Beyond the Hype: The Status of the ATLAS Experiment and the Large Hadron Collider at CERN. Kenneth Johns University of Arizona

Transcription

1 Beyond the Hype: The Status of the ATLAS Experiment and the Large Hadron Collider at CERN Kenneth Johns University of Arizona

2 A Dream LHC Schedule

3 LHC (Large Hadron Collider) 3

4 First Beam in the LHC September 10, 2008 in the ATLAS control room

5 First Malfunction at the LHC September 19, 2008 in the LHC tunnel

6 Beam Re-established in the LHC 14 months later in the ATLAS control room

7 First Collisions at 900 GeV November 23, 2009

8 First Collisions at 2.36 TeV December 8, 2009 World record

9 First Collisions at 7 TeV ¾March 30, 2010

10 LHC Dipole Magnets Bending is provided by m 8.33 T

11 LHC Dipole Magnets Busbar interconnections are used to carry the current between magnets

12 LHC Dipole Busbars Carrying up to 13 ka

13 LHC Dipole Busbars The copper busbar must take the current during the current decay after a quench

14 LHC Dipole Busbars Unfortunately conceptual mistakes plus design errors plus execution errors =

15 September 19 th Incident The electrical arc destroyed the busbars

16 September 19 th Incident The large pressure forces resulted in magnet displacements

17 September 19 th Incident As well as broken ground supports

18 September 19 th Incident And beam vacuum contamination

19 LHC Repairs

20 LHC Dipole Busbars In the LHC there are 3372 RB interconnect splices 6744 RQ interconnect splices

21 LHC Operating Energy For the LHC to operate safely at a certain energy, there is a limit to how big a splice resistance can be Cannot run at 14 TeV without replacing all splices by new clamped, shunted ones Ditto even for 10 TeV; it s just too risky One year shutdown in 2012 to install shunts, repair bad joints, and make other modifications It was concluded that running at 7 TeV was safe With what safety margin?

22 LHC Interconnect Busbars For safe running at 14 TeV, all 10k interconnect splices must be repaired

23 23 Nov 2009 First collisions 8 Dec 2009 ATLAS 2009 Running Collisions at 2.36 TeV 16 Dec 2009 End run Data Samples Total 900 GeV w Stable Beams 2.36 TeV (World record) # Events 920k 540k 34k Integrated luminosity (<30% uncertainty) 20 μb μb -1 1 μb -1

24 ATLAS 2010 Running Integrated and peak luminosity

25 LHC Running Proceeding cautiously!

26 LHC Running Current thinking

27 ATLAS Detector 1/2 x length, 2 x height of PAS

28 ATLAS Detector ATLAS is fully operational! 100 M channels in total

29 Particle Identification in ATLAS 29

30 ATLAS Calorimeters LAr EMB resolution σ ( E) / E = 10% / E 0.7% Tile hadronic resolution σ ( E) / E = 50% / E 3%

31 ATLAS Calorimeters Di-photon invariant mass distribution

32 ATLAS Calorimeters Missing transverse energy in the x direction

33 ATLAS Muon Spectrometer Resolution σ ( p )/ p =10% at 1TeV T T

34 ATLAS CSC Muon Detectors

35 ATLAS Muon Spectrometer Muon transverse momentum distribution

36 ATLAS Muon Spectrometer Muon pseudorapidity (polar angle) distribution

37 23 Nov 2009 First collisions 8 Dec 2009 ATLAS 2009 Running Collisions at 2.36 TeV 16 Dec 2009 End run Data Samples Total 900 GeV w Stable Beams 2.36 TeV (World record) # Events 920k 540k 34k Integrated luminosity (<30% uncertainty) 20 μb μb -1 1 μb -1

38 First Physics Publication from ATLAS Charged-particle multiplicities in pp interactions at s = 900 GeV measured with the ATLAS detector at the LHC What? Various distributions associated with charged particles with p T >500 MeV and η < 2.5 Why? Measurement of charged particles in inclusive pp reactions can be used to constrain phenomenological models of soft QCD These models are important since they are related to underlying event tunes for high transverse momentum physics measurements

39 Minimum Bias Events What happens when two protons collide?

40 Minimum Bias Monte Carlo predictions for the total cross section at s = 14 TeV

41 Minimum Bias at ATLAS How? - Triggered using the Minimum Bias Trigger Scintillators (MBTS)

42 How? TRT 73 layers 130 μm Rφ resolution SCT 6M channels 17 μm Rφ resolution Pixels 80M channels 10 μm Rφ resolution Minimum Bias at ATLAS

43 ATLAS Minimum Bias Analysis Data Monte Carlo comparisons for inner detector

44 ATLAS Minimum Bias Analysis Trigger and vertex reconstruction efficiencies were determined using data Track reconstruction efficiency was determined using Monte Carlo

45 ATLAS Minimum Bias Analysis Momentum scale and resolution uncertainties were checked using K s mass

46 ATLAS Minimum Bias Results Charged particle multiplicity as a function of pseudorapidity and transverse momentum

47 ATLAS Minimum Bias Results Comparison with other experiments

48 LHC Running at 7 TeV Physics program Rediscover the Standard Model and calibrate ATLAS against standard candles Minimum 7 TeV Jet production Direct photon production Low mass resonance production (J/ψ, Υ) W and Z production t-tbar production A wide range of physics can be accomplished with 250 pb -1 of data

49 LHC Running at 7 TeV At 7 TeV, the cross section to produce a mass M x of 350 GeV is reduced x5 for gg scattering 1 TeV is reduced x5 for q-qbar scattering Relative to 14 TeV

50 LHC Running at 7 TeV But the advantage compared to the Tevatron (1.96 TeV) is still significant 20x for t-tbar production 100x for W (1 TeV) production

51 ATLAS Running at 7 TeV Extending the discovery reach of Z to > 1 TeV and W to > 1.5 TeV

52 ATLAS Running at 7 TeV

53 ATLAS Running at 7 TeV

54 ATLAS Running at 7 TeV

55 Standard Model Summary Local Gauge Invariance Higgs Mechanism Massive Higgs Boson Massive Gauge Bosons

56 Where to Search for the Higgs A direct search for the Higgs was carried out by the four LEP experiments from CMS energy of GeV The production and decay was primarily by e * Z + e H Z b b q q

57 Where to Search for the Higgs The combined result was > % CL m H Of course there were interesting events

58 Where to Search for the Higgs Indirect constraints on the Higgs mass can be found by considering electroweak radiative corrections like

59 Where to Search for the Higgs D0 and CDF presently rule out a Higgs boson with mass 163 < m H < 166 GeV

60 Higgs Production at the LHC

61 VBF (Vector Boson Fusion) Higgs production with a distinctive topology Forward jets No central jet activity because no color flow Jet Jet

62 Higgs Decay Modes The Standard Model rules say the Higgs decays into the heaviest pair of particles that is kinematically allowed

63 H WW * eνμν Counting mode Effective for 2M W <m H <2M Z Two methods: no jets (GGF) and 2 jets (VBF) Only consider eνμν There is no mass peak because of the two neutrinos from heavy W s Instead use transverse mass m T and other variables m T = E 2 T v p 2 T

64 H WW * eνμν No jets Main backgrounds are WW * and t-tbar Leptons are used to infer the W spin direction

65 H WW * eνμν 2 jets Exploit the VBF topology using forward jet tagging and central jet veto requirements Main background: t-tbar

66 Higgs Hunting at 7 TeV Likely only exclusion with 1 fb -1 at 7 TeV Preliminary from a talk by P. Jenni

67 Higgs Hunting at 14 TeV Discovery and exclusion

68 What s It Like to Do Physics on ATLAS?

69 How Can One Stand Out on ATLAS?

70 What Do We Expect to Discover at the LHC? 70

71 Conclusions The LHC physics program is underway at 7 TeV and we expect 1 fb -1 by end 2011 The ATLAS experiment is performing extremely well and will be re-discovering the Standard Model in the coming months A Higgs boson discovery is unlikely before 14 TeV running though one expects exclusion for 130 < m H < 180 by end 2011 However stay tuned for the unexpected!