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Welcome/Introduction to RAL (STFC)
Norman McCubbin
Director of Particle Physics
Particle Physics Department
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~80 people in Particle Physics Department (PPD), ~60 have PhDs, plus
engineering, instrumentation, accelerator, and computing in other parts of the
laboratories.
In many respects we are just like a large university PP department (eg Oxford),
but no requirement for undergraduate teaching (though a few do some), and a
relatively small number of PhD students for a department of this size.
We provide an ‘interface’ for the whole PP UK community to specialist skills in
other RAL/STFC departments:
– Technology: electronics, mechanical engineering;
– Computing: the UK Tier-1 is here, and we are part of the South Grid Tier-2
consortium;
– Accelerator R&D: ASTEC, which works closely with the Cockcroft and
Adams Institutes;
– Project management and administration: e.g financial tendering
RAL site has been, and is, undergoing massive change: much more building
over last 5 years than in previous 25…. : Diamond, ISIS Target Station 2, new
hostel, new main gate, new computer building, new research building,….
All this is part of transformation to Harwell Science and Innovation Campus
(HSIC).
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Current projects in PPD
Project
Approx.
FTE
Funding
Located at
Programme 2010-2012
ATLAS
18
STFC
CERN
M&O, analysis, tracker upgrade
CMS
11
STFC
CERN
M&O, analysis, upgrade
LHCb
5
STFC
CERN
M&O, analysis, upgrade
Computing
8
STFC, EU
RAL
Grid software, Tier (1,2,3) support
Neutron EDM
4
STFC
ILL
Deploy cryo-detector, M&O, analysus
Dark Matter
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STFC
Boulby
Laboratory
Zeplin III M&O, analysis; plus management of
Boulby facility.
Detector R&D
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STFC
RAL, university
collaborators
Developments for future PP experiments, and
non-PP applications
Neutrino
experiments
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STFC
Fermilab
J-PARC
MINOS; T2K
Neutrino
accelerator R&D
2+…
STFC(+ EU)
RAL
MICE; Neutrino Factory design studies;
FFAG/EMMA
NExT
3 (joint)
RAL + So’ton +
RHUL+Sussex
(Virtual) Institute for Phenomenology.
STFC/HEFCE
STFC
RAL, UKLO
Programme support for UK community
Support
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Programme Support
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STFC/PPD is an essential pillar of UK particle physics
– An amplifier for the national programme
– PPD co-located at an institution with powerful engineering and
technology capabilities enables Particle Physics UK to carry out
projects that it could not otherwise do. For example clean-room for
ATLAS, FE and thermal calculations for CMS, ….
• Especially critical for smaller university groups
– PPD is held in high esteem throughout the worldwide PP community,
and we are sought-after collaborators.
– We are involved in almost all UK PP projects.
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Provides a significant support role for UK Particle Physics
– Annual HEP summer school for all UK students
– Management and reporting of budgets
– Travel processing, booking and reimbursement
– Manage UK Liaison Office (UKLO) at CERN. (Previously also smaller
offices at DESY, SLAC, FNAL)
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Some big questions
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The Standard Model, which works so well at lower energies, falls apart
above a few TeV
– Is there a Higgs boson? Other new particles or forces?
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The Large Hadron Collider ..getting ready..
CMS calorimeter
crystal
CMS Half ECAL
installed June 2007
ATLAS tracker at RAL
NExT
Phenomenology
initiative with
Southampton,
RHUL and
Sussex
ATLAS tracker installed June 2007
LHC computing
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Oct 2010
and the
Grid
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The Large Hadron Collider ..data at last!
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Some big questions
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The Standard Model, which works so well at lower energies, falls apart
above a few TeV
– Is there a Higgs boson? Other new particles or forces?
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What is the cosmic dark matter?
– Can we detect it? Is it particles we can make at colliders?
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Direct detection of Dark Matter
 low rate, small energy deposits
– Very sensitive detectors
– Well shielded
– Underground to avoid cosmic
rays
1100 m
STFC operates the Boulby
underground facility,
Palmer Lab.
PPD led ZEPLIN-I and
ZEPLIN-II liquid xenon
projects. ZEPLIN-II
published world class
result. ZEPLIN-III running
well; beyond Nov 2010?
Palmer Lab also hosts
DRIFT, SKY,…
Long-term
future of Boulby?
• Being addressed now…
• LAGUNA in long-term?
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Some big questions
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The Standard Model, which works so well at lower energies, falls apart
