DDDiffractive Results from

Workshop on low x physics, Antwerp 2002

Brian Cox

E

• Diffractive W and Z

• Observation of double diffractive dijets

• Run 1 highlights

• Run II Beginnings

Central Calorimeter

End Calorimeter

Hadronic Calorimeter

EM Calorimeter

L0 Detector

beam

nL0 = # hit tiles in L0 detector

ncal = # cal towers with energy above threshold

Energy Threshold coverage EM Calorimeter 150 MeV 2.0<||<4.1 Had Calorimeter 500 MeV 3.2<||<5.2

Diffraction in the DØ detector

Diffractive W and Z production DDCentral and Forward electron W Event and Z event selections: Start with Run1b W e and Z ee candidate samples

DØ Preliminary

Diffractive selection DD•Measure forward calorimeter tower multiplicities in range 3.0<||<5.2

•Look at minimum multiplicity side of detector (not necessarily opposite side to electron)

Central W Multiplicity DD

-1.1 0 1.1 3.0 5.2

Minimum side

ncal

L0nL0

ncal

Peak at (0,0) is diffractive W-bosonSignal: 68 of 8724 events in (0,0) bin

DØ Preliminary

Forward W multiplicity DD

-2.5 -1.1 0 1.1 3.0 5.2

Minimum side

L0nL0 ncal

Peak at (0,0) indicates forward diffractive W-boson in forward electron sample:23 of 3898 events in (0,0) bin

DØ Preliminary

Central W event distributions DD

DØ Preliminary

Standard W Events Diffractive W Candidates

ET=37.12

ET=35.16

ET=36.08

MT=70.64 MT=70.71

Electron ET

Neutrino ET

Transverse Mass

ET=35.27

Z multiplicity

DØ Preliminary

-2.5 -1.1 0 1.1 3.0 5.2

Minimum side

ncal

L0

DD

Peak at (0,0) indicates diffractive Z-boson:9 of 811 events in (0,0) bin

Extracting the Signal DD•2-D fits of multiplicity plots

32 //

32

1 sysx eess

sS

xybybxbbB 3210

Data Fit

Fit SignalFit Background

Use high statistics background DD

Solid line: Central W Dashed: Cen+Fwd

W

ncal

Solid line: Central W Dashed: Cen+Fwd W

ncal

DØ Preliminary Background shapes agree, but fit more reliable with higher stats

Results DD

Sample Diffractive Probability Background All Fluctuates to Data Central W (1.08 + 0.21 - 0.19)% 1 x 10-13 7.7Forward W (0.64 + 0.19 - 0.16)% 6 x 10-7 5.3All W (0.89 + 0.20 – 0.19)%Z (1.44 + 0.62 - 0.54)% 5 x 10-5 4.4

DØ Preliminary

*Observed clear Diffractive W and Diffractive Z signals*Measured Diffractive W/All W and Diffractive Z/All Z

CDF {PRL 78 2698 (1997)} measured RW = 1.15 ± 0.55% with a significance of 3.8

A challenge to the Monte Carlos: DD

DØ Preliminary

W + jet and forward / central W production rates

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)%

Jet ET Data Quark Hard Gluon>8GeV (10 ± 3)% 14-20% 89 %>15GeV (9 ± 3)% 4-9 % 53 %>25GeV (8 ± 3)% 1-3 % 25 %

W + jet rates : very sensitive to IP structure

DDDouble Diffraction at 1800 GeV

|Jet | < 1.0, ET>15 GeVGap Region 2.5<||<5.2

DDDouble Diffraction at 630 GeV

|Jet | < 1.0, ET>12 GeVGap Region 2.5<||<5.2

Gaps Between Jets

jet

jet

2.14.3)Data(6301800 R

DD

Cox, Forshaw & Lonnblad, JHEP10 (1999) 023

Enberg, Ingleman & Motyka Phys. Lett. B524:273-282,2002

Diffractive Dijets at 630 and 1800 GeV

-4.0 -1.6 -1.0 1.0 3.0 5.2

orMeasure Multiplicity here

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 > Central Jets Gap Fraction

* 630 GeV Gap Fraction > 1800 GeV Gap Fraction

Forward jet trigger

ET > 12 GeV

Central jet trigger

ET > 15 (12) GeV @ 1800 (630) GeV

DD

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

DDDiffractive Dijets at 630 and 1800 GeV

s = 1800 GeV forward

central

s = 630 GeV forward

central

i

yT

s

eE i

i

The Run II Pots DD

• 8 detectors fully installed (D1, D2, A1I, A2I, P1U, P1D, P2D)

• All will be in place after October shutdown

Acceptance of quadrupole pots DD

Data distributions DD

DØ not Preliminary at all really

Elastic distribution peaks at 0

Highlights DD

• Two new Run I analyses due for publication :

Diffractive W (+ jets) and Z

Double Diffractive Dijets

•We’re all looking forward to Run II analysis !

Detectors working fine

First physics in December / January