1. Welcome to RAL (STFC) Norman McCubbin Director of Particle Physics

2. Graduate Lecture. NMcC Oct 2008 2 ~90 people in Particle Physics Department (PPD), ~70 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). Particle Physics Department Particle Physics Department

3. Graduate Lecture. NMcC Oct 2008 3 Current projects in PPD ProjectApprox. FTE FundingLocated atProgramme 2008-2011 ATLAS24STFCCERN Construction  M&O, analysis, tracker upgrade CMS10STFCCERN Construction  M&O, analysis (upgrade) LHCb8STFCCERN Construction  M&O, analysis (upgrade) Computing10STFC, EURALGrid software Tier 1 centre BaBar2STFCSLAC Analysis  LHCb Neutron EDM4STFCILLCryo-detector (continous improvements) Dark Matter4STFCBoulby Laboratory Zeplin II analysis  Zeplin III installation  ton- scale detector Linear Collider Detector R&D 4STFCRAL, university collaborators Vertex detector and calorimeter development. Programme being redefined. Neutrino experiments 6STFCFermilab J-PARC MINOS  T2K Neutrino accelerator R&D 1 + …STFC(+ EU)RALMICE Neutrino Factory design studies NExT3 (joint) soon STFC RAL + So’ton + RHUL+Sussex (Virtual) Institute for Phenomenology. Major new HEFCE support. Other1STFCDESY, SNOlabSunsetting Support5OverheadRAL, liaison offices overseas Programme support

4. Graduate Lecture. NMcC Oct 2008 4 Programme Support 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. 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)

5. Graduate Lecture. NMcC Oct 2008 5 Some big questions 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?

6. Graduate Lecture. NMcC Oct 2008 6 The Large Hadron Collider ATLAS tracker at RAL ATLAS tracker installed June 2007 CMS calorimeter crystal LHC computing and the Grid Physics data in 2009! NExT project Phenomenology initiative with Southampton. Will expand to RHUL and Sussex CMS Half ECAL installed June 2007

7. Graduate Lecture. NMcC Oct 2008 7 Some big questions 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? What is the cosmic dark matter? –Can we detect it? Is it particles we can make at colliders?

8. Graduate Lecture. NMcC Oct 2008 8 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 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

9. Graduate Lecture. NMcC Oct 2008 9 Some big questions 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? What is the cosmic dark matter? –Can we detect it? Is it particles we can make at colliders? What is the origin of the matter-antimatter asymmetry in the universe? –See effects in quark decays?

10. Graduate Lecture. NMcC Oct 2008 10 Flavour physics Using decays of particles containing b-quarks to explore the small matter- antimatter asymmetry in quark decays –BaBar experiment at SLAC (ends 2008) –LHCb experiment at CERN (starts 2009) LHCb cavern LHCb RICH2 detector BaBar Simulation 10 9 events/year at RAL

11. Graduate Lecture. NMcC Oct 2008 11 Neutron Electric Dipole Moment 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) goal A permanent neutron EDM would imply Parity and Time Reversal Violation Indirect test of matter-antimatter asymmetry Complementary to accelerator searches

12. Graduate Lecture. NMcC Oct 2008 12 Some big questions 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? What is the cosmic dark matter? –Can we detect it? Is it particles we can make at colliders? What is the origin of the matter-antimatter asymmetry in the universe? –See effects in quark decays? –Neutrinos?

13. Graduate Lecture. NMcC Oct 2008 13 Explore CP violation Neutrino Factory Build community, international scoping study  design study RAL is one credible site Learn more about neutrino mixing angles (govern CP violation) T2K A strong role in detector and accelerator development and in physics analysis Build up UK neutrino community MINOS Operations and analysis The Neutrino Programme MICE Demonstrate muon cooling Technology demonstration

14. Graduate Lecture. NMcC Oct 2008 14 Room to dream! ISIS ISIS 1MW upgrade ESS-class 5MW spallation source Neutrino factory Ultimate multi-TeV muon collider Harwell Science and Innovation Campus

15. Graduate Lecture. NMcC Oct 2008 15 Knowledge Exchange 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. We are part of a joint project (BASROC) to develop this within the UK. Future accelerator and detector projects are likely to make significantly greater use of industry to develop equipment – “KE through procurement” Our biggest KE impact is probably through our ability to attract and train students and postdocs who go on to careers in other areas

16. Graduate Lecture. NMcC Oct 2008 16 Some physics…. 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. The discovery of the J/ψ:

17. Graduate Lecture. NMcC Oct 2008 17 J/ψ: the winners 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.

18. Graduate Lecture. NMcC Oct 2008 18 J/ψ discovery 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: (How?)

19. Graduate Lecture. NMcC Oct 2008 19 Cabibbo and… 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: –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: –And this process was not observed at anything like the expected rate.

20. Graduate Lecture. NMcC Oct 2008 20 Cabibbo and GIM –GIM fixed this problem by postulating a 4 th quark, c, and additional vertices: –This gives an extra diagram for the K L decay that cancels (in the limit m c =m u ) 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: –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! –DRAW SOME DIAGRAMS!

21. Cabibbo-GIM mechanism Now the diagrams cancel.

22. Graduate Lecture. NMcC Oct 2008 22 J/ψ width (1) 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: M J/ψ = 3096.917 ± 0.010 ± 0.007 MeV The widths are much tougher to measure: Γ total = 93+- 2 keV; Γ ee = Γ µµ = 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:

23. Graduate Lecture. NMcC Oct 2008 23 J/ψ width (2) 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 Γ ee = 1.3 Γ ee = 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 …. CAN decay via three gluons, but this implies (α strong ) 6..and THAT’s why the J/ψ is so narrow!

24. Graduate Lecture. NMcC Oct 2008 24..other vector mesons and SU(2) To finish off, let’s look at leptonic widths of the light vector mesons: –ρ(770): Γ ee = Γ µµ = 7.0 keV –ω(780): Γ ee = Γ µµ = 0.60 keV (actually dimuon mode is not that well measured.) –Φ(1020): Γ ee = Γ µµ = 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 Λ QCD. 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.

25. Graduate Lecture. NMcC Oct 2008 25.. SU(2) The u and d quarks form strong isospin doublet: 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: The ω is an isospin single (I=0) and the ρ is I=1 – there are three: ρ +,ρ 0,ρ -. Assuming (correctly) that ubar has I 3 =-1/2 and dbar has I 3 =+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

26. Graduate Lecture. NMcC Oct 2008 26.. SU(2) (contd) Which is indeed a factor ~10…. BUT THE WRONG WAY ROUND! (predicts Γ ee for ω > Γ ee for ρ ) As is often the case, you have to be just a leeetle careful handling antiparticles! It is correct that ubar has I 3 =-1/2 and dbar has I 3 =+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 transforms exactly like To see this I’ll mimic the discussion given in Halzen and Martin so you can check it later.

27. Graduate Lecture. NMcC Oct 2008 27.. SU(2) (contd) A rotation of π/2 about the ‘2’ axis is where τ 2 is the appropriate Pauli spin matrix. Applying this to a doublet gives: Now apply the charge conjugation operator, C. So Which is equivalent to:

28. Graduate Lecture. NMcC Oct 2008 28.. SU(2) (contd) So the doublet transforms exactly like 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!