Particle Physics II

1. Particle Physics II 5th Handout • Beyond the Standard Model: • Neutrinos, SUSY, dark matter • Solar neutrino problem • Neutrino oscillations • Supersymmetry • Astro-particle physics: Dark matter, high-energy cosmic rays Chris Parkes

2. Neutrinos in SM Revision • Massless • Left-handed • Only weak interactions (no EM, strong) • Electron,muon,tau neutrinos • Only 3 (with mass <Mz/2) Beyond the SM • Neutrino Oscillations • Neutrinos have mass • Only BSM phenomena discovered • As yet experiments have not resolved how to include in theory

3. Neutrino Discovery PM γ Scintillator e++e- p Water Scintillator γ PM "Dear radioactive ladies and gentlemen", • Electron neutrino • Suggested to ensure energy conservation in Nuclear beta decay Pauli, 1931 • Discovered through inverse beta decay on water target • using anti-neutrinos from a nuclear reactor Observed two photons from positron-electron annihilation (also detected neutron) F. Reines 1956

4. Muon Neutrino Lederman, Schwartz, Steinberger 1962 • Identification that there are different types of neutrino • Proton beam on Be target produces Pions • Pions decay Experiment • Large iron filter – absorb everything except neutrinos • (heavy) target & tracking detector to interact with neutrinos Produce muons ? Or electrons? Only muons seen, hence Tau Neutrino • Tau discovered as resonance in e+e- in 1975 • Assumed to have neutrino, and missing momentum observed in decays • 3 neutrinos measurement at LEP from z lineshape • Direct observation in 2000 (latest SM particle to be discovered)

5. Solar neutrino problem • Sun produces neutrinos in several nuclear interactions • e.g. pp fusion • Well known from solar models • Expect N(ne)=6.4x1010ne cm-2s-1 at earth • (64 billion through your fingernail per second) • Measure rate….

6. Solar neutrino’s & Cleaning Fluid Homestake Mine, South Dakota 390m3 (520tons) of cleaning fluid C2Cl2~103037Cl atoms ne+37Cl37Ar+e Flush~1/month with He and separate 37Ar Look for 37Ar decay via 2.8KeV K-shell x-ray Solar model predicts 7.6±1.3 SNU Measure 2.56±0.6±0.15 SNU SNU = Solar Neutrino Unit 1 SNU= one capture per 1036 atoms s-1 Deep (1600m) underground to shield from cosmic rays

7. Solar neutrino problem Homestake mine Discrepancy between ne predicted by solar model and measured • Homestake mine (Cl) • Kamiokande (water) • Gallium expts

8. Sudbury Neutrino Observatory (SNO) 2002 • SNO: 1000 tonnes D20, 10000 PMTs Sensitive to: Charged current interaction: ne+dp+p+e-0.35±0.02 SSM Neutral current: nx+d  n+p+nx 1.01±0.12 SSM SSM=solar standard Model ne only ne,nm,nt (also elastic scattering, not discussed here) • Current number • of neutrinos • Deficit of • electron neutrinos • Electron neutrinos • have oscillated to • other types

9. Detection – Cherekov light • Charged current: • Highly energetic electron • 2000 times lighter than proton • Travels faster than local speed of light • Cherenkov light given off • Analagous to sonic boom • Detect light in PMTs • Neutral current: • Neutron captures on deuterium nucleus – giving off 6 MeV photon • photon interacts with electrons giving off Cherenkov light

10. Neutrino mixing Flavour states and mass states analogous to the quarks • Similar to the case we discussed for Kaons PMNS matrix Electron ν Muon ν Tau ν Three mixing angles,θ23~45o

11. Implications • Neutrinos oscillate •  n have mass • Oscillations depend on square of mass differences • (m1-m2)2=8x10-5 eV2, (m2-m3)2=2x10-3 eV2 • Unlike K (or B) meson oscillations there are three eigenstates •  lepton flavour violation •  First results beyond standard model of particle physics! How neutrinos can be included in theory not yet understood Experiments underway…. One of mixing angles unknown, CP violation ?, mass order… T2K neutrino beam to Super Kamiokande, neutrinoless double beta decay experiments

12. Supersymmetry • In Q.M. connection between • Global transformations and conserved quantities, e.g. • Translational Invariance Linear momentum conservation • Rotational InvarianceAngular momentum conservation • Translations in timeEnergy conservation Noether’s theorem – Symmetries (invariances) naturally lead to conserved quantities Finding symmetries now a guiding principle in new physical theories Propose new symmetry of nature: Supersymmetry Spin ½ Fermions (quarks, leptons)  spin 0 boson superpartner Spin 1 Bosons  spin ½fermion superpartner • SUSY not an exact symmetry • Mass of SUSY particles ≠Mass of normal particles • Since none discovered yet

