T-odd quarksin the Littlest Higgs model

Giacomo CacciapagliaIPNL

15 April 2010MC4BSM

Niels Bohr Institute, København

arXiv:0911:4630, with S.Rai Choudhury, A.Deandrea, N.Gaur and M.Klasen

The model

Stabilisation of the EW scale: Higgs as a Pseudo-Goldstone boson

Global symmetry G broken to subgroup H at a scale f (Λ = 4πf)

Higgs part of the coset G/H

Gauged subgroup contains SM gauge groups

Quadratic divergences cancelled at one loop by same spin particles!

The model: Littlest Higgs

G = SU(5) broken to H = SO(5)

Gauged 2X [SU(2) x U(1) ] → SU(1)L xU(1)Y

24-10=14 Nambu-Goldstone bosons: Heavy gauge bosons (4) + H (4) + heavy triplet φ (6)

Many new states: AH , WH , ZH , φ; mass O(f)

Tree level corrections to EWPTs: f > few TeV! The naturalness problem is reintroduced!

The model: Littlest Higgswith T-parity

To avoid EWP bounds, I.Low proposed a discrete parity (T-parity) that exchanges the two SU(2)xU(1) gauged groups

W = W1+W2 even; WH = W1-W2 odd!

Requires T-odd partner for all fermions: QH and LH!

bound (loops) softened to f > 500 GeV!

AH plays the role of dark matter candidate.

Vector masses:

Fermion masses (κ = Yukawa coupling, κ < 3.5 f/TeV, flavour blind and universal):

Numerically:

The model: Littlest Higgswith T-parity

Branching ratios

0

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For κ ≥ 0.46, QH→WH q→AH Wq→AH lνq→ l jet MET60% 100% 21%

Chain branching ratio: 12%

Production cross sections

Only strong production from gluons and quark annihilation

Dominated by s-channel diagrams (fall-off rapidly with s)

Only opposite sign dilepton signatures

In previous work, i.e. Freitas/Wyler and Choudhuri/Gosh:

Production cross sections

We consider both strong and weak processes

Weak t-channel (heavy gauge bosons) give a large contribution in the forward region (exp. at large κ)

We included corrections to the vertices

We included NLO k-factors for both signal and background

In our work:

Opposite sign dilepton ⇒

Same sign dilepton ⇒

pp→QH QH (QCD+EW)pp→UH DH (EW)

_

pp→UH DH + UH DH (EW)_ _

v2

f2

Belyaev, Chen, Tobe, Yuan

Production cross sections @ 14TeV

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"!= 1

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Same sign leptons

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Same sign leptons

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Same sign leptons

RED: only QCD (Choudhuri et al)BLACK: QCD+EW oposite-sign processesBLUE: EW same-sign processes

Note: EW more impfor large κ

Our simulation:3 benchmark points

Signal generated with CalcHEP 2.5.4 + PYTHIA 6.4.21CalcHEP model files can be found in

http://deandrea.home.cern.ch/deandrea/LHTmodl.tgz

Opposite sign leptons: backgrounds

t tbar, with both tops decaying leptonically and bottoms misidentified for light jets

WWjj, with both W decaying leptonically

ZZjj, with one Z decaying leptonically and the other invisible

two leptons with pt > 15 GeV and η < 2.5

b-jet veto, with a b-tagging accuracy of 60%

two light jets with pt > 30 GeV and η < 2.5

MET > 30 GeV

dilepton invariant mass > 15 GeV

and cuts:

