Diffractive Physics at D

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Diffractive Physics at DØ

• Silvia Tentindo Repond
• For the DØ Collaboration
• Hadron Collider Physics
• Karlsruhe - 29 September 2002

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Outline

• Diffractive Processes
• Dø Detector
• Results
• Hard Single Diffraction (W, Z and Di-Jets)
• Hard Double Diffraction
• Double Pomeron Exchange
• Conclusions
• FPD and Future Prospects

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Diffractive Processes

• In diffractive events one (or both) incoming
  particles remain intact, or dissociate into
  products emitted at small angle. The virtual
  particle exchanged in diffractive events (the
  Pomeron) carries the quantum numbers of the
  vacuum.
• Diffraction can occur in p-p and e-p collisions.
  Inclusive Diffractive cross section is about 10
  at Tevatron.
• Two basic types
• Soft diffraction (non-perturbative QCD regime)
• Hard diffraction (perturbative QCD), allows
  probing of structure of Pomeron
• Seen in calorimeter through rapidity gaps
  (regions of the detector with no particles above
  threshold) and/or tagging the intact final
  particle.

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Diffractive Processes at Tevatron
Diffractive Higgs
(or Hard Double Diffraction)
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Hard Single Diffraction W/Z production
Central W
electron ET,and missing ET, gt 25 GeV, central
e h lt 1.
forward e 1.5 lt
h lt 2.5 Look for forward gap 3.0 lt h
gap lt5.2
Count L0 tiles and EM Calorimeter Towers in 3.0 lt
h lt 5.2
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DØ Calorimeter,L0 and Tracking
L0 Detector (3.2 lt ? lt 5.2)
Forward
EM Calorimeter
Central
(ncal cal towers with energy above threshold)
Central Calorimeter
(nl0 hit tiles in L0 detector)
Hadronic Calorimeter
Central Drift Chamber
Calorimeter thresholds EM Calorimeter
Central ET gt 200 MeV h lt 1.0 EM
Calorimeter Forward E gt 150 MeV 2.0 lt ? lt
4.1 Had. Calorimeter E gt 500 MeV

(ntrk charged tracks with h lt 1.0)
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W/Z 2D Multiplicities
nL0
ncal
?
vs
?
W forward
W central
nL0
ncal

Z All
Observed peak at (0,0) Diffractive
events Gap Fractions Diffractive W/All W
Diffractive Z/All Z
DØ Preliminary
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Central W Multiplicity Fit
Data
Fit
Background
Signal


10 STentindo,HCP02
DØ Preliminary
10/1/02
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DØ Preliminary
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W/Z Gap Fractions Results
Sample Gap Fraction ()
Probability that Background
Diffractive/All () would fluctuate
to the Data in
the (0,0) bin
for W and Z Data W cent 1.08 0.19 -
0.17 1 x 10-14
7.7s W fwd 0.64 0.18 - 0.16
6 x 10-8 5.3s W All
0.89 0.20 0.19 3 x
10-14 7.5s Z 1.44 0.62 -
0.54 5 x 10-6
4.4s
DØ Preliminary
First observation of Z Diffractive
() Includes correction for multiple interaction
contamination. Sys error dominated by
background fitting.
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W/Z Gap Fractions Comparisons with Models()
Note - MC Gap Fraction is corrected for gap
efficiency 20-30
W/Z GAP FRACTION () MC() and Data
Sample Quark Hard Gluon
DATA W cent 4.1 ? 0.8 0.15 ? 0.02
1.08 - 0.21 W fwd 7.2 ? 1.3
0.25 ? 0.04 0.64 - 0.19
Z 3.8 ? 0.7 0.16 ? 0.02
1.44 - 0.62

• W jets GAP FRACTION ()
• Jet Et Quark Hard Gluon
  DATA
• gt8GeV 14-20 89
  10 -3
• gt15GeV 4-9 53
  9 -3
• gt25Gev 1-3 25
  8 -3

DØ Preliminary
() Ingelman-Schlein Model () POMPYT MonteCarlo
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Hard Single Diffraction Di-Jets Production

• 2 forward jets, ET gt 12 GeV, h gt 1.6
• 2 central jets, ET gt15(12) GeV, h lt 1.0
• Forward gap 3.0 lth gap lt 5.2

