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The Future for Particle Physics ?

The Future for Particle Physics ?. QuarkNet Institute, June 17, 2008 U. Cincinnati Brian Meadows. Outline. Introduction Particle physics at UC What Particle physics is about: the forces of nature Before the Standard Model Some basics of the Standard Model Beyond … dark matter, LHC, ….

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The Future for Particle Physics ?

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  1. The Future for Particle Physics ? QuarkNet Institute, June 17, 2008 U. Cincinnati Brian Meadows Brian Meadows, U. Cincinnati.

  2. Outline • Introduction • Particle physics at UC • What Particle physics is about: the forces of nature • Before the Standard Model • Some basics of the Standard Model • Beyond … dark matter, LHC, … Brian Meadows, U. Cincinnati

  3. Particle Physics (HEP) at UC • Philip Argyres Theory • Randy Johnson Experiment n’s at FNAL • Alex Kagan Theory • Kay Kinoshita Experiment CPV at KEK • Brian Meadows Experiment CPV at SLAC • Joe Scanio Theory • Alan Schwartz Experiment CPV at KEK • Mike Sokoloff Experiment CPV at SLAC • Peter Suranyi Theory • Rohana Wijewardhana Theory • Louis Witten Theory Brian Meadows, U. Cincinnati

  4. Forces of Nature Particle physics is all about fundamental forces: Are there other forces ? What is dark energy ? Brian Meadows, U. Cincinnati

  5. Before the Standard Model Brian Meadows, U. Cincinnati

  6. Discovery of Anti-matter in Cosmic Rays Cloud chamber event observes an e+ (Anderson, 1932): • Magnetic field produces curvature • Energy loss in metal barrier indicates direction of motion is that of positively charged particle • Ionization density (light) indicates electron mass (relativistic speed) e+ Brian Meadows, U. Cincinnati

  7. Discovery of Charged Pion (p§ ) e + e + e + • Emulsion pictures showing p+ decays: • m+ is mono-energetic • e+ is NOT • NOTE large angle between p+ and m+ tracks indicates decay at rest rather than scatter. e + m+ m+ m+ m+ p+ p+ p+ p+ Brian Meadows, U. Cincinnati

  8. A p0 Dalitz decay • Bubble chamber event: • Most often p0 decays: p0!g + g • For ~1/84 decays: p0!e+e- + g Known as “Dalitz decays” (internal conversion) g n e- e+ p- Brian Meadows, U. Cincinnati

  9. The “V0” – Discovery of Strangeness • L0 (S=-1) and K 0 (S=+1) are made in pairs • Strangeness (S) is conserved Brian Meadows, U. Cincinnati

  10. Strangeness is a “Flavour” Flavour • is conserved in strong interactions • Is not conserved in weak interactions e- Bubble chamber event: e+ g L Brian Meadows, U. Cincinnati

  11. Discovery of the W- Hyperon VERY Strange (S = -3) I was almost there! Brian Meadows, U. Cincinnati

  12. Charm – another “flavour” (C) • Bubble chamber event (Samios, et al, 1975) Brian Meadows, U. Cincinnati

  13. First Resonance – the ++ • Observed as broad peak in the p+p scattering cross section by Fermi and U. Chicago experimenters • Many more resonances now known – baryons and mesons - §, 0, 0, K§,0, *, §,0,++, … !! • Central mass 1236 MeV/c2 • Width G 120 MeV/c2 • Named D++(1236) • D++ p + p+ (strong) Brian Meadows, U. Cincinnati

  14. Some Basics of the Standard Model “… elementary particle physics has come of age. Although we obviously have much more to learn, there now exists a coherent and unified theoretical structure that is simply too exciting and important to save for graduate school or to serve up in diluted qualitative form as a subunit of modern physics.” David Griffiths,ISBN-10:0-471-60386-4 Brian Meadows, U. Cincinnati

  15. Quarks and Flavours • Just 6 quarks are building blocks for all strongly interacting particles (hadrons) • They come in two charges u c t - charge +2/3 e d s b - charge -1/3 e • Each has a unique “flavour”: “Isospin” : u (I = ½ ,I3 = + ½ ); d (I = ½ ,I3 = + ½ ) “Strangeness” : s (S = -1) “Charm” : c (C = +1) “Beauty” : b (B = +1) “Top” : t (T = +1) • “Baryon number” (B#) of each is 1/3. • Antiquarks have opposite charges, flavors and B#. Brian Meadows, U. Cincinnati

