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The Large Hadron Collider & the Compact Muon Solenoid Experiment

Delve into the world of particle physics, from fundamental particles to the hunt for the elusive Higgs boson at the LHC. Discover how theories like Supersymmetry and Grand Unification are being tested at this groundbreaking facility.

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The Large Hadron Collider & the Compact Muon Solenoid Experiment

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  1. The Large Hadron Collider & the Compact Muon Solenoid Experiment Darin Acosta

  2. The LHC in the News Also National Geographic, March 2008 The LHC

  3. Today’s Program • The Cast: Fundamental Particles • The Script (unfinished): The Standard Model • The Stage: The Large Hadron Collider • The Scenes: The CMS Experiment The LHC

  4. The Cast: Fundamental Particles Fermions Vector bosons EM quantized by Einstein in 1905 Proton recipe: Take 2u, add 1d mu,d ~ 5 MeV m = 0 EM mt = 172 GeV mg = 0 Strong Hydrogen recipe: Take 1p, add 1e (net charge = 0) m >0 mZ= 91.188 GeV Weak me = 0.511 MeV mW = 80.4 GeV 1 eV = 1.6  10–19 J Nice picture, but why 3 families and these masses? The LHC

  5.  - W e- e The Script: The Standard Model • Theoretical framework to make very precise calculations of particle interactions • e.g. Muon decay • Calculation: • e.g. Muon magnetic dipole moment •  = 1.0011659208(6) eh/2m • Agrees to 9 significant digits with theory! • Note slight discrepancy…  = 2.2 sStudent lab Time (s) g-2, E821 Expt. The LHC

  6. Missing Acts in the Standard Model • The precision of SM calculations depends on the Higgs mechanism in the theory, which generates mass for particles • But the Higgs boson not directly observed yet! • There is a vast gulf between the electroweak energy scale (102 GeV) and the Planck energy scale (1019 GeV) • Hierarchy problem • The Higgs mass must be fine-tuned to extremely high precision, as it receives radiative corrections to its mass • Supersymmetry, other new particles, or extra dimensions? • Model contains a large number of degrees of freedom • Quark and lepton masses are not predicted • There is no explanation for why quarks and leptons are related, and why charge is quantized • Grand unification? • The strong force not unified with electroweak • Grand unification? • Does not incorporate gravity • String Theory? (which requires Supersymmetry) The LHC

  7. Theoretical Higgs Mass Constraints • Self consistency of the Standard Model places upper and lower bounds on the Higgs mass • Wide mass range up to ~1 TeV allowed if new physics comes in at scale of 1 TeV • The Higgs mass measurement tells us the energy scale of new physics 1018 1015 Excluded 1012 Mass scale for new physics (GeV) Excluded 109 106 103 0 200 400 800 600 MH (GeV) The LHC

  8. Experimental Constraints Direct mW, mt measurements Indirect from electro-weak parameters Predictions, with new physics & with Standard Model only Consistent picture emerging from Standard Model: Higgs exists! Light Higgs preferred, but mH<114 GeV/c2ruled by direct searches at LEP(also null search at Tevatron, so far) The LHC

  9. Hints of Grand Unification • Coupling “constants” vary with the energy scale • Appear to unify at a very high energy scale (1016 GeV) that is also suggestively “close” to the Planck scale Fine structure constant EM 137 128 Gravity Weak 1 / coupling Strong MPlanck = 1019 GeV 102 GeV 1016 GeV The LHC

  10. Hints of Grand Unification II • Neutrinos have mass! • Neutrino oscillations observed • Atmospheric neutrinos • Solar neutrinos SNO  • Very roughly speaking: • m2 ~ 10-410-5 eV2for e , • m < few eV (beta-decay expts.) • But why are neutrinos so light? (me=511,000 eV) • One possibility is the “see-saw” mechanism: • In GUTs, unlike SM, can have right-handed neutrinos • Mass matrix will give one neutrino with mass m1~MGUT and another with mass m2~m2/MGUT • For m~100 GeV, MGUT~1016 GeV, m2~10-3 eV m2 m1 The LHC

  11. Supersymmetry • Proposes a spin conjugation operator: • Q fermion = boson • Analogous to charge conjugation, which leads to anti-matter: • C e- = e+ • Predicted by P.A.M. Dirac in 1928, observed in 1932 • Thus predicts partners to all known particles with opposite spin statistics • A symmetry between bosons and fermions: • e.g. scalar electrons, which would not obey the Pauli Exclusion principle (must have mass >0.11 TeV since not seen) • Not so good for a theory, which ought to reduce the number of free parameters (28 for the Standard Model) ! • Avoids fine-tuning of the Standard Model • Points the way to a larger theory • When Supersymmetry is required to be a local symmetry, it can incorporate gravity (Supergravity) • Supersymmetry is a prerequisite for String Theories • Allows for Grand Unification The LHC

