coll lc

Report
Why a Linear Collider Now?
S. Dawson, BNL
October, 2002
Asian, European, and American communities
all agree
High Energy Linear Collider is next large
accelerator
 WHY???
Where are we going?
• US high energy community just completed
long range planning process
• 20 year roadmap for the future
• HEPAP subpanel:
We recommend that the highest priority of the U.S.
program be a high-energy, high-luminosity, electronpositron linear collider, wherever it is built in the world
Linear Collider Basics
• Initial design, e+e- at s=500 GeV
• Luminosity 1034 cm2/sec
300 fb-1/yr
• 80% e- polarization
• Energy upgrade to .8-1.2 TeV in future
• Physics in  2012
NLC
High Power
Klystron
• The international accelerator community
believes that a TeV-scale linear collider
can be successfully built
JLC
Accelerator
Test Facility
TESLA
Superconducting
Cavity
Preliminary designs
for Linear Colliders
TESLA
NLC
?????
• What are the big questions we want to
answer?
• Why do we think we can predict where
we want to go?
– What do we know now?
– What do we expect to learn from the
Tevatron and LHC?
– What questions will remain unanswered?
What is particle physics?
Study of Space, Time, Matter
Bagger/Barish report
The Big Questions?
• What is the origin of
mass?
• Do protons decay?
• Do forces unify at a
large scale?
• Are there more than
four dimensions?
• Why are there 4
forces?
No unification of couplings in SM
Cosmic Connections
• What is dark matter?
• How are particle
physics & cosmology
connected?
• What is dark energy?
• Where did the antimatter go?
Planning for the Future Based on
Success of last 20 years….
• Model of electroweak physics verified
at .1% level
• The problem of mass remains
• W and Z bosons discovered at CERN
in 1983
M W  80 GeV
M Z  91 GeV
• Masses not zero….or even small
Why is Mass a Problem?
• Lagrangian for gauge field (spin 1):
L=-¼ FF
F=A-A
• L is invariant under transformation:
A (x) A(x)-(x)
• Gauge invariance is guiding principle
• Mass term for gauge boson
½ m2 AA
• Violates gauge invariance
• So we understand why photon is massless
Simplest possibility for Origin of Mass is
Higgs Boson
• Higgs mechanism gives gauge invariant masses
for W, Z
• Requires physical, scalar particle, H, with
unknown mass
• Observables predicted in terms of:
–
–
–
–
MZ=91.1875.0021 GeV
GF=1.16639(1) x 10-5 GeV-2
=1/137.0359895(61)
Mh
• Higgs and top quark enter into quantum
corrections,  Mt2, log(Mh)
Precision Measurements sensitive to top
quark before it was discovered!
Large number of
measurements fit
electroweak
predictions
Indirect Indications for Light Higgs
Mass
• Direct measurements
of MW, Mt agree well
with indirect
measurements
• Prefer Higgs in 100200 GeV range
• ASSUMES no new
physics
Where is the Higgs boson?
• Higgs couplings of fixed
g ffh 
mf
Precision measurements:
M h  193 GeV @ 95 % cl
v
g W W h  gM
W
• Production rates at LEP,
Tevatron, LHC fixed in terms
of mass
• Direct search limit from LEP:
M h  114 GeV @ 95 % cl
• Higgs contributions to
precision measurements
calculable
G. Mylett, Moriond02
Tantalizingly close…..
Direct limit: Mh>114.1 GeV
Indirect limit: Mh<193 GeV
New Physics is just around the corner!
Fits assume Standard Model….if
Standard Model incorrect, even more
exciting new physics….
Higgs mass and scale of new physics
correlated…..
130 < Mh < 170 GeV
Sensible
theory
here
Fermilab Tevatron
• p p at s=2 TeV
• May discover Higgs if
very lucky
• Requires light Higgs
and high luminosity
• Physics in 2002-2008
p p  Wh , h  b b
Upgraded
Detectors for
RunII
CDF
Enhanced capabilities for b
tagging aid Higgs search
D0
CERN Large Hadron Collider (LHC)
•
pp interactions ats =14
TeV
• LHC will discover Higgs
boson if it exists
• Sensitive to Mh from 1001000 GeV
• Higgs signal in just a few
channels
• Physics circa 2008
ATLAS TDR
Discovery isn’t enough….
• Is this a Higgs or something else?
• Linear Collider can answer critical
questions
– Does the Higgs generate mass for the W,Z
bosons?
– Does the Higgs generate mass for fermions?
– Does the Higgs generate its own mass?
Is it a Higgs?
• How do we know what we’ve
found?
• Measure couplings to
fermions & gauge bosons
 (h  bb )


