1. Luminosity measurments roadmap for luminosity determinations relative luminosity monitors luminosity from machine parameters luminosity from physics processes luminosity from elastic scattering how to access luminosity information

2. Dresden 15.05.2008 luminosity measurements, H.Stenzel 2 roadmap for luminosity determinations from machine parameters (2008) ●absolute luminosity at start-up will uniquely come from the machine ●expected precision is 20-30% ●this will improve with special dedicated runs, 10% is feasible from physics processes (2009) ●using γ γ →μμ (not discussed here) ●using W/Z counting: 3-5% can be reached from elastic scattering (>2009) ●with the optical theorem ●with small-angle scattering in the Coulomb region ●3% accuracy is anticipated combinations of all above... from machine parameters (2008) ●absolute luminosity at start-up will uniquely come from the machine ●expected precision is 20-30% ●this will improve with special dedicated runs, 10% is feasible from physics processes (2009) ●using γ γ →μμ (not discussed here) ●using W/Z counting: 3-5% can be reached from elastic scattering (>2009) ●with the optical theorem ●with small-angle scattering in the Coulomb region ●3% accuracy is anticipated combinations of all above...

3. Dresden 15.05.2008 luminosity measurements, H.Stenzel 3 relative luminosity monitor: LUCID Cherenkov light is emitted at 3 o and is read-out after 3 reflections on the inner tube walls.

4. Dresden 15.05.2008 luminosity measurements, H.Stenzel 4 M. Bruschi – INFN Bologna (ITALY) Off-line On and Off-line

5. Dresden 15.05.2008 luminosity measurements, H.Stenzel 5 other luminosity monitors ●MBTS (limited lifetime) ●TILE calorimeter (Monitoring/Minimum Bias path) ●LARG (current in HV lines) ●Beam Condition Monitor  precision of about 1% on relative luminosity is expected ●MBTS (limited lifetime) ●TILE calorimeter (Monitoring/Minimum Bias path) ●LARG (current in HV lines) ●Beam Condition Monitor  precision of about 1% on relative luminosity is expected

6. Dresden 15.05.2008 luminosity measurements, H.Stenzel 6 Luminosity from machine parameters Simplest case, beams colliding head-on, Gaussian beam profiles In presence of a crossing angle the luminosity is reduced by In presence of a crossing angle the luminosity is reduced by

7. Dresden 15.05.2008R.Bailey, DESY, December 20077 Overall commissioning strategy for protons (est d. 2005) Hardware commissioning Machine checkout Beam commissioning 43 bunch operation 75ns ops 25ns ops I Install Phase II and MKB 25ns ops II Stage A BC No beamBeam D I.Pilot physics run First collisions First collisions 43 bunches, no crossing angle, no squeeze, moderate intensities 43 bunches, no crossing angle, no squeeze, moderate intensities Push performance Push performance Performance limit 10 32 cm -2 s -1 (event pileup) Performance limit 10 32 cm -2 s -1 (event pileup) II.75ns operation Establish multi-bunch operation, moderate intensities Establish multi-bunch operation, moderate intensities Relaxed machine parameters (squeeze and crossing angle) Relaxed machine parameters (squeeze and crossing angle) Push squeeze and crossing angle Push squeeze and crossing angle Performance limit 10 33 cm -2 s -1 (event pileup) Performance limit 10 33 cm -2 s -1 (event pileup) III.25ns operation I Nominal crossing angle Nominal crossing angle Push squeeze Push squeeze Increase intensity to 50% nominal Increase intensity to 50% nominal Performance limit 2 10 33 cm -2 s -1 Performance limit 2 10 33 cm -2 s -1 IV.25ns operation II Push towards nominal performance Push towards nominal performance

8. Dresden 15.05.2008 luminosity measurements, H.Stenzel 8 Luminosity from beam parameters Adjustment of the orbits to equalize the position differences left/right of the IP, determination of the overlap integral. Tuning based on Beam position monitors with ~ 50 μm resolution. Adjustment of the orbits to equalize the position differences left/right of the IP, determination of the overlap integral. Tuning based on Beam position monitors with ~ 50 μm resolution. Optimize luminosity in separation scans (Van der Meer-method) Optimize luminosity in separation scans (Van der Meer-method) LEP example

9. Dresden 15.05.2008 luminosity measurements, H.Stenzel 9 Expected precision from machine parameters Factors entering in the luminosity calculation: ●beam current (intensity) 1-2% ●crossing angle (reduction factor) ●hour glass effect (1% at high lumi, ß*=0.55m) ●bunch-by-bunch variations ●non-gaussian beam shapes ●suppression of tails by scraping A precision of 10% can be reached ●... and can be further reduced with dedicated runs/special studies ●at start-up a precision of 20-30% can be expected ●ultimately a few % level is not unrealistic, ●at the ISR an error of < 1% was achieved! Important: cross calibration of machine- and experiment-based methods! More info: H.Burkhardt and P.Grafstrom, LHC Project Report 1019 Factors entering in the luminosity calculation: ●beam current (intensity) 1-2% ●crossing angle (reduction factor) ●hour glass effect (1% at high lumi, ß*=0.55m) ●bunch-by-bunch variations ●non-gaussian beam shapes ●suppression of tails by scraping A precision of 10% can be reached ●... and can be further reduced with dedicated runs/special studies ●at start-up a precision of 20-30% can be expected ●ultimately a few % level is not unrealistic, ●at the ISR an error of < 1% was achieved! Important: cross calibration of machine- and experiment-based methods! More info: H.Burkhardt and P.Grafstrom, LHC Project Report 1019

10. Dresden 15.05.2008 luminosity measurements, H.Stenzel 10 Luminosity from W/Z counting ●large cross section, high rate ●clean experimental signature (leptonic modes) ●precise theoretical calculations ●large cross section, high rate ●clean experimental signature (leptonic modes) ●precise theoretical calculations Recent results on W/Z counting in CSC note: experimental systematic uncertainty dominated by acceptance, is 2-3% (accounts for ISR, kT, UE, EW and PDF uncertainties) Recent results on W/Z counting in CSC note: experimental systematic uncertainty dominated by acceptance, is 2-3% (accounts for ISR, kT, UE, EW and PDF uncertainties) For 1fb -1

11. Dresden 15.05.2008 luminosity measurements, H.Stenzel 11 theoretical cross section QCD NNLO calculation for inclusive W/Z production, perturbative uncertainty from scale variations is about 1%. QCD NNLO calculation for inclusive W/Z production, perturbative uncertainty from scale variations is about 1%. However, 2-loop EW corrections are important at large pT, no complete QCD x EW are available! However, 2-loop EW corrections are important at large pT, no complete QCD x EW are available! EW corrections

12. Dresden 15.05.2008 luminosity measurements, H.Stenzel 12 theoretical cross section: PDF uncertainty PDF-uncertainty using CTEQ6.6: 3.3-3.5% using NLO+NLL PDF-uncertainty using CTEQ6.6: 3.3-3.5% using NLO+NLL New NNLO MRSW2006 compared to MRST2004 (6% change) New NNLO MRSW2006 compared to MRST2004 (6% change) Currently a 3-5% accuracy of luminosity from W/Z seems in reach and will improve in the course of LHC.... Currently a 3-5% accuracy of luminosity from W/Z seems in reach and will improve in the course of LHC....

13. Dresden 15.05.2008luminosity measurements, H.Stenzel13 elastic scattering with ALFA Absolute Luminosity For ATLAS

14. Dresden 15.05.2008 luminosity measurements, H.Stenzel 14 The elastic t-spectrum schematically ALFA simulation

15. Dresden 15.05.2008 luminosity measurements, H.Stenzel 15 Luminosity from elastic scattering Our baseline method for the absolute luminosity calibration requires the measurement of elastic scattering in the Coulomb-nuclear interference region down to t ≈6·10 -4 GeV 2 Our baseline method for the absolute luminosity calibration requires the measurement of elastic scattering in the Coulomb-nuclear interference region down to t ≈6·10 -4 GeV 2 This is only possible if ALFA can be operated very close to the beam ≈12σ under optimal beam conditions. Alternatively at larger t the optical theorem can be used: This is only possible if ALFA can be operated very close to the beam ≈12σ under optimal beam conditions. Alternatively at larger t the optical theorem can be used: Requires μrad angle measurements and detector distance to beam ≈1.5 mm! Requires μrad angle measurements and detector distance to beam ≈1.5 mm! Requires measurements of the total rate and extra- polation of elastic rate to 0! Requires measurements of the total rate and extra- polation of elastic rate to 0!

16. Dresden 15.05.2008 luminosity measurements, H.Stenzel 16 How to measure the total inelastic rate? From the CSC note on minimum bias: MBTS acceptance SCT+Pixel Systematic uncertainty ≈3% + physics model uncertainties Systematic uncertainty ≈3% + physics model uncertainties

17. Dresden 15.05.2008 luminosity measurements, H.Stenzel 17 Single diffraction with forward detectors RP IP 240m RP ZDC 140m LUCID ZDC 140m LUCID ATLAS 17m single diffraction Cross sections[mb]PythiaPhojet Elastic scattering 34.2 (modified) 22.2 (default) 34.5 Single diffraction14.311.0 Double diffraction10.24.1 Minimum bias non-diffractive 54.767.9 Total cross section101119 Complement central detector measurement of single diffraction with measurements in the forward region to get the total rate. In addition for the Luminosity there is an uncertainty of the extrapolation of the elastic slope to t=0 ~1% (TOTEM) Complement central detector measurement of single diffraction with measurements in the forward region to get the total rate. In addition for the Luminosity there is an uncertainty of the extrapolation of the elastic slope to t=0 ~1% (TOTEM)

18. Dresden 15.05.2008 luminosity measurements, H.Stenzel 18 Elastic scattering in the CNI region 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*

19. Dresden 15.05.2008 luminosity measurements, H.Stenzel 19 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!

20. Dresden 15.05.2008 luminosity measurements, H.Stenzel 20 t-resolution The t-resolution is dominated by the divergence of the incoming beams. σ’=0.23 µrad ideal case real world

21. Dresden 15.05.2008 luminosity measurements, H.Stenzel 21 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

22. Dresden 15.05.2008 luminosity measurements, H.Stenzel 22 systematic uncertainties for the luminosity Details are give in the ALFA TDR CERN-LHCC-2008-006 and in ATL-LUM-PUB-2007-001

23. Dresden 15.05.2008 luminosity measurements, H.Stenzel 23 How to get your cross-section? Marjorie Shapiro

24. Dresden 15.05.2008 luminosity measurements, H.Stenzel 24 The concept of luminosity blocks Marjorie Shapiro

25. Dresden 15.05.2008 luminosity measurements, H.Stenzel 25 How to get the luminosity for your sample Marjorie Shapiro More info: Luminosity Working Group https://twiki.cern.ch/twiki/bin/view/ATLAS/LuminosityGroup LTF report: http://cdsweb.cern.ch/record/970678

26. Dresden 15.05.2008 luminosity measurements, H.Stenzel 26 Conclusion Expected precision of luminosity measurements ●relative monitoring to 1% (LUCID) ●initial absolute calibration from machine parameters 20-30% ●improving with special runs to 10% or better ●W/Z production yield 3-5% calibration, likely to improve with LHC data ●elastic scattering in the CNI region and/or with the optical theorem will yield a 3% accuracy Expected precision of luminosity measurements ●relative monitoring to 1% (LUCID) ●initial absolute calibration from machine parameters 20-30% ●improving with special runs to 10% or better ●W/Z production yield 3-5% calibration, likely to improve with LHC data ●elastic scattering in the CNI region and/or with the optical theorem will yield a 3% accuracy

27. Dresden 15.05.2008R.Bailey, DESY, December 200727 Staged commissioning plan for protons Hardware commissioning 450 GeV and 7TeV 2008 Machine checkout Beam commissioning 450 GeV Machine checkout Beam commissioning 7TeV 43 bunch operation Shutdown BC No beamBeam Shutdown Machine checkout Beam Setup 75ns ops25ns ops IShutdown 2009 No beamBeam A

28. Dresden 15.05.2008 luminosity measurements, H.Stenzel 28 Forward detectors

29. Dresden 15.05.2008 luminosity measurements, H.Stenzel 29 acceptance for t and ξ global acceptance: PYTHIA 45 % PHOJET 40.1 % global acceptance: PYTHIA 45 % PHOJET 40.1 %