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THE LHC/LC SYNERGY. S. Dawson, BNL December, 2002 Why we need both the LC and the LHC Examples: EWSB, SUSY, top quark The cosmological connection. Why are we here?. Not to compare/ contrast LHC/LC

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The lhc lc synergy

S. Dawson, BNL

December, 2002

  • Why we need both the LC and the LHC

  • Examples: EWSB, SUSY, top quark

  • The cosmological connection

Why are we here
Why are we here?

  • Notto compare/ contrast LHC/LC

  • Rather to see how physics info from one machine can influence physics results from the other

  • Goal: Working group document, Spring 03

Weiglein, Oreglia

What do we want to know
What do we want to know?

  • What is the origin of EWSB?

    • Is it a Higgs?

    • Is it something else?

  • What is the origin of fermion masses?

    • Understanding the top quark

  • Is there physics at an intermediate scale? (and what is the scale?)

    • Is it SUSY?

    • Is it little Higgs?

    • Is it extra dimensions?

    • …..

Is mass due to a higgs boson
Is mass due to a Higgs boson?

Precision measurements:

  • Production rates at LEP, Tevatron, LHC fixed in terms of mass

  • Direct search limit from LEP

  • Higgs contributions to precision measurements calculable

G. Mylett, Moriond02

Higgs discovery at tevatron or lhc
Higgs Discovery at Tevatron or LHC



Carena, Conway, Haber, Hobbs, hep-ph/0010338


Is it a higgs

How do we verify role in EWSB?

Measure Yukawa couplings

Measure spin/parity

Reconstruct Higgs potential

Is it a Higgs?

Higgs properties at lhc

LHC measures B

Eg, ggh depends on ggh and h couplings

Result is combination of coupling constants

Significant PDF uncertainties

Cancel in ratios

Weak boson fusion depends on SU(2) assumption about WWh and ZZh couplings

Precision measurement for Mh>140 GeV from WBF

Higgs properties at LHC

Zeppenfeld, Belyaev, Reina

Higgs measurements at lhc

Mh<140 GeV, H/H10-20%

Not all channels possible

tth, h+- critical

Higgs Measurements at LHC

200 fb-1

300 fb-1

(tth,h, Wh,hbb)

Belyaev & Reina, hep-ph/0205270

Untangle higgs couplings

PDF uncertainties cancel in ratios

Improved precision by fixing bbh/h coupling to SM value

Note lousy precision on bbh

Theory systematic error:

20% (ggh)

5% (WBF)

10% (pptth)

Untangle Higgs Couplings

200 fb-1

Belyaev & Reina, hep-ph/0205270

Well determined initial state

Precision masses with recoil technique

Higgs mass independent of Higgs decay

Model independent Higgs BRs

Van Kooten

Coupling constant measurements at lc
Coupling Constant Measurements at LC


Compare LHC:


WBF, 600 fb-1

gbbh 10-20%

Piccinini & Polosa, hep-ph/0211170

At LC, largest uncertainty is theory from mb!

L=500 fb-1, s=350 GeV

Battaglia & Desch,


Who cares about higgs couplings and how well do we need to do
Who cares about Higgs Couplings?And how well do we need to do?

  • SUSY models, gbbh enhanced at large tan , small MA …info about SUSY parameters

  • Little Higgs, topcolor models, new physics in gtth


Higgs mass measurements



Direct reconstruction of

LC @ 350 Gev

Higgs mass measurements

Primarily interesting for comparison with precision EW measurements

Conway, hep-ph/0203206

Higgs spin parity in e e zh

Angular correlations of decay products distinguish scalar/pseudoscalar

Threshold behavior measures spin

Higgs spin/parity in e+e-Zh

[20 fb-1 /point]

Miller, hep-ph/0102023

Higgs self couplings difficult at lhc
Higgs self couplings difficult at LHC scalar/pseudoscalar



Baur, Plehn, Rainwater, hep-ph/021124

Measuring higgs self couplings at lc

Must measure scalar/pseudoscalar

e+e- Zhh

Small rate

.2 fb for Mh=120 GeV large background

Large effects in SUSY


ghhh suppressed MA < 300 GeV

Measuring Higgs Self Couplings at LC

Castanier, Gay, Lutz, Orloff, hep-ph/0101028

Lafaye, hep-ph/0002238

Is the world supersymmetric
Is the world Supersymmetric? scalar/pseudoscalar

Find SUSY particles

Find SUSY partners

Check impact on precision measurements

Measure SUSY couplings

Reconstruct underlying GUT theory

Light susy consistent with precision measurements

SUSY predicts light Higgs, M scalar/pseudoscalarh<130 GeV

For MA, SUSY Higgs sector looks like SM

Can we tell them apart?

Higgs BR are different in SUSY

Find all SUSY Higgs

Light SUSY consistent with Precision Measurements

Find all the Higgs Bosons scalar/pseudoscalar



 collider sensitive

4 years at !

Carena, hep ph/9907422


Into the wedge

e scalar/pseudoscalar+e- H+H-, H0A0

Observable to MH=460 GeV

at s=1 TeV

e+e- H+,H+tb

L=1000 fb-1, s=500 GeV,

3 signal for MH 250 GeV

e+e- W+H-

Largest at low tan 

s=500 GeV, .01 fb

Moretti, hep-ph/0209210

Into the wedge

Logan & Su, hep-ph/0206135

Msugra simplest version of susy
mSUGRA simplest version of SUSY scalar/pseudoscalar

  • 4 parameters, 1 sign

    • m0 (scalar mass at MGUT)

    • m1/2 (gaugino mass at MGUT)

    • A0 (mixing term)

    • tan  (ratio of Higgs VEVs)

      Measure m(gluino) at LHC

      predict m(neutralino) at LC

Very predictive…all masses and couplings predicted

Relationships are different for GMSB, AMSB…..

