hunting the last missing particle of the standard model

Hunting the Last Missing Particle of the Standard Model

Hunting the Last Missing Particle of the Standard Model

Shufang Su • CaltechShufang Su • CaltechShufang Su • CaltechShufang Su • Caltech

S. Su U. Arizona - Colloquium 2

Particles and Forces Particles and Forces

• Fundamental interactionsFundamental interactions – GravityGravity– Electromagnetic forceElectromagnetic force– Weak interaction Weak interaction nuclear nuclear -decay, burning of the sun …-decay, burning of the sun …– Strong interaction Strong interaction -decay, holds proton and neutron …-decay, holds proton and neutron …

forcesforces

• Building blocks of matter -- elementary particlesBuilding blocks of matter -- elementary particles

smaller distance : higher energysmaller distance : higher energy

??


Exp Discovery and Theory Development

Exp Discovery and Theory Development

e

ma

ss (

Ge

V) e

u

sd

c

bt

ZW

g

1 GeV = 109 eV=1.8x10-24 g

pp nn

theorytheory

• Electromagnetic Electromagnetic • Weak interaction Weak interaction Z,WZ,W

• Strong interaction Strong interaction gg

Standard ModelStandard Model


Standard Model Standard Model

mmWW=80 GeV m=80 GeV mZZ=91 =91 GeVGeV

Is there anything Is there anything missing ?missing ?

Simply impose massSimply impose mass

theory not self-theory not self-consistentconsistent

Create mass for “gauge Create mass for “gauge boson”boson”

predict a predict a HiggsHiggs particle particleHowever, we have not However, we have not find this particle yet …find this particle yet …


Outline Outline

• Why need a Higgs ? Why need a Higgs ?

• How to search the Higgs ?How to search the Higgs ?

• Is it really a (Standard Model) Higgs ? Is it really a (Standard Model) Higgs ?

• How to probe new physics using Higgs How to probe new physics using Higgs

study ?study ?

prediction prediction

evidenceevidence

confirmation confirmation

establishmentestablishment


Why need a Higgs ? Why need a Higgs ?


Electroweak Symmetry Breaking Electroweak Symmetry Breaking

EMEM Photon Photon

m=0m=0

WeakWeak WW++,W,W--

ZZmmWW=80 =80 GeVGeV

mmZZ=91 GeV=91 GeVBegin with a unified theory of EM and weak interactionBegin with a unified theory of EM and weak interaction

We want something thatWe want something that not disturb electromagnetic forcenot disturb electromagnetic force make weak interaction short-rangemake weak interaction short-range

• How to give mass to W and Z boson ? How to give mass to W and Z boson ? • How to give mass to quarks and leptons ?How to give mass to quarks and leptons ?

2x102x10-18-18 m m

Higgs mechanismHiggs mechanism• P.W. Higgs (1964, 1966)• Weinberg(1967), Salam (1968)

• Universe filled with Universe filled with backgroundbackground Higgs fieldHiggs field• Particle get mass via Particle get mass via interactioninteraction with the background Higgs with the background Higgs fieldfield


Higgs Mechanism (Particle Physics) Higgs Mechanism (Particle Physics)

HiggsHiggs

Potential Potential V= - mV= - m22 H H22 + ½ + ½ H H44

HH00=v=v left-over degree of freedomleft-over degree of freedom physical Higgs particlephysical Higgs particle

minimize the potential minimize the potential mmHSMHSM

22 vv2 2 (100 GeV) (100 GeV)22

gauge transformationgauge transformation

degree of freedom eaten bydegree of freedom eaten byWW and Z and Z longitudinal modeslongitudinal modes WW ,Z obtain mass ,Z obtain mass

WW,Z mass,Z mass

WW

WW

HHgg

XXHH00=v=v

mmW W gv gv v=246 GeVv=246 GeV


Higgs Property Higgs Property

Advantage of Higgs mechanismAdvantage of Higgs mechanism

• quark and lepton massquark and lepton mass • SM (with Higgs) agrees well SM (with Higgs) agrees well with experiments with experiments

Other model:Other model: composite Higgscomposite Higgs

• hard to fit with hard to fit with experimental dataexperimental data• hard to build modelhard to build model

ff

ff

HHyy

XXHH00=v=v

mmf f y v y v

However, However, Higgs is still missing ...Higgs is still missing ...

