July CMS experiment at LHC Geoff Hall Imperial College London Geoff Hall

July 2009Geoff Hall 2 Large Hadron Collider Latest CERN accelerator started km circumference ring ~100m underground Beams 7 TeV protons or ions, eg Pb very high intensity collisions per year very high rate beams 40MHz few “interesting” events ~100 Higgs decays per year (but a small problem occurred - with a big impact)

July 2009Geoff 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

July 2009 Geoff Hall 4 Forces hold matter together Strong nuclear Electromagnetic Weak nuclear Gluons Quarks Mesons Baryons Mesons Baryons Nuclei Photon Atoms Light Chemistry Electronics Atoms Light Chemistry Electronics Atoms electrons Atoms electrons Neutron decay Beta radioactivity Neutrino interactions Solar burning Neutron decay Beta radioactivity Neutrino interactions Solar burning W & Z Bosons quarks leptons neutrinos quarks leptons neutrinos Forces are transmitted by fields, also represented by particles ( , 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) Forces are transmitted by fields, also represented by particles ( , 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)

July 2009Geoff Hall 5 Experiment by collisions Colliding beams maximises the energy available to create new particles u u d u u d Actually hadron collisions are between their constituent parts… gluons quarks and the particles they exchange (Z, W,…)

July 2009Geoff Hall 6 Experiment design Measure high p T 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 p pTpT pLpL

July 2009Geoff Hall 7 CMS Compact Muon Solenoid ECAL Tracker HCAL 4T solenoid Muon chambers Total weight: 12,500 t Overall diameter: 15 m Overall length 21.6 m Magnetic field 4 T

July 2009Geoff Hall 8 Muon System 195k DT channels 210k CSC channels 162k RPC channels Gaseous planar ionisation detectors embedded in iron magnet return yoke to measure particle trajectories

YB0 Feb 2007 July 2009Geoff Hall 9

December 2007 July 2009Geoff Hall 10

YE-1 Jan 2008 July 2009Geoff Hall 11

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 July 2009

Geoff Hall 13 The luminosity challenge cm -2 s Full LHC luminosity ~20 interactions/bx Proposed SLHC luminosity ~ interactions/bx H  ZZ   ee, M H = 300 GeV for different luminosities in CMS

July 2009Geoff Hall 14 TOB TID TIB TEC 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 m 2 of silicon, 9.3M channels 3 layers, 1m 2 pixels, 66M channels Radiation environment ~10Mrad ionising ~10 14 hadrons.cm -2

July 2009Geoff Hall 15 Microstrip Tracker automated module assembly Outer barrel 3.1M channels Inner barrel 2.4M channels Endcaps 3.9M channels

July 2009Geoff Hall 16 Electromagnetic Calorimeter Scine ParameterBarrelEndcaps Depth in X # of crystals Volume8.14m 3 2.7m 3 Xtal mass (t) Scintillating crystals of heavy material – PbWO 4 Light produced by electromagnetic showers Light signal proportional to electron or photon energy

July 2009Geoff 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 < ms Trigger requirements High efficiency for selecting processes of interest for physics analysis Large reduction of rate from unwanted high-rate processes Decision must be fast Operation should be deadtime free Flexible to adapt to experimental conditions Affordable

July 2009Geoff Hall 18 p p H jet e + e - Z Z 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

July 2009Geoff Hall 19 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 p p H µ + µ - µ + µ - Z Z Much new physics New forces New particles New symmetries

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 July 2009Geoff Hall 20 improve monitoring repair magnets restart summer 2009 Since September, impressive diagnosis of what happened…so: