E6 GUT model & the Higgs boson search

Gökhan Ünel / UC Irvine & CERNSaleh Sultansoy / Ankara

11 October 2006 Flavour at the LHC workshop

Recall the model

1. In-family mixing bigger than between family mixing2. D quark is the lightest, like SM: most accessible in LHC3. E6 gauge bosons heavy & don’t interact w/ SM bosons

2

!uLdL

",uR,dR,DL,DR

!cLsL

",cR,sR,SL,SR

!tLbL

", tR,bR,BL,BR

D, S, B: New iso-singlet quarks (Q=−⅓)

Assumptions:

The measured values of CKM elements & unitarity of the 3x4 CKM rows constrains ϕ : sin ϕ < 0.07 .

θ : CKM mixing angle ϕ : d - D mixing angle

LD =

!

4!"em

2!

2 sin #W

!

u!$" (1 " $5) d cos % + u!$" (1 " $5) D sin%"

W" (1)

"

!

4!"em

4 sin #W

#

sin% cos %

cos #W

d$" (1 " $5) D

$

Z"

"

!

4!"em

12 cos #W sin #W

!

D$"

%

4 sin2 #W " 3 sin2 %(1 " $5)&

D + d$"

%

4 sin2 #W " 3 cos2 %(1 " $5)&

d"

Z" + h.c.

Higgs Interaction3

isosinglet D quark width

10-3

10-2

10-1

1

10

200 400 600 800 1000 1200 1400 1600MD(GeV)

! (G

eV)

•The D-d mixing, before the SSB,will introduce D-h interaction.

•A straightforward calculation gives:

•New width calculation

LMh =

mD

!sin2 "LDMDMh (1)

!

sin"L cos "L

2!DM

!

(1 ! #5) mD + (1 + #5) md

"

dM h (2)

!

sin"L cos "L

2!dM

!

(1 + #5) mD + (1 ! #5) md

"

DM h (3)

+md

!cos2 "LdMdMh (4)

Illustrative case: mH=120 GeV, sinϕ=0.045, blue=w/ Higgs IA, black=w/o Higgs IA

New cross sections & BRs4

1

10

10 2

10 3

10 4

10 5

10 6

200 300 400 500 600 700 800 900 1000

Total cross sectiong-g contributionq-q

_ contribution

MD(GeV)

! (f

b)

0

10

20

30

40

50

60

70

80

90

100

200 300 400 500 600 700 800MD(GeV)

BR

• 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.

DD pair production at LHC

Impact on Higgs searches 5

ATLAS DETECTOR AND

PHYSICS PERFORMANCE

1

10

102

102

103

mH

(GeV)

Sig

nal

sign

ific

an

ce

H !!! "!"! !"! WH, ttH (H !!! "!"!)

WH, ttH (H !!! bb)

H !!! ZZ(*)

!!! 4 l

H !!! ZZ !!! ll##

H !!! WW !!! l#jj

H !!! WW(*)

!!! l#l#

Total significance

5 $

100 fb-1

(no K-factors)

Technical Design ReportIssue: 1Revision: 0Reference: ATLAS TDR 15, CERN/LHCC 99-15Created: 25 May 1999Last modified: 25 May 1999Prepared By: ATLAS Collaboration

Volume II

at mH=120 GeV, best significance is from H→γγ channel, 8σ at 100fb-1

source: ATLAS TDR

• Could we use the D quarks to improve the Higgs search potential of ATLAS?

•Consider: • D quark pair production• a light Higgs

BR(H→γγ )=0.2%

MC study on h discovery

•>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:

6

|!p| ! 3.2 ,

PT p " 20 GeV ,

Rp > 0.4

D1 D2 BR #expected Higgs/100fb!1 expected final state

D ! h j D ! h j 0.029 (0.053) 0.58"106(2.65"104 ) 2j 4jb

D ! h j D ! Z j 0.092 (0.120) 0.92"106(3.0"104) 2j 2jb 2l

D ! h j D ! W j 0.190 (0.235) 1.9"106( 5.88"104) 2j 2jb l ET,miss

Event Kinematics•Example for mD = 500 GeV

7

GeVTP0 50 100 150 200 250 300 350 400 450 500

pdf

0

0.02

0.04

0.06

0.08

0.1

jb jb !cos -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

pdf

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

GeVTH0 200 400 600 800 1000 1200 1400

pdf

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

Signal hard jet

BG hard jetBG b-jet

PT jet

θjb

jb

BG

signal

signal

BG

HT = !particles

|PT |

D and H Reconstruction 1/28

GeV0 100 200 300 400 500 600 700 800 9001000

#eve

nts/

20G

eV/1

0fb^

-1

0

500

1000

1500

2000

2500

(GeV)bj - bjM0 50 100 150 200 250 300 350 400

#eve

nts/

20G

eV/1

0fb^

-1

0

500

1000

1500

2000

2500

3000

3500

mD

=25

0GeV

mH

=12

0GeV

mD

=25

0GeV

mH

=12

0GeV

10fb-1

--- SM background++ Signal

✓ With these parameters, using 10fb-1 integrated luminosity, both the Higgs boson and the D quark can be discovered.

