Status of Diffractive Physics at DØ Run II

1. Status of Diffractive Physics at DØ Run II • Outline • Color Singlet Exchange • Diffractive Z Production • The FPD: Diffractive Scattering • Conclusions Jorge Barreto Instituto de Física - UFRJ Rio de Janeiro – RJ - Brazil Low_x 2004 - Prague

2. Color Singlet Exchange (Diffraction) |t| = (pf – pi)2 • = 1 – pf / pi • The Tevatron collides protons and antiprotons at √s = 1.96 TeV at a crossing rate of 1.7 MHz • About 40% of the total pp cross-section is elastic or diffractive scattering • Diffractive processes involve the exchange of a color singlet: • Quantum numbers of the vacuum • Often referred to as Pomeron exchange • Diffractive studies used to probe nature of the Pomeron p • Experimental Signature • Rapidity Gap: absence of particles or energy above threshold in some region of rapidity in detector • Tagged proton: p or p scattered at small angle from the beam measured in a detector far from the interaction (pf ) (pi ) X I P J2 (pi ) p X X J1 Low_x 2004 - Prague

3. Measuring Rapidity Gaps at DØ Run II • Use the following detectors to identify rapidity gaps: • Forward Calorimeters • Luminosity Monitors (LM) p p VC: 5.2 < |h|< 5.9 LM: 2.7 < |h| < 4.4 Forward Calorimeter Low_x 2004 - Prague

4. Calorimeter Liquid argon/uranium calorimeter Cells arranged in layers: • electromagnetic (EM) • fine hadronic (FH) • coarse hadronic (CH) • Sum E of Cells in EM and FH layers above threshold: EEM > 100 MeV EFH > 200 MeV 2.7 LM range 4.4 2.6 Esum range 4.1 - 5.3 IP LM EM CH FH Low_x 2004 - Prague

5. Calorimeter Energy Sum • Use energy sum to distinguish proton break-up from empty calorimeter: • Esum < 10 GeV for current study • Final value will be optimized using full data sample Areas normalized to 1 WORK IN PROGRESS empty events physics samples 10 GeV Log10(cell energy sum / GeV): • Compare 'empty event' sample with physics samples: • Empty event sample: random trigger. Veto LM signals and primary vertex, i.e. mostly empty bunch crossings • Physics samples: minimum bias (coincidence in LM), jet and Z→μμ events Low_x 2004 - Prague

6. Search for Z→μμ in Diffraction DØ Run II preliminary Summer 2003 • Run I publication ”Observation of diffractively produced W and Z bosons in pp Collisions at sqrt(s)=1.8 TeV”, Phys. Lett. B 574, 169 (2003) Nine single diffractive Z→e+e- events. No result in muon channel. • Run II: first search forforward rapidity gaps in Z→μ+μ- events • Inclusive Z→μμ selection: • di-muon (|η|<2) or single muon (|η|< ~1.6) trigger • 2 muons, pT > 15GeV, opposite charge • at least one muon isolated in tracker and calorimeter • cosmics cuts Mμμ (GeV) Low_x 2004 - Prague

7. Z Mass of rapidity gap candidates No Gap Gap WORK IN PROGRESS WORK IN PROGRESS 89.8 ± 0.1 GeV 89.6 ± 1.0 GeV • Add Esum requirement to define gap • Invariant mass peak consistent with Drell-Yan/Z events • Will be able to compare Z boson kinematics (pT, pz, rapidity) Low_x 2004 - Prague

8. Z→μμ with rapidity gaps: Summary • Preliminary definition of rapidity gaps at DØ Run II • Study of Z→μ+μ- events with a rapidity gap signature • Current Status • Evidence of Z events with a rapidity gap signature • Quantitative studies of gap definition, backgrounds, efficiency in progress • Plans • Measurement of the fraction of diffractively produced Z events • Diffractive W→μν, W/Z→ electrons, jets and other channels • Use tracks from Forward Proton Detector outgoing anti-proton side outgoing proton side muon muon muon muon Low_x 2004 - Prague

