O U T L I N E

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DØ Hard Diffraction in Run I and II
Andrew Brandt (DØ/UTA)
DIS2000 April 26, 2000 Liverpool, UK
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Learning about the Pomeron

• QCD is theory of strong interactions, but 40
  of
• total cross section is attributable to
  Pomeron
• exchange -- not calculable and poorly
  understood
• Does it have partonic structure?
• Soft? Hard? Super-hard? Quark? Gluon?
• Is it universal -- same in ep and ?
• Is it the same with and without jet
  production?
• Answer questions in HEP tradition -- collide it
  
• with something that you understand to learn
  
• its structure
• Note variables of diffraction are t and x
  M2
• with FPD measure
• without FPD just measure s

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EVENT TOPOLOGIES
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DØ Calorimeter and Tracking
Central Calorimeter
End Calorimeter
Hadronic Calorimeter
Central Drift Chamber (Tracking) ntrk
charged tracks with h lt 1.0
EM Calorimeter ncal EM towers with ET gt
200 MeV and h lt 1.0 (use E for h gt 2.0)
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Gap Definition
Detector coverage for gap definition
Calorimeter Coverage EM HAD
Thresholds EM 125 MeV HAD
500 MeV HAD-END 50 MeV
Level 0 scintillator
Gap definitions 1) Ncal0 in h (2.0,4.1) 2)
Ncal0 in h (2.0,5.2) 3) Ncal0 in h (2.5,5.2)
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beam
.
.
.
.
.
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Hard Single Diffraction
Measure Mult here
-4.0 -1.6 h 3.0
5.2
Measure Mult here
OR
-5.2 -3.0 -1. h 1. 3.0
5.2
Measure Gap Fraction (diffractive dijet
events/all dijet events) _at_1800 and 630 GeV
Forward Jet Trigger two 12GeV
Jets hgt1.6 Inclusive Jet Trigger
two 15(12)GeV Jets hlt1.0
Study SD Characteristics Single
Veto Trigger _at_1800 and 630 GeV two
15(12)GeV Jets
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1800 and 630 GeV Multiplicities
D0 Preliminary
?s 1800 GeV
?s 630 GeV
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1800 GeV Forward Jet Fit
D0 Preliminary
Measured gap fraction 0.65 ?0.04 (fit)
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Event Characteristics
D0 Preliminary
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Single Diffractive ? Distributions
? distribution for forward and central jets using
(0,0) bin

Dp p

D0 Preliminary
central
?s 1800 GeV forward
central
?s 630 GeV forward
? ? 0.2 for ?s 630 GeV
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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
(Diffractive Dijet Events/All
Dijets) 1800 Forward Jets 0.65 0.04 -
0.04 1800 Central Jets 0.22 0.05 -
0.04 630 Forward Jets 1.19 0.08 - 0.08 630
Central Jets 0.90 0.06 - 0.06
D0 Preliminary
Data Sample Ratio 630/1800 Forward
Jets 1.8 0.2 - 0.2 630/1800 Central Jets 4.1
0.8 - 1.0 1800 Fwd/Cent Jets 3.0 0.7 -
0.7 630 Fwd/Cent Jets 1.3 0.1 - 0.1
Forward Jets Gap Fraction gt Central Jets Gap
Fraction 630GeV Gap Fraction gt 1800GeV Gap
Fraction
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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 Flat Gluon Quark
1800 FWD JET (2.2 ? 0.3) (2.2 ? 0.3) (0.8
? 0.1) 1800 CEN JET (2.5 ? 0.4) (3.5 ?
0.5) (0.5 ? 0.1) 630 FWD JET (3.9 ? 0.9)
(3.1 ? 0.9) (2.2 ? 0.5) 630 CEN JET (5.2 ?
0.7) (6.3 ? 0.9) (1.6 ? 0.2)
Evt Sample Soft Gluon DATA 1800 FWD JET
(1.4 ? 0.2) (0.65 ? 0.04) 1800 CEN
JET (0.05 ? 0.01) (0.22 ? 0.05) 630
FWD JET (1.9 ? 0.4) (1.19 ?
0.08) 630 CEN JET (0.14 ? 0.04) (0.90
? 0.06)
Hard Gluon Flat Gluon rates higher than
observed in data (HG 1800fwd ?gap7410, SG
1800fwd ?gap223)
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630 and 1800 GeV Ratios
D0 Preliminary

Event Sample Hard Glu Flat Glu
Quark 630/1800 FWD 1.7 ? 0.4
1.4 ? 0.3 2.7 ? 0.6 630/1800 CEN 2.1 ?
0.4 1.8 ? 0.3 3.2 ? 0.5 1800
FWD/CEN 0.9 ? 0.2 0.6 ? 0.1 1.6 ?
0.3 630 FWD/CEN 0.8 ? 0.2 0.5 ? 0.1
1.4 ? 0.3
Event Sample Soft Glu DATA 630/1800 FWD
1.4 ? 0.3 1.8 ? 0.2 630/1800 CEN 3.1 ?
1.1 4.1 ? 0.9 1800 FWD/CEN 30. ? 8.
3.0 ? 0.7 630 FWD/CEN 13. ? 4. 1.3
? 0.1

