Signatures of alternative models beyond the Standard Model

이강영 ( 건국대학교 )

@ 연세대학교 2009. 10. 15.

Contents

• Introduction• Z’• W’• H+

• H++

• t’, b’• Q, L• Dark matter• Summary

Introduction

• LHC will explore for the first time a relevant energy range, well above the Fermi scale.

• LHC is the Energy frontier machine best to search for the new (heavy) particles.

• We concentrate on the new particles

discovery. • The detailed phenomenology depends upon

the model.

2008 년 9 월 10 일 공식적으로 가동 .

올 11 월부터 정식 가동 .

둘레 27km 에 이르는 지구상 최대의 실험장치 .

다음과 같은 세계를 탐구하는 양성자 - 양성자 충돌장치 .

ECM = 14 TeV (max) ~ v = 0.999999991c (c= 빛의 속도 ) ~ d = 0.000000000000000000014 m

LHC The voyage to the ultimate world

Z’

• Z’ : Extra neutral gauge boson• Exists when there is extra gauge symmetries.

• U(1) extensions of the SM• LR model• Other gauge extended models

• Other species : excited states of Z • Little Higgs model• Extra dimensional models

Underlying Physics

Examples of U(1) extensions

E6 models breaking chain

χ model : β=0ψ model : β=π/2η model : β=arctan(-√5/3)

LR model

Diagonalized to give eigenvalues

(WL3, WR3, B) basis

Unknown model parameters are

MZ’ Z-Z’ mixing angle

Note that

where

and eigenstates

Z’ couplings to quarks and leptons

The Z-Z’ mixing angle is given by

Lagrangian for a Z’ in E6 model

e.g. Couplings for E6 inspired models and LR model

where

Phenomenology

Drell-Yan process

Z’

Experimental limits

PDG 2008

CDF collab., Phys. Rev. Lett., 95, 252001 (2005)

Identification of Z’ using t and b

S. Godfrey and T. A. W. Martin, Phys. Rev. Lett., 101, 151803 (2008)

Kq depends on QCD and EW corrections.

e.g.

S. Godfrey and T. A. W. Martin, PRL 101, 151803 (2008)

• Z’ mass and total width• Cross section to• Forward-backward asymmetry• Rapidity ratio• Off-peak asymmetry

Basic Observables

Measuring Z’ couplings at the LHCe.g.

F. Petriello and S. Quackenbush, Phys. Rev. D 77, 115004 (2008).

• Forward-backward asymmetry

where

• Rapidity ratio

y1 is introduced to exclude low Z’ rapidity events.

M. Dittmar, Phys. Rev. D 55, 161 (1997)

• Detector resolution effects are ignored.• Reconstruction efficiency of Z’ production is near

90% from CMS simulation.• CTEQ 6.5 NLO PDF used.• Integrated luminosity 100fb-1 unless stated

otherwise.

• Factorization and renormalization scale : MZ’

Acceptance Cuts

Differential cross section

Parity symmetric couplings

Parity violating couplings

Calculation

Rewrite the differential cross section

Absorbing

We have

Define four observables

which are expressed in terms of observables

where

We derive the Master equation

e.g. If we let

Solving the Master equation to have

Results

• If MZ’ =1.5 TeV, 100 fb-1 luminosity and y1=0.8 can discriminate the example models with 90% C.L. and 1 ab-1 luminosity (SLHC) will provide precise determination.

• If MZ’ =3 TeV, 100 fb-1 luminosity and y1=0.4 can discriminate some models.

• For MZ’ =3 TeV, 1 ab-1 luminosity (SLHC) will provide reasonable determination.

Exotic Z’

• Generation-dependent couplings

• Leptophobic

• Hadrophobic

• Flavour-violating

• And more…

W’

• W’ : Extra charged gauge boson• Exists when there are extra gauge symmetries more

than U(1).

• LR model• Other gauge extended models

• Other species : excited states of W• Little Higgs model• Extra dimensional models

Underlying Physics

LR model (e.g.)

Diagonalized to give

(WL+, WR

+) basis

where

Search for W’

• High energy single lepton final states

• Single top production

W’ → l- ν

W’ → t b

D0 collaboration, PRL 100, 031804 (2008)

2 22 ( ) ( ) ( ) ( )

2 ( ) ( ) 1 cos

T T T T T

T T

M p e p p e p

p e p

Transverse mass

Edges of transverse mass distribution are crucially related to the mass of W’.

Experimental limits

PDG 2008

CDF constraints

D0 observations

D0 collaboration, PRL 100, 031804 (2008)

Feasibility of W’ at the CMS

C. Hof, Acta. Phys. Pol. B 38, 443 (2007)

Reference models : same couplings as the SM

e.g.

