CMS experiment at LHC

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

2. Latest CERN accelerator started 2008 very high intensity 1015 collisions per year very high rate beams cross @ 40MHz few “interesting” events ~100 Higgs decays per year Beams 7 TeV protons => 14 TeV energy also ions (eg Pb) Large Hadron Collider (but a small problem occurred - with a big impact) Geoff Hall

3. Geoff Hall

4. Colliding beams maximises the energy available to create new particles (compared to shooting at a target) d d u u u u Experiment by collisions • Hadron collisions are actually between their constituent parts… •  ~ 1/p ≈ 1/E • gluons • quarks: both valence and sea (≈ real and virtual) • and the particles they exchange (Z, W,…) Geoff Hall

5. What do we actually do? • We design, build and operate the experiments • LHC was & is enormously challenging so it’s taken a long time… • some illustrations of how the experiments are built • We analyse the data • in the LHC energy range, theory eventually fails • so something new must be found • for the first time in many years, only experiment can tell us what • Now the construction has finished most effort will go into looking at data • PhD students and young researchers will be doing most of the work • Snapshot of some typical work in progress Geoff Hall

6. 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

7. high pT lepton and quarks are signatures of possible new physics Large solenoidal (4T) magnet iron yoke - returns B field, absorbs particles Muon detection –penetration detectors in yoke measure muons Electromagnetic calorimeter – absorb E good energy resolution for e & g + Hadronic calorimeter for pions,… Tracking system – bend in B field reconstruct trajectories of most charged particles momentum measurements from bending observe directly many decays complement muon & ECAL measurements Design philosophy 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. YE+3 Nov 2006 Geoff Hall

10. YB0 Feb 2007 Geoff Hall

11. December 2007 Geoff Hall

12. YE-1 Jan 2008 Geoff Hall

13. CMS August 2008 Geoff Hall

14. 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 T. Virdee CMS Week Dec08

15. 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

16. Look at interactions for unexpected behaviour like large energy at large angle to beam (how Rutherford discovered the atomic nucleus) evidence of short-lived particles visible evidence Indirect, by peaks in mass spectra Discoveries… Old picture of a charmed particle production and decay in a bubble chamber Geoff Hall

17. Mass peak one means of discovery => small s(pT) eg H => ZZ or ZZ* => 4l± typical pT(µ) ~ 5-50GeV/c Background suppression measure lepton charges good geometrical acceptance - 4 leptons background channel t => b => l require m(l+l-) = mZ GZ ~ 2.5GeV precise vertex measurement identify b decays, or reduce fraction in data Physics requirements (I) Geoff Hall

18. p resolution large B and L high precision space points detector with small intrinsic smeas well separated particles good time resolution low occupancy => many channels good pattern recognition minimise multiple scattering minimal bremsstrahlung, photon conversions material in tracker most precise points close to beam Physics requirements (II) Geoff Hall

19. µ + µ - Z p H p Z µ + µ - What we hope to find at LHC • Higgs discovery and measurement eg. simplest SM variant • several detectable decay channels • but, ultimately, modest numbers of events are expected at LHC H-> 4µ 30fb-1 • plus much possible new physics • eg SUSY, extra dimensions,… Geoff Hall

20. The Higgs Model • The Higgs is different ! • Higgs is the only scalar particle in the SM • All the matter particles are s=½ fermions • All the force carriers are s=1 bosons • Postulated to give rise to mass throughspontaneous electroweak symmetry breaking • Also to neutrinos if Dirac particles • It would be the first fundamental scalar ever discovered • Frankly, almost nothing is known about the Higgs • Nothing is known for the Yukawa-coupling • Nothing is known for the Higgs self-coupling • Single Higgs? Two Higgs field doublets? Additional singlet? • SUSY? MSSM? NMSSM? Extra-dimensions? • If the Higgs is discovered, mapping the potential is crucial V()=µ2++(+)2 = (v+H)/√2 mH2=2v2=-2µ2 Geoff Hall

21. Production of the Higgs The production cross-section is calculable. It depends on the Higgs mass, and the production mechanisms. The Higgs mass is not known and there are few theoretical constraints on it. NLO Geoff Hall

22. H -> ZZ(*) ->4l - golden mode • Background: tt, ZZ, llbb (“Zbb”) • Selections : • lepton isolation in tracker and calo • lepton impact parameter, mm, ee vertex • mass windows MZ(*), MH H->ZZ->ee mm Geoff Hall

23. 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

24. 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

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

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

27. 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

28. 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 • Tracker not part of L1 trigger • Data volume enormous • Technically not possible for LHC Geoff Hall

29. LHC Trigger Levels Geoff Hall

30. Snapshot of work in progress Geoff Hall

31. Supersymmetry • A new symmetry of nature? • each fermion has a boson partner (& vice versa) • not yet observed! - therefore likely to be heavy • SUSY solves some problems with Higgs mass (in GUTs) • there is a lightest SUSY state into which others decay • it does not interact with ordinary matter • could therefore be the explanation for dark matter • it would not be directly observed in CMS • the signature would be large missing energy • – this relies on good hadron calorimetry • but it would wise not to depend on a single technique • If SUSY exists, it may show up very early at LHC Geoff Hall

32. Early SUSY searches with the all-hadronic n-jet channel. Tom Whyntie On behalf of the CMS IC SUSY Group (+ friends)

33. Overview • Introduction • How can we discover SUSY with CMS? • The dijet search channel • A calo-MET independent SUSY search? • The n-jet search channel • How do we go from n to 2 jets? • A suggested strategy for n-jets • S/B ~7 for LM1 SUSY? • Conclusions and plans

34. Introduction: SUSY at CMS • Goal: discover SUSY at CMS • Early data, L < 1 fb-1; • Minimal understanding of the detector. • SUSY parameter space considered: • CMS benchmarks: LM1-9 (TDR) • Low mass MSuGra SUSY • e.g. LM1: m0 = 60GeV, m1/2 = 250, A0, tan b = 10, sign(m) = +

35. q q q LSP + similar q q q LSP The Dijet Search Channel Analysis note recently approved: CMS AN-2008/071 (Flaecher, Jones, Rommerskirchen, Stoye) • Two high pt jets • Large missing energy Missing energy relies on calorimeter – is there a way of just using the jets? Is it possible to formulate a discriminating observable based on jet kinematics? • Backgrounds • QCD dijet events • Z nn + jets • tt + jet(s), W + jet(s), etc.

36. Results for the Dijet System