D0 Run II Trigger

1
Rapidity Gaps at DØ
Jorge Barreto DØ Collaboration / I. Fisica of
UFRJ
1. Introduction 2. Single Diffractive Data _at_
1800 630 GeV 3. Monte Carlo 4. Hard Double
Pomeron Exchange 5. Central Gaps 6. Summary
ISMD 99 August 11,1999 Brown
2
Diffraction
p p ? p p
p p ? p (p) X
p p ? p (p) j j
p p ? p p j j
3
DØ Detector
(Forward Gaps)
Energy Threshold ? coverage EM Calorimeter 150
MeV 2.0lt?lt4.1 Had Calorimeter 500
MeV 3.2lt?lt5.2
Central Gaps EM Calorimeter (200 MeV
ET Threshold) Tracking (number of tracks)
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L0 Detector
beam
.
.
.
.
.
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Event Displays
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Hard Single Diffraction
Measure Multiplicity here
or
-4.0 -1.6 -1.0 h 1.0 3.0
5.2
Measure Gap Fraction Forward Jet
Trigger 2-12GeV Jets hgt1.6
46K events _at_ 1800 26K events _at_ 630
Inclusive Jet Trigger
2-15(12)GeV Jets hlt1.0 14K events
_at_ 1800 27K events _at_ 630 Study SD
Characteristics Single Veto
Trigger 2-15(12)GeV Jets
_at_ 1800 GeV (22K,38K) _at_ 630 GeV
(1K,24K)
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1800GeV Multiplicities
D0 Preliminary
NL0
NL0
NCAL
NCAL
NL0
NL0
NCAL
NCAL
8
630GeV Multiplicities
D0 Preliminary
NL0
NL0
NCAL
NCAL
NL0
NL0
NCAL
NCAL
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2D Fitting
Signal and Background fit simultaneously
Comments A) Fit background where ?2/dof
stable. B) If unprobable ?2/dof ( gt1.0), then
to be conservative scale errors by square root.
(only needed when large statistics) C) Error
statistical and from variation of fit parameters
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1800GeV Forward Jet Fit
D0 Preliminary
Measured gap fraction 0.64 ?0.05 (fit)
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Systematics/cross-checks
D0 Preliminary
Data Cut 1800 Fwd Jet Fitted Gap Fraction
Standard 0.64 0.05 - 0.05 Jet Quality
Cuts 0.64 0.05 - 0.05 Vary Energy Scale
1? 0.64 0.04 - 0.06 Vary Energy Scale
-1? 0.62 0.04 - 0.05 Luminositylt0.2E30 0.6
3 0.06 - 0.06 Luminositygt0.2E20 0.65
0.07 - 0.07 Threshold 1 0.68 0.04 -
0.06 (200MeV,600MeV,70MeV) Threshold 2 0.61
0.05 - 0.05 (300MeV,700MeV,100MeV) Vary
Background fit 0.64 0.05 - 0.05 15GeV
Jets 0.62 0.05 - 0.04
Measured Fraction is Stable
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Single Diffractive Results
Measure Multiplicity here
or
-4.0 -1.6 -1.0 h 1.0 3.0
5.2
Data Sample Measured Gap Fraction 1800
Forward Jets 0.64 0.05 - 0.05 1800 Central
Jets 0.20 0.08 - 0.05 630 Forward Jets 1.23
0.10 - 0.09 630 Central Jets 0.91 0.07 -
0.05
D0 Preliminary
Data Sample Ratio 630/1800 Forward
Jets 1.9 0.2 - 0.2 630/1800 Central Jets 4.6
1.2 - 1.8 1800 Fwd/Cent Jets 3.2 0.8 -
0.5 630 Fwd/Cent Jets 1.4 0.1 - 0.1
Forward Jets Gap Fraction gt Central Jets Gap
Fraction 630GeV Gap Fraction gt 1800GeV Gap
Fraction
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1800GeV Event Characteristics
Diffractive Inclusive (solid) Non-Diffractive
Inclusive (dashed)
D0 Preliminary
Diffractive Events Quieter Overall
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POMPYT Monte Carlo
p p ? p (or p) j j

Model pomeron exchange POMPYT26
(Bruni Ingelman) based on PYTHIA
define pomeron as beam particle
Structure Functions 1) Hard Gluon
xG(x) x(1-x) 2) Flat Gluon (flat in x) 3)
Soft Gluon xG(x) x (1-x)5 4) Quark xQ(x)
x(1-x)
Pomeron Exchanges dominate for ? lt 0.05
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Monte Carlo Multiplicity
D0 Preliminary
POMPYT
NCAL
NL0
PYTHIA
NCAL
NL0
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POMPYT Hard Gluon Event Characteristics
POMPYT (0,0) inclusive ? (solid) PYTHIA (dashed)
D0 Preliminary
Hard Gluon 1800GeV (??0.1)
Hard Gluon 630GeV (??0.2)
POMPYT hard gluon events quieter and jets
narrower than PYTHIA events
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MC Rate Comparison
f visible ?gap f predicted
? ?gap Add multiplicity to background data
distribution Fit to find percent of signal
events extracted
? Find predicted rate POMPYT2 / PYTHIA Apply
same jet ? cuts as data, jet ETgt12GeV Full
detector simulation

