LEP programme Final report Peter Kluit

15 november 2004 SAC presentation 1

LEP programme Final reportPeter Kluit

Thanks to: Wes Metzger, Jan Timmermans

and my LEP collegues


LEP construction


L3

DELPHI


• First study B. Richter 1976

C~43 km, E=2*100 GeV, L=1032 cm-2s-1, 8 interaction points

•Les Houches study 1979

study of Z production and decay

study of WW production

Higgs search

searches for new leptons, quarks

3 and 4 jet structures

• Start construction 1983: C=27 km

• NIKHEF joins DELPHI & L3


Events/experiment:

4.5 M Z events LEP1

10000 WW events 600 ZZ events 250 single-W events

LEP1 (1989-1995): ~200 pb-1/exp LEP2 (1996-2000): ~700 pb-1/exp

LEP2


Z line shape

Moriond 1990:

mZ = 91171 ± 12 ± 32 (incl. ELEP) MeV

Z = 2538 ± 26 ± 28 MeV

N = 3.04 ± 0.12

First evidence 3 generations

Now status up to end 2003:

mZ = 91187.5 ± 2.1 MeV

Z = 2495.2 ± 2.3 MeV

N = 2.9841 ± 0.0083

One of the main LEP results


Beam energy precision 0.2 MeV from resonant depolarisation

But corrections needed due to:

TIDES LEVEL LAKE TGV


Vertex Detectors:

Precise -lepton

b-quark studieshere the DELPHI LEP2

vertex detector


Rb = b / had and top quark mass

Summer 1992:

b = 3739 MeV I3b = -1/2

(370 MeV; for I3b =0: 24 MeV)

Top quark must exist

Now (end 2003):

Rb determined with 0.3%

Rb is also sensitive to top quark mass,

but much less than sin2qeff !


Top mass: predicted by LEP

Prediction mtop from EW fit

EPS93 Marseille:

mtop = 166 –19 -22 GeV

ICHEP94 Glasgow:

mtop = 178 -11 -19 GeV

and CDF saw excess due to top at

mtop = 174 -10 -23 GeV

EPS95 Brussels: both CDF and D0 observed top at predicted mass.

+17 +19

+11 +18

+10 +13

Great success Standard Model

(Nobel prizes for ‘t Hooft and Veltman)


Two most precise sin2eff values from

SLD ALR and LEP A0,b differ by 2.9

lept

FB

SM: 0.1036

A0,b (and also A0,c ) prefer a high

value for the Higgs boson massFBFB

A puzzle left ….. : comparison sin2qefflept


lepton: a puzzle solved

lifetime related to lifetime, mass, mass and leptonic branching ratio

Up to 1992 a 2-2.3 discrepancy between the coupling constants g and g

In 1992 a new, more precise mass by BES

Now - -e universality tested at few per-mille, thanks to high precision vertex detectors


Bs oscillations: to be discovered

00

expcos(11

)( 00

ss B

s

B

ss

ttmABBP

ms > 14.4 ps-1 at 95% C.L.

Continuous improvements in analysis techniques

Bd oscillations discovered at LEP


B physics and CKM matrix

Excellent agreement with sin2bfrom BaBar/Belle

Profound test of SM charged current sector

• |Vtd| from Bd0 – Bd

0 oscillations

• |Vts| from Bs0 - Bs

0 oscillations

• |Vcb| from semileptonic bcl transitions

• |Vub| from semileptonic bul transitions


QCD: test of gluon selfcouplingFrom fit to angular distributions in 4-jet events.

Rel. strength of couplings qqg, ggg, gqq depends on gauge group through Casimir factors CF , CA , TF

TF /

CF


QCD: running of s

Results from fits to different event shape variables.

Combined fit at all energies:

s(MZ) = 0.1201 0.0003

0.0009

0.0009

0.0047

(Note this year Nobel Prize)

(stat)

(exp.syst)

(theor.hadr.)

(theor.ev.shapes)


only exchange

No ZWW vertex

WW cross section

Clear evidence for the

SU(2) x U(1) Gauge structure

CC03 diagrams:

Theory predictions include full O(em) corrections; theory error 0.5%

Triple

Gauge Coupling


Single W WW

DLO

Quartic Gauge Couplings


W mass reconstruction• Reconstructed directly from the decay products

•Constrained fits improve mass

resolution from 8 GeV to 3 GeV

before 4C fit

after 4C fit

qqqq

qq

qqqqe


W mass: LEP combined results (end 2003)

•Not yet final

•Working on systematics, mainly in 4q

Apart from NuTeV result ( scattering)

Very good agreement between direct and indirect measurements


We searched…..

and searched…..

and searched…..

and searched…..

and searched…..But sometimes……

No Higgses, 4th-generation, sleptons, squarks, charginos, neutralinos....

Large part of the MSSM parameter space excluded


•1995: 130-136 GeV

•4-jet events•Sum of di-jet masses

with smallest M

•16 events (8.3 exptd)

•Prob. accumulation in 6.3 GeV bin: 0.01%

ALEPH

Why it is good to have more than one experiment


SM Higgs search

Higgs strahlung: dominant WW fusion: small(can go beyond ‘kinematical limit’)

Final states: (Higgs to bb or )

• bbqq (4-jet channel)

• bb (missing energy channel)

• bbee, bb (leptonic channel)

• bb, bb (tau channel)


ALEPH Higgs candidate


•Small excess around 116 GeV but less than 2 (mainly coming from ALEPH candidates and from four-jet events)

•Excess was 2.9 on 3/11/2000

• CLs = CLs+b / CLb

• when CLs < 0.05 the hypothesis is rejected at 95% CL

Lower limit on Higgs mass

MH > 114.4 GeV (115.3 expected)

Final LEP Higss search results


Results of different fits:

• using only Z pole data

• using all data

• using all data but NuTeV

%3.1410/7.14/

89

5.171

2

12245

9.114.9

probndof

GeVm

GeVm

H

t

%5.415/4.25/

96

3.174

2

6038

5.44.4

probndof

GeVm

GeVm

H

t

%5.2714/7.16/

91

3.175

2

5536

4.43.4

probndof

GeVm

GeVm

H

t

Global electroweak fit


• Good consistency between direct and indirect measurement of mt and mW

• Both prefer low Higgs boson mass

mH < 219 GeV at 95% CL

Light Higgs to be discovered at LHC


Conclusions LEP was great!

Full gauge structure of the SM has been measured, and many measurements in good agreement with the SM prediction

Fantastic precision measurements of W and Z boson, b quark and lepton properties, including the CKM matrix

SM Higgs boson not yet found: MH > 114.4 GeV

NIKHEF was involved in many important analyses: total output: ~ 300 journal papers/experiment

PhD theses: 14 DELPHI, 35 L3 (of which 22 KUN)

Papers still to come: ~55 DELPHI and ~20 L3

LEP programme Final report Peter Kluit

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