Lhc tevatron will find susy

SUSY mass differences from cascade decays;eg scalar/pseudoscalar

M0 limits extraction of other masses

Fit to SUGRA parameters

LHC/Tevatron will find SUSY


Catania, CMS

Lc makes precision mass measurements

Chargino pair production, S-wave scalar/pseudoscalar

Rises steeply near threshold

This example:

LC makes precision mass measurements

How do we distinguish a chargino from a 4th generation lepton?

Feng, hep-ph/0210390

Blair, hep-ph/99910416

Lc can step through energy thresholds run time scenario for l 1000 fb 1
LC can step through Energy Thresholds scalar/pseudoscalarRun-time Scenario for L=1000 fb-1

  • SUSY masses to .2-.5 GeV from sparticle threshold scans

  • M0/M0 7% (Combine with LHC data)

  • 445 fb-1 at s=450-500 GeV

  • 180 fb-1 at s=320-350 GeV (Optimal for Higgs BRs)

  • Higgs mass and couplings measured, gbbh1.5%

  • Top mass and width measured, Mt150 GeV

    Battaglia, hep-ph/0201177

Lhc fits to susy parameters
LHC: Fits to SUSY Parameters scalar/pseudoscalar

LHC: Mass reconstruction limited by LSP mass

 LHC sensitive to mass


Bachacou, Hinchliffe, Paige, hep-ph/9907518

LC accuracy

Measurement of LSP mass

at LC improves LHC

mass resolution

Susy lc lhc
SUSY: LC+LHC scalar/pseudoscalar

  • LHC sensitive to heavy squarks

  • Use neutralino mass, couplings from LC

  • CMS study:10 fb-1 gives squark, gluino masses to 1-2% if neutralino mass known from LC

R. Van Kooten: “Bands, not blobs”

Combine lc lhc mass measurements window to high scales

LC measures chargino, neutralino, selectron masses from thresholds

LC extracts mixing parameters from cross section measurements

LHC measures gluino, squark masses

RGE evolve parameters to GUT scale

Sample mass measurements




Combine LC/LHC mass measurementsWindow to high scales?

Do gaugino scalar masses unify in msugra
Do gaugino & Scalar masses unify in mSugra? thresholds

Scalar masses

Gaugino masses

Freitas, hep-ph/0211076

Susy couplings

Compare rates at NLO: thresholds

Lowest order,

Super-oblique corrections sensitive to higher scales

Masses from endpoints


Tests coupling to 1% with 20 fb-1

SUSY Couplings:


Probes mechanism of SUSY breaking

Are we being too simplistic
Are we being too simplistic? thresholds

  • Many possibilities beyond MSSM

  • Suppose explicit CP violation

    • Complex tri-linear mixing

  • Instead of h,H, and A

     3 states which mix

  • Holes in LEP limits on Higgs search

  • New phenomenology

Carena, Mrenna

Cosmic connections

LC/LHC can give insight into origin of dark matter thresholds

SUSY provides dark matter candidate, LSP

LSP is weakly interacting, neutral and stable

Cosmic Connections

mSUGRA predicts everything in terms of 5 parameters thresholds

Calculate 0 relic density

Assume 2 around central value

Assume Dark Matter is 0


Forbidden by 3 g-2

.07 <Xh2<.21


m1/2>300-400 GeV

M(+)>240 GeV

M(o)>120 GeV

Arnowitt and Dutta, hep-ph/0204187

Dark matter at large tan

CLEO bound from b thresholdss

Similar allowed region from dark matter

Does this picture persist for more complicated SUSY models?

Dark Matter at large tan 

1.8 x 10-4<B(bs)

<4.5 x 10-4

Understanding the top quark
Understanding the Top Quark thresholds

  • Why is Mtv/2 ?

  • Kinematic reconstruction of tt threshold gives pole mass at LC

  • Compare LHC

2Mt (GeV)

Groote , Yakovlov, hep-ph/0012237

QCD effects well understood

NNLO ~20% scale uncertainty

Who cares about precision m t

Precision M thresholdst, MW test consistency of SM

Limits Higgs mass, SUSY parameters

Who cares about precision Mt?

Top yukawa coupling tests models

tth coupling sensitive to strong dynamics thresholds

Above tth threshold


Theoretically clean

s=700 GeV, L=1000 fb-1

Large scale dependence in tth rate at LHC

L=300 fb-1

Top Yukawa coupling tests models

Baer, Dawson, Reina, hep-ph/9906419

Juste, Merino, hep-ph/9910301

Reina, Dawson, Orr, Wackeroth, hep-ph/0211438

Beenacker, hep-ph/0107081

Tth at lc
tth at LC thresholds

  • 20 % measurement of gtth to mh=200 GeV using hWW decay

  • Needs s=800 GeV

Gay, 02

What if the lhc doesn t find a higgs

Still have to understand M thresholdsW, precision measurements

Fit to S, T0

Without Higgs, effective theory

For new physics at 3 TeV scale, EW fits give a,b1

Models which satisfy EW constraints without Higgs tend to have new Z’ or light t’s

What if the LHC doesn’t find a Higgs????

Bagger, Falk, & Schwartz, hep-ph/9908327

Hill & Simmons, hep-ph/0203079

Exciting physics ahead
Exciting physics ahead thresholds

  • LHC/Tevatron finds Higgs

    LC makes precision measurements of

    couplings to determine underlying model

  • LHC finds evidence for SUSY, measures mass differences

    LC untangles spectrum, finds sleptons

    LHC/LC combination makes precision

    measurements of couplings and masses;

    Untangles GUT theory