D0 Preliminary
Evt Sample Hard Gluon Quark 1800 FWD JET
2.1 ? 0.3 0.9 ? 0.1 1800 CEN JET 2.8
? 0.5 0.5 ? 0.2 630 FWD JET 4.6 ? 0.8
2.2 ? 0.5 630 CEN JET 5.1 ? 0.7
1.4 ? 0.7
Evt Sample Soft Gluon DATA 1800 FWD JET
1.6 ? 0.3 0.64 ? 0.05 1800 CEN JET
0.1 ? 0.1 0.20 ? 0.08 630 FWD JET 0.9
? 0.7 1.23 ? 0.10 630 CEN JET 0.1 ?
0.1 0.91 ? 0.07
Hard Gluon Flat Gluon rates higher than
observed in data Quark and soft gluon rates are
similar to observed (HG 1800fwd ?gap7411,
SG 1800fwd ?gap235)
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CDF Dijet Result
1800 GeV Forward Jets Calorimeter twr 2.4lt ?
lt4.2 BBC 3.2lt ? lt5.9 opposite jets 2 jets
ETgt20 (1.8lt?lt3.5) PRL179 2636 (1997)
Rjj 0.75 0.10 (corrected with Hard
Gluon Gap Efficiency)
DØ 1800 Forward Gap fraction (w/same correction)
0.86 0.07
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MC Combined Ratios
D0 Preliminary

Event Sample Hard Glu Quark DATA
630/1800 FWD 2.2 ? 0.5 2.4 ? 0.6
1.9 0.2 - 0.2 630/1800 CEN 1.8 ? 0.4
2.8 ? 1.4 4.6 1.2 - 1.8 1800 FWD/CEN 0.8
? 0.2 1.8 ? 0.7 3.2 0.8 - 0.5 630
FWD/CEN 0.9 ? 0.2 1.6 ? 0.9 1.4
0.1 - 0.1

