luminosity measurments roadmap for luminosity determinations relative luminosity monitors

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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. roadmap for luminosity determinations. - PowerPoint PPT Presentation


  • Luminosity measurments

    roadmap for luminosity determinationsrelative luminosity monitorsluminosity from machine parametersluminosity from physics processesluminosity from elastic scatteringhow to access luminosity information

    luminosity measurements, H.Stenzel

  • roadmap for luminosity determinations

    from machine parameters (2008)

    absolute luminosity at start-up will uniquely come from the machineexpected precision is 20-30%this will improve with special dedicated runs, 10% is feasible

    from physics processes (2009)

    using (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

  • 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

  • M. Bruschi INFN Bologna (ITALY)Off-lineOn and Off-lineOn and Off-line

    luminosity measurements, H.Stenzel

  • 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

  • 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

  • Overall commissioning strategy for protons (estd. 2005)Stage ABCNo beamBeamDPilot physics runFirst collisions43 bunches, no crossing angle, no squeeze, moderate intensitiesPush performancePerformance limit 1032 cm-2 s-1 (event pileup)75ns operation Establish multi-bunch operation, moderate intensitiesRelaxed machine parameters (squeeze and crossing angle)Push squeeze and crossing angle Performance limit 1033 cm-2 s-1 (event pileup)25ns operation INominal crossing anglePush squeezeIncrease intensity to 50% nominalPerformance limit 2 1033 cm-2 s-125ns operation IIPush towards nominal performance

    Hardware commissioningMachine checkoutBeam commissioning43 bunch operation75ns ops25ns ops IInstall Phase II and MKB25ns ops II

    luminosity measurements, H.Stenzel

  • 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 m resolution.Optimize luminosity in separation scans (Van der Meer-method)LEP example

    luminosity measurements, H.Stenzel

  • 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, *=0.55m)bunch-by-bunch variationsnon-gaussian beam shapes suppression of tails by scraping

    A precision of 10% can be reached

    ... and can be further reduced with dedicated runs/special studiesat start-up a precision of 20-30% can be expectedultimately 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

  • Luminosity from W/Z counting

    large cross section, high rateclean experimental signature (leptonic modes) precise theoretical calculationsRecent results on W/Z counting in CSC note: experimental systematic uncertaintydominated by acceptance, is 2-3%

    (accounts for ISR, kT, UE, EW and PDF uncertainties) For 1fb-1

    luminosity measurements, H.Stenzel

  • theoretical cross section QCD NNLO calculation for inclusive W/Z production, perturbative uncertainty fromscale variations is about 1% .However, 2-loop EW corrections are important at large pT, no complete QCD x EW are available!EW corrections

    luminosity measurements, H.Stenzel

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

    luminosity measurements, H.Stenzel

  • elastic scattering with ALFA Absolute Luminosity For ATLAS

    luminosity measurements, H.Stenzel

  • The elastic t-spectrum schematicallyALFA simulation

    luminosity measurements, H.Stenzel

  • Luminosity from elastic scattering Our baseline method for the absolute luminosity calibration requires themeasurement of elastic scattering in the Coulomb-nuclear interference region down to t 610-4GeV2This is only possible if ALFA can be operated very close to the beam 12 under optimal beam conditions.Alternatively at larger t the optical theorem can be used: Requires rad anglemeasurements and detector distance to beam 1.5 mm!Requires measurements of the total rate and extra-polation of elastic rate to 0!

    luminosity measurements, H.Stenzel

  • How to measure the total inelastic rate? From the CSC note on minimum bias:MBTS acceptanceSCT+PixelSystematicuncertainty 3%+ physics modeluncertainties

    luminosity measurements, H.Stenzel

  • Single diffraction with forward detectors RPIP240m240mRPRPRPRPRPRPRPZDCZDC140mLUCIDLUCIDZDCZDC140mLUCIDLUCIDATLASATLAS17m17msingle diffractionComplement 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)

    Cross sections[mb]PythiaPhojetElastic scattering 34.2 (modified)22.2 (default)34.5Single diffraction14.311.0Double diffraction10.24.1Minimum biasnon-diffractive54.767.9Total cross section 101119

    luminosity measurements, H.Stenzel

  • Elastic scattering in the CNI region t reconstruction:hit pattern for 10 M elastic events simulated with PYTHIA + MADX for the beam transport

    special opticsparallel-to-point focusinghigh *

    luminosity measurements, H.Stenzel

  • acceptance Global acceptance = 67%at yd=1.5 mm, including losses in the LHC aperture.Require tracks 2(R)+2(L) RPs.distance of closest approach to the beam Detectors have to be operated as close as possible to the beam in order to reach the coulombregion! -t=610-4 GeV2decoupling of L and TOT only via EM amplitude!

    luminosity measurements, H.Stenzel

  • t-resolution The t-resolution is dominated by the divergence of the incoming beams.

    =0.23 radideal casereal world

    luminosity measurements, H.Stenzel

  • L from a fit to the t-spectrum Simulating 10 M events,running 100 hrsfit range 0.00055-0.055large stat.correlation between L and other parameters

    inputfiterrorcorrelation L8.10 10268.151 10261.77 %tot101.5 mb101.14 mb0.9%-99%B18 Gev-217.93 Gev-20.3%57%0.150.1434.3%89%

    luminosity measurements, H.Stenzel

  • systematic uncertainties for the luminosity Details are give in the ALFA TDR CERN-LHCC-2008-006and in ATL-LUM-PUB-2007-001

    luminosity measurements, H.Stenzel

  • How to get your cross-section? Marjorie Shapiro

    luminosity measurements, H.Stenzel

  • The concept of luminosity blocks Marjorie Shapiro

    luminosity measurements, H.Stenzel

  • How to get the luminosity for your sample Marjorie ShapiroMore info: Luminosity Working Group report:

    luminosity measurements, H.Stenzel

  • 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

  • Staged commissioning plan for protons2008BCNo beamBeam2009No beamBeamA

    Hardware commissioning450 GeV and 7TeV

    Machine checkoutBeam commissioning450 GeV

    Machine checkoutBeam commissioning7TeV43 bunch operationShutdown

    ShutdownMachine checkoutBeam Setup75ns ops25ns ops IShutdown

    luminosity measurements, H.Stenzel

  • Forward detectors

    luminosity measurements, H.Stenzel

  • acceptance for t and global acceptance:PYTHIA 45 %PHOJET 40.1 %

    luminosity measurements, H.Stenzel