  12. New Gauge Bosons • New Forces: • Obligated to look for signatures of new gauge bosons since the LHC crosses a new energy frontier • e.g. Z with couplings similar to Z bosonbut higher mass • Di-lepton mass spectrum is a very clear signature • Little Higgs Theories: • Solves problem of quadratic divergences in Higgs mass without SUSY by introducing more gauge bosons with opposite couplings to known ones • But no explanation of where these new forces come from  The LHC

  13. Extra Dimensions • The apparent weakness of gravity compared to the other forces may be only because we observe gravity in 3 dimensions • In reality, perhaps gravity is strong in >3 dimensions (the “bulk”), but we (and the other forces) live on a 3-D “brane” • Other dimensions are compactified and could be accessible at the TeV energy scale  LHC • Might even create infinitesimal black holes at this energy • Variety of signatures possibledepending on the model • Missing energy lostto other dimensions • “Kaluza-Klein Towers” give resonance signatures like Z(but several states) • Black holes ?! Nth D brane 3D brane Gravity strong Gravity weak The LHC

  14. The Stage: The Large Hadron Collider The LHC

  15. LHC Details • 7 TeV on 7 TeV proton-proton collider, 27km ring • 7 times higher energy than Tevatron, design luminosity: L=1034 • 1232 superconducting 8.4T dipole magnets @ T=1.9ºK The LHC

  16. Collider Evolution • The LHC will be the first machine to cross a new energy threshold in two decades • Specifically designed to explore physics at the TeV energy scale D.Green, 2005 The LHC

  17. Needle in a Haystack • The cross-sections for TeV scale physics will increase significantly for the LHC • Still 1113 orders of magnitude smaller than total interaction rate! • Need lots of collisions, and precision detectors to disentangle the collisions The LHC

  18. Machine Challenges • 7-fold increase in proton energy over Tevatron • Requires 8T super-conducting dipole magnets for ring world’s largest cryogenic structure! • 100-fold increase in proton collision rate • L =1034 cm-2s-1 • 2808 bunches crossing every 25 ns • 100-fold increase in stored machine energy • 362 MJ ! • Commissioning will be a slow and careful process The LHC

  19. Status of LHC cool down (May 21, 2008) 45 23 12 34 56 78 67 81 Cool-down rates compatible with 6 wks to reach < 2K, below helium Lamda point Tuning to give “Ready for powering” in less than 4 wks, with target at 2 wks The LHC

  20. Results from first LHC Cooldown: Sector 7-8 Magnet temperature profile along Sector 7-8 during final cool down to He II  • From RT to 80K pre-cooling with LN2. 1200 tons of LN2 (64 trucks of 20 tons). Three weeks for the first sector. • From 80K to 4.2K. Cool-down with refrigerator. Three weeks for the first sector. 4700 tons of material to be cooled. • From 4.2K to 1.9K. Cold compressors at 15 mbar. Four days for the first sector. • First sector cooled down to nominal temperature and operated with superfluid helium; teething problems with cold compressor operation have now been fixed. The LHC

  21. Recent change: Lower beam energy to 5 TeV for 2008Should have first beams in August! Note that ultimately we have 2808 colliding bunches (every 25 ns, 20 collisions take place!) The LHC

  22. Decay Modes of the Higgs Boson • BR (H bb) ~ 1 • BR (H WW 2) ~ 0.01 • BR (H ZZ 4) ~ 3x10-4 • BR (H ) ~ 10-3 Need b-quark and -lepton tagging (light Higgs)good photon energy resolution (light Higgs), andgood lepton identification (mediumheavy mass Higgs) The LHC

  23. The Compact Muon Solenoid (CMS) Experiment One of two large general purpose experiments at the LHC 4T solenoid Muon chambers Detectors are preassembled into complete structures for rapid installation in underground cavern given late occupancy Forward calorimeter Silicon Strip & Pixel Tracker PbWO4 Crystals Hadronic calorimeterBrass/Scintillator The LHC

  24. CMS Muon Systems • 3 technologies, all self-triggering • drift-tubes, cathode strip chambers, resistive plate chambers • 25000 m2 of active detection planes • 100m precision on position for DT and CSC • About 1M electronic channels • All muon chambers installed Complete DT – 5 wheels RPC – endcap and barrel CSC – 8 disks UF participation The LHC

