My job today is to convince/remind you:

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TITLE
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My job today is to convince/remind you
That there is likely to be physics Beyond the
Standard Model
That this physics is important, and the search
for it deserves our full attention
That the Large Hadron Collider is likely to be
the best place to do this work over the next 10
to15 years
That I have a valuable role to play in the
process of discovering the truth
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Large Hadron Collider and ATLAS in 1 minute
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Simple experimental aim
Collide protons and see what happens.
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Large Hadron Collider (LHC)
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Collider (LHC) nearing completion in CERN, Geneva
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ATLAS Experiment to look at the collisions
MORE ON THIS LATER
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Note about the brief

• Talk about
• Your vision for your future research programme
  at Cambridge
• In context of the LHC we have
• predictable items
• Make the detector work
• Commissioning understand MET resolution, jet
  energy scale, alignment
• unpredictable items
• What new physics may nature hold?
• What will we see of it?
• How will we measure it?

MANYUNKNOWNS
ADAPTABILITY IS THE KEY
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Physics Case

• Why Physics beyond the Standard Model?

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The Standard Model not the final story

• Higgs not yet found
• Top-quark charge undetermined!
• Quark masses poorly measured

• Fine-tuning / hierarchy problem (technical)
  Why are particles light?
• Does not explain Dark Matter
• No gauge coupling unification
• Why three generations?

None of these criticisms need necessarily be
cause for alarm
But new Physics, e.g. Supersymmetry, can help.
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Possibilities for new physics

• Supersymmetry?
• Minimal
• Non-minimal
• R-parity violating or conserving
• Gauge mediated
• Gravity mediated
• Extra Dimensional Models
• Large (particles trapped on brane)
• Universal (particles everywhere)
• With/without small black holes
• Littlest Higgs ?
• .

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Theres a strange guarantee

• Something new will be found at the LHC
• If the Higgs Boson exists
• It will be found!
• If the Higgs Boson doesnt exist
• Cross-section for W-boson scattering will be
  observed to deviate from Standard Model

• Strategic gamble
• Anticipate large
• Look for everything
• Do not concentrate on Higgs

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What I Contribute
Ana
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High Energy Physics forthe 21st Century

• Step one into the unknown

Christopher Lester
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Standard Model Bad
Standard Model Good

• Higgs not yet found
• Quark mixing not over-constrained yet
• Quark masses poorly measured
• Top-quark charge undetermined!

• No conflict with experiment (yet)
• Parts (QED) in extremely good agreement with
  experiment even with atomic physics! (Lamb
  Shift, magnetic moments)
• Elementary particle content reasonably small

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Dark corners of the Standard Model
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Standard Model Bad
Standard Model Good

• Higgs not yet found
• Quark mixing not over-constrained yet
• Top-quark charge undetermined!
• Quark masses poorly measured
• Fine-tuning / hierarchy problem (technical)
  Why are particles light?
• Does not explain Dark Matter
• No gauge coupling unification

• No conflict with experiment (yet)
• Parts (QED) in extremely good agreement with
  experiment even with atomic physics! (Lamb
  Shift, magnetic moments)
• Elementary particle content reasonably small

New Physics, e.g. Supersymmetry, can help.
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Four Questions

• What might the new physics be?
• (2) What sort of experiment will help us?
• (3) How will we go about extracting answers from
  the data?
• (4) Can we trust the answers?

Will describe some later.
Coming next!
Very much the work of people in The Cavendish.
Are they robust?
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Large Hadron Collider (LHC)
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Collider nearing completion
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ATLAS Experiment
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Note concerning units

• eV electron-volt 1.6 x 10-19 J
• GeV 10 9 eV 1.6 x 10-10 J
• TeV 1012 eV 1.6 x 10-7 J
• ( K.E. of 1.3mg mosquito at 0.5 m/s)
• Express most particle energies and masses in GeV
  
• but LHC proton beams are 7 TeV each
  (14 mosquitos in
  total)

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Anatomy of the detector
Layered like Onion
Different layers for different types of particles
Neutrino
Muon
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So main things we can do
Average direction of things which were invisible

