Transcript Waiting for the LHC S. Dawson BNL April 2, 2007

Waiting for the LHC
S. Dawson
BNL
April 2, 2007
The Punch Line

Great physics is coming from the Tevatron
collider


This is the era of precision tests of the
Standard Model
We expect great discoveries from the LHC
The LHC will test a fundamentally different
energy regime than the Tevatron
 This is a program for the next few decades

A Decade of Discovery


Electroweak Theory
Neutrino flavor oscillations





Three separate neutrino species with mass
Understanding QCD
Discovery of top quark
B meson decays violate CP
Flat universe dominated by dark matter & energy
Electromagnetism and
Radioactivity

Maxwell unified Electricity and Magnetism
with his famous equations (1873)
Electromagnetic Theory



Dirac introduced theory of electron 1926
Theoretical work of Feynman,
Schwinger, Tomonga resulted in a
theory of electrons and photons with
precise predictive power
Example: magnetic dipole of the
electron [(g-2)/2]

current values of electron (g-2)/2
theory: 0.5 (a/p) - 0.32848 (a/p)2 + 1.19 (a/p)3 +..
= (115965230  10) x 10-11
experiment = (115965218.7  0.4) x 10-11
We can calculate!
Electromagnetism and
Radioactivity

Matter spontaneously emits penetrating radiation
 Becquerel found uranium emissions in 1896

The Curies find radium emissions by 1898
Can this new interaction (the weak
force) be related to E&M?
Enter Electroweak Unification


Glashow, Weinberg, and Salam realized that the
field responsible for the EM force (the photon)
And the fields responsible for the Weak force

…the yet undiscovered W+ and W- bosons

Could be unified if another field existed

…the then undiscovered heavy neutral boson (Z)
W and Z bosons discovered at CERN in 1983

Electroweak Theory is Predictive
Theory has few free parameters
 Mass of the Z boson, MZ=91.1875  .0021 GeV
 Strength of the coupling of the photon to the
electron, a=1/137.0359895(61)
 Strength of the weak interactions (measured in
muon decay) GF=1.16637(1) x 10-5 GeV-2
 Then the W mass is predicted
M W (Theory )  80.358 GeV
M W ( Experiment)  80.398  0.025 GeV
Electroweak Theory: Precision
Theory
2007
We have a model….
And it works to the 1% level
Gives us confidence
to predict the future!
Standard Model is Inconsistent
Without a Higgs boson
•Requires physical, scalar particle, h, with unknown mass
Mh is ONLY unknown parameter of EW sector
No evidence (yet) for existence of Higgs boson
Everything is calculable….testable theory
LEP Looked for the Higgs
Looked for e+e-  Z h
 Excluded a Higgs up to Mh=114 GeV
 This limit assumes a Higgs with the
properties predicted by the Standard
Model

W Bosonof MZ and a, we can
With precise measurements
predict
MassMW:
2
MW =
pa
√2GF (1 - MW2/MZ2)(1 - Dr)
Dr: Quantum corrections dominated by tb and
Higgs loops
DMW  Mt2
DMW  ln (MH/MZ)
2
Tevatron is World’s Highest
Energy Accelerator
Top Quark Discovered at
Fermilab in 1995
CDF
DØ
New Measurements of Top
Quark Mass
2007
Mt (and error) steadily
decreasing
M t
Mt
M t
Mt
1
170
t .9GeV
M
Mt
1
170.9GeV
M t
Mt
World’s most precise
measurement of Mw
2007

CDF has world’s most
precise measurement
of W mass:
MW=80.4130.048 GeV
MW (and error) steadily
decreasing
M W
MW
MW
1
80.398GeV
Consistency of Standard Model
Strongly Restricts Mh
•Best fit: Mh = 76 GeV
•One sided 95% c.l. upper
limit: Mh < 144 GeV
•Including direct search limit,
Mh < 182 Gev
114 GeV < Mh < 182 GeV
2007
Quantum Corrections Restrict
Higgs Mass
• Direct
observation of W
boson and top
quark (purple)
• Inferred values
from precision
measurements
(grey)
Plot includes 2007 MW, Mt values
Mh increasingly restricted
Mh central value
Mh 95% c.l. upper limit
Understanding Higgs Limit
 Mh 
Mh 
2
  0.008 ln 