9. Forward Proton Detector Layout p P1U P2O Q4 Q3 Q2 Q2 S D Q3 Q4 S A1 A2 D2 D1 P1D P2I Veto p 57 59 23 0 33 23 33 • 9 momentum spectrometers each composed of 2 Scintillating fiber detectors housed in(Roman Pots) can bebrought close (~6 mm) to the beam. • Reconstruct scattered protons and anti-protons to calculate their momentum fraction and scattering angle • Much better resolution than available with gaps alone • Combine tracks with central high-pT scattering (main detector) • Cover a kinematic region 0 < |t| < 3 GeV2 never before explored at Tevatron energies Z(m) |t| = (pf – pi)2 = – 2k2(1 – cosq) ~ q 2 (small angles) • = 1 – xp = 1 – pf / pi < 0.05 (diffraction) Low_x 2004 - Prague

10. FPD Detector Setup • 6 layers per detector in 3 planes and a trigger scintillator • U and V at 45 degrees to X, 90 degrees to each other • Layers in a plane offset by ~2/3 fiber. Fibers in each layer of a plane taken together define a segment (0.27mm) used to define hits. • 2 detectors in a spectrometer. Hits used to define tracks. 17.39 mm V’ V Trigger X’ X U’ U 17.39 mm 1 mm 0.8 mm 3.2 mm Low_x 2004 - Prague

11. Detector Hit Resolutions • Starting in January 2004, all 18 detectors regularly inserted (dipoles since February 2003) • Commissioning underway on quadrupoles • Resolutions calculated by the difference of the x value of a hit calculated from u/v segments compared to the x value of the x segment show that most of the detectors are working as expected WORK IN PROGRESS Low_x 2004 - Prague

12. FPD Dipole Data Analysis(Diffraction) beam x y (0,0) D0 D2 D1 WORK IN PROGRESS pbar Y_D2 X_D2 WORK IN PROGRESS p halo pbar halo X_D1 Y_D1 • Read out using AFE (Analog Front End) board • Trigger minimum of one jet with pT > 25 GeV and North luminosity counters not firing • Harsh multiplicity cut applied on number of segments (1) allowed to fire to help deal with spray background • This correlation is from a small sample Low_x 2004 - Prague

13. Dipole Diffraction Acceptance Simple MC Geometrical Acceptance (14σ from beam) Data (No Cuts) WORK IN PROGRESS WORK IN PROGRESS flat |t| distribution • Fair agreement between data and MC Low_x 2004 - Prague

14. Dipole Tagged Dijets • Comparison of dijet events with (dashed) and without (solid) tags in the dipole detectors • areas normalized to one • Studies underway to calibrate detectors and refine tag definition WORK IN PROGRESS WORK IN PROGRESS Low_x 2004 - Prague

15. Summary • The full FPD system has been installed and is working as designed • Full commissioning studies • Detector alignment and calibration • Initial analysis using FPD data: • Dijets using dipole tags • Z→ μμ using tags • (elastics!) • Initial definition of a gap in the calorimeter made • Evidence of Z→ μμ with gap signature found, further work needed to finalize results and interpretation in terms of diffractive physics p I P I P p Low_x 2004 - Prague

16. DØ Run II Diffractive Topics Soft Diffraction and Elastic Scattering: Inclusive Single Diffraction Elastic scattering (t dependence) Total Cross Section Centauro Search Inclusive double pomeron Search for glueballs/exotics Hard Diffraction: Diffractive jet Diffractive b,c ,t , Higgs Diffractive W/Z Diffractive photon Other hard diffractive topics Double Pomeron + jets Other Hard Double Pomeron topics Rapidity Gaps: Central gaps+jets Double pomeron with gaps Gap tags vs. proton tags Topics in RED were studied with gaps only in Run I E <100 W boson events in Run I, >1000 tagged events expected in Run II   Low_x 2004 - Prague