• Distinguish the following from each other
• Hadronic Jets,
• B-jets (sometimes)
• Electrons, Positrons, Muons, Anti-Muons
• Tau leptons (sometimes)
• Photons
• Measure Directions and Momenta of the above.
• Infer total transverse momentum of invisible
  particles. (eg neutrinos)

electron
Here Be Monsters
Hadronic Jet
photon
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Muon Detector
MAGNETIC FIELD
MAGNETIC FIELD
Muons bend away from us. Anti-muons bend toward
us.
Man for scale
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Calorimetersand Central Solenoid
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Transition Radiation Tracker (TRT) tracks
charged particles and distinguishes electrons
from pions
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The SemiConductor Tracker (SCT)
Records tracks of charged particles
Most of the data-acquisition and
calibration/monitoring software designed and
written in Cambridge
Many components designed and built in The
Cavendish
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SCT contains 4088 Modules
10cm
768 sensitive-strip diodes per side. (200 V) 3
infra-red communication channels. Collisions
recorded _at_ 40MHz (every 25 ns)
Neutron bombardment will degrade silicon over
time. Individual strips will need
recalibration. Optical properties need
adjustment. May need to use redundant links.
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SCT Data Acquisition Software

• Present size
• 350,000 lines of code
• 6 developers
• Much still to be done
• Have managed to control 500 modules at once
• only 1/8th of final number
• multi-crate development - parallelisation
• Needs to become usable by non-experts
• Needs to recover from anomalies automatically

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Evidence that it will work
First cosmic rays seen in SCT and TRT!
PRELIMINARY
Data from morning of 18th May 2006
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Back to the new physics

• Fine-tuning / hierarchy problem (technical)
  Why are particles light?
• Does not explain Dark Matter
• No gauge coupling unification

Remember the aim was to fix some of these
problems with the Standard Model

• Possibilities
• Supersymmetry
• Minimal
• Non-minimal
• R-parity violating or conserving
• Extra Dimensional Models
• Large (SM trapped on brane)
• Universal (SM everywhere)
• With/without small black holes
• Littlest Higgs ?
• .

We will look at supersymmetry (SUSY)
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Supersymmetry!CAUTION!

• It may exist
• It may not
• First look for deviations from Standard Model!

Experiment must lead theory.

• Gamble
• IF DEVIATIONS ARE SEEN
• Old techniques wont work
• New physics not simple
• Can new techniques in SUSY but can apply them
  elsewhere.

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What is Supersymmetry?
Reverse the charges, retain the spins.
Matter
Antimatter
Retain the charges,reverse the spins.(exchange
boson with fermions).
Supersymmetric Matter
For technical reasons each sparticle can be
heavier than its partner by no more than a TeV or
so.
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Great!
Neutralinos The collective name of the
supersymmetric partners of the photon, the
Z-boson and the higgs boson. LSP Lightest
Supersymetric Particle. Often the lightest
neutralino.

• Fix Hierarchy Problem
• The Lightest Neutralino (LSP) is a prime
  candidate for neutral stable cold Dark Matter
• Can have gauge coupling unification

OCDMh2 0.103 0.009(WMAP 3-year data)
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Unfortunately

• Doubling of particle content
• Conservation of R-parity
• LSPs generated in pairs
• LSPs invisible to ATLAS
• Large number of tuneable parameters
• Assume just five of them exist for the moment
  unification arguments

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What might events look like?
What we can see
Here Be Monsters! (again)
What we can see
This is the high energy physics of the 21st
Century!
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(What they really look like)
b
soft gluon radiation?
An example of an event where a higgs boson
decayed to a pair of b-quarks/
b
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So main EASY signatures are

• Lots of missing energy
• Lots of leptons
• Lots of jets
• ATLAS Trigger ETmiss gt 70 GeV, 1 jetgt80 GeV.
  (or 4 lower energy jets). Gives 20Hz at low
  luminosity.

Just Count Events!
Indicates deviation from The Standard Model.
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• Papers for RAE ?
• Multidimensional likelihood maps
• String inspired susy models
• MT2 and friends
• Courses
• No need to revise
• Mathematics (all)
• Computational Physics

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Squark/gluon mass scale
What you measure
Peak of Meff distribution correlates well with
SUSY scale as defined above for mSUGRA and GMSB
models. (Tovey)
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The real test comes when you want to measure
individual masses etc.
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Technique 1 Kinematic Edges
Plot distributions of the invariant masses of
what you can see
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Technique 1 Kinematic Edges
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Technique 1 Kinematic Edges

• Account for all ambiguities

Both look the same to the detector
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Technique 1 Kinematic Edges
Use custom Markov-Chain algorithms to sample
efficiently from the high dimensional parameter
spaces of the model according to the Bayesian
posterior probability.
Shape of typical set is often something quite
horrible.
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Determine how edge positions depend on sparticle
masses
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Technique 1 Kinematic Endpoints

• Finally, project onto space of interest

Correlation between slepton mass measurement and
neutralino mass measurement.
Slepton mass
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Other Techniques

• Look at the shapes of the distributions
• Systematic errors harder to control
• Create new variables
• Cambridge MT2 Variablenow international used
  methodfor sparticle mass measurementin pair
  production
• Incorporate cross sections and branching ratio
  measurements
• again, Cambridge leading the way as home to the
  most developed samplers for H.E.P.

