Young-Kee KimUniversity of California, Berkeley

(LBNL / Fermilab)

CDF Experiment

SLAC Summer InstituteSLAC, Aug. 13 – 17, 2001

Studying EWSB at the Tevatron

(Lecture #3)

Mw(GeV)

MH(GeV)

Mtop (GeV) year

1 prediction

1991 Mtop limit

1991

2001

1995

EW Measurements (last ~10 years)

Higgs Standard Model

114 < MHiggs < 222 GeV Precision Electroweak Measurements

favor light Higgs (MHiggs < ~222 GeV @95% CL)

Direct Searches for SM Higgs MHiggs > 114 GeV @95% CL

2 Hint @115 GeV Higgs

MSSM h0

behaves very similar to SM Higgs Mh0 < ~130 GeV Most of MSSM

models

Possible to observe Higgs at the Tevatron if it is light.

If the light Higgs exists Both Tevatron (2000 GeV pp collider)

and LEP 2 (200 GeV e+e- collider)produce them.

But hard to observe The Higgs coupling to stable matter is very small.

a low production rate H bb events are swamped by other processes.

a poor signal to background ratio

Strategies Search for ZH or WH events.

e+e- Z* Z H u d W+* W+ H

A low production rate, but clean signature

Light Higgs Searches

H

e+

e-

H

u

u

He+

e- b

b

ge

gu

u b

b

gu

Higgs Searches at LEP 2 (e+e- collider)

e+e- ZHcross section (fb)

e+e- cm energy (GeV)

M > 109 GeV3.0 ZH, 3.6 bgrn, 6 observed

~2 excess observed in agreement with MH ~ 115 GeV

or MH > 114 GeV at 95% CL

ZH Candidates at LEP 2

e+e-bb bb ee++ee--bb bb

L3L3ALEPHALEPH

& girls

TevatronLEP 2

Higgs Searches : LEP 2 Tevatron

SM Higgs Decays

Higgs Hunting at the Tevatron

H bb

H WW

Dominant decay mode

(Higgs + X) vs MHiggs

pb

o gg H bb : too difficult (swampt by QCD bgrnd)

o MHiggs < ~135 GeV : qq W* WH, qq Z* ZHo MHiggs > ~135 GeV : gg H WW*

topgg H WW*

ZH

WH

Tests top quark Yukawa coupling

Higgs Hunting at the Tevatron (cont.)T tt-bar + Higgs : Cross section very low (few fb) but low signal/background

H bb

H WW

Dominant decay mode

(Higgs + X) vs MHiggs

pb

Major background : t t-bar + jets

SM Higgs Signatures (Run I)

b-tagging and Mbb resolution are critical for a light Higgs(see b tagging in Lecture #2)

Mbb Resolution

CDF Run I : Z bb-barMC H bb-bar

Run I : WH l + bb-bar

Run I : WH, ZH qq-bar + bb-bar

Run I : ZH -bar + bb-bar

Run I : ZH l+l- + bb-bar

Run I Higgs Limits

CDF b-tagged events

Tevatron Higgs Potential (Luminosity Limited)

MHiggs (GeV)

MSSM

SM

Run IIb

Run IIa

Parameterized Simulation

MSSM Higgs Searches

MSSM Higgs Production @ Tevatron

MSSM Higgs Branching Ratios

Run I qq bb-bar bb-bar bb-bar

tan = 35

bb + (h/A) 4b

CDF Run I3 b tags

170 GeV

SUSY Higgs limits (b b decay)

~ 1 pb for tan = 30 & Mh = 130 GeV

bb + h/H/A enhanced at large tan

Run I Charged Higgs Searches

Run I Charged Higgs Results

Run I Bosophilic/Fermiophobic Higgs

Run I Bosophilic Higgs Limits

Searches for New Phenomenae.g. Large Extra Dimensions : search for Graviton exchange in the e+e- and Minv vs. cos* distributions

No evidence for Extra Dimensions (ED).

Set limits on the energy scale of extra dimensions: 1.0 TeV for ED=2 1.3 TeV for ED=7.

DØ

signal region

Direct Searches for SM & MSSM Higgs Particles

Tevatron Run IIHiggs Discovery Potential

Run IIa ~2fb-1 by 2003 potential increase ~50 we are at limit set by LEP 2 and should have a small

number of WH or ZH candidates if MH ~ 115 GeV.

Run IIb ~15 fb-1 by ~2007 We should have 3 coverage over most of mass range,

MH < 180 GeV.

** MSSM predict Mh < 130 GeV

spin ½ fermions spin 1 bosons

Higgs : spin 0 boson

Conclusions The origin of mass the Higgs boson

Indirect probe from precision Electroweak Measurements such as Mw, sin2w, Mz, Mtop.

The Higgs boson is around the corner ! Possible senarios in this decade

1. Discover Higgs bosons with MH < 130 GeV Is this the Standard Model Higgs ? If not, implies new physics

2. Discover Higgs bosons with MH > 130 GeV Rules out some extensions of the Standard Model Does it agree with Electroweak measurements ?

3. No discovery upto LHC Detectable effects appear in the production rate and properties of W boson

pairs at ~1 TeV. Discover SUSY particles Other new Phenomena Whatever the outcome,

It will be extremely interesting. At present, it is essentially an experimental question.