Go look for it!Go look for it!

Higgs propertyHiggs property v=246 GeVv=246 GeV• CP even scalarCP even scalar• coupling coupling mass mass

- fermion fermion mmff/v/v - gauge boson gauge boson mmWW/v , m/v , mZZ/v/v

• mass : mass : mmHSMHSM22 vv2 2 (100 GeV) (100 GeV)22

mass not predictedmass not predicted


Theoretical Constraint on mHSM Theoretical Constraint on mHSM

Landau poleLandau pole

potential unbounded from belowpotential unbounded from below

101055 GeV GeV

116 GeV116 GeV

SM valid up to scale SM valid up to scale

K. Riesselmann (1997) V= - mV= - m22 H H22 + ½ + ½ H H44

mmHH22= = vv22

= M= Mpl pl 10 101919 GeV GeV 130 GeV < m130 GeV < mHH < 180 GeV < 180 GeV

((yyttyytt

… …


Indirect Constraint from Electroweak Data

Indirect Constraint from Electroweak Data

LEP EWWG

mmHSMHSM=81=81+52 +52 GeVGeV

mmHSMHSM<193 GeV at 95% C.L.<193 GeV at 95% C.L.-33-33

indirect bounds: mindirect bounds: mtt= 171= 171-9-9 GeV GeVdirect search: mdirect search: mtt=174.3 =174.3 5.1 GeV 5.1 GeV

+11+11

indirectdirect

without NuTeV


How to search the Higgs ? How to search the Higgs ?

Decay right after it is producedDecay right after it is produced

does not exist in nature anymoredoes not exist in nature anymore produced it at high-energy collidersproduced it at high-energy colliders look for its decay products at detectorslook for its decay products at detectors


Higgs Decay (SM) Higgs Decay (SM)

M. Spira (1998) mHSM (GeV)

gold-plated gold-plated mode for LHC mode for LHC seaches:seaches: ZZee++ee-- / / ++--

mmHSMHSM 135 GeV 135 GeV mmHSM HSM 135 GeV 135 GeV

Bra

nch

ing

rat

io

BrBrHSM HSM = = (H (HSMSM final state) final state)

(H(HSMSM everything) everything)


LEP Search : Current mHSM Limit LEP Search : Current mHSM Limit

LLarge arge EElectron lectron PPositron Collider (ositron Collider (CERNCERN))

Ecm Ecm 189 GeV 189 GeV 2461 Pb2461 Pb-1-1

Ecm Ecm 206 GeV 206 GeV 536 Pb536 Pb-1-1

Add plotAdd plot

exclusion boundexclusion bound

mmHSMHSM 114.4 GeV 95% C.L. 114.4 GeV 95% C.L.

possible signal possible signal mmHSMHSM 116 GeV 116 GeV– signal+background 37% C.L.signal+background 37% C.L.– backgroundbackground 8% C.L.8% C.L.

ee--ee++

1 pb= 10-12 b; 1b=10-28 m2

ee++ee-- ZH ZHSMSMfour jets Hbb, Zqq

missing energy

Hbb, Z

leptonic Hbb, Zll

tau lepton Hbb, ZH, Zqq


Higgs Prodcution at Tevatron (Run II) Higgs Prodcution at Tevatron (Run II)

Tevatron Tevatron (Fermilab) (Fermilab) pp collider pp collider CDF, D0CDF, D0

huge huge backgroundbackground

W,Z W,Z leptons leptons

mmHSM HSM 135 GeV 135 GeV

HHSMSM bb bb

mmHSMHSM 135 GeV 135 GeV

HHSMSM W W++WW--

Ecm = 2 TeVEcm = 2 TeV

L=L= 2 fb2 fb-1 -1 / year/ year

cros

s se

ctio

n (

pb)

events/year

2x104

2x102

2

M. Spira (1998)

-- //


Higgs Search at Tevatron (Run II)

Higgs Search at Tevatron (Run II)

Tevatron Tevatron (Fermilab)(Fermilab) Ecm = 2 TeV, L= 2 fbEcm = 2 TeV, L= 2 fb-1-1 / year / year

