Waiting for the LHC

1
Waiting for the LHC

• S. Dawson
• BNL
• April 2, 2007

2
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

3
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

4
Electromagnetism and Radioactivity

• Maxwell unified Electricity and Magnetism with
  his famous equations (1873)

5
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!
6
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 EM?
7
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

8
Electroweak Theory is Predictive

• Theory has few free parameters
• Mass of the Z boson, MZ91.1875 ? .0021 GeV
• Strength of the coupling of the photon to the
  electron, ?1/137.0359895(61)
• Strength of the weak interactions (measured in
  muon decay) GF1.16637(1) x 10-5 GeV-2
• Then the W mass is predicted

9
Electroweak Theory Precision Theory
2007
We have a model. And it works to the 1 level
Gives us confidence to predict the future!
10
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
11
LEP Looked for the Higgs

• Looked for ee- ? Z h
• Excluded a Higgs up to Mh114 GeV
• This limit assumes a Higgs with the properties
  predicted by the Standard Model

12
W Boson Mass
With precise measurements of MZ and ?, we can
predict MW
pa
MW2
v2GF (1 - MW2/MZ2)(1 - Dr)
?r Quantum corrections dominated by tb and
Higgs loops
DMW µ Mt2
DMW µ ln (MH/MZ)
2
13
Tevatron is Worlds Highest Energy Accelerator
14
Top Quark Discovered at Fermilab in 1995
CDF
DØ
15
New Measurements of Top Quark Mass
2007
16
Mt (and error) steadily decreasing
17
Worlds most precise measurement of Mw
2007

• CDF has worlds most precise measurement of W
  mass MW80.413?0.048 GeV

18
MW (and error) steadily decreasing
19
Consistency of Standard Model Strongly Restricts
Mh

• Best fit Mh 76 GeV
• One sided 95 c.l. upper limit Mh lt 144 GeV
• Including direct search limit, Mh lt 182 Gev

2007
114 GeV lt Mh lt 182 GeV
20
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
21
Mh increasingly restricted
Mh central value Mh 95 c.l. upper limit
22
Understanding Higgs Limit
MW(experiment)80.398 ? 0.025 GeV
Increasing Mh moves MW further from experimental
value
LEPEWWG World average
23
Higgs at the Tevatron Very Hard!!!
?(gg?h)?1 pb ltlt ?(bb)
24
Can the Tevatron discover the Higgs?
Tevatron expects around 6-7 fb -1 by 2009
2009
2007
This relies on statistical combination of
multiple weak channels
25
Higgs Search, Summer, 06
Limits are within a factor of 5-10 of Standard
Model predictions
26
New and Better Limits on the Way
27
Where is the Higgs ?

• We need to find the Higgs (Standard Model is
  inconsistent without it)
• We didnt find it at LEP
• We havent found it at Fermilab
• The end is in sight..if we dont find it at the
  LHC, the Standard Model as it stands cannot be
  the whole story (because precision measurements
  would be inconsistent)

28
Large Hadron Collider (LHC)

• proton-proton collider at CERN (2007)
• 14 TeV energy
• 7 mph slower than the speed of light
• cf. 2TeV _at_ Fermilab
• ( 307 mph slower than the speed of light)

29
Stored Energy of Beams unprecedented

• Ebeam1.5 Giga Joule
• LHC beams have same kinetic energy as aircraft
  carrier at 15 knots!
• Largest scientific project ever attempted

30
Requires Detectors of Unprecedented Scale

• CMS is 12,000 tons (2 xs ATLAS)
• ATLAS has 8 times the volume of CMS

31
CMS
ATLAS
32
LHC Schedule

• Aug. 31, 2007
• Machine and experiments closed
• November, 2007
• Engineering run at ?s900 GeV
• April, 2008
• Physics run at ?s14 TeV
• Prospects for integrated luminosity
• 2008 1 fb-1
• 2009 5 fb-1

33
Typical Collision Energy at LHC 1
TeV
b
W
t
p
p
t
W-
b
34
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

35
Quantum Corrections Connect Weak and Planck Scales
Quantum corrections drag weak scale to Planck
scale
Tevatron/LHC Energies
Weak
GUT
Planck
1019 GeV
103 GeV
1016
36
Quantum Corrections to Higgs Mass

• Higgs mass grows quadratically with high scale,
  ?

Mh ? 200 GeV requires ? TeV
Points to 1 TeV as scale of new physics
37
We expect much at the TeV Energy Scale

• Maybe a Higgs
• Maybe supersymmetry (lots of new particles)
• Maybe extra dimensions
• Maybe other new symmetries

Were not sure what will be there, but were sure
there will be something!
38
vs14 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

39
LHC will find Standard Model Higgs
LHC Will find SM Higgs if it exists
Consistency of SM REQUIRES a Higgs Boson or
something like it
40
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

41
Discovery isnt 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?

42
Is it a Higgs?

• Measure couplings to fermions gauge bosons
• Measure spin/parity
• Measure self interactions

This is a long term program
43
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?

44
Is Dark Matter a Particle?
Can we produce dark matter in a collider and
study all its properties?
45
Quantum Corrections and Supersymmetry
Tevatron/LHC Energies
Weak
GUT
Planck
1019 GeV
103 GeV
1016
Quantum corrections cancel order by order in
perturbation theory
46
Supersymmetric Theories

• Predict many new undiscovered particles (gt29!)
• 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

47
LHC will find Supersymmetry

• Discovery of many SUSY particles is
  straightforward
• Untangling spectrum is difficult
• ? all particles produced
• together
• SUSY mass differences from complicated decay
  chains

48
Physics Landscape in 2010?

• LHC should have told us by 2010 (with 30 fb-1)
• Whether a light (or heavy) Higgs exists
• But it wont measure all Higgs properties
• Whether the world is supersymmetric
• But is wont 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

49
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

50
Physics with High Luminosity
MSSM Heavy Higgs reach
3000fb-1/95 CL
Heavy Higgs observation increased by 100 GeV.
51
Two Paths to Discovery

• High Energy
• 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
52
Linear Collider is Next Step

• Initial design,
• Luminosity
• ? 15 miles long
• International project
• 80 e- polarization
• Physics arguments for 1 TeV energy scale
• Energy upgrade a must!

ee- collisions are pointlike
53
Linear Collider is a Higgs Factory

• ee-?Zh produces 40,000 Higgs/yr
• Clean initial state gives precision Higgs mass
  measurement
• Mh2s-2?sEZMZ2
• Model independent Higgs branching ratios
• Clean probe of underlying model

54
ILC Goal Precision Measurements of Higgs
Couplings

• ?BR(h?bb)?2 with L500 fb-1
• New phenomena can cause variations of Yukawa
  couplings from SM predictions

Z
Coupling Strength to Higgs Particle
Particle Mass (GeV)
Sensitivity to novel phenomena
55
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
56
Progress on the International Front

• International Team recommended cold technology in
  August, 2004
• Global Design Effort (GDE) for International
  Linear Collider (ILC)
• Barry Barish, Director
• Regional Centers in Asia, Europe, North America
• Site independent design
• Cost in Feb. 2007
• Optimistic time frame has construction decision
  in 2010, physics in 2019

LHC results before construction decision
57

• The GDE Plan

2005 2006 2007 2008
2009 2010
Global Design Effort
Project
LHC Physics
Baseline configuration
Reference Design
Technical Design
ILC RD Program
Expression of Interest to Host
International Mgmt
58
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

59
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

?