 (h    )
3
mb
m
2
2
• Measure spin/parity

J
0
• Measure self interactions
PC
V 
Mh
2
2
h
Mh
2v
2
h 
3
Mh
8v
2
2
h
4
Coupling Constant Measurements
• LHC measures combinations of
coupling constants
• Typical accuracy, 10-20%
• Only some subset of couplings
• Assumptions necessary to get
couplings
L=200 fb-1
Zeppenfeld, hep-ph/0203123
Linear Collider is Higgs Factory!
• e+e-Zh produces 40,000
Higgs/year
• Clean initial state gives
precision Higgs mass
measurement
Mh2=s-2sEZ+MZ2
• Model independent Higgs
branching ratios
WWh vertex
ZZH vertex
Higgs mass measurements
LC @ 350 Gev
• LC:
M
h
 M
 120 GeV , 500 fb
h
1
 50 MeV
• LHC:
Direct reconstruction of
h  
M
h
 150 GeV , 300 fb
 M
h
 100 MeV
1
Conway, hep-ph/0203206
Precision Measurements of Higgs
Couplings
• Dots are experimental
error
• 1-2% measurement
• Measure ALL Higgs
couplings
• Bands are theory error
– Larger than experiment
– Largest error from mb
Battaglia & Desch, hep-ph/0101165
Higgs measurements test model!
Standard
Model
• Couplings to fermions
very different in
SUSY models
• LC can distinguish
SM from SUSY up to
MA=600 GeV
Higgs spin/parity in e+e-Zh
Threshold behavior measures spin
[20 fb-1 /point]
Miller, hep-ph/0102023
• Angular correlations of decay products
distinguish scalar/pseudoscalar
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
1000 fb

• Large effects in SUSY
1
 g hhh
 24 %
g hhh
Lafaye, hep-ph/0002238
Problem with this picture…
• Fundamental Higgs is not natural
• Quantum corrections to Mh are
quadratically divergent
Mh22
• So enormous fine-tuning needed to keep
Higgs light
Mh2\Mh2MW2\Mpl210-32
Solution is Supersymmetry
• Quadratic contributions to Higgs mass
cancel between scalars and fermions
• To make cancellation hold to all orders need
symmetry
• Bose-Fermi symmetry….supersymmetry
Do the forces unify?
• Coupling constants
change with energy
• Coupling constants unify
in supersymmetric
models
Hint for new physics?
New particles in SUSY Theory
Spin ½ quarks  spin 0 squarks
Spin ½ leptons  spin 0 sleptons
Spin 1 gauge bosons spin ½ gauginos
Spin 0 Higgs spin ½ Higgsino
Experimentalists dream….many particles to search
for!
What mass scale?
Supersymmetry is broken….no scalar with mass of
electron
•
•
•
•
Supersymmetry
• Can we find it?
• Can we tell what it is?
• Masses of new particles depend on
mechanism for breaking Supersymmetry
• Couplings of new particles predicted in
terms of few parameters
• Simplest version has 105 new parameters
Simplifying Assumption:
• Assume masses unify at same scale as
couplings
• Everything specified in terms of
scalar/fermion masses at high scale and 3
parameters
• Predictive anzatz…..
•LHC/Tevatron will find SUSY
• Discovery of many SUSY
particles is straightforward
• Untangling spectrum is
difficult
 all particles produced
together
• SUSY mass differences from
cascade decays;eg
~ 
0
~
~
qL   2 q  l l
0  
 ~1 l l q
• M0 limits extraction of other
masses
Catania, CMS
Light SUSY consistent with Precision
Measurements
• SUSY predicts light Higgs
M
SUSY
h
 130 GeV
• SUSY predicts 5 scalars
0
0
0
h , H , A , H

• For MA, SUSY Higgs
sector looks like SM
• Can we tell them apart?
• Higgs BR are different in
SUSY
Find all the Higgs Bosons
Tevatron
LHC
Carena, hep-ph/9907422
Into the wedge with a LC
s>2MH
e+e- H+H-, H0A0
observable to MH=460 GeV at s=1 TeV
• s<2MH
e+e- H+, H+tb
L=1000 fb-1, s=500 GeV,
3 signal for MH 250 GeV
•
LC can step through Energy Thresholds
Run-time Scenario for L=1000 fb-1
Year
1
L (fb-1) 10
•
•
•
•
•
•
2
4
5
6
7
40
150
200
250
250
SUSY masses to .2-.5 GeV from sparticle threshold scans
M0/M0 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, gbbh1.5%
Top mass and width measured, Mt150 MeV
Battaglia, hep-ph/0201177
How do we know it’s SUSY?
• Need to measure masses,
couplings
• Observe SUSY partners,
eg
~ ~
R
e , Le
• Polarization can help
separate states
• Discovery is straightforward
 


e e  e~ L , R e~ L , R
0
e~  e ~
• e energies measure masses
2
M ~e  E CM
2
E e , max E e , min
( E e , max  E e , min )
me1 GeV
L=50 fb-1
LC Study, hep-ex/0106056
2
SUSY Couplings: g ffX  g f~f X~
• Compare rates at NLO:


e e  qq g
~
 
~
e e  qqg
~~
 
e e  qq g
• Lowest order,
g s  g~ s
• Super-oblique corrections
sensitive to higher scales
 g~
g~

~
g
16 
2
2
~
m
ln  
m
• e  e   e~  L , R e~  L , R
• Masses from endpoints
~e  e B~
• Assume
~
B e~ e
• Tests
coupling to
1% with 20 fb-1
What is the universe made of?
•
•
•
•
•
Stars and galaxies are only 0.1%
Neutrinos are ~0.1–10%
Electrons and protons are ~5%
Dark Matter ~25%
Dark Energy ~70%
H. Murayama
Supersymmetry provides
understanding of dark matter?
LSP is dark matter
Mh=115 GeV
M1/2
• Lightest SUSY particle
(LSP) could be dark
matter candidate!
• LSP is weakly interacting,
neutral, and stable
• LSP in range of LC/LHC
• LC can determine LSP
mass; check dark matter
predictions
g-2
M0 (GeV)
Drees, hep-ph/0210142
Standard Model Needs Top Quark
• Top quark completes
3rd generation
– Why are there 3
generations, anyways?
• Theory inconsistent
without top
Top Quark discovery at Fermilab in 1995
Why is Mt(=175 GeV)>>Mb(=5 Gev)??
D0 top event
CDF top event
Understanding the Top Quark
• Why is
Mt 
v
?
2
• Kinematic reconstruction
of tt threshold gives pole
mass at LC
40 fb

1
  M t  200 MeV
• Compare LHC
50 fb
2Mt (GeV)
Groote , Yakovlov, hep-ph/0012237
QCD effects well understood
1
M
t
 1  2 GeV
NNLO ~20% scale uncertainty
Top Yukawa coupling tests models
•
tth coupling sensitive to
strong dynamics
• Above tth threshold
e+etth
• Theoretically clean
• s=700 GeV, L=1000 fb-1
 g tth
• Large scale dependence in tth
rate at LHC
 6 .5 %
g tth
Baer, Dawson, Reina, hep-ph/9906419
Juste, Merino, hep-ph/9910301
Reina, Dawson, Orr, Wackeroth
Beenacker, hep-ph/0107081
• L=300 fb-1
g tth
g
tth
 16 %
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
• etc

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