Transcript Jet Reconstruction

Welcome to RAL (STFC)
Norman McCubbin
Acting Director of Particle Physics
Particle Physics Department
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~100 people in Particle Physics Department (PPD), 72 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 is undergoing massive change: much more building now than I can
remember: Diamond, ISIS Target Station 2, new hostel, new main gate, new
computer building. (We may even get something done about this building, R1)
All this is part of transformation to Harwell Science and Innovation Campus
(HSIC).
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Current projects in PPD
Project
FTE (06)
Funding
Located at
Programme 2006-2011
ATLAS
26.8
STFC
CERN
Construction  M&O, analysis, tracker upgrade
CMS
11.3
STFC
CERN
Construction  M&O, analysis (upgrade)
LHCb
8
STFC
CERN
Construction  M&O, analysis (upgrade)
Computing
14.6
STFC, EU
RAL
Grid software
Tier 1 centre
BaBar
4.6
STFC
SLAC
Analysis  LHCb
Neutron EDM
3 + 1 joint
STFC
ILL
Cryo-detector (continous improvements)
Dark Matter
5.3
STFC
Boulby
Laboratory
Zeplin II analysis  Zeplin III installation  tonscale detector
Linear Collider
Detector R&D
6.75
STFC
RAL, university
collaborators
Vertex detector and calorimeter development
Neutrino
experiments
5.8
STFC
Fermilab
J-PARC
MINOS
 T2K
Neutrino
accelerator R&D
1+…
STFC(+ EU)
RAL
MICE
Neutrino Factory design studies
NExT project
1 joint
RAL + So’ton
+??
Virtual Institute for Phenomenology
STFC xCCLRC
DESY, SNOlab
Sunsetting
Other
0.8
STFC
Support
4.9
Overhead
RAL, liaison
Programme support
offices
Graduate Lecture.
overseas
NMcC Oct 2007
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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
– Provide UK liaison officers for users working at major overseas labs
(CERN, DESY, FNAL, SLAC)
Graduate Lecture. NMcC Oct 2007
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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
CMS calorimeter
crystal
CMS Half ECAL
installed June 2007
ATLAS tracker at RAL
NExT
project
Phenomenology
inititiative with
Southampton.
Plan to expand
to RHUL and
Sussex
ATLAS tracker installed June 2007
LHC computing
Graduate Lecture. NMcC
Oct 2007
and the
Grid
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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?
Graduate Lecture. NMcC Oct 2007
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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 Boulb
underground facility
PPD led ZEPLIN-I and
ZEPLIN-II liquid xenon
projects. ZEPLIN-II
published world class
result
Funding for Zeplin III
confirmed July 2007
Future of Boulby?
• Underground lab support
(currently only through
experiments)
• CPL/University approach to
RDA
Graduate Lecture. NMcC Oct 2007
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The International Linear Collider
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Discoveries at the LHC will
likely leave us more questions
than answers:
– Have we really discovered
the Higgs?
• The right properties?
• Is it responsible for
mass?
– Have we really discovered
dark matter?
The ILC is the way to answer
these questions
Just to show
the scale: one
possible area
location
Fermilab
Global Project
Construction Decision >2010
STFC is strongly involved in
detector and accelerator work
– Detector development in
PPD for vertex detector
(LCFI) and calorimeter
(CALICE)
– Accelerator work primarily
in ASTeC
Graduate Lecture. NMcC Oct 2007
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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?
Graduate Lecture. NMcC Oct 2007
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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 (ends 2008)
– LHCb experiment at CERN (starts 2007-8)
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 (by 2009)
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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?
Graduate Lecture. NMcC Oct 2007
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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
Learn more about
neutrino mixing angles
(govern CP violation)
MICE
• Demonstrate
muon cooling
Explore CP violation
Neutrino Factory
• Build community, international
scoping study  design study
• RAL is one 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 is spending 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. 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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Programme priorities
1. scientific exploitation of LHC
2. R&D to prepare both for linear collider and for future neutrino
facilities, with a decision time around 2010-12
3. breadth of programme through smaller experiments where we can
have a key impact
Well matched to CERN Council’s European Strategy for Particle Physics
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Some physics….
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After that introductory ‘blah-blah’, I want to exercise your physics a bit.
As you are the generation of graduate students who will see the
‘revolution’ (we hope) from LHC – you are probably heartily fed up with
hearing that – let’s talk a bit about the ‘November 1974’ revolution, just
after I had completed my PhD.
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The discovery of the J/ψ:
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J/ψ: the winners
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Discovered simultaneously by:
Ting in pA at BNL
and
by Richter in e+e- at SLAC
And they went on to share the 1976 Nobel Prize.
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J/ψ discovery
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What was so special about the J/ψ?
It was massive (~3 GeV), at least for
1974, but the real ‘shocker’ is the
width (i.e. lifetime).
It was immediately clear that it decays
copiously to hadrons (SLAC), and one
would expect a (strong interaction)
width O(100) MeV.
From both BNL and (particularly)
SLAC data, it was immediately
clear that the J/ψ was MUCH
narrower.
In fact the first SLAC data tells us:
ee    0.05total
(How?)
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Cabibbo and…
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In fact it took some time to establish the precise nature of the J/ψ.
Particle Data Group, 1976 version, said
– ..”is large enough to suggest that the J/ψ is probably a hadron.”
The idea of a bound ccbar system was one of the strongest candidates right from the
start.
The charm (c) quark had been proposed just a few years earlier (1970) by Glashow,
Iliopoulos and Maiani :
– In order to bring some order to weak decays involving strange quarks, Cabibbo in
the 1960’s introduced the weak-decay vertices:
ud cos c and us sin  c couplingtoa W
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At the time there were only three known quark flavours: u,d,s
This worked fine, but also predicted Flavour Changing Neutral Currents (FCNC) for
processes like:
K L  
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And this process was not observed at anything like the expected rate.
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Cabibbo and GIM
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GIM fixed this problem by postulating a 4th quark, c, and additional vertices:
csc os c and  cd sin  c couplingtoa W
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This gives an extra diagram for the KL decay that cancels (in the limit mc=mu) the
diagram involving u,d, and s.
The way we usually say this is that the weak eigenstates (that couple to W) are
mixtures of the strong eigenstates:
d weak  d cos c  s sin  c and sweak  s cos c  d sin  c
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Note that it is entirely arbitrary whether we choose to mix the d and s quarks or the u
and c quarks. What counts are the vertices!
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DRAW SOME DIAGRAMS!
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Cabibbo-GIM mechanism
Now the diagrams cancel.
J/ψ width (1)
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Returning to the J/ψ….
It 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 (consistent with the first SLAC
data)
The decay into lepton pairs is (of course) through a virtual photon.
Creation (in e+e- 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 theu, d forma ' doublet'in thisstrongisospin 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 single (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 

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 
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!
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