young-kee kim university of california, berkeley (lbnl / fermilab) cdf experiment
DESCRIPTION
Studying EWSB at the Tevatron (Lecture #3). Young-Kee Kim University of California, Berkeley (LBNL / Fermilab) CDF Experiment SLAC Summer Institute SLAC, Aug. 13 – 17, 2001. EW Measurements (last ~10 years). 1991 M top limit. M w (GeV). M H (GeV). 2001. 1991. 1995. - PowerPoint PPT PresentationTRANSCRIPT
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Young-Kee KimUniversity of California, Berkeley
(LBNL / Fermilab)
CDF Experiment
SLAC Summer InstituteSLAC, Aug. 13 – 17, 2001
Studying EWSB at the Tevatron
(Lecture #3)
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Mw(GeV)
MH(GeV)
Mtop (GeV) year
1 prediction
1991 Mtop limit
1991
2001
1995
EW Measurements (last ~10 years)
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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.
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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
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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
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ZH Candidates at LEP 2
e+e-bb bb ee++ee--bb bb
L3L3ALEPHALEPH
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& girls
TevatronLEP 2
Higgs Searches : LEP 2 Tevatron
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SM Higgs Decays
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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
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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
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SM Higgs Signatures (Run I)
b-tagging and Mbb resolution are critical for a light Higgs(see b tagging in Lecture #2)
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Mbb Resolution
CDF Run I : Z bb-barMC H bb-bar
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Run I : WH l + bb-bar
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Run I : WH, ZH qq-bar + bb-bar
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Run I : ZH -bar + bb-bar
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Run I : ZH l+l- + bb-bar
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Run I Higgs Limits
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CDF b-tagged events
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Tevatron Higgs Potential (Luminosity Limited)
MHiggs (GeV)
MSSM
SM
Run IIb
Run IIa
Parameterized Simulation
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MSSM Higgs Searches
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MSSM Higgs Production @ Tevatron
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MSSM Higgs Branching Ratios
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Run I qq bb-bar bb-bar bb-bar
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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
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Run I Charged Higgs Searches
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Run I Charged Higgs Results
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Run I Bosophilic/Fermiophobic Higgs
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Run I Bosophilic Higgs Limits
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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
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Direct Searches for SM & MSSM Higgs Particles
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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
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spin ½ fermions spin 1 bosons
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Higgs : spin 0 boson
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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.