M W (GeV )  80.358  0.0579 ln 
 100 GeV 
 100 GeV 
2
 M


t
  1
0.525
 171 GeV 

MW(experiment)=80.398  0.025 GeV*
Increasing Mh moves MW further
from experimental value
* LEPEWWG World average
Higgs at the Tevatron Very Hard!!!
(ggh)1 pb << (bb)
Can the Tevatron discover the
Higgs?
2009
2007
Tevatron expects
around 6-7 fb -1 by
2009
This relies on statistical combination of
multiple weak channels
Higgs Search, Summer, 06
Limits are
within a factor
of 5-10 of
Standard Model
predictions
New and Better Limits on the Way
Where is the Higgs ?

We need to find the Higgs
(Standard Model is
inconsistent without it)



We didn’t find it at LEP
We haven’t found it at
Fermilab
The end is in sight…..if we
don’t find it at the LHC, the
Standard Model as it
stands cannot be the whole
story (because precision
measurements would be
inconsistent)
Large Hadron Collider (LHC)


proton-proton collider at
CERN (2007)
14 TeV energy
 7 mph slower than
the speed of light
 cf. 2TeV @ Fermilab
( 307 mph slower
than the speed of
light)
Stored Energy of Beams
unprecedented
Ebeam=1.5 Giga Joule
 LHC beams have same
kinetic energy as aircraft
carrier at 15 knots!
 Largest scientific project
ever attempted

Requires Detectors of
Unprecedented Scale
• CMS is 12,000 tons
(2 x’s ATLAS)
• ATLAS has 8 times
the volume of CMS
December 2006
QuickTime™ et un
décompresseur TIFF (non compressé)
sont requis pour visionner cette image.
CMS
ATLAS
LHCb
LHC Schedule

Aug. 31, 2007


November, 2007

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Engineering run at s=900 GeV
April, 2008


Machine and experiments closed
Physics run at s=14 TeV
Prospects for integrated luminosity


2008 1 fb-1
2009 5 fb-1
Typical Collision Energy at LHC:
1 TeV
l

q
q
W+
b
t
t
p
p
W-
b
q
q

l
Discoveries of last decade point
to new discoveries
Incredibly successful model
 Our model cannot explain dark matter,
dark energy, neutrino masses, why the top
quark is so heavy……
 It points to an energy scale of 1 TeV as
place where physics explaining our
questions might lurk

Quantum Corrections Connect
Weak and Planck Scales
Quantum corrections drag
weak scale to Planck scale
M H2  M Pl2
Tevatron/LHC
Energies
Weak
103 GeV
GUT
1016
Planck
1019 GeV
Quantum Corrections to Higgs Mass
• Higgs mass grows quadratically with high scale, 
 

M   
200 GeV 
 0.7 TeV

2
2
h
Mh  200 GeV requires  ~ TeV
Points to 1 TeV as scale of new physics
We expect much at the TeV
Energy Scale
Maybe a Higgs
 Maybe supersymmetry (lots of new
particles)
 Maybe extra dimensions
 Maybe other new symmetries

We’re not sure what will be
there, but we’re sure there will
be something!
√s=14 TeV-- the first 10 pb-1
Similar statistics to CDF, D0
LHC is a W,Z, top factory
• Small statistical errors in precision measurements
• Search for rare processes
• Large samples for studies of systematic effects
LHC Will
findfind
SM Higgs
if it exists
LHC
will
Standard
Model Higgs
Consistency of SM
REQUIRES a Higgs Boson
or something like it
LHC and the Higgs

LHC will discover a
Standard Model
Higgs boson if it
exists

Sensitive to Mh from
100-1000 GeV

Higgs signal in just a
few channels
Discovery isn’t Enough
Is this a Higgs or something else?
 We must 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?

Measure couplings to fermions & gauge bosons
 ( h  bb )
mb

3
2
(h     )
m
2

Measure spin/parity
J PC  0  

Measure self interactions
2
2
2
Mh
Mh 3 Mh 4
V
h
h  2 h
2
2v
8v
This is a long term program
Even if we find a Higgs….
We know the Standard Model is
incomplete
 It leaves too many open questions
 Such as “What is the dark matter?”