Exotic W’

• Left-right asymmetric : coupling constants and CKM

• Leptophobic

• Hadrophobic

• Flavour-dependent SU(2)

• Exotic gauge self-couplings : W’-W-Z, W’-W’-Z …

• And more…

H+

• H+: Charged scalar• Exists when there is extra Higgs sector more than

SM singlet.

• 2HD model• MSSM and more extensions (NMSSM etc.)• LR model• Other GUT-based model

Underlying Physics

Higgs sector in the LR model

Two triplets

a bidoublet

: breaking of SU(2)R and its L-R partner

: electroweak symmetry breaking and fermion masses

with VEVs

Note that

define

Charged Higgs boson in the LR model

Mass matrix

where

Charged Higgs mass

Diagonalization by

relevant tbH+ couplings

similarly for lepton sector

Phenomenology Light charged Higgs from t Hb at Tevatron

Light charged Higgs boson :

Absence of observed charged Higgs boson

Constrained by

CDF collaboration, PRL 96, 042003 (2006)

Pair production of charged Higgs boson at LEP

ALEPH collaboration, PLB 543, 1 (2002)

B and charged Higgs boson

R. Barlow, ICHEP 2006

Experimental constraints for LR charged Higgs

allowedallowed

D.-W. Jung, K. Y. Lee., Phys. Rev. D 76, 095016 (2007)

Light charged Higgs production at the LHC

sequential decay after tt pair production

108 top quarks produced

More than 105 charged Higgs expected

D.-W. Jung, K. Y. Lee., Phys. Rev. D 78, 015022 (2008)

Heavy charged Higgs production at the LHC

dominant channel :

K-factors for the NNLO QCD corrections

considered

N. Kidonakis, JHEP 05, 011 (2005).

D.-W. Jung, K. Y. Lee., Phys. Rev. D 78, 015022 (2008)

D.-W. Jung, K. Y. Lee., Phys. Rev. D 78, 015022 (2008)

in the LR model

in the 2HD model

Decay of produced charged Higgs boson

D.-W. Jung, K. Y. Lee., Phys. Rev. D 78, 015022 (2008)

• Different structure of the Yukawa couplings in the LR model leads to different phenomenology of the Higgs bosons from those of the 2HD model.

• Production cross section of the charged Higgs in the LR model is generically larger than that of the 2HD model at the LHC.

• Decays of the heavy charged Higgs boson in the

LR model combined with the production cross section might discriminate the LR charged Higgs from the 2HD charged Higgs boson.

H++

• H++: Doubly charged scalar• appears when there exist Higgs triplets or higher

multiplets.

• LR model• 3-3-1 model• Little Higgs model• Higgs triplet model for neutrinos

Underlying Physics

H++ in the LR model

• Production depends on WR mass

• Phenomenology depends on neutrino structure and see-saw mechanism.

Lepton number violating terms are

∝ mWR

Productions

Decays

Reconstructed pp→H++H-- →μ+ μ+ μ- μ-

CMS collab., J. Phys., G 34, N47 (2007)

Expected discovery of pp→H++H-- →μ+ μ+ μ- μ-

CMS collab., J. Phys., G 34, N47 (2007)

100% dilepton assumed

a. 100 fb-1

b. 300 fb-1

ATLAS collab., J. Phys., G 32, 73 (2006)

q’

• t’, b’: Fourth generation quarks

• Generically heavier than t and b since they are not observed yet.

• Why not even in the SM?

• LEP data on invisible decay of Z boson restricts the number of generations =3

: 4th neutrino should be heavier than mZ/2.

Underlying Physics

Why 3 generations?

LEP data on invisible decays

n =

Astrophysical data of He production

D.N. Schramm and M.S. Turner., Rev. of Mod. Phys. 70, 303 (1998)

Decays

• Charged current decays

• FCNC decays

…

Present bounds

PDG 2008

Q, L

• Excited quarks and leptons : Heavy states of quarks and leptons sharing quantum numbers with ordinary quarks and leptons.

• Appear in the composite models.

• Quarks and leptons are bound states of some constituents. (“Preon”)

• Experimentally similar to 4th generations.

Underlying Physics

• Excited fermions can be pair-produced via gauge couplings.

• If the compositeness scale is high enough, the compositeness manifests through effective 4-fermion contact interactions

PDG 2008

Dark Matter

• Dark matter : (Large) missing energy at the collider

• Appears in various models

• LSP in the MSSM• Lightest heavy states in the Little Higgs model• Lightest KK states in the extra dimensional model• And many other models…

Underlying Physics

• Many possibilities are open at the LHC.

Summary