Run II Higgs working group

(1 year)

(15 year)

(5 year)

If no Higgs is foundIf no Higgs is found95% C.L. exclusion limit95% C.L. exclusion limit


Higgs Search at Tevatron (Run II) Higgs Search at Tevatron (Run II)

Tevatron Tevatron (Fermilab)(Fermilab) Ecm = 2 TeV, L= 2 fb-1 / yearEcm = 2 TeV, L= 2 fb-1 / year

Run II Higgs working group130130

20 fb20 fb-1-1

(1 year)

(5 year)

(15 year)

Discovery reachDiscovery reach


Higgs Producction at LHC Higgs Producction at LHC

LLarge arge HHadron adron CCollider ollider (CERN) (CERN) pp pp ATLAS, CMSATLAS, CMSEcm = 14 TeVEcm = 14 TeV

L=L= 10 fb10 fb-1 -1 / year/ year

cros

s se

ctio

n (

pb)

mHSM (GeV)

ggH mmHSM HSM 135 GeV 135 GeV

HHSMSM

mmHSMHSM 135 GeV 135 GeV

HHSMSM W W++WW--, ZZ, ZZ

HHSMSM , , ,,WW++WW--, ZZ, ZZ

120 GeV120 GeV H HSMSM 180 180 GeVGeV

events/year

106

104

102

1M. Spira (1998)

pppp

102

10

10-4

10-3

10-2

10-1

1


Higgs Search at LHC Higgs Search at LHC

LLarge arge HHadron adron CCollider ollider (CERN) (CERN) pppp

ggHggHtt

cover entire Higgs mass region of SM with cover entire Higgs mass region of SM with more than 5 more than 5 significance. significance.

L=10 fbL=10 fb-1 -1 / year/ year

CMS, ATLAS (2002)

5 5


Need precise study of Higgs properties at a e+e- colliderNeed precise study of Higgs properties at a e+e- collider

• basic properties: basic properties: mass, width, spin and CP quantum mass, width, spin and CP quantum numbernumber

• origin of particle mass origin of particle mass Higgs coupling Higgs coupling particle particle massmass

• reconstruct Higgs potential: reconstruct Higgs potential: Higgs self-couplingHiggs self-coupling

Is it really a Higgs ? Is it really a Higgs ?

If we see something at LHC looks like a If we see something at LHC looks like a Higgs …Higgs …

Is it the Standard Model Higgs ?Is it the Standard Model Higgs ?


Higgs Prodcution at LC Higgs Prodcution at LC

LLinear inear CCollider e+e- ollider e+e- clean environmentclean environment Ecm = 500 GeV / 1 TeV ; L= 500 / 1000 fbEcm = 500 GeV / 1 TeV ; L= 500 / 1000 fb-1 -1 / year/ year

LC source book

cros

s se

ctio

n (

fb)

mHSM (GeV)

HeeHee

HHZ

H

HZ

copiously produced, thousands of eventscopiously produced, thousands of events


Higgs Mass, Decay Width and JPC Higgs Mass, Decay Width and JPC

• final state angular distributionfinal state angular distribution• angular and polarization angular and polarization

asymmetryasymmetry

Higgs mass:Higgs mass: mmHSM HSM = 40 MeV= 40 MeV• reconstruct Higgs in ZH productionreconstruct Higgs in ZH production• compare with indirect bounds from compare with indirect bounds from global fitglobal fit

Miller et. al. (2001)Garcia et al. (2001)

ee++ee-- Z Z

Higgs decay width:Higgs decay width: HSMHSM// HSM HSM = 6%= 6%

HSM HSM = = (H (HSMSM W W++WW--))

Br (HBr (HSMSM W W++WW--))

Higgs production HHiggs production H

Higgs decay HHiggs decay HSMSM W W++WW--

ee++ee--

ZZ

HH


Higgs Coupling Higgs Coupling

mmHSM HSM 150 GeV 150 GeV • Higgs decay branching ratioHiggs decay branching ratio• Higgs production cross sectionHiggs production cross section