  25. CMS Electromagnetic Crystal Calorimeter • PbWO4 crystals • 61K in the barrel, 22 x 22 mm2, avalanche photodiode readout • 15K in the endcaps, 28 x 28 mm2, vacuum phototriode readout • Ultimate precision of energy resolution: 0.5% • Requires measurements of crystal transparency using laser monitoring system due to irradiation dependence • Preshower detector for endcaps • Silicon sensors, 4300 modules, 137K channels More crystals (in volume or number) than in all previous HEP experiments combined The LHC

  26. CMS Silicon Strip Tracker • Strip Tracker: • 200 m2 coverage • More than all HEP experiments combined • 10m precision measurements • 15K modules, 11M electronic channels • For comparison, CDF inner vertex detector < 1M Complete The LHC

  27. May 2006: Underground Cavern at P5 The LHC

  28. Heavy Lifting Campaign: 15 major pieces Endcap disks and barrel wheels, January 2007 First element: Forward hadron calorimeter, November 2006 The LHC

  29. Midpoint: Central Yoke and 4T Solenoid YB0: central wheel and magnet (2000 tons)Feb. 28, 2007 The LHC

  30. The Final Heavy Element: 22 Jan. 2008 22 Jan 08 The LHC

  31. The Campaign to Cable • Installed >200km of cables and optical fibers (~6000 cables) to service the detectors placed inside the solenoid • Installed 20km of cooling pipes (~1000 pipes) • Mostly for inner tracker • >100 people/day needed at peak of installation • 50,000 man-hours over 5 month period! The LHC

  32. Thermal screens Central Wheel Services Completed Dec 07 The LHC

  33. Silicon Strip Tracker Inserted (Dec 2007) Cabling completed March 2008 The LHC

  34. Beam Pipe Installation status • Minus-end pipe and the central pipe have been installed • Beam pipe bakeout to complete mid-June • Pixel system to be inserted afterwards • Successful trial insertion of pixelmock-up, 7 May 2008 The LHC

  35. Commissioning My current job on the experiment is to coordinate the commissioning of the detectors for physics

  36. Magnet Test and Cosmic Challenge(MTCC) • Aug. – Nov. 2006 • Tested the 2.7 GJ solenoid in surface assembly building for first time • Operated a vertical slice of CMS: • Muon Detectors (6–8%): • DT, CSC, RPC • Barrel HCAL (22%) • Barrel ECAL (5%) • Tracker (~1%) • DAQ and Trigger  • Two Phases: • Phase 1: all detector elements participate, B=0, 3.8T • Phase 2: remove Tracker+ECAL, insert B field mapper, B4T The LHC

  37. Recorded ~200M cosmics Trigger rates up to 200 Hz B field mapped statistical precision of 10-4achieved, map transferred to offline software The Magnet, Detectors, Trigger, DAQ worked! ECAL HCAL Tracker HCAL 4.0T 3.8T 3.8T 3.5T 3T Run 2605 / Event 3981 / B=3.8 T / 27.08.06, 22h 2T August 2006 10 Oct to 3 Nov 2006 The LHC

  38. First Measurements: Cosmic Muon Charge Ratio CMS NOTE-2008/016DT Muon system measurement Such measurements push on getting calibration and alignment correct(more later) The LHC

  39. 2007/8: Scale of Global Operations Underground Final power, cooling, gas become available Muons Surface test, Aug-Nov.’06 The LHC

  40. Highlights of May Global Commissioning Run • Ran a significant fraction of the experiment (except for tracking for purposes of exercising procedures and data-taking using cosmic ray muons • Sustained runs lasting many hours at 240Hz trigger rate (n.b. cosmic flux underground is 1% of surface flux) with all systems read out • Logged more than 30M cosmic muon events • 3.5 TB raw data, 10 TB reconstruction data • Prompt reconstruction of runs at Tier-0 computing centre with a latency of less than 1 hour • Data copied worldwide The LHC

  41. Cosmic Muon Coincidence HCAL ECAL DT and RPC The LHC

  42. Muon Crossing CSC system Endcap was pushed against cavern wall away from central detector The LHC

  43. CRUZET: Showering Muon Energy: ~290 GeV, normally is 0.25 GeV The LHC

  44. Supermodules intentionally left susceptible to noise for diagnosis HV problem caught by prompt analysis team ECAL Barrel Occupancy • Cosmic signal is reconstructed as cluster in 5x5 region with seed crystal(s) above a threshold (~100 MeV) • Generally see full detector systems operational! Masked trigger tower EB+ EB- TOP BOTTOM The LHC

  45. Cathode Strip Chamber Occupancy station 1 station 3 station 2 • Commissioning underground only began in February • Positive endcap nearly complete, negative endcap underway • Occupancy of reconstructed positions station 4 The LHC

  46. Next Step: Physics! • Collisions should take place this Fall, many years of physics analyses to follow! The LHC

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