Highlights vom e e Collider LEP am CERN

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Highlights vom ee- Collider LEP am CERN

• Günther Dissertori
• Physik-Kolloqium
• Uni Innsbruck, 25.6.2002

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LEP
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Imagine a...
LEP annual meeting in 2002
LEP annual meeting in 1989

• Agenda
• Electroweak Physics (ALEPH)
• Heavy Flavour Physics (DELPHI)
• QCD (L3)
• Searches (OPAL)

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Electroweak Physics 1989
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The Standard Model
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Electroweak Physics 1989

• What do we know ?

• What is LEP for?
• Precision tests of the Standard Model , check
  internal consistency, sensitive to quantum
  corrections?
• via measuring couplings and masses gV , gA
  (sin2qW), MZ , MW , mtop , MH

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Tests of the SM a) at Born Level
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Tests of the SM b) beyond Born Level
a a0(1Dr) sin2qWeff 1 - MW2/MZ2(1Dr) Dr a
b ...
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Electroweak Physics in 2002
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Electroweak Physics in 2002

• The SM has indeed been tested at the Quantum
  Level!

• eg. Rb Rb0 0.2183, measurement 2.8 s lower.
  Can be explained by
• mtop155 20 GeV/c2

now mtopLEP 180.5 10 GeV/c2
mtopTeV 174.3 5.1 GeV/c2
mtop

• eg. Gl measurement for a 4.7 s away from
  1/2. Can be explained by
• Dr0.005 0.001

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Z line shape
MZ 91187.6 2.1 MeV/c2 GZ 2495.2 2.3
MeV/c2 s0 41.450 0.037 nb Rl 20.767
0.025

• Possible because of
• precise LEP energy (1-2 MeV)
• precise luminosity meas. ( lt 0.1 )
• excellent final state separation
• of LEP experiments

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Detectors
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Final States
-
e) Z-gtnn
-

• Z ? nn
• Not detectable.

• Z ? tt- Two low multiplicity jets missing
• energy carried by the decay
  neutrinos

-

• Z ? qq Two jets, large particle multiplicity.
• Z ? ee-, mm- Two charged particles (e or ?.)

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Heavy Flavour Detection
mean lifetime t 1.5 10-12 sec ?x? b g c t a
few millimeters
interaction point
0
1cm
x ?
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Silicon Vertex Detectors
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The W mass
mW(LEP) 80.450 ? 0.026 ? 0.030 GeV/c2
(stat.)
(syst.)
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W / Top / Higgs
direct measurements
precision measurements
Standard Model prediction
remember MW2 MZ2(1??)cos2?W
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putting it all together...
MH lt 196 GeV/c2 at 95 C.L. MHEW 8853-35 GeV/c2
Impressive consistency of the Standard Model in
the global fit!
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Heavy Flavours 1989
m
nm
W-
b
B-
c
u
D0
u
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What do we know, what is possible?

• Inclusive B lifetime tB1.31 0.14 ps
• Not yet observed B0s , Lb, oscillations

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Why HF measurements?
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similarly to neutral K system !
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Heavy Flavour Physics in 2002
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Heavy Flavour Physics in 2002

• Bs and Lb observed
• Individual lifetimes measured, precision well
  below 10 !

• tB- gt tB0 gt tb-baryon as
  expected, but

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Oscillations
How ?
One can indeed see the oscillation
Signal

• Find a Bx

• Measure decay time

• Find production flavour

1-cos(Dm t) ? Dmd0.4970.035 ps-1 (OPAL)
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Impact of LEP measurements Now the players are
the B factories (BaBar, Belle) and LHCb at LHC
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QCD in 1989
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Anatomy of the process ee- Z Hadrons
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The running coupling constant
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QCD in 1989
as(Mz) 0.11 0.01
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QCD in 2002
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Searches in 1989
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Searches in 1989

• What are we going to find?
• Technicolour ?
• Supersymmetry ?
• Higgs ?
• anything else ?

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Searches in 2002
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Higgsproduction at LEP
cross section nb
Higgsstrahlung MHmax ECM - MZ
centre-of-mass energy (ECM) GeV
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Higgs Decays
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then end of sommer 2000...
further candidates in ALEPH, L3, DELPHI, OPAL
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adding up all experiments
slight indication for Higgs production, with
MH115 GeV/c2
Expectation, if Higgs is not produced
Expectation, if Higgs is produced (with
MH115.6 GeV/c2)
has to be 0.00006 in order to talk of discovery
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Conclusions(using P. Janots words...)
EP
ife
Thanx to F. Teubert, F. Palla, D.
TreillePlots from E. Lançon, P. Janot, Y.
Rozen, C. Haag, R. Assmann, D. Ward, K.
Hamacher, E. Barberio