13. SUSY particles Interactions are the same e.g. squarks interact via strong interaction

14. SUSY Motivation 1/Strength Log Energy GeV 1.SUSY allows unification of the forces 2.SUSY cancels divergences in SM 4. SUSY provides a theoretical route to include gravity in “standard model”, and needed in string / M-theory 3. Lightest SUSY particle (LSP) is candidate for dark matter Most models LSP is stable neutralino SUSY: theoretically beautiful and convenient – but is it true ?

15. SUSY Experimentally • “normal” particles and “SUSY” particle have opposite R-parity • R-Parity conserved (assumed!) • R-parity conservation  stable LSP Neutralino, neutral weakly interacting particle missing energy in event, key signature! • Measure missing transverse momentum/energy Candidate event in D0 (TeVatron) No evidence

16. Dark Matter • Compelling astrophysical evidence for dark matter • e.g. rotation curves of spiral galaxies • ‘dark matter’ is a term of ignorance • Neutrinos, small contribution • Weakly Interacting Massive Particles (WIMPs) ? • e.g. SUSY neutralino Observed Expected no DM

17. Dark Matter Searches • Collider expts (as discussed) • Direct Detection Experiments • WIMP annihilation e.g. CDMS, detect the heat produced when a particle hits an atom in a crystal of germanium, operates at 10mK e.g. Gamma- ray space telescope - FERMI, detect gamma rays from WIMP annihilation. Launched June 2008

18. High Energy Cosmic rays • Detect ultra-high-energy cosmic rays: single particles E > 1020 eV • (c.f. tennis serve). • Rate 1 per km2 per century • Source: Proton accelerated by magnetic fields of black-holes in active galactic nuclei ? • Pierre Auger Observatory • Cosmic ray reacts in atmosphere • shower 109 particles • 1600 water cherenkov detectors • 3000 Km2in Argentina • (also flourescence detectors)

19. Physics beyond the standard model • SM almost complete • But still a Higgs to find….. • Neutrinos: first physics BSM • Neutrino oscillations  neutrino mass • Some big unanswered questions in SM • Why is there more matter than anti-matter in the universe ? • What is Dark Matter / Dark Energy • Why three generations ? Why hierarchy of mass scales ? • How to incorporate gravity ? • Supersymmetry • Allows unification of the forces • Allow inclusion of gravity • BUT not observed yet, • Many other possibilities • Extra dimensions, Compositeness • But so far no evidence! • Wide experimental programme • LHC is biggest highest profile project • Many other active experiments

20. Start of the LHC You tube: LHC rap xkcd.com

21. Start of the LHC - September 2008 • First beams circulated round full ring • Particles seen in all detectors The First Event 22nd August 2008

22. Friday 19th September 2008 • CERN Press Release: Incident in LHC sector 34 • Geneva, 20 September 2008. During commissioning (without beam) of the final LHC sector (sector 34) at high current for operation at 5 TeV, an incident occurred at mid-day on Friday 19 September resulting in a large helium leak into the tunnel. Preliminary investigations indicate that the most likely cause of the problem was a faulty electrical connection between two magnets, which probably melted at high current leading to mechanical failure.

23. November / December 2009 • First Collisions • World Record collision Energy, 2.36 TeV

24. Calibration & Detector Performance • Re-finding particles • Measuring Resolutions 3µm σ= 4.3 ± 0.1 MeV/c2 M(Ks) = 497.3 ± 0.2 MeV/c2 M(KsPDG) = 497.7MeV/c2

25. First Results KShort ptdistribution integrated Black: Data 2009 Red: MC Blue : background prel. Charged Particles • Already two publications – number of charged particles • Prelim. results on particle rates and ratios

26. 2010 Status • Shutdown for repairs & servicing • Operations started again at end of February • Hope to increase collision energy to ~ 7 TeV this month • Significant Physics results expected from 2010-2011 run

27. Large Hadron Collider End of the world postponed as broken Hadron Collider out of commission for months • 2008: “It’s the end of the world as we know it” • 2010 onwards: “It’s the end of physics as we know it” ? • Higgs, Susy, Dark Matter, matter anti-matter asymmetry….. • Not the time for speculation, but to wait (a little longer) and see what Nature has in store….