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Overview of the CMS experiment at LHC

Overview of the CMS experiment at LHC. Guido Tonelli University of Pisa/INFN/CERN Why and how CMS was designed Status of the experiment Preparation for physics. CMS and LHC@ CERN.

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Overview of the CMS experiment at LHC

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  1. Overview of the CMS experiment at LHC • Guido Tonelli • University of Pisa/INFN/CERN • Why and how CMS was designed • Status of the experiment • Preparation for physics

  2. CMS and LHC@ CERN LHC: 9300 Superconducting Magnets; 1232 Dipoles (15m), 448 Main Quads, 6618 Correctors. Operating temperature: 1.9o K; 26.7 km tunnel LHC SPS CERN Site (Meyrin)

  3. Why everything is so complex? • We are trying to solve some of the main puzzles of nature • What is the origin of mass • What could be the dark matter that keeps together the clusters of galaxies • Why the main interactions are so different in strength • Why gravity is not included so far in our picture • How many are really the dimensions of our world • The answer to some of these questions is probably hidden in the so far unexplored TeV region

  4. What is wrong with the Standard Model? The SM is still among the most successfull theories tested so far(accuracy <10-4). LEP, CDF-D0: we really understand physics up to 100GeV. Why we are not happy with it ?

  5. Why the masses of elementary constituents (matter and fields) are so different ? The bare SM could be consistent with massless particles but matter particles range from almost 0 to about 170GeV while force particles range from 0 to about 90GeV. How can it be that a massless photon can carry the same electroweak interaction of a 80-90 GeV W or Z? The simplest solution (Higgs, Kibble, Brout, Englert 1960’s) All particles are massless !! A new scalar field pervades the universe. Particles interacting with this field acquire mass: the stronger the interaction the larger the mass.

  6. Mathematical (in)-consistency of the SM At energies larger than 1TeV the probability of scattering of one W boson off another one becomes >1 ?! The SM gives nonsense! An elegant solution would be to introduce a Higgs exchange that would cancel the bad high energy behaviour.

  7. How heavy is the Higgs: the TeV scale. LEP+ CDF-D0 data indicate Higgs could quite light (but logarithmic dependences are tricky). To be sure to be able to catch it (if it does exist) a safe attitude is to explore the entire region between 100 and 1000GeV.

  8. Hierarchy problem and supersymmetry But a Higgs boson “alone” would bring with him new problems.There would be large quantum mechanics corrections to its mass thus leading to large instabilities for  > > 1/ √GF. The “standard trick” to remove instabilities is to introduce new massive particles: If each SM particle has a partner with spin differing by 1/2 unit, infinities “magically” disappear. Fantastic! but this implies the existence of a completely new form of matter: “super-matter” or SUSY particles.

  9. Super-symmetry Each SM particle could have a super-symmetric (SUSY) partner with spin 1/2 difference. In super-matter the carriers of the interactions are fermions and the particles are bosons. Elegant and nice symmetry of nature (similar to matter-antimatter where the spin plays the role of the charge). Since none of them have been discovered yet they must be heavy and SUSY must be a broken symmetry! But if SUSY is supposed to solve the issue of naturalness they must populate the TeV mass region: |M2spart - M2part| < O (1 TeV2)

  10. Susy and cosmology The production cross sections could be high in the √s=14TeV region In one of the simplest SUSY model we have gluinos, squarks, sleptons, 4 neutralinos, 2 charginos and a whole family of Higgs bosons h0, H0, A0, H Sparticles would be produced in pairs to conserve R-parity. The Lightest Super-symmetric Particle would be a massive, stable and weakly interacting neutralino: ideal candidate to explain dark matter. A gas of heavy neutralinos could hold together clusters of galaxies (including ours). Major breakthrough in our understanding of the universe.

  11. Gaseous Matter Dark Matter 25-30% of our universe is made of “unknown matter” Collision of two galaxies “Bullet Cluster” Clowe et al. Direct evidence for collisionless Dark Matter Chandra, Magellan, HST, Gravitational Lensing

  12. 96% of our universe is still a “dark thing” WMAP Convergence Model

  13. Other exciting possibilities for naturalness If the Higgs boson is discovered and Super-symmetry does not manifest itself in the TeV region again we have to find other mechanisms to fight against the radiative corrections to the Higgs mass. • MH2 MH2 (o) + c 2 • is the scale of the theory. If L~MGUT ~ 1015 GeV an incredible, un-natural fine tuning would be needed to allow for a “light” Higgs Two major sets of possibilities to save naturalness: Protected by other new forces/particles? (Z’, W’, technicolor). Protected by (compactified) extra dimensions? …. New signatures of new physics.

