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High Energy Physics for the 21st Century

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Parts (QED) in extremely good agreement with experiment even with ... Something's coming, something good, (West Side Story) Progress in the last Century ... – PowerPoint PPT presentation

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Title: High Energy Physics for the 21st Century


1
High Energy Physics for the 21st Century
  • Step one into the unknown

Christopher Lester
2
Where are we now?
3
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

4
Dark corners of the Standard Model
5
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.
6
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.
if time allows
7
Simple experimental aim
Collide protons and see what happens.
8
Large Hadron Collider (LHC)
9
Inside the LHC
10
ATLAS Experiment
11
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)

12
Anatomy of the detector
Layered like Onion
Different layers for different types of particles
Neutrino
Muon
13
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
14
Muon Detector
MAGNETIC FIELD
MAGNETIC FIELD
Muons bend away from us. Anti-muons bend toward
us.
Man for scale
15
Calorimeters and Central Solenoid
16
Transition Radiation Tracker (TRT) tracks
charged particles and distinguishes electrons
from pions
17
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
18
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.
19
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

20
Evidence that it will work
First cosmic rays seen in SCT and TRT!
PRELIMINARY
Data from morning of 18th May 2006
21
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)
22
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.

23
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.
24
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)
25
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

26
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!
27
(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
28
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.
29
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)
30
The real test comes when you want to measure
individual masses etc.
31
Technique 1 Kinematic Edges
Plot distributions of the invariant masses of
what you can see
32
Technique 1 Kinematic Edges
33
Technique 1 Kinematic Edges
  • Account for all ambiguities

Both look the same to the detector
34
Determine how edge positions depend on sparticle
masses
35
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.
36
Technique 1 Kinematic Endpoints
  • Finally, project onto space of interest

Correlation between slepton mass measurement and
neutralino mass measurement.
Slepton mass
37
Other Techniques
  • Look at the shapes of the distributions
  • Systematic errors harder to control
  • Create new variables
  • Cambridge MT2 Variable now international used
    method for sparticle mass measurement in 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.

38
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
39
2D Slices of 5D SUSY parameter space tell you
very little
Roszkowski et.al.
40
Even worse news Standard Model errors are very
important!
41
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
42
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
43

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)
44
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.
45
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!

46
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 .

47
The End, and the ATLAS Collaboration
Cambridge Office
Christopher Lester 2006
48
Spare slides
49
Posterior maps
50
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 ??
51
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52
Anatomy of a Detector
53
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54
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55
ATLAS blind data challenge
  • Didnt discover anything that wasnt there.

56
What do events look like?
RPV
RPV
(Lepton number violating)
(Baryon number violating)
RPC
RPC
57
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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