Diffractive 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 n L0 = # hit tiles in L0 detector n cal = # cal towers with energy above threshold Energy Threshold  coverage EM Calorimeter150 MeV2.0<|  |<4.1 Had Calorimeter500 MeV3.2<|  |<5.2 Diffraction in the DØ detector

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

Diffractive selection 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   Minimum side n cal L0 n L0 n cal Peak at (0,0) is diffractive W-boson Signal: 68 of 8724 events in (0,0) bin DØ Preliminary

Forward W multiplicity   Minimum side L0 n L0 n cal 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 DØ Preliminary Standard W Events Diffractive W Candidates E T =37.12 E T =35.16 E T =36.08 M T =70.64 M T =70.71 Electron E T Neutrino E T Transverse Mass E T =35.27

Z multiplicity DØ Preliminary   Minimum side n cal L0 Peak at (0,0) indicates diffractive Z-boson: 9 of 811 events in (0,0) bin

Extracting the Signal 2-D fits of multiplicity plots Data Fit Fit Signal Fit Background

Use high statistics background Solid line: Central W Dashed: Cen+Fwd W n cal Solid line: Central W Dashed: Cen+Fwd W n cal DØ Preliminary Background shapes agree, but fit more reliable with higher stats

Results Sample Diffractive Probability Background All Fluctuates to Data Central W ( )% 1 x  Forward W ( )% 6 x  All W ( – 0.19)% Z ( )% 5 x  DØ Preliminary *Observed clear Diffractive W and Diffractive Z signals *Measured Diffractive W/All W and Diffractive Z/All Z CDF {PRL (1997)} measured R W = 1.15 ± 0.55% with a significance of 3.8 

A challenge to the Monte Carlos: DØ Preliminary W + jet and forward / central W production rates Sample Data Quark Hard Gluon Cen W ( )% (4.1  0.8)% (0.15  0.02)% For W ( )% (7.2  1.3)% (0.25  0.04)% Z ( )% (3.8  0.7)% (0.16  0.02)% Jet E T 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

Double Diffraction at 1800 GeV |Jet  | 15 GeV Gap Region 2.5<|  |<5.2

Double Diffraction at 630 GeV |Jet  | 12 GeV Gap Region 2.5<|  |<5.2

Gaps Between Jets jet    Cox, Forshaw & Lonnblad, JHEP10 (1999) 023 Enberg, Ingleman & Motyka Phys. Lett. B524: ,2002

Diffractive Dijets at 630 and 1800 GeV  or Measure Multiplicity here Data Sample Measured Gap Fraction 1800 Forward Jets 0.65% % % 1800 Central Jets 0.22% % % 630 Forward Jets 1.19% % % 630 Central Jets 0.90% % % * 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) 1800 (630) GeV Monte Carlo analysis (hep-ex/ ) – gluon dominated IP (hard + soft) + reduced flux factor accounts for data

Diffractive Dijets at 630 and 1800 GeV  s = 1800 GeV forward central  s = 630 GeV forward central

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

Acceptance of quadrupole pots

Data distributions DØ not Preliminary at all really Elastic  distribution peaks at 0

Highlights 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