Hard Gluon Flat Gluon forward jet rate is
lower than central jet rate -- and lower 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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Diffractive W
nL0
?s 1800 GeV
ncal
nL0
ncal
Peak at (0,0) indicates diffractive W with a
signal on the 1 level
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Double Gaps at 630 GeVJet h lt 1.0, ETgt12 GeV
Gap Region 2.5lthlt5.2
Demand gap on one side, measure multiplicity on
opposite side
DØ Preliminary
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Gap Summary

• Pioneered central gaps between jets, 3 papers,
  3 Ph. Ds
• Observed and measured forward gaps in jet
  events
• at ?s 630 and 1800 GeV. Rates much smaller
  than
• expected from naïve Ingelman-Schlein model.
• Require a different normalization and
  significant
• soft component to describe data. Large
  fraction
• of proton momentum frequently involved in
  collision.
• Observed jet events with forward/backward gaps
• at ?s 630 and 1800 GeV
• Observed W and Z boson events with gaps
• Finalizing papers and attempting to combine
  results

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Forward Proton Detector Layout
Roman Pot
Bellows
p
Detector
A1Q
P1Q
A1S
P1S
Q4
Q2
Q3
Q3
Q4
Q2
S
D
S
A2Q
A2S
AD1
AD2
P2Q
P2S
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33
59
57
33
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0
Z(m)
Series of 18 Roman Pots forms 9
independent momentum spectrometers allowing
measurement of proton momentum and angle.
1 Dipole Spectrometer ( p ) x gt xmin 8
Quadrupole Spectrometers (p or p, up or
down, left or right) t gt tmin
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Physics Topics with the FPD
1) Diffractive jet production 2) Hard double
pomeron exchange 3) Diffractive heavy flavor
production 4) Diffractive W/Z boson
production 5) New physics 6) Inclusive double
pomeron 7) High-t elastic scattering 8)
Total cross section 9) Inclusive single
diffraction FPD allows DØ to maximize Run II
physics
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Run II Event Displays
Hard Diffractive Candidtate
Hard Double Pomeron Candidate
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Acceptance
x
Quadrupole ( p or )
450 400 350 280 200
MX(GeV)
Geometric (f) Acceptance
x
Dipole ( only)
GeV2
450 400 350 280 200
MX(GeV)
GeV2
Dipole acceptance better at low t, large
x Cross section dominated by low t
x 0 0.02 0.04 1.4 1.4 1.3 2
35 95
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Quadrupole Dipole Spectrometers
The combination of quadrupole and dipole
spectrometers gives 1) Detection of protons
and anti-protons a) tagged double pomeron
events b) elastics for alignment,
calibration, luminosity monitoring
c) halo rejection from early time hits
2) Acceptance for low and high t 3)
Over-constrained tracks for
understanding detectors and backgrounds
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Roman Pot Castle Design
Worm gear assembly
50 l/s ion pump
Detector
Beam
Step motor

• Constructed from 316L Stainless Steel
• Parts are degreased and vacuum degassed
• Plan to achieve 10-11 Torr
• Will use Fermilab style controls
• Bakeout castle, then insert fiber detectors

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Roman Pot Arm Assembly
Detector is inserted into cylinder until it
reaches thin window
Threaded Cylinder
Motor
Bellows
Flange connecting to vacuum vessel
Thin window and flange assembly
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NIKHEF Window

• Used finite element analysis to model different
  window options
• Built three types of pots and studied deflection
  with pressurized helium.
• 150 micron foil with elliptical cutout gives
  excellent results

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The Detector
Six planes (u,u,v,v,x,x) of 800 m
scintillator fibers () planes offset by
2/3 fiber
20 channels/plane(U,V) 16 channels/plane(X,X) 11
2 channels/detector 2016 total channels 80 m
theoretical resolution
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The Detector
4 Fiber bundle fits well the pixel size of H6568
16 Ch. MAPMT 7 PMTs/detector (most of the cost)
U
U
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Data Taking

• No special conditions required
• Read out Roman Pot detectors for all events
• (cant miss )
• A few dedicated global triggers for diffractive
• jets, double pomeron, and elastic events
• Use fiber tracker trigger board -- select
• x , t ranges at L1, readout DØ standard
• Reject fakes from multiple interactions
• (Ex. SD dijet) using L0 timing, silicon
• tracker, longitudinal momentum conservation,
• and scintillation timing
• Obtain large samples (for 1 fb-1)
• 1K diffractive W bosons
• 3K hard double pomeron
• 500K diffractive dijets

with minimal impact on standard DØ
physics program
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Overall Conclusions
DØ has made significant progress in hard
diffraction in Run I

A lot more to do in Run II