  14. … and if no Higgs boson will be found Several dynamical mechanisms have been proposed for the symmetry breaking. QCD inspired WL and ZL could be sort of ‘pions’ of a new interaction rescale f to 1/√GF leading to strong interaction in TeV range VL- VL scattering analog of  -  scattering Technicolour The Higgs-less SM is saved by a techni- Whole family of new states predicted Strong breaking of E-W symmetry No Higgs boson but a triplet of massive bound states - vector bosons V0, V (similar to techni-) New particles and new signatures.

  15. SUSY, Large Extra Dimensions and GUT • The coupling constants "run" in quantum field theories due to vacuum fluctuations. For example, in EM the e charge is shielded by virtual  fluctuations into e+e- pairs on a distance scale set by, le ~ 1/me. Thus a increases as M decreases, a(0) = 1/137, a(MZ) = 1/128. • If SUSY is really a symmetry of nature and the mass of the super-partners is ~ 1 TeV, then the GUT unification is good - at 1016 GeV. A local SUSY GUT could incorporates naturally gravity. • But, if gravity does change at some mass scale 1/R, then the Planck mass could be a “mirage”.The law of gravity depends on the number of space dimensions. Space-time may have more than 4 dimensions: extra-dimensions that are not visible because they are curled-up. Standard Model Supersymmetry (MSSM) Large Extra Dimensions

  16. Higgs Production in pp Collisions14TeV q Z0 q W W H q p p q Z0 MH ~ 1000 GeV EW ≥ 500 GeV Eq ≥ 1000 GeV (1 TeV) Ep ≥ 6000 GeV (6 TeV)  Proton Proton Collider with Ep ≥ 5-7 TeV

  17. SM Higgs production at LHC NLO 10 fb-1 (104 pb-1) O(105) events for MH<200 GeV BR(HZZ)*BR(ZZ4l) ~ 10-4, 10-5 Few tens of H4l events for 30 fb-1

  18. SM Higgs Branching ratios • Low mass (MH<2MZ): • bb dominant, but huge QCD background  only ttH accessible • Also accessible: H, HZZ*4l, HWW*ll, H • MH>2MZ: • HZZ4l, WW modes

  19. The Higgs signal in CMS Low MH < 150 GeV Medium 130<MH<500 GeV High MH > ~500 GeV

  20. Signal and background1034 Cross sections for various physics processes vary over many orders of magnitude Higgs (600 GeV/c2): 1pb @1034 10–2 Hz Higgs (100 GeV/c2): 10pb @10340.1 Hz t t production: 10 Hz W l n: 102 Hz Inelastic: 109 Hz Selection needed: 1:1010–11 Before branching fractions... CDF and D0 successfully found the top quark facing similar rejection factors Fast detectors: 25ns bunch crossing High granularity: 20 overlapping complex events High radiation resistance: 10 years of operation

  21. Basic principles • Need “general-purpose” experiments covering as much of the solid angle as possible (“4p”) since we don’t know how New Physics will manifest itself •  detectors must be able to detect as many particles and signatures as possible: e, , , , , jets, b-quarks, …. • Momentum / charge of tracks and secondary vertices (e.g. from b-quark decays) are measured in central tracker (Silicon layers). • Energy and positions of electrons and photons measured in electromagnetic calorimeters. • Energy and position of hadrons and jets measured mainly in hadronic calorimeters. • Muons identified and momentum measured in external muon spectrometer (+central tracker). • Neutrinos “detected and measured” through measurement of missing transverse energy (ETmiss) in calorimeters.

  22. Particles through a CMS slice

  23. Total weight : 12,500 t Overall diameter : 15 m Overall length : 21.6 m Magnetic field : 4 Tesla The Compact Muon Solenoid (CMS) CALORIMETERS SUPERCONDUCTING ECAL Scintillating PbWO4 HCAL Plastic scintillator COIL Crystals copper sandwich IRON YOKE TRACKERs MUON ENDCAPS MUON BARREL Silicon Microstrips Pixels Resistive Plate Cathode Strip Chambers (CSC) Drift Tube Resistive Plate Chambers (RPC) Chambers (RPC) Chambers (DT)

  24. Belgium Bulgaria Austria Finland USA CERN France Germany Greece Russia Hungary Italy Uzbekistan Ukraine Georgia Belarus Poland UK Armenia Portugal Turkey Brazil Serbia China, PR Spain Pakistan China (Taiwan) Switzerland Lithuania Colombia Mexico Iran Korea New-Zealand Croatia Cyprus Ireland India Estonia The CMS Collaboration 1772 physicists. 134 universities and research centers. 38 countries and regions of all continents. Iran participation in CMS 7 physicists from IPM. Important contribution to the construction of HF. Strong commitment for physics. Interest in participating in the RE up-scope project.

  25. UXC/USC5: CMS caverns • Delivered to the experiment on • February 1-st 2005. • The main components of the whole • experiment assembled in the surface hall • and lowered 100m underground.

