Heavy Flavour: Identification (I)b- and c-hadrons decay weaklyb- and c-hadrons decay weakly towards c- and s-hadrons, with a towards c- and s-hadrons, with a

macroscopic lifetime (macroscopic lifetime (1.6 ps1.6 ps for b’s), corresponding to for b’s), corresponding to few mm’sfew mm’s at LEP at LEP

10 cm10 cm

1 cm1 cm

3d-vertexing3d-vertexing determines determinessecondary and tertiarysecondary and tertiaryvertices.vertices.

High resolutionHigh resolution is crucial. is crucial.

Impact parametersImpact parameters of ofreconstructed tracksreconstructed tracksallow b quarks to be allow b quarks to be tagged with very goodtagged with very goodpurity.purity.

Mass of secondary vertexMass of secondary vertextracks is a very powerfultracks is a very powerfuldiscriminator of flavourdiscriminator of flavour(b, c, and light quarks):(b, c, and light quarks):

Heavy Flavour: Identification (II)

Vertex Mass for EventsVertex Mass for EventsWith a Secondary VertexWith a Secondary Vertex

In SLDIn SLD

Vertex Mass (GeV/cVertex Mass (GeV/c22))

b (MC)b (MC)

c (MC)c (MC)

uds (MC)uds (MC)

DataData

Vertex detectors (Si Vertex detectors (Si -strips, CCD’s, pixels):-strips, CCD’s, pixels):

• At At LEPLEP: inner radius : inner radius 6 cm6 cm, good resolution;, good resolution;• At At SLCSLC: inner radius : inner radius 2.3 cm2.3 cm, superior resolution., superior resolution.

SLD can do both b- and c-tagging with good purity.SLD can do both b- and c-tagging with good purity.

Heavy Flavour:ResultsUse Use double-tag methoddouble-tag method to reduce uncertainties to reduce uncertainties from the simulation, e.g., in bb events:from the simulation, e.g., in bb events:

2udsuds

2ccb

2bb

hemi2

udsudsccbbhemi

1

)1(

RRRf

RRRf

Take Take cc, , udsuds, and , and bb (all small) from simulation. (all small) from simulation.

Solve for Solve for bb and R and Rbb ! !

Rate Value Error

Rb 21.646% 0.075%

Rc 17.19% 0.31%

3 103 10-3-3

With this measurement alone:

mtop 150 25 GeV/c2

(dependence on m(dependence on mHH, , ss, … cancel in the ratio), … cancel in the ratio)

Rb = bb / had--

Prediction of Mtop

A top mass of 177 GeV/c2 was predicted by

LEP & SLC with a precision of

10 GeV/c2 in March 1994.

One month later, FNALannounced the first 3

evidence of the top.

2directtop

2EWtop

GeV/ 3.40.178

GeV/ 0.105.179

cm

cm

In 2005:In 2005:

Perfect Perfect consistencyconsistency between prediction between predictionand direct measurement. Allows a globaland direct measurement. Allows a globalfit of the SM (fit of the SM (with mwith mHH) to be performed.) to be performed.

/ SLD/ SLD

/ SLD/ SLD

/ SLD/ SLD

/ SLD/ SLD

Detour - Top @ TEVATRON

last discovery of a fundamental particle

# of Physicists for Particle Discovery

Tevatron ~ 800

Year Discovered

Nu

mb

er

of

Ph

ysic

ists

LHC

The Tevatron Collider

– Beam energy =980 GeV

– 36x36 bunches, 396 ns coll. sep.

– Recycler and e-cooling in use

– Pbar “stashes” >350e9 in recycler

Tevatron LuminosityTevatron Luminosity

• Peak luminosity record: 2.2 x1032 cm-2 s-1

• Integrated luminosity– Weekly record: 33 pb-1 /week/expt – Total delivered: 1.7 fb-1 /expt. Total recorded: 1.5 fb-1 /expt

• Doubling time: ~1 year • Future: ~2 fb-1 by 2006, ~4 fb-1 by 2007, ~6-8 fb-1 by 2009

Today’s Presentation:300 pb-1 ~ 1 fb-1

Peak Luminosity Integ. Lum. (delivered) / Experiment2002 2003 2004 2005 2002 2003 2004 2005

The CDF Detector

The DØ Detector

Why top physics is interesting?

Production cross section can be

accurately predicted by QCD calculations

BR(tWb)≈1 in SM.Measurement of Vtb is test standard model

Spin of W boson is direct probe of top spin and the only

way to measure spin correlations in

unbound quarks

Are there resonances in the top quark pair

spectrum?

Measure top quark mass - dominant term in electro-weak radiative loop corrections provide constraint of

Higgs boson mass

Are there other objects that decay to b quarks

and W bosons?