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Can even bring these techniques to bear on the
data we have today

• Dont know

• Know

• m0
• M1/2
• A0
• Tan beta
• Sgn mu
• mb
• mt
• as(Mz)

Quantity Measured value
ODMh2 (WMAP) 0.1126 0.0081 -0.0091
muon (g-2)/2 (19.0 9.4) 10-10
BR(b-gts ?) (3.52 0.42)10-4
mb 4.2 0.2 GeV
mt 172.7 2.9 GeV
as(Mz) 0.1187 0.002
SUSY params
SM params
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2D Slices of 5D SUSY parameter space tell you
very little
Roszkowski et.al.
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Even worse newsStandard Model errors are very
important!
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Standard Model uncertainty
Top Quark Mass
Experiment mtop 178 4.3 GeV in 2006 (was
174.3 3.2 GeV in 2004)
mtop 170 GeV
mtop 180 GeV
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Standard Model uncertainty
Bottom Quark Mass
Experiment mbot 4.1 to 4.4 GeV in MS scheme
mbot 4.0 GeV
mbot 4.5 GeV
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The parts of Supersymmetric Parameter Space are
consistent with Todays data
First analysis able to fold everything together
was from Cambridge Multi-Dimensional mSUGRA
Likelihood Maps, B.C. Allanach C.G. Lester
(Phys.Rev. D73 (2006) 015013)
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What if the Dark Matter isnt all SUSY?
Dark matter is just made of SUSY neutralinos
Other sources of Dark Matter allowed in addition
to SUSY
Favoured regions of SUSY model dont change an
awful lot! Prediction fairly robust.
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Future plans

• The whole programme is about the future.
• If we knew what the experiment will tell us we
  wouldnt need to build it. Experiment must lead.
• In short term, must continue to integrate further
  with CERN physics analysis teams.
• Analysis will be in collaboration
• In 10 years the SCT will have been radiation
  damaged beyond repair, and the LHC may be
  upgraded.
• Need to start work on SCT version 2 long before
  10 year lifetime of version 1 is reached
• LHC luminosity upgrade will place more demands on
  tracking systems
• Cavendish HEP group in ideal position to play
  leading role in that endeavour.
• Must strive to draw maximum inference from LHC
  data!

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Conclusions

• Expect new particles, new physics and other
  discoveries at the LHC
• May include a Dark Matter candidate ?
• Many competing physical theories
• Supersymmetry is one possibility
• There are many others
• (UED, Large Extra Dimensions, Littlest Higgs )
• An example experimental technique was presented
  in the context of Supersymmetry
• Kinematic endpoints and other measurements care
  efficient sampling from Posterior Distribution
  on parameter space
• Supersymmetry may not be what nature has chosen!
• Techniques will be applicable to any theory with
  large particle content and Dark Matter candidate
  and to others too
• Many more things I would like to have shown you
• How to measure particle spins and distinguish
  SUSY from UED etc .

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The End, and the ATLAS Collaboration
Cambridge Office
Christopher Lester 2006
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Spare slides
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Posterior maps
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Progress in the last Century

• 19th Century
• 1897 Electron (Thomson)
• 20th Century
• 1911 Nucleus (Rutherford)
• 1930 Neutrino postulated (Pauli, beta decay)
• 1936 Muon (Anderson, cosmic rays)
• 1956 Neutrino observed (Cowan, Reines, et al)
• 1960s and 1970s Growing support for light quarks
• 1960s Higgs boson postulated
• 1970s Tau discovery
• 1996 Top quark discovered (Tevatron)
• 21st Century
• Somethings coming, something good, (West Side
  Story)

25 year wait for neutrino
20-30 year wait for top quark
45 year wait for Higgs ??
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Anatomy of a Detector
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ATLAS blind data challenge

• Didnt discover anything that wasnt there.

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What do events look like?
RPV
RPV
(Lepton number violating)
(Baryon number violating)
RPC
RPC
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The SCT Software
Various
and
GUIs
users
etc.
SctApi
Overall SCT Controller
VME Crate Controller
VME Crate Controller
VME Crate Controller
Module
Module
Module
Module
Module
Module
Module
Module
Module
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