Diffractive Physics E   Andrew Brandt, U. Texas at Arlington DØ Physics Workshop July 30, 2004 Fermilab A1UA2U P2DP1D P Pbar LM VC Focus on mature analyses: 1)Diffractive Z 2)Elastic Scattering

Search for diffractive Z → μμ DØ Run II preliminary Summer 2003 Inclusive Z→μμ sample well understood: 2 muons, p T > 15GeV, opposite charge at least one muon isolated in tracker and calorimeter cosmic rejection 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) M μμ (GeV)

Gap Definition: Luminosity Monitor North (η<0) South (η>0) p p 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 Run II LM

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

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

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

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

Elastic Scattering A2UA2UA1UA1U P2DP1D p p p P Measure dN/dt for elastic scattering using early stand-alone FPD data: Quadrupole acceptance: t > 0.8 GeV 2 (requires sufficient scattering angle to leave beam envelope) all ξ (no longitudinal momentum loss necessary) proton side: quadrupole ‘down’ spectrometer full detector read-out antiproton side: quadrupole ‘up’ spectrometer trigger only Elastic scattering: ξ = 0 (no momentum lost by beam particle) veto on LM and VETO counters, early time hits (halo tracks)

Preliminary Elastic Results The dσ/dt data collected by different experiments at different energies A factor of 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, This analysis based on Jorge Molina’s thesis:first FPD Ph D

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. Separator plates

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)

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 Separator corrected No acc. for low t ! 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

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

  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 1000 tagged events expected in Run II DØ Run II Diffractive Topics

Diffractive Topics and Students! New student, Vlatislav Hynek (Czech), working on forward diffractive jets Student Year InstituteAdvisorSubject Tamsin Edwards 2004 ManchesterB. CoxDiffractive Z production using gaps Ana Carolina de Jesus 2007 RioA. SantoroHeavy Flavor production in diffraction Helena Malbouisson 2007 RioA. SantoroDiffractive dijet structure function Luis Mendoza 2007 BogotáC. AvilaDiffractive W, Z James Monk 2006 ManchesterB. CoxDouble Pomeron+jets Renata Rodrigues 2007 RioA. SantoroElastic/Diffractive/Doubl e Pomeron Michael Strang 2004ish UTAA.BrandtDiffractive jets tagged with FPD

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 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 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 Clone QCD tree, add matching FPD branch, compare each entry in trees for matching event numbers and output to a merged tree for analysis Diffractive Data Samples New UTA post-doc Duncan Brown leading diffractive analysis group