Carena et. Al. (2002) mmHSM HSM = 120 GeV= 120 GeV

mmHSM HSM 150 GeV 150 GeV • HHSMSM cc, gg, cc, gg, too small too small • HHSMSM W W++WW--,ZZ ,ZZ precisely measuredprecisely measured• HHSMSM bb bb precision reduced when precision reduced when mmHSM HSM 200 GeV 200 GeV • HHSMSM tt tt possible when mpossible when mHSM HSM 2 m 2 mtt

reconstruct Higgs potentialreconstruct Higgs potential

vv


Photon Collider Photon Collider

ee++ee--collider operating in collider operating in mode mode EcmEcm=0.8 Ecm=0.8 Ecmeeee

• measure measure (H (HSMSM ) )

bb (H (HSMSM ) Br(H) Br(HSMSM bb) bb)

sensitive to heavy statessensitive to heavy states

• Higgs decay width Higgs decay width HSM HSM = = (H (HSMSM ) / Br(H) / Br(HSM SM ) )

• mmHSM HSM 200 GeV , directly measure 200 GeV , directly measure HSM HSM

• photon polarization photon polarization CP quantum number CP quantum number

every particle (get mass every particle (get mass from Higgs) contributesfrom Higgs) contributes


There must be new physics beyond minimal There must be new physics beyond minimal Standard ModelStandard Model

• What is it ? What is it ? • How to probe it using Higgs How to probe it using Higgs

study ? study ?

What can we learn ? What can we learn ?

If we find deviation from Standard Model If we find deviation from Standard Model prediction … prediction …


What New Physics ? What New Physics ?

• SM is an effective theory below some energy scale SM is an effective theory below some energy scale

Hierarchy problem:Hierarchy problem: MMEWEW100 GeV , M100 GeV , Mplankplank 10101919 GeV ? GeV ? Naturalness problem:Naturalness problem: mass of a fundamental scalar mass of a fundamental scalar (like (like Higgs) receive Higgs) receive huge huge quantum corrections: quantum corrections:

(m(mHH22))physicalphysical (m (mHH

22))0 0 + + 22 (100 GeV)(100 GeV)22

-(10-(101919 GeV) GeV)22precise cancellation precise cancellation up to 10up to 1034 34 orderorder

• SupersymmetrySupersymmetry SM particle superpartnerSM particle superpartner Spin differ by 1/2Spin differ by 1/2

MMinimal inimal SSupersymmetric upersymmetric SStandard tandard MModel (MSSM)odel (MSSM)

(10(101919 GeV) GeV)22

HH

- - 22

HH


Higgs Sector in MSSM Higgs Sector in MSSM

SMSM MSSMMSSM

HHSMSM HHdd, H, Huu

HHSMSM00=v=v

v=246 GeVv=246 GeV

HHdd00=v=v1 1 ,,HHuu

00=v=v

22

vv22=v=v112 2 +v+v22

22

tantan=v=v22/v/v11

HH44 gg1122+g+g22

22

HHSMSM

(m(mHSMHSM22

vv22))

hh0 0 (m(mh0h0))

HH0 0 ,A,A0 0 ,H,H

((mmA0A0))

CP-even Higgs hCP-even Higgs h00

• decoupling limit: decoupling limit: mmA0 A0 m mZZ

hh00 similar to SM Higgs similar to SM Higgs

• hh00 mass mass tree level: mtree level: mh0h0mmZZ

loop corrections: loop corrections: mmh0h0 135 GeV 135 GeV

MSSM Higgs sector determined MSSM Higgs sector determined byby tantan andand m mA0A0

SM Higgs searches at low massSM Higgs searches at low massregion could be applied to the region could be applied to the light MSSM Higgs hlight MSSM Higgs h00

gauge gauge

couplingcoupling


LEP Search Limit (MSSM) LEP Search Limit (MSSM)

AA00hh00

ZhZh00

0.5 0.5 tan tan 2.42.4

mmh0h0 91.0 91.0 GeVGeV

mmA0A0 91.9 91.9 GeVGeV

sinsin22((--effeff))

ee++ee-- Zh Zh00 ee++ee-- A A00hh00

coscos22((--effeff))


