Diffractive Physics

1. LM A1U A2U VC Pbar P E P1D P2D f h Diffractive Physics Andrew Brandt, U. Texas at Arlington • Focus on mature analyses: • Diffractive Z • Elastic Scattering DØ Physics Workshop July 30, 2004 Fermilab

2. DØ Run II preliminary Summer 2003 • RunI 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. • RunII: first search for forward rapidity gaps in Z→μ+μ- events (Tamsin Edwards) Search for diffractive Z→μμ • Inclusive Z→μμ sample well understood: • 2 muons, pT > 15GeV, opposite charge • at least one muon isolated in tracker and calorimeter • cosmic rejection Mμμ (GeV)

3. Run II LM South (η>0) North (η<0) p p Gap Definition: Luminosity Monitor • LM is Scintillating detector • 2.7 < |η| < 4.4 • Charge from wedges on one side are summed: Detector is on/off on each side, North and South

4. Gap Definition: Calorimeter • Use energy sum to distinguish proton break-up from empty calorimeter: Log(energy sum) on North side: Areas are normalised to 1 empty events physics samples 10 GeV • Esum cut of 10GeV was chosen for current study • Final value will be optimised using full data sample • 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

5. Z Mass Comparison No GAP • Add Esum<10 GeV requirement • to LM gap samples: One GAP • Invariant mass for gap events looks like standard Z sample • Will be able to compare Z boson kinematics (pT, pz, rapidity)

6. Problem: Run Dependent Esum Two different run ranges show different noise distributions; forward noise study in progress 6

7. Z→μμ + gaps: Summary • Preliminary definition of rapidity gap at DØ Run II • Study of Z→μ+μ- events with a rapidity gap signature (little or no energy detected in the forward direction) • Current status: • Evidence of Z events with a rapidity gap signature • Quantitative studies of gap definition, backgrounds, efficiency in progress • No interpretation in terms of diffractive physics possible yet • Plans: • Understand run dependent effects • Measurement of the fraction of diffractively produced Z events; properties of gap candidate events • Diffractive W→μν, W/Z→electrons, jets and other channels • Use tracks from Forward Proton Detector 7

8. p P A2U A1U p p P1D P2D Elastic Scattering • Elastic scattering: ξ = 0 (no momentum lost by beam particle) • Quadrupole acceptance: • t > 0.8 GeV2 (requires sufficient scattering angle to leave beam envelope) • all ξ (no longitudinal momentum loss necessary) • Measure dN/dt for elastic scattering using early stand-alone FPD data: • antiproton side: • quadrupole ‘up’ spectrometer • trigger only • proton side: • quadrupole ‘down’ spectrometer • full detector read-out veto on LM and VETO counters, early time hits (halo tracks)

9. Preliminary Elastic Results • The dσ/dt data collected by different experiments at different energies • A factor of 10-2 must be applied to each curve • New DØ dN/dt distribution has been normalized by E710 data • Compare slope with model: Block et al, Phys. Rev. D41, pp 978, 1990. This analysis based on Jorge Molina’s thesis:first FPD Ph D

10. Separator plates Fall 2003 shutdown survey data (points A+B) made available by accelerator in March shows offsets of up to 0.7 cm! Required rewriting of MC to separate separators, reanalysis of acceptance.

11. ACCEPTANCE The acceptance for the PD spectrometer: Before sep correction: After sep correction: Much better high-t acceptance (previously high-t data thought to be halo)

12. CORRELATION OF AU-PD When the correlations are introduced, the acceptance is reduced, beginning at higher values of |t| due to the positions reached by the AU pots Which acceptance to use? Note that trigger is based only on scintillator hits and dominated by halo spray (only 2% real tracks), so low-t data is presumably single arm elastics, high-t double arm elastics No acc. for low t ! Separator corrected

13. Elastic Summary • Re-evaluating acceptance and backgrounds • Will decide soon if sufficient confidence in results to publish • Silver lining: nearly 100% of effort directly transferable to new analyses

14. DØ Run II Diffractive Topics E   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 <100 W boson events in Run I, >1000 tagged events expected in Run II

15. Diffractive Topics and Students! New student, Vlatislav Hynek (Czech), working on forward diffractive jets

16. Diffractive Data Samples • Start with a list of all global physics runs for which the FPD pots are inserted that have not been declared bad by another sub-detector group • Filter out interesting triggers (from diffractive POV) on a run by run basis Extract raw fpd fiber information from raw (pre-Nov 03), DST (post-Nov 03) put in a root tree Use QCD_analyze to extract all other information from TMBs and put in a root tree (using fixtmb2 version) Sort tree by event number Sort tree by event number Clone QCD tree, add matching FPD branch, compare each entry in trees for matching event numbers and output to a merged tree for analysis • With p17, FPD information is in TMB so everything will be done with QCD_analyze • Current Status • Final merging of pre-Nov 03 data underway • post-Nov 03 stripping started New UTA post-doc Duncan Brown leading diffractive analysis group