CMS experiment at LHC Geoff Hall Imperial College

CMS experiment at LHC Geoff Hall Imperial College London July 2009 Geoff Hall 1

Large Hadron Collider n Latest CERN accelerator n 26 km circumference ring n n n started 2008 (but a small problem occurred - with a big impact) ~100 m underground Beams n 7 Te. V protons n or ions, eg Pb very high intensity 15 collisions per year n 10 very high rate n beams cross @ 40 MHz few “interesting” events n ~100 Higgs decays per year July 2009 2 Geoff Hall

Particle physics in two slides n Matter originated in the Big Bang n LHC energies correspond to tiny fraction of a second in the life of the universe n n Leptons n n n Make up hadronic matter, eg n proton (uud) n neutron (udd) n mesons (q + anti-quark) 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 3 Geoff Hall

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) July 2009 4 Weak nuclear W & Z Bosons quarks leptons neutrinos Neutron decay Beta radioactivity Neutrino interactions Solar burning Geoff Hall

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

Experiment design n Measure high p. T lepton and quarks to identify possible new physics n Large solenoidal (4 T) magnet n p. T iron yoke - returns B field, absorbs particles p. L Then, going outwards from beam n Tracking system – bend in B field n n n reconstruct trajectories of most charged particles momentum measurements from bending Calorimeters – absorb energy n n p good energy resolution Muon detection – penetration n detectors in yoke measure muon momentum from bending July 2009 6 Geoff Hall

CMS Compact Muon Solenoid HCAL Muon chambers Tracker ECAL 4 T solenoid July 2009 Total weight: 12, 500 t Overall diameter: 15 m Overall length 21. 6 m Magnetic field 4 T 7 Geoff Hall

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

YB 0 Feb 2007 July 2009 9 Geoff Hall

December 2007 July 2009 10 Geoff Hall

YE-1 Jan 2008 July 2009 11 Geoff Hall

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 12 Geoff Hall

The luminosity challenge n H ZZ ee, MH= 300 Ge. V for different luminosities in CMS 1032 cm-2 s-1 1033 1034 1035 Full LHC luminosity ~20 interactions/bx July 2009 Proposed SLHC luminosity ~300 -400 interactions/bx 13 Geoff Hall

Tracker system n Two main sub-systems: Silicon Strip Tracker and Pixels n n n 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. 3 M channels 3 layers, 1 m 2 pixels, 66 M channels TOB TIB Radiation environment ~10 Mrad ionising ~1014 hadrons. cm-2 TEC TID PD July 2009 14 Geoff Hall

Microstrip Tracker Outer barrel n automated module assembly 3. 1 M channels Endcaps 3. 9 M channels Inner barrel 2. 4 M channels July 2009 15 Geoff Hall

Electromagnetic Calorimeter Scine Scintillating crystals of heavy material – Pb. WO 4 Light produced by electromagnetic showers Light signal proportional to electron or photon energy Parameter Barrel Endcaps Depth in X 0 25. 8 24. 7 # of crystals 61200 14648 Volume 8. 14 m 3 2. 7 m 3 Xtal mass (t) 67. 4 22. 0 July 2009 16 Geoff Hall

Trigger and DAQ systems n n 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 n 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 n Trigger requirements n n n n 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 2009 17 Geoff Hall

Triggering n Primary physics signatures in the detector are combinations of: n n n 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 n n up to 100 k. Hz with no dead-time Higher level selection in software jet p H Z p Z e+ e- July 2009 18 Geoff Hall

What we hope to find n µ+ p Z H Higgs discovery (simplified!) n µ- n n Will be produced with many other particles ~20 events per beam crossing hundreds of secondary particles/25 ns p e- Z + µ q - µ n Much new physics n n n New forces New particles New symmetries - c 1 ~ q ~ g p ~ q q ne ~ c 20 q p + ~0 c 1 July 2009 19 Geoff Hall

Machine incident n A superconducting cable connecting magnets and carrying ~9 k. A “quenched” – became resistive - and began to heat up n n in < 1 s the cable failed 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 July 2009 20 Geoff Hall