1. The ATLAS experiment The ATLAS Detector Physics at the LHC Luminosity determination Hasko Stenzel

2. ATLAS H.Stenzel, January 2007 2 pp  s = 14 TeV L design = 10 34 cm -2 s -1 (after 2009) L initial  few x 10 33 cm -2 s -1 (until 2009) Heavy ions (e.g. Pb-Pb at  s ~ 1000 TeV) TOTEM ALICE : ion-ion, p-ion ALICE : ion-ion, p-ion ATLAS and CMS : general purpose ATLAS and CMS : general purpose 27 km LEP ring 1232 superconducting dipoles B=8.3 T TOTEM (integrated with CMS): pp, cross-section, diffractive physics TOTEM (integrated with CMS): pp, cross-section, diffractive physics LHCb : pp, B-physics, CP-violation LHCb : pp, B-physics, CP-violation The LHC

3. ATLAS H.Stenzel, January 2007 3 An Aerial View of Point-1

4. ATLAS H.Stenzel, January 2007 4 The ATLAS Detector Calorimetry: Tracking: Length : ~45 m Radius : ~12 m Weight : ~ 7000 tons Electronic channels : ~ 10 8 ~ 3000 km of cables Tracking (|  |<2.5, B=2T) : -- Si pixels and strips -- Transition Radiation Detector (e/  separation) Calorimetry (|  |<5) : -- EM : Pb-LAr with Accordion shape -- HAD: Fe/scintillator (central), Cu/W-LAr (fwd) Muon Spectrometer (|  |<2.7) : air-core toroids with muon chambers

5. ATLAS H.Stenzel, January 2007 5 Central Solenoid 2T field with a stored energy of 38 MJ Integrated design within the barrel LAr cryostat Magnet System

6. ATLAS H.Stenzel, January 2007 6 Magnet System Toroid Barrel Toroid parameters 25.3 m length 20.1 m outer diameter 8 coils 1.08 GJ stored energy 370 tons cold mass 830 tons weight 4 T on superconductor 56 km Al/NbTi/Cu conductor 20.5 kA nominal current 4.7 K working point End-Cap Toroid parameters 5.0 m axial length 10.7 m outer diameter 2x8 coils 2x0.25 GJ stored energy 2x160 tons cold mass 2x240 tons weight 4 T on superconductor 2x13 km Al/NbTi/Cu conductor 20.5 kA nominal current 4.7 K working point

7. ATLAS H.Stenzel, January 2007 7 Inner Detector The Inner Detector (ID) is organized Into four sub-systems: Pixels (0.8 10 8 channels) Silicon Tracker (SCT) (6 10 6 channels) Transition Radiation Tracker (TRT) (4 10 5 channels) Common ID items

8. ATLAS H.Stenzel, January 2007 8 PIXELS The system consists of three barrels at average radii of ~ 5 cm, 9 cm, and 12 cm (1456 modules) and three disks on each side, between radii of 9 and 15 cm (288 modules).

9. ATLAS H.Stenzel, January 2007 9 SILICON TRACKER (SCT) The SCT system is designed to provide eight precision measurements per track It is constructed using 4088 silicon micro-strip modules arranged as 4 barrels in the central region and 2 x 9 annular wheels in the forward region The SCT covers a pseudo-rapidity-range < 2.5

10. ATLAS H.Stenzel, January 2007 10 TRANSITION RADIATION TRACKER (TRT) Straw tracker 50,000 in barrel 320,000 in endcaps Gas Mixture Xe,CO 2,O 2 (70%,27%,3%) Barrel radial coverage 56cm -107 cm Endcap radial coverage 64cm – 103 cm Drift time measurements & Transition Radiation detection Average of 36 points on a track

11. ATLAS H.Stenzel, January 2007 11 SCT TRT Insertion of the SCT into barrel TRT Three completed Pixel disks (one end-cap) with 6.6 M channels

12. ATLAS H.Stenzel, January 2007 12 LAr and Tile Calorimeters Tile barrelTile extended barrel LAr forward calorimeter (FCAL) LAr hadronic end-cap (HEC) LAr EM end-cap (EMEC) LAr EM barrel