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Di-jets 2D Multiplicities
?
?
?
?
forward jets ?s 1800
GeV central jets
?s 630 GeV
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Hard Single Diffraction Results
hep-ex/991261 v1 23Dec1999
()
Gap Fraction () for Data and MC ()
Sample Data 1800 Fwd
0.65 - 0.04 1800 Cent 0.22 - 0.05
630 Fwd 1.19 - 0.08 630 Cent 0.90
- 0.06
Hard Gluon Quark Soft Gluon
2.2 - 0.3 0.79 -0.12 1.4
-0.2 2.5 -0.4 0.49 -0.06 0.05
-0.01 3.9 -0.9 2.2 -0.5
1.9 -0.4 5.2 -0.7 1.6 -0.2
0.14 -0.04
Ratio of Gap Fraction () for Data and MC
Hard Gluon Quark Soft Gluon
Sample Data Ratio 630/1800
Fwd 1.8 - 0.2 630/1800 Cent
4.1 - 0.9
1.7 - 0.4 2.7 -0.6 1.4
-0.3 2.1-0.4 3.2 -0.5 1.8
-0.3 0.88-0.18 1.6 -0.3 30.
-8. 0.75 -0.16 1.4 -0.3 13. -4.
1800 Fwd/Cent 3.0 - 0.7 630 Fwd/Cent
1.3 - 0.1
()Ingelman Schlein Model, and POMPYT MonteCarlo
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Hard Single Diffractive Data and Models for
Pomeron Structure
Phys. Lett. B 531 52(2002)

• W,Z Diffractive data support quark component.
• Di-jets data support soft gluon.
• For the Ingelman-Schlein model to describe Dø
  data as well as other measurements (HERA), a
  normalization factor convoluted with a gluonic
  Pomeron containing significant soft and hard
  components is required.
• Need more data and more accurate Monte Carlo
  calculations.

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Hard Double Diffraction (or Color Singlet
Exchange, CSE)
Jet ET gt 12 (15, 30) GeV, Jet h gt 1.9, Dh gt
4.0 Look for central gap h gap lt1.
Count tracks and EM Calorimeter Towers in h lt
1.0
STentindo,HCP02
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Measurement of fs
(CSE)
?
High-ET sample (ET gt 30 GeV, ?s 1800 GeV)
?
nL0
ncal
vs

fS Gap fraction (Ndata- Nfit)/Ntotal
fS 1800 0.94 ? 0.04stat ? 0.12sys
ET gt30 GeV
(Includes correction for multiple interaction
contamination. Sys error dominated by background
fitting.)
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Models for Hard Double Diffraction

• 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
• () BFKL calculations made at LO only
  NLO corrections are relevant

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Model Fits to Hard Double Diffraction Data
?s 1800 GeV

• BFKL gluons
• Soft Color quarks rearrangement
• Measured fraction (1) rises with initial quark
  content
• Consistent with a soft color rearrangement model
  preferring initial quark states.
• Inconsistent with BFKL() two-gluon, photon, or
  U(1) models
• () BFKL calculations made at LO only NLO
  corrections are relevant

Phys. Lett. B 440 189 (1998), hep-ex / 9809016
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Modifications to Theory

• BFKL Cox, Forshaw use a non-running as to
  flatten the falling ET prediction of BFKL

• Soft Color Gregores does a more careful counting
  of state that produce color singlets to improve
  prediction.

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Double Pomeron 1800 Gev Jet h lt 1.0, ETgt15 GeV
Gap Region 2.5lthlt5.2
Double Gap
DØ Preliminary
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Double Pomeron 630 Gev Jet h lt 1.0, ETgt12 GeV
Gap Region 2.5lthlt5.2
DØ Preliminary
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DØ Forward Proton Detector

• Diffractive and elastic physics program
• need special detectors at very small angles FPD
• FPD consists of 2 arms (outgoing proton and
  anti-proton)
• 18 Roman pots in 4 quadrupole and 2 dipole
  castles
• From hits in scintillating fiber detectors
  installed in Roman pots
• fractional energy lost by the proton and
  scattering angle
• trigger on elastic, diffractive, double pomeron
  events

• Routinely insert pots during collisions
• Recorded gt 2 M elastic events with stand-alone
  DAQ
• Working on integration of FPD with the rest of
  DØ
• First diffractivejet data by December

Dipole Castle
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Conclusions

• New definitive observation of diffractive W boson
• f W 0.89 0.190.17 ()
• First observation of diffractive Z boson
• f Z 1.44 0.62 0.54 ()
• Hard Single Diffractive data
• W,Z data support quark component.
• Di-Jets data support soft gluon component
• Hard Double Diffractive data favor
• Soft Color rearrangement models.
• Double Pomeron
• Observation of D0 of new process at 630 and 1800
  GeV.
• To tie descriptions together, need more
  sophisticated models, with latest HERA
  diffractive structure functions, and more precise
  data of RunII.

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Future Prospects

• Forward Proton Detector (FPD)
• First measurements on elastic events done.
• FPD integration with Dø by December 2002
• Measurements planned Hard Single and Double
  Diffractive (with and without rapidity gaps), W
  and Z , Double Pomeron etc.
• Diffractive Higgs
• Extremely small cross sections at Tevatron.
• But very good resolution in invariant mass
  spectra.

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END
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Diffractive W,Z Production at D0
Measured Gap Fraction Fs (1.08 0.19 0.17)
nL0
ncal
electron ET,and missing ET, gt 25 GeV, e
hlt1. Look for forward gap 3.0 lt h gap
lt5.2
p
P
v
W Diffractive production probes the STRUCTURE of
the Pomeron
p
e
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Diffractive Events
CSE topology