Luminosity measurments roadmap for luminosity determinations relative luminosity monitors

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. 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 ... luminosity measurements, H.Stenzel

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

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

7. Overall commissioning strategy for protons (estd. 2005) Stage A D B C No beam Beam • Pilot physics run • First collisions • 43 bunches, no crossing angle, no squeeze, moderate intensities • Push performance • Performance limit 1032 cm-2 s-1 (event pileup) • 75ns operation • Establish multi-bunch operation, moderate intensities • Relaxed machine parameters (squeeze and crossing angle) • Push squeeze and crossing angle • Performance limit 1033 cm-2 s-1 (event pileup) • 25ns operation I • Nominal crossing angle • Push squeeze • Increase intensity to 50% nominal • Performance limit 2 1033 cm-2 s-1 • 25ns operation II • Push towards nominal performance R.Bailey, DESY, December 2007

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. LEP example Optimize luminosity in separation scans (Van der Meer-method) 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 luminosity measurements, H.Stenzel

10. Luminosity from W/Z counting • 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) For 1fb-1 luminosity measurements, H.Stenzel

11. theoretical cross section EW corrections 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! luminosity measurements, H.Stenzel

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

13. Absolute • Luminosity • For • ATLAS elastic scattering with ALFA luminosity measurements, H.Stenzel

14. The elastic t-spectrum schematically ALFA simulation 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 ≈6·10-4GeV2 Requires μrad angle measurements and detector distance to beam ≈1.5 mm! 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 measurements of the total rate and extra- polation of elastic rate to 0! 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 luminosity measurements, H.Stenzel

17. Single diffraction with forward detectors single diffraction ATLAS RP RP LUCID LUCID RP RP ZDC ZDC IP RP RP LUCID ATLAS LUCID RP RP ZDC ZDC 240m 140m 17m 17m 140m 240m 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) luminosity measurements, H.Stenzel

18. Elastic scattering in the CNI region hit pattern for 10 M elastic events simulated with PYTHIA + MADX for the beam transport t reconstruction: • special optics • parallel-to-point focusing • high β* luminosity measurements, H.Stenzel

19. acceptance distance of closest approach to the beam Global acceptance = 67% at yd=1.5 mm, including losses in the LHC aperture. Require tracks 2(R)+2(L) RP’s. Detectors have to be operated as close as possible to the beam in order to reach the coulomb region! -t=6·10-4 GeV2 decoupling of L and σTOT only via EM amplitude! 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 luminosity measurements, H.Stenzel

21. L from a fit to the t-spectrum Simulating 10 M events, running 100 hrs fit range 0.00055-0.055 large stat.correlation between L and other parameters 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 luminosity measurements, H.Stenzel

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

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

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

27. Staged commissioning plan for protons 2008 A No beam Beam 2009 B C No beam Beam R.Bailey, DESY, December 2007

28. Forward detectors luminosity measurements, H.Stenzel

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