Hard Gluon Flat Gluon higher central than
forward jet rate --and higher than observed in
data Quark rates and ratios are similar to
observed Combination of Soft Gluon and harder
gluon structure is also possible for pomeron
structure
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? Calculation
Rates, Gap efficiency, Event characteristics all
dependent on ? probed. Can use calorimeter
only to measure Weights particles in
well-measured region Can define for all events
Collins (hep-ph/9705393)
D0 Preliminary
?true ?calc 2.2 0.3
? calculation works well not dependent on
structure function or center-of-mass energy
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Single Diffractive ? Distribution, 1800GeV
? distribution for forward and central jets
(0,0)bin nominal (solid), high (dotted), and
low (dashed)
D0 Preliminary
? ? 0.1 at 1800GeV
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Single Diffractive ? Distribution, 630GeV
? distribution for forward and central jets
(0,0)bin nominal (solid), high (dotted), and
low (dashed)
D0 Preliminary
? ? 0.2 at 630GeV
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? Distribution, 1800GeV
? distribution for forward and central jets
single diffractive (0,0) bin nominal
(solid) non-diffractive (calculate to ? 3.0)
(dotted)
D0 Preliminary
non-diffractive contribution extends tail ?
distribution very different between diffractive
and non-diffractive data
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? Data/POMPYT
? distribution for 1800 GeV jets (0,0) bin
nominal Diffractive data (solid) POMPYT
Hard Gluon (dashed)
D0 Preliminary
similar ? distributions
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Double Gaps at 1800GeV Jet h lt 1.0, ETgt15 GeV
Gap Region 2.5lthlt5.2
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Double Gaps at 630 GeV
Gap Region 2.5lthlt5.2
DØ Preliminary
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Central Gaps
Count tracks and EM Calorimeter Towers in ?lt1.0
f
Dh
jet
jet
(ET gt 30 GeV, ?s 1800 GeV)
h
Measure fraction of events due to color-singlet
exchange
Measured fraction (1) rises with initial quark
content Consistent with a soft color
rearrangement model preferring initial quark
states Inconsistent with two-gluon, photon, or
U(1) models
Phys. Lett. B 440 189 (1998), hep-ex / 9809016
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Fit Results
Apply Bayesian fitting method, calculate
likelihood relative to free-factor model
Color factors for free-factor model Cqq Cqg
Cgg 1.0 0.04 0 (coupling to quarks
dominates)
Data favor free-factor and soft-color
models single-gluon not excluded, but all other
models excluded (assuming S not dependent on ET
and Dh)
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630 vs 1800
Jet ET gt 12 GeV, Jet h gt 1.9, Dh gt 4.0
Opposite-Side Data
Same-Side Data
1800 GeV
ncal
ncal
ntrk
ntrk
630 Gev
ncal
ncal
ntrk
ntrk
fS 1800 (ET 19.2 GeV) 0.54 ? 0.06stat ?
0.16sys fS 630 (ET 16.4 GeV) 1.85 ?
0.09stat ? 0.37sys
630
R1800 3.4 ? 1.2
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Summary
I - SINGLE DIFFRACTIVE DATA - Measure SD
rapidity gap signal at both 1800 GeV and 630
GeV for forward and central jets - Diffractive
events quieter and jets thinner than non-
diffractive events -
Diffractive jet ET distribution matches
non-diffractive jet ET
-f(forward)gtf(central) f(630GeV)gtf(1800GeV) 1
800 FWD JETS 0.64 ? 0.05 1800 CENT JETS
0.20 ? 0.08 630 FWD JETS 1.23 ? 0.10
630 CENT JETS 0.91 ? 0.07 - Measure SD ?
distribution (0,0) (higher than expected) - ?
? 0.1 _at_ 1800GeV - ? ? 0.2 _at_ 630GeV POMPYT
OBSERVATIONS - Event Characteristics
consistent with harder structures - Rates and
ratios prefer quark structure or combination
hard/flat gluon with soft gluons II -
DOUBLE GAP DATA - Observe Double Gaps at both
1800 and 630 GeV
III - CENTRAL GAPS Phys. Lett. B440 189(1998)
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630GeV Event Characteristics
D0 Preliminary
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MC Rates
D0 Preliminary
? Find predicted rate POMPYT2 / PYTHIA Apply
same jet ? cuts as data, jet ETgt12GeV
Full detector simulation (error statistical)
MC Sample 1800 FWD JET 1800 CENT JET Hard
Gluon 2.8 ? 0.1 7.1 ? 0.1 Flat Gluon 3.6 ?
0.1 6.2 ? 0.1 Quark 1.5 ? 0.1 2.6 ?
0.1 Soft Gluon 6.8 ?0.1 1.8 ? 0.1
MC Sample 630 FWD JET 630 CENT JET Hard
Gluon 5.4 ? 0.1 10.5 ? 0.1 Flat Gluon 4.3 ?
0.1 10.1 ? 0.1 Quark 4.2 ? 0.1 5.7 ?
0.1 Soft Gluon 8.6 ? 0.1 1.8 ? 0.1
f visible f predicted ?gap
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POMPYT Hard Gluon Jet ET
D0 Preliminary
Hard Gluon 630GeV
HG 630 ?? 0.1 (instead of 0.2) solid line PYTHIA
dashed line
POMPYT events need ?? 0.1 at 1800GeV and ?? 0.2
at 630GeV to match PYTHIA Jet ET distribution
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POMPYT Flat Gluon Event Characteristics
D0 Preliminary
Flat Gluon 1800GeV (??0.1)
Flat Gluon 630GeV (??0.2)
POMPYT Flat Gluon events quieter and jets thinner
than PYTHIA events
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POMPYT Quark Event Characteristics
D0 Preliminary
Quark 1800GeV (??0.1)
Quark 630GeV (??0.2)
POMPYT quark structrure events quieter and jets
thinner than PYTHIA events
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POMPYT Soft Gluon Event Characteristics
D0 Preliminary
Soft Gluon 1800GeV (??0.1)
Soft Gluon 630GeV (??0.2)
POMPYT soft gluon jet Et falls faster than PYTHIA
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Survival Probability

• Assumed to be independent of parton x (ET , Dh)
• Originally weak ?s dependence
• Gotsman, Levin, Maor Phys. Lett B 309
  (1993)
• Recently recalculated
• GLM hep-ph/9804404
• Using free-factor and soft-color model
• 
  (uncertainty from MC stats and model difference)
• with

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Color-Singlet Models

• If color-singlet couples preferentially to
  quarks or gluons, fraction depends on initial
  quark/gluon densities (parton x)
• larger x ? more quarks
• Gluon preference perturbative two-gluon models
  have 9/4 color factor for gluons
• Naive Two-Gluon model (Bj)
• BFKL model LLA BFKL dynamics
• Predictions
• fS (ET) falls, fS (Dh)
  falls/rises
• Quark preference
• Soft Color model non-perturbative
  rearrangement prefers quark initiated processes
  (easier to neutralize color)
• Photon and U(1) couple only to quarks
• Predictions
• fS (ET) fS (Dh) rise

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Monte Carlo Models

• Use Herwig 5.9 to simulate color-singlet model
• Includes higher-order effects and DØ detector
  simulation
• BFKL two-gluon exchange and t-channel photon
  exchange processes
• Divide by QCD prediction to get fS (MC)
• Construct coupling factor models color-singlet
  fraction is a function of pdfs weighted by
  coupling factors
• fS depends on x (ET, Dh,?s) through pdfs
• fS fnormCqqq1q2 Cqgq1(2)g2(1) Cgg g1g2
• (Cij ? coupling to initial state ij )
• Two-gluon Cqq1,Cqg 9/4,Cgg(9/4)2
• Soft color Cqq1/9,Cqg1/24,Cgg1/64
• Single-gluon Cqq Cqg Cgg 1
• Free-factor color factors given by fit