Top Quark Mass Today

CDF & D0: The top quark mass measurement

has become a precision determination. crucial for SM tests

Mtop & MzObs. Value Error

mZ 91187.5 2.1 MeV

Z 2495.2 2.3 MeV

0 41.540 0.037 nb

Rl 20.767 0.025

Mtop & MZ are very precisely

known today

2

2

2

2

Log4 Z

H

Z

t

m

m

m

m

Prediction of MW

PredictPredict mmWW in the SM: in the SM:

mmWW22 = = mmZZ

22(1+ (1+

))coscos22WW

effeff

Direct Measurements*

Precision Measurements

mmHH dependence in the SM dependence in the SMthrough quantum correctionsthrough quantum corrections

(see later)(see later)

WW++WW-- q q11qq22ll:: Two hadronic jets, Two hadronic jets,

One lepton, missing energy.One lepton, missing energy.

W mass at LEP 2

WW++WW-- q q11qq22qq33qq44:: Four well separated jets.Four well separated jets.

---- ---WW++WW-- l l1111ll2222::

Two leptons, missing energyTwo leptons, missing energy

s s 2m 2mWW

45.6%45.6% 43.8%43.8% 10.8%10.8%

W mass at LEP 2

mmWW (thresh.) = (80.40 (thresh.) = (80.40 0.22) 0.22) GeV/cGeV/c22

Systematics: Beam energySystematics: Beam energy

W mass at LEP II11,Ep

22 ,Ep

44 ,Ep

33 ,Ep

11,Ep

22 ,Ep

33 ,Ep

44 ,Ep

WW

4

1

4

1

,0 ,

mm

psEi

ii

i

5 Constraints:5 Constraints:

0 unknowns, 0 unknowns, 5C fit5C fit

3 unknowns, 3 unknowns, 2C fit2C fit

Fitted Mass (GeV/cFitted Mass (GeV/c22))

80.448 80.448 0.043 GeV 0.043 GeV

80.457 80.457 0.062 GeV 0.062 GeV

W mass at LEP II

• Good consistency between experiments;Good consistency between experiments;

• Good consistency with hadron collidersGood consistency with hadron colliders

• Fair consistency with Z data (LEP/SLD).Fair consistency with Z data (LEP/SLD).

mmWW(LEP) = 80.392 (LEP) = 80.392 0.0290.029

Standard Model FitKnowing mKnowing mtop,top, most electroweak observables have a sensitivity to m most electroweak observables have a sensitivity to mHH through through

2directtop

2EWtop

GeV/ 1.24.171

GeV/ 0.105.179

cm

cm

Standard Model Fit Global fit of Global fit of mmHH and and mmtoptop:: 239

28EWHiggs GeV/ 85 cm

C.L. 95%at GeV/ 166 2Higgs cm

Standard Model FitInternal Consistency of the Standard Model Internal Consistency of the Standard Model

Largest discrepancy Largest discrepancy (-2.7(-2.7) well ) well inside statistical expectation;inside statistical expectation;

22 probability ~ 20%. probability ~ 20%. Just fine.Just fine.

A great success but we are still missing one

very important ingredient

need to find the Higgs

Precision SM Tests: Summary– The 0.1% precision tests of the theory have taken

approximately 20,000 man-years of effort!!!• > 2000 physicists working for about 10 years

– Its significance cannot be underestimated …• the first fundamental force unification since Maxwell unified

electricity and magnetism 100 years earlier

• points the way to greater unification and, perhaps, to a fully unified theory of fundamental interactions …

• demonstrates the relevance of Yang-Mills Gauge theories for an accurate description of nature at sub-atomic length scales

• validates the use of quantum field theory to determine higher order corrections to the tree-level processes

• provides support for the Higgs mechanism and suggests the existence of a light Higgs boson (with mass < 200 GeV)

Direct Higgs Searches at LEP 2

s = ms = mZZ

Z Z Hff Hff--

s s m mHH+m+mZZ

HH

HH

HeHeee

HqqHqq

--

--

sensitivity for sensitivity for 200 pb200 pb-1-1::

• s = 192 GeV for ms = 192 GeV for mH H = 100 GeV/c= 100 GeV/c22;;

• s = 210 GeV for ms = 210 GeV for mH H = 115 GeV/c= 115 GeV/c22;;

A few more candidatesat 115 GeV

31-Jul-200031-Jul-2000Mass: 112 GeVMass: 112 GeVs/bs/b115115 = 2.0 = 2.0

21-Aug-200021-Aug-2000Mass: 110 Mass: 110 GeVGeVs/bs/b115115 = 0.9 = 0.9

21-Jul-200021-Jul-2000Mass: 114 Mass: 114 GeVGeVs/bs/b115115 = 0.4 = 0.4

e+e- bb__

DELPHIDELPHI

L3L314-Oct-200014-Oct-2000Mass: 114 Mass: 114 GeVGeVs/bs/b115115 = 2.0 = 2.0

27-Jun-200027-Jun-2000Mass: 113 Mass: 113 GeVGeVs/bs/b115115 = 0.52 = 0.52

ALEPHALEPH

LEP Summary

205 GeV

208+ GeV

206.5 GeV

220 pb220 pb-1-1 delivered in 2000: delivered in 2000:

• starting at 204-205 GeV starting at 204-205 GeV (April-May)(April-May)

• Regularly above 206 GeVRegularly above 206 GeV (from June onwards)(from June onwards)

• Only above 206.5 GeVOnly above 206.5 GeV (September to November)(September to November)

mmHH 114.4 GeV/c 114.4 GeV/c22

Excluded at 95% C.L.Excluded at 95% C.L.

(144 cavities)(144 cavities)

(176)(176)

(240)(240)

(272)(272)

(288)(288)

NotesNotes::

• 372 cavities: 372 cavities: E = 220 GeV;E = 220 GeV;

• 4 straight sections4 straight sections E = 240 GeV.E = 240 GeV.

SM Higgs - where can it be?

In the Standard In the Standard Model:Model:

LHC : 27 km long100m underground

General Purpose,pp, heavy ions

General Purpose,pp, heavy ions

CMS+TOTEM

ATLAS

Heavy ions, pp

ALICE

pp, B-Physics,CP Violation

Higgs Search at the LHC

The CMS Detector The CMS Detector today at point 5today at point 5

The ATLAS The ATLAS Barrel Toroid.Barrel Toroid.End of November 2005End of November 2005

NLO

v is vev of Higgs field = 246 GeV

Right bottom plot includes uncertainties fromthe quark masses mt, mb, mc and s(MZ)

tree level couplingsSM Higgs Couplings and BR

Important Decay Modes

• Discovery of the inclusive Higgs boson Discovery of the inclusive Higgs boson production with decay modes:production with decay modes:– H->ZZ->4lH->ZZ->4l– H->H->– H->WW->2lH->WW->2l

Background: tt, ZZ, Background: tt, ZZ, llllbb (“Zbb”)bb (“Zbb”)

Selections :Selections :- lepton isolation in tracker and calolepton isolation in tracker and calo- lepton impact parameter, lepton impact parameter, , ee vertex , ee vertex - mass windows Mmass windows MZ(*)Z(*), M, MHH

H->ZZ->ee

H ZZ* 4l

Signal and background at 5 sigma discoverySignal and background at 5 sigma discovery

ee ee

CMSCMSat 5at 5 sign. sign.

CMSCMSat 5at 5 sign. sign.

H ZZ* 4l

Mh ~140 GeV Mh ~200 GeV

Signal significance: new vs old results; no big changeSignal significance: new vs old results; no big change

~ 125 GeV~ 125 GeV

H ZZ* 4l

H

Discovery potential of H->

SMSM

light h->light h-> in MSSM in MSSMinclusive searchinclusive search

CMS CMS ECAL TDRECAL TDR

CMS PTDRCMS PTDR ATLASATLAS

NLONLO

count. expcount. exp

NLONLO

cut basedcut based

NLONLO

optimized*optimized*

TDR (LO)TDR (LO) New, NLONew, NLO

Cut basedCut based

New, NLONew, NLO

likelihoodlikelihood

~ 7.5~ 7.5 6.06.0 8.28.2 3.93.9 6.36.3 8.78.7

Significance for SM Higgs MSignificance for SM Higgs MHH=130 GeV for 30 fb=130 GeV for 30 fb-1-1

* NN with kinematics and * NN with kinematics and isolation as input, s/b per event isolation as input, s/b per event

Stat. error onlyStat. error only

H ZZ* + H

Luminosity needed for 5 Luminosity needed for 5 discovery discoveryfor incl. Higgs boson production for incl. Higgs boson production

with K factors

LHC: Higgs Discovery Potential

Bottom line: If the Higgs exists the LHC will find it …

Summary/Conclusions– The Standard Model is one of the great triumphs of 20th

century science ...

– However, there are many unanswered questions which point the way to the need for new physics - and a more complete theory of elementary particles ... (see lecture of A. Hocker)

– Particle Physics has great relevance to Cosmology and the Early Universe and addresses many fundamental questions of the “what are we?” , “why are we here?” kind …

– Plenty remains to be done and the key to the origin of mass and (maybe CP violation) may be just round the corner for the next generation of graduate students !

Without the Higgs (mechanism) …• Quarks and Leptons would remain massless•

Tevatron SM Higgs Search

Updated in 2003 in the low Higgs mass region

W(Z)Hl(,ll)bb to include

better detector understanding

optimization of analysis

Sensitivity in the mass region above LEP limit starts at ~2 fb-

1

Meanwhile optimizing analysis techniques understanding detectors better searching for non-SM Higgs with higher production cross sections or enhanced branching into modes with lower backgrounds

LEP

Tevatron

Ldt (fb-

1)

Tevatron Outlook:2007: improve LEP limit of 114 GeV

2009: exclude up to 180 GeV - have 5 Sigma on Mh=115 GeV(2009 less optimistic: exclude up to 140 GeV - have 3 Sigma on Mh=115 GeV)