23rd October 2006Alan Barr1 Discovering and exploring the new world Why we’re looking for new particles Making dark matter in the lab My work: discovering and understanding new particles ATLAS semiconductor tracker upgrade Grand objectives Alan Barr

23rd October 2006Alan Barr2 Why high energies? (1) See deeper –High energy  high momentum  small wavelength cells: 50 μm DNA: 2 nm atom nucleus: 2 fm quarks: < fm x 25,000 x 1,000,000 x up to 2,000 wavelength Planck’s constant Momentum Scatters off bulk Scatters off constituent λ

23rd October 2006Alan Barr3 Energy Why high energies? (2) Create new particles –Energy  matter interchangeable –High energies can make heavy particles Heavy particle production is the main purpose of the new highest energy colliders anti-quark quark annihilate Produce new heavy-weight speed / c Velocity factor Speed of light Mass Velocity factor

23rd October 2006Alan Barr4 The new periodic table Building blocks and mathematical theory understood Mostly extremely well tested –Higgs (h) and Graviton (G) not directly observed yet Electron, e d quark Photon, γ Gluon, g Diagrammatic only Commonplace particles u quark Matter Particles u Quarks d c s t b Leptons νeνe νμνμ ντντ e μ τ Known force carriers WZ γ g Others h G

23rd October 2006Alan Barr5 The whole story? Stuff we understand ~ 4% Evidence for Dark Matter from: –Rotation curves of galaxies –Microwave background radiation –Galaxy cluster collision  astro-ph/ Invisible mass Visible mass Colliding galactic clusters Normal matter mostly in interstellar gas –X-ray detection –Hits and slows down But the bulk of the mass has not interacted –From gravitational lensing  Large Dark Matter component Particle physicists should hunt: Weakly Interacting, Stable, Massive Particles

23rd October 2006Alan Barr6 Candidates? Particles related to “normal” matter by a symmetry: –Supersymmetry Relationship between particles with spins differing by ½ h –Spatial symmetry With extra dimensions –“Gauge” symmetry Extra force interactions (and often matter particles) electron quarks exotic partners? Force-carriers Related by symmetry neutrino x3x2 …? Already observed _

23rd October 2006Alan Barr7 Producing exotics? Time standard exotic Time standard exotic Time standard exotics Time standard exotics If exotics can be produced singly they can decay –No good for Dark Matter candidate If they can only be pair- produced they are stable –Only disappear on collision (rare) Require an even number of exotic legs to/from blobs (Conserved multiplicative quantum number) Require an even number of exotic legs to/from blobs (Conserved multiplicative quantum number)

23rd October 2006Alan Barr8 How do they then behave? Events build from blobs with 2 “exotic legs” A pair of cascade decays results Complicated end result Events build from blobs with 2 “exotic legs” A pair of cascade decays results Complicated end result Time standard 2 exotics Production part Time standard heavy exotic lighter exotic Decay part Time Complete “event” = exotic = standard

23rd October 2006Alan Barr9 How to discover at colliders? Can’t see dark matter particles themselves –Weakly interacting –Pass through detector –“Invisible” Observe some visible decay products Plus apparent non-conservation of momentum (Perpendicular to beams) “Missing” momentum is sum of momenta of invisible particles Can’t see dark matter particles themselves –Weakly interacting –Pass through detector –“Invisible” Observe some visible decay products Plus apparent non-conservation of momentum (Perpendicular to beams) “Missing” momentum is sum of momenta of invisible particles proton short-lived exotic Invisible exotic Visible particle missing z x

23rd October 2006Alan Barr10 The “real thing” (a simulation of…) Two high-energy jets of particles –Visible decay products Missing momentum –From two invisible particles More complicated than on previous page Proton beams perpendicular to screen Invisible particles

23rd October 2006Alan Barr11 The new machine at CERN Large –27 km circumference Hadron –Mostly protons Collider ~ 7 x higher collision energy ~ 100 x increase in collision rate Compared to current best machine (Tevatron near Chicago) Timeline: –Currently in commissioning –First collisions: November 2007 –First high-energy run: Spring 2008 –Much background work already done in simulations Magnets to bend beams Detectors at collision points

23rd October 2006Alan Barr12 My work (1) Digging out the exotic stuff: –Want to isolate ~ one event per billion –Lots of less interesting stuff going on –Intelligent choice vastly improves quality of selection Relevance: –Major discovery about nature –Motivates further study… International Linear Collider “interesting” “less interesting” hep-ph/ hep-ph/

23rd October 2006Alan Barr13 My work (2) Measuring particle masses –Interpreting incomplete information –Reconstructing complex decays Relevance: –Supersymmetry breaking –Sizes of extra dimensions –Unification of masses at very high energies? –Dark matter relic “predictions” Mass hep-ph/ hep-ph/ hep-ph/

23rd October 2006Alan Barr14 My work (3) Measuring the particle angular momenta –How much spin do the exotic particles posses –Previously thought to require a precision machine ($) –I have found good methods for measuring it at ATLAS Relevance? –Which of the candidate theories is relevant? –Supersymmetry? Extra dimensions? Measure spin hep-ph/ hep-ph/

23rd October 2006Alan Barr15 Spin determination θ*θ* p S Measure invariant mass => find angle Measure invariant mass => find angle P S Fermions Polarised fermion (Partner of W 0 ) Chiral couplings Scalar Scalar: spin-0 Fermion: spin-½ Scalar: spin-0 Fermion: spin-½ hep-ph/

23rd October 2006Alan Barr16 Detecting the debris ATLAS: Diameter ~ 20 m Module Length ~ 12 cm Tracker: Diameter ~ 2 m

23rd October 2006Alan Barr17 Silicon detectors Cross-section through a sensor –Charged particle excites electrons in silicon –Electric field sweeps them towards electrode –Electrical signal amplified and digitised –Data sent to off-detector electronics One of 4088 ATLAS semiconductor tracker modules –Complete tracker is like a 6 MegaPixel digital camera –Our camera takes 40 million photos per second 12 cm

23rd October 2006Alan Barr18 My contributions R&D Assembly Commissioning Irradiations and beam tests at CERN Performance tests of prototypes Functional testing during assembly Verification of performance Cosmic ray detection at CERN Getting ready for physics At each of these stages I’ve played major roles in making the system work, reading out the detectors, and understanding the results NIM.A 538: ,2005 June 06, CERN Sep 2004, downstairs June 2000, CERN

23rd October 2006Alan Barr19 Into the future? Various important measurements are likely to be statistics-limited Motivates study of luminosity upgrade –Need about a factor of 10 increase in collision rate –Redesign detectors Various important measurements are likely to be statistics-limited Motivates study of luminosity upgrade –Need about a factor of 10 increase in collision rate –Redesign detectors International R&D effort started –UK involved in several aspects of upgraded tracker design Grant proposal submitted –My continuing interest is in the off-detector electronics (and associated readout and calibration systems) –Compliments optical design and super-module testing already planned in Oxford International R&D effort started –UK involved in several aspects of upgraded tracker design Grant proposal submitted –My continuing interest is in the off-detector electronics (and associated readout and calibration systems) –Compliments optical design and super-module testing already planned in Oxford High significance spin-determination often requires hundreds of fb -1 hep-ph/

23rd October 2006Alan Barr20 Grand Objectives Discover new particles –Focus on Dark Matter-motivated signals Extract maximum information about them –What type of particles are these? –What can they us about: New symmetries of nature? Dark Matter? Higher-scale physics? (Unification …) Upgrade tracker for high luminosity –Construct UK demonstrator prototype in Oxford