D

1
DØ Hard Diffraction in Run I and Prospects for
Run II

• Andrew Brandt
• DØ / University of Texas, Arlington

• Intro and Run I Hard Diffraction Results
• Forward Proton Detector

Low-x Physics 2001 June 28, 2001 Krakow, Poland
2
Event Topologies
p p ? p p
p p ? p (p) X
p p ? p (p) j j
p p ? p p j j
3
Event Characteristics
4
Hard Color-Singlet Exchange
f
Count tracks and EM Calorimeter Towers in h lt
1.0
Dh
jet
jet
h
(ET gt 30 GeV, ?s 1800 GeV)
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)
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1800 and 630 GeV Multiplicities
?s 1800 GeV
?s 630 GeV
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SD Event Characteristics
7

POMPYT Monte Carlo
p p ? p (or p) j j

Model pomeron exchange POMPYT26
(Bruni Ingelman) based on PYTHIA
define pomeron as beam particle
P
p
Structure Functions 1) Hard Gluon
xG(x) x(1-x) 2) Flat Gluon (flat in x) 3)
Quark xG(x) x(1-x) 4) Soft Gluon xG(x)
(1-x)5
p
p
? 1 - xp (momentum loss of proton)
P
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hep-ex/9912061
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Single Diffractive ? Distributions
? distribution for forward and central jets using
(0,0) bin
Dp p

central
?s 1800 GeV forward
central
?s 630 GeV forward
? ? 0.2 for ?s 630 GeV
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Double Gaps at 1800 GeVJet h lt 1.0, ETgt15 GeV
Gap Region 2.5lthlt5.2
Demand gap on one side, measure multiplicity on
opposite side
DØ Preliminary
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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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Diffractive W
nL0
?s 1800 GeV
ncal
ncal
nL0
Peak at (0,0) indicates diffractive W with a
signal on the 1 level
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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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A Few New Interesting Things

• Gap fractions at 630 are higher than
• 1800 for Central Gaps and Hard SD,
• but comparable for Double Gaps
• Double gap events with 15 GeV jets
• are about as rare as top events
• Diffractive Ws and Zs have similar
• gap fractions

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FPD Layout
Roman Pot
Bellows
p
Detector
P1UP
P2OUT
Q4
D
S
Q3
S
Q2
Q4
Q3
Q2
D1
P1DN
P2IN
D2
A1
A2
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33
59
57
33
23
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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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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Run II Event Displays
Hard Diffractive Candidate
Hard Double Pomeron Candidate
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Diffractive Variables
pBeam
pF
P
Pomeron Exchange
Non-diffractive
For TeV
For
GeV
GeV
(Note
)
GeV
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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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FPD Commissioning
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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
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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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Detector Construction

• Being completed at UTA
• Four fibers are aligned together in the frame to
  make a channel
• X frame also includes trigger scintillating rod
• Bicron optical epoxy is used to secure the fibers
  into the frame once completely assembled
• After curing, channels are mapped to appropriate
  location in cookie, PMT calibration fibers are
  included, lengths are measured and final gluing
  with optical epoxy is done

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• FPD Installation
• All of the castles installed and tested,
  maintaining vacuum.
• All the tunnel electronics installed and cables
  laid.
• The PU spectrometer is instrumented with full
  detectors and phototubes.
• The other vertical pots and dipole spectrometer
  are instrumented with pseudodetectors (trigger
  scintillators only) to study halo.
• Cameras installed and safety review
• complete
• 63 MAPMTs have been ordered from Hamamatsu,
  expected delivery in late August

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Castles Installed
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Pot Motion LVDT vs. Encoder
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Hit Reconstruction

• This event (from Engineering Run data)
• represents a hit in our detector at the location
• xd 5.6 mm
• yd 3.8 mm

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Run II HSD Improvements

• Measure ?, t over large kinematic range
• Integrated FPD trigger allows large data samples
• Higher ET jets allow smaller systematic errors
• Comparing measurements of HSD with track tag vs.
  gap
• tag yields new insight into process
• Can calibrate calorimeter ? measurement without
  MC

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June-August Run Plan

• Dedicated FPD shifts with pots inserted
• close to beam
• Start with stand-alone DAQ then integrate
• into DØ
• Full system tests
• Debugging, data-taking, algorithm
• development, pot insertion procedure,
• documentation, etc.

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Long Range Plan

• Install 8 more detectors (total of 10) during
• September shutdown
• Begin data taking with full DØ detector
• and trigger list in October
• Demonstrate working system, usefulness
• of horizontal plane, and secure funding
• for remaining MAPMT in 2002
• Early papers
• NIM
• Elastic t-distribution
• Single diffraction distributions
• Diffractive jet production
• Double tagged double pomeron exchange

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Conclusion

• Tremendous progress in installation and
• commissioning
• Entering a new phase of FPD
• 1) Installation almost complete
• 2) We have funding!
• Emphasis shifts to software and operations
• Trigger hardware and firmware still a big
• concern
• Starting to think about physics a little!

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Tevatron Reconfiguration
BEFORE
Power Leads
Bypass
Run I
Separator
DØ
Q1
Dipole (C48-5)
P type spool
Low Beta
AFTER
(Same for D11 side)
Extended Bypass
Run II
Castle
Castle
Separator
DØ
Low Beta
S type spool
Dipole (C48-5)
Modified girder
Girder modified Bypass construction
completed Valves and other vacuum equipment
purchased
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Dipole Region
Quadrupole Region
(Arbitrary Scale)
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