3
from DD→Whjj 5! H boson discovery
5! D quark discovery
3! H boson signal
channel can be made in 3! D quark signal
10 2
one year of running at
design luminosity if mD
<700 GeV 10
• If mD<630 GeV, this
channel becomes as 1
efficient as H→γγ . (i.e. 8σ
in 100 fb-1) -1
10
300 400 500 600 700 800 900 1000
MD (GeV)

11. Outlook
11
‣ The 3 sigma signal from a light Higgs, can be seen within a year
(100 fb-1) via the E6 quarks if mQ< 800 GeV.
‣ The outcome should be checked against the full simulation
(Geant) results. (working for a CSC note)
‣ The impact of the heavy quark(s) to the Higgs production via
loop diagrams could be interesting.
‣ BG in this analysis is ~20% overestimated: we did σ=2*(W+4j)
but σ(W- 4j) = 0.8*σ(W+ 4j)
‣ Multi jet background to be checked. (thanks to Juan Antonio for
the hint!)