  16. Quarks and Hadrons • Hadrons are particles that feel the Strong Force. BARYONS-p, n, , , , , c, … • Basic composition - 3 quarks p = uud, n = udd, W- = sss, p = uud, … etc. MESONS-, K, D, Ds, B, , , , f, a, … • Basic composition - quark-antiquark pairs + = ud, - = ud, K- = su, D+ = cd Ds+ = cs , B0 = bd, … etc. • Additional quark-antiquark pairs are not excluded in the SM. Brian Meadows, U. Cincinnati

  17. Forces Between Quarks • E/M forces arise from “2 charges”. • They are governed by Quantum ElectroDynamics (QED) • Force between charged particles are mediated by exchange of photons • The potential isU(r) = -kq / r • Strong forces arise from “3 colours”. • They are governed by Quantum ChromoDynamics (QCD) • Force between coloured quarks are mediated by exchange of gluons and • The potential isU(r) = - a / r + k r Brian Meadows, U. Cincinnati

  18. Forces Between Quarks • At extremely small distances, quarks are almost free • “Asymptotic freedom” • BUT at large distances, they cannot escape from other quarks in their parent hadron • “Infra-red slavery” • They are “confined” • Guess - U(r) = -/r + kr Confinement potential Brian Meadows, U. Cincinnati

  19. Experimental Evidence for Quarks Even today, free quarks have never been seen • This is probably because they are so tightly bound together • Best experimental evidence for their existence (within protons): • e- p scattering at high energies (similar to Rutherford scattering) reveals inner structure in three “lumps” • Also, “jets” are seen in e+e-! hadrons events Brian Meadows, U. Cincinnati

  20. Experimental Evidence for Quarks • Also, “jets” are seen in e+e-! hadrons events Event from JADE detector (at DESY, Hamburg, Germany) Shows e+e-! q q CMS energy 31 GeV Brian Meadows, U. Cincinnati

  21. u, d, s, c, b  11/9 u, d, s, c  10/9 u, d, s  2/32+(-1/3)2+(-1/3)2=2/3 Experimental Evidence for Colours • ++ and - show that quarks must come in three colours. • Measurements of e+e- annihilations into hadrons show that there are, indeed, three colours Simple prediction is based On sum of squared charges Of quarks that can be produced R is about 3 x simple prediction without colour Brian Meadows, U. Cincinnati

  22. Experimental Evidence for Gluons Event from JADE detector (at DESY, Hamburg, Germany) Shows e+e-! q q g CMS energy 31 GeV Brian Meadows, U. Cincinnati

  23. u + u d All flavors conserved ++ u d u p u u Strong Decays • Decays occur in ~10-23 sec. (c x 10-23 ~ nuclear radius) u 0 u u All flavors conserved + u d + d Brian Meadows, U. Cincinnati

  24. d Quarks and Weak Decays • Weak b decay p !n + e+ + e • Weak decay Ds+!K0 + K+ e+ W § Flavors NOT Conserved (u!d) u e u p d d n u d s K0 c Flavors NOT Conserved (c!s) Ds+ W § u s K+ s Brian Meadows, U. Cincinnati

  25. s “Cabbibo Suppressed” Weak Decays • Weak decay L!p + e+ +ne • Weak decay Ds+! 0 + K+ e+ W § Flavors NOT Conserved (u!s) s e L u u d p u d s 0 c Flavors NOT Conserved (c!s AND u s) Ds+ W § u s K+ s Brian Meadows, U. Cincinnati

  26. Other Weak Interactions • Charged current interaction  + p !- + n + + • Neutral current interaction  + p !- + p -  Flavors NOT Conserved (u!d) W § p u u d d n u d   Flavors ARE Conserved (uu) Z 0 p u u d u p u d Brian Meadows, U. Cincinnati

  27. Brian Meadows, U. Cincinnati

  28. The Future of Particle Physics Brian Meadows, U. Cincinnati

  29. BaBar and Belle • Found that SM mechanism for CPV works well • Discovered many new states that could be either: • “Ordinary hadrons” with additional qq pairs OR • Threshold effects OR • Other ?? • Discovered “mixing” between D0 and D0 • A few hints that new particles (beyond the SM) may be playing a role in the decays of B mesons. All experiments so far agree that SM works well – with very few “smoking guns”. Brian Meadows, U. Cincinnati

  30. Mixing • It has long been known that neutral mesons can “mix” • For instance, the B0 and B^0 are thought to be quantum mixtures of a heavy state B1 and a light one B2 B0 = B1 + B2 B0 = B1 – B2 • These states have complex masses so they evolve in time with an exponential decay with a sinusoidal oscillation superimposed. • Their masses are slightly different so that these sinusoidal variations “beat” and lead to oscillations from B0 to B0. • The K0 and D0 mesons behave in a similar way, though this phenomenon has only recently been observed (in BaBar and Belle) for the D0 mesons. B1 = e-t/t1 x ei m1t cos m1t + i sin m1t Brian Meadows, U. Cincinnati

  31. Neutrino Mixing • It is now known, from cosmic rays, that neutrinos also “mix” • This implies that they do have masses • This is the one place where evidence exists for the breakdown of the SM ! • This is regarded as a “friendly amendment” to the SM by most theorists and experimentalists, since we have never been able to obtain reliable measurements of n masses in any case. • One of the most interesting things to look for now is,given that n’s are not really so different from quarks after all, whether or not this means that we should getCPV in the n sectorjust as we do in the quark sector. ne <-> nm, etc. Brian Meadows, U. Cincinnati

  32. Cosmology and Particle PhysicsDark Matter Velocity • When we look into space, all we can view in a telescope is consistent with being made up from quarks, leptons and the gauge particles in the standard model. • Yet we know that the universe consists of more matter than we can see. • One observation that strongly suggests this is the observed rotation curves for galaxies that clearly disagree with Kepler’s laws as derived using only visible mass. • The curves disagree with the notion that all the matter resides at the galactic nucleus. Bulge or “nucleus” Brian Meadows, U. Cincinnati

  33. Cosmology and Particle PhysicsDark Matter • Further evidence is seen in • Velocities of galaxies relative to one another in clusters • Gravitational lensing • Colliding galaxies (e.g. Bullet cluster) • In the Bullet cluster two galaxies collided: • Stars interacted gravitationally, passing through one another with little slowing • Gases interacted electromagnetically and were slowed the most • Dark matter hardly interacted. Bullet cluster map revealed by lensing of objects behind it • Blue areas are best guess at where the dark matter is • Red areas indicate where hot gas is. Brian Meadows, U. Cincinnati

  34. What is Dark Matter ? • It does not reflect or emit enough EM radiation to be seen in normal observation techniques (visible, IR, UV, radio,..) • It could be ordinary (SM) particles in unusual or hard-to-see form, or something else: • Light or heavy’s • WIMPS (weakly interacting massive particles) • MACHO’s (“Brown Dwarfs” and planets) • Primordial black holes • Non-luminous gas clouds • Preferred explanation is that it consists of “non-baryonic” particles expected beyond the Standard Model. Brian Meadows, U. Cincinnati

  35. “SM” Particles • To recap, the SM contains • Leptons (spin ½) • Quarks (spin ½): • Gauge Bosons (spin 1) • Higgs (spin 0) (Simplest is single particle) Weak E/M Strong Brian Meadows, U. Cincinnati

  36. “Non-Baryonic” (Beyond SM) Particles ? • Supersymmetric particles are • Sleptons (spin 0) • Squarks (spin 0): • Photino, Wino/Zino, gluino (spin ½) • Higgsino (spin ½) • NOTE – Higgsino, Zino and photino all have spin 1/2 Brian Meadows, U. Cincinnati

  37. The “WIMP” ? • The neutral, spin ½ gauginos are called “neutralinos”. • The lightest of these is called the LSP (Lightest Supersymmetric Particle • Most supersymmetric theories allow Lepton number (L) and Baryon number (B) to be violated, but the R-parity conserved: • The LSP cannot decay without violating R-parity • So this could be a major component of dark matter (the “WIMP”) • To be consistent with the fact that we have yet to observe this in the experiments performed so far: • Its mass is probably between 1000-10000 GeV/c2. • It interacts weakly • It is electically neutral (neutralino) R = (-1)2J+3B+L = -1 (supersymmetric) but = +1 (SM) Brian Meadows, U. Cincinnati

  38. The Large Hadron Collider (LHC) • Circumference ~27 km (Recycled LEP accelerator) • Magnets - superconducting Nb-Ti 7,000 dipoles @ 8 Tesla • High “Luminosity” 3,000 bunches @ 1011 p (or Pb) 40 x 106 crossings per second • 800 x 106 collisions per second • High Energy 7 TeV x 7 TeV (1 TeV = 1000 mp) p-p collisions @ 14 TeV Pb-Pb collisions @ 1150 TeV Brian Meadows, U. Cincinnati

  39. The LHC and CERN Experiments LHCb will make studies similar to ones by BaBar & Belle ALICEwill study Pb-Pb collisions n experiments ATLAS & CMS Multi-purpose detectors I used this in my thesis experiment! Proton Synchrotron the “source” 24 GeV x 24 GeV Brian Meadows, U. Cincinnati

  40. Discoveries at the High Energy Frontier • Origin of Mass Higgs Boson is simplest way to create scalar field that makes mass observable in most particles. Will probably be produced at the LHC • Supersymmetry and Dark Matter Grand unified theories predict existence of Sparticles. The lightest of these is a favourite candidate for Dark Matter. • Extra Dimensions Some particle physics theories predict more than the “usual 4” dimensions. The observation of new particles may result from this. ATLAS Brian Meadows, U. Cincinnati

  41. The Atlas Detector • Large, multi-purpose detector About 45 m long x 25 m high ~ ½ x Notre Dame Cathedral (Paris) Weight 7,000 tons ~ Eiffel tower (Paris) Toroidal Magnetic Field • Data rate ~ 200 TB / sec Uses a “trigger” to decide which events to record. Records ~ 27 GB / min. • Will occupy time of ~2,200 collaborators for next 10-15 years http://atlas.ch/detector-overview/index.html Brian Meadows, U. Cincinnati

  42. The CMS Detector • Large, multi-purpose detector About 21.5 m long x 15 m high ~ ½ x Notre Dame Cathedral (Paris) Weight 12,500 tons ~ Eiffel tower (Paris) Dipole Magnetic Field 4T • Data rate similar to ATLAS • Approximately another 2,000 collaborators. (Not me, though!) • http://cms.cern.ch/ Brian Meadows, U. Cincinnati

  43. The Future for Accelerator Physics ? • If LHC finds new particles (as it MUST!) we may need a super high intensity Babar/Belle to interpret what they are from their effects in reactions studied by Babar/Belle. • Plans for a SuperB (~BaBar x 100) in Rome/Italy exist • Belle also plans a (~Belle x 10-50) upgrade in Japan. • The ILC is another obvious way to study new particles (“somewhere”) • As with BaBar and Belle, e+e- collisions, which lend themselves to a very clean physics interpretation, will be used BUT • It may take a long time and $$$$ to build an ILC of the required energy • It may even take a long time before the LHC tells us what that energy needs to be. Brian Meadows, U. Cincinnati

  44. The Future ? • There are many things left to do, as Griffiths said two decades ago. • It is possible that we will look to cosmic rays for some of the new things there are to learn about this universe. • We may even need to look at the universe as astrophysicists do – through telescopes. • Or we can use our new, state-of-art, detectors to look at the cosmic rays themselves • We certainly have much to learn from those ’s which do come mostly from space • The future of accelerators is not dead yet either ! • LHC - the energy frontier • Super B - the intensity (flavour) frontier. Brian Meadows, U. Cincinnati

  45. The next 15 years (or more) promise to be exciting ! “… elementary particle physics has come of age. Although we obviously have much more to learn, there now exists a coherent and unified theoretical structure that is simply too exciting and important to save for graduate school or to serve up in diluted qualitative form as a subunit of modern physics.” David Griffiths,ISBN-10:0-471-60386-4 Brian Meadows, U. Cincinnati

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