Bounds on mA0 From Higgs Coupling

Measurements Bounds on mA0 From Higgs Coupling

Measurements

Br(HBr(HWW++WW--)=5%)=5%

Carena et. al. (2002)

hh00 coupling m coupling mZZ22

HHSMSM coupling m coupling mA0A022

-1 -1

• non-zero deviationnon-zero deviation

constraints on mconstraints on mA0A0

mmA0A0 650-800 650-800 GeVGeV

mmA0 A0 controls the degree of controls the degree of decouplingdecoupling

• mmA0 A0 m mZZ

decoupling regiondecoupling region no deviationno deviation


Three SUSY Breaking Scenarios Three SUSY Breaking Scenarios

• supersymmetry must be brokensupersymmetry must be broken electron: m=0.511 MeV, electron: m=0.511 MeV, nono scalar-electron scalar-electron

• MSSM:MSSM: 105 new SUSY breaking parameters105 new SUSY breaking parameters out of out of controlcontrol

• mechanism for SUSY breaking: mechanism for SUSY breaking: (flavor blind)(flavor blind)

greatly reduce SUSY parametersgreatly reduce SUSY parameters

low energy MSSMlow energy MSSM(visible sector)(visible sector)105 parameters105 parameters

SUSY-breakingSUSY-breaking(hidden sector)(hidden sector)

a few parametersa few parameters

somethingsomething gravity gravity

gravity-mediated SUSY breaking gravity-mediated SUSY breaking (SUGRA)(SUGRA) gauge-mediated SUSY breaking (GMSB)gauge-mediated SUSY breaking (GMSB)

gauge interactiongauge interaction

anomaly-mediated SUSY breaking (AMSB)anomaly-mediated SUSY breaking (AMSB)

anomaly anomaly


• LEP search bound LEP search bound

MSSMMSSM SUGRASUGRA GMSGMSBB

AMSAMSBB

mmh0h0max max

(GeV)(GeV)135135 127127 123123 125125

tantanminmin 0.5 or 0.5 or 2.42.4

2.92.9 3.13.1 3.83.8

Distinguish SUSY Breaking Scenario Distinguish SUSY Breaking Scenario

• deviation from SM Higgs coupling deviation from SM Higgs coupling constrains on constrains on mmA0A0

Dedes, Heinemeyer, SS, weiglein (2001, 2002)

mmA0A0 1000 GeV 1000 GeV

mmA0A0 500 GeV 500 GeV


GMSB and AMSB GMSB and AMSB

mmA0A0 1100 1100 GeVGeV

mmA0A0 1300 1300 GeVGeV


500 GeV 500 GeV m mA0 A0 600 GeV , tan 600 GeV , tan 30 30

Distinguish SUSY Breaking Scenario Distinguish SUSY Breaking Scenario

• if we know ranges if we know ranges of of mmA0A0, tan, tan from LHC from LHC • if we see if we see deviations deviations of coupling at LCof coupling at LC

Can we distinguish Can we distinguish various SUSY various SUSY

breaking scenario? breaking scenario?

SUGRASUGRA

GMSBGMSB

AMSBAMSB


Conclusion Conclusion

• Why need a Higgs ? Why need a Higgs ?

• How to search the Higgs ?How to search the Higgs ?

• Is it really a (Standard Model) Higgs ? Is it really a (Standard Model) Higgs ?

• How to probe new physics using Higgs study ?How to probe new physics using Higgs study ?

Higgs mechanism provides a simple and elegant wayHiggs mechanism provides a simple and elegant way

to explain the origin of the massto explain the origin of the mass

- Tevatron Run II exclude Higgs up to 180 GeV (10 fbTevatron Run II exclude Higgs up to 180 GeV (10 fb-1-1))- LHC would find the Higgs if it is thereLHC would find the Higgs if it is there

- detail study at Linear Colliderdetail study at Linear Collider- measure Higgs mass, decay width, coupling… at high precisionmeasure Higgs mass, decay width, coupling… at high precision

Minimal Supersymmetric Standard Model (MSSM)Minimal Supersymmetric Standard Model (MSSM)

- constrain parameter space (mconstrain parameter space (mA0A0))

- distinguish various SUSY breaking scenariosdistinguish various SUSY breaking scenarios Heavy Higgs searchHeavy Higgs search


The hunting is The hunting is continuing …continuing …

pppp

LHCLHC

2007--2007--

TevatronTevatron

Now --Now --

pp--

pp

hunting the last missing particle of the standard model

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