13. ATLAS H.Stenzel, January 2007 13 Barrel Endcap Forward

14. ATLAS H.Stenzel, January 2007 14 Muon Spectrometer Instrumentation Precision chambers: - MDTs in the barrel and end-caps - CSCs at large rapidity for the innermost end-cap stations Trigger chambers: - RPCs in the barrel - TGCs in the end-caps The Muon Spectrometer is instrumented with precision chambers and fast trigger chambers A crucial component to reach the required accuracy is the sophisticated alignment measurement and monitoring system

15. ATLAS H.Stenzel, January 2007 15 ‘Big Wheel’ end-cap muon MDT sector assembled in Hall 180 ‘Big Wheel’ end-cap muon TGC sector assembled in Hall 180 End-cap muon chamber sector preparations Altogether 72 TGC and 32 MDT ‘Big-Wheel’ sectors have to be assembled

16. ATLAS H.Stenzel, January 2007 16 The large-scale system test facility for alignment, mechanical, and many other system aspects, with sample series chamber station in the SPS H8 beam Shown in this picture is the end-cap set-up, it is preceded in the beam line by a barrel sector

17. ATLAS H.Stenzel, January 2007 17 ATLAS online follow online what happens at http://atlas.web.cern.ch/Atlas

18. ATLAS H.Stenzel, January 2007 18 H  ZZ  4 “Gold-plated” channel for Higgs discovery at LHC Simulation of a H   ee event in ATLAS Signal expected in ATLAS after 1 year of LHC operation Physics example

19. ATLAS H.Stenzel, January 2007 19 Physics processes at the LHC PDFs partonic cross section

20. ATLAS H.Stenzel, January 2007 20 Physics with ATLAS Search for the Standard Model Higgs boson over ~ 115 < m H < 1000 GeV Search for physics beyond the SM (Supersymmetry, q/ compositeness, leptoquarks, W’/Z’, heavy q/, Extra-dimensions, mini-black holes,….) in the TeV-range Precision measurements : -- W mass -- top mass, couplings and decay properties -- Higgs mass, couplings, spin (if Higgs found) -- B-physics (complementing LHCb): CP violation, rare decays, B 0 oscillations -- QCD jet cross-section and  s -- W/Z cross sections (+jets) Extensions of the physics program -- heavy ion running, phase transition to q/g plasma -- diffraction & forward physics

21. ATLAS H.Stenzel, January 2007 21 Physics of the first years Expected event rates at production in ATLAS at L = 10 33 cm -2 s -1 Process Events/s Events for 10 fb -1 Total statistics collected at previous machines by ‘07 W  e 15 10 8 10 4 LEP / 10 7 Tevatron Z  ee 1.5 10 7 10 7 LEP 1 10 7 10 4 Tevatron 10 6 10 12 – 10 13 10 9 Belle/BaBar ? H m=130 GeV 0.02 10 5 ? m= 1 TeV 0.001 10 4 --- Black holes 0.0001 10 3 --- m > 3 TeV (M D =3 TeV, n=4)

22. ATLAS H.Stenzel, January 2007 22 Higgs Physics Search for the Higgs Boson, study of the electroweak SU(2)xU(1) symmetry breaking -- discovery of the Higgs boson & mass determination -- measurement of the Higgs couplings to verify the mass generation mechanism -- determination of the Higgs parameters (width, spin, parity, Charge (MSSM),...) coupling to fermions ~ m f /v coupling to Bosons ~ m v 2 /v Need to measure both H-> ff and H-> VV channels!

23. ATLAS H.Stenzel, January 2007 23 Higgs production

24. ATLAS H.Stenzel, January 2007 24 SM Higgs cross section

25. ATLAS H.Stenzel, January 2007 25 Higgs Decays

26. ATLAS H.Stenzel, January 2007 26 Higgs-> γγ

27. ATLAS H.Stenzel, January 2007 27 Higgs-> ZZ -> 4l

28. ATLAS H.Stenzel, January 2007 28 Higgs-> WW -> 2l2ν

29. ATLAS H.Stenzel, January 2007 29 VBF H->ττ

30. ATLAS H.Stenzel, January 2007 30 Higgs discovery potential

31. ATLAS H.Stenzel, January 2007 31 Higgs couplings Relative precision on the measurement of  H  BR for various channels, as function of m H, at  L dt = 300 fb –1. The dominant uncertainty is from Luminosity: 10% (open symbols), 5% (solid symbols). (ATLAS-TDR-15, May 1999) Large uncertainty contribution from Luminosity!

32. ATLAS H.Stenzel, January 2007 32 Methods of Luminosity measurements Absolute luminosity ●from the parameters of the LHC machine ●rate of pp  Z 0 / W ±  l + l - / lν ●rate of pp  γγ  μ + μ - ●Optical theorem: forward elastic+ total inelastic rate, extrapolation t  0 (but limited |η| coverage in ATLAS) ●cross-check with ZDC in heavy ion runs ●from elastic scattering in the Coulomb region ●combinations of all above Relative luminosity ●LUCID Cerenkov monitor, large dynamic range, excellent linearity ATLAS aims for 2-3% accuracy in L

33. ATLAS H.Stenzel, January 2007 33 Luminosity from elastic scattering

34. ATLAS H.Stenzel, January 2007 34 Roman Pots for ATLAS RP IP 240m RP PMT baseplate optical connectors scintillating fibre detectors glued on ceramic supports 10 U/V planes overlap&trigger Roman Pot MAPMTs FE electronics & shield Roman Pot Unit

35. ATLAS H.Stenzel, January 2007 35 Roman Pot location

36. ATLAS H.Stenzel, January 2007 36 The scintillating fibre tracker

37. ATLAS H.Stenzel, January 2007 37 detector prototypes for testbeam 2006 10 x 2 x 16 resolution studies 2 x 2 x 64 construction studies 2 x 2 x 30 overlaps Fabrication of prototypes at CERN with support from Lisbon (LIP) for  fibre machining, aluminum coating, QC  testbeam mechanics and from Giessen for  gluing of fibres  optical connectors  Plan to produce a full-scale prototype in 2007 (1/8 of the full set-up)

38. ATLAS H.Stenzel, January 2007 38 Simulation of the LHC set-up elastic generator PYTHIA6.4 with coulomb- and ρ-term SD+DD non-elastic background, no DPE beam properties at IP1 size of the beam spot σ x,y beam divergence σ ’ x,y momentum dispersion beam transport MadX tracking IP1  RP high β * optics V6.5 including apertures ALFA simulation track reconstruction t-spectrum luminosity determination later: GEANT4 simulation

39. ATLAS H.Stenzel, January 2007 39 Simulation of elastic scattering t reconstruction: hit pattern for 10 M elastic events simulated with PYTHIA + MADX for the beam transport  special optics  parallel-to-point focusing  high β*

40. ATLAS H.Stenzel, January 2007 40 acceptance Global acceptance = 67% at yd=1.5 mm, including losses in the LHC aperture. Require tracks 2(R)+2(L) RP’s. distance of closest approach to the beam Detectors have to be operated as close as possible to the beam in order to reach the coulomb region! -t=6·10 -4 GeV 2 decoupling of L and σ TOT only via EM amplitude!

41. ATLAS H.Stenzel, January 2007 41 t-resolution The t-resolution is dominated by the divergence of the incoming beams. σ’=0.23 µrad ideal case real world

42. ATLAS H.Stenzel, January 2007 42 L from a fit to the t-spectrum inputfiterror correl ation L8.10 10 26 8.151 10 26 1.77 % σ tot 101.5 mb101.14 mb0.9%-99% B18 Gev -2 17.93 Gev -2 0.3% 57% ρ0.150.1434.3%89% Simulating 10 M events, running 100 hrs fit range 0.00055-0.055 large stat.correlation between L and other parameters

43. ATLAS H.Stenzel, January 2007 43 experimental systematic uncertainties Currently being evaluated  beam divergence  detector resolution  acceptance  alignment  beam optics  background ΔL/L ≈ 2.8-3.2 %

44. ATLAS H.Stenzel, January 2007 44 conclusion ●LHC start up in 2007 ●ATLAS detector on track ●running at low luminosity 10 33 cm -2 s -1 and in 2008 ●switch to design luminosity 10 34 cm -2 s -1 after 2009 ●luminosity calibration from elastic scattering in 2009 ? ●LHC start up in 2007 ●ATLAS detector on track ●running at low luminosity 10 33 cm -2 s -1 and in 2008 ●switch to design luminosity 10 34 cm -2 s -1 after 2009 ●luminosity calibration from elastic scattering in 2009 ?