Download - Single Diffractive Cross Section Calorimeter Gaps Approach Soft QCD Meeting 14 th Oct 2 0 10
1Single Diffractive Cross SectionCalorimeter Gaps ApproachSoft QCD Meeting14th Oct 2010
Tim Martin, Paul NewmanUniversity of Birmingham
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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 PT spectrum.• Large forward energy flow.• Less activity in the inner detector.
PythiaSingle Diff.TransverseMomentum
Transfer
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Diffractive Mass Distributions
Pythia8
• Measure dσ/dξ over 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!
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Truth Level EnergyFlow• Normalised to a single event
in ξ.• Differential in η.• Expect rapidity gap devoid of
all soft activity.Single Diffraction
• Linear relation between η of leading particle and log(ξ), slope = 1 for ln(ξ).
• Part hadronisation, mostly kinematics.
ηmax = η of Leading Truth Particle in X System
Are there any MC diffractive models which do not use the lund string hadronisation
model?
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Trigger Efficiency• Trigger events with the MBTS. Trigger is fully within
calorimeter acceptance so use loose trigger requirement. L1_MBTS_2.
`Here be dragons’
Unexploreable phase space with
Calo + MBTS analysis.
Correct for trigger
inefficiency in data using MC
here
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Experimental Re-definiton• In Double Diffraction, if the smaller system (MY) is too small
to 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
Reclassify as Single
Diffractive.Name the new sample Single
Diffractive Like
New Definition:Double
Diffractive Like Systematic Check: Location of cut
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New Cross Sections• Single and 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.
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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• ~600k L1_MBTS_2 & BCID = 1 Events• 7719 mb.
• Noise in TILE show non-Gaussian profile (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_r1307mc09_7TeV.106097.PhojetSdiff.recon.ESD.e514_s764_s767_r1307mc09_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
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EM Barre
l
EMEndcapInner
EMEndcapOuter
FCALHEC
Tile
CaloCellSignificance
Data10 MBTS_2Data10 RD0_EMPTYMC Py8 InelasticMC Empty
Very Bad
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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.
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Gap Finding
Largestη Gap
E.G. SingleDiffractive
EventMX
MY
η
•Trigger on L1_MBTS_2.•Negligible pileup, 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.
MBTS
Being Quantified
Systematic Check
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Overall Trigger Eff.o Trigger efficiency calculated
from MC on a bin-by-bin basis.
o Fractional breakdown of event types in each bin displayed below.
OverallTrigger
EfficiencyMC
Bin-by-binBreakdown ofEvent types
Key
Totally FullDetector Bin
Totally EmptyDetector Bin
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Tr. Eff Correctiono Trigger efficiency corrections are applied bin-by-bin to the
data histogram.o Bins with a MC trigger efficiency of < 50 % are not used in
the fit.o These are the `here be dragons bins’
Before Correction After Correction
Low Efficienc
y
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Formation of MC Templates
ND SDDD
o Map 2D distribution onto 1D plot for the purpose of fitting.o Pre-trigger MC distributions.o Normalise each MC shape to a single event.o Bins with overall trigger efficiency < 50% are plotted last – beyond the black line.o These bins are not
included in the fit.
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Check of Fit
oForm pseudo-data by applying bin-by-bin Poisson smear to MC prediction.oFit relative SD, DD and ND templates to pseudo-data.oFit constrained to sum to 1
One Trial
Residuals for one trial
1000 Trials
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Fit to Data – Pythia8
o Fit to data normalization in fitted bins.
oLog likelihood fit.
oMC shapes do not fully describe the data. Poor χ2
Pythia8:ND: 73.6%SD Like: 23.7%DD Like: 2.7%
Fit:ND: 74.2%SD Like: 18.1%DD Like: 7.74%
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Detector Acceptance• To convert to a cross-section, need to correct back to the
particle level.• Run gap finding 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)
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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.
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Cross Section• This slide 0 MeV PT cut 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 noise AND +10% Cell energy scale AND 111% Lumi.
• E/σ > 6 noise AND -10% Cell energy scale AND 89% Lumi.
Last two bins have Trigger Efficiency < 50%
Suggestion from R. Barlow! Will check
adding in quad as well.
Systematic Band(systematics invert)
Default & fittedfractional visible
Xsec MC linesStatistical error
negligible
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Cross Section• This slide 100 MeV PT cut gap definition
• Interesting sensitivity to choice of PT cut defining cross section.
• Most effect at small gaps, explained as increasing pollution from non-diffractive events.
• Flick back and forth...
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Cross Section• This slide 200 MeV PT cut gap definition
• Flick back and forth...
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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
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Cross Section• Combination into a single result.
• Pythia8 taken 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
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Conclusion• Single diffractive like cross section dσ/dη = 1 mb η-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.