Is Dark Matter a Particle?
Can we produce
dark matter in a
collider and study
all its properties?
Quantum Corrections and
Supersymmetry
M H2   M Pl2
M H2  M Pl2
Tevatron/LHC Energies
Weak
103 GeV
GUT Planck
1016 1019 GeV
Quantum corrections cancel order by
order in perturbation theory
Supersymmetric Theories


•
Predict many new undiscovered particles (>29!)
Very predictive models
 Can calculate particle masses, interactions,
everything you want in terms of a few parameters
Any Supersymmetric particle eventually decays to the
lightest supersymmetric particle (LSP) which is stable
and neutral!!!
Dark Matter Candidate
LHC will find Supersymmetry

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Discovery of many SUSY
particles is straightforward
Untangling spectrum is
difficult
 all particles produced
together
SUSY mass differences from
complicated decay chains
Physics Landscape in 2010?

LHC should have told us by 2010 (with ~30 fb-1)
 Whether a light (or heavy) Higgs exists
 But

it won’t measure all Higgs properties
Whether the world is supersymmetric
 But
is won’t measure all particle masses and couplings
Whether we can produce dark matter in the lab
 Whether there are more space time dimensions
 Whether there is nothing new

Luminosity Upgrade of the LHC?
•Higher luminosity ~1035cm-2 s-1 (SLHC)
–Needs changes in machine and detectors
 Change to SLHC 2015
 ~3000 fb-1/experiment in 3-4 years
Rich new physics menu with increased
luminosity
Physics with High Luminosity
MSSM Heavy Higgs reach
3000fb-1/95% CL
Heavy Higgs observation increased by ~100 GeV.
Two Paths to Discovery

High Energy
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Operating at the energy frontier
Direct discovery of new particles
Tevatron and LHC
High Precision

Infering new physics effects from high energy scales
through precision measurements at low energy
Combining both stategies gives much more complete
understanding than either one alone
Linear Collider is Next Step


Initial design, s  500 GeV
Luminosity  1034 / cm 2 / sec
1
 300 fb / year

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e+e- collisions are
pointlike
 15 miles long
International project
80% e- polarization
Physics arguments for 1 TeV energy scale
Energy upgrade a must!
Linear Collider is a Higgs Factory


e+e-Zh produces 40,000 Higgs/yr
Clean initial state gives precision Higgs mass
measurement
Mh2=s-2sEZ+MZ2

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Model independent Higgs branching ratios
Clean probe of underlying model
Coupling Strength to Higgs Particle
ILC Goal: Precision Measurements of Higgs
Couplings
Z
•BR(hbb)2% with
L=500 fb-1
•New phenomena can
cause variations of
Yukawa couplings from
SM predictions
Particle Mass (GeV)
Sensitivity to novel phenomena
Measuring the spin of the Higgs
Threshold behavior measures spin
[20 fb-1 /point]
Linear collider
can change initial
state energy to do
energy scans
Very hard to do at the LHC
Progress on the International Front


International Team recommended cold
technology in August, 2004
Global Design Effort (GDE) for International
Linear Collider (ILC)
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Regional Centers in Asia, Europe, North America
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Barry Barish, Director
Site independent design
Cost in Feb. 2007
Optimistic time frame has construction decision
in 2010, physics in 2019
LHC results before construction decision
The GDE Plan
2005
2006
2007
2008
2009
2010
Global Design Effort
Baseline configuration
Reference Design
Project
LHC
Physics
Technical Design
ILC R&D Program
Expression of Interest to Host
International Mgmt
ILC Cost
Total Value Cost (FY07)
4.87B ILC Units - Shared
+
1.78B ILC Units - Site Specific
+
13.0 K person-years
1 ILC Unit = 1 US 2007$
Quantum Leaps:

From LEP to the Tevatron to the LHC
Confirmation of the validity of the Standard
Model
 We need to find the Higgs!
 A long term program to understand LHC
discoveries

 Followed
by LHC upgrades and ILC
?