•Only e & μ are considered for W decays•Missing ET is assumed to come from ν•Analysis cuts (example at mD = 750 GeV) are :

•only HT & PTjet optimized

cut value %!si %!bg

#lep = 1 82.6 79.1

#jet = 4 98.7 99.4

#bjet=2 33.7 36.2

PT lep>20 GeV 96.0 93.5

PT jet>140 GeV 86.3 36.2

cos"jet > -0.8 97.8 90.4

Mjet!jet > 90 GeV 99.9 83.1

HT > 1300 GeV 77.0 20.2

!mD < 100 GeV 55.7 32.9

combined 9.54 0.48

1

Reconstructed invariant mass of D

Reconstructed invariant mass of h

D and H Reconstruction 2/29

GeV0 50 100 150 200 250 300 350 400

#events/20GeV/30fb^-1

0

20

40

60

80

100

120

140

160

180

mD = 500 GeV

GeV0 50 100 150 200 250 300 350 400

#events/16GeV/300fb^-1

0

50

100

150

200

250

mD = 750 GeV

•For higher D quark masses lets concentrate only on Higgs searches:

300fb-130fb-1

• 30fb-1 ∫Luminosity yields:

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Figure 6: The reconstructed masses for the Higgs particles for different D quark mass values of 250, 750 & 1000 GeV for 30, 100 and 3000

fb!1 integrated luminosities.

(GeV)D

M0 100 200 300 400 500 600 700 800 900 1000

#even

ts/2

0G

eV

/30fb

^-1

0

1000

2000

3000

4000

5000

6000

7000

8000

(GeV)bj - bj

M0 50 100 150 200 250 300 350 400

#even

ts/1

6G

eV

/100fb

^-1

0

10

20

30

40

50

60

70

(GeV)bj - bj

M0 50 100 150 200 250 300 350 400

#even

ts/1

6G

eV

/3000fb

^-1

0

50

100

150

200

250

300

Table III: The expected number of signal (S) and background (B) events for D quark and Higgs boson searches after 30 fb!1 integrated

luminosity. The counted events are in a range of ±50 GeV (±20 GeV) from the generator level value of theD quark (Higgs boson).

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

B. Extension to other mass values

An analysis similar to the one presented in the previous section was performed for the other three D quark masses: 250, 750

and 1000 GeV. For each mass, the cut values were re-optimized to get the best statistical significance in the Higgs boson search.

The invariant mass distribution of the reconstructed Higgs boson for differentD quark mass values is given in Fig. 6 where the

dashed line shows the SM background, the red data points are for the signal events only and the black data points are the sum

of the signal and the background events. For each case enough integrated luminosity is considered to observe the Higgs boson

signal.

Table III gives the number of events for signal and background processes after 3 years of low luminosity data taking time (30

fb!1 integrated luminosity) for all consideredD quark mass values. With such integrated luminosity, the 3! signal observationlimit for the D quark is at 750 GeV. If mD ! 1000 GeV, the required luminosities can be attained either by running the LHCfor many years at the design parameters or by considering an eventual upgrade, named as Super-LHC, which would yield 1000

fb!1 per year.

V. CONCLUSIONS

This work gives the Lagrangian for the D quark including its interaction with the known SM particles and Higgs boson.

Two implications of the Higgs interaction are discussed: the differentiation between models and the boost to the Higgs discovery

potential at the LHC. It is shown that the ATLAS experiment can use theD quark decay channels to enhance the Higgs discovery

potential independent of the mixing angle between d and D quarks. The prospects for the Higgs discovery are discussed using

Monte Carlo and fast simulation techniques for a light Higgs particle (120 GeV) and some exemplary D quark mass values

ranging from 250 to 1000 GeV. Fig. 7 contains the 3! (dashed lines) and the 5 ! (solid lines) reaches of Higgs boson (triangles)and D quark (circles) searches for the above mentioned values. Therefore, a light Higgs boson could be discovered with a 5!statistical significance using theDD " hWjj channel within the first year of low luminosity data taking (integrated luminosityof 10 fb!1) if mD < 500 GeV. Under the same conditions but with one year of design luminosity (integrated luminosity of100 fb!1), the 5 ! Higgs discovery can be reached if mD # 700 GeV. This is to be compared with the studies from the

ATLAS TDR, where the most efficient channel to discover such a light Higgs is the h " "" decay. This search yields about8! signal significance with 100 fb!1 integrated luminosity. The presently discussed model could give the same significance

(or more) with the same integrated luminosity if mD < 630 GeV. Therefore, if the isosinglet quarks exist and their masses aresuitable, they will provide a considerable improvement for the Higgs discovery potential. The same channel also provides the

possibility to search for the lightest of the isosinglet quarks, providing a 5 ! discovery signal if mD < 800 GeV, within 100fb!1 of integrated luminosity. The study of other channels involving leptonic decays of the Z boson and therefore offering more

Higgs and D signal reach

•5σ Higgs discovery from DD→Whjj channel can be made in one year of running at design luminosity if mD <700 GeV

•If mD<630 GeV, this channel becomes as efficient as H→γγ . (i.e. 8σ in 100 fb-1)

10

5! D quark discovery5! H boson discovery

3! D quark signal3! H boson signal

MD (GeV)

L ( f

b-1)

10-1

1

10

10 2

10 3

300 400 500 600 700 800 900 1000

Outlook‣ 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!)

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