PYTHIA 6.4.21

⇐ suppress t tbar

⇐ suppress photons

Same-sign leptons

(GeV)TE

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10)! = 0.6 (!f = 1000 GeV,

10)! = 1.5 (!f = 700 GeV,

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W W jj

Z Z jj

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(GeV)TH

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# o

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eV10

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10)! = 0.6 (!f = 1000 GeV,

10)! = 1.5 (!f = 700 GeV,

10)! = 1 (!f = 1000 GeV,

tt

W W jj

Z Z jj

ATLFASTLuminosity 100 fb-1

Naveen Gaur

Same-sign leptons

(GeV)TE

0 200 400 600 800 1000 1200 1400

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(GeV)TE

0 200 400 600 800 1000 1200 1400

# o

f ev

ents

/ 1

5 G

eV

1

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10)! = 0.6 (!f = 1000 GeV,

10)! = 1.5 (!f = 700 GeV,

10)! = 1 (!f = 1000 GeV,

tt

W W jj

Z Z jj

(GeV)TH

0 500 1000 1500 2000 2500 3000 3500 4000

# o

f ev

ents

/ 4

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eV10

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410

(GeV)TH

0 500 1000 1500 2000 2500 3000 3500 4000

# o

f ev

ents

/ 4

0 G

eV10

210

310

410

10)! = 0.6 (!f = 1000 GeV,

10)! = 1.5 (!f = 700 GeV,

10)! = 1 (!f = 1000 GeV,

tt

W W jj

Z Z jj

ATLFASTLuminosity 100 fb-1

Naveen Gaur

Numerical results

MET cut very effective to reduce backgrounds!

Discovery for O(100 fb-1)

MET cut very effective to reduce backgrounds!

Discovery for O(100 fb-1)

Numerical results

Numerical results

MET cut very effective to reduce backgrounds!

Discovery for O(100 fb-1)

Opposite-sign leptons

(GeV)TE

0 200 400 600 800 1000 1200

# o

f ev

ents

/ 1

5 G

eV

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(GeV)TE

0 200 400 600 800 1000 1200

# o

f ev

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/ 1

5 G

eV

0

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120 5)! = 0.6 (!f = 1000 GeV,

5)! = 1.5 (!f = 700 GeV,

5)! = 1 (!f = 1000 GeV,

W W jj

W W W

(GeV)TH

0 500 1000 1500 2000 2500 3000 3500 4000

# o

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ents

/ 4

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eV

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(GeV)TH

0 500 1000 1500 2000 2500 3000 3500 4000

# o

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/ 4

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eV

0

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20

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70 5)! = 0.6 (!f = 1000 GeV,

5)! = 1.5 (!f = 700 GeV,

5)! = 1 (!f = 1000 GeV,

W W jj

W W W

ATLFASTLuminosity 100 fb-1

Naveen Gaur

Numerical results

T-odd Leptons: 2 lepton signal

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"l = 0.3, #s = 14 TeV"l = 0.5, #s = 14 TeV"l = 0.7, #s = 14 TeV"l = 0.3, #s = 10 TeV"l = 0.5, #s = 10 TeV"l = 0.7, #s = 10 TeV

(GeV)TE

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410 = 0.4l!f = 500 GeV,

= 0.35l!f = 700 GeV,

= 0.45l!f = 600 GeV,

ZZ

WW

pp -> lH lH

lH -> AH l @ 100%

T-odd Leptons: 1 lepton signal

pp -> νH lH

νH/lH -> AH ν/l @ 100%

Conclusion

Light quark (and lepton) partner are a necessary ingredient in Little Higgs models with T-parity

We show that the EW interactions give an important (previously ignored) contribution to the production cross section

Opposite-sign and same-sign dilepton signatures offer a good discovery channel for quarks at large luminosities (L = 100 fb-1)

single lepton and dilepton are discovery channels at low luminosity for leptons

Bonus track

The model: Littlest Higgswith T-parity

To avoid EWP bounds, I.Low proposed a discrete parity (T-parity) that exchanges the two SU(2)xU(1) gauged groups

W = W1+W2 even; WH = W1-W2 odd!

Requires T-odd partner for all fermions: QH and LH!

bound (loops) softened to f > 500 GeV!

AH plays the role of dark matter candidate:

from Hubitz and Meade

Same sign leptons: backgrounds and cuts

WWW, with same sign Ws decaying leptonically and the other in jets

WWjj, with same sign Ws decaying leptonically

two same sign leptons with pt > 15 GeV and η < 2.5

two light jets with pt > 30 GeV and η < 2.5

MET > 30 GeV

Cuts:

One lepton: backgrounds and cuts

on-shell W, decaying leptonically

WZ, with W decaying leptonically and Z invisibly (neutrinos)

one isolated lepton with pt > 10 GeV and η < 3

jet veto, with pt > 30 GeV and η < 3

Cuts:

Two leptons: backgrounds and cuts

WW, both decaying leptonically

ZZ, with one Z decaying leptonically and the other invisibly (neutrinos)

two isolated lepton with pt > 10 GeV and η < 3

jet veto, with pt > 30 GeV and η < 3

MET threshold 30 GeV

Cuts: