# Presentation: 491018

## Studying EWSB at the Tevatron

- University of California, Berkeley
- (LBNL / Fermilab)
- CDF Experiment
- SLAC Summer Institute
- August 13 – 24, 2001

**Studying EWSB at the Tevatron**
**(Lecture #2)**

## OUTLINE

- Indirect Probe of the Higgs Boson from Precision Electroweak Measurements
- Overview
- Electroweak Parameters at Z pole: Mz, sin2W, ...
- 	(Patrick Janot’s Lecture)
- Mw
- Tevatron Measurement
- Comparision to LEP-II Measurement
- Mtop
- SM Implication of EW Measurements

## Defects of the Standard Model

- It agrees with all confirmed accelerator data.
- But, it is theoretically very unsatisfactory.
- No explanations for particle quantum #’s (Q, I, Y, C).
- Contains >= 19 arbitrary parameters
- 3 gauge couplings : g3,g2,g1
- 1 CP-violating vacuum angle 3
- untidy gauge structure : 3 independent groups
- 6 quark masses, Mu,d,s,c,b,t
- 3 charged-lepton masses, Me,,
- 3 “Cabibbo” weak mixing angles, 
- 1 CP-violating Kobayashi-Maskawa phase, 
- Arbitrary Yukawa Couplings
- 1 W mass, Mw
- 1 Higgs mass, MH
- Higgs Potential

## Defects of the Standard Model

- As if that was not enough, ...
- 3 neutrino masses, M1,2,3
- 3 neutrino mixing angles, 1,2,3
- 3 CP-violating phases, 
- without even talking about mechanism for  mass generation : more Higgs ? Heavy R ? ...
- and do not forget gravity :
- 1 Neuton’s constant : GN = 1 / Mp2
- 1 Cosmological “constant” : 
- is it ?  Or (t) ?
- Also keep in mind :
- >= 1 inflation parameter : l
- >= 1 parameter for baryon asymmetry nB/n

## Standard Model and Beyond

- Unification                   Flavor                         Mass

- single framework
- for all gauge forces
- Grand Unified Theory
- (GUT)

- origin of particle masses ?
- Higgs boson ?
- why are masses so small ?
- Supersymmetry ?

- Standard Model

- Theory of Everything

- why so many types of q, l?
- weak mixing ?  CP ?
- Composite ?
- Extra symmetry ?

- include gravity
- reconcile it with quantum mechanics
- origin of space-time
- why 4 dimensions ?
- .....
- Superstring ?
- M theory ?

- Open questions :

## The Electroweak Vacuum

- Generating particle masses requires breaking Gauge symmetry

- W

- f

- H

## 

**x**

**x**

**x**

**x**

**x**

**x**

**x**

**x**

**x**

**x**

**x**

**x**

**x**

**x**

**x**

**x**

**x**

**x**

- MZ= MW / cosW

- M = 0

- W

- Z

- e

- t

- MW= 1⁄2 g <>o

- Me= ge <>o      ge ~ 10-6

- Mt= gt <>o        gt ~ 1

- MW = 37.3 GeV / sinW

**Higgs Particles Condensed**

- 

- e

- W

- g

- B

- W3

- A

- Z

- W

- EW

## SM Higgs Mass : No specific prediction

- Standard Model Limitations :
- ~100 < MH < ~ 1,000 GeV depending on the scale, 
- where the SM might break down, i.e. new physics must appear.
- 130 < MH < 180 GeV @  = MPlanck

- not allowed

- not allowed

- Potential
- unstable

- Precision EW meas.s
- MH > ~200 GeV

- Direct searches
- MH > 114 GeV

- Couplings
- blow up !

- Experiments

- SM Theory

## Supersymmetry

- It quacks like Supersymmetry
- To avoid vaccum collapse,
- 	must introduce new bosons
- 22 |H|2 ||2 ( isomultiplets I)
- damage of non-perturbative blow-up
- 	can be avoided by coupling to fermions, ...
- 	to survive up to MP ~ 1019 GeV
- couplings must be finely tuned
- 	automatic within supersymmetry
- _New Physics must be fine-tuned_
- 	to steer between
- 		potential collapse
- 		blow-up of couplings

## Elementary particle masses

- Mass
- (GeV)

- gt ~ 1
- Special ?

- Lecture #2
- Mw, Mtop, ...

## EW observables probe the Higgs bosons indirectly
	by means of quantum corrections.
Large quantum corrections to EW observables come from
	the top quark.

- EW observables probe the Higgs bosons indirectly
- 	by means of quantum corrections.
- Large quantum corrections to EW observables come from
- 	the top quark.

- EW Precision Measurements

## Mtop : measurement vs. predition

**Tevatron**

**(Tevatron)**

- Mtop : measurement vs. predition

## EW Precision Measurements

## You should go to the masses, learn from them, and synthesize their experience into better, articulated principles and methods, ......

**- Mao -**

## The EW strengths are specified by 3 parameters:
two gauge couple constants: g,g’
vacuum expectation value of the Higgs field: v

The theory is democratic: any 3 variables may be chosen.
Choose the 3 parameters most accurately measured so that the predictions for any other measurements become as precise as possible, allowing sensitive tests of the theory.
In the early 1980s, e or , GF, sin2W
Since August 1989 when MZ = 160 MeV (LEP), em(MZ2), GF, MZ
Current accuracy
MZ : 2.1 MeV (2 x 10-5) (LEP)
GF : 1 x 10-5 ( lifetime)
(MZ2) : 2 x 10-4 : dominant uncertainty 

- two gauge couple constants: g,g’
- vacuum expectation value of the Higgs field: v
- The theory is democratic: any 3 variables may be chosen.
- Choose the 3 parameters most accurately measured so that the predictions for any other measurements become as precise as possible, allowing sensitive tests of the theory.
- In the early 1980s, e or ****, GF, sin2W
- Since August 1989 when MZ = 160 MeV (LEP), ******em**(MZ2), GF, MZ
- Current accuracy
- MZ : 2.1 MeV (2 x 10-5) (LEP)
- GF : 1 x 10-5 ( lifetime)
- (MZ2) : 2 x 10-4 : dominant uncertainty

- (Tree-level)

- Electroweak Input Parameters

## em(MZ2) Evaluation

- Can not be reliable calculated.
- With application of dispersion relations,
- measured R values are used to determine it.
- R = (e+e-  qq) / ****0(e+e-  +-)
****0(e+e-  +-) = 4 2(0) / 3Ecm2

- R

- Ecm (GeV)

- BES 2000

- 0

- 10 GeV

- em(MZ2) Evaluation

## Slide 17

## Lepton vs Hadron Colliders

- LEP

- SLC

- x f(x,2) : q, g energy dist. func.

- x

**Lepton vs Hadron Colliders**

## Precision Measurements of MZ, sin2W

- (pb)

- e+e- cm energy (GeV)

- 12

- (s- MZ2)2 + s2Z2/MZ2

- MZ2

- s Z2

- ee ff

- Z2

- e+

- e-

- f

- Z

- f

- e+

- e-

- f

- 

- f

- ff =  + /Z +

- ff ~

- +

- 2

- sin2W

- Mz (LEP1) = 91.1871 +- 0.0021 GeV    ~ 2 x 10-5
- sin2eff (LEP1 + SLC) = 0.23156 +- 0.00017    ~ 7 x 10-4

**Precision Measurements of M****Z****, sin****2********W**

## W Production

- ~10k events / expt.                   ~40k events / expt.

- W  l (e,) + (30%)
- W  qq’ (70%)

## Precision Measurement of MW

- W-

- W+

- W+

- u

- e-

- e+

- p

- p

- W+  e+W-  ud                       W+  e+

- i=1

- 2

- 3

-   MW =   2PeP(1–cos3D)       MTW =   2 PTePT (1–cos2D)

- Pi(W+) + Pi(W-) = 0, i=1,2,3             Pi(W+) = 0, i=1,2

- E(W+) + E(W-) = E(e+) + E(e-)

- PT

- PTe=PT

- e

- 

**Precision Measurement of M****W**

## Precision Measurements of MW

- LEP 2 (e+e-)                     Tevatron (pp)

- Mw(CDF+D0)
- = 80.452 +- 0.062 GeV

- Mw(ALEPH+DELPHI+L3+OPAL)
- = 80.450 +- 0.039 GeV

- CDF
- W  e

- D0
- W  e

- 20 GeV

- WW  qqqq

- WW  qql

**Precision Measurements of M****W**

## Precision Measurements of MW

**Precision Measurements of M****W**

## Precision Measurements of MW

- QCD rad.

## Precision Measurements of MW

## LEP II
25 MeV (stat.), 30 MeV (syst.)
Limited by systematic uncertainties on final state interactions (WW  qqqq)
“Hadroniszation” effect may not be independent between W’s in WW  qqqq.

- LEP II
- 25 MeV (stat.), 30 MeV (syst.)
- Limited by systematic uncertainties on final state interactions (WW  qqqq)
- “Hadroniszation” effect may not be independent between W’s in WW  qqqq.

- Tevatron
****M(stat.)     M(syst.)
- M(syst.) – limited by Z  ee,  sample
- Lepton E, p scales + resolution
- W Pt, recoil energy response

- < 0.1fm

- ~1fm

- q

## MW Uncertainties on P,E scale & resolution

## MW Uncertainties on W Production 

## MW Uncertainties on gluon energy against W 

## Tevatron MW Measurements since 1990

- MW (MeV)

- NW
- NZ
- NW

## Top Production at Hadron Colliders

- NLO corrections ~20%
- Soft gluon resummation
- Theor. uncert. 10–20%

- q

- g

## In SM, assuming V-A coupling with a CKM mixing para. |Vtb|=1 for the t  bW decay vertex, one gets (LO) :
(t  bW)    175 MeV (Mt/MW)3
				(Mt, MW >> Mb)
(t  bW)    1.5 GeV
	 (top)    4 x 10-25 s
Non-perturbative QCD hadronization takes place in a time of orderQCD-1 ~ (100 MeV)-1 ~ 10-23 s
Top decays as free quark (no top hadrons, no toponium spectroscopy)
Top decay will remember its original spin-1/2 state
t  Ws and t  Wd allowed but suppressed by factors of ~10-3 and ~5 x 10-5, respectively.

- (t  bW)    175 MeV (Mt/MW)3
- 				(Mt, MW >> Mb)
- (t  bW)    1.5 GeV
- 	 (top)    4 x 10-25 s
- Non-perturbative QCD hadronization takes place in a time of orderQCD-1 ~ (100 MeV)-1 ~ 10-23 s
- Top decays as free quark (no top hadrons, no toponium spectroscopy)
- Top decay will remember its original spin-1/2 state
- t  Ws and t  Wd allowed but suppressed by factors of ~10-3 and ~5 x 10-5, respectively.

| Dilepton | BR = 1/9 |
| --- | --- |
| Lepton + Jets | BR = 4/9 |
| All-hadronic | BR = 4/9 |

- Top Decay

- PT(b1,b2,l), (l)

## CDF

## b-quark identification (b tagging)

## Mtop MHiggs information via higher order corrections
MW-Mtop-Mhiggs Relation
Top is very heavy,	gt (ttH ~ Mt2 / MW2) ~ 1, 	so understanding its properties may lead to clues about the mechanism behind EWSB.

Everything we currently know about the top quark is based on ~100 tt-bar events / experiment from Run I.
Run II : 
	~100k top events expected.

- Mtop MHiggs information via higher order corrections
- MW-Mtop-Mhiggs Relation
- Top is very heavy,	gt (ttH ~ Mt2 / MW2) ~ 1, 	so understanding its properties may lead to clues about the mechanism behind EWSB.
- Everything we currently know about the top quark is based on ~100 tt-bar events / experiment from Run I.
- Run II :
- 	~100k top events expected.

- What we can measure from tt-bar

## Constraints
MW+ =M W-
Mtop(W+b) = Manti-top(W-b)

- MW+ =M W-
- Mtop(W+b) = Manti-top(W-b)

- The Transverse view & Pt()
- We don’t know the total longitudinal momentum in any event.
- The total transverse momentum of all “detected” particles ~ 0.
- Px = - Pxi, Py = - Pyi

- Top mass measurement

- g

- g

## General Selection of tt-bar events 

- in the lepton + jet channel

## Measurement of Mtop CDF (l + jets)

| Systematic | Mtop(GeV) |
| --- | --- |
| Jet energy scale
Initial, Final state rad.
Background spectrum
b-tagging bias
Parton distribution func.
Monte Carlo generators | 4.4
2.6
1.3
0.4
0.3
0.1 |
| Total | 5.3 |

- MW =
- 77.2 +- 4.6
- GeV

- Mtop= 176.1 +- 5.1 (stat.)
- +- 5.3 (syst.)
- Gev

**Measurement of M****top ****CDF (l + jets)**

## Measurement of Mtop CDF

**Measurement of M****top ****CDF**
**Two leptons, All hadrons**

## Measurement of Mtop D0 (l + jets)

- Mtop= 173.3 +- 5.6 (stat.)
- +- 5.5 (syst.)
- Gev

**Measurement of M****top ****D0 (l + jets)**

## Summary of Run I Mtop measurements

- The Top quark has the best measured mass of all quarks

## Run I tt-bar cross section  measurements

- No excess
- observed.

## Search for X  tt-bar

- Studies of the tt-bar invariant mass spectrum provide a general search for heavy objects decaying to top pairs, for example, in models which use tt-bar condensates in the EWSB mechanism.

## Search for X  tt-bar

## Study of the top Pt distributions

## Top Spin Correlation

## Measurement of (single top)

## Measuremnts of Top decay properties

## Helicity of W bosons from Top decay

## Measurement of Helicity of W from Top decay

## Branching ratios and |Vtb|

## Rare Decays of Top

## Implication of Precision EW Measurements

- Precision EW measurements favor Light Higgs.
- MHiggs = 88+60–37 GeV,    MHiggs = 108+57–38 GeV
- MHiggs < 196~222 GeV at 95% CL

## Implication of Precision EW Measurements

- Year 2000                        Year 2001

- MHiggs = 60+52– 29 GeV
- MHiggs < 165 – 196 GeV @95%CL

- MHiggs = 88+60–37 GeV
- MHiggs = 108+57–38 GeV
- MHiggs < 206 – 222 GeV @95%CL

## EW Measurements (last ~10 years)

- (GeV)

- MH
- (GeV)

- Mtop (GeV)

- year

- 1 prediction

- 1991 Mtop limit

- 1991

- 2001

- 1995

## Summary of Top measurements and Future expectations

- All top quark measurements have been consistent within SM framework, though are presently limited by low statistics.
- Run II top measurements will provide much stiffer tests for SM, and because of the proximity of the top mass to the EWSB scale could be sensitive to new physics.

## Tevatron Run II EW Measurements

-  SM test and ****MHiggs / MHiggs

- Run IIa IIb

- Mtop (GeV)

- MW ~ 25 MeV – 20 MeV, ****Mtop ~ 2 GeV – 1.5 GeV
****MHiggs / MHiggs ~ 30% – 20%

## LEP, SLC, Tevatron Run I EW Measurements

- SM : Higgs around the corner !!
-  Lecture #3 (Monday)