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Single Diffractive Cross Section Calorimeter Gaps Approach Soft QCD Meeting 14 th Oct 2 0 10

Single Diffractive Cross Section Calorimeter Gaps Approach Soft QCD Meeting 14 th Oct 2 0 10. Tim Martin , Paul Newman University of Birmingham. Soft Diffraction. Diffractive Events Colour singlet exchange. Can be Single or Double proton dissociation .

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Single Diffractive Cross Section Calorimeter Gaps Approach Soft QCD Meeting 14 th Oct 2 0 10

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  1. Single Diffractive Cross SectionCalorimeter Gaps ApproachSoft QCD Meeting14th Oct 2010 Tim Martin, Paul Newman University of Birmingham

  2. Soft Diffraction • Diffractive Events • Colour singlet exchange. • Can be Single or Double proton dissociation. • Diffractive mass can be anything from p+π0 up large systems with hundreds of GeV invariant mass. • Soft PTspectrum. • Large forward energy flow. • Less activity in the inner detector. Pythia Single Diff. Transverse Momentum Transfer

  3. Diffractive Mass Distributions • Measure dσ/dξover the ξ range accessible at ATLAS • Constrain the relative weights of SD, DD and ND At 7 TeV we should be getting really big diffractive systems! Pythia8

  4. Truth Level EnergyFlow • Normalised to a single event in ξ. • Differential in η. • Expect rapidity gap devoid of all soft activity. ηmax = η of Leading Truth Particle in X System Single Diffraction • Linear relation between η of leading particle and log(ξ), slope = 1 for ln(ξ). • Part hadronisation, mostly kinematics. Are there any MC diffractive models which do not use the lund string hadronisation model?

  5. Trigger Efficiency • Trigger events with the MBTS. Trigger is fully within calorimeter acceptance so use loose trigger requirement.L1_MBTS_2. Correct for trigger inefficiency in data using MC here `Here be dragons’ Unexploreable phase space with Calo + MBTS analysis.

  6. Experimental Re-definiton • In Double Diffraction, if the smaller system (MY) is too smallto get into the ATLAS calorimeters, then the event is experimentally indistinguishable (exc. ZDC) from a single diffractive event. This occurs around ξY of 10-6 New Definition: Double Diffractive Like Systematic Check: Location of cut Reclassify as Single Diffractive. Name the new sample Single Diffractive Like

  7. New Cross Sections • Singleand Double Diffractive Like take into account the migration of events from the Double Diffractive to Single Diffractive samples. • Visible refers to the subset of the samples which can be triggered with the MBTS.

  8. Samples & Calo Cells • Current data sample of ~750k, Pythia8, Phojet, Pythia6; ND, SD, DD • MC Empty • MinBias and RNDM stream for 1st 7 TeV run: • Run 152166 • ~600kL1_MBTS_2 & BCID = 1Events • 7719 mb. • Noise in TILEshow non-Gaussianprofile (double Gaussian). • TILE is not required for hermetic coverage of ATLAS and is currently excluded from the analysis. mc09_7TeV.105003.pythia_sdiff.recon.ESD.e514_s764_s767_r1307/ mc09_7TeV.105004.pythia_ddiff.recon.ESD.e514_s764_s767_r1307 mc09_7TeV.105001.pythia_minbias.recon.ESD.e517_s764_s767_r1307 data10_7TeV.00152166.physics_MinBias.recon.ESD.r1239/ data10_7TeV.00152166.physics_RNDM.recon.ESD.r1239/ mc09_7TeV.106096.PhojetNdiff.recon.ESD.e514_s764_s767_r1307 mc09_7TeV.106097.PhojetSdiff.recon.ESD.e514_s764_s767_r1307 mc09_7TeV.106098.PhojetDdiff.recon.ESD.e514_s764_s767_r1307 mc09_7TeV.108316.Pythia8_minbias_ND.recon.ESD.e533_s764_s767_r1307 mc09_7TeV.108317.Pythia8_minbias_SD.recon.ESD.e533_s764_s767_r1307 mc09_7TeV.108318.Pythia8_minbias_DD.recon.ESD.e533_s764_s767_r1307 Oldrich & Pavel EM Barrel

  9. EM Endcap Inner EM Barrel CaloCellSignificance EM Endcap Outer Data10 MBTS_2 Data10 RD0_EMPTY MC Py8 Inelastic MC Empty Tile Very Bad FCAL HEC

  10. Cell Requirement • Using an Energy Veto • Currently require 1 cell above 5.5 E/σ. • Can perhaps improve our sensitivity by combining cells? • No good for all cells in a slice. • E.G Barrel slice: 39,925 cells • RMS Noise of all cells combined: 8.6 GeV! • Swamps any minimum bias energy deposition. • However, combination of cells with E/σ > 3 looks more promising. • Order 50 cells per η slice, RMS noise of ~100 MeV– manageable. Under current investigation, may improve systematics.

