Diffractive Results from

1
Diffractive Results from
Brian Cox
Workshop on low x physics, Antwerp 2002

• Diffractive W and Z
• Observation of double diffractive dijets
• Run 1 highlights
• Run II Beginnings

E
?
?
2
Diffraction in the DØ detector
L0 Detector
nL0 hit tiles in L0 detector
ncal cal towers with energy above threshold
beam
Central Calorimeter
End Calorimeter
EM Calorimeter
Energy Threshold ? coverage EM Calorimeter 150
MeV 2.0lt?lt4.1 Had Calorimeter 500
MeV 3.2lt?lt5.2
Hadronic Calorimeter
3
Diffractive W and Z production
Central and Forward electron W Event and Z event
selections Start with Run1b W en and
Z ee candidate samples
DØ Preliminary
4
Diffractive selection

• Measure forward calorimeter tower multiplicities
  in range 3.0lthlt5.2
• Look at minimum multiplicity side of detector
  (not necessarily opposite side to electron)

5
Central W Multiplicity
nL0
L0
ncal
ncal
Peak at (0,0) is diffractive W-boson Signal 68
of 8724 events in (0,0) bin
DØ Preliminary
6
Forward W multiplicity
Minimum side
?
? -2.5 -1.1 0 1.1 3.0
5.2
nL0
ncal
L0
Peak at (0,0) indicates forward diffractive
W-boson in forward electron sample 23 of 3898
events in (0,0) bin
DØ Preliminary
7
Central W event distributions
ET35.27
DØ Preliminary
8
Z multiplicity
Peak at (0,0) indicates diffractive Z-boson 9 of
811 events in (0,0) bin
DØ Preliminary
9
Extracting the Signal

• 2-D fits of multiplicity plots

Fit
Data
Fit Background
Fit Signal
10
Use high statistics background
Solid line Central W Dashed CenFwd W
ncal
Solid line Central W Dashed CenFwd W
ncal
DØ Preliminary
Background shapes agree, but fit more reliable
with higher stats
11
Results
Observed clear Diffractive W and Diffractive Z
signals Measured Diffractive W/All W and
Diffractive Z/All Z
Sample Diffractive
Probability Background
All Fluctuates to
Data Central W (1.08 0.21 - 0.19)
1 x 10-13 7.7s Forward W (0.64 0.19 -
0.16) 6 x 10-7 5.3s All W
(0.89 0.20 0.19) Z (1.44 0.62 -
0.54) 5 x 10-5 4.4s
CDF PRL 78 2698 (1997) measured RW 1.15
0.55 with a significance of 3.8?
DØ Preliminary
12
A challenge to the Monte Carlos
W jet and forward / central W production rates
b(1-b)
Sample Data Quark
Hard Gluon Cen W (1.08 0.21 -
0.19) (4.1 ? 0.8) (0.15 ? 0.02) For W
(0.64 0.19 - 0.16) (7.2 ? 1.3) (0.25 ?
0.04) Z (1.44 0.62 - 0.54) (3.8 ? 0.7)
(0.16 ? 0.02)
W jet rates very sensitive to IP structure
Jet ET Data Quark
Hard Gluon gt8GeV (10 3)
14-20 89 gt15GeV (9 3)
4-9 53 gt25GeV (8
3) 1-3 25
DØ Preliminary
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Double Diffraction at 1800 GeV
Jet h lt 1.0, ETgt15 GeV Gap Region 2.5lthlt5.2
14
Double Diffraction at 630 GeV
Jet h lt 1.0, ETgt12 GeV Gap Region 2.5lthlt5.2
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Gaps Between Jets
f
Dh
jet
jet
h
Cox, Forshaw Lonnblad, JHEP10 (1999)
023 Enberg, Ingleman Motyka Phys. Lett.
B524273-282,2002
16
Diffractive Dijets at 630 and 1800 GeV
Measure Multiplicity here
or
-4.0 -1.6 -1.0 h 1.0
3.0 5.2
Forward jet trigger ET gt 12 GeV
Central jet trigger ET gt 15 (12) GeV _at_ 1800 (630)
GeV
Data Sample Measured Gap Fraction
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
Forward Jets Gap Fraction gt Central Jets Gap
Fraction 630 GeV Gap Fraction gt 1800 GeV Gap
Fraction

• Monte Carlo analysis (hep-ex/9912061) gluon
  dominated IP (hard soft) reduced flux factor
  accounts for data

17
Diffractive Dijets at 630 and 1800 GeV
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The Run II Pots

• 8 detectors fully installed (D1, D2, A1I, A2I,
  P1U, P1D, P2D)
• All will be in place after October shutdown

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Acceptance of quadrupole pots
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Data distributions
Elastic x distribution peaks at 0
DØ not Preliminary at all really
21
Highlights

• Two new Run I analyses due for publication
• Diffractive W ( jets) and Z
• Double Diffractive Dijets

• Were all looking forward to Run II analysis !
• Detectors working fine
• First physics in December / January