2. Lishep06 Gilvan Alves1 Overview of Diffraction from DØ Gilvan Alves Lafex/Brazil  Introduction  Diffraction @ DØ RunI x RunII  Special Runs  Outlook

3. Lishep06 Gilvan Alves2 Why Diffraction?  We want to understand the strong interactions ♦ ~ 40% of  tot is related to diffraction ♦ QCD needs diffraction soft x hard ♦ What is this Pomeron anyway? Virtual particle which carries no net charge, isospin, baryon number or color IP IP

4. Lishep06 Gilvan Alves3 Diffractive signatures

5. Lishep06 Gilvan Alves4 RunI Gaps - Calorimeter and L  EM Calorimeter L0 Detector (n l0 = # tiles in L0 detector with signal 2.3 < |  | < 4.3) Central Drift Chamber (n trk = # charged tracks with |  | < 1.0) End Calorimeter Central Calorimeter (n cal = # cal towers with energy above threshold) Hadronic Calorimeter Central Gaps EM Calorimeter E T > 200 MeV |  | < 1.0 Forward Gaps EM Calorimeter E > 150 MeV 2.0 < |  | < 4.1 Had. Calorimeter E > 500 MeV 3.2 < |  | < 5.2) beam

6. Lishep06 Gilvan Alves5 Diffraction @ D  RunI Observed events w/double gaps @

7. Lishep06 Gilvan Alves6 Calorimeter+LM+VC  New Gap  Use signals from Luminosity Monitor (and later Veto Counters) to trigger on rapidity gaps with calorimeter towers for gap signal  Use calorimeter at Level 2 to further refine rapidity gaps VC: 5.2 < |  < 5.9 LM: 2.5 < |  < 4.4

8. Lishep06 Gilvan Alves7 RunII Improvements Forward Proton Detector  9 momentum spectrometers composed of 18 Roman Pots  Scintillating fiber detectors can be brought close (~6 mm) to the beam to track scattered protons and anti- protons  Reconstructed track is used to calculate momentum fraction and scattering angle ♦ Much better resolution than available with gaps alone  Cover a t region (0 < t < 3 GeV 2 ) never before explored at Tevatron energies  Allows combination of tracks with high-p T scattering in the central detector

9. Lishep06 Gilvan Alves8 beam Roman Pot Layout D SQ 4 Q 3 Q 2 S A 1 A 2 P 1 P 2 p p z (m) D 2 D 1 A 2 Q 2 Q 3 Q 4 5957 33 230 2333 ● 6 layers per detector in 3 planes and a trigger scintillator ● U and V at 45 degrees to X, 90 degrees to each other ● U and V planes have 20 fibers, X planes have 16 fibers ● Layers in a plane offset by ~2/3 fiber ● Each channel filled with four fibers ● 2 detectors in a spectrometer 0.8 mm 3.2 mm 1 mm 17.39 mm U U’ X X’ V V’ Trigger beam Scat. p

10. Lishep06 Gilvan Alves9 Dipole Data (Running since 2003)  In events with hits in each detector of the spectrometer, the hits tend to fall in correlation bands  Due to the location of the dipole spectrometer, particles from the next incoming bunch can be passing through the detector at the same time as outgoing particles.  Diffracted antiprotons have lost a fraction of their momentum, and therefore are bent more by the dipole magnets leading to a noticeable angle between hits in the detector  Halo particles have beam momentum and therefore do not exhibit this angle  Particles in the upper y d correlation band are candidate tracks beam view top view

11. Lishep06 Gilvan Alves10 Hit Resolution and Hit Map  Hit resolution (after mapping correction) gives: ♦ 159  m for D1I ♦ 160  m for D2I  Hit maps for validated hits (independent for each detector) fills out the detector showing the expected edges

12. Lishep06 Gilvan Alves11  Diffractive Z (GAP)  Diffractive W  Diffractive HF  Diffractive Forward Jets  Diffractive Structure Function  Double Pomeron + Jets  Inclusive Double Pomeron  Exclusive Events in Double Pomeron  Elastic FPD Theses 10 PhD Students

13. Lishep06 Gilvan Alves12 Current Triggers (Oct. 05)

14. Lishep06 Gilvan Alves13 FPGA based L1 trigger Fiber segments

15. Lishep06 Gilvan Alves14 A2UA2UA1UA1U P2DP1D LUMINOSITY MONITOR DØ VETO COUNTERS p p p P P1D · P2D · A1U · A2U · (VT + LM + EAU + EPD ) VETO COUNTERS LUMINOSITY MONITOR Triggering on Diffraction @ D 

16. Lishep06 Gilvan Alves15 New tool for halo rejection

17. Lishep06 Gilvan Alves16 FPD Triggered data

18. Lishep06 Gilvan Alves17 Requested Special Stores

19. Lishep06 Gilvan Alves18 Good gain on acceptance

20. Lishep06 Gilvan Alves19 MC expectations

21. Lishep06 Gilvan Alves20 Limits on |t| acceptance t range accessible with injection tune pot positioninteg. luminosity

22. Lishep06 Gilvan Alves21 Spectrometer Correlations

23. Lishep06 Gilvan Alves22 Outlook  DØ has a rich diffractive program with several analyses underway.  FPD is performing as expected  Track based trigger working  enlarge our data sample  Requested low luminosity (low+high  *) – Millions of events on tape. ♦ Better understanding of alignment. ♦ Kinematical region previously unexplored.  New tools for Background/Halo rejection.  Optimization of proton ID, reconstruction and alignment will lead to better measurements with lower systematic effects.