  26. HF Lowering: the first one (the lightest baby)

  27. YE1 Lowering: the most difficult one.

  28. YB0 lowering: the heaviest one (1920t) Touchdown after 11 hours. Two days to align it better than a fraction of a mm in all coordinates.

  29. An incredible series of complex activities

  30. Three years later: no much room left over

  31. 25/08/2008: 16 years after the Letter of Intent, CMS is completed

  32. 2 shots of clockwise beam: 2x109 protons per beam 10/09/2008: first beam in LHC

  33. Good use also of the beam-on-collimators events HCAL energy EB vs HB Energy correlation ECAL energy

  34. An incident occurred during a powering test of one LHC sector for commissioning beam operation to 5 TeV. Massive helium loss in one arc of the tunnel; cryogenics and vacuum lost and important mechanical damage to tens of dipoles and quadrupoles The cause of the incident was determined to be a faulty electrical connection (“bus bar”) between a dipole and a quadrupole. 19/09/2008: our black friday Superfluid helium in quick expansion can easily displace a string of many 20t magnets… … and these are the consequences: ~1 year of work to replace/repair/re-check 53 magnets and to put in place any sort of test and all possible preventive actions to avoid the same incident could happen again.

  35. CRAFT: 300 millions of cosmics to study the most subtle features of our detector

  36. CRAFT Results: tracker and calorimetry. Alignment in Inner Tracker Energy deposited by muons The whole tracking system aligned with an accuracy planned to be achieved only after the first 50pb-1 of data. Detailed cross-check of timing and calibration issues in our calorimetry response. Excellent starting points for many early physics goals. rms=24um Si Tracker TOB ECAL total Points- data radiative ionisation Barrel Pixels rms=47um HCAL

  37. CRAFT results: Muon DT chambers Muon Chambers Point Resolution MB4 240 chambers aligned; magnetic field simulation corrected; TDR resolution (250mm) achieved before data taking. Another excellent starting point for many early physics goals. s~250um MB3 MB2 MB1

  38. CMS has been opened again to repair defective components and install the last sub-detector 38 T. Virdee JOG Apr09

  39. Installation of the pre-shower: the very last component of CMS Transporting ES towards EE ES attached to support cone Installation and commissioning finished Friday April 17 99.9% of the 136K channels are OK The two separate ES Dees ES cabled 39

  40. Latest news from LHC • Repair work is going on as scheduled • Good understanding of the incident and better diagnostic tools put in place to prevent any kind of additional problem. • 39 dipoles and 14 quadrupoles of the Short Straight Sections have been replaced/repaired. All magnets back in the tunnel since Friday April 17-th. 2-3 weeks of delay accumulated wrt the schedule foreseen in December • Action to pass from 2shifts/dayx5 days/week to 3 shift/day 7 days/week to recover the delay • Expect beam in September !

  41. Possible scheme for LHC running 2009/2010 Run period ~ 1year October 2009-September 2010 Expectations for ~200pb-1 integrated luminosity at 10 TeV.

  42. First pb-1 • Careful cross check of the trigger performance • Improved calibration and quality control (efficiencies) • Reconstruction of the basic physics objects: muons, electrons, photons, jets… • Re-discovery of p0, Ko, J/psi, Upsilon …

  43. 10pb-1 re-discovering SM In 10pb-1105W–> l,n In 10pb-12x104Z–> l+,l-

  44. 100pb-1 Z’--->ee, µµ Discovery potential for new massive bosons through dilepton invariant mass distributions and detailed understanding of the Drell-Yan continuum. Z’

  45. Large missing momentum from escaping invisible particles Classic signature of minimal supersymmetric models with a dark matter candidate Energetic “jets” from supersymmetric particle decays. 100pb-1 Supersymmetry SUSY

  46. First few hundred pb-1 starts the Higgs hunting Signals and backgrounds are scaled from 14 TeV Plots are indicative of CMS reach Higgs • With 200 pb-1, reach current Tevatron sensitivity for Higgs

  47. Our Schedule Maintenance & Operation Software, Computing & Physics Release CMSSW3_0 (limited validation, step towards 3_1) Install ES1 Install ES2 Deadline for Input for 3_1 CRAFT, Trigger Review (menu), Phys… Release CMSSW3_1 (LHC Startup) Tracker Cooling Plant Revised Full validation of 3_1 (incl. production and physics) Close CMS Start Fullsim production 3_1 Magnet Tests Use 3_1 widely CMS gets familiar with 3_1 CRAFT CRAFT Contingency & pre-beam maintenance Start Fastsim production 3_1 CMS READY for Beam CMS READY for Beam

  48. Conclusion Within a few months we shall start the systematic exploration of the TeV region with an excellent scientific instrument. My hope is that there will be many un-expected results and our current understanding of nature will change in depth thereafter. Excellent time for brilliant students and post-docs to join the effort and contribute to it with their enthusiasm and (hopefully) new ideas.

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