  11. Being Quantified Gap Finding • •Trigger on L1_MBTS_2. • •Negligiblepileup, no prescales, low beam backgrounds. • •Divide the calorimeter into 10x rings spanning 1 unit of η. • •Ring is full if 1 or more calo cells satisfy E/σCell > Threshold • •Look for largest continuous gap of empty rings. • •Plot Start of Gap [|η|] vs. Size of Gap [Δη]. • •The start of the gap is defined as the |η| of it’s farthest edge from η=0 • •Provides separation of diffractive and non-diffractive. Systematic Check E.G. Single Diffractive Event MX Largest η Gap MBTS MY η

  12. Overall Trigger Efficiency MC • Trigger efficiency calculated from MCon a bin-by-bin basis. • Fractional breakdown of event types in each bin displayed below. Overall Trigger Eff. Totally Empty Detector Bin Totally Full Detector Bin Bin-by-bin Breakdown of Event types Key

  13. Tr. Eff Correction • Trigger efficiency corrections are applied bin-by-bin to the data histogram. • Bins with a MCtrigger efficiency of < 50 % are not used in the fit. • These are the `here be dragons bins’ Low Efficiency Before Correction After Correction

  14. Formation of MC Templates ND SD DD • Map 2D distribution onto 1D plot for the purpose of fitting. • Pre-trigger MC distributions. • Normalise each MC shape to a single event. • Bins with overall trigger efficiency < 50% are plotted last – beyond the black line. • These bins are not included in the fit.

  15. Check of Fit 1000 Trials One Trial • Form pseudo-data by applying bin-by-bin Poisson smear to MC prediction. • Fit relative SD, DD and ND templates to pseudo-data. • Fit constrained to sum to 1 Residuals for one trial

  16. Fit to Data – Pythia8 Pythia8: ND: 73.6% SD Like: 23.7% DD Like: 2.7% Fit: ND: 74.2% SD Like: 18.1% DD Like: 7.74% • Fit to data normalization in fitted bins. • Log likelihood fit. • MC shapes do not fully describe the data. Poor χ2

  17. Detector Acceptance • To convert to a cross-section, need to correct back to the particle level. • Run gapfinding algorithm over truth level data. • Move from Calo Cells  Truth Particles • Move from E/σ cut  PT cut • Build bin-by-bin correction histogram to apply to data. • c.f the trigger efficiency correction. Correction factors manageable in Single Diffractive Like (edge gap) region. Large correction factors in Double Diffractive Like region (central gaps)

  18. Single-Diffractive • Comparison of algorithms at: • Truth (PT > 200 MeV) • Reco (E/σ > 5.5) • Hatched boxes denote located gaps. • Correct effects such as: • Low PT particles not reaching callo. • Multiple scattering.

  19. Cross Section Last two bins have Trigger Efficiency < 50% • This slide 0 MeV PTcut gap definition • Data is... • Corrected for Trigger Efficiency & for Detector Acceptance. • Scaled to Lumi of run. • Plotted systematics, `best and worse case scenarios’ • E/σ > 5 noiseAND +10% Cell energy scale AND 111% Lumi. • E/σ > 6 noise AND -10% Cell energy scale AND 89% Lumi. Suggestion from R. Barlow! Will check adding in quad as well. Default & fitted fractional visible Xsec MC lines Statistical error negligible Systematic Band (systematics invert)

  20. Cross Section • This slide 100 MeV PTcut gap definition • Interesting sensitivity to choice of PTcut defining cross section. • Most effect at small gaps, explained as increasing pollution from non-diffractive events. • Flick back and forth...

  21. Cross Section • This slide 200 MeV PT cut gap definition • Flick back and forth...

  22. Cross Section • This slide 500 MeV PT cut gap definition • Flick back and forth... Work ongoing to match a sensible PT cut with the E/σ cut. No particles in the gap (PT > 0 cut) looks sensible. Can also publish differential in PT

  23. Cross Section • Combination into a single result. • Pythia8taken as trigger and acceptance correction MC • Maximum deviation per data point for Pythia6 and Phojet taken as systematic. • Added in quad., last two (low trigg. Eff.) bins not plotted. 0 MeV PT Definition 100 MeV PT Definition

  24. Conclusion • Single diffractive like cross section dσ/dη = 1 mbη-1 • Measurement of the single diffractive like cross section at 7 TeV possible with very little minimum bias data. • Many cross checks, systematic checks, systematic quantification is underway. • Still a bit more work to do with Calo Cell selection & PT dependence on acceptancecorrection. • We are working to compare with Tevatronresults at 2 TeV. • We are writing, detailed internal note for the analysis being produced atthe moment. • Details theory, all steps & cross checks.

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