above a few TeV
– Is there a Higgs boson? Other new particles or forces?
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What is the cosmic dark matter?
– Can we detect it? Is it particles we can make at colliders?
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What is the origin of the matter-antimatter asymmetry in the universe?
– See effects in quark decays?
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Flavour physics
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Using decays of particles containing b-quarks to explore the small matterantimatter asymmetry in quark decays
– BaBar experiment at SLAC (ended 2008)
– LHCb experiment at CERN
BaBar
Simulation
109 events/year at RAL
LHCb RICH2
detector
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LHCb cavern
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Neutron Electric Dipole Moment
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A permanent neutron EDM would
imply Parity and Time Reversal
Violation
Indirect test of matter-antimatter
asymmetry
Complementary to accelerator
searches
goal
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Cryogenic apparatus at ILL in
Grenoble
– Sussex, RAL, Oxford, Kure, ILL
Builds on previous successful
experiment
– world’s best limit 3 10-26 e cm
Installation complete and device
now cooled to 2K
Goal is sensitivity of
few  10-28 e cm
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Some big questions
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The Standard Model, which works so well at lower energies, falls apart
above a few TeV
– Is there a Higgs boson? Other new particles or forces?
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What is the cosmic dark matter?
– Can we detect it? Is it particles we can make at colliders?
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What is the origin of the matter-antimatter asymmetry in the universe?
– See effects in quark decays?
– Neutrinos?
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The Neutrino Programme
MINOS
• Operations
and
analysis
Technology demonstration
T2K
• A strong role in detector and
accelerator development and in
physics analysis
• Build up UK neutrino community
First events seen.
Beam power
increasing.
MICE
• Demonstrate
muon cooling
Explore CP violation
Neutrino Factory
• Build community, international
scoping study, EUROnu  design
study
• RAL is a credible site
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Room to dream!
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Harwell Science and
Innovation Campus
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ISIS
ISIS 1MW
upgrade
ESS-class 5MW
spallation source
Neutrino factory
Ultimate
multi-TeV muon
collider
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Knowledge Exchange
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Two examples
– The LCFI project spent over £500k in industry (e2v) on collaborative
development of novel silicon detectors for the International Linear
Collider. Patent application in progress.
– FFAG accelerators, being developed for future neutrino facilities, also
have significant promise in hadron/ion therapy applications. EMMA is
an FFAG “proof of principle”, and has just circulated (e-)beam. We are
part of a joint project (BASROC) to develop this within the UK.
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Future accelerator and detector projects are likely to make significantly
greater use of industry to develop equipment – “KE through procurement”
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Our biggest KE impact is probably through our ability to attract and train
students and postdocs who go on to careers in other areas
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A little bit of physics…
Bound states
of u,d,s
(anti-)quarks
Charm
(anti-)quarks
Bottom
(anti-)quarks
Graduate
UK-HEP_Forum'10-tsv
Lecture. NMcC Oct 2010
.. and the
Z
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The di-muon mass spectrum..
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A significant fraction of the (history of the) Standard Model is directly
visible in, or implied by, this mass spectrum:
– it’s a quark “directory”, seen through the quark-antiquark bound
states;
– We see the Z;
– Even the non-resonant continuum is “real physics” – though this is a
‘publicity’ plot, and I don’t know how much off-line selection has been
done: eg it would be possible, in principle to subtract out the
contribution from two semi-leptonic decays, but I would be surprised
if this has been done yet.
And the rich range of physics topics include:
– ρ/ω interference;
– “Quarkonium” structure of excited states for c and b systems;
– Narrow width of J/ψ and Υ (and large width of ρ/ω);
– Drell-Yan continuum;
– And the Z width bears directly on number of (light, non-sterile)
neutrinos.
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J/ψ width (1)
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J/ψ is by now probably one of the best studied particles in physics. The
Beijing e+e- collider (BEPC) has collected ~58 million of them, and studied
many rare decays.
The mass has been measured by the VEPP-4M ring with astonishing
precision, using the technique of resonance depolarisation:
MJ/ψ= 3096.917 ± 0.010 ± 0.007 MeV
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The widths are much tougher to measure:
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Γtotal = 93+- 2 keV; Γee = Γµµ = 5.6 +- 0.1 keV
The decay into lepton pairs is (of course) through a virtual photon.
Creation (in fermion-antifermion collision) and decay:
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J/ψ width (2)
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This same process can also give decay into quark-antiquark pairs,
observed (of course) as hadronic jets:
For uubar (via virtual photon) we expect: 3.(2/3)2 Γee = 1.3 Γee = 7.4 keV.
Do you understand the factors?
So, width into u, d and s pairs via virtual photon: ~7.4+1.9+1.9 = ~11keV.
Total width is 93 keV, so decay is not ALL ELECTROMAGNETIC.
Why not decay involving gluons? Which would presumably give us a
‘strong interaction’ width ~ 100 MeV.
First note that the J/psi cannot just ‘fall apart’ into charmed mesons (Why
not?)
But why not decay via a gluon (analogous to photon diagram)?
Can’t decay via one gluon, because of….
Can’t decay via two gluons because of ….
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CAN decay via three gluons, but this implies (αstrong)6
..and THAT’s why the J/ψ is so narrow!
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..other vector mesons and SU(2)
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To finish off, let’s look at leptonic widths of the light vector mesons:
– ρ(770): Γee = Γµµ = 7.0 keV
– ω(780): Γee = Γµµ = 0.60 keV (actually dimuon mode is not that well measured.)
– Φ(1020): Γee = Γµµ = 1.2 keV
Can we understand the relative magnitudes?
Just as for J/ψ, decay involves coupling to virtual photon.
The φ is ssbar: electric charge factor (-1/3)2
Both ρ and ω are mixtures of u.ubar and d.dbar, but there’s a factor of ~10
difference in leptonic width…
The u and d quarks play a special role in the strong interactions because
their masses and more importantly the mass difference between them are
very small compared to ΛQCD.
In other words, seen by the strong interaction the u and d are pretty much
identical (coloured) objects.
This gives rise to the valuable (for particle physics) and fundamental (for
nuclear physics) concept of strong isospin. Mathematically SU(2)
symmetry.
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.. SU(2)
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The u and d quarks form strong isospin doublet:
u 
u  1 / 2;1 / 2 and d  1 / 2;1 / 2 So the u, d form a ' doublet' in this strong isospin space :  
d 
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And combinations of u and d quarks get isospin quantum numbers in a manner that is
completely analogous to the usual QM angular momentum rules. And the strong
interactions conserve strong isospin.
Angular momentum coupling gives us things like:
0;0 
1
1;0 
1
2
2
( 1 / 2;1 / 2 1 / 2;1 / 2  1 / 2;1 / 2 1 / 2;1 / 2 )
( 1 / 2;1 / 2 1 / 2;1 / 2  1 / 2;1 / 2 1 / 2;1 / 2 )
The ω is an isospin singlet (I=0) and the ρ is I=1 – there are three: ρ+,ρ0,ρ-.
Assuming (correctly) that ubar has I3=-1/2 and dbar has I3=+1/2 would suggest:
ω=1/√2(u.ubar – d.dbar) and ρ=1/√2(u.ubar + d.dbar)
Giving electric charge factors of (2/3-(-1/3))2/2 for ω and (2/3+(-1/3))2/2 for ρ
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.. SU(2) (contd)
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Which is indeed a factor ~10….
BUT THE WRONG WAY ROUND! (predicts Γee for ω > Γee for ρ )
As is often the case, you have to be just a leeetle careful handling
antiparticles!
It is correct that ubar has I3=-1/2 and dbar has I3=+1/2.
But it is not correct that the SU(2) rotations on ubar and dbar are IDENTICAL
to those on u and d. And that messes up the coupling rules for isospin if you
have both quarks and antiquarks.
 
Fortunately, there is a neat way out: it turns out that the doublet   d 

u 
transforms exactly like  u 


 
d 
To see this I’ll mimic the discussion given in Halzen and Martin so you can
check it later.
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.. SU(2) (contd)
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 i 2 / 2
A rotation of π/2 about the ‘2’ axis is e
where τ2 is the
appropriate Pauli spin matrix. Applying this to a  u  doublet gives:
 
d 
 u '   0  1 u 
   
 
 d '   1 0  d 
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Now apply the charge conjugation operator, C.
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So
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Which is equivalent to:
Cu  u and Cd  d
 u '   0  1 u 
   
 
 d '  1 0  d 
 
  
  d '   0  1  d 

  




u   1 0 
u 

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.. SU(2) (contd)
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 
 d 
 
u 


transforms exactly like  u 
 
d 
So, we CAN use standard angular momentum coupling, provided we write
–dbar, whenever we want a dbar quark.
So
ω=1/√2(u.ubar – d.(-dbar)) and ρ=1/√2(u.ubar + d.(-dbar))
And all is well!
So the doublet
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