CMS experiment at LHC

1. CMS experiment at LHC Geoff Hall Imperial College London Geoff Hall

2. Latest CERN accelerator started 2008 26km circumference ring ~100m underground Beams 7 TeV protons or ions, eg Pb very high intensity 1015 collisions per year very high rate beams cross @ 40MHz few “interesting” events ~100 Higgs decays per year Large Hadron Collider (but a small problem occurred - with a big impact) Geoff Hall

3. Particle physics in two slides • Matter originated in the Big Bang • LHC energies correspond to tiny fraction of a second in the life of the universe • Make up hadronic matter, eg • proton (uud) • neutron (udd) • mesons (q + anti-quark) • Leptons • Families - like quarks • e- makes atoms with nuclei • µ and  are like heavy electrons • each has a neutrino partner • All quarks and leptons have mass Geoff Hall

4. Forces hold matter together Strong nuclear Electromagnetic Gluons Photon Quarks Atoms Light Chemistry Electronics Mesons Baryons Atoms electrons Nuclei • Forces are transmitted by fields, also represented by particles (g, W, Z, gluon) • The “Standard Model” has unified some of the (4) forces of nature … astonishingly successfully • The most significant missing item is mass • It may be explained by a new field (and particle) - Higgs (boson) Weak nuclear W & Z Bosons Neutron decay Beta radioactivity Neutrino interactions Solar burning quarks leptons neutrinos Geoff Hall

5. Colliding beams maximises the energy available to create new particles d d u u u u Experiment by collisions • Actually hadron collisions are between their constituent parts… • gluons • quarks • and the particles they exchange (Z, W,…) Geoff Hall

6. Measure high pT lepton and quarks to identify possible new physics Large solenoidal (4T) magnet iron yoke - returns B field, absorbs particles Then, going outwards from beam Tracking system – bend in B field reconstruct trajectories of most charged particles momentum measurements from bending Calorimeters – absorb energy good energy resolution Muon detection –penetration detectors in yoke measure muon momentum from bending Experiment design p pT pL Geoff Hall

7. HCAL Muon chambers Tracker ECAL 4T solenoid CMS Compact Muon Solenoid Total weight: 12,500 t Overall diameter: 15 m Overall length 21.6 m Magnetic field 4 T Geoff Hall

8. Muon System Gaseous planar ionisation detectors embedded in iron magnet return yoke to measure particle trajectories 195k DT channels210k CSC channels162k RPC channels Geoff Hall

9. YB0 Feb 2007 Geoff Hall

10. December 2007 Geoff Hall

11. YE-1 Jan 2008 Geoff Hall

12. First data First LHC Beam(10 Sept) 10 September 2008: beams were steered into collimators and secondary particles detected in CMS before and after September ~ 300 M cosmic ray events recorded Geoff Hall

13. 1032 cm-2 s-1 1033 1034 1035 The luminosity challenge • HZZ  ee, MH= 300 GeV for different luminosities in CMS Full LHC luminosity ~20 interactions/bx Proposed SLHC luminosity ~300-400 interactions/bx Geoff Hall

14. TOB TOB TEC TEC TIB TIB TID TID PD PD Tracker system • Two main sub-systems: Silicon Strip Tracker and Pixels • as many measurement points as possible with the most precise measurements close to the interaction point • ionisation in silicon produces small current pulses • silicon sub-divided into small measuring elements: strips or pixels • ~14 layers, ~210 m2 of silicon, 9.3M channels • 3 layers, 1m2 pixels, 66M channels Radiation environment ~10Mrad ionising ~1014 hadrons.cm-2 Geoff Hall

15. Microstrip Tracker Outer barrel 3.1M channels • automated module assembly Endcaps 3.9M channels Inner barrel 2.4M channels Geoff Hall

16. Scine Electromagnetic Calorimeter Scintillating crystals of heavy material – PbWO4 Light produced by electromagnetic showers Light signal proportional to electron or photon energy Geoff Hall

17. Trigger and DAQ systems • Trigger selects particle interactions that are potentially of interest for physics analysis • DAQ collects the data from the detector system, formats and records to permanent storage • First-level trigger: very fast selection using custom digital electronics • Higher level trigger: commercial computer farm makes more sophisticated decision, using more complete data, in < 40-50 ms • Trigger requirements • High efficiency for selecting processes of interest for physics analysis • Largereduction of rate from unwanted high-rate processes • Decision must be fast • Operation should be deadtime free • Flexible to adapt to experimental conditions • Affordable Geoff Hall

18. jet jet Z H p p Z e + e - Triggering • Primary physics signatures in the detector are combinations of: • Candidates for energetic electron(s) (ECAL) • Candidates for µ(s) (muon system) • Hadronic jets (ECAL/HCAL) • Vital not to reject interesting events • Fast Level-1 decision (≈3.2 µs) in custom hardware • up to 100kHz with no dead-time • Higher level selection in software Geoff Hall

19. µ + µ - Z p H p n - e e Z µ + q - c µ - 1 ~ q q ~ g p p ~ q + m - q ~ m 0 c 2 ~ 0 c 1 What we hope to find • Higgs discovery (simplified!) • Will be produced with many other particles • ~20 events per beam crossing • hundreds of secondary particles/25ns • Much new physics • New forces • New particles • New symmetries Geoff Hall

20. Machine incident • A superconducting cable connecting magnets and carrying ~9kA “quenched” – became resistive - and began to heat up • in < 1s the cable failed and an arc punctured the helium enclosure, releasing gas at high pressure • all the protection systems worked, but the pressure rose higher than expected Since September, impressive diagnosis of what happened…so: improve monitoring repair magnets restart summer 2009 Geoff Hall