Transcript coll lc
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 FF
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 AA
• 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 ats =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-2sEZ+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
Mh22
• So enormous fine-tuning needed to keep
Higgs light
Mh2\Mh2MW2\Mpl210-32
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
• M0 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
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 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 )
me1 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+etth
• 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