why a linear collider now?
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Why a Linear Collider Now?. S. Dawson, BNL October, 2002 The Physics case Why we need both the LC and the LHC Examples: EWSB, SUSY, top quark. LC is Next. European, Asian, American communities all agree: LC is next step Initial design, Luminosity - PowerPoint PPT PresentationTRANSCRIPT
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Why a Linear Collider Now?
S. Dawson, BNL
October, 2002
The Physics case Why we need both the LC and the LHC Examples: EWSB, SUSY, top quark
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LC is Next• European, Asian, American communities all agree:
LC is next step • Initial design, • Luminosity
• 80% e- polarization• Physics arguments for 1 TeV energy scale
Energy upgrade a must!
GeVs 500sec//10 234 cmyearfb /300 1
Combination of LHC/LC physics probes EWSB
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Is mass due to a Higgs boson?• Higgs couplings of SM fixed
• Production rates at LEP, Tevatron, LHC fixed in terms of mass
• Direct search limit from LEP:
• Higgs contributions to precision measurements calculable
WWWh
fffh
gMgv
mg
clGeVM h %95@114
clGeVM h %95@196
Precision measurements:
G. Mylett, Moriond02
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LHC
Higgs Discovery at Tevatron or LHC
Tevatron
ATLAS TDR
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• Well determined initial state– Precision masses with
recoil technique
– Higgs mass independent of Higgs decay
– Model independent Higgs BRs
yrHiggs
GeVM h
/000,40
120
Zhee
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Higgs mass measurements
• LC:
• LHC:
Direct reconstruction of
LC @ 350 Gev
Conway, hep-ph/0203206
MeVM
fbGeVM
h
h
50
500,120 1
h
MeVM
fbGeVM
h
h
100
300,150 1
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Is it a Higgs?• How do we verify role in
EWSB?• Measure Yukawa couplings
• Measure spin/parity
• Reconstruct Higgs potential
2
2
3)(
)(
m
m
h
bbh b
0PCJ
42
23
22
822h
v
Mh
v
Mh
MV hhh
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Coupling Constant Measurements
Battaglia & Desch,
hep-ph/0101165
LC
%21hWWg
%2hbbg
Zeppenfeld, hep-ph/0203123
LHC
L=200 fb-1L=100 fb-1, s=350 GeV
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• Angular correlations of decay products distinguish scalar/pseudoscalar
Miller, hep-ph/0102023
Threshold behavior measures spin
[20 fb-1 /point]
Higgs spin/parity in e+e-Zh
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Measuring Higgs Self Couplings
• ghhh, ghhhh completely predicted by Higgs mass
• Must measure e+e- Zhh
• Small rate (.2 fb for Mh=120 GeV), large background
• Large effects in SUSY
%24
1000 1
hhh
hhh
g
g
fb
Lafaye, hep-ph/0002238
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Light SUSY consistent with Precision Measurements
• SUSY predicts light Higgs
• For MA, SUSY Higgs sector looks like SM
• Can we tell them apart?
• Higgs BR are different in SUSY
• Find all SUSY Higgs,
HAHh ,,, 000
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LHC
Find all the Higgs Bosons
Carena, hep-ph/9907422
Tevatron
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Into the wedge
• s>2MH
e+e- H+H-, H0A0
observable to MH=460 GeV ats=1 TeV
• s<2MH
e+e- H+, H+tb
L=1000 fb-1, s=500 GeV,
3 signal for MH 250 GeV
Moretti, hep-ph/0209210
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•LHC/Tevatron will find SUSY• SUSY mass differences
from cascade decays;eg
• M0 limits extraction of other masses
• Fit to SUGRA parameters
qll
llqqL
0
1
02
~
~~~
%10tan
tan
%,15%,32/1
2/1
0
0
m
m
m
m
Catania, CMS
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LHC: Fits to SUSY Parameters
Bachacou, Hinchliffe, Paige, hep-ph/9907518
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LC can step through Energy Thresholds Run-time Scenario for L=1000 fb-1
Year 1 2 4 5 6 7
L (fb-1) 10 40 150 200 250 250
• SUSY masses to .2-.5 GeV from sparticle threshold scans M0/M0 7% (Combine with LHC data)
• 445 fb-1 at s=450-500 GeV• 180 fb-1 at s=320-350 GeV (Optimal for Higgs BRs)
• Higgs mass and couplings measured, gbbh1.5%
• Top mass and width measured, Mt150 GeV
Battaglia, hep-ph/0201177
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How do we know it’s SUSY?• Need to measure masses,
couplings
• Observe SUSY partners, eg
• Polarization can help separate states
• Discovery is straightforward
• e energies measure massesRL ee ~,~0
,,
~~
~~
ee
eeee RLRL
2min,max,
min,max,22~
)( ee
eeCMe EE
EEEM
LC Study, hep-ex/0106056
me1 GeV
L=50 fb-1
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SUSY Couplings:
• Compare rates at NLO:
• Lowest order,
• Super-oblique corrections sensitive to higher scales
•
• Masses from endpoints
• Assume
• Tests coupling to 1% with 20 fb-1
XffffX gg ~~
gqqee
gqqee
gqqee
~~
~~
ss gg ~
m
mg
g
g ~ln
16
~
~
~ 2
2
RLRL eeee ,,~~
Bee~~
eeB~~
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(e+e-Zh) sensitive to SUSY Parameters
Dawson, Heinemeyer hep-ph/0203067
TESLA:
ZH2-3%,
L=500 fb-1
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Understanding the Top Quark
• Why is ?
• Kinematic reconstruction of tt threshold gives pole mass at LC
• Compare LHC
2
vM t
MeVM
fb
t 200
40 1
Groote , Yakovlov, hep-ph/0012237
QCD effects well understood
NNLO ~20% scale uncertaintyGeVM
fb
t 21
50 1
2Mt (GeV)
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Top Yukawa coupling tests models
• tth coupling sensitive to strong dynamics
• Above tth threshold
e+etth
• Theoretically clean s=700 GeV, L=1000 fb-1
• Large scale dependence in tth rate at LHC
• L=300 fb-1
%5.6tth
tth
g
g
Baer, Dawson, Reina, hep-ph/9906419
Juste, Merino, hep-ph/9910301
Reina, Dawson, Orr, Wackeroth
Beenacker, hep-ph/0107081
% 16 tth
tth
g
g
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Exciting physics ahead
• LHC/Tevatron finds Higgs LC makes precision measurements of
couplings to determine underlying model• LHC finds evidence for SUSY, measures mass
differences
LC untangles spectrum, finds